U.S. patent application number 17/691213 was filed with the patent office on 2022-06-23 for semiconductor device and manufacturing method of semiconductor device.
This patent application is currently assigned to SEMICONDUCTOR ENERGY LABORATORY CO., LTD.. The applicant listed for this patent is SEMICONDUCTOR ENERGY LABORATORY CO., LTD.. Invention is credited to Tatsuya ONUKI, Katsuaki TOCHIBAYASHI, Shunpei YAMAZAKI.
Application Number | 20220199613 17/691213 |
Document ID | / |
Family ID | 1000006193558 |
Filed Date | 2022-06-23 |
United States Patent
Application |
20220199613 |
Kind Code |
A1 |
YAMAZAKI; Shunpei ; et
al. |
June 23, 2022 |
SEMICONDUCTOR DEVICE AND MANUFACTURING METHOD OF SEMICONDUCTOR
DEVICE
Abstract
A semiconductor device having favorable electrical
characteristics is provided. The semiconductor device includes a
transistor and a capacitor. The transistor includes a first
conductor and a second insulator over a first insulator; a third
insulator over the first conductor and the second insulator; a
fourth insulator over the third insulator; a first oxide over the
fourth insulator; a second oxide and a third oxide over the first
oxide; a second conductor in contact with a top surface of the
third insulator, a side surface of the fourth insulator, a side
surface of the first oxide, a side surface of the second oxide, and
a top surface of the second oxide; a third conductor in contact
with the top surface of the third insulator, a side surface of the
fourth insulator, a side surface of the first oxide, a side surface
of the third oxide, and a top surface of the third oxide; a fourth
oxide over the first oxide; a fifth insulator over the fourth
oxide; and a fourth conductor over the fifth insulator. The
capacitor includes a fifth conductor over the first insulator, the
third insulator over the fifth conductor, and the second conductor
over the third insulator.
Inventors: |
YAMAZAKI; Shunpei; (Tokyo,
JP) ; ONUKI; Tatsuya; (Atsugi, JP) ;
TOCHIBAYASHI; Katsuaki; (Isehara, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SEMICONDUCTOR ENERGY LABORATORY CO., LTD. |
Atsugi-shi |
|
JP |
|
|
Assignee: |
SEMICONDUCTOR ENERGY LABORATORY
CO., LTD.
ATSUGI-SHI
JP
|
Family ID: |
1000006193558 |
Appl. No.: |
17/691213 |
Filed: |
March 10, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
16695385 |
Nov 26, 2019 |
11289475 |
|
|
17691213 |
|
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|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 29/78696 20130101;
H01L 29/458 20130101; H01L 27/0635 20130101 |
International
Class: |
H01L 27/06 20060101
H01L027/06; H01L 29/45 20060101 H01L029/45; H01L 29/786 20060101
H01L029/786 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 25, 2019 |
JP |
2019-011582 |
Claims
1. A semiconductor device comprising: a transistor; and a
capacitor, wherein the transistor comprises: a first insulator; a
first conductor and a second insulator over the first insulator; a
first oxide and second oxide over the second insulator, a second
conductor and a third conductor over the first oxide and the second
oxide, a third insulator over the second conductor and the third
conductor, wherein the capacitor comprises: a fourth conductor over
the first insulator; and the second insulator over the fourth
conductor, wherein the third conductor is in contact with a top
surface of the second oxide, wherein the second insulator is in
contact with a top surface of the first conductor and a top surface
of the fourth conductor, wherein the first conductor and the fourth
conductor are formed on the same layer, and wherein the first
conductor and the fourth conductor comprise the same material.
2. A semiconductor device comprising: a transistor; and a
capacitor, wherein the transistor comprises: a first insulator; a
first conductor and a second insulator over the first insulator; a
first oxide and second oxide over the second insulator, a second
conductor and a third conductor over the first oxide and the second
oxide, a third insulator over the second conductor and the third
conductor, wherein the capacitor comprises: a fourth conductor over
the first insulator; and the second insulator over the fourth
conductor, wherein the third conductor is in contact with a top
surface of the second oxide, wherein the second insulator is in
contact with a top surface of the first conductor and a top surface
of the fourth conductor, wherein the first conductor and the fourth
conductor are formed on the same layer, wherein the first conductor
and the fourth conductor comprise the same material, and wherein
the first oxide and the second oxide each comprises an oxide
comprising, indium, element M, and zinc.
3. The semiconductor device according to claim 2, wherein element M
is gallium.
4. The semiconductor device according to claim 1, wherein the
second insulator comprises any one of aluminum, hafnium, zirconium,
and tantalum.
5. The semiconductor device according to claim 2, wherein the
second insulator comprises any one of aluminum, hafnium, zirconium,
and tantalum.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 16/695,385, filed Nov. 26, 2019, now allowed, which claims the
benefit of a foreign priority application filed in Japan on Jan.
25, 2019, as Application No. 2019-011582, both of which are
incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0002] One embodiment of the present invention relates to a
semiconductor device and a manufacturing method thereof. Another
embodiment of the present invention relates to a semiconductor
wafer, a module, and an electronic device.
[0003] In this specification and the like, a semiconductor device
generally means a device that can function by utilizing
semiconductor characteristics. A semiconductor element such as a
transistor, a semiconductor circuit, an arithmetic device, and a
memory device are each an embodiment of a semiconductor device. A
display device (e.g., a liquid crystal display device and a
light-emitting display device), a projection device, a lighting
device, an electro-optical device, a power storage device, a memory
device, a semiconductor circuit, an imaging device, an electronic
device, and the like may include a semiconductor device.
[0004] Note that one embodiment of the present invention is not
limited to the above technical field. One embodiment of the
invention disclosed in this specification and the like relates to
an object, a method, or a manufacturing method. One embodiment of
the present invention relates to a process, a machine, manufacture,
or a composition of matter.
2. Description of the Related Art
[0005] In recent years, semiconductor devices have been developed
to be used typically for an LSI, a CPU, and a memory. A CPU is an
aggregation of semiconductor elements, and a CPU has a
semiconductor integrated circuit (including at least a transistor
and a memory) separated from a semiconductor wafer, and an
electrode of a connection terminal.
[0006] A semiconductor circuit (IC chip) of an LSI, a CPU, a
memory, or the like is mounted on a circuit board such as a printed
wiring board to be used as one of components of a variety of
electronic devices.
[0007] A technique by which a transistor is formed using a
semiconductor thin film formed over a substrate having an
insulating surface has attracted attention. The transistor is
applied to a wide range of electronic devices such as an integrated
circuit (IC) and an image display device (also simply referred to
as a display device). Silicon-based semiconductor materials are
widely known as materials for semiconductor thin films that can be
used in a transistor. As other materials, oxide semiconductors have
been attracting attention.
[0008] It is known that a transistor including an oxide
semiconductor has an extremely low leakage current in an off state.
For example, a low-power-consumption CPU utilizing a characteristic
of a low leakage current of the transistor including an oxide
semiconductor has been disclosed (see Patent Document 1).
Furthermore, a memory device that can retain stored data for a long
time by utilizing a characteristic of a low leakage current of the
transistor including an oxide semiconductor has been disclosed, for
example (see Patent Document 2).
[0009] Recently, integrated circuits are required to have a higher
density as electronic devices become smaller and lighter. In
addition, the productivity of a semiconductor device including an
integrated circuit is required to be improved.
REFERENCE
Patent Document
[Patent Document 1] Japanese Published Patent Application No.
2012-257187
[Patent Document 2] Japanese Published Patent Application No.
2011-151383
SUMMARY OF THE INVENTION
[0010] An object of one embodiment of the present invention is to
provide a semiconductor device having favorable electrical
characteristics. Another object of one embodiment of the present
invention is to provide a semiconductor device with normally-off
electrical characteristics. Another object of one embodiment of the
present invention is to provide a highly reliable semiconductor
device. Another object of one embodiment of the present invention
is to provide a semiconductor device with a high on-state current.
Another object of one embodiment of the present invention is to
provide a semiconductor device with high frequency characteristics.
Another object of one embodiment of the present invention is to
provide a semiconductor device that can be miniaturized or highly
integrated. Another object of one embodiment of the present
invention is to provide a semiconductor device that can be
manufactured with high productivity.
[0011] Another object of one embodiment of the present invention is
to provide a semiconductor device capable of retaining data for a
long time. Another object of one embodiment of the present
invention is to provide a semiconductor device capable of
high-speed data writing. Another object of one embodiment of the
present invention is to provide a semiconductor device with high
design flexibility. Another object of one embodiment of the present
invention is to provide a semiconductor device with low power
consumption. Another object of one embodiment of the present
invention is to provide a novel semiconductor device.
[0012] Note that the descriptions of these objects do not disturb
the existence of other objects. One embodiment of the present
invention does not have to achieve all the objects. Other objects
will be apparent from and can be derived from the descriptions of
the specification, the drawings, the claims, and the like.
[0013] One embodiment of the present invention is a semiconductor
device including an oxide in a channel formation region. The
semiconductor device includes a transistor and a capacitor. The
transistor includes a first conductor and a second insulator over a
first insulator; a third insulator over the first conductor and the
second insulator; a fourth insulator over the third insulator; a
first oxide over the fourth insulator; a second oxide and a third
oxide over the first oxide; a second conductor in contact with a
top surface of the third insulator, a side surface of the fourth
insulator, a side surface of the first oxide, a side surface of the
second oxide, and a top surface of the second oxide; a third
conductor in contact with the top surface of the third insulator, a
side surface of the fourth insulator, a side surface of the first
oxide, a side surface of the third oxide, and a top surface of the
third oxide; a fourth oxide over the first oxide; a fifth insulator
over the fourth oxide; and a fourth conductor over the fifth
insulator. The capacitor includes a fifth conductor over the first
insulator; the third insulator over the fifth conductor; and the
second conductor over the third insulator.
[0014] The first to third oxides preferably include In, an element
M (M is Al, Ga, Y, or Sn), and Zn.
[0015] The third insulator preferably includes any one of aluminum,
hafnium, zirconium, and tantalum.
[0016] The first insulator preferably includes silicon and
nitrogen.
[0017] One embodiment of the present invention can provide a
semiconductor device having favorable electrical characteristics.
One embodiment of the present invention can provide a semiconductor
device with normally-off electrical characteristics. One embodiment
of the present invention can provide a highly reliable
semiconductor device. One embodiment of the present invention can
provide a semiconductor device with a high on-state current. One
embodiment of the present invention can provide a semiconductor
device with high frequency characteristics. One embodiment of the
present invention can provide a semiconductor device that can be
miniaturized or highly integrated. One embodiment of the present
invention can provide a semiconductor device that can be
manufactured with high productivity.
[0018] One embodiment of the present invention can provide a
semiconductor device capable of retaining data for a long time. One
embodiment of the present invention can provide a semiconductor
device capable of high-speed data writing. One embodiment of the
present invention can provide a semiconductor device with high
design flexibility. One embodiment of the present invention can
provide a semiconductor device with low power consumption. One
embodiment of the present invention can provide a novel
semiconductor device.
[0019] Note that the descriptions of the effects do not disturb the
existence of other effects. One embodiment of the present invention
does not necessarily achieve all the effects. Other effects will be
apparent from and can be derived from the description of the
specification, the drawings, the claims, and the like.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] In the accompanying drawings:
[0021] FIG. 1A is a top view of a structure example of a
semiconductor device, and FIGS. 1B to 1D are cross-sectional views
of a structure example of a semiconductor device;
[0022] FIG. 2A is a top view of a structure example of a
semiconductor device, and FIGS. 2B to 2D are cross-sectional views
of a structure example of a semiconductor device;
[0023] FIG. 3A is a top view of a structure example of a
semiconductor device, and FIGS. 3B to 3D are cross-sectional views
of a structure example of a semiconductor device;
[0024] FIG. 4A is a top view illustrating a manufacturing method of
a semiconductor device, and FIGS. 4B to 4D are cross-sectional
views illustrating a manufacturing method of a semiconductor
device;
[0025] FIG. 5A is a top view illustrating a manufacturing method of
a semiconductor device, and FIGS. 5B to 5D are cross-sectional
views illustrating a manufacturing method of a semiconductor
device;
[0026] FIG. 6A is a top view illustrating a manufacturing method of
a semiconductor device, and FIGS. 6B to 6D are cross-sectional
views illustrating a manufacturing method of a semiconductor
device;
[0027] FIG. 7A is a top view illustrating a manufacturing method of
a semiconductor device, and FIGS. 7B to 7D are cross-sectional
views illustrating a manufacturing method of a semiconductor
device;
[0028] FIG. 8A is a top view illustrating a manufacturing method of
a semiconductor device, and FIGS. 8B to 8D are cross-sectional
views illustrating a manufacturing method of a semiconductor
device;
[0029] FIG. 9A is a top view illustrating a manufacturing method of
a semiconductor device, and FIGS. 9B to 9D are cross-sectional
views illustrating a manufacturing method of a semiconductor
device;
[0030] FIG. 10A is a top view illustrating a manufacturing method
of a semiconductor device, and FIGS. 10B to 10D are cross-sectional
views illustrating a manufacturing method of a semiconductor
device;
[0031] FIG. 11A is a top view illustrating a manufacturing method
of a semiconductor device, and FIGS. 11B to 11D are cross-sectional
views illustrating a manufacturing method of a semiconductor
device;
[0032] FIG. 12A is a top view illustrating a manufacturing method
of a semiconductor device, and FIGS. 12B to 12D are cross-sectional
views illustrating a manufacturing method of a semiconductor
device;
[0033] FIG. 13A is a top view illustrating a manufacturing method
of a semiconductor device, and FIGS. 13B to 13D are cross-sectional
views illustrating a manufacturing method of a semiconductor
device;
[0034] FIG. 14A is a top view illustrating a manufacturing method
of a semiconductor device, and FIGS. 14B to 14D are cross-sectional
views illustrating a manufacturing method of a semiconductor
device;
[0035] FIG. 15A is a table showing a classification of crystal
structures of IGZO, FIG. 15B is a graph showing an XRD spectrum of
the quartz glass, and FIG. 15C is a graph showing an XRD spectrum
of crystalline IGZO;
[0036] FIG. 16 is a cross-sectional view of a structure example of
a semiconductor device;
[0037] FIG. 17 is a cross-sectional view of a structure example of
a semiconductor device;
[0038] FIG. 18 is a cross-sectional view of a structure example of
a semiconductor device;
[0039] FIG. 19 is a cross-sectional view of a structure example of
a memory device;
[0040] FIG. 20 is a cross-sectional view of a structure example of
a memory device;
[0041] FIG. 21 is a diagram of the memory hierarchy;
[0042] FIG. 22A is a block diagram of a structure example of a
memory device, and FIG. 22B is a perspective view of a structure
example of a memory device;
[0043] FIGS. 23A to 23C are circuit diagrams of structure examples
of a memory device;
[0044] FIGS. 24A and 24B are diagrams of examples of electronic
components;
[0045] FIGS. 25A to 25E are schematic diagrams of structure
examples of memory devices; and
[0046] FIGS. 26A to 26D, 26E1 and 26E2, and 26F are diagrams
showing electronic devices.
DETAILED DESCRIPTION OF THE INVENTION
[0047] Embodiments will be hereinafter described with reference to
the drawings. Note that the embodiments can be implemented with
various modes, and it will be readily appreciated by those skilled
in the art that modes and details can be changed in various ways
without departing from the spirit and scope of the present
invention. Thus, the present invention should not be interpreted as
being limited to the following description of the embodiments.
[0048] In the drawings, the size, the layer thickness, or the
region is sometimes exaggerated for clarity. Therefore, the size,
the layer thickness, or the region is not limited to the
illustrated scale. Note that the drawings are schematic views
showing ideal examples, and embodiments of the present invention
are not limited to shapes or values shown in the drawings. For
example, in the actual manufacturing process, a layer, a resist
mask, or the like might be unintentionally reduced in size by
treatment such as etching, which is not illustrated in some cases
for easy understanding. In the drawings, the same portions or
portions having similar functions are denoted by the same reference
numerals in different drawings, and explanation thereof will not be
repeated in some cases. The same hatching pattern is applied to
portions having similar functions, and the portions are not denoted
by specific reference numerals in some cases.
[0049] In a top view (also referred to as a plan view), a
perspective view, or the like, some components might not be
illustrated for easy understanding of the invention. In addition,
some hidden lines and the like might not be shown.
[0050] The ordinal numbers such as "first" and "second" in this
specification and the like are used for convenience and do not
denote the order of steps or the stacking order of layers.
Therefore, for example, description can be made even when "first"
is replaced with "second", "third", or the like as appropriate. In
addition, the ordinal numbers in this specification and the like
are not necessarily the same as those used to specify one
embodiment of the present invention.
[0051] In this specification and the like, the terms for describing
arrangement, such as "over", "above", "under", and "below", are
used for convenience to describe a positional relation between
components with reference to drawings. Furthermore, the positional
relation between components is changed as appropriate in accordance
with the direction from which each component is described. Thus,
the positional relation is not limited to that described with a
term used in this specification and can be explained with other
terms as appropriate depending on the situation.
[0052] For example, when this specification and the like explicitly
state that X and Y are connected, the case where X and Y are
electrically connected, the case where X and Y are functionally
connected, and the case where X and Y are directly connected are
regarded as being disclosed in this specification and the like.
Accordingly, without limitation to a predetermined connection
relation, for example, a connection relation shown in drawings or
text, another connection relation is regarded as being disclosed in
the drawings or the text.
[0053] Here, X and Y each denote an object (e.g., a device, an
element, a circuit, a wiring, an electrode, a terminal, a
conductive film, or a layer).
[0054] Furthermore, functions of a source and a drain might be
switched when a transistor of opposite polarity is employed or when
a direction of current flow is changed in circuit operation, for
example. Therefore, the terms "source" and "drain" can be
interchanged in some cases in this specification and the like.
[0055] Note that in this specification and the like, depending on
the transistor structure, the channel width in a region where a
channel is actually formed (channel formation region) (hereinafter
also referred to as an effective channel width) is different from
the channel width shown in a top view of a transistor (hereinafter
also referred to as an apparent channel width) in some cases. For
example, in a transistor having a gate covering a side surface of a
semiconductor, an effective channel width is greater than an
apparent channel width and has a non-negligible influence in some
cases. For example, in a miniaturized transistor having a gate
covering a side surface of a semiconductor, the proportion of a
channel formation region formed in a side surface of a
semiconductor is increased in some cases. In that case, the
effective channel width is larger than the apparent channel
width.
[0056] In such cases, an effective channel width is sometimes
difficult to estimate by measuring. For example, to estimate an
effective channel width from a design value, it is necessary to
assume that the shape of a semiconductor is known. Accordingly, in
the case where the shape of a semiconductor is not known exactly,
it is difficult to measure an effective channel width
accurately.
[0057] In this specification, the simple term "channel width"
denotes an apparent channel width in some cases. In other cases,
the simple term "channel width" denotes an effective channel width.
Note that the values of a channel length, a channel width, an
effective channel width, an apparent channel width, and the like
can be determined by analyzing a cross-sectional TEM image and the
like.
[0058] Note that an impurity in a semiconductor refers to, for
example, elements other than the main components of the
semiconductor. For example, an element with a concentration lower
than 0.1 atomic % is regarded as an impurity. When an impurity is
contained, the density of states (DOS) in a semiconductor may be
increased, or the crystallinity may be decreased. In the case where
the semiconductor is an oxide semiconductor, examples of an
impurity which changes the characteristics of the semiconductor
include Group 1 elements, Group 2 elements, Group 13 elements,
Group 14 elements, Group 15 elements, and transition metals other
than the main components of the oxide semiconductor, such as
hydrogen, lithium, sodium, silicon, boron, phosphorus, carbon, and
nitrogen. Water may be an impurity for an oxide semiconductor. In
the case of an oxide semiconductor, entry of impurities may form
oxygen vacancies, for example. When the semiconductor is silicon,
examples of an impurity which changes the characteristics of the
semiconductor include oxygen, Group 1 elements except hydrogen,
Group 2 elements, Group 13 elements, and Group 15 elements.
[0059] In this specification and the like, silicon oxynitride
contains more oxygen than nitrogen as its composition and silicon
nitride oxide contains more nitrogen than oxygen as its
composition.
[0060] In this specification and the like, the term "insulator" can
be replaced with an insulating film or an insulating layer. The
term "conductor" can be replaced with a conductive film or a
conductive layer. The term "semiconductor" can be replaced with a
semiconductor film or a semiconductor layer.
[0061] In this specification and the like, the term "parallel"
indicates that the angle formed between two straight lines is
greater than or equal to -10.degree. and less than or equal to
10.degree.. Thus, the case where the angle is greater than or equal
to -5.degree. and less than or equal to 5.degree. is also included.
The term "substantially parallel" indicates that the angle formed
between two straight lines is greater than or equal to -30.degree.
and less than or equal to 30.degree.. The term "perpendicular"
indicates that the angle formed between two straight lines is
greater than or equal to 80.degree. and less than or equal to
100.degree.. Thus, the case where the angle is greater than or
equal to 85.degree. and less than or equal to 95.degree. is also
included. In addition, the term "substantially perpendicular"
indicates that the angle formed between two straight lines is
greater than or equal to 60.degree. and less than or equal to
120.degree..
[0062] Note that in this specification, a barrier film refers to a
film having a function of inhibiting the transmission of oxygen and
impurities such as water or hydrogen. The barrier film that has
conductivity may be referred to as a conductive barrier film.
[0063] In this specification and the like, a metal oxide means an
oxide of metal in a broad sense. Metal oxides are classified into
an oxide insulator, an oxide conductor (including a transparent
oxide conductor), an oxide semiconductor (also simply referred to
as an OS), and the like. For example, a metal oxide used in a
semiconductor layer of a transistor is referred to as an oxide
semiconductor in some cases. An OS FET or an OS transistor is a
transistor including an oxide or an oxide semiconductor.
[0064] In this specification and the like, the term "normally off"
means that current per micrometer of a channel width flowing in a
transistor is lower than or equal to 1.times.10.sup.-20 A at room
temperature, lower than or equal to 1.times.10.sup.-18 A at
85.degree. C., or lower than or equal to 1.times.10.sup.-16 A at
125.degree. C. when potential is not applied to a gate or the gate
is supplied with a ground potential.
Embodiment 1
[0065] An example of a semiconductor device of one embodiment of
the present invention including a transistor 200 and a capacitor
100 and a manufacturing method of the semiconductor device are
described below.
<Structure Example of Semiconductor Device>
[0066] FIGS. 1A to 1D are a top view and cross-sectional views of
the semiconductor device including the transistor 200 and the
capacitor 100 of one embodiment of the present invention.
[0067] FIG. 1A is a top view of the semiconductor device including
the transistor 200 and the capacitor 100. FIGS. 1B to 1D are
cross-sectional views of the semiconductor device. FIG. 1B is a
cross-sectional view taken along the dashed-dotted line A1-A2 in
FIG. 1A, which is a cross-sectional view of the transistor 200 and
the capacitor 100 in the channel length direction. FIG. 1C is a
cross-sectional view taken along the dashed-dotted line A3-A4 in
FIG. 1A, which is a cross-sectional view of the transistor 200 in
the channel width direction. FIG. 1D is a cross-sectional view
taken along the dashed-dotted line A5-A6 in FIG. 1A, which is a
cross-sectional view of the capacitor 100 in the channel width
direction. Note that for simplification, some components are not
illustrated in the top view in FIG. 1A.
[0068] The semiconductor device of one embodiment of the present
invention includes an insulator 214 over a substrate (not
illustrated), the transistor 200 and the capacitor 100 over the
insulator 214, an insulator 280 over the transistor 200 and the
capacitor 100, an insulator 282 over the insulator 280, an
insulator 283 over the insulator 282, an insulator 284 over the
insulator 283, and an insulator 274 over the insulator 284. The
insulators 214, 216, 280, 282, 283, and 274 each function as an
interlayer film The semiconductor device also includes a conductor
240 that is electrically connected to the transistor 200 and
functions as a plug. Note that an insulator 241 is provided in
contact with the side surface of the conductor 240 functioning as a
plug. A conductor 246, which is electrically connected to the
conductor 240 and functions as a wiring, is provided over the
insulator 283 and the conductor 240. The insulator 284 is provided
over the conductor 246 and the insulator 283.
[0069] The insulator 241 is provided in contact with the inner wall
of an opening formed in the insulators 272, 273, 280, 282, and 283,
a first conductor of the conductor 240 is provided in contact with
the side surface of the insulator 241, and a second conductor of
the conductor 240 is provided in contact with the side surface of
the first conductor of the conductor 240. The top surface of the
conductor 240 can be substantially level with the top surface of
the insulator 283. Although the first conductor of the conductor
240 and the second conductor of the conductor 240 are stacked in
the transistor 200, the present invention is not limited thereto.
For example, the conductor 240 may have a single-layer structure or
a stacked-layer structure of three or more layers. In the case
where a stacked-layer structure is employed, the layers may be
distinguished by numbers corresponding to the formation order.
[Transistor 200]
[0070] As shown in FIG. 1B, the transistor 200 includes an
insulator 216 over the insulator 214; a conductor 205 (a conductor
205a and a conductor 205b) embedded in the insulator 216;
[0071] an insulator 222 over the insulator 216 and the conductor
205; an insulator 224 over the insulator 222; an oxide 230a over
the insulator 224; an oxide 230b over the oxide 230a, an oxide 243a
and an oxide 243b over the oxide 230b; a conductor 242a in contact
with a top surface of the insulator 222, a side surface of the
insulator 224, a side surface of the oxide 230a, a side surface of
the oxide 230b, a side surface of the oxide 243a, and a top surface
of the oxide 243a; a conductor 242b in contact with the top surface
of the insulator 222, a side surface of the insulator 224, a side
surface of the oxide 230a, a side surface of the oxide 230b, a side
surface of the oxide 243b, and a top surface of the oxide 243b; an
insulator 272 in contact with the top surface of the insulator 222,
a side surface of the conductor 242a, the top surface of the
conductor 242a, a side surface of the conductor 242b, and a top
surface of the conductor 242b; an insulator 273 over the insulator
272; an oxide 230c over the oxide 230b; an insulator 250 over the
oxide 230c; and a conductor 260 (a conductor 260a and a conductor
260b) which is over the insulator 250 and overlaps with the oxide
230c. The oxide 230c is in contact with a side surface of the oxide
243a, a side surface of the oxide 243b, a side surface of the
conductor 242a, a side surface of the conductor 242b, a side
surface of the insulator 272 and a side surface of the insulator
273. The conductor 260 includes the conductor 260a and the
conductor 260b. The conductor 260a is positioned to cover the
bottom surface and the side surfaces of the conductor 260b. As
shown in FIG. 1B, a top surface of the conductor 260 is
substantially aligned with a top surface of the insulator 250 and a
top surface of the oxide 230c. The insulator 282 is in contact with
top surfaces of the conductor 260, the insulator 250, the oxide
230c, and the insulator 280.
[0072] Hereinafter, the oxide 243a and the oxide 243b are
collectively referred to as an oxide 243 in some cases. The
conductor 242a and the conductor 242b are collectively referred to
as a conductor 242 in some cases.
[0073] Here, the conductor 260 functions as a gate electrode of the
transistor 200, and the conductor 242a and the conductor 242b
function as a source electrode and a drain electrode of the
transistor 200. The conductor 260 functioning as a gate is formed
in a self-aligned manner to be fit into an opening formed in the
insulators 280, 273, and 272, the conductor 242, and the oxide 243.
The formation of the conductor 260 in this manner allows the
conductor 260 to be set in a desired position certainly between the
conductor 242a and the conductor 242b without alignment.
[0074] At least one of the insulators 214, 222, 272, 273, 282, and
283 preferably has a function of inhibiting diffusion of hydrogen
(at least one of hydrogen atoms and hydrogen molecules, for
example) or water molecules. In particular, the insulators 214,
273, and 283 each preferably have an excellent function of
inhibiting diffusion of hydrogen (at least one of hydrogen atoms
and hydrogen molecules, for example) or water molecules. At least
one of the insulators 214, 222, 272, 273, 282, and 283 preferably
has a function of inhibiting diffusion of oxygen (at least one of
oxygen atoms and oxygen molecules, for example). For example, at
least one of the insulators 214, 222, 272, 273, 282, and 283 less
easily transmits one or both of oxygen and hydrogen than the
insulator 224. At least one of the insulators 214, 222, 272, 273,
282, and 283 less easily transmits one or both of oxygen and
hydrogen than the insulator 250. At least one of the insulators
214, 222, 272, 273, 282, and 283 less easily transmits one or both
of oxygen and hydrogen than the insulator 280.
[0075] Aluminum oxide, hafnium oxide, gallium oxide, indium gallium
zinc oxide, silicon nitride, or silicon nitride oxide can be used
for the insulators 214, 222, 272, 273, 282, and 283, for example.
In particular, the insulator 214 and the insulator 283 are
preferably formed using silicon nitride or silicon nitride oxide
with a higher hydrogen barrier property.
[0076] In one embodiment of the semiconductor device described in
this embodiment, part of side surfaces of the insulator 224 is in
contact with the conductor 242, the conductor 242 is covered with
the insulator 272, and the insulator 273 is positioned over the
insulator 272, which is shown in FIG. 1B. The insulator 242 is
sealed by the insulators 272 and 273; this inhibits oxidation of
the conductor 242. The structure also yields a preferable result in
some cases that hydrogen in the insulator 224 is absorbed into the
insulator 272 through the conductor 242.
[0077] The oxide 230 preferably includes the oxide 230a over the
insulator 224, the oxide 230b over the oxide 230a, and the oxide
230c that is over the oxide 230b and is at least partly in contact
with the top surface of the oxide 230b. The side surfaces of the
oxide 230c are preferably in contact with the oxides 243a and 243b,
the conductors 242a and 242b, and the insulators 272, 273, and
280.
[0078] The transistor 200 employs a structure where the three
layers of the oxides 230a, 230b, and 230c are stacked in the
channel formation region and its vicinity; however, the present
invention is not limited to this structure. For example, the
transistor 200 may have a single-layer structure of the oxide 230b,
a two-layer structure of the oxide 230b and the oxide 230a or 230c,
or a stacked-layer structure of four or more layers. For example,
the transistor 200 may have a four-layer structure of the oxides
230a and 230b, and two layers of the oxide 230c.
[0079] The oxide 230 (oxides 230a, 230b, and 230c) which includes
the channel formation region preferably contains a metal oxide
functioning as an oxide semiconductor (hereinafter referred to
simply as oxide semiconductor). The metal oxide functioning as an
oxide semiconductor preferably has an energy gap of 2 eV or more,
preferably 2.5 eV or more, for example. The metal oxide with a wide
energy gap makes leakage current in a non-conduction state
(off-state current) of the transistor 200 extremely small. Such a
transistor enables a semiconductor device with low power
consumption.
[0080] For example, as the oxide 230, a metal oxide such as an
In--M--Zn oxide (M is one or more of aluminum, gallium, yttrium,
tin, copper, vanadium, beryllium, boron, titanium, iron, nickel,
germanium, zirconium, molybdenum, lanthanum, cerium, neodymium,
hafnium, tantalum, tungsten, magnesium, and the like) is used. In
particular, aluminum, gallium, yttrium, or tin is preferably used
as the element M. Alternatively, an In oxide, an In--M oxide, an
In--Zn oxide, or an M--Zn oxide is used as the oxide 230.
[0081] The oxide 230 includes the oxide 230a, the oxide 230b over
the oxide 230a, and the oxide 230c over the oxide 230b. The oxide
230a under the oxide 230b inhibits diffusion of impurities into the
oxide 230b from the components formed below the oxide 230a. The
oxide 230c over the oxide 230b inhibits diffusion of impurities
into the oxide 230b from the components formed above the oxide
230c.
[0082] The oxide 230 preferably has a stacked-layer structure of
oxides with different atomic ratios of each metal element.
Specifically, the atomic ratio of the element M to constituent
elements in the metal oxide used as the oxide 230a is preferably
higher than that in the metal oxide used as the oxide 230b. The
atomic ratio of the element M to In in the metal oxide used as the
oxide 230a is preferably higher than that in the metal oxide used
as the oxide 230b. The atomic ratio of In to the element M in the
metal oxide used as the oxide 230b is preferably higher than that
in the metal oxide used as the oxide 230a. The oxide 230c can be
formed using a metal oxide that can be used as the oxide 230a or
the oxide 230b.
[0083] Specifically, as the oxide 230a, a metal oxide having an
atomic ratio of In:Ga:Zn=1:3:4 or in the vicinity thereof, or
In:Ga:Zn=1:1:0.5 or in the vicinity thereof can be used. As the
oxide 230b, a metal oxide having an atomic ratio of In:Ga:Zn=4:2:3
or in the vicinity thereof, or In:Ga:Zn=1:1:1 or in the vicinity
thereof can be used. As the oxide 230c, a metal oxide having an
atomic ratio of In:Ga:Zn=1:3:4 or in the vicinity thereof,
In:Ga:Zn=4:2:3 or in the vicinity thereof, In:Ga:Zn=5:1:3 or in the
vicinity thereof, In:Ga:Zn=10:1:3 or in the vicinity thereof,
Ga:Zn=2:1 or in the vicinity thereof, or Ga:Zn=2:5 or in the
vicinity thereof can be used. When the oxide 230c has a
stacked-layer structure, a stacked layer structure of a metal oxide
having an atomic ratio of In:Ga:Zn=4:2:3 or in the vicinity thereof
and a metal oxide having an atomic ratio of In:Ga:Zn=1:3:4 or in
the vicinity thereof, a stacked-layer structure of a metal oxide
having an atomic ratio of In:Ga:Zn=4:2:3 or in the vicinity thereof
and a metal oxide having an atomic ratio of In:Ga:Zn=5:1:3 or in
the vicinity thereof, a stacked-layer structure of a metal oxide
having an atomic ratio of Ga:Zn=2:1 or in the vicinity thereof and
a metal oxide having an atomic ratio of In:Ga:Zn=4:2:3 or in the
vicinity thereof, a stacked-layer structure of a metal oxide having
an atomic ratio of Ga:Zn=2:5 or in the vicinity thereof and a metal
oxide having an atomic ratio of In:Ga:Zn=4:2:3 or in the vicinity
thereof, or a stacked-layer structure of gallium oxide and a metal
oxide having an atomic ratio of In:Ga:Zn=4:2:3 or in the vicinity
thereof can be given as specific examples. Note that the vicinity
of the atomic ratio includes .+-.30% of an intended atomic
ratio.
[0084] The oxide 230b preferably has crystallinity. For example,
the oxide 230b preferably has a c-axis-aligned crystalline oxide
semiconductor (CAAC-OS) described later. An oxide having
crystallinity, such as a CAAC-OS, has a dense structure with small
amounts of impurities and defects (e.g., oxygen vacancies) and high
crystallinity. This reduces oxygen extraction from the oxide 230b
by the source or the drain electrode. This inhibits oxygen
extraction from the oxide 230b even when heat treatment is
performed; hence, the transistor 200 is stable against high
temperatures in the manufacturing process (i.e., thermal
budget).
[0085] The energy of the conduction band minimum of each of the
oxides 230a and 230c is preferably higher than that of the oxide
230b. In other words, the electron affinity of each of the oxides
230a and 230c is preferably smaller than that of the oxide
230b.
[0086] Here, Ec can be obtained from Ip and Eg, where Ec is the
electron affinity or the energy level of the conduction band
minimum; Ip is an ionization potential, which is a difference
between the vacuum level and the energy level Ev of the valence
band maximum; Eg is an energy gap. The ionization potential Ip can
be measured with, for example, an ultraviolet photoelectron
spectroscopy (UPS) apparatus. The energy gap Eg can be measured
with, for example, a spectroscopic ellipsometer.
[0087] The energy level of the conduction band minimum gradually
varies at a junction portion of each of the oxides 230a, 230b, and
230c. In other words, the energy levels of the conduction band
minimum at a junction portion of each of the oxides 230a, 230b, and
230c continuously vary or are continuously connected. This can be
achieved in such a way that the density of defect states in a mixed
layer formed at the interface between the oxides 230a and 230b and
the interface between the oxides 230b and 230c is decreased.
[0088] The oxide 230b serves as a main carrier path. When the
oxides 230a, 230b, and 230c have the above composition, the density
of defect states at the interface between the oxides 230a and 230b
and the interface between the oxides 230b and 230c can be made low.
This reduces the influence of interface scattering on carrier
conduction, and the transistor 200 can have a high on-state current
and high frequency characteristics.
[0089] An oxide semiconductor with low carrier density is
preferably used for the oxide 230, such as the oxide 230b. The
concentration of impurities and the density of defect states are
lowered in order to make the carrier density of the oxide
semiconductor low. In this specification and the like, a state with
a low impurity concentration and a low density of defect states is
referred to as a highly purified intrinsic or substantially highly
purified intrinsic state. Examples of impurities contained in an
oxide semiconductor include hydrogen, nitrogen, alkali metal,
alkaline earth metal, iron, nickel, and silicon.
[0090] Hydrogen contained in an oxide semiconductor reacts with
oxygen, which reacts with metal atoms, to generate oxygen vacancies
(also referred to as Vo) in the oxide semiconductor in some cases.
Defects which are formed by the bonding of oxygen vacancies and
hydrogen (hereinafter referred to as VoH in some cases) serve as
donors and generate electrons serving as carriers in some cases. In
other cases, some hydrogen is bonded to oxygen, which reacts with
metal atoms, to generate electrons serving as carriers. Thus, a
transistor including an oxide semiconductor that contains much
hydrogen tends to have normally-on characteristics. Moreover,
hydrogen in an oxide semiconductor easily moves by stress such as
heat and electric field; thus, the reliability of a transistor may
be low when an oxide semiconductor contains a plenty of
hydrogen.
[0091] VoH can serve as donors of an oxide semiconductor. However,
it is difficult to evaluate the VoH quantitatively. In some cases,
a carrier density is selected for evaluation of an oxide
semiconductor instead of a donor density; accordingly, a carrier
density is used for a parameter of an oxide semiconductor when an
electric field is not applied, instead of a donor density. Hence,
"carrier density" in this specification can be replaced with "donor
density" in some cases.
[0092] Therefore, when an oxide semiconductor is used for the oxide
230, the VoH in the oxide 230 is reduced as long as possible to
make the oxide semiconductor highly purified or substantially
highly purified, which is preferable. It is effective to remove
impurities such as water and hydrogen in an oxide semiconductor
(sometimes described as dehydration or dehydrogenation treatment)
and to compensate for oxygen vacancies by supplying oxygen to the
oxide semiconductor (sometimes described as oxygen supplying
treatment) to obtain an oxide semiconductor whose VoH is reduced
enough. When an oxide semiconductor with an impurity such as VoH
sufficiently reduced is used for a channel formation region of a
transistor, the transistor can have stable electrical
characteristics.
[0093] When an oxide semiconductor is used for the oxide 230, the
carrier density of the oxide semiconductor at a channel formation
region is preferably lower than or equal to
1.times.10.sup.18cm.sup.-3, further preferably lower than
1.times.10.sup.17cm.sup.-3, further preferably lower than
1.times.10.sup.16cm.sup.-3, further preferably lower than
1.times.10.sup.13cm.sup.-3, further preferably lower than
1.times.10.sup.12cm.sup.-3. The minimum carrier density of an oxide
semiconductor at a channel formation region is not limited and can
be 1.times.10.sup.-9 cm.sup.-3, for example.
[0094] Interlayer insulating films, such as the insulators 216,
274, and 280, and gate insulating films such as the insulators 224
and 250, may be deposited by a gas with no or less hydrogen atoms
to reduce hydrogen concentration in these insulating films, whereby
the amount of hydrogen entering a channel formation region of an
oxide semiconductor can be reduced.
[0095] A gas including molecules having silicon atoms is mainly
used for depositing the insulating films described above. The gas
including molecules having silicon atoms preferably includes a
small amount of hydrogen, and further preferably includes no
hydrogen to deposit the insulating films with reduced hydrogen. A
deposition gas other than that including molecules having silicon
atoms preferably includes less hydrogen atoms, further preferably
includes no hydrogen atoms.
[0096] At least one of an isocyanate group (--N.dbd.C.dbd.O), a
cyanate group (--O--C.ident.O), a cyano group --O.ident.O), a diazo
group (.dbd.N.sub.2), an azido group (--N.sub.3), a nitroso group
(--NO), and a nitro group (--NO.sub.2) can be used as a functional
group R when the molecule having a silicon atom is represented by
Si.sub.x--R.sub.y. For example, 1.ltoreq.x.ltoreq.3 and
1.ltoreq.y.ltoreq.8 may be employed. For example,
tetraisocyanatesilane, tetracyanatesilane, tetracyanosilane,
hexaisocyanatesilane, or octaisocyanatesilane can be used as the
molecule having a silicon atom. The molecules with the same kind of
functional group bonded are shown above, but this embodiment may
include more kinds of examples other than the above examples.
Different kinds of functional groups may be bonded to a silicon
molecule.
[0097] A halogen (Cl, Br, I, or F) can be used for the functional
group R, for example. For example, 1.ltoreq.x.ltoreq.2, and
1.ltoreq.y.ltoreq.6 are employed. Examples of such a molecule
containing a silicon atom are tetrachlorosilane (SiCl.sub.4),
hexachlorodisilane (Si.sub.2Cl.sub.6), and the like. Although an
example of using chlorine as the functional group is described
here, halogens other than chlorine, such as bromine, iodine, or
fluorine, can alternatively be used. Different kinds of halogens
can be bonded to silicon atoms.
[0098] The insulators 216, 274, 280, 224, and 250 are deposited by
a chemical vapor deposition (CVD) method using the gas, as
described above, containing molecules having silicon atoms. A CVD
method is preferable for depositing the insulators 280, 274, and
216, which are thick films, because a CVD method deposits films
relatively fast.
[0099] For a CVD method, a plasma enhanced CVD (PECVD) method,
which uses plasma, or a thermal CVD (TCVD), which uses heat, is
preferable. For a TCVD method, an atmospheric pressure CVD (APCVD)
method, which deposits a film in an atmospheric pressure, or a low
pressure CVD (LPCVD) method, which deposits a film in a pressure
lower than an atmospheric pressure, can be employed.
[0100] To deposit the insulators 216, 274, 280, 224, and 250 by a
CVD method, an oxidizer is preferably used. For an oxidizer, a gas
with no hydrogen atoms, such as O.sub.2, O.sub.3, NO, NO.sub.2,
N.sub.2O, N.sub.2O.sub.3, N.sub.2O.sub.4, N.sub.2O.sub.5, CO, and
CO.sub.2, is preferably used.
[0101] An atomic layer deposition (ALD) method may be used for
depositing the insulators 216, 274, 280, 224, and 250. For an ALD
method, a first source gas (hereinafter referred to as a precursor
or a metal precursor) and a second source gas (hereinafter referred
to as a reactant or a nonmetal precursor) for reaction are
alternately introduced into a chamber to deposit films.
[0102] An ALD method deposits a film by a single layer of atoms
when deposition is performed by alternate introduction of source
gases, using self-regulating characteristics of the atom. Hence, an
ALD method has various advantages such as deposition of an
extremely thin film, deposition on a component with a large aspect
ratio, deposition of a film with a small number of detects such as
pinholes, and deposition with excellent coverage. Thus, the
insulators 250 and 224 are preferably formed by an ALD method.
[0103] For an ALD method, either a thermal ALD method, in which a
precursor reacts with a reactant only by thermal energy, or a
plasma enhanced ALD (PEALD) method, which uses a reactant excited
by plasma, can be employed.
[0104] For an ALD method, an example of a precursor includes the
gas containing molecules having silicon atoms mentioned above and
an example of a reactant includes the oxidizer mentioned above.
This yields a drastic reduction of hydrogen absorbed into the
insulators 216, 274, 280, 224, and 250.
[0105] An example of molecules having silicon atoms without
hydrogen atoms is shown above; however, this embodiment can include
other examples. For the molecules having silicon atoms, some
functional groups can be replaced with hydrogen atoms. The number
of hydrogen atoms included in the above molecules having silicon
atoms is less than that of silane (SiH.sub.4). Accordingly, it is
preferable that the molecules having silicon atoms include three or
less hydrogen atoms on a silicon atom. It is also preferable that
the gas containing molecules having silicon atoms include three or
less hydrogen atoms on a silicon atom.
[0106] Depositing at least one of the insulators 216, 274, 280,
224, and 250 with the deposition methods described above, which
uses a gas with less or no hydrogen atoms, can reduce the amount of
hydrogen contained in these insulators 216, 274, 280, 224, and
250.
[0107] The transistor 200 shown in FIGS. 1B to 1D has a structure
in which the insulators 282 and 250 are directly in contact with
each other. The structure inhibits absorption of oxygen contained
in the insulator 280 into the conductor 260. The insulator 280 can
effectively provide oxygen to the oxides 230a and 230b via the
oxide 230c, which reduce oxygen vacancies in the oxides 230a and
230b to improve the electric characteristics and the reliability of
the transistor 200. The structure can also inhibit entry of
impurities such as hydrogen in the insulator 280 into the insulator
250, which can further reduce the hydrogen concentration of the
insulator 250 and the oxide 230. Thus, adverse effects on the
electric characteristics and the reliability of the transistor 200
can be suppressed. For the insulator 282, silicon nitride,
silicon
[Capacitor 100]
[0108] As illustrated in FIG. 1B, the capacitor 100 includes the
insulator 216 over the insulator 214, a conductor 204 (a conductor
204a and a conductor 204b) which is embedded in the insulator 216,
the insulator 222 over the insulator 216 and the conductor 205, and
the conductor 242a over the insulator 222.
[0109] For the capacitor 100, the conductor 204 functions as one
electrode of the capacitor 100 and the conductor 242a functions as
the other electrode of the capacitor 100. The insulator 222
functions as a dielectric of the capacitor 100. The conductor 204
is formed using the same material as the conductor 205.
[0110] The conductor 204 is formed in the same layer as the
conductor 205 included in the transistor 200. The conductor 242a
also functions as the source or the drain electrode of the
transistor 200. The insulator 222 also functions as a gate
insulator of the transistor 200. As described above, the transistor
and the capacitor can share some components to shorten the process
of fabricating a semiconductor device including the transistor 200
and the capacitor 100, whereby the cost is decreased and the yield
is improved; this is a favorable result.
[0111] Consequently, a semiconductor device that has stable
electrical characteristics with small variation and has high
reliability can be provided. A semiconductor device with
normally-off electrical characteristics can be provided. A
semiconductor device including a transistor with a high on-state
current can be provided. A semiconductor device including a
transistor with high frequency characteristics can be provided. A
semiconductor device including a transistor with a low off-state
current can be provided.
[0112] The following describes a detailed structure of a
semiconductor device including the transistor 200 and the capacitor
100 of one embodiment of the present invention.
[0113] The conductor 205 is overlapped by the oxide 230 and the
conductor 260. The conductor 205 is preferably embedded in the
insulator 216.
[0114] The conductor 260 functions as a first gate (also referred
to as a top gate) of the transistor 200 in some cases. The
conductor 205 functions as a second gate (also referred to as a
bottom gate) of the transistor 200 in some cases. The conductor 205
with a potential independent of the potential of the conductor 260
can control the V.sub.th of the transistor 200. In particular, when
a negative potential is applied to the conductor 205, the V.sub.th
of the transistor 200 becomes higher than 0 V to reduce the
off-state current of the transistor. This means that the conductor
205 with a negative potential can reduce drain current when 0 V is
applied to the conductor 260, compared to the conductor 205 without
a negative potential.
[0115] It is preferable that the conductor 205 have a larger size
than the region of the oxide 230 which is not overlapped by the
conductors 242a and 242b as shown in FIG. 1A. It is particularly
preferable that the conductor 205 extend beyond the end portions in
the channel width direction of the oxides 230a and 230b, as
illustrated in FIG. 1C. That is, the conductor 205 and the
conductor 260 preferably overlap with each other with the insulator
positioned therebetween in a region beyond the side surfaces of the
oxides 230a and 230b in the channel width direction. A large
conductor 205 can sometimes reduce local charging, which is called
"charge up", at a treatment using plasma after forming the
conductor 205. However, one embodiment of the present invention is
not limited thereto. The conductor 205 is at least overlapped by
the oxide 230 positioned between the conductors 242a and 242b.
[0116] As illustrated in FIGS. 1A and 1B, the conductor 204 is
preferably overlapped by a region of the conductor 242a where the
conductor 242a does not overlap the oxides 230a and 230b.
[0117] As shown in FIG. 1C, in a region where the conductor 260 and
the oxides 230a and 230b do not overlap, it is preferable that the
bottom surface of the conductor 260 is lower than the bottom
surface of the oxide 230b in a condition where the bottom surface
of the insulator 224 is the bottom. The difference of the height
between the bottom surfaces of the conductor 260 and the oxide 230b
in the region is greater than or equal to 0 nm and less than or
equal to 100 nm, preferably greater than or equal to 3 nm and less
than or equal to 50 nm, and further preferably greater than or
equal to 5 nm and less than or equal to 20 nm.
[0118] As described above, the conductor 260, which functions as
the gate, covers the side surfaces and the top surface of the oxide
230b, which functions as the channel formation region, with the
oxide 230c and the insulator 250 therebetween; this enables the
electrical field of the conductor 260 to exert an effect over the
oxide 230b. Hence, the transistor 200 can have a higher on-state
current and higher frequency characteristics. In this
specification, such a transistor structure in which the channel
formation region is electrically surrounded by the electric fields
of the first gate electrode and the second gate electrode is
referred to as a surrounded channel (S-channel) structure.
[0119] The conductor 205a preferably suppresses transmission of
impurities such as water or hydrogen. For example, titanium,
titanium nitride, tantalum, or tantalum nitride can be used for the
conductor 205a. A conductive material containing tungsten, copper,
or aluminum as its main component is preferably used for the
conductor 205b. Although the conductor 205 is illustrated as a two
layers, the conductor 205 can have a multilayer structure including
three or more layers.
[0120] It is preferable that an oxide semiconductor, an insulator
or a conductor under the oxide semiconductor, and an insulator or a
conductor over the oxide semiconductor are deposited successively
with different kinds of materials without being exposed to the air,
whereby a substantially highly purified intrinsic oxide
semiconductor film whose impurity (hydrogen and water, in
particular) concentration is reduced can be formed.
[0121] At least one of the insulators 214, 222, 272, 273, 282, 283,
and 284 preferably functions as a barrier insulating film that
inhibits entry of impurities such as water or hydrogen into the
transistor 200 from the substrate side or the upper side. Thus, at
least one of the insulators 214, 222, 272, 273, 282, 283, and 284
is preferably formed using an insulating material having a function
of inhibiting diffusion of impurities such as hydrogen atoms,
hydrogen molecules, water molecules, nitrogen atoms, nitrogen
molecules, nitrogen oxide molecules (e.g., N.sub.2O, NO, and
NO.sub.2), and copper atoms, that is, an insulating material
through which the impurities are less likely to pass.
Alternatively, at least one of the insulators 214, 222, 272, 273,
282, 283, and 284 is preferably formed using an insulating material
having a function of inhibiting diffusion of oxygen (e.g., at least
one of oxygen atoms and oxygen molecules), that is, an insulating
material through which oxygen is less likely to pass.
[0122] For example, the insulators 283 and 284 are preferably
formed using silicon nitride or silicon nitride oxide, and the
insulators 214, 222, 272, 273, and 282 are preferably formed using
aluminum oxide or hafnium oxide. Accordingly, it is possible to
inhibit diffusion of impurities such as water or hydrogen into the
transistor 200 from the substrate side through the insulator 214.
Additionally, it is possible to inhibit diffusion of oxygen
contained in the insulator 224 and the like to the substrate side
through the insulator 214. In addition, it is possible to inhibit
diffusion of impurities such as water or hydrogen into the
transistor 200 from the insulators 280, 274, and the like, which
are provided over the insulators 272, 273, 282, and 283.
[0123] It is sometimes preferable to reduce the resistivity of the
insulator 284; for example, when the resistivity of the insulator
284 is approximately 1.times.10.sup.13 .OMEGA.cm, the insulator 284
can relieve charge up of the conductor 204, 205, 242, 260, or 246
in some cases at a treatment using plasma after forming the
insulator 284 in the process of fabricating a semiconductor device.
The resistivity of the insulator 284 is preferably higher than or
equal to 1.times.10.sup.10 .OMEGA.cm and lower than or equal to
1.times.10.sup.15 .OMEGA.cm.
[0124] The dielectric constants of the insulators 216, 280, and 274
are preferably lower than that of the insulator 214. The use of a
material having a low dielectric constant for the interlayer film
can reduce the parasitic capacitance between wirings. For example,
for the insulators 216, 280, and 274, silicon oxide, silicon
oxynitride, silicon nitride oxide, silicon nitride, silicon oxide
to which fluorine is added, silicon oxide to which carbon is added,
silicon oxide to which carbon and nitrogen are added, porous
silicon oxide, or the like is used as appropriate.
[0125] The insulators 222 and 224 have a function as a gate
insulator.
[0126] Here, it is preferable that the insulator 224 in contact
with the oxide 230 release oxygen by heating. In this
specification, oxygen that is released by heating is referred to as
excess oxygen in some cases. For example, silicon oxide, silicon
oxynitride, or the like may be used for the insulator 224
appropriately. When such an insulator containing oxygen is provided
in contact with the oxide 230, oxygen vacancies in the oxide 230
can be reduced, leading to an improvement in reliability of the
transistor 200.
[0127] Specifically, an oxide material that releases some oxygen by
heating is preferably used for the insulator 224. An oxide that
releases oxygen by heating is an oxide film in which the amount of
released oxygen molecule is greater than or equal to
1.0.times.10.sup.18 molecules/cm.sup.3, preferably greater than or
equal to 1.0.times.10.sup.19 molecules/cm.sup.3, further preferably
greater than or equal to 2.0.times.10.sup.19 molecules/cm.sup.3 or
greater than or equal to 3.0.times.10.sup.20 molecules/cm.sup.3 in
thermal desorption spectroscopy (TDS) analysis. In the TDS
analysis, the film surface temperature is preferably higher than or
equal to 100.degree. C. and lower than or equal to 700.degree. C.,
or higher than or equal to 100.degree. C. and lower than or equal
to 400.degree. C.
[0128] The insulator 222 preferably functions as a barrier
insulating film that inhibits entry of impurities such as water or
hydrogen into the transistor 200 from the substrate side. For
example, it is preferable that the insulator 222 less transmit
hydrogen than the insulator 224. Surrounding the insulator 224, the
oxide 230, and the like with the insulators 222 and 283 can inhibit
entry of impurities such as water or hydrogen into the transistor
200 from outside.
[0129] Furthermore, the insulator 222 preferably has a function of
inhibiting oxygen (e.g., at least one of oxygen atoms and oxygen
molecules) diffusion; that is, it is preferable that oxygen is less
likely to pass through the insulator 222. For example, it is
preferable that the insulator 222 less transmit oxygen than the
insulator 224. The insulator 222 preferably has a function of
inhibiting diffusion of oxygen and impurities, so that oxygen
contained in the oxide 230 less reach the region under the
insulator 222. The insulator 222 can also inhibit oxidization of
the conductor 205 with oxygen contained in the insulator 224 and
the oxide 230.
[0130] As the insulator 222, an insulator containing an oxide of
aluminum and/or an oxide of hafnium, which are insulating
materials, is preferably used. For the insulator containing an
oxide of aluminum and/or an oxide of hafnium, aluminum oxide,
hafnium oxide, an oxide containing aluminum and hafnium (hafnium
aluminate), or the like is preferably used. The insulator 222 with
such a material can function as a layer inhibiting oxygen diffusion
from the oxide 230 and entry of impurities such as hydrogen into
the oxide 230 from the periphery of the transistor 200.
[0131] Aluminum oxide, bismuth oxide, germanium oxide, niobium
oxide, silicon oxide, titanium oxide, tungsten oxide, yttrium
oxide, or zirconium oxide may be added to the insulators, for
example. Alternatively, the insulators may be subjected to
nitriding treatment. Silicon oxide, silicon oxynitride, or silicon
nitride may be stacked over the insulator.
[0132] The insulator 222 may have a single-layer structure or a
stacked-layer structure using an insulator containing what is
called a high-k material such as aluminum oxide, hafnium oxide,
tantalum oxide, zirconium oxide, lead zirconate titanate (PZT),
strontium titanate (SrTiO.sub.3), or (Ba,Sr)TiO.sub.3 (BST). For a
stacked-layer structure of the insulator 222, a three-layer
structure with zirconium oxide, aluminum oxide, and zirconium oxide
in this order, or a four-layer structure with zirconium oxide,
aluminum oxide, zirconium oxide, and aluminum oxide in this order
can be employed, for example. For the insulator 222, a compound
containing hafnium and zirconium may be employed. When the
semiconductor is minimized and highly integrated, a dielectric used
for a gate insulator and a capacitor become thin, which causes a
problem of leak current from a transistor and a capacitor. When a
high-k material is used for an insulator functioning as a gate
insulator and a dielectric used for a capacitor, a gate potential
at the time when the transistor operates can be reduced while the
physical thickness of a gate insulator and a capacitor is
maintained.
[0133] Note that the insulators 222 and 224 may each have a
stacked-layer structure of two or more layers. In that case, the
stacked layers are not necessarily formed of the same material and
may be formed of different materials.
[0134] The oxide 243 (the oxides 243a and 243b) may be provided
between the oxide 230b and the conductor 242 (the conductors 242a
and 242b), which functions as the source electrode or the drain
electrode. This structure eliminates the contact of the conductor
242 and the oxide 230, so that oxygen in the oxide 230 is less
absorbed into the conductor 242. That is, inhibiting oxidization of
the conductor 242 can inhibit the decrease in conductivity of the
conductor 242. Accordingly, the oxide 243 preferably has a function
of inhibiting oxidization of the conductor 242.
[0135] Accordingly, the oxide 243 preferably has a function of
inhibiting oxygen transmission. When the oxide 243, which has a
function of inhibiting oxygen transmission, is provided between the
conductor 242, functioning as the source electrode or the drain
electrode, and the oxide 230b, the electrical resistance between
the conductor 242 and the oxide 230b can be reduced, which is
preferable. Such a structure improves the electrical
characteristics and reliability of the transistor 200.
[0136] A metal oxide including an element M may be used for the
oxide 243. In particular, aluminum, gallium, yttrium, or tin is
preferably used for the element M. The concentration of the element
M in the oxide 243 is preferably higher than that in the oxide
230b. Alternatively, gallium oxide may be used for the oxide 243. A
metal oxide such as In--M--Zn oxide may be used for the oxide 243.
Specifically, the atomic ratio of the element M to In in the metal
oxide used for the oxide 243 is preferably higher than that in the
metal oxide used for the oxide 230b. The thickness of the oxide 243
ranges preferably from 0.5 nm to 5 nm, further preferably from 1 nm
to 3 nm. The oxide 243 preferably has crystallinity. The oxide 243
with crystallinity efficiently inhibits release of oxygen from the
oxide 230. When the oxide 243 has a hexagonal crystal structure,
for example, release of oxygen from the oxide 230 can sometimes be
inhibited.
[0137] Note that the oxide 243 is not necessarily provided. Without
the oxide 243, the conductor 242 is sometimes oxidized by oxygen
diffused from the oxide 230, when the conductor 242 (the conductors
242a and 242b) and the oxide 230 are in contact with the oxide 230.
It is highly possible that oxidation of the conductor 242 lowers
the conductivity of the conductor 242. Note that diffusion of
oxygen from the oxide 230 into the conductor 242 can be interpreted
as absorption of oxygen in the oxide 230 by the conductor 242.
[0138] When oxygen in the oxide 230 is diffused into the conductor
242 (the conductors 242a and 242b), other layers are sometimes
formed between the conductor 242a and the oxide 230b, and between
the conductor 242b and the oxide 230b. The layers contain more
oxygen than the conductor 242, so that the layers presumably have
an insulating property. The three-layer structure of the conductor
242, the layer, and the oxide 230b can be the structure with a
metal, an insulator, and a semiconductor, which is sometimes called
a metal-insulator-semiconductor (MIS) structure or a diode junction
structure having an MIS structure as its main part.
[0139] The above another layer is not necessarily formed between
the conductor 242 and the oxide 230b, but the another layer may be
formed between the conductor 242 and the oxide 230c, or other
layers are formed both between the conductor 242 and the conductor
230b, and the conductor 242 and the conductor 230c.
[0140] The conductor 242 (the conductors 242a and 242b) functioning
as a source electrode and a drain electrode is provided over the
oxide 243. The thickness of the conductor 242 is, for example,
greater than or equal to 1 nm to less than or equal to 50 nm,
preferably greater than or equal to 2 nm to less than or equal to
25 nm.
[0141] For the conductor 242, it is preferable to use a metal
element selected from aluminum, chromium, copper, silver, gold,
platinum, tantalum, nickel, titanium, molybdenum, tungsten,
hafnium, vanadium, niobium, manganese, magnesium, zirconium,
beryllium, indium, ruthenium, iridium, strontium, and lanthanum; an
alloy containing any of the above metal elements; an alloy
containing a combination of the above metal elements; or the like.
For example, tantalum nitride, titanium nitride, tungsten, a
nitride containing titanium and aluminum, a nitride containing
tantalum and aluminum, ruthenium oxide, ruthenium nitride, an oxide
containing strontium and ruthenium, an oxide containing lanthanum
and nickel, or the like is preferably used. Tantalum nitride,
titanium nitride, a nitride containing titanium and aluminum, a
nitride containing tantalum and aluminum, ruthenium oxide,
ruthenium nitride, an oxide containing strontium and ruthenium, and
an oxide containing lanthanum and nickel are preferable because
they are oxidation-resistant conductive materials or materials that
retain their conductivity even after absorbing oxygen.
[0142] The insulator 272 is provided in contact with the top
surface of the conductor 242 and preferably functions as a barrier
layer. The structure enables less absorption of excess oxygen in
the insulator 280 into the conductor 242. Furthermore, by
suppressing oxidation of the conductor 242, an increase in the
contact resistance between the transistor 200 and a wiring can be
suppressed. Consequently, the transistor 200 can have favorable
electrical characteristics and reliability.
[0143] Thus, the insulator 272 preferably has a function of
inhibiting oxygen diffusion. For example, the insulator 272
preferably has a function of inhibiting oxygen diffusion more than
the insulator 280. The insulator 272 can be formed of an insulator
containing an oxide of one or both of aluminum and hafnium, for
example. An insulator containing aluminum nitride can also be used
for the insulator 272, for example.
[0144] As illustrated in FIG. 1D, the insulator 272 is in contact
with the top surface and the side surfaces of the conductor 242a.
Although not illustrated, the insulator 272 is in contact with the
top surface and the side surfaces of the conductor 242b. The
insulator 273 is provided over the insulator 272. This structure
can prevent oxygen, which is added to the insulator 280, from being
absorbed into the conductor 242.
[0145] The insulator 250 functions as a gate insulator. The
insulator 250 is preferably positioned in contact with the top
surface of the oxide 230c. For the insulator 250, any of silicon
oxide, silicon oxynitride, silicon nitride oxide, silicon nitride,
silicon oxide to which fluorine is added, silicon oxide to which
carbon is added, silicon oxide to which carbon and nitrogen are
added, and porous silicon oxide can be used. Silicon oxide and
silicon oxynitride, which have thermal stability, are particularly
preferable.
[0146] The insulator 250 is preferably formed using an insulator
from which oxygen is released by heating as in the insulator 224.
When an insulator from which oxygen is released by heating is
provided as the insulator 250 in contact with the top surface of
the oxide 230c, oxygen can be efficiently supplied to the channel
formation region of the oxide 230b. As in the insulator 224, the
concentration of impurities such as water or hydrogen in the
insulator 250 is preferably reduced. The thickness of the insulator
250 is preferably greater than or equal to 1 nm and less than or
equal to 20 nm.
[0147] A metal oxide may be provided between the insulator 250 and
the conductor 260. The metal oxide preferably prevents oxygen
diffusion from the insulator 250 into the conductor 260. Providing
the metal oxide that inhibits oxygen diffusion inhibits diffusion
of oxygen from the insulator 250 to the conductor 260. That is, the
reduction in the amount of oxygen supplied to the oxide 230 can be
inhibited. Moreover, oxidation of the conductor 260 due to oxygen
in the insulator 250 can be inhibited.
[0148] Note that the metal oxide has a function as the part of the
gate insulator in some cases. Therefore, when silicon oxide,
silicon oxynitride, or the like is used for the insulator 250, a
metal oxide that is a high-k material with a high dielectric
constant is preferably used as the metal oxide. The gate insulator
having a stacked-layer structure of the insulator 250 and the metal
oxide can be thermally stable and have a high dielectric constant.
Accordingly, a gate potential applied during operation of the
transistor can be reduced while the physical thickness of the gate
insulator is maintained. In addition, the equivalent oxide
thickness (EOT) of the insulator functioning as the gate insulator
can be reduced.
[0149] Specifically, a metal oxide containing one or more of
hafnium, aluminum, gallium, yttrium, zirconium, tungsten, titanium,
tantalum, nickel, germanium, magnesium, and the like can be used.
It is particularly preferable to use an insulator containing an
oxide of one or both of aluminum and hafnium, for example, aluminum
oxide, hafnium oxide, or an oxide containing aluminum and hafnium
(hafnium aluminate).
[0150] The metal oxide has a function as part of the gate in some
cases. In this case, a conductive material containing oxygen is
preferably provided on the channel formation region side, in which
case oxygen released from the conductive material is easily
supplied to the channel formation region.
[0151] It is particularly preferable to use, for the conductor
functioning as the gate electrode, a conductive material containing
oxygen and a metal element contained in a metal oxide in which the
channel is formed. A conductive material containing any of the
above metal elements and nitrogen may also be used. Indium tin
oxide, indium oxide containing tungsten oxide, indium zinc oxide
containing tungsten oxide, indium oxide containing titanium oxide,
indium tin oxide containing titanium oxide, indium zinc oxide, or
indium tin oxide to which silicon is added may be used. Indium
gallium zinc oxide containing nitrogen may be used. With use of
such a material, hydrogen contained in the metal oxide in which the
channel is formed can be captured in some cases. Hydrogen entering
from a surrounding insulator or the like can also be captured in
some cases.
[0152] Although the conductor 260 has a two-layer structure in
FIGS. 1A to 1C, the conductor 260 may have a single-layer structure
or a stacked-layer structure of three or more layers.
[0153] The conductor 260a is preferably formed using a conductive
material which has a function of inhibiting diffusion of impurities
such as hydrogen atoms, hydrogen molecules, water molecules,
nitrogen atoms, nitrogen molecules, nitrogen oxide molecules (e.g.,
N.sub.2O, NO, and NO.sub.2), and copper atoms. Alternatively, the
oxide 260a is preferably formed using a conductive material which
has a function of inhibiting diffusion of oxygen (e.g., at least
one of oxygen atoms, oxygen molecules, and the like).
[0154] When the conductor 260a has a function of inhibiting
diffusion of oxygen, the conductivity of the conductor 260b can be
prevented from being lowered because of oxidization of the
conductor 260b due to oxygen in the insulator 250. As a conductive
material which has a function of inhibiting diffusion of oxygen,
for example, tantalum, tantalum nitride, ruthenium, ruthenium
oxide, or the like is preferably used.
[0155] Furthermore, the conductor 260b is preferably formed using a
conductive material including tungsten, copper, or aluminum as its
main component. The conductor 260 also functions as a wiring and
thus is preferably a conductor having high conductivity. For
example, a conductive material containing tungsten, copper, or
aluminum as its main component can be used. The conductor 260b may
have a stacked-layer structure, for example, a stacked-layer
structure of the above conductive material and titanium or titanium
nitride.
[0156] The insulator 280 preferably includes, for example, silicon
oxide, silicon oxynitride, silicon nitride oxide, silicon oxide to
which fluorine is added, silicon oxide to which carbon is added,
silicon oxide to which carbon and nitrogen are added, or porous
silicon oxide. Silicon oxide and silicon oxynitride are
particularly preferable because of their thermal stability. Silicon
oxide, silicon oxynitride, and porous silicon oxide are
particularly preferable because a region whose oxygen is released
by heating can be easily formed in these materials. The insulator
280 may have a stacked-layer structure of the above materials;
silicon oxide formed by a sputtering method and silicon oxynitride
formed by a CVD method thereover, for example. Silicon nitride can
be stacked over the above stacked structure.
[0157] The insulator 280 preferably contains a reduced
concentration of impurities such as water or hydrogen. The top
surface of the insulator 280 may be planarized.
[0158] The insulators 282 and 283 preferably function as barrier
insulating films for inhibiting entry of impurities such as water
or hydrogen into the insulator 280 from the upper side. The
insulators 282 and 283 preferably function as barrier insulating
films for inhibiting transmission of oxygen. The insulators 282 and
283 may be formed using an insulator such as aluminum oxide,
silicon nitride, or silicon nitride oxide. The insulator 282 may be
formed using aluminum oxide, which has high barrier property
against oxygen and the insulator 283 may be formed from silicon
nitride, which has high barrier property against hydrogen, for
example.
[0159] The insulator 274 as an interlayer film is preferably
provided over the insulator 283. As in the insulator 224 or the
like, the concentration of impurities such as water or hydrogen in
the insulator 274 is preferably lowered.
[0160] The conductor 240 is preferably formed using a conductive
material containing tungsten, copper, or aluminum as its main
component. The conductor 240 may have a stacked-layer structure.
Although the conductor 240 has a circular shape in the top view of
FIG. 1A, the shape is not limited thereto. For example, the
conductor 240 may have an almost circular shape such as an ellipse,
a polygonal shape such as a square, or a polygonal shape such as a
square with rounded corners.
[0161] Moreover, the insulator 240 is preferably formed using a
conductive material which has a function of inhibiting the
transmission of oxygen and impurities such as water and hydrogen
when the insulator 240 has a stacked-layer structure. For example,
tantalum, tantalum nitride, titanium, titanium nitride, ruthenium,
ruthenium oxide, or the like is preferably used. The conductive
material having a function of inhibiting the transmission of oxygen
and impurities such as water and hydrogen may have a single-layer
structure or a stacked-layer structure. When the conductive
material is used, the amount of impurities such as hydrogen and
water that enter the oxide 230 from the insulator 280 through the
conductor 240 can be further reduced. Moreover, oxygen added to the
insulator 280 can be prevented from being absorbed by the conductor
240.
[0162] For the insulator 241, for example, an insulator such as
silicon nitride, aluminum oxide, or silicon nitride oxide can be
used. The insulator 241 is provided in contact with the insulators
283, 282, 280, 273, and 272, which inhibits entry of impurities
such as water or hydrogen into the oxide 230 through the conductor
240. Silicon nitride is particularly preferable for the insulator
241 because of its high blocking property against hydrogen.
Moreover, oxygen contained in the insulator 280 can be inhibited
from being absorbed into the conductor 240.
[0163] The conductor 246 functioning as a wiring can be provided in
contact with the top surface of the conductor 240. The conductor
246 is preferably formed using a conductive material containing
tungsten, copper, or aluminum as its main component. The conductor
may have a stacked-layer structure, for example, a stack of
titanium or titanium nitride and the above conductive material.
Note that the conductor may be formed to be embedded in an opening
provided in an insulator.
[0164] The insulator 284 can be formed over the conductor 246 and
the insulator 283. In such a structure, the conductor 246 can be
surrounded by the insulators 283 and 284. This inhibits oxidization
of the conductor 246 and entry of impurities such as hydrogen into
the transistor 200 through the conductor 246. For the insulator
284, for example, an insulator such as silicon nitride, aluminum
oxide, or silicon nitride oxide can be used. The insulator 274 may
be formed over the insulator 284. The insulator 274 can be formed
using the same material as that used for the insulator 280.
<Materials Constituting Semiconductor Device>
[0165] Materials that can be used for the semiconductor device are
described below.
<Substrate>
[0166] As a substrate where the transistor 200 is formed, an
insulator substrate, a semiconductor substrate, or a conductor
substrate can be used, for example. Examples of the insulator
substrate include a glass substrate, a quartz substrate, a sapphire
substrate, a stabilized zirconia substrate (e.g., an
yttria-stabilized zirconia substrate), and a resin substrate.
Examples of the semiconductor substrate include a semiconductor
substrate of silicon or germanium and a compound semiconductor
substrate of silicon carbide, silicon germanium, gallium arsenide,
indium phosphide, zinc oxide, or gallium oxide. Other examples
include a semiconductor substrate in which an insulator region is
provided in the above semiconductor substrate such as a silicon on
insulator (SOI) substrate. Examples of the conductor substrate
include a graphite substrate, a metal substrate, an alloy
substrate, and a conductive resin substrate. A substrate containing
a nitride of a metal, a substrate including an oxide of a metal, or
the like can also be used. Moreover, an insulator substrate
provided with a conductor or a semiconductor, a semiconductor
substrate provided with a conductor or an insulator, a conductor
substrate provided with a semiconductor or an insulator, or the
like may be used. Alternatively, any of these substrates provided
with an element may be used. Examples of the element provided over
the substrate include a capacitor, a resistor, a switching element,
a light-emitting element, and a memory element.
<Insulator>
[0167] Examples of an insulator include an insulating oxide, an
insulating nitride, an insulating oxynitride, an insulating nitride
oxide, an insulating metal oxide, an insulating metal oxynitride,
and an insulating metal nitride oxide.
[0168] With miniaturization and high integration of a transistor,
for example, a problem such as generation of leakage current may
arise because of a thin gate insulator. When a high-k material is
used for an insulator functioning as a gate insulator, the driving
voltage of the transistor can be reduced while the physical
thickness of the gate insulator is kept. When a material having a
low dielectric constant is used for an insulator functioning as an
interlayer film, the parasitic capacitance between wirings can be
reduced. A material is preferably selected depending on the
function of an insulator.
[0169] Examples of the insulator having a high dielectric constant
include gallium oxide, hafnium oxide, zirconium oxide, an oxide
containing aluminum and hafnium, an oxynitride containing aluminum
and hafnium, an oxide containing silicon and hafnium, an oxynitride
containing silicon and hafnium, and a nitride containing silicon
and hafnium.
[0170] Examples of the insulator having a low dielectric constant
include silicon oxide, silicon oxynitride, silicon nitride oxide,
silicon oxide to which fluorine is added, silicon oxide to which
carbon is added, silicon oxide to which carbon and nitrogen are
added, porous silicon oxide, and a resin.
[0171] A transistor using an oxide semiconductor can have stable
electrical characteristics when surrounded by an insulator having a
function of inhibiting transmission of oxygen and impurities such
as hydrogen. The insulator having a function of inhibiting
transmission of oxygen and impurities such as hydrogen can have,
for example, a single-layer structure or a stacked-layer structure
of an insulator including boron, carbon, nitrogen, oxygen,
fluorine, magnesium, aluminum, silicon, phosphorus, chlorine,
argon, gallium, germanium, yttrium, zirconium, lanthanum,
neodymium, hafnium, or tantalum. Specifically, as the insulator
having a function of inhibiting transmission of oxygen and
impurities such as hydrogen, a metal oxide such as aluminum oxide,
magnesium oxide, gallium oxide, germanium oxide, yttrium oxide,
zirconium oxide, lanthanum oxide, neodymium oxide, hafnium oxide,
or tantalum oxide or a metal nitride such as aluminum nitride,
aluminum titanium nitride, titanium nitride, silicon nitride oxide,
or silicon nitride can be used.
[0172] An insulator functioning as a gate insulator preferably
includes a region containing oxygen that is released by heating.
For example, silicon oxide or silicon oxynitride that includes a
region containing oxygen released by heating is provided in contact
with the oxide 230 to compensate for the oxygen vacancies in the
oxide 230.
<Conductor>
[0173] For the conductor, it is preferable to use a metal element
selected from aluminum, chromium, copper, silver, gold, platinum,
tantalum, nickel, titanium, molybdenum, tungsten, hafnium,
vanadium, niobium, manganese, magnesium, zirconium, beryllium,
indium, ruthenium, iridium, strontium, lanthanum, and the like; an
alloy containing any of the above metal elements; an alloy
containing a combination of the above metal elements; or the like.
For example, tantalum nitride, titanium nitride, tungsten, a
nitride containing titanium and aluminum, a nitride containing
tantalum and aluminum, ruthenium oxide, ruthenium nitride, an oxide
containing strontium and ruthenium, an oxide containing lanthanum
and nickel, or the like is preferably used. Tantalum nitride,
titanium nitride, a nitride containing titanium and aluminum, a
nitride containing tantalum and aluminum, ruthenium oxide,
ruthenium nitride, an oxide containing strontium and ruthenium, and
an oxide containing lanthanum and nickel are preferable because
they are oxidation-resistant conductive materials or materials that
retain their conductivity even after absorbing oxygen.
Alternatively, a semiconductor having high electric conductivity,
typified by polycrystalline silicon containing an impurity element
such as phosphorus, or silicide such as nickel silicide may be
used.
[0174] Conductive layers formed using any of the above materials
may be stacked. For example, a stacked-layer structure combining a
material containing any of the above metal elements and a
conductive material containing oxygen may be used. Alternatively, a
stacked-layer structure combining a material containing any of the
above metal elements and a conductive material containing nitrogen
may be used. Alternatively, a stacked-layer structure combining a
material containing any of the above metal elements, a conductive
material containing oxygen, and a conductive material containing
nitrogen may be used.
[0175] When an oxide is used for the channel formation region of
the transistor, a conductor functioning as the gate electrode
preferably employs a stacked-layer structure using a material
containing any of the above metal elements and a conductive
material containing oxygen. In this case, the conductive material
containing oxygen is preferably provided on the channel formation
region side. When the conductive material containing oxygen is
provided on the channel formation region side, oxygen released from
the conductive material is easily supplied to the channel formation
region.
[0176] It is particularly preferable to use, for the conductor
functioning as the gate electrode, a conductive material containing
oxygen and a metal element contained in a metal oxide in which the
channel is formed. A conductive material containing any of the
above metal elements and nitrogen can also be used. For example, a
conductive material containing nitrogen, such as titanium nitride
or tantalum nitride, can be used. Indium tin oxide, indium oxide
containing tungsten oxide, indium zinc oxide containing tungsten
oxide, indium oxide containing titanium oxide, indium tin oxide
containing titanium oxide, indium zinc oxide, or indium tin oxide
to which silicon is added can be used. Indium gallium zinc oxide
containing nitrogen can be used. With the use of such a material,
hydrogen contained in the metal oxide in which the channel is
formed can be captured in some cases. Furthermore, hydrogen
entering from a surrounding insulator or the like can be captured
in some cases.
<Metal oxide>
[0177] For the oxide 230, a metal oxide functioning as an oxide
semiconductor is preferably used. A metal oxide that can be used
for the oxide 230 according to the present invention is described
below.
[0178] The metal oxide preferably contains at least indium or zinc.
In particular, indium and zinc are preferably contained. In
addition, aluminum, gallium, yttrium, tin, or the like is
preferably contained. Furthermore, one or more elements selected
from boron, titanium, iron, nickel, germanium, zirconium,
molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum,
tungsten, magnesium, and the like may be contained.
[0179] Here, the case where the metal oxide is In--M--Zn oxide,
which contains indium, an element M, and zinc is considered. The
element M may be aluminum, gallium, yttrium, or tin. Other examples
that can be used as the element M include boron, titanium, iron,
nickel, germanium, zirconium, molybdenum, lanthanum, cerium,
neodymium, hafnium, tantalum, tungsten, and magnesium. Note that
two or more of the above elements can be used in combination as the
element M in some cases.
[0180] Note that in this specification and the like, a metal oxide
containing nitrogen is also referred to as a metal oxide in some
cases. A metal oxide containing nitrogen may also be referred to as
a metal oxynitride.
<Composition of Metal Oxide>
[0181] The compositions of a cloud-aligned composite oxide
semiconductor (CAC-OS) and a c-axis-aligned crystalline oxide
semiconductor (CAAC-OS), which are metal oxides that can be used in
the OS transistor, will be described.
[0182] A CAC-OS or a CAC-metal oxide has a conducting function in
part of the material and has an insulating function in other part
of the material, and has a semiconductor function as a whole
material. In the case where the CAC-OS or the CAC-metal oxide is
used in an active layer of a transistor, the conducting function is
to allow electrons (or holes) serving as carriers to flow, and the
insulating function is to not allow electrons serving as carriers
to flow. By the complementary function of the conducting function
and the insulating function, the CAC-OS or the CAC-metal oxide can
have a switching function (on/off function). In the CAC-OS or the
CAC-metal oxide, separation of the functions can maximize each
function.
[0183] The CAC-OS or the CAC-metal oxide includes conductive
regions and insulating regions. The conductive regions have the
above-described conducting function, and the insulating regions
have the above-described insulating function. In some cases, the
conductive regions and the insulating regions in the material are
separated at the nanoparticle level. In some cases, the conductive
regions and the insulating regions are unevenly distributed in the
material. The conductive regions are observed to be coupled in a
cloud-like manner with their boundaries blurred, in some cases.
[0184] In the CAC-OS or the CAC-metal oxide, the conductive regions
and the insulating regions each have a size of greater than or
equal to 0.5 nm and less than or equal to 10 nm, preferably greater
than or equal to 0.5 nm and less than or equal to 3 nm and are
dispersed in the material in some cases.
[0185] The CAC-OS or the CAC-metal oxide includes components having
different band gaps. For example, the CAC-OS or the CAC-metal oxide
includes a component having a wide gap due to the insulating region
and a component having a narrow gap due to the conductive region.
In this case, carriers mainly flow in the component having a narrow
gap. Furthermore, the component having a narrow gap complements the
component having a wide gap, and carriers also flow in the
component having a wide gap in conjunction with the component
having a narrow gap. Therefore, in the case where the
above-described CAC-OS or CAC-metal oxide is used for a channel
formation region of a transistor, the transistor in the on state
can have high current drive capability, that is, a high on-state
current and high field-effect mobility.
[0186] In other words, the CAC-OS or the CAC-metal oxide can also
be called a matrix composite or a metal matrix composite.
[Structure of Metal Oxide]
[0187] An oxide semiconductor (metal oxide) is classified into a
single crystal oxide semiconductor and a non-single-crystal oxide
semiconductor. Examples of a non-single-crystal oxide semiconductor
include a CAAC-OS, a polycrystalline oxide semiconductor, an nc-OS,
an amorphous-like oxide semiconductor (a-like OS), and an amorphous
oxide semiconductor.
[0188] Oxide semiconductors might be classified in a manner
different from the above-described one when classified in terms of
the crystal structure. The classification of the crystal structures
of oxide semiconductor will be explained with FIG. 15A. FIG. 15A is
a diagram showing a classification of a crystal structures of an
oxide semiconductor, typically IGZO (a metal oxide containing In,
Ga, and Zn).
[0189] IGZO is classified into "amorphous", "crystalline", and
"crystal", as shown in FIG. 15A. "Amorphous" includes completely
amorphous structure. "Crystalline" includes c-axi-aligned
crystalline (CAAC), nanocrystalline (nc), and cloud-aligned
composite (CAC) structures. "Crystal" includes single crystal and
poly crystal structures.
[0190] The structure shown in the thick frame in FIG. 15A is a new
crystalline phase. This structure is positioned in a boundary
region between "amorphous" and "crystal". "Amorphous", which is
energetically unstable, and "crystalline" are completely different
structures.
[0191] A crystal structure of a film or a substrate can be analyzed
with X-ray diffraction (XRD) images. XRD spectra of quartz glass
and IGZO, which has a crystal structure classified into
crystalline, are shown in FIGS. 15B and 15C. FIG. 15B shows an XRD
spectrum of quartz glass and FIG. 15C shows an XRD spectrum of
crystalline IGZO. The crystalline IGZO whose spectrum is shown in
FIG. 15C contains In:Ga:Zn=4:2:3 (atomic ratio) and has a thickness
of 500 nm.
[0192] The peak of the XRD spectrum of quartz glass has a
symmetrical shape, as shown by the arrows in FIG. 15B. On the other
hand, the peak of the XRD spectrum of crystalline IGZO has an
asymmetrical shape, as shown by arrows in FIG. 15C. The
asymmetrical curve shows the existence of crystal. In other words,
the structure cannot be regarded as "amorphous" unless it has a
bilaterally symmetrical peak in the XRD spectrum.
[0193] The CAAC-OS has c-axis alignment, its nanocrystals are
connected in the a-b plane direction, and its crystal structure has
distortion. Note that distortion refers to a portion where the
direction of a lattice arrangement changes between a region with a
uniform lattice arrangement and another region with a uniform
lattice arrangement in a region where the nanocrystals are
connected.
[0194] The shape of the nanocrystal is basically a hexagon but is
not always a regular hexagon and is a non-regular hexagon in some
cases. A pentagonal lattice arrangement, a heptagonal lattice
arrangement, and the like are included in the distortion in some
cases. Note that it is difficult to observe a clear crystal grain
boundary even in the vicinity of distortion in the CAAC-OS. That
is, a lattice arrangement is distorted and thus formation of a
grain boundary is inhibited. This is because the CAAC-OS can
tolerate distortion owing to a low density of oxygen atom
arrangement in the a-b plane direction, a change in interatomic
bond distance by substitution of a metal element, and the like.
[0195] The CAAC-OS tends to have a layered crystal structure (also
referred to as a stacked-layer structure) in which a layer
containing indium and oxygen (hereinafter an In layer) and a layer
containing the element M, zinc, and oxygen (hereinafter an (M, Zn)
layer) are stacked. Note that indium and the element M can be
replaced with each other, and when the element M of the (M, Zn)
layer is replaced with indium, the layer can be referred to as an
(In, M, Zn) layer. When indium of the In layer is replaced with the
element M, the layer can be referred to as an (In, M) layer.
[0196] The CAAC-OS is a metal oxide with high crystallinity. By
contrast, in the CAAC-OS, a reduction in electron mobility due to a
grain boundary is less likely to occur because it is difficult to
observe a clear grain boundary. Entry of impurities, formation of
defects, or the like might decrease the crystallinity of a metal
oxide. This means that the CAAC-OS has small amounts of impurities
and defects such as oxygen vacancies (V.sub.o). Thus, a metal oxide
including the CAAC-OS is physically stable. Accordingly, the metal
oxide including the CAAC-OS is resistant to heat and has high
reliability.
[0197] In the nc-OS, a microscopic region (e.g., a region with a
size greater than or equal to 1 nm and less than or equal to 10 nm,
in particular, a region with a size greater than or equal to 1 nm
and less than or equal to 3 nm) has a periodic atomic arrangement.
A regularity of crystal orientation of nanocrystals of the nc-OS is
not observed. Thus, the orientation in a whole film is not
observed. Accordingly, in some cases, the nc-OS cannot be
distinguished from an a-like OS or an amorphous oxide semiconductor
depending on the analysis method.
[0198] Indium-gallium-zinc oxide (hereinafter referred to as IGZO)
that is a kind of metal oxide containing indium, gallium, and zinc
has a stable structure in some cases when formed of the
above-described nanocrystals. In particular, IGZO crystals tend not
to grow in the air. Thus, a stable structure is obtained when IGZO
is formed of smaller crystals (e.g., the above-described
nanocrystals) rather than larger crystals (here, crystals with a
size of several millimeters or several centimeters).
[0199] The a-like OS is a metal oxide having a structure between
that of the nc-OS and that of the amorphous oxide semiconductor.
The a-like OS has a void or a low-density region. That is, the
a-like OS has low crystallinity as compared with the nc-OS and the
CAAC-OS.
[0200] An oxide semiconductor (metal oxide) can have various
structures that show various different properties. Two or more of
the amorphous oxide semiconductor, the polycrystalline oxide
semiconductor, the a-like OS, the nc-OS, and the CAAC-OS may be
included in an oxide semiconductor of one embodiment of the present
invention.
[0201] Note that a structure of an oxide semiconductor (metal
oxide) in the semiconductor device of one embodiment of the present
invention is not particularly limited; however, the oxide
semiconductor (metal oxide) preferably has crystallinity. For
example, the oxide 230 can have a CAAC-OS structure and the oxide
243 can have a hexagonal crystal structure. The semiconductor
device can have high reliability when the oxides 230 and 243 have
the above crystal structures. The oxide 230a, the oxide 230c, and
the oxide 243 can have substantially the same composition.
<Transistor Including Oxide Semiconductor>
[0202] Next, a transistor using the above oxide semiconductor is
described.
[0203] The transistor using the above oxide semiconductor can have
high field-effect mobility and high reliability.
[0204] The transistor preferably has an oxide semiconductor with a
low carrier concentration. In order to reduce the carrier density
of an oxide semiconductor film, the impurity concentration in the
oxide semiconductor film is reduced so that the density of defect
states can be reduced. In this specification and the like, a state
with a low impurity concentration and a low density of defect
states is referred to as a highly purified intrinsic or
substantially highly purified intrinsic state.
[0205] A highly purified intrinsic or substantially highly purified
intrinsic oxide semiconductor film has a low density of defect
states and accordingly has low density of trap states in some
cases.
[0206] Charges trapped by the trap states in an oxide semiconductor
take a long time to be released and may behave like fixed charges.
A transistor whose channel formation region is formed in an oxide
semiconductor having a high density of trap states has unstable
electrical characteristics in some cases.
[0207] In order to obtain stable electrical characteristics of the
transistor, it is effective to reduce impurity concentrations in
the oxide semiconductor. In order to reduce the concentration of
impurities in the oxide semiconductor, impurity concentrations in a
film that is adjacent to the oxide semiconductor is preferably
reduced. Examples of impurities include hydrogen, nitrogen, alkali
metal, alkaline earth metal, iron, nickel, and silicon.
<Impurities>
[0208] The influence of impurities in the oxide semiconductor is
described.
[0209] When silicon or carbon, which is a Group 14 element, is
contained in an oxide semiconductor, defect states are formed in
the oxide semiconductor. The concentration of silicon or carbon in
the oxide semiconductor, the concentration thereof at the interface
and in the vicinity of the interface between the oxide
semiconductor and, for example, an insulator (measured by secondary
ion mass spectrometry (SIMS)) are lower than or equal to
2.times.10.sup.18 atoms/cm.sup.3, preferably lower than or equal to
2.times.10.sup.17 atoms/cm.sup.3.
[0210] When the oxide semiconductor contains alkali metal or
alkaline earth metal, defect states are formed and carriers are
generated in some cases. A transistor using an oxide semiconductor
that contains alkali metal or alkaline earth metal tends to have
normally-on characteristics. Therefore, it is preferable to reduce
the concentration of alkali metal or alkaline earth metal in the
oxide semiconductor. Specifically, the concentration of alkali
metal or alkaline earth metal in the oxide semiconductor, which is
measured by SIMS, is lower than or equal to 1.times.10.sup.18
atoms/cm.sup.3, preferably lower than or equal to 2.times.10.sup.16
atoms/cm.sup.3.
[0211] An oxide semiconductor containing nitrogen easily becomes
n-type by generation of electrons serving as carriers and an
increase in carrier concentration. A transistor using an oxide
semiconductor that contains nitrogen as the semiconductor tends to
have normally-on characteristics. For this reason, the amount of
nitrogen in the oxide semiconductor is preferably reduced as much
as possible. The nitrogen concentration of the oxide semiconductor
measured by SIMS is, for example, lower than 5.times.10.sup.19
atoms/cm.sup.3, preferably lower than or equal to 5.times.10.sup.18
atoms/cm.sup.3, further preferably lower than or equal to
1.times.10.sup.18 atoms/cm.sup.3, still further preferably lower
than or equal to 5.times.10.sup.17 atoms/cm.sup.3.
[0212] Hydrogen contained in an oxide semiconductor reacts with
oxygen, which reacts with metal atoms, to be water, and thus causes
an oxygen vacancy in some cases. Entry of hydrogen into the oxygen
vacancy generates an electron serving as a carrier in some cases.
Furthermore, in some cases, some hydrogen reacts with oxygen, which
reacts with metal atoms, to generate an electron serving as a
carrier. Thus, a transistor including an oxide semiconductor that
contains hydrogen tends to have normally-on characteristics.
Accordingly, hydrogen in the oxide semiconductor is preferably
reduced as much as possible. Specifically, the hydrogen
concentration in the oxide semiconductor measured by SIMS is lower
than 1.times.10.sup.20 atoms/cm.sup.3, preferably lower than
1.times.10.sup.19 atoms/cm.sup.3, further preferably lower than
5.times.10.sup.18 atoms/cm.sup.3, still further preferably lower
than 1.times.10.sup.18 atoms/cm.sup.3.
[0213] An oxide semiconductor with sufficiently reduced impurities
is used for a channel formation region of a transistor, so that the
transistor can have stable electrical characteristics.
<Other Semiconductor Materials>
[0214] Semiconductor materials that can be used for the oxide 230
is not limited to the above metal oxides. A semiconductor material
which has a band gap (a semiconductor material that is not a
zero-gap semiconductor) can be used. For example, a single element
semiconductor such as silicon, a compound semiconductor such as
gallium arsenide, and a layered material, which can be called as an
atomic layered material or a two-dimensional material, are
preferably used as a semiconductor material. A layered material
having semiconductor property is preferably used for a
semiconductor material.
[0215] In this specification and the like, the layered material is
a group of materials having a layered crystal structure. In the
layered crystal structure, layers formed by covalent bonding or
ionic bonding are stacked with a bonding such as the Van der Waals
force, which is weaker than covalent bonding or ionic bonding. The
layered material has high electrical conductivity in a monolayer,
that is, high two-dimensional electrical conductivity. When a
material with a high two-dimensional electrical conductivity that
functions as a semiconductor is used for a channel formation
region, the transistor can have a high on current.
[0216] Examples of the layered material include graphene, silicene,
and chalcogenide. Chalcogenide is a compound containing chalcogen.
Chalcogen is a general term of elements belonging to Group 16,
which contains oxygen, sulfur, selenium, tellurium, polonium, and
livermorium. Chalcogenide includes transition metal chalcogenide
and chalcogenide of Group 13 elements.
[0217] The oxide 230 is preferably formed using a transition metal
chalcogenide functioning as a semiconductor, for example. Examples
of transition metal chalcogenide which can be used for the oxide
230 include molybdenum sulfide (typically MoS.sub.3), molybdenum
selenide (typically MoSe.sub.2), molybdenum telluride (typically
MoTe.sub.2), tungsten sulfide (WS.sub.2), tungsten selenide
(typically WSe.sub.2), tungsten telluride (typically WTe.sub.2),
hafnium sulfide (HfS.sub.2), hafnium selenide (HfSe.sub.2),
zirconium sulfide (ZrS.sub.3), zirconium selenide (ZrSe.sub.2).
<Method for Manufacturing Semiconductor Device>
[0218] A manufacturing method for a semiconductor device shown in
FIGS. 1A to 1D including the transistor 200 and the capacitor 100
of the present invention will be described with reference to FIGS.
4A to 4C to FIGS. 14A to 14D. FIG. 4A, FIG. 5A, FIG. 6A, FIG. 7A,
FIG. 8A, FIG. 9A, FIG. 10A, FIG. 11A, FIG. 12A, FIG. 13A, and FIG.
14A are top views. FIG. 4B, FIG. 5B, FIG. 6B, FIG. 7B, FIG. 8B,
FIG. 9B, FIG. 10B, FIG. 11B, FIG. 12B, FIG. 13B, and FIG. 14B are
cross-sectional views taken along dashed-dotted lines A1-A2 in FIG.
4A, FIG. 5A, FIG. 6A, FIG. 7A, FIG. 8A, FIG. 9A, FIG. 10A, FIG.
11A, FIG. 12A, FIG. 13A, and FIG. 14A which correspond to
cross-sectional views in the channel length direction of the
transistor 200 and the capacitor 100. FIG. 4C, FIG. 5C, FIG. 6C,
FIG. 7C, FIG. 8C, FIG. 9C, FIG. 10C, FIG. 11C, FIG. 12C, FIG. 13C,
and FIG. 14C are cross-sectional views taken along dashed-dotted
lines A3-A4 in FIG. 4A, FIG. 5A, FIG. 6A, FIG. 7A, FIG. 8A, FIG.
9A, FIG. 10A, FIG. 11A, FIG. 12A, FIG. 13A, and FIG. 14A which
correspond to cross-sectional views in the channel width direction
of the transistor 200. FIG. 4D, FIG. 5D, FIG. 6D, FIG. 7D, FIG. 8D,
FIG. 9D, FIG. 10D, FIG. 11D, FIG. 12D, FIG. 13D, and FIG. 14D are
cross-sectional views taken along dashed-dotted lines A5-A6 in FIG.
4A, FIG. 5A, FIG. 6A, FIG. 7A, FIG. 8A, FIG. 9A, FIG. 10A, FIG.
11A, FIG. 12A, FIG. 13A, and FIG. 14A which correspond to
cross-sectional views in the channel width direction of the
capacitor 100. For simplification, some components are not
illustrated in the top view in FIG. 4A, FIG. 5A, FIG. 6A, FIG. 7A,
FIG. 8A, FIG. 9A, FIG. 10A, FIG. 11A, FIG. 12A, FIG. 13A, and FIG.
14A.
[0219] First, a substrate (not illustrated) is prepared, and the
insulator 214 is formed over the substrate. The insulator 214 can
be formed by a sputtering method, a chemical vapor deposition (CVD)
method, a molecular beam epitaxy (MBE) method, a pulsed laser
deposition (PLD) method, an atomic layer deposition (ALD) method,
or the like.
[0220] Note that CVD methods can be classified into a plasma
enhanced CVD (PECVD) method using plasma, a thermal CVD (TCVD)
method using heat, a photo CVD method using light, and the like.
Moreover, CVD methods can be classified into a metal CVD (MCVD)
method and a metal organic CVD (MOCVD) method according to a source
gas. In addition, depending on the pressure in a deposition
chamber, CVD methods can be classified into an atmospheric pressure
CVD (APCVD) method, where deposition is performed under atmospheric
pressure, a low pressure CVD (LPCVD) method, where deposition is
performed under pressure lower than atmospheric pressure, and the
like.
[0221] A high-quality film can be obtained at a relatively low
temperature through a PECVD method. A thermal CVD method does not
use plasma and thus causes less plasma damage to an object. For
example, a wiring, an electrode, an element, such as a transistor
or a capacitor included in a semiconductor device may be charged up
by receiving charge from plasma. In that case, accumulated charge
may break the wiring, electrode, element, or the like included in
the semiconductor device. A thermal CVD method, which does not
using plasma, does not cause such plasma damage, and thus can
increase the yield of the semiconductor device. The thermal CVD
method yields a film with few defects because of no plasma damage
during film formation.
[0222] As an ALD method, a thermal ALD method, in which a precursor
and a reactant react with each other only by a thermal energy, a
plasma-enhanced ALD (PEALD) method, in which a reactant excited by
plasma is used, and the like can be used.
[0223] In an ALD method, one atomic layer can be deposited at a
time using self-regulating characteristics of atoms. Hence, an ALD
method has various advantages such as deposition of an extremely
thin film, deposition on a component with a large aspect ratio,
deposition of a film with a small number of detects such as
pinholes, deposition with excellent coverage, and low-temperature
deposition. The use of plasma is sometimes preferable because
deposition at a lower temperature is possible in a PEALD method. A
precursor used in an ALD method sometimes contains impurities such
as carbon. Thus, a film formed by an ALD method may contain
impurities such as carbon in a larger amount than a film formed by
another deposition method. Note that impurities can be quantified
by X-ray photoelectron spectroscopy (XPS).
[0224] Unlike in the film formation method in which particles
ejected from a target or the like are deposited, a film is formed
by reaction at a surface of an object in a CVD method and an ALD
method. Thus, a CVD method and an ALD method can provide good step
coverage, almost regardless of the shape of an object. In
particular, an ALD method allows excellent step coverage and
excellent thickness uniformity and can be suitably used to cover a
surface of an opening portion with a high aspect ratio, for
example. Note that an ALD method has a relatively low deposition
rate; hence, in some cases, an ALD method is preferably combined
with another film formation method with a high deposition rate,
such as a CVD method.
[0225] When a CVD method or an ALD method is employed, the
composition of a film to be formed can be controlled with the flow
rate ratio of the source gases. For example, in a CVD method or an
ALD method, a film with a certain composition can be formed by
adjusting the flow rate ratio of the source gases. Moreover, in a
CVD method or an ALD method, by changing the flow rate ratio of the
source gases during the film formation, a film whose composition is
continuously changed can be formed. In the case where a film is
formed while the flow rate ratio of the source gases is changed, as
compared to the case where a film is formed using a plurality of
deposition chambers, the time taken for the deposition can be
shortened because the time taken for transfer and pressure
adjustment is omitted. Consequently, semiconductor devices can be
manufactured with high productivity in some cases.
[0226] In this embodiment, as the insulator 214, silicon nitride is
formed by a CVD method. Next, the insulator 216 is formed over the
insulator 214. The insulator 216 can be formed by a sputtering
method, a CVD method, an MBE method, a PLD method, an ALD method,
or the like. In this embodiment, silicon oxide or silicon
oxynitride is used for the insulator 216. The insulator 216 is
preferably formed by a deposition method using the gas in which the
number of hydrogen atoms is reduced or hydrogen atoms are removed.
In this case, the hydrogen concentration in the insulator 216 can
be reduced.
[0227] Then, an opening reaching the insulator 214 is formed in the
insulator 216. Examples of the opening include a groove and a slit.
A region where an opening is formed may be referred to as an
opening portion. The opening may be formed by wet etching; however,
dry etching is preferable for microfabrication. The insulator 214
is preferably an insulator that functions as an etching stopper
film when a groove is formed by etching of the insulator 216. For
example, in the case where a silicon oxide film is used as the
insulator 216 in which the groove is to be formed, the insulator
214 is preferably a silicon nitride film, an aluminum oxide film,
or a hafnium oxide film.
[0228] After formation of the openings, conductive films to be the
conductor 204a and the conductor 205a are formed. The conductive
film preferably contains a conductor that has a function of
inhibiting transmission of oxygen. For example, tantalum nitride,
tungsten nitride, or titanium nitride can be used. Alternatively, a
stacked-layer film of the conductor and tantalum, tungsten,
titanium, molybdenum, aluminum, copper, or a molybdenum-tungsten
alloy can be used. The conductive film to be the conductor 204a and
the conductor 205a can be formed by a sputtering method, a CVD
method, an MBE method, a PLD method, an ALD method, or the
like.
[0229] In this embodiment, the conductive film to be the conductors
204a and 205a has a multi-layer structure. First, tantalum nitride
is formed by a sputtering method and titanium nitride is formed
over the tantalum nitride. Even when a metal that is easily
diffused, such as copper, is used for the conductive film to be the
conductors 204b and 205b that are described later, the use of such
metal nitride for a lower layer of a conductive film to be
conductors 204 and 205 can inhibit diffusion of the metal to the
outside through the conductors 204a and 205a.
[0230] Next, the conductive film to be the conductors 204b and 205b
is formed. This conductive film can be formed by a plating method,
a sputtering method, a CVD method, an MBE method, a PLD method, an
ALD method, or the like. The conductive film to be the conductors
204b and 205b is formed using a low-resistant conductive material
such as copper.
[0231] Next, a chemical mechanical polishing (CMP) treatment is
performed to remove part of the conductive film to be the
conductors 204a and 205a, and the conductive film to be the
conductors 204b and 205b, so that the insulator 216 is exposed. As
a result, the conductors 204a, 204b, 205a, and 205b remain only in
the opening portion. Thus, the conductors 204 and 205 having flat
top surfaces can be formed. Note that the CMP treatment may remove
part of the insulator 216 (referring to FIGS. 4A to 4D).
[0232] Although the conductors 204 and 205 are formed to be
embedded in the opening portion of the insulator 216, this
embodiment is not limited thereto. For example, the following
process may be employed; the conductors 204 and 205 are formed over
the insulator 214, the insulator 216 is formed over the conductors
204 and 205, and part of the insulator 216 is removed by a CMP
treatment to expose the surfaces of the conductors 204 and 205.
[0233] Next, the insulator 222 is formed over the insulator 216,
the conductor 204, and the conductor 205. The insulator 222 is
preferably formed using an insulator containing an oxide of one or
both of aluminum and hafnium. As the insulator containing an oxide
of one or both of aluminum and hafnium, aluminum oxide, hafnium
oxide, an oxide containing aluminum and hafnium (hafnium
aluminate), or the like is preferably used. The insulator
containing an oxide of one or both of aluminum and hafnium has a
barrier property against oxygen, hydrogen, and water. When the
insulator 222 has a barrier property against hydrogen and water,
diffusion of hydrogen and water contained in a structure body
provided around the transistor 200 into the transistor 200 through
the insulator 222 is inhibited, and accordingly oxygen vacancies
are less likely to be generated in the oxide 230.
[0234] The insulator 222 can be formed by a sputtering method, a
CVD method, an MBE method, a PLD method, an ALD method, or the
like.
[0235] Then, the insulator 224 is formed over the insulator 222.
The insulator 224 can be formed by a sputtering method, a CVD
method, an MBE method, a PLD method, an ALD method, or the like. In
this embodiment, silicon oxide or silicon oxynitride is used for
the insulator 224. The insulator 224 is preferably formed by a
deposition method using a gas in which the number of hydrogen atoms
is reduced or hydrogen atoms are removed. This reduces the hydrogen
concentration in the insulator 224. The hydrogen concentration in
the insulator 224 is preferably reduced because the insulator 224
is in contact with the oxide 230a in a later step.
[0236] Next, heat treatment is preferably performed. The heat
treatment is performed at a temperature higher than or equal to
250.degree. C. and lower than or equal to 650.degree. C.,
preferably higher than or equal to 300.degree. C. and lower than or
equal to 500.degree. C., further preferably higher than or equal to
320.degree. C. and lower than or equal to 450.degree. C. The heat
treatment is performed under a nitrogen atmosphere, an inert gas
atmosphere, or an atmosphere containing an oxidizing gas at 10 ppm
or more, 1% or more, or 10% or more. The heat treatment may be
performed under a reduced pressure. Alternatively, the heat
treatment may be performed in such a manner that heat treatment is
performed under a nitrogen atmosphere or an inert gas atmosphere,
and then another heat treatment is performed under an atmosphere
containing an oxidizing gas at 10 ppm or more, 1% or more, or 10%
or more in order to compensate for released oxygen.
[0237] In this embodiment, heat treatment is performed at
400.degree. C. under a nitrogen atmosphere for one hour, and
another heat treatment is successively performed at 400.degree. C.
under an oxygen atmosphere for one hour. By the heat treatments,
impurities such as water and hydrogen included in the insulator 224
can be removed.
[0238] The above heat treatment may be performed after the
insulator 222 is formed. For the heat treatment, the
above-described heat treatment conditions can be employed.
[0239] Plasma treatment using oxygen may be performed on the
insulator 224 under a reduced pressure to form excess oxygen
regions. The plasma treatment using oxygen is preferably performed
with an apparatus including a power source for generating
high-density plasma using microwaves, for example. Alternatively, a
power source may be provided to apply a high-frequency such as RF
to the substrate side. The use of high-density plasma generates
high-density oxygen radicals, and application of the RF to the
substrate side allows the oxygen radicals to be efficiently
introduced into the insulator 224. Furthermore, after plasma
treatment using an inert gas with the apparatus, plasma treatment
using oxygen may be performed to compensate for released oxygen.
Note that the impurities such as hydrogen and water contained in
the insulator 224 can be removed by appropriate selection of the
conditions of the plasma heat treatment. In this case, heat
treatment is not necessarily performed.
[0240] Aluminum oxide may be deposited over the insulator 224 by a
sputtering method, for example, and then subjected to CMP treatment
until the insulator 224 is exposed. The CMP treatment can planarize
and smooth the surface of the insulator 224. When the CMP treatment
is performed on the aluminum oxide placed over the insulator 224,
it is easy to detect the endpoint of the CMP treatment. Part of the
insulator 224 may be polished by the CMP treatment so that the
thickness of the insulator 224 may be reduced; the thickness of the
insulator 224 can be adjusted at the time of forming the insulator
224. Planarizing and smoothing the surface of the insulator 224 can
sometimes improve the coverage with an oxide deposited later and a
decrease in yield of the semiconductor device. Aluminum oxide is
preferably deposited over the insulator 224 by a sputtering method,
in which case oxygen can be added to the insulator 224.
[0241] Next, oxide films 230A and 230B are formed in this order
over the insulator 224 (see FIGS. 4A to 4D). The oxide films are
preferably formed successively without exposure to the air.
Formation of the oxide films 230A and 230B without exposure to the
air prevents attachment of impurities or moisture from the air, so
that the vicinity of the interface between the oxide films 230A and
230B can be kept clean.
[0242] The oxide films 230A and 230B can be formed by a sputtering
method, a CVD method, an MBE method, a PLD method, an ALD method,
or the like.
[0243] When the oxide films 230A and 230B are formed by a
sputtering method, for example, oxygen or a mixed gas of oxygen and
a rare gas is used as a sputtering gas. An increase in the
proportion of oxygen in the sputtering gas can increase the amount
of excess oxygen contained in the oxide film to be formed. In the
case where the above oxide films are formed by a sputtering method,
the above In--M--Zn oxide target can be used.
[0244] In particular, in the formation of the oxide film 230A, part
of oxygen contained in the sputtering gas is supplied to the
insulator 224 in some cases. Therefore, the proportion of oxygen in
the sputtering gas for formation of the oxide film 230A is
preferably 70% or higher, further preferably 80% or higher, and
still further preferably 100%.
[0245] When the oxide film 230B is formed by a sputtering method
and the oxygen proportion of the sputtering gas is higher than or
equal to 1% and lower than or equal to 30%, preferably higher than
or equal to 5% and lower than or equal to 20%, an oxygen-deficient
oxide semiconductor is formed. A transistor including an
oxygen-deficient oxide semiconductor in a channel formation region
can have relatively high field-effect mobility. In addition, when
the oxide film is formed while the substrate is heated, the
crystallinity of the oxide film can be improved. However, one
embodiment of the present invention is not limited thereto. When
the oxide film 230B is formed by a sputtering method and the oxygen
proportion of oxygen in the sputtering gas is higher than 30% and
lower than or equal to 100%, preferably higher than or equal to 70%
and lower than or equal to 100%, an oxygen-excess oxide
semiconductor is formed. A transistor including an oxygen-excess
oxide semiconductor in a channel formation region can have
relatively high reliability.
[0246] In this embodiment, the oxide film 230A is formed using a
target with an atomic ratio of In:Ga:Zn=1:1:0.5 (In:Ga:Zn=2:2:1) or
In:Ga:Zn=1:3:4 by a sputtering method. The oxide film 230B is
formed using a target with an atomic ratio of In:Ga:Zn=4:2:4.1 or
In:Ga:Zn=1:1:1 by a sputtering method. Note that each of the oxide
films is formed by appropriate conditions of the film formation and
the atomic ratio to have characteristics required for the oxide
230.
[0247] Next, heat treatment may be performed. For the heat
treatment, the conditions for the heat treatment stated above can
be used. The heat treatment can remove impurities such as water and
hydrogen in the oxide films 230A and 230B. In this embodiment,
treatment is performed at 400.degree. C. under a nitrogen
atmosphere for one hour, and another treatment is successively
performed at 400.degree. C. under an oxygen atmosphere for one
hour.
[0248] Next, the oxide film 243A is formed over the oxide film 230B
(see FIGS. 4A to 4D). The oxide film 243A can be formed by a
sputtering method, a CVD method, an MBE method, a PLD method, an
ALD method, or the like. The atomic ratio of Ga to In in the oxide
film 243A is preferably greater than that in the oxide film 230B.
In this embodiment, the oxide film 243A is formed using a target
with an atomic ratio of In:Ga:Zn=1:3:4 by a sputtering method.
[0249] Next, the insulator 224, the oxide film 230A, the oxide film
230B, and the oxide film 243A are processed into an island shape by
a lithography method, so that the insulator 224, the oxide 230a,
the oxide 230b, and an oxide layer 243B are formed (see FIGS. 5A to
5D). The insulator 224, the oxides 230a and 230b, and the oxide
layer 243B are formed to overlap with the conductor 205 at least
partly. The insulator 224, the oxides 230a and 230b, and the oxide
layer 243B are formed to include a region not overlapping at least
with the conductor 204. The processing can be performed by a dry
etching method or a wet etching method. A dry etching method is
suitable for microfabrication.
[0250] It is preferable that side surfaces of the oxide 230a, the
oxide 230b, and the oxide layer 243B be substantially perpendicular
to the top surface of the insulator 222. It is preferable that the
side surfaces of the oxide 230a, the oxide 230b and the conductive
layer 243B be substantially perpendicular to the top surface of the
insulator 222, in which case a plurality of transistors 200 can be
provided in a smaller area and at a higher density. Not limited to
this, the angle formed between the side surfaces of the oxide 230a,
the oxide 230b, and the oxide layer 243B, and the top surface of
the insulator 224 may be an acute angle.
[0251] In the lithography method, first, a resist is exposed to
light through a mask. Next, a region exposed to light is removed or
left using a developing solution, so that a resist mask is formed.
Then, etching through the resist mask is conducted to form a
conductor, a semiconductor, or an insulator into a desired shape.
The resist mask is formed, for example, by exposing the resist to
KrF excimer laser light, ArF excimer laser light, or extreme
ultraviolet (EUV) light. A liquid immersion technique may be
employed in which a portion between a substrate and a projection
lens is filled with a liquid (e.g., water) to perform light
exposure. An electron beam or an ion beam may be used instead of
the above-mentioned light. Note that a mask is not necessary in the
case of using an electron beam or an ion beam. To remove the resist
mask, dry etching treatment such as ashing or wet etching treatment
can be performed; alternatively, wet etching treatment may be
performed after dry etching treatment or dry etching treatment may
be performed after wet etching treatment.
[0252] A hard mask formed of an insulator or a conductor may be
used instead of the resist mask. In the case where a hard mask is
used, a hard mask with a desired shape can be formed in the
following manner: an insulating film or a conductive film that is
the material of the hard mask is formed over the oxide layer 243B,
a resist mask is formed thereover, and then the material of the
hard mask is etched. The etching of the oxide layer 243B may be
performed after or without removal of the resist mask. In the
latter case, the resist mask sometimes disappears during the
etching. The hard mask may be removed by etching after the etching
of the oxide layer 243B. The hard mask does not need to be removed
when the hard mask material does not affect the following process
or can be utilized in the following process.
[0253] As a dry etching apparatus, a capacitively coupled plasma
(CCP) etching apparatus including parallel plate electrodes can be
used. The apparatus may have a structure in which high-frequency
power is applied to one of the parallel plate electrodes.
Alternatively, different high-frequency powers may be applied to
one of the parallel plate electrodes. Alternatively, high-frequency
powers with the same frequency may be applied to the parallel plate
electrodes. Alternatively, high-frequency powers with different
frequencies may be applied to the parallel plate electrodes. A dry
etching apparatus including a high-density plasma source can be
used. As the dry etching apparatus including a high-density plasma
source, an inductively coupled plasma (ICP) etching apparatus can
be used, for example.
[0254] Next, a conductive film to be the conductor layer 242A is
formed over the oxide layer 243B (see FIGS. 6A to 6D). The
conductive film to be the conductor layer 242A can be formed by a
sputtering method, a CVD method, an MBE method, a PLD method, an
ALD method, or the like.
[0255] Next, the conductive film to be the conductor layer 242A is
processed by a lithography method, so that the conductor layer 242A
is formed (see FIGS. 7A to 7D).
[0256] Next, the insulator 272 is formed over the conductor layer
242A (see FIGS. 7A to 7D). The insulator 272 can be formed by a
sputtering method, a CVD method, an MBE method, a PLD method, an
ALD method, or the like. In this embodiment, aluminum oxide is
deposited as the insulator 272 by a sputtering method. When
aluminum oxide is deposited by a sputtering method, oxygen can be
supplied to the insulator 224.
[0257] Then, the insulator 273 is formed over the insulator 272.
The insulator 273 can be formed by a sputtering method, a CVD
method, an MBE method, a PLD method, an ALD method, or the like. In
this embodiment, aluminum oxide is formed by an ALD method as the
insulator 273 (see FIGS. 7A to 7D).
[0258] Next, an insulating film to be the insulator 280 is formed.
The insulating film can be formed by a sputtering method, a CVD
method, an MBE method, a PLD method, an ALD method, or the like.
For example, as the insulator 280, a silicon oxide film is formed
by a sputtering method, and a silicon oxide film may be formed
thereover by a PEALD method or a thermal ALD method. The insulating
film to be the insulator 280 is preferably formed by a deposition
method using a gas in which the number of hydrogen atoms is reduced
or hydrogen atoms are removed. This reduces the hydrogen
concentration of the insulator 280.
[0259] Next, a CMP treatment is performed to form the insulator 280
with a flat top surface (see FIGS. 7A to 7D). As in the insulator
224, aluminum oxide is formed over the insulator 280 by a
sputtering method, and then the aluminum oxide is subjected to a
CMP treatment to expose the insulator 280.
[0260] Next, an opening is formed to reach the oxide 230b by
removing part of the insulator 280, part of the insulator 273, part
of the insulator 272, part of the conductor layer 242A, and part of
the oxide layer 243B (see FIGS. 8A to 8D). The opening is
preferably formed to overlap with the conductor 205. The conductors
242a and 242b and the oxides 243a and 243b are formed by the
formation of the opening.
[0261] The insulator 280, the insulator 273, the insulator 272, the
oxide layer 243B, and the conductor layer 242A can be partly
processed by a dry etching method or a wet etching method. A dry
etching method is suitable for microfabrication. The process may be
performed under different conditions. For example, part of the
insulator 280 may be processed by a dry etching method, part of the
insulator 273 may be processed by a wet etching method, part of the
insulator 272 may be processed by a dry etching method, and part of
the oxide layer 243B and part of the conductor layer 242A may be
processed by a dry etching method.
[0262] In some cases, treatment such as dry etching performed in
the above process causes the attachment or diffusion of impurities
due to an etching gas or the like to the surface or an inside of
the oxide 230a, the oxide 230b, or the like. Examples of the
impurities include fluorine and chlorine.
[0263] Cleaning is performed to remove the impurities. Examples of
the cleaning method include a wet cleaning using a cleaning
solution or the like, plasma treatment using plasma, cleaning by
heat treatment, and any of these cleaning methods may be used in
appropriate combination.
[0264] The wet cleaning may be performed using an aqueous solution
in which oxalic acid, phosphoric acid, ammonia water, hydrofluoric
acid, or the like is diluted with carbonated water or pure water.
Alternatively, ultrasonic cleaning using pure water or carbonated
water may be performed.
[0265] Through the processing such as dry etching or the cleaning
treatment, a region of the oxide 230b that does not overlap with
the oxides 243a and 243b is sometimes thinner than regions of the
oxide 230b that overlap with the oxides 243a and 243b (see FIGS. 8A
to 8D).
[0266] After the etching or the cleaning, heat treatment may be
performed. The heat treatment may be performed at a temperature
higher than or equal to 100.degree. C. and lower than or equal to
450.degree. C., preferably higher than or equal to 350.degree. C.
and lower than or equal to 400.degree. C., for example. The heat
treatment is performed under an atmosphere of a nitrogen gas or an
inert gas, or an atmosphere containing an oxidizing gas at 10 ppm
or more, 1% or more, or 10% or more. For example, the heat
treatment is preferably performed under an oxygen atmosphere. This
provides oxygen to the oxides 230a and 230b, and reduces oxygen
vacancies. The heat treatment may be performed under a reduced
pressure. Alternatively, the heat treatment may be performed under
an oxygen atmosphere and then, without exposure to the air, heat
treatment may be successively performed under a nitrogen
atmosphere.
[0267] Next, an oxide film 230C is formed (see FIGS. 9A to 9D).
Heat treatment can be performed before the oxide film 230C is
formed; it is preferable that the heat treatment be performed under
a reduced pressure and the oxide film 230C be successively formed
without exposure to the air. The heat treatment is preferably
performed in an atmosphere containing oxygen. The treatment removes
moisture and hydrogen absorbed onto the surface of the oxide 230b
and the like, and reduces moisture concentration and hydrogen
concentration in the oxides 230a and 230b. The heat treatment is
preferably performed at a temperature higher than or equal to
100.degree. C. and lower than or equal to 400.degree. C., further
preferably performed at a temperature higher than or equal to
150.degree. C. and lower than or equal to 350.degree. C. In this
embodiment, the heat treatment is performed at 200.degree. C. under
a reduced pressure.
[0268] It is preferable that the oxide film 230C be provided in
contact with at least part of the top surface of the oxide 230b,
part of the side surfaces of the oxide 243, part of the side
surfaces of the conductor 242, part of the side surfaces of the
insulator 272, part of the side surfaces of the insulator 273, and
part of the side surfaces of the insulator 280. When the conductor
242 is surrounded by the oxide 243, the insulator 272, the
insulator 273, and the oxide film 230C, a decrease in the
conductivity of the conductor 242 due to oxidation in a later step
can be inhibited.
[0269] The oxide film 230C can be formed by a sputtering method, a
CVD method, an MBE method, a PLD method, an ALD method, or the
like. The oxide film 230C is formed by a sputtering method using a
target having an atomic ratio of In:Ga:Zn=4:2:4.1, a target having
an atomic ratio of In:Ga:Zn=5:1:3, a target having an atomic ratio
of 10:1:3, a target having an atomic ratio of In:Ga:Zn=1:3:4, or a
target of indium oxide. A target with a high proportion of indium
for the oxide film 230C can improve the on current and the
field-effect mobility of the transistor 200.
[0270] The oxide film 230C may have a stacked-layer structure. For
example, the oxide film 230C may be formed by a sputtering method
using a target with an atomic ratio of In:Ga:Zn=4:2:4.1 and
successively using a target with an atomic ratio of
In:Ga:Zn=1:3:4.
[0271] Some oxygen contained in a sputtering gas which is used for
forming the oxide film 230C is sometimes supplied to the oxides
230a and 230b. Some oxygen contained in a sputtering gas which is
used for forming the oxide film 230C is also sometimes supplied to
the insulator 280. Therefore, the proportion of oxygen in the
sputtering gas for the oxide film 230C is preferably 70% or higher,
further preferably 80% or higher, still further preferably
100%.
[0272] Next, heat treatment may be performed. The heat treatment
may be performed under a reduced pressure, and an insulating film
250A may be successively formed without exposure to the air. The
heat treatment can remove moisture and hydrogen absorbed onto the
surface of the oxide film 230C or the like, and can reduce the
moisture and hydrogen concentration of the oxides 230a and 230b and
the oxide film 230C. The heat treatment is preferably performed at
a temperature higher than or equal to 100.degree. C. and lower than
or equal to 400.degree. C. In this embodiment, the heat treatment
is performed at 200.degree. C.
[0273] Next, an insulating film 250A is formed over the oxide film
230C (see FIGS. 9A to 9D). The insulating film 250A can be formed
by a sputtering method, a CVD method, an MBE method, a PLD method,
an ALD method, or the like. The insulating film 250A is preferably
formed by a deposition method using a gas in which the number of
hydrogen atoms is reduced or hydrogen atoms are removed. This
reduces the hydrogen concentration of the insulating film 250A. The
hydrogen concentration in the insulating film 250A is preferably
reduced because the insulating film 250A becomes the insulator 250
that is in contact with the oxide 230c in a later step.
[0274] Next, microwaves or high-frequency waves such as RF may be
irradiated with. The microwaves or the high-frequency waves such as
RF permeate the insulator 280, oxide 230b, and the oxide 230a to
remove hydrogen therein. In particular, in the oxides 230a and
230b, a reaction in which a bond of V.sub.OH is cut, i.e., a
reaction of V.sub.oH.fwdarw.V.sub.o+H, occurs, and the oxides 230a
and 230b are dehydrogenated. Some hydrogen generated at this time
is bonded to oxygen to be H.sub.2O, and removed from the oxide 230
and insulator 280, in some cases. Some hydrogen may be gettered by
into the conductor 242. The irradiation with the microwaves or the
high-frequency waves such as RF can reduce hydrogen in the
insulator 280, the oxide 230a and the oxide 230b.
[0275] Oxygen gas is irradiated with the microwaves or the
high-frequency waves such as RF to be plasma, which generates
oxygen radicals. The treatment can be performed on the insulator
280, the oxides 230a and 230b under an atmosphere containing
oxygen. The treatment may be referred to as oxygen plasma treatment
below. The oxygen radicals can supply oxygen to the insulator 280,
the oxide 230a, and the oxide 230b. When the plasma treatment is
performed on the insulator 280, the oxide 230a, and the oxide 230b
under an atmosphere containing oxygen, the oxide 230 may be less
likely to be irradiated with a microwave or a high-frequency wave
such as RF.
[0276] The oxygen plasma treatment is preferably performed with a
microwave treatment apparatus including a power source for
generating high-density plasma using microwaves, for example. A
power source may be provided to the microwave treatment apparatus
to apply RF to the substrate side. Oxygen radicals at a high
density can be generated with high-density plasma. Furthermore,
application of RF to the substrate side allows oxygen ions
generated by the high-density plasma to permeate the insulator 280
and the oxide 230 efficiently. The oxygen plasma treatment is
preferably performed under a reduced pressure, and the pressure is
set to be 60 Pa or higher, preferably 133 Pa or higher, further
preferably 200 Pa or higher, and still further preferably 400 Pa or
higher. The treatment is performed with the oxygen flow rate
(O.sub.2/O.sub.2+Ar) of 50% or lower, preferably 10% or more and
30% or lower. The treatment can be performed at approximately
400.degree. C., for example. The oxygen plasma treatment can be
followed successively by heat treatment without exposure to
air.
[0277] Next, a conductive film 260Aa and a conductive film 260Ab
are formed (see FIGS. 10A to 10D). The conductive film 260Aa and
the conductive film 260Ab can be formed by a sputtering method, a
CVD method, an MBE method, a PLD method, an ALD method, or the
like. A CVD method is preferably used, for example. In this
embodiment, the conductive film 260Aa is formed by an ALD method,
and the conductive film 260Ab is formed by a CVD method.
[0278] Then, the oxide film 230C, the insulating film 250A, the
conductive film 260A, and the conductive films 260Aa and 260Ab are
polished by a CMP treatment until the insulator 280 is exposed,
whereby the oxide 230c, the insulator 250, and the conductor 260
(the conductors 260a and 260b) are formed (see FIGS. 11A to
11D).
[0279] Next, heat treatment may be performed. In this embodiment,
the heat treatment is performed at 400.degree. C. under a nitrogen
atmosphere for one hour. The heat treatment can reduce the moisture
concentration and the hydrogen concentration in the insulators 250
and 280. The insulator 282 can be deposited successively after the
heat treatment without exposure to the air.
[0280] Next, the insulator 282 is formed over the conductor 260,
the oxide 230c, the insulator 250, and the insulator 280. The
insulator 282 can be formed by a sputtering method, a CVD method,
an MBE method, a PLD method, an ALD method, or the like (see FIGS.
12A to 12D). The insulator 282 is preferably formed using aluminum
oxide by a sputtering method. Forming the insulator 282 with an
atmosphere containing oxygen by a sputtering method can provide
oxygen to the insulator 280. The formation of the insulator 282 is
preferably performed while the substrate is heated. The formation
of the insulator 282 in contact with the top surface of the
conductor 260 inhibits absorption of oxygen in the insulator 280
into the conductor 260 in the later heat treatment.
[0281] Then, the insulator 283 is formed over the insulator 282
(see FIGS. 13A to 13D). The insulator 283 can be formed by a
sputtering method, a CVD method, an MBE method, a PLD method, an
ALD method, or the like. The insulator 283 may have a multilayer
structure. For example, silicon nitride may be formed by a
sputtering method and silicon nitride may be formed by a CVD method
over the silicon nitride.
[0282] Next, heat treatment may be performed. In this embodiment,
the heat treatment is performed at 400.degree. C. in a nitrogen
atmosphere for one hour. The heat treatment allows oxygen added by
forming the insulator 282 to diffuse in the insulator 280, and to
be provided to the oxides 230a and 230b through the oxide 230c. The
oxygen adding treatment performed in this manner on the oxide 230
can promote a reaction in which oxygen vacancies in the oxide 230
(the oxide 230b) are filled with oxygen, i.e., a reaction of
V.sub.o+O.fwdarw.null. Furthermore, hydrogen remaining in the oxide
230 reacts with supplied oxygen, so that the hydrogen can be
removed as H.sub.2O (dehydrogenation). This can inhibit
recombination of hydrogen remaining in the oxide 230 with oxygen
vacancies and formation of V.sub.oH. Note that the heat treatment
is not necessarily performed after the formation of the insulator
283 and may be performed after the formation of the insulator
282.
[0283] Next, an opening is formed in the insulators 272, 273, 280,
282, and 283 to reach the conductor 242b (see FIGS. 13A to 13D).
The opening are formed by a lithography method. Although the
opening in FIG. 13A has a circular shape in the top view, the shape
is not limited thereto. For example, the opening may have an almost
circular shape such as an ellipse, a polygonal shape such as a
square, or a polygonal shape such as a square with rounded
corners.
[0284] Next, an insulating film to be the insulator 241 is formed
and subjected to anisotropic etching, so that the insulator 241 is
formed. The insulating film to be the insulator 241 can be formed
by a sputtering method, a CVD method, an MBE method, a PLD method,
an ALD method, or the like. The insulating film to be the insulator
241 preferably has a function of inhibiting the transmission of
oxygen. For example, an aluminum oxide film is preferably formed by
a PEALD method. Alternatively, silicon nitride is preferably formed
by a PEALD method. Silicon nitride is preferable because it has
high blocking property against hydrogen.
[0285] As an anisotropic etching for the insulating film to be the
insulator 241, a dry etching method may be performed, for example.
The insulator 241 is provided on the sidewall of the opening. This
inhibits transmission of oxygen from outside to inhibit oxidation
of the conductor 240. Furthermore, impurities such as water and
hydrogen can be prevented from diffusing from the conductor 240 to
the outside.
[0286] Next, a conductive film to be the conductor 240 is formed.
The conductive film to be the conductor 240 preferably has a
stacked-layer structure which includes a conductor having a
function of inhibiting the transmission of impurities such as water
and hydrogen. For example, a stacked-layer structure of tantalum
nitride, titanium nitride, or the like and tungsten, molybdenum,
copper, or the like can be employed. The conductive film to be the
conductor 240 can be formed by a sputtering method, a CVD method,
an MBE method, a PLD method, an ALD method, or the like.
[0287] Next, a CMP treatment removes part of the conductive film to
be the conductor 240 to expose the top surface of the insulator
283. Thus, the conductive film remains only in the opening (see
FIGS. 13A to 13D), which yields the conductor 240 with a flat
surface. The CMP treatment may remove part of the top surface of
the insulator 283.
[0288] Next, a conductive film to be the conductor 246 is formed.
The conductive film to be the conductor 246 can be formed by a
sputtering method, a CVD method, an MBE method, a PLD method, an
ALD method, or the like.
[0289] Next, the conductive film to be the conductor 246 is
processed by a lithography method to form the conductor 246, which
is in contact with the top surface of the conductor 240 (see FIGS.
14A to 14D). Although not illustrated, the thickness of the
insulator 283 in a region that does not overlap with the insulator
283 might be reduced.
[0290] Next, the insulator 284 is formed over the conductor 246 and
the insulator 283 (see FIGS. 1A to 1D). The insulator 284 can be
formed by a sputtering method, a CVD method, an MBE method, a PLD
method, an ALD method, or the like. The insulator 284 may have a
multilayer structure. For example, silicon nitride may be deposited
by a sputtering method and another silicon nitride may be deposited
by a CVD method over the silicon nitride. By depositing the
insulator 284 over the conductor 246 and the insulator 283, the top
surface and a side surface of the conductor 246 are in contact with
the insulator 284, and part of the bottom surface of the conductor
246 is in contact with the insulator 283. In other words, the
conductor 246 can be surrounded by the insulators 284 and 283. The
structure can inhibit transmission of oxygen from the outside and
oxidation of the conductor 246. Furthermore, this can inhibit
diffusion of impurities such as water or hydrogen from the
conductor 246 to the outside, which is preferable.
[0291] Next, the insulator 274 can be formed over the insulator 284
(see FIGS. 1A to 1D). The insulator 274 can be formed by a
sputtering method, a CVD method, an MBE method, a PLD method, an
ALD method, or the like. The insulator 274 is preferably formed by
the deposition method using a gas in which hydrogen atoms are
reduced or removed. This reduces the hydrogen concentration of the
insulator 274.
[0292] Through the above process, the semiconductor device
including the transistor 200 shown in FIGS. 1A to 1D can be
manufactured. By the manufacturing method of a semiconductor device
which is described in this embodiment and illustrated in FIGS. 4A
to 4D to FIGS. 14A to 14D, the semiconductor device including the
transistor 200 and the capacitor 100 can be formed.
<Modification Example of Semiconductor Device>
[0293] Examples of a semiconductor device of one embodiment of the
present invention including the transistor 200 and the capacitor
100 which is different from the semiconductor device described
above in <Structure example of semiconductor device> will be
described below with reference to FIGS. 2A to 2D, FIGS. 3A to 3D,
FIGS. 15A to 15C, FIG. 16, FIG. 17, FIG. 18, and FIG. 19. Note that
in the semiconductor devices illustrated in FIGS. 2A to 2D, FIGS.
3A to 3D, FIGS. 15A to 15C, FIG. 16, FIG. 17, FIG. 18, and FIG. 19,
components having the same functions as the components in the
semiconductor device described in <Structure example of
semiconductor device> (see FIGS. 1A to 1D) are denoted by the
same reference numerals. Note that the materials for the transistor
200 and the capacitor 100 described in detail in <Structure
example of semiconductor device> can be used as materials for
the transistor 200 and the capacitor 100 in this section.
<Modification Example 1 of Semiconductor Device>
[0294] FIG. 2A is a top view of the semiconductor device including
the transistor 200 and the capacitor 100. FIGS. 2B to 2D are
cross-sectional views of the semiconductor device. FIG. 2B is a
cross-sectional view taken along the dashed-dotted line A1-A2 in
FIG. 2A, which corresponds to a cross-sectional view in the channel
length direction of the transistor 200 and the capacitor 100. FIG.
2C is a cross-sectional view taken along the dashed-dotted line
A3-A4 in FIG. 2A, which corresponds to a cross-sectional view in
the channel width direction of the transistor 200. FIG. 2D is a
cross-sectional view taken along the dashed-dotted line A5-A6 in
FIG. 2A, which corresponds to a cross-sectional view in the channel
width direction of the capacitor 100. Note that for simplification,
some components are not illustrated in the top view in FIG. 2A.
[0295] The cross sectional-views of the capacitor 100 shown in
FIGS. 2B and 2D are different from those of the capacitor 100 shown
in FIGS. 1B and 1D. Specifically, the conductor 204b forms
projections and depressions in the channel length direction and in
the channel width direction and the insulator 222 over the
conductor 204b is formed along the projections and the depressions,
as is shown in FIGS. 2B and 2D. This structure allows the conductor
204, which serves as one electrode of the capacitor 100, and the
conductor 242a, which serves as the other electrode of the
capacitor 100, to overlap with the insulator 222, which is a
dielectric of the capacitor 100, therebetween with a wider area
than an area seen from the top. In other words, this structure can
increase the capacity of the capacitor 100 without increasing the
area in the top view where one electrode and the other electrode
overlap with each other, which yields miniaturization of the
capacitor.
[0296] To form the projections and the depressions as shown in
FIGS. 2B and 2D, for example, the conductor 204 which is the
conductor 204b with a flat top surface is formed shown in FIGS. 1B
and 1D, and then a lithography method forms the projections and the
depressions on the conductor 204b. In this modification example,
the projections and the depressions are formed both in the channel
length direction and in the channel width direction, but this
example can include another structure. For example, the projections
and the depressions can be formed in either the channel length
direction or the channel width direction. The number of the
projections and the depressions is not limited. The number and the
direction of the projections and the depressions to be formed can
be determined by the required capacity of the capacitor of the
semiconductor device. The other structures and the effects can
refer to those in FIGS. 1A to 1D.
<Modification Example 2 of Semiconductor Device>
[0297] FIG. 3A is a top view of the semiconductor device including
the transistor 200 and the capacitor 100. FIGS. 3B to 3D are
cross-sectional views of the semiconductor device. FIG. 3B is a
cross-sectional view taken along the dashed-dotted line A1-A2 in
FIG. 3A, which corresponds to a cross-sectional view in the channel
length direction of the transistor 200 and the capacitor 100. FIG.
3C is a cross-sectional view taken along the dashed-dotted line
A3-A4 in FIG. 3A, which corresponds to a cross-sectional view in
the channel width direction of the transistor 200. FIG. 3D is a
cross-sectional view taken along the dashed-dotted line A5-A6 in
FIG. 3A, which corresponds to a cross-sectional view in the channel
width direction of a source region or a drain region of the
transistor 200. Note that for simplification, some components are
not illustrated in the top view in FIG. 2A.
[0298] FIG. 3A shows the following features. The conductor 205 is
used as the second gate of the transistor 200 and one electrode of
the capacitor 100. The conductor 242b, which functions as the
source electrode or the drain electrode of the transistor 200, is
connected to the conductor 204 through an opening 238. There are no
conductor 240, which functions as the plug connected to the source
electrode or the drain electrode of the transistor 200, no
conductor 246, which is connected to the conductor 240, and no
insulator 241, which is in contact with a side surface of the
insulator 240. Accordingly, this modification example is different
from the structure described in <Structure example of
semiconductor device> with reference to FIGS. 1A to 1D. The
following description explains the different points of the
structure.
[0299] FIG. 3B shows that the capacitor 100 includes the conductor
205 over the insulator 214, the insulator 222 over the conductor
205, and the conductor 242a over the insulator 222.
[0300] The conductor 205 functions as one electrode of the
capacitor 100 and the conductor 242a functions as the other
electrode of the capacitor 100. The insulator 222 functions as a
dielectric of the capacitor 100.
[0301] FIG. 3D shows that the conductor 204 over the insulator 214
is connected to the conductor 242b through the opening 238. The
conductor 204 is formed in the same layer as the conductor 205.
FIG. 3A shows that the conductor 204 is provided in parallel to the
conductor 205 in the A1-A2 direction.
[0302] Such a structure eliminates the process of forming the
conductor 240, which functions as a plug, the conductor 246, and
the insulator 241, and simplifies the fabrication of the
semiconductor device including the transistor 200 and the capacitor
100, leading to reduction in manufacturing costs and improvement in
yield.
[0303] The other structures and the effects can refer to the
semiconductor device shown in FIGS. 1A to 1D.
<Modification Example 3 of Semiconductor Device>
[0304] An example of a semiconductor device of one embodiment of
the present invention including a transistor 200a, a transistor
200b, a capacitor 100a, and a capacitor 100b is described
below.
[0305] FIG. 16 is a cross-sectional view in the channel length
direction of the semiconductor device including the transistors
200a and 200b, the capacitors 100a and 100b. FIG. 16 shows a
line-symmetric semiconductor device with respect to the
dashed-dotted line A3-A4. A conductor 242c functions as a source
electrode or a drain electrode of the transistor 200a and a source
electrode or a drain electrode of the transistor 200b. The
conductor 240, which functions as a plug, connects the conductor
246, which functions as a wiring, and the transistors 200a and
200b. The structure of the connection of the two transistors, the
two capacitors, the wiring, and the plug allows the semiconductor
device which can be miniaturized or highly integrated.
[0306] The structure example of the semiconductor device shown in
FIGS. 1A to 1D can be referred to for the components and the
effects of the transistors 200a and 200b and the capacitors 100a
and 100b.
<Modification Example 4 of Semiconductor Device>
[0307] In the above description, the semiconductor device including
the transistors 200a and 200b and the capacitors 100a and 100b is
given as a structure example; however, the semiconductor device
according to this embodiment is not limited to this example. For
example, semiconductor devices having the same structure may share
a capacitor portion as shown in FIG. 17. Note that in this
specification, a semiconductor device including the transistors
200a and 200b and the capacitors 100a and 100b is referred to as a
cell. The above descriptions for the transistors 200a and 200b and
the capacitors 100a and 100b can be referred to for the structures
of the transistors 200a and 200b and the capacitors 100a and 100b
in this modification example.
[0308] FIG. 17 is a cross-sectional view of a cell 60 and a cell 61
that are connected through a capacitor portion. The cell 60
includes the transistors 200a and 200b and the capacitors 100a and
100b, and the cell 61 has a similar structure to that of the cell
60.
[0309] FIG. 17 shows that a conductor 204_2, which functions as one
electrode of the capacitor 100b of the cell 60, and the conductor
242b, which functions as the other electrode of the capacitor 100b
of the cell 60, function as one electrode and the other electrode
of a capacitor of the cell 61, which has a similar structure as
that of the cell 60. Although not illustrated, a conductor 204_1,
which functions as one electrode of the capacitor 100a of the cell
60, and the conductor 242a, which functions as the other electrode
of the capacitor 100a of the cell 60, function as one electrode and
the other electrode of a capacitor of a semiconductor device next
to the cell 60 in the A1 direction or on the left in FIG. 17. The
same applies to a capacitor of a semiconductor device next to the
cell 61 in the A2 direction or on the right in FIG. 17. Thus, a
cell array 600 can be formed. With this structure of the cell array
600, the space between the adjacent cells can be reduced; thus, the
projected area of the cell array 600 can be reduced and high
integration can be achieved. The cell arrays 600 shown in FIG. 17
are arranged in line and cross each other, which forms a matrix of
cell arrays.
[0310] By forming the transistors 200a and 200b and the capacitors
100a and 100b in a structure in this embodiment, the structure can
reduce the area of the cell and the semiconductor device including
the cell array can be miniaturized or highly integrated.
[0311] Stacked cell arrays may be used instead of the single-layer
cell array. FIG. 18 shows a cross-sectional view of a structure in
which n+1 cell arrays 600 are stacked. The stacked cell array
structure in FIG. 18 allows cells to be integrated without
increasing the occupation area of the cell arrays. That is, a 3D
cell array can be structured.
<Modification Example 5 of Semiconductor Device>
[0312] An example of a semiconductor device including the 3D cell
array shown in FIG. 18 will be described below. FIG. 19 is a
cross-sectional view of the semiconductor device. The semiconductor
device includes a substrate 311, an insulator 211 over the
substrate 311, an insulator 212 over the insulator 211, and an
insulator 214 over the insulator 212, and a 3D cell array in which
n+1 cell arrays 600 are stacked is positioned over the insulator
214. The cell arrays 600 are electrically connected to each other
through the conductors 240 functioning as plugs. The 3D cell array
is sealed by the insulator 211, the insulator 212, the insulator
214, an insulator 287, the insulator 282, the insulator 283, and
the insulator 284. Such a structure is referred to as a sealing
structure below for convenience. The insulator 274 is provided near
the insulator 284. A conductor 430 is provided in the insulators
274, 283, 284, and 211, and is electrically connected to the
substrate 311.
[0313] The insulator 280 is provided in the sealing structure. The
insulator 280 has a function of releasing oxygen by heating. The
insulator 280 includes an excess oxygen region.
[0314] The insulators 211, 283, and 284 are suitably formed using a
material having a high blocking property against hydrogen. The
insulators 214, 282, and 287 are suitably formed using a material
having a function of capturing or fixing hydrogen.
[0315] Examples of the material having a high blocking property
against hydrogen include silicon nitride and silicon nitride oxide.
Examples of the material having a function of capturing or fixing
hydrogen include aluminum oxide, hafnium oxide, and an oxide
containing aluminum and hafnium (hafnium aluminate).
[0316] A barrier property in this specification means a function of
inhibiting diffusion of a particular substance (also referred to as
a function of less easily transmitting the substance).
Alternatively, a barrier property in this specification means a
function of capturing or fixing (also referred to as gettering) a
particular substance.
[0317] Materials for the insulators 211, 212, 214, 287, 282, 283,
and 284 may have an amorphous or crystal structure, although the
crystallinity of the materials is not limited thereto. For example,
an amorphous aluminum oxide film is suitably used for the material
having a function of capturing or fixing hydrogen. Amorphous
aluminum oxide may capture or fix hydrogen more than aluminum oxide
with high crystallinity.
[0318] The following model can be given for the reaction of excess
oxygen in the insulator 280 with hydrogen from an oxide
semiconductor in contact with the insulator 280.
[0319] The insulator 280, which is in contact with the oxide
semiconductor, transmits hydrogen in the oxide semiconductor to
another structure body. The hydrogen in the oxide semiconductor
react with the excess oxygen in the insulator 280, which yields the
OH bonding to diffuse the insulator 280. The hydrogen atom having
the OH bonding reacts with the oxygen atom bonded to an atom (such
as a metal atom) in the insulator 282 in reaching a material which
has a function of capturing or fixing hydrogen (typically the
insulator 282), and is trapped or fixed in the insulator 282. This
enables the insulator 282 to capture the hydrogen atom or to fix it
inside the insulator 282. The oxygen atom which had the OH bonding
of the excess oxygen may remain as an excess oxygen in the
insulator 280. The excess oxygen in the insulator 280 presumably
transmits the hydrogen.
[0320] A manufacturing process of the semiconductor device is one
of important factors for the model.
[0321] For example, the insulator 280 containing excess oxygen is
formed over the oxide semiconductor, and then the insulator 282 is
formed. Next, heat treatment is preferably performed. The heat
treatment is performed at 350.degree. C. or higher, preferably
400.degree. C. or higher under an atmosphere containing oxygen, an
atmosphere containing nitrogen, or a mixed atmosphere of oxygen and
nitrogen. The heat treatment is performed for one hour or more,
preferably four hours or more, further preferably eight hours or
more.
[0322] The heat treatment enables diffusion of hydrogen from the
oxide semiconductor to the outside through the insulators 280, 282,
and 287. This reduces the absolute amount of hydrogen in and near
the oxide semiconductor.
[0323] The insulator 283 and the insulator 284 are formed after the
heat treatment. The insulators 283 and 284 have a high blocking
property against hydrogen. Thus, the insulators 283 and 284
inhibits enter of outside hydrogen or the hydrogen which has been
diffused to the outside into the inside, specifically, the oxide
semiconductor or insulator 280 side.
[0324] The heat treatment is performed after the insulator 282 is
formed in the above example; however, one embodiment of the present
invention is not limited thereto. The heat treatment can be
performed after each of the cell arrays 600_1 to the cell array
600_n+1 is formed, for example. Hydrogen diffuses in the upward or
lateral direction.
[0325] The above manufacturing process yields the sealing structure
by bonding the insulators 211 and 283.
[0326] The above-described structure and manufacturing process
enable a semiconductor device using an oxide semiconductor with
reduced hydrogen concentration. Thus, a highly reliable
semiconductor device can be provided. One embodiment of the present
invention can provide a semiconductor device with favorable
electrical characteristics.
[0327] The structures, the methods, and the like described in this
embodiment can be combined as appropriate with any of the
structures, the methods, and the like described in the other
embodiments.
Embodiment 2
[0328] In this embodiment, one embodiment of a semiconductor device
will be described with reference to FIG. 20.
[Memory Device 1]
[0329] A memory device shown in FIG. 20 includes the transistor
200, the capacitor 100, and a transistor 300. FIG. 20 is a
cross-sectional view of the transistors 200 and 300 in the channel
length direction.
[0330] The transistor 200 is a transistor whose channel is formed
in a semiconductor layer containing an oxide semiconductor. The
transistor 200 has a low off-state current. Thus, a memory device
including the transistor 200 can retain stored data for a long
time. This means that the memory device needs no refresh operation
or an extremely small number of refresh operations, which
sufficiently reduces the power consumption of the memory
device.
[0331] In the memory device shown in FIG. 20, a wiring 1001 is
electrically connected to one of the source and the drain of the
transistor 300. A wiring 1002 is electrically connected to the
other of the source and the drain of the transistor 300. A wiring
1007 is electrically connected with the gate of the transistor 300.
A wiring 1003 is electrically connected to one of the source and
the drain of the transistor 200. A wiring 1004 is electrically
connected to the first gate of the transistor 200. A wiring 1006 is
electrically connected to the second gate of the transistor 200. A
wiring 1005 is electrically connected to the other electrode of the
capacitor 100.
[0332] The semiconductor device shown in FIG. 20 can be used as a
memory device having a transistor whose channel is formed in a
semiconductor layer including an oxide semiconductor. Since the
potential of one electrode of the capacitor 100 can be retained
owing to the low off-state current of the transistor 200, data can
be written, retained, and read.
<Structure of Memory Device 1>
[0333] The semiconductor device of one embodiment of the present
invention includes the transistor 300, the transistor 200, and the
capacitor 100 as shown in FIG. 20. The transistor 200 is provided
over the transistor 300, and the transistor 200 and the capacitor
100 are provided in the same layer. Note that the above embodiment
can be referred to for the structures of the transistor 200 and the
capacitor 100.
[0334] The transistor 300 is provided in and on the substrate 311
and includes a conductor 316, an insulator 315, a semiconductor
region 313 that is part of the substrate 311, and a low-resistance
region 314a and a low-resistance region 314b functioning as a
source region and a drain region.
[0335] The transistor 300 can be a p-channel transistor or an
n-channel transistor.
[0336] It is preferable that a region of the semiconductor region
313 where a channel is formed, a region in the vicinity thereof,
the low-resistance regions 314a and 314b functioning as the source
and drain regions, and the like contain a semiconductor such as a
silicon-based semiconductor, or single crystal silicon.
Alternatively, a material including germanium (Ge), silicon
germanium (SiGe), gallium arsenide (GaAs), gallium aluminum
arsenide (GaAlAs), or the like can be used. Alternatively, silicon
whose effective mass is adjusted by applying stress to crystal
lattices and thereby changing the lattice spacing can be used.
Alternatively, a high electron mobility transistor (HEMT) may be
employed as the transistor 300 with use of GaAs and GaAlAs or the
like.
[0337] The low-resistance regions 314a and 314b contain an element
that imparts n-type conductivity (e.g., arsenic or phosphorus) or
an element that imparts p-type conductivity (e.g., boron), in
addition to a semiconductor material used for the semiconductor
region 313.
[0338] The conductor 316 functioning as a gate electrode can be
formed using a semiconductor material such as silicon containing an
element that imparts n-type conductivity (e.g., arsenic or
phosphorus) or an element that imparts p-type conductivity (e.g.,
boron), or a conductive material such as a metal material, an alloy
material, or a metal oxide material.
[0339] Note that the work function depends on a material used for
the conductor; therefore, changing the material for the conductor
can adjust the threshold voltage of the transistor. Specifically,
titanium nitride, tantalum nitride, or the like is preferably used
for the conductor. Furthermore, in order to ensure the conductivity
and embeddability of the conductor, stacked layers of metal
materials such as tungsten and aluminum are preferably used for the
conductor. In particular, tungsten is preferable in terms of heat
resistance.
[0340] The transistor 300 shown in FIG. 20 is only an example. The
transistor can have a different structure and an appropriate
transistor for a circuit configuration or a driving method can be
used.
[0341] An insulator 320, an insulator 322, an insulator 324, and an
insulator 326 are stacked in this order to cover the transistor
300.
[0342] For the insulators 320, 322, 324, and 326, for example,
silicon oxide, silicon oxynitride, silicon nitride oxide, silicon
nitride, aluminum oxide, aluminum oxynitride, aluminum nitride
oxide, or aluminum nitride can be used.
[0343] The insulator 322 may function as a planarization film for
eliminating a level difference caused by the transistor 300 or the
like underlying the insulator 322. For example, a chemical
mechanical polishing (CMP) method or the like may be employed to
smooth the top surface of the insulator 322.
[0344] The insulator 324 is preferably formed using a film having a
barrier property that prevents hydrogen or impurities from the
substrate 311, the transistor 300, or the like from diffusing to a
region where the transistor 200 is provided.
[0345] For the film having a barrier property against hydrogen,
silicon nitride deposited by a CVD method can be used, for example.
The hydrogen diffusion into a semiconductor element including an
oxide semiconductor, such as the transistor 200, impairs the
characteristics of the semiconductor element in some cases.
Therefore, a film that inhibits hydrogen diffusion is preferably
provided between the transistor 200 and the transistor 300.
Specifically, the film that inhibits hydrogen diffusion is a film
from which a small amount of hydrogen is released.
[0346] The amount of released hydrogen can be measured by thermal
desorption spectroscopy (TDS), for example. The amount of hydrogen
released from the insulator 324 is less than or equal to
10.times.10.sup.15 atoms/cm.sup.2, preferably less than or equal to
5.times.10.sup.15 atoms/cm.sup.2 in the following conditions, for
example: the amount is measured by TDS analysis, the amount of
released hydrogen is converted into hydrogen atoms per unit area of
the insulator 324, and a film-surface temperature range is
50.degree. C. to 500.degree. C.
[0347] The dielectric constant of the insulator 326 is preferably
lower than that of the insulator 324. For example, the dielectric
constant of the insulator 326 is preferably lower than 4, further
preferably lower than 3. The dielectric constant of the insulator
326 is, for example, preferably 0.7 times or less, further
preferably 0.6 times or less that of the insulator 324. The use of
a material having a low dielectric constant for the interlayer film
can reduce the parasitic capacitance between wirings.
[0348] A conductor 328, a conductor 330, and the like that are
electrically connected to the transistor 300 are embedded in the
insulators 320, 322, 324, and 326. Note that the conductor 328 and
the conductor 330 each function as a plug or a wiring. A plurality
of conductors functioning as plugs or wirings are collectively
denoted by the same reference numeral in some cases. Furthermore,
in this specification and the like, a wiring and a plug
electrically connected to the wiring may be a single component.
That is, part of a conductor functions as a wiring in some cases,
and part of a conductor functions as a plug in other cases.
[0349] As a material for each of the plugs and wirings (e.g., the
conductor 328 and the conductor 330), a conductive material such as
a metal material, an alloy material, a metal nitride material, or a
metal oxide material can be used in a single-layer structure or a
layered structure. It is preferable to use a high-melting-point
material that has both heat resistance and conductivity, such as
tungsten or molybdenum, and it is particularly preferable to use
tungsten. Alternatively, it is preferable to use a low-resistance
conductive material such as aluminum or copper. A low-resistance
conductive material can reduce wiring resistance.
[0350] A wiring layer may be provided over the insulator 326 and
the conductor 330. For example, an insulator 350, an insulator 352,
and an insulator 354 are stacked in this order in FIG. 20. A
conductor 356 is formed in the insulators 350, 352, and 354. The
conductor 356 functions as a plug or a wiring. Note that the
conductor 356 can be formed using a material similar to that for
the conductor 328 and the conductor 330.
[0351] For example, the insulator 350 is preferably formed using an
insulator having a barrier property against hydrogen, like the
insulator 324. Furthermore, the conductor 356 preferably includes a
conductor having a barrier property against hydrogen. The conductor
having a barrier property against hydrogen is formed in an opening
of the insulator 350 having a barrier property against hydrogen.
The structure can separate the transistor 300 and the transistor
200 by a barrier layer and inhibit diffusion of hydrogen from the
transistor 300 to the transistor 200.
[0352] Note that as the conductor having a barrier property against
hydrogen, tantalum nitride can be used, for example. A stacked
structure of tantalum nitride and tungsten having high conductivity
can inhibit hydrogen diffusion from the transistor 300 while the
conductivity of a wiring is ensured. In this case, a tantalum
nitride layer having a barrier property against hydrogen is
preferably in contact with the insulator 350 having a barrier
property against hydrogen.
[0353] In the above, a wiring layer including the conductor 356 is
described; however, the memory device of this embodiment is not
limited thereto. The number of wiring layers similar to the wiring
layer including the conductor 356 may be three or less, or five or
more.
[0354] An insulator 210, the insulator 212, and the insulator 214
are stacked in this order over the insulator 354. At least one of
the insulators 210, 212, and 214 includes a material having a
barrier property against oxygen or hydrogen.
[0355] The insulator 210 can be formed using a material similar to
that for the insulator 320, for example. An interlayer film with a
relatively low dielectric constant can reduce the parasitic
capacitance between wirings. A silicon oxide film or a silicon
oxynitride film can be used as the insulator 212, for example.
[0356] Each of the insulators 211 and 212 is preferably formed
using a film having a barrier property, and the film prevents
diffusion of hydrogen or impurities from the substrate 311, a
region where the transistor 300 is provided, or the like to a
region where the transistor 200 is provided, for example.
Therefore, each of the insulators 210 and 212 can be formed using a
material similar to that for the insulator 324.
[0357] For a film having a barrier property against hydrogen,
silicon nitride formed by a CVD method can be used, for example.
The diffusion of hydrogen to a semiconductor element including an
oxide semiconductor, such as the transistor 200, degrades the
characteristics of the semiconductor element in some cases.
Therefore, a film that prevents hydrogen diffusion is preferably
provided between the transistor 200 and the transistor 300.
Specifically, the film that prevents hydrogen diffusion is a film
from which a small amount of hydrogen is released.
[0358] As the film having a barrier property against hydrogen, for
example, a metal oxide such as aluminum oxide, hafnium oxide, or
tantalum oxide is preferably used for the insulator 214.
[0359] In particular, aluminum oxide has an excellent blocking
effect that prevents transmission of oxygen and impurities such as
hydrogen and moisture, which cause a change in electrical
characteristics of the transistor. Accordingly, aluminum oxide can
prevent the entry of impurities such as hydrogen and moisture into
the transistor 200 during and after a manufacturing process of the
transistor. In addition, aluminum oxide can inhibit release of
oxygen from the oxide contained in the transistor 200. Therefore,
aluminum oxide is suitably used for a protective film of the
transistor 200.
[0360] A conductor 218, a conductor included in the transistor 200,
a conductor included in the capacitor 100, and the like are
provided in the insulators 210, 211, 212, 214, and 216. The
conductor 218 functions as a plug or a wiring electrically
connected to the transistor 200 or the transistor 300. The
conductor 218 can be formed using a material similar to that for
the conductors 328 and 330.
[0361] In particular, part of the conductor 218 that is in contact
with the insulators 210 and 214 is preferably a conductor having a
barrier property against oxygen, hydrogen, and water. The structure
can separate the transistors 300 and 200 by a layer having a
barrier property against oxygen, hydrogen, and water. As a result,
the diffusion of hydrogen from the transistor 300 to the transistor
200 can be inhibited.
[0362] The transistor 200 and the capacitor 100 are provided over
the insulator 214. Note that the structures of the transistor 200
and the capacitor 100 described in the above embodiment can be used
as those of the transistor 200 and the capacitor 100 described
here. Note that the transistor 200 and the capacitor 100 in FIG. 20
are examples and are not limited to the structures; an appropriate
transistor and a capacitor may be used in accordance with a circuit
structure or a driving method.
[0363] Furthermore, the conductor 240 is provided in contact with
the conductor 218 so that a conductor which is connected to the
transistor 300 is connected to a conductor over the transistor 200.
Although the wiring 1002 is extended above the transistor 200 in
FIG. 20, one embodiment of the present invention is not limited
thereto. The wiring 1001, the wiring 1007, or the like may be
extended above the transistor 200.
[0364] The above is the description of the structure example. The
structure can reduce variation in electrical characteristics, and
improve the reliability of a semiconductor device including a
transistor using an oxide semiconductor.
[0365] The structures, the methods, and the like described in this
embodiment can be combined as appropriate with any of the
structures, the methods, and the like described in the other
embodiments.
Embodiment 3
[0366] In this embodiment, a memory device of one embodiment of the
present invention including a transistor in which an oxide is used
for a semiconductor (hereinafter referred to as an OS transistor in
some cases), and a capacitor (hereinafter, such a memory device is
also referred to as an OS memory device in some cases), is
described with reference to FIGS. 22A and 22B, and 23A to 23C. The
OS memory device includes at least a capacitor and an OS transistor
that controls the charging and discharging of the capacitor. Since
the OS transistor has an extremely low off-state current, the OS
memory device has excellent retention characteristics and can
function as a nonvolatile memory.
[0367] In general, a variety of memory devices (memory) are used as
semiconductor devices such as a computer in accordance with the
intended use. FIG. 21 is a hierarchy diagram showing various memory
devices with different levels. The memory devices at the upper
levels of the diagram require high access speeds, and the memory
devices at the lower levels require large memory capacity and high
record density. In FIG. 21, sequentially from the top level, a
memory combined as a register in an arithmetic processing device
such as a CPU, a static random access memory (SRAM), a dynamic
random access memory (DRAM), and a 3D NAND memory are shown.
[0368] The memory as the register of the arithmetic logic unit such
as CPU is accessed by the arithmetic processing device frequently
because an operation result is temporarily stored in it.
Accordingly, rapid operation is more important than the capacity of
the memory. The register also has a function of holding setting
data or the like of the arithmetic processing device.
[0369] An SRAM is used for a cache, for example. The cache has a
function of holding a copy of part of data held in a main memory.
Copying data which is frequently used and holding the copy of the
data in the cache facilitates rapid data access.
[0370] A DRAM is used for a main memory, for example. The main
memory has a function of holding a program or data which are read
from the storage space. The record density of a DRAM is
approximately 0.1 to 0.3 Gbit/mm.sup.2.
[0371] A 3D NAND memory is used for a storage space, for example. A
storage space has a function of holding data which need to be
stored for a long time and programs used for an arithmetic
processing device, for example. Therefore, a storage space needs to
have high memory capacity and a high recording density rather than
operation speed. The memory density for a storage space is
approximately 0.6 to 6.0 Gbit/mm.sup.2.
[0372] The memory device of one embodiment of the present invention
operates fast and can hold data for a long time. The memory device
of one embodiment of the present invention can be favorably used as
a memory device in a boundary region 901 including both the level
in which cache is placed and the level in which main memory is
placed. The memory device of one embodiment of the present
invention can be favorably used as a memory device in a boundary
region 902 including both the level in which main memory is placed
and the level in which storage space is placed.
<Structure Example of Memory Device>
[0373] FIG. 22A shows a structure example of an OS memory device. A
memory device 1400 includes a peripheral circuit 1411 and a memory
cell array 1470. The peripheral circuit 1411 includes a row circuit
1420, a column circuit 1430, an output circuit 1440, and a control
logic circuit 1460.
[0374] The column circuit 1430 includes, for example, a column
decoder, a precharge circuit, a sense amplifier, a write circuit,
and the like. The precharge circuit has a function of precharging
wirings. The sense amplifier has a function of amplifying a data
signal read from a memory cell. The wirings mentioned above are
connected to memory cells included in the memory cell array 1470,
which will be described later in detail. The amplified data signal
is output as a data signal RDATA to the outside of the memory
device 1400 through the output circuit 1440. The row circuit 1420
includes a row decoder and a word line driver circuit, for example,
and can select a row to be accessed.
[0375] As power supply voltages from the outside, a low power
supply voltage (VSS), a high power supply voltage (VDD) for the
peripheral circuit 1411, and a high power supply voltage (VIL) for
the memory cell array 1470 are supplied to the memory device 1400.
Control signals (CE, WE, and RE), an address signal ADDR, and a
data signal WDATA are also input to the memory device 1400 from the
outside. The address signal ADDR is input to the row decoder and
the column decoder, and the data signal WDATA is input to the write
circuit.
[0376] The control logic circuit 1460 processes the signals (CE,
WE, and RE) input from the outside, and generates control signals
for the row decoder and the column decoder. The signal CE is a chip
enable signal, the signal WE is a write enable signal, and the
signal RE is a read enable signal. Signals processed by the control
logic circuit 1460 are not limited thereto and other control
signals may be input as necessary.
[0377] The memory cell array 1470 includes a plurality of memory
cells MC arranged in a matrix and a plurality of wirings. The
number of wirings that connect the memory cell array 1470 and the
row circuit 1420 depends on the configuration of the memory cell
MC, the number of memory cells MC in one column, and the like. The
number of wirings that connect the memory cell array 1470 and the
column circuit 1430 depends on the configuration of the memory cell
MC, the number of memory cells MC in one row, and the like.
[0378] FIG. 22A shows an example in which the peripheral circuit
1411 and the memory cell array 1470 are formed on the same plane;
however, this embodiment is not limited thereto. For example, as
illustrated in FIG. 22B, the memory cell array 1470 may be provided
to partly overlap the peripheral circuit 1411. For example, the
sense amplifier may be provided below the memory cell array 1470 so
that they overlap each other.
[0379] FIGS. 23A to 23C illustrate configuration examples of memory
cells that can be used as the memory cell MC.
[DOSRAM]
[0380] FIGS. 23A to 23C illustrate a circuit configuration example
of a memory cell of a DRAM. In this specification and the like, a
DRAM using a memory cell including one OS transistor and one
capacitor is sometimes referred to as a dynamic oxide semiconductor
random access memory (DOSRAM). A memory cell 1471 shown in FIG. 23A
includes a transistor M1 and a capacitor CA. Note that the
transistor M1 includes a gate (also referred to as a front gate in
some cases) and a back gate.
[0381] A first terminal of the transistor M1 is connected to a
first terminal of the capacitor CA. A second terminal of the
transistor M1 is connected to a wiring BIL. The gate of the
transistor M1 is connected to a wiring WOL. The back gate of the
transistor M1 is connected to a wiring BGL. A second terminal of
the capacitor CA is connected to a wiring CAL.
[0382] The wiring BIL functions as a bit line, and the wiring WOL
functions as a word line. The wiring CAL functions as a wiring for
applying a predetermined potential to the second terminal of the
capacitor CA. A low-level potential is preferably applied to the
wiring CAL at the time of data writing and data reading. The wiring
BGL functions as a wiring for applying a potential to the back gate
of the transistor M1. The threshold voltage of the transistor M1
can be increased or decreased by supplying a given potential to the
wiring BGL.
[0383] The memory cell MC is not limited to the memory cell 1471
and can have a different circuit configuration. For example, in the
memory cell MC, the back gate of the transistor M1 may be connected
to the wiring WOL instead of the wiring BGL as in a memory cell
1472 illustrated in FIG. 23B. As another example of the memory cell
MC, the transistor M1 may be a single-gate transistor, that is, a
transistor without a back gate as in a memory cell 1473 illustrated
in FIG. 23C.
[0384] When the semiconductor device shown in the above embodiment
is used in the memory cell 1471 and the like, the transistor 200
can be used as the transistor M1 and the capacitor 100 can be used
as the capacitor CA. The use of an OS transistor for the transistor
M1 enables extremely low leakage current of the transistor M1. This
also enables written data to be retained for a long time, and thus
decreases the frequency of refresh operation for the memory cell or
eliminates refresh operation for the memory cell. In addition,
since the OS transistor has an extremely low leakage current,
multi-level data or analog data can be held in the memory cells
1471, 1472, and 1473.
[0385] In the DOSRAM, when the sense amplifier is provided below
the memory cell array 1470 so that they overlap each other as
described above, the bit line can be shortened. This reduces bit
line capacity, which reduces the storage capacity of the memory
cell.
[0386] The structures, the methods, and the like described in this
embodiment can be combined as appropriate with any of the
structures, the methods, and the like described in the other
embodiments.
Embodiment 4
[0387] This embodiment shows examples of an electronic component
and an electronic device that include the memory device of the
above embodiments and the like.
<Electronic Component>
[0388] First, FIGS. 24A and 24B show examples of an electronic
component including a memory device 1000.
[0389] FIG. 24A is a perspective view of an electronic component
700 and a substrate (circuit board 704) on which the electronic
component 700 is mounted. The memory device 1000 includes a driver
circuit layer 1500 and a memory layer 1200, which includes a
plurality of memory cell arrays. The electronic component 700 in
FIG. 24A includes a storage device 1000 in a mold 711. FIG. 24A
omits part of the electronic component to show the inside of the
electronic component 700. The electronic component 700 includes a
land 712 outside the mold 711. The land 712 is electrically
connected to an electrode pad 713, and the electrode pad 713 is
electrically connected to the memory device 1000 via a wire 714.
The electronic component 700 is mounted on a printed circuit board
702, for example. A plurality of such electronic components are
combined and electrically connected to each other on the printed
circuit board 702, which forms the circuit substrate 704.
[0390] FIG. 24B is a perspective view of an electronic component
730. The electronic component 730 is an example of a system in
package (SiP) or a multi-chip module (MCM). In the electronic
component 730, an interposer 731 is provided over a package
substrate 732 (printed circuit board) and a semiconductor device
735 and a plurality of memory devices 100 are provided over the
memory device 1000.
[0391] The electronic component 730 using the memory device 1000 as
a high bandwidth memory (HBM) is illustrated as an example. An
integrated circuit (a semiconductor device) such as a CPU, a GPU,
or an FPGA can be used as the semiconductor device 735.
[0392] As the package substrate 732, a ceramic substrate, a plastic
substrate, a glass epoxy substrate, or the like can be used. As the
interposer 731, a silicon interposer, a resin interposer, or the
like can be used.
[0393] The interposer 731 includes a plurality of wirings and has a
function of electrically connecting a plurality of integrated
circuits with different terminal pitches. The plurality of wirings
have a single-layer structure or a layered structure. The
interposer 731 has a function of electrically connecting an
integrated circuit provided on the interposer 731 to an electrode
provided on the package substrate 732. Accordingly, the interposer
is sometimes referred to as a redistribution substrate or an
intermediate substrate. A through electrode may be provided in the
interposer 731 to be used for electrically connecting the
integrated circuit and the package substrate 732. In the case of
using a silicon interposer, a through-silicon via (TSV) can also be
used as the through electrode.
[0394] A silicon interposer is preferably used as the interposer
731. The silicon interposer can be manufactured at lower cost than
an integrated circuit because the silicon interposer is not
necessarily provided with an active element. Moreover, since
wirings of the silicon interposer can be formed through a
semiconductor process, the formation of minute wirings, which is
difficult for a resin interposer, is easily achieved.
[0395] An HBM needs to be connected to many wirings to achieve a
wide memory bandwidth. Therefore, an interposer on which an HBM is
mounted requires minute and densely formed wirings. For this
reason, a silicon interposer is preferably used as the interposer
on which an HBM is mounted.
[0396] In an SiP, an MCM, or the like using a silicon interposer, a
decrease in reliability due to a difference in expansion
coefficient between an integrated circuit and the interposer is
less likely to occur. Furthermore, a surface of a silicon
interposer has high planarity, and a poor connection between the
silicon interposer and an integrated circuit provided thereon less
likely occurs. It is particularly preferable to use a silicon
interposer for a 2.5D package (2.5D mounting) in which a plurality
of integrated circuits are arranged side by side on the
interposer.
[0397] A heat sink (radiator plate) may be provided to overlap with
the electronic component 730. In this case, the heights of
integrated circuits provided on the interposer 731 are preferably
equal to each other. In the electronic component 730 of this
embodiment, the heights of the memory device 1000 and the
semiconductor device 735 are preferably equal to each other, for
example.
[0398] An electrode 733 may be provided on the bottom portion of
the package substrate 732 to mount the electronic component 730 on
another substrate. FIG. 24B shows an example in which the electrode
733 is formed of a solder ball. Solder balls are provided in a
matrix on the bottom portion of the package substrate 732, whereby
a ball grid array (BGA) can be achieved. Alternatively, the
electrode 733 may be formed of a conductive pin. When conductive
pins are provided in a matrix on the bottom portion of the package
substrate 732, a pin grid array (PGA) can be achieved.
[0399] The electronic component 730 can be mounted on another
substrate in various manners, not limited to the BGA and the PGA.
For example, a staggered pin grid array (SPGA), a land grid array
(LGA), a quad flat package (QFP), a quad flat J-leaded package
(QFJ), or a quad flat non-leaded package (QFN) can be employed.
[0400] This embodiment can be implemented in combination with any
of the structures described in the other embodiments and the like,
as appropriate.
Embodiment 5
[0401] In this embodiment, application examples of a memory device
using the semiconductor device described in the above embodiment
will be described. The semiconductor device described in the above
embodiment can be applied to, for example, memory devices of a
variety of electronic devices (e.g., information terminals,
computers, smartphones, e-book readers, digital cameras (including
video cameras), video recording/reproducing devices, and navigation
systems). Here, the computers refer not only to tablet computers,
notebook computers, and desktop computers, but also to large
computers such as server systems. The semiconductor device
described in the above embodiment is applied to removable memory
devices such as memory cards (e.g., SD cards), USB memories, and
solid state drives (SSD). FIGS. 25A to 25E schematically shows some
structure examples of removable memory devices. For example, the
semiconductor device described in the above embodiment is processed
into a packaged memory chip and used in a variety of memory devices
and removable memories.
[0402] FIG. 25A is a schematic diagram of a USB memory. A USB
memory 1100 includes a housing 1101, a cap 1102, a USB connector
1103, and a substrate 1104. The substrate 1104 is placed in the
housing 1101. A memory chip 1105 and a controller chip 1106 are
attached to the substrate 1104, for example. The semiconductor
device described in the above embodiment can be incorporated in the
memory chip 1105 or the like on the substrate 1104.
[0403] FIG. 25B is a schematic external diagram of an SD card, and
FIG. 25C is a schematic diagram illustrating the internal structure
of the SD card. An SD card 1110 includes a housing 1111, a
connector 1112, and a substrate 1113. The substrate 1113 is placed
in the housing 1111. A memory chip 1114 and a controller chip 1115
are attached to the substrate 1113, for example. The memory chip
1114 provided on the rear side of the substrate 1113 increases the
capacity of the SD card 1110. In addition, a wireless chip with a
wireless communication function may be provided on the substrate
1113. This enables data reading and writing of the memory chip 1114
by wireless communication between a host device and the SD card
1110. The semiconductor device described in the above embodiment
can be incorporated in the memory chip 1114 or the like on the
substrate 1113.
[0404] FIG. 25D is a schematic external diagram of an SSD, and FIG.
25E is a schematic diagram of the internal structure of the SSD. An
SSD 1150 includes a housing 1151, a connector 1152, and a substrate
1153. The substrate 1153 is placed in the housing 1151. A memory
chip 1154, a memory chip 1155, and a controller chip 1156 are
attached to the substrate 1153, for example. The memory chip 1155
is a work memory for the controller chip 1156, and a DOSRAM chip
can be used, for example. The memory chip 1154 provided on the rear
side of the substrate 1153 increases the capacity of the SSD 1150.
The semiconductor device described in the above embodiment can be
incorporated in the memory chip 1154 or the like on the substrate
1153.
[0405] The structures, the methods, and the like described in this
embodiment can be combined as appropriate with any of the
structures, the methods, and the like described in the other
embodiments.
Embodiment 6
[0406] FIGS. 26A, 26B, 26C, 26D, 26E1, 26E2, and 26F show specific
examples of electronic devices in which the semiconductor device of
one embodiment of the present invention can be used.
[0407] Specifically, the semiconductor device of one embodiment of
the present invention can be used for processors such as a CPU or a
GPU, or chips. FIGS. 26A, 26B, 26C, 26D, 26E1, 26E2, and 26F show
specific examples of electronic devices including a processor, such
as a CPU or a GPU, or a chip of one embodiment of the present
invention.
<Electronic Devices and Systems>
[0408] The GPU or the chip of one embodiment of the present
invention can be mounted on a variety of electronic devices.
Examples of electronic devices include an electronic device with a
large screen, such as a television device, a desktop or laptop
personal computer, a monitor of a computer or the like, digital
signage, and a large game machine (e.g., a pachinko machine); a
camera such as a digital camera or a digital video camera; a
digital photo frame; a mobile phone; a portable game console; a
portable information terminal; and an audio reproducing device. In
addition, when the integrated circuit or the chip of one embodiment
of the present invention is provided in the electronic device, the
electronic device can include artificial intelligence.
[0409] The electronic device of one embodiment of the present
invention may include an antenna. With the antenna receiving
signal, the electronic device can display an image, data, or the
like on a display portion. When the electronic device includes an
antenna and a secondary battery, the antenna may be used for
contactless power transmission.
[0410] The electronic device of one embodiment of the present
invention may include a sensor (a sensor having a function of
measuring force, displacement, position, speed, acceleration,
angular velocity, rotational frequency, distance, light, liquid,
magnetism, temperature, chemical substance, sound, time, hardness,
electric field, electric current, voltage, electric power,
radiation, flow rate, humidity, gradient, oscillation, odor, or
infrared rays).
[0411] The electronic device of one embodiment of the present
invention can have a variety of functions. For example, the
electronic device of one embodiment of the present invention can
have a function of displaying a variety of data (a still image, a
moving image, a text image, and the like) on the display portion, a
touch panel function, a function of displaying a calendar, date,
time, and the like, a function of executing a variety of software
(programs), a wireless communication function, and a function of
reading out a program or data stored in a recording medium. FIGS.
26A, 26B, 26C, 26D, 26E1, 26E2, and 26F show examples of electronic
devices.
[Mobile Phone]
[0412] FIG. 26A illustrates a mobile phone (smartphone) which is a
type of an information terminal. The information terminal 5500
includes a housing 5510 and a display portion 5511. As input
interfaces, a touch panel and a button are provided in the display
portion 5511 and the housing 5510, respectively.
[0413] The information terminal 5500 can execute an application
utilizing artificial intelligence, with the use of the chip of one
embodiment of the present invention. Examples of the application
utilizing artificial intelligence include an application for
interpreting a conversation and displaying its content on the
display portion 5511; an application for recognizing letters,
figures, and the like input to the touch panel of the display
portion 5511 by a user and displaying them on the display portion
5511; and an application for biometric authentication using
fingerprints, voice prints, or the like.
[Information Terminal 1]
[0414] FIG. 26B shows a desktop information terminal 5300. The
desktop information terminal 5300 includes a main body 5301 of the
information terminal, a display 5302, and a keyboard 5303.
[0415] The desktop information terminal 5300 can execute an
application utilizing artificial intelligence with the use of the
chip of one embodiment of the present invention as the information
terminal 5500 described above. Examples of the application
utilizing artificial intelligence include design-support software,
text correction software, and software for automatic menu
generation. Furthermore, with the use of the desktop information
terminal 5300, novel artificial intelligence can be developed.
[0416] Note that although FIGS. 26A and 26B shows a smartphone and
a desktop information terminal, respectively, as examples of the
electronic device, one embodiment of the present invention can also
be applied to an information terminal other than the smartphone and
the desktop information terminal. Examples of information terminals
other than a smartphone and a desktop information terminal include
a personal digital assistant (PDA), a laptop information terminal,
and a workstation.
[Household Appliance]
[0417] FIG. 26C shows an electric refrigerator-freezer 5800 which
is an example of a household appliance. The electric
refrigerator-freezer 5800 includes a housing 5801, a refrigerator
door 5802, a freezer door 5803, and the like.
[0418] When the chip of one embodiment of the present invention is
used in the electric refrigerator-freezer 5800, the electric
refrigerator-freezer 5800 including artificial intelligence can be
obtained. Utilizing the artificial intelligence enables the
electric refrigerator-freezer 5800 to have a function of
automatically making a menu based on foods stored in the electric
refrigerator-freezer 5800 and food expiration dates, for example, a
function of controlling the temperature to be appropriate for the
foods stored in the electric refrigerator-freezer 5800, and the
like.
[0419] Although the electric refrigerator-freezer is described here
as an example of a household appliance, other examples of a
household appliance include a vacuum cleaner, a microwave oven, an
electric oven, a rice cooker, a water heater, an IH cooker, a water
server, a heating-cooling combination appliance such as an air
conditioner, a washing machine, a drying machine, and an audio
visual appliance.
[Game Machines]
[0420] FIG. 26D shows a portable game machine 5200 as an example of
a game machine. The portable game machine 5200 includes a housing
5201, a display portion 5202, a button 5203, and the like.
[0421] With the use of the GPU or the chip of one embodiment of the
present invention in the portable game machine 5200, the portable
game machine 5200 with low power consumption can be obtained.
Furthermore, heat generation from a circuit can be reduced owing to
low power consumption; thus, the influence of heat generation on
the circuit, the peripheral circuit, and the module can be
reduced.
[0422] Furthermore, when the GPU or the chip of one embodiment of
the present invention is used in the portable game machine 5200,
the portable game machine 5200 including artificial intelligence
can be obtained.
[0423] In general, the progress of a game, the actions and words of
game characters, and expressions of a phenomenon in the game are
programed in the game; however, the use of artificial intelligence
in the portable game machine 5200 enables expressions not limited
by the game program. For example, questions posed by the player,
the progress of the game, time, and actions and words of game
characters can be changed for various expressions.
[0424] The artificial intelligence can construct a virtual game
player; thus, a game that needs a plurality of players can be
played by only one human game player with the portable game machine
5200, with the use of a virtual game player constructed by the
artificial intelligence as an opponent.
[0425] Although the portable game machine is illustrated as an
example of a game machine in FIG. 26D, the game machine using the
GPU or the chip of one embodiment of the present invention is not
limited thereto. Examples of the game machine using the GPU or the
chip of one embodiment of the present invention include a home
video game console, an arcade game machine installed in an
entertainment facility (a game center, an amusement park, or the
like), and a throwing machine for batting practice installed in
sports facilities.
[Moving Vehicle]
[0426] The GPU or the chip of one embodiment of the present
invention can be used in an automobile, which is a moving vehicle,
and around a driver's seat in the automobile.
[0427] FIG. 26E1 shows an automobile 5700 as an example of a moving
vehicle, and FIG. 26E2 shows the periphery of a windshield inside
the automobile. FIG. 26E2 shows a display panel 5701, a display
panel 5702, and a display panel 5703 which are attached to a
dashboard, and a display panel 5704 attached to a pillar.
[0428] The display panels 5701 to 5703 can provide various kinds of
information by displaying a speedometer, a tachometer, a mileage, a
fuel meter, a gearshift indicator, air-conditioning settings, and
the like. Items displayed on the display panel, their layout, and
the like can be changed as appropriate to suit the user's
preferences, resulting in more sophisticated design. The display
panels 5701 to 5703 can also be used as lighting devices.
[0429] The display panel 5704 can compensate for the view
obstructed by the pillar (blind areas) by displaying an image taken
by an imaging device (not illustrated) provided on the exterior of
the automobile 5700. That is, displaying an image taken by the
imaging device provided on the exterior of the automobile 5700
eliminates blind areas and enhances safety. Moreover, displaying an
image to compensate for the area that a driver cannot see makes it
possible for the driver to confirm safety more easily and
comfortably. The display panel 5704 can also be used as a lighting
device.
[0430] Because the GPU or the chip of one embodiment of the present
invention can be used as a component of artificial intelligence,
the chip can be used in the automatic driving system of the
automobile 5700, for example. The chip can also be used for a
system for navigation, risk prediction, or the like. The display
panels 5701 to 5704 may display information regarding navigation
information, risk prediction, and the like.
[0431] Although an automobile is described above as an example of a
moving vehicle, moving vehicles are not limited to an automobile.
Examples of moving vehicles include a train, a monorail train, a
ship, and a flying object (a helicopter, an unmanned aircraft (a
drone), an airplane, and a rocket), and these moving vehicles can
include a system utilizing artificial intelligence when equipped
with the chip of one embodiment of the present invention.
[Broadcasting System]
[0432] The GPU or the chip of one embodiment of the present
invention can be used in a broadcasting system.
[0433] FIG. 26F schematically shows data transmission in a
broadcasting system. Specifically, FIG. 26F shows a path in which a
radio wave (a broadcasting signal) transmitted from a broadcast
station 5680 is delivered to a television receiver (TV) 5600 of
each household. The TV 5600 includes a receiving device (not
illustrated), and the broadcast signal received by an antenna 5650
is transmitted to the TV 5600 through the receiving device.
[0434] Although an ultra-high frequency (UHF) antenna is
illustrated as the antenna 5650 in FIG. 26F, a BS/110.degree. CS
antenna, a CS antenna, or the like can also be used.
[0435] A radio wave 5675A and a radio wave 5675B are broadcast
signals for terrestrial broadcasting; a radio wave tower 5670
amplifies the received radio wave 5675A and transmits the radio
wave 5675B. Each household can view terrestrial TV broadcasting on
the TV 5600 by receiving the radio wave 5675B with the antenna
5650. Note that the broadcasting system is not limited to the
terrestrial broadcasting shown in FIG. 26F and may be satellite
broadcasting using an artificial satellite, data broadcasting using
an optical line, or the like.
[0436] The above-described broadcasting system may utilize
artificial intelligence by including the chip of one embodiment of
the present invention. When the broadcast data is transmitted from
the broadcast station 5680 to the TV 5600 at home, the broadcast
data is compressed by an encoder. The antenna 5650 receives the
compressed broadcast data, and then the compressed broadcast data
is decompressed by a decoder of the receiving device in the TV
5600. With the use of the artificial intelligence, for example, a
display pattern included in an image can be recognized in motion
compensation prediction, which is one of the compressing methods
for the encoder. In addition, in-frame prediction, for instance,
can also be performed utilizing artificial intelligence.
Furthermore, for example, when the broadcast data with low
resolution is received and displayed on the TV 5600 with high
resolution, image interpolation such as upconversion can be
performed in the broadcast data decompression by the decoder.
[0437] The above-described broadcasting system utilizing artificial
intelligence is suitable for ultra-high definition television
(UHDTV: 4K and 8K) broadcasting, which needs a large amount of
broadcast data.
[0438] As an application of artificial intelligence in the TV 5600,
a recording device with artificial intelligence may be provided in
the TV 5600, for example. With such a structure, the artificial
intelligence in the recording device can learn the user's
preference, so that TV programs that suit the user's preference can
be recorded automatically.
[0439] The electronic device and its functions, an application
example of the artificial intelligence and its effects, and the
like described in this embodiment can be combined as appropriate
with the description of another electronic device.
[0440] The structures, the methods, and the like described in this
embodiment can be combined as appropriate with any of the
structures, the methods, and the like described in the other
embodiments.
[0441] This application is based on Japanese Patent Application
Serial No. 2019-011582 filed with Japan Patent Office on Jan. 25,
2019, the entire contents of which are hereby incorporated by
reference.
* * * * *