U.S. patent application number 10/335874 was filed with the patent office on 2003-07-17 for semiconductor integrated circuit device and method of manufacturing the same.
Invention is credited to Asano, Isamu, Fukuda, Takuya, Hirasawa, Masayoshi, Kawakita, Keizo, Nakamura, Yoshitaka, Sekiguchi, Toshihiro, Tadaki, Yoshitaka, Tamaru, Tsuyoshi, Yamada, Satoru.
Application Number | 20030132479 10/335874 |
Document ID | / |
Family ID | 17203754 |
Filed Date | 2003-07-17 |
United States Patent
Application |
20030132479 |
Kind Code |
A1 |
Nakamura, Yoshitaka ; et
al. |
July 17, 2003 |
Semiconductor integrated circuit device and method of manufacturing
the same
Abstract
In order to improve connection reliability of a feeding
interconnection connected to an electrode of each of the
information storage capacitive elements of a DRAM, the formation of
a through hole for connecting the information storage capacitive
element formed over each memory cell selection MISFET and a feeding
interconnection is performed in a process different from that for
the formation of a through hole for connecting an interconnection
of a second wiring layer in a peripheral circuit, which is formed
over the information storage capacitive element and an
interconnection corresponding to a first wiring layer.
Inventors: |
Nakamura, Yoshitaka; (Tokyo,
JP) ; Hirasawa, Masayoshi; (Tokyo, JP) ;
Asano, Isamu; (Iruma-shi, JP) ; Tamaru, Tsuyoshi;
(Tokyo, JP) ; Yamada, Satoru; (Tokyo, JP) ;
Kawakita, Keizo; (Tokyo, JP) ; Sekiguchi,
Toshihiro; (Hidaka-shi, JP) ; Tadaki, Yoshitaka;
(Hannou-shi, JP) ; Fukuda, Takuya; (Tokyo,
JP) |
Correspondence
Address: |
ANTONELLI TERRY STOUT AND KRAUS
SUITE 1800
1300 NORTH SEVENTEENTH STREET
ARLINGTON
VA
22209
|
Family ID: |
17203754 |
Appl. No.: |
10/335874 |
Filed: |
January 3, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10335874 |
Jan 3, 2003 |
|
|
|
09880959 |
Jun 15, 2001 |
|
|
|
09880959 |
Jun 15, 2001 |
|
|
|
09389231 |
Sep 3, 1999 |
|
|
|
6258649 |
|
|
|
|
Current U.S.
Class: |
257/315 ;
257/E21.008; 257/E21.279; 257/E21.576; 257/E21.577; 257/E21.585;
257/E21.656; 257/E21.66; 257/E23.16 |
Current CPC
Class: |
H01L 23/53223 20130101;
H01L 27/10894 20130101; H01L 21/76801 20130101; H01L 2924/0002
20130101; H01L 27/10882 20130101; H01L 28/40 20130101; H01L
21/28518 20130101; H01L 21/76843 20130101; H01L 21/31612 20130101;
H01L 21/76828 20130101; H01L 21/76816 20130101; H01L 21/76855
20130101; H01L 21/02164 20130101; H01L 21/02211 20130101; H01L
21/02274 20130101; H01L 2924/0002 20130101; H01L 2924/00
20130101 |
Class at
Publication: |
257/315 |
International
Class: |
H01L 029/788 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 3, 1998 |
JP |
10-250162 |
Claims
What is claimed is:
1. A semiconductor integrated circuit device, comprising: memory
cells, each memory cell being comprised of a memory cell selection
MISFET and an information storage capacitive element connected in
series with said memory cell selection MISFET, the memory cells
including bit lines; a first interconnection formed over said
memory cell selection MISFET; a first insulating film formed over
said first interconnection; a second insulating film formed over
said information storage capacitive element; a second
interconnection formed over said second insulating film; a first
conductive layer formed within a first through hole defined in said
second insulating film and said first insulating film below said
second insulating film, said first conductive layer connecting said
second interconnection and said first interconnection; a third
insulating film formed over said second interconnection; a feeding
interconnection for supplying a predetermined potential to an upper
electrode of said information storage capacitive element formed
over said third insulating film; and a second conductive layer
formed within a second through hole defined in said third
insulating film and said second insulating film placed in a layer
therebelow; wherein said second conductive layer connects said
upper electrode and said feeding interconnection; wherein said
first insulating film includes a plurality of grooves; wherein a
lower electrode of said information storage capacitive element is
formed over an inner surface of a groove of said plurality of
grooves; wherein a dielectric film of said information storage
capacitive element is formed over said lower electrode; wherein an
upper electrode is formed over said dielectric film and over said
first insulating film outside said groove; wherein said upper
electrode formed over said first insulating film outside said
groove is located in a first region; and wherein said feeding
interconnection and said upper electrode are connected in said
first region.
2. The semiconductor integrated circuit device according to claim
1, wherein a bottom surface of said upper electrode in said first
region is higher than a level of one-half of the depth of said
groove.
3. The semiconductor integrated circuit device according to claim
1, wherein said upper electrode in said first region is formed over
a top surface of said first insulating film.
4. The semiconductor integrated circuit device according to claim
1, wherein an aspect ratio of said first through hole is larger
than that of said second through hole.
5. The semiconductor integrated circuit device according to claim
1, further comprising a third interconnection formed over said
third insulating film; and a third conductive layer formed within a
third through hole defined in said third insulating film below said
third interconnection, said third conductive layer connecting said
third interconnection and said second interconnection, wherein said
third interconnection and said feeding interconnection are formed
in a same wiring layer.
6. The semiconductor integrated circuit device according to claim
5, wherein an aspect ratio of said second through hole is larger
than that of said third through hole.
7. The semiconductor integrated circuit device according to claim
1, wherein each of said bit lines is formed in a same wiring layer
as a first interconnection of a peripheral circuit of the device
and is formed below the information storage capacitive
elements.
8. The semiconductor integrated circuit device according to claim
2, wherein said first and second interconnections are disposed in a
peripheral circuit region.
9. The semiconductor integrated circuit device according to claim
2, wherein the lower electrode of each information storage
capacitor element is electrically connected to a source region or a
drain region of a respective memory cell selection MISFET.
10. The semiconductor integrated circuit device according to claim
2, wherein said lower electrode is a layer of conductive material
extending along said side wall of said groove.
11. The semiconductor integrated circuit device according to claim
2, wherein said lower electrode of each information storage
capacitive element is in contact with said side wall of said
groove.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a semiconductor integrated
circuit device and to a technique for the manufacture thereof; and,
more particularly, the invention relates to a technique which is
effective for application to a semiconductor integrated circuit
device having a DRAM (Dynamic Random Access Memory).
[0002] Memory cells of a DRAM are respectively placed at points
where a plurality of word lines and a plurality of bit lines,
disposed over a principal or main surface of a semiconductor
substrate, intersect in matrix form. The memory cell comprises one
memory cell selection MISFET (Metal Insulator Semiconductor Field
Effect Transistor) and one information capacitive element
(capacitor) electrically connected in series with the memory cell
selection MISFET.
[0003] The memory cell selection MISFET is formed in an active
region whose periphery is surrounded by a device separation region.
The memory cell selection MISFET is composed principally of a gate
oxide film, a gate electrode formed integrally with each word line,
and a pair of semiconductor regions which form a source and a
drain. Each bit line is placed above the memory cell selection
MISFET and is electrically connected to one of the source and drain
shared by two memory cell selection MISFETs disposed adjacent to
each other in its extending direction. Similarly, the information
storage capacitive element is disposed above the memory cell
selection MISFET and is electrically connected to the other of the
source and drain.
[0004] Japanese Patent Application Laid-Open No. Hei 7-7084
discloses a DRAM of a capacitor over bitline (COB) structure
wherein information storage capacitive elements are placed over the
bit lines. According to the DRAM described in the publication, a
lower electrode (storage electrode) of each information storage
capacitive element disposed above the bit line is processed into
cylindrical form to make up for a reduction in the amount of an
electrical charge stored in each information storage capacitive
element with macro-fabrication of each memory cell, whereby the
surface area thereof is increased, and a capacitive insulating film
and an upper electrode (plate electrode) are formed over the lower
electrode.
[0005] According to the DRAM described in the publication as well,
a frame-shaped groove (channel), which surrounds a memory array, is
defined in the boundary between the memory array and a peripheral
circuit region, and a thick insulating film is deposited over the
peripheral circuit region outside the channel, whereby a step-like
offset between the memory array and the peripheral circuit is
settled and the flattening of the peripheral circuit region is
implemented together. The groove is defined simultaneously in a
process step for processing the lower electrode of each information
storage capacitive element into cylindrical form. An inner wall of
the groove is composed of the same material (polycrystal silicon
film) as the lower electrode.
SUMMARY OF THE INVENTION
[0006] According to the DRAM of the prior art, since the wall
surface of the lower electrode which is processed into cylindrical
form, is utilized as an effective region for ensuring the amount of
stored electrical charges, the height of the lower electrode and
the depth of the groove (channel) increase as each memory cell is
miniaturized. With such increase in size, the insulating film
formed in the peripheral circuit region lying outside the groove
(channel) also further increases in thickness. As a result, a
through hole for connecting an upper-layer wire or interconnection
formed over the thick insulating film in the peripheral circuit
region and a lower-layer interconnection formed below the
insulating film also further increases in aspect ratio
(depth/diameter of the through hole).
[0007] However, when the aspect ratio of the through hole defined
in the thick insulating film in the peripheral circuit region
increases, a through hole defined in an insulating film between a
feeding interconnection fox supplying predetermined power to the
upper electrode of each information storage capacitive element and
the upper electrode and a through hole for connecting an
upper-layer interconnection formed over a thick insulating film in
a peripheral circuit region and a lower-layer interconnection
formed below the insulating film are greatly different in aspect
ratio from each other. Therefore, when one attempts to
simultaneously form the two through holes in the same process step,
the through hole having a small aspect ratio, which is formed over
the upper electrode of the information storage capacitive element,
is over-etched when an etching condition for the insulating film is
matched to the through hole having the large aspect ratio in the
peripheral circuit region, thereby penetrating the upper electrode.
Therefore, a lower portion of the through hole might reach the
lower-layer interconnection at the worst. On the other hand, when
the etching condition for the insulating film is matched to the
through hole having a low aspect ratio, which is formed above the
upper electrode, the bottom of the through hole having the large
aspect ratio, which is formed in the peripheral circuit region,
does not reach the lower-layer interconnection.
[0008] In the DRAM of the prior art as well, metal interconnections
corresponding to two layers are formed in a layer above each
information storage capacitive element. Since these metal
interconnections provided in the layer above the information
storage capacitive element are formed with a thickness which is
greater than an interconnection formed in a layer below the
information storage capacitive element, an insulating film
deposited by the normal CVD method lacks in gap-filling
characteristic in an interconnection densified region and so
difficulties are encountered in embedding it into spaces defined
between the interconnections.
[0009] As countermeasures against this problem, one may consider
that an insulating film covering the metal interconnections is
deposited by a high-density plasma CVD method having an excellent
gap-filling characteristic. However, the insulating film deposited
by the high-density plasma CVD method has a feature that it is apt
to be charged up by an electrical charge in a plasma. Therefore,
when the insulating film is deposited over a feeding metal
interconnection for supplying power to the upper electrode of each
information storage capacitive element by the high-density plasma
CVD method, electrical charges borne by charged particles in a
plasma are transferred to the upper electrode through the feeding
metal inter-connection, whereby the information storage capacitive
element might cause dielectric breakdown.
[0010] An object of the present invention is to provide a technique
capable of improving the accuracy of processing of a through hole
defined in an insulating film between a feeding interconnection for
supplying power to an upper electrode of each capacitive element
and the upper electrode to thereby enhance the connection
reliability of the feeding interconnection.
[0011] Another object of the present invention is to provide a
technique capable of preventing dielectric breakdown of a
capacitive insulating film, which is caused by charge-up of a
capacitive element upon growing an insulating film deposited over
an interconnection connected to an upper electrode of the
capacitive electrode.
[0012] The above, and other objects and novel features of the
present invention will become more apparent from the description of
the present specification and the accompanying drawings.
[0013] A summary of typical aspect and features of the invention
disclosed in the present application will be briefly explained as
follows:
[0014] (1) A method of manufacturing a semiconductor integrated
circuit device according to the present invention includes the
following steps:
[0015] (a) a step of forming memory cell selection MISFETs in a
memory array region on a main surface of a semiconductor substrate
and forming MISFETs for a peripheral circuit in a peripheral
circuit region;
[0016] (b) a step of forming a first interconnection over the
MISFET and thereafter forming a first insulating film over the
first interconnection;
[0017] (c) a step of defining grooves in the first insulating film
in the memory array region and thereafter patterning a first
conductive film formed over the first insulating film including the
interior of the grooves to thereby form a lower electrode of an
information storage capacitive element inside each groove;
[0018] (d) a step of patterning a second conductive film formed
over the lower electrode through a capacitive insulating film to
thereby form an upper electrode of each information storage
capacitive element;
[0019] (e) a step of forming a second insulating film over each
information storage capacitive element and thereafter defining a
first through hole in an insulating film including the second
insulating film and the first insulating film placed in a layer
therebelow;
[0020] (f) a step of patterning a third conductive film formed over
the second insulating film to thereby form a second interconnection
electrically connected to the first interconnection via the first
through hole;
[0021] (g) a step of forming a third insulating film over the
second interconnection, thereafter defining a second through hole
in the third insulating film provided over each information storage
capacitive element and defining a third through hole in the third
insulating film provided over the second interconnection; and
[0022] (h) a step of patterning a fourth conductive film formed
over the third insulating film to thereby form a feeding
interconnection electrically-connected to the upper electrode of
each information storage capacitive element via the second through
hole, and a third interconnection electrically connected to the
second interconnection via the third through hole.
[0023] (2) In the method of manufacturing the semiconductor
integrated circuit device according to the present invention as
described above, the third insulating film formed over the second
interconnection includes an insulating film formed by a
high-density plasma CVD method, and the second insulating film
formed over the information storage capacitive element excludes the
insulating film formed by the high-density plasma CVD method.
[0024] Typical ones of various aspects of the present invention
have been described in brief. However, various features of the
present application and specific configurations thereof will be
better understood from the following description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] While the specification concludes with claims particularly
pointing out and distinctly claiming the subject matter which is
regarded as the invention, it is believed that the invention, the
objects and features of the invention and further objects, features
and advantages thereof will be better understood from the following
description taken in connection with the accompanying drawings in
which:
[0026] FIG. 1 is an overall plan view showing a semiconductor chip
on which a DRAM according to an embodiment 1 of the present
invention is formed;
[0027] FIG. 2 is an equivalent circuit diagram of the DRAM
according to the embodiment 1 of the present invention;
[0028] FIG. 3 is a fragmentary cross-sectional view of a
semiconductor substrate, showing respective parts of a memory array
and a peripheral circuit of a DRAM according to one embodiment of
the present invention;
[0029] FIG. 4 is a fragmentary plan view of a semiconductor
substrate, showing part of the memory array of the DRAM according
to one embodiment of the present invention;
[0030] FIG. 5 is a fragmentary cross-sectional view of a
semiconductor substrate, illustrating a step in the method of
manufacturing a DRAM according to one embodiment of the present
invention;
[0031] FIG. 6 is a fragmentary plan view of the semiconductor
substrate, showing a step in the method of manufacturing the DRAM
according to one embodiment of the present invention;
[0032] FIG. 7 is a fragmentary cross-sectional view of the
semiconductor substrate, depicting a step in the method of
manufacturing the DRAM according to one embodiment of the present
invention;
[0033] FIG. 8 is a fragmentary plan view of the semiconductor
substrate, showing a step of the method of manufacturing the DRAM
according to one embodiment of the present invention;
[0034] FIG. 9 is a fragmentary cross-sectional view of the
semi-conductor substrate, showing a step of the method of
manufacturing the DRAM according to one embodiment of the present
invention;
[0035] FIG. 10 is a fragmentary cross-sectional view of the
semiconductor substrate, illustrating a step of the method of
manufacturing the DRAM according to one embodiment of the present
invention;
[0036] FIG. 11 is a fragmentary cross-sectional view of the
semiconductor substrate, showing a step of the method of
manufacturing the DRAM according to one embodiment of the present
invention;
[0037] FIG. 12 is a fragmentary cross-sectional view of the
semiconductor substrate, depicting a step of the method of
manufacturing the DRAM according to one embodiment of the present
invention;
[0038] FIG. 13 is a fragmentary cross-sectional view of the
semiconductor substrate, showing a step of the method of
manufacturing the DRAM according to one embodiment of the present
invention;
[0039] FIG. 14 a fragmentary cross-sectional view of the method of
semiconductor substrate, illustrating a step of the method of
manufacturing the DRAM according to one embodiment of the present
invention;
[0040] FIG. 15 is a fragmentary cross-sectional view of the
semiconductor substrate, showing a step of the method of
manufacturing the DRAM according to one embodiment of the present
invention;
[0041] FIG. 16 is a fragmentary cross-sectional view of the
semiconductor substrate, depicting a step of the method of
manufacturing the DPAM according to one embodiment of the present
invention;
[0042] FIG. 17 a fragmentary plan view of the semiconductor
substrate, showing a step of the method of manufacturing the DPAM
according to one embodiment of the present invention;
[0043] FIG. 18 is a fragmentary cross-seczional view of the
semiconductor substrate, illustrating a step of the method of
manufacturing the DPAM according to one embodiment of the present
invention;
[0044] FIG. 19 is a fragmentary cross-sectional view of the
semiconductor substrate, showing a step of the method of
manufacturing the DRAM according to one embodiment of the present
invention;
[0045] FIG. 20 is a fragmentary cross-sectional view of the
semiconductor substrate, illustrating a step of the method of
manufacturing the DRAM according to one embodiment of the present
invention;
[0046] FIG. 21 is a fragmentary cross-sectional view of the
semiconductor substrate, showing a step of the method of
manufacturing the DRAM according to one embodiment of the present
invention;
[0047] FIG. 22 is a fragmentary cross-sectional view of the
semiconductor substrate, depicting a step of the method of
manufacturing the DRAM according to one embodiment of the present
invention;
[0048] FIG. 23 is a fragmentary cross-sectional view of the
semiconductor substrate, showing a step of the method of
manufacturing the DRAM according to one embodiment of the present
invention;
[0049] FIG. 24 is a fragmentary cross-sectional view of the
semiconductor substrate, illustrating a step of the method of
manufacturing the DRAM according to one embodiment of the present
invention;
[0050] FIG. 25 is a fragmentary cross-sectional view of the
semiconductor substrate, showing a step of the method of
manufacturing the DPAM according to one embodiment of the present
invention;
[0051] FIG. 26 is a fragmentary cross-sectional view of the
semiconductor substrate, illustrating a step of the method of
manufacturing the DRAM according to one embodiment of the present
invention;
[0052] FIG. 27 is a fragmentary cross-sectional view of the
semiconductor substrate, depicting a step of the method of
manufacturing the DRAM according to one embodiment of the present
invention;
[0053] FIG. 28 is a fragmentary cross-sectional view of the
semiconductor substrate, showing a step of the method of
manufacturing the DP-AM according to one embodiment of the present
invention;
[0054] FIG. 29 is a fragmentary cross-sectional view of the
semiconductor substrate, illustrating a step of the method of
manufacturing the DRAM according to one embodiment of the present
invention;
[0055] FIG. 30 is a fragmentary cross-sectional view of the
semiconductor substrate, depicting a step of the method of
manufacturing the DRAM according to one embodiment of the present
invention;
[0056] FIG. 31 is a fragmentary cross-sectional view of the
semiconductor substrate, showing a step of the method of
manufacturing the DRAM according to one embodiment of the present
invention;
[0057] FIG. 32 is a fragmentary cross-sectional view of the
semiconductor substrate, illustrating a step of the method of
manufacturing the DRAM according to one embodiment of the present
invention;
[0058] FIG. 33 is a fragmentary cross-sectional view of the
semiconductor substrate, showing a step of the method of
manufacturing the DRAM according to one embodiment of the present
invention;
[0059] FIG. 34 is a fragmentary cross-sectional view of the
semiconductor substrate, depicting a step of the method of
manufacturing the DRAM according to one embodiment of the present
invention;
[0060] FIG. 35 a fragmentary cross-sectional view of the
semiconductor substrate, showing a method of manufacturing the DRAM
according to one embodiment of the present invention;
[0061] FIG. 36 is a fragmentary cross-sectional view of
thelsemiconductor substrate, illustrating a method of manufacturing
the DRAM according to one embodiment of the present invention;
[0062] FIG. 37 is a fragmentary cross-sectional view of the
semiconductor substrate, showing a step of the method of
manufacturing the DRAM according to one embodiment of the present
invention;
[0063] FIG. 38 is a fragmentary cross-sectional view of the
semiconductor substrate, depicting a step of the method of
manufacturing the DRAM according to one embodiment of the present
invention;
[0064] FIG. 39 is a fragmentary cross-sectional view of the
semiconductor substrate, showing a step of the method of
manufacturing the DRAM according to one embodiment of the present
invention;
[0065] FIG. 40 is a fragmentary cross-sectional view of the
semiconductor substrate, illustrating a step of the method of
manufacturing the DRAM according to one embodiment of the present
invention;
[0066] FIG. 41 is a fragmentary cross-sectional view of the
semiconductor substrate, depicting a step of the method of
manufacturing the DRAM according to one embodiment of the present
invention; and
[0067] FIG. 42 is a fragmentary cross-sectional view of the
semiconductor substrate, illustrating a method of manufacturing the
DRAM according to one embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0068] Preferred embodiments of the present invention will
hereinafter be described in detail with reference to the
accompanying drawings. In all the drawings for describing the
embodiments, components or members having the same function are
identified by the same reference numerals and their repetitive
description will be omitted.
[0069] FIG. 1 is an overall plan view of a semiconductor chip over
which a DRAM according to the present embodiment is formed. As
shown in the drawing, a large number of memory arrays MARY are
disposed over a main or principal surface of a semiconductor chip
1A comprised of monocrystal silicon in matrix form along an X
direction (corresponding to the longitudinal direction of the
semiconductor chip 1A) and a Y direction (corresponding to the
transverse direction of the semiconductor chip 1A). Sense
amplifiers SA are disposed between the memory arrays MARY disposed
adjacent to one another along the X direction. Word drivers WD,
control circuits such as data line Selection circuits, etc.,
input/output circuits, bonding pads, etc. are disposed in the
central portion of the main surface of the semiconductor chip
1A.
[0070] FIG. 2 is an equivalent circuit diagram of the DRAM. As
shown in the drawing, each of the memory arrays (MARY) of the DRAM
comprises a plurality of word lines WL (WLn-1, WLn, WLn+1, . . . )
and a plurality of bit lines BL disposed in matrix form, and a
plurality of memory cells (MC) respectively placed at points where
the word lines WL and the bit lines BL intersect. Each memory cell,
which stores on-bit information therein, comprises one information
storage capacitive element C and one memory cell selection MISFET
Qs electrically series-connected thereto. One of the source and
drain of each memory cell selection MISFET Qs is electrically
connected to the information storage capacitive element C and the
other thereof is electrically connected to its corresponding bit
line BL. One end of each word line WL is electrically connected to
its corresponding word driver WD and one end of each bit line BL is
electrically connected to its corresponding sense amplifier SA.
[0071] FIG. 3 is a fragmentary cross-sectional view of a
semiconductor substrate, showing respective parts of a memory alloy
and a peripheral circuit of a DRAM. FIG. 4 is a schematic plan view
of the semiconductor substrate, showing part of each memory array.
Incidentally, FIG. 4 shows only conductive layers (except for plate
electrodes which constitute each individual memory cell. Each
insulating film provided between the conductive layers and a metal
wire or interconnections disposed over each plate electrode are
omitted from the drawing.
[0072] Each memory cell of the DRAM is formed in a p-type well 2
formed over the principal surface of a semiconductor substrate 1
comprised of p-type monocrystal silicon. In order to prevent noise
from entering from the input/output circuit or the like formed in
the other region of the semiconductor substrate 1, the p-type well
2 lying in an area or region (memory array) in which each memory
cell is formed, is electrically separated from the semiconductor
substrate 1 by an n-type semiconductor region 3.
[0073] The memory cell is made up of a stacked structure wherein
each information storage capacitive element C is placed above its
corresponding memory cell selection MISFET Qs. The memory cell
selection MISFET Qs is comprised of an n channel MISFET and is
formed in each active region L of the p-type well 2. The active
regions L are shaped in a slender island-shaped pattern extending
straightforward along the X direction in FIG. 4. The two memory
cell selection MISFETs Qs, which share one (n-type semiconductor
region 9) of the source and drain with each other, are formed in
their corresponding active regions L so as to be disposed adjacent
to each other in the X direction.
[0074] A device separation region, which surrounds each active
region L, is defined or constructed by a device separation groove 6
formed by embedding a silicon oxide film 5 into shallow grooves
defined in the p-type well 2. The silicon oxide film 5 embedded in
the device separation groove 6 is flattened so that its surface
takes substantially the same height as the surfaces of the active
regions L. Since no bird's beak is formed at the end of each active
region L, the device separation region constructed by such a device
separation groove 6 increases in effective area as compared with
each device separation region (field oxide film) having the same
size, which is formed by a LOCOS (localized oxidation) method.
[0075] Each memory cell selection MISFET Qs is composed principally
of a gate oxide film 7, a gate electrode 8A and a pair of n-type
semiconductor regions 9 constituting the source and drain. The gate
electrodes 8A are formed integrally with their corresponding word
lines WL and linearly extend with the same widths and spaces along
the Y direction. The gate electrode 8A (each word line WL) has a
polymetal structure constructed of a low-resistance polycrystalline
silicon film doped with an n-type impurity such as P (phosphorous),
a barrier metal layer composed of a WN (tungsten nitride) film or
the like, which is formed over the low-resistance polycrystalline
silicon film, and a high-melting metal film such as a W (tungsten)
film, which is formed over the barrier metal layer. Since each gate
electrode 8A having a polymetal structure is lower in electrical
resistance than a gate electrode composed of a polycrystal silicon
film or polysilicide film, it is possible to reduce the signal
delay developed in each word line.
[0076] Each of the peripheral circuits of the DRAM comprises an n
channel MISFET Qn and a p channel MISFET Qp. The n channel MISFET
Qn is formed in the p-type well 2 and is composed principally of a
gate oxide film 7, a gate electrode 8B and a pair of n+-type
semiconductor regions 10 constituting a source and a drain.
Further, the p channel MISFET Qp is formed in an n-type well 4 and
is composed principally of a gate oxide film 7, a gate electrode 8C
and a pair of p.sup.+-type semiconductor regions 11 constituting a
source and a drain. The gate electrodes 8B and 8C are respectively
formed by the same polymetal structure as that for the gate
electrode 8A (word line WL) The n channel MISFET Qn and the p
channel MISFET Qp constituting each peripheral circuit are
fabricated in accordance with a design rule which is reduced as
compared with the memory cell.
[0077] A silicon nitride film 12 is formed at a portion above the
gate electrode 8A (word line WL) of each memory cell selection
MISFET Qs. A silicon nitride film 13 is formed over the silicon
nitride film 12 and over the side walls thereof and the side walls
of the gate electrodes 8A (word lines WL). Silicon nitride films 12
are formed over the gate electrodes 8B and 8C of the MISFETS of the
peripheral circuit. Further, side wall spacers 13s each composed of
the silicon nitride film 13 are formed over the side walls of the
gate electrodes 8B and 8C.
[0078] As will be described later, the silicon nitride film 12 and
silicon nitride film 13 of the memory array are used as etching
stoppers utilized upon defining contact holes in portions above the
source and drain (n-type semiconductor regions 9) of each memory
cell selection MISFET Qs on a self-aligned basis. Further, the side
wall spacers 13s of the peripheral circuit are used to bring the
source and drain of each n channel MISFET Qn and the source and
drain of each p channel MISFET Qs to LDD (Lightly Doped Drain)
structures.
[0079] An SOG film 16 is formed over the memory cell selection
MISFETs Qs, n channel MISFETs Qn and p channel MISFETs Qp. Further,
silicon oxide films 17 and 18 corresponding to two layers are
formed over the SOG film 16. The surface of the upper-layer silicon
oxide film 18 is flattened so as to take substantially the same
height over the whole area of the semiconductor substrate 1.
[0080] Contact holes 19 and 20, which extend through the silicon
oxide films 18 and 17 and the SOG film 16, are defined in the
portions above the pair of n-type semiconductor regions 9
constituting the source and drain of each memory cell selection
MISFET Qs. Plugs 21 each composed of a polycrystal silicon film
having low resistance, which is doped with the n-type impurity
(e.g., P (phosphorous)), are embedded inside these contact holes 19
and 20.
[0081] Each of the diameters, in the X direction of the bottoms of
the contact holes 19 and 20 is defined according to a space defined
between the silicon nitride film 13 on the side wall of one of the
opposed two gate electrodes 8A (word lines WL) and the silicon
nitride film 13 on the side wall of the other thereof. Namely, the
contact holes 19 and 20 are formed in self-alignment with the gate
electrodes 8A (word lines WL).
[0082] As shown in FIG. 4, the diameter in the Y direction, of one
contact hole 20 of the pair of contact holes 19 and 20 is
substantially identical to the size in the Y direction of each
active region L. On the other hand, the diameter in the Y direction
of the other contact hole 19 (corresponding to the contact hole
over the n-type semiconductor region 9 shared between the two
memory cell selection MISFETs Qs) is larger than the size in the Y
direction of the active region L. Namely, each contact hole 19 is
shaped in a substantially rectangular plan pattern in which the
diameter in the Y direction is larger than the diameter in the X
direction. Some fall outside the active regions L and extend over
the device separation groove 6. Owing to the formation of the
contact holes 19 in such patterns, it is unnecessary to partly make
the width of each bit line BL thick so as to extend up to the
portion above the active region L and to extend part of each active
region L in the direction of the bit line BL when the bit line BL
and the n-type semiconductor region 9 are electrically connected to
each other through the contact hole 19. It is therefore possible to
reduce the size of each memory cell.
[0083] A silicon oxide film 28 is formed over the silicon oxide
film 18. Through holes 22 are defined in the silicon oxide films 28
provided over the contact holes 19. Plugs 35 each comprised of a
conductive film obtained by stacking a Ti (Titanium) film, a TiN
(titanium nitride) film and a W film on one another in order from
the lower layer are embedded inside the through holes 22.
TiSi.sub.2 (titanium silicide) layers 37 produced by reaction
between the Ti films constituting parts of the plugs 35 and the
polycrystal silicon films constituting the plugs 21 are
respectively formed at interfaces between the plugs 35 and the
plugs 21 embedded in the contact holes 19 placed below the through
holes 22. The through holes 22 are disposed above the device
separation groove 6 out of the active regions L.
[0084] Each bit line BL is formed over the silicon oxide film 28.
The bit lines BL are disposed above the device separation groove 6
and linearly extend along the X direction with the same width and
space. The bit line BL is made up of the W film and is electrically
connected to one (corresponding to the n-type semiconductor region
9 shared between the two memory cell selection MISFETs Qs) of the
source and drain of each memory cell selection MISFET Qs via the
through hole 22 defined in each silicon oxide film 28 and the
contact hole 19 defined in its lower insulating films (silicon
oxide films 28, 18, 17, SOG film 16 and gate oxide film 7). Since
each bit line BL can be reduced in sheet resistance by constructing
the bit line BL of a metal (W), the reading and writing of
information can be performed at high speed. Since the bit lines BL
and wires or interconnections 23 through 26 of the peripheral
circuit, which are to be described later, can be simultaneously
formed with the same process, it is possible to simplify a process
for manufacturing the DRAM. Owing to the formation of each bit line
BL of a metal (W) high in heat resistance and electromigration
resistance, each bit line BL can be prevented from breaking even
when the width of the bit line BL is miniaturized.
[0085] The interconnections 23 through 26 corresponding to the
first wiring layer are formed over the silicon oxide film 28 of the
peripheral circuit. These interconnections 23 through 26 are made
up of the same conductive material (W) as that for the bit line BL
and are formed simultaneously in a process for forming each bit
line BL as will be described later. The interconnections 23 through
26 are respectively electrically connected to MISFETs (n channel
MISFETs Qn and p channel MISFETS Qp) of the peripheral circuit
through contact holes 30 through 34 defined in the silicon oxide
films 28, 18, 17 and SOG film 16.
[0086] The plugs 35 each comprised of the conductive film obtained
by laminating the Ti (Titanium) film, the TiN (titanium nitride)
film and the W film on one another in order from the lower layer
are embedded inside the contact holes 30 through 34 for connecting
the MISFETs of the peripheral circuit and the interconnections 23
through 26. The TiSi.sup.2-layers 37 produced by reaction between
the Ti films constituting parts of the plugs 35 and the
semiconductor substrate 1 (Si) are respectively provided at the
bottoms of the contact holes (30 through 33) of these contact holes
30 through 34, which are defined in their corresponding portions
above the sources and drains (n.sup.+-type semiconductor regions 10
and p.sup.+-type semiconductor regions 11) of the MISFETs of the
peripheral circuit, whereby the contact resistances between the
plugs 35 and the sources and drains (n.sup.+-type semiconductor
regions 10 and p.sup.+-type semiconductor regions 11) can be
reduced.
[0087] Silicon oxide films 38 and 39 are respectively formed over
the bit lines BL and the interconnections 23 through 26
corresponding to the first wiring layer. The upper silicon oxide
film 39 is flattened so that the surface thereof takes the same
height over the entire area of the semiconductor substrate 1.
[0088] A silicon nitride film 44 is formed over the silicon oxide
film 39 of the memory array. Each information storage capacitive
element C is further formed over the silicon nitride film 44. The
information storage capacitive element C is made-up of a lower
electrode (storage electrode) 45, an upper electrode (plate
electrode) 47 and a Ta.sub.2O.sub.5 (tantalum oxide) film
(dielectric film) 46 provided between those electrodes. The lower
electrode 45 is composed of a low-resistance poly-crystal silicon
film doped with P (phosphorous), for examples whereas the upper
electrode 47 is composed of a TiN film, for example.
[0089] The lower electrode 45 of each information storage
capacitive element C is formed in a slender pattern straightforward
along the X direction of FIG. 4. Each lower electrode 45 is
electrically connected to the plug 21 defined in the contact hole
20 through a plug 49 embedded in a through hole 49 extending
through the silicon nitride film 44 and the silicon oxide films 39,
38 and 28 used as the lower layers. Further, the lower electrode 45
is electrically connected to the other (n-type semiconductor region
9) of the source and drain of each memory cell selection MISFET Qs
through the plug 21. The plug 49 composed of a low-resistance
polycrystal silicon film doped with P (phosphorous), for example,
is embedded inside each through hole 48 defined between the lower
electrode 45 and the contact hole 20.
[0090] A silicon oxide film 50 having a film thickness
corresponding to substantially the same height as the lower
electrode 45 of each information storage capacitive element C is
formed above the silicon oxide film 39 of the peripheral circuit.
Owing to the formation of the silicon oxide film 50 of the
peripheral circuit with such a large film thickness, the surface of
a silicon oxide film 51 formed over the information storage
capacitive element C takes substantially the same height at the
memory array and the peripheral circuit. Therefore, a grounding
step-like offset or difference between interconnections 53 and 54
corresponding to a second wiring layer, which are provided at a
layer above the silicon oxide film 51, can be reduced.
[0091] Silicon oxide films 51 and 52 corresponding to two layers
are formed over each information storage capacitive element C.
Further, the interconnections 53 and 54 corresponding to the second
wiring layer are formed over the silicon oxide films 51 and 52. The
interconnections 53 and 54 corresponding to the second wiring layer
are respectively comprised of a conductive layer with an Al
(Aluminum) alloy as a principal part. The interconnection 54
corresponding to the second wiring layer formed in the peripheral
circuit is electrically connected to the interconnection 26 of the
first wiring layer through a through hole 55 having a large aspect
ratio, which is defined in insulating films (silicon oxide films
52, 51, 50, silicon nitride film 44 and silicon oxide films 39 and
38) provided at a layer below the interconnection 54. A plug 56
comprised of, for example, the Ti film, TiN film and W film is
embedded into the through hole 55.
[0092] Silicon oxide films 57, 58 and 59 corresponding to three
layers are formed over the interconnections 53 and 54 corresponding
to the second wiring layer. Of the silicon oxide films 57, 58 and
59 corresponding to the three layers, the silicon oxide film 57
corresponding to the lower layer is formed by a high density plasma
CVD method which has an excellent gap-filling characteristic. The
silicon oxide film 58 provided over the silicon oxide film 57 is
flattened so that the surface thereof is brought to substantially
the same height over the entire area of the semiconductor substrate
1.
[0093] Wires or interconnections 60, 61 and 62 corresponding to a
third wiring layer are formed over the silicon oxide film 59. The
interconnections 60, 61 and 62 corresponding to the third wiring
layer are composed of a conductive film with Al alloy as the
principal part in a manner similar to the interconnections 53 and
54 corresponding to the second wiring layer.
[0094] Of the interconnections 60, 61 and 62 corresponding to the
third wiring layer, the interconnection 60 corresponding to the
third wiring layer formed in the memory array is electrically
connected to its corresponding interconnection 53 of the second
wiring layer via a through hole 63 defined in the silicon oxide
films 59, 58 and 57 placed in the layer below the interconnection
60. Further, the interconnection 61 is electrically connected to
its corresponding upper electrode 47 of each information storage
capacitive element C via a through hole 64 defined in the silicon
oxide films 59, 58, 57, 52 and 51 placed in the layer below the
interconnection 61. Namely, the interconnection 61 makes up a
power-supply or feeding interconnection for supplying a
predetermined source of power (e.g., 1/2 Vcc) to the upper
electrode 47 of each information storage capacitive element C.
[0095] The interconnection 62 corresponding to the third wiring
layer formed in a peripheral circuit region is electrically
connected to its corresponding interconnection 54 of the second
wiring layer via a through hole 65 defined in the silicon oxide
films 59, 58 and 57 placed in the layer therebelow. Plugs 66 each
comprised of, for example, the Ti film, TiN film and W film are
embedded inside their corresponding through holes 63 through
65.
[0096] One example of a method of manufacturing the DRAM
constructed in the above-described manner will next be described in
process order with reference to FIGS. 5 through 42.
[0097] As shown in FIG. 5, a device separation groove 6 is defined
in a device separation region of a main or principal surface of a
semiconductor substrate 1 comprised of monocrystal silicon which is
of a p type and whose resistivity is about 10 .OMEGA./cm. The
device separation groove 6 is formed as follows. The surface of the
semiconductor substrate 1 is etched to define a groove having a
depth which ranges from about 300 to 400 nm. Next, a silicon oxide
film 5 is deposited over the semiconductor substrate 1 including
the groove by the CVD method. Afterwards, the silicon oxide film 5
is polished back and formed by a chemical mechanical polishing
(CMP) method. The silicon oxide film 5 is flattened so that the
surface thereof takes substantially the same height as that of each
active region. Owing to the definition of the device separation
groove 6, active regions L having slender island-shaped patterns
surrounded by the device separation groove 6 are simultaneously
formed in the region (memory array) for forming each memory cell as
shown in FIG. 6. Unillustrated active regions surrounded by the
device separation groove 6 are simultaneously formed even in the
region for forming the peripheral circuit.
[0098] Next, an n-type impurity, e.g., P (phosphorous) is
ion-implanted in the semiconductor substrate 1 of the memory array
to form an n-type semiconductor region 3. Thereafter, a p-type
impurity, e.g., B (boron) is ion-implanted in part (region for
forming each n channel MISFET Qn) of the peripheral circuit of the
memory array to form a p-type well 2. Further, the n-type impurity,
e.g., P(phosphorous) is ion-implanted in the other part (region for
forming each p-channel MISET Qp) of the peripheral circuit to form
an n-type well 4.
[0099] Subsequently, an impurity for controlling or adjusting the
threshold voltage of each MISFET, e.g., BF2 (boron fluoride) is
ion-implanted in the p-type well 2 and n-type well 4. Next, the
surfaces of the p-type well 2 and n-type well 4 are cleaned with a
cleaning fluid made up of HF (hydrofluoric acid). Thereafter, the
semiconductor substrate 1 is subjected to wet oxidation to thereby
form a clean gate oxide film 7 over the p-type well 2 and n-type
well 4.
[0100] Next, gate electrodes 8A (word lines WL) and gate electrodes
8B and 8C are formed over the gate oxide film 7 as shown in FIGS. 8
and 9. The gate electrodes 8A (word lines WL) and the gate
electrodes 8B and 8C are formed by depositing a polycrystal silicon
film doped with the n-type impurity such as P (phosphorous) over
the semiconductor substrate 1 by the CVD method, followed by
depositing a WN (tungsten nitride) film and a W film over the
polycrystal silicon film by sputtering, depositing a silicon
nitride film 12 over the WN film and W film by the CVD method, and
thereafter patterning these films with a photoresist film as a
mask. The WN film serves as a barrier layer for preventing the
formation of a high-resistance silicide layer at the interface
between the W film and the polycrystal silicon film by the reaction
between the W film and the polycrystal silicon film upon
high-temperature heat treatment. A WN-film high-melting point metal
nitride film, e.g., TiN (titanium nitride) film may be used for the
barrier layer. Since the gate electrode 8A (word line WL) having a
polymetal structure, which is comprised principally of the
high-melting point metal film and the polycrystal silicon film, is
low in electrical resistance as compared with a gate electrode
composed of a polycrystal silicon film and a polysilicide film
(corresponding to a film obtained by stacking a high-melting point
metal silicide film and a polycrystal silicon film on each other),
it is possible to reduce the signal delay developed in each word
line.
[0101] Next, a p-type impurity such as B. (boron) is ion-implanted
in the n-type well 4 to form p.sup.--type semiconductor regions 15
in the n-type well 4 on both sides of each gate electrode 8C as
shown in FIG. 10. Further, an n-type impurity, e.g., P
(phosphorous) is ion-implanted in the p-type well 2 to form
n.sup.--type semiconductor regions 9a in the p-type well 2 on both
sides of each gate electrode 8B and to form n.sup.--type
semiconductor regions 14 in the p-type well 2 on both sides of each
gate electrode 8B. Each memory cell selection-MISFET Qs is
substantially completed according to the process steps used so
far.
[0102] Next, as shown in FIG. 11, a silicon nitride film 13 is
deposited over the semiconductor substrate 1 by the CVD method and
thereafter the silicon nitride film 13 of the memory array is
covered with a photoresist film (not shown). Further, the silicon
nitride film 13 of the peripheral circuit is subjected to
anisotropic etching, whereby sidewall spacers 13s are respectively
formed over the side walls of the gate electrodes 8B and 8C of the
peripheral circuit. This etching is performed using gas for etching
the silicon nitride film 13 at a high selection ratio in order to
minimize the amount of cutting of the silicon oxide film 5 embedded
in the device separation groove 6 and the gate oxide film 7. In
order to minimize the amount of cutting of the silicon nitride
films 12 over the gate electrodes 8B and 8C, the amount of
overetching is allowed to remain fixed to the required minimum.
[0103] Next, as shown in FIG. 12, a p-type impurity, e.g., B
(boron) is ion-implanted in the n-type well 4 of the peripheral
circuit to form p.sup.+-type semiconductor regions 11 (source and
drain) of each p channel MISFET Qp. Further, an n-type impurity,
e.g., As (arsenic) is ion-implanted in the p-type well 2 of the
peripheral circuit to form n.sup.+-type semiconductor regions 10
(source and drain) of each n channel MISFET Qn. The p channel
MISFET Qp and n channel MISFET Qn each having an LDD structure are
substantially completed according to the process steps used so
far.
[0104] Next, as shown in FIG. 13, an SOG film 16 is spin-applied
onto the semiconductor substrate 1 and is subjected to bake
processing in an oxygen atmosphere containing water vapor at about
400.degree. C., followed by heat treatment at 80.degree. C. for
about one minute, thereby densifying the SOG film 16. The SOG film
16 makes use of an inorganic SOG of polysilazane, for example. The
SOG film 16 is high in reflow characteristic as compared with a
glass flow film such as a BPSG film and is excellent in terms of a
gap-filling characteristic of a micro space. Therefore, no void
occurs even if the SOG film is embedded in a space of each gate
electrode 8A (word line WL) miniaturized to the order of a
resolution limit of photolithography. Since the SOG film 16 can
obtain a high reflow characteristic even though a high-temperature
and long-time heat treatment necessary for the BPSG film or the
like is not performed, it is possible to restrain the diffusion of
heat of the impurities implanted in the source and drain of each
memory cell selection MISFET Qs and the source and drain of each
MISFET (n channel MISFET Qn and p channel MISFET Qp) and thereby
achieve a shallow junction. Since the SOG film can restrain the
oxidation of the metal (W film) constituting the gate electrodes 8A
(word lines WL) and gate electrodes 8B and 8C upon heat treatment,
each memory cell selection MISFET Qs and each MISFET of the
peripheral circuit can be enhanced in performance.
[0105] Next, a silicon oxide film 17 is deposited gate electrodes
8B and 8C of the MISFETS of the peripheral circuit. Further, side
wall spacers 13s each composed of the silicon nitride film 13 are
formed over the side walls of the gate electrodes 8B and 8C. As
will be described later, the silicon nitride film 12 and silicon
nitride film 13 of the memory array are used as etching stoppers
utilized upon defining contact holes in portions above the source
and drain (n-type semiconductor regions 9 and 9) of each memory
cell selection MISFET Qs on a self-aligned basis. Further, the side
wall spacers 13s of the peripheral circuit are used to bring the
source and drain of each n channel MISFET Qn and the source and
drain of each p channel MISFET Qs to LDD (Lightly Doped Drain)
structures.
[0106] An SOG film 16 is formed over the memory cell selection
MISFETs Qs, n channel MISFETs Qn and p channel MISFETS Qp. Further,
silicon oxide films 17 and 18 corresponding to two layers are
formed over the SOG film 16. The surface of the upper-layer silicon
oxide film 18 is flattened so as to take substantially the same
height over the whole area of the semiconductor substrate 1.
[0107] Contact holes 19 and 20, which extend through the silicon
oxide films 18 and 17 and the SOG film 16, are defined in the
portions above the pair of n-type semiconductor regions 9
constituting the source and drain of each memory cell selection
MISFET Qs. Plugs 21 each composed of a polycrystal silicon film
having low resistance, which is doped with the n-type impurity
(e.g., P (phosphorous)), are embedded inside these contact holes 19
and 20.
[0108] Each of the diameters, in the X direction, of the bottoms of
the contact holes 19 and 20 is defined according to a space defined
between the silicon nitride film 13 on the side wall of one of the
opposed two gate electrodes 8A (word lines WL) and the silicon
nitride film 13 on the side wall of the other thereof. Namely, the
contact holes 19 and 20 are formed in self-alignment with the gate
electrodes 8A (word lines WL).
[0109] As shown in FIG. 4, the diameter in the Y direction, of one
contact hole 20 of the pair of contact holes 19 and 20 is
substantially identical to the size in the Y direction of each
active region L. On the other hand, the diameter in the Y direction
of the other contact hole 19 (corresponding to the contact hole
over the n-type semiconductor region 9 shared between the two
memory cell selection MISFETs Qs) is larger than the size in the Y
direction of the active region L. Namely, each contact hole 19 is
shaped in a substantially rectangular plan pattern in which the
diameter in the Y direction is larger than the diameter in the X
direction. Some fall outside the active regions L and extend over
the device separation groove 6. Owing to the formation of the
contact holes 19 in such patterns, it is unnecessary to partly make
the width of each bit line BL thick so as to extend up to the
portion above the active region L and to extend part of each active
region L in the direction of the bit line BL when the bit line BL
and the n-type semiconductor region 9 are electrically connected to
each other through the contact hole 19. It is therefore possible to
reduce the size of each memory cell.
[0110] A silicon oxide film 28 is formed over the silicon oxide
film 18. Through holes 22 are defined in the silicon oxide films 28
provided over the contact holes 19. Plugs 35 each comprised of a
conductive film obtained by stacking a Ti (Titanium) film, a TiN
(titanium nitride) film and a W film on one another in order from
the lower layer are embedded inside the through holes 22.
TiSi.sub.2 (titanium silicide) layers 37 produced by reaction
between the Ti films constituting parts of the plugs 35 and the
polycrystal silicon films constituting the plugs 21 are
respectively formed at interfaces between the plugs 35 and the
plugs 21 embedded in the contact holes 19 placed below the through
holes 22. The through holes 22 are disposed above the device
separation groove 6 out of the active regions L.
[0111] Each bit line BL is formed over the silicon oxide film 28.
The bit lines BL are disposed above the device separation groove 6
and linearly extend along the X direction with the same width and
space. The bit line BL is made up of the W film and is electrically
connected to one (corresponding to the n-type semiconductor region
9 shared between the two memory cell selection MISFETs Qs) of the
source and drain of each memory cell selection MISFET Qs via the
through hole 22 defined in each silicon oxide film 28 and the
contact hole 19 defined in its lower insulating films (silicon
oxide films 28, 18, 17, SOG film 16 and gate oxide film 7). Since
each bit line BL can be reduced in sheet resistance by constructing
the bit line BL of a metal (W), the reading and writing of
information can be performed at high speed. Since the bit lines BL
and wires or interconnections 23 through 26 of the peripheral
circuit, which are to be described later, can be simultaneously
formed with the same process, it is possible to simplify a process
for manufacturing the DRAM. Owing to the formation of each bit line
BL of a metal (W) high in heat resistance and electromigration
resistance, each bit line BL can be prevented from breaking even
when the width of the bit line BL is miniaturized.
[0112] The interconnections 23 through 26 corresponding to the
first wiring layer are formed over the silicon oxide film 28 of the
peripheral circuit. These interconnections 23 through 26 are made
up of the same conductive material (W) as that for the bit line BL
and are formed simultaneously in a process for forming each bit
line BL as will be described later. The interconnections 23 through
26 are respectively electrically connected to MISFETs (n channel
MISFETs Qn and p channel MISFETS Qp) of the peripheral circuit
through contact holes 30 through 34 defined in the silicon oxide
films 28, 18, 17 and SOG film 16.
[0113] The plugs 35 each comprised of the conductive film obtained
by laminating the Ti (Titanium) film, the TiN (titanium nitride)
film and the W film on one another in order from the lower layer
are embedded inside the contact holes 30 through 34 for connecting
the MISFETs of the peripheral circuit and the interconnections 23
through 26. The TiSi.sub.2 layers 37 produced by reaction between
the Ti films constituting parts of the plugs 35 and the
semiconductor substrate 1 (Si) are respectively provided at the
bottoms of the contact holes (30 through 33) of these contact holes
30 through 34, which are defined in their corresponding portions
above the sources and drains (n.sup.+-type semiconductor regions 10
and p.sup.+-type semiconductor regions 11) of the MISFETs of the
peripheral circuit, whereby the contact resistances between the
plugs 35 and the sources and drains (n.sup.+-type semiconductor
regions 10 and p.sup.+-type semiconductor regions 11) can be
reduced.
[0114] Silicon oxide films 38 and 39 are respectively formed over
the bit lines BL and the interconnections 23 through 26
corresponding to the first wiring layer. The upper silicon oxide
film 39 is flattened so that the surface thereof takes the same
height over the entire area of the semiconductor substrate 1.
[0115] A silicon nitride film 44 is formed over the silicon oxide
film 39 of the memory array. Each information storage capacitive
element C is further formed over the silicon nitride film 44. The
information storage capacitive element C is made up of a lower
electrode (storage electrode) 45, an upper electrode (plate
electrode) 47 and a Ta.sub.2O.sub.5 (tantalum oxide) film
(dielectric film) 46 provided between those electrodes.
[0116] The lower electrode 45 is composed of a low-resistance
polycrystal silicon film doped with P (phosphorous), for example,
whereas the upper electrode 47 is composed of a TiN film, for
example.
[0117] The lower electrode 45 of each information storage
capacitive element C is formed in a slender pattern straightforward
along the X direction of FIG. 4. Each lower electrode 45 is
electrically connected to the plug 21 defined in the contact hole
20 through a plug 49 embedded in a through hole 49 extending
through the silicon nitride film 44 and the silicon oxide films 39,
38 and 28 used as the lower layers. Further, the lower electrode 45
is electrically connected to the other (n-type semiconductor region
9) of the source and drain of each memory cell selection MISFET Qs
through the plug 21. The plug 49 composed of a low-resistance
polycrystal silicon film doped with P (phosphorous), for example is
embedded inside each through hole 48 defined between the lower
electrode 45 and the contact hole 20.
[0118] A silicon oxide film 50 having a film thickness
corresponding to substantially the same height as the lower
electrode 45 of each information storage capacitive element C is
formed above the silicon oxide film 39 of the peripheral circuit.
Owing to the formation of the silicon oxide film 50 of the
peripheral circuit with such a large film thickness, the surface of
a silicon oxide film 51 formed over the information storage
capacitive element C takes substantially the same height at the
memory array and the peripheral circuit. Therefore, a grounding
step-like offset or difference between interconnections 53 and 54
corresponding to a second wiring layer, which are provided at a
layer above the silicon oxide film 51, can be reduced.
[0119] Silicon oxide films 51 and 52 corresponding to two layers
are formed over each information storage capacitive element C.
Further, the interconnections 53 and 54 corresponding to the second
wiring layer are formed over the silicon oxide films 51 and 52. The
interconnections 53 and 54 corresponding to the second wiring layer
are respectively comprised of a conductive layer with an Al
(Aluminum) alloy as a principal part. The interconnection 54
corresponding to the second wiring layer formed in the peripheral
circuit is electrically connected to the interconnection 26 of the
first wiring layer through a through hole 55 having a large aspect
ratio, which is defined in insulating films (silicon oxide films
52, 51, 50, silicon nitride film 44 and silicon oxide films 39 and
38) provided at a layer below the interconnection 54. A plug 56
comprised of, for example, the Ti film, TiN film and W film is
embedded into the through hole 55.
[0120] Silicon oxide films 57, 58 and 59 corresponding to three
layers are formed over the interconnections 53 and 54 corresponding
to the second wiring layer. Of the silicon oxide films 57, 58 and
59 corresponding to the three layers, the silicon oxide film 57
corresponding to the lower layer is formed by a high density plasma
CVD method providing an excellent in gap-filling characteristic.
The silicon oxide film 58 provided over the silicon oxide film 57
is flattened so that the surface thereof is brought to
substantially the same height over the entire area of the
semiconductor substrate 1.
[0121] Wires or interconnections 60, 61 and 62 corresponding to a
third wiring layer are formed over the silicon oxide film 59. The
interconnections 60, 61 and 62 corresponding to the third wiring
layer are composed of conductive film with an Al alloy as the
principal part in a manner similar to the interconnections 53 and
54 corresponding to the second wiring layer.
[0122] Of the interconnections 60, 61 and 62 corresponding to the
third wiring layer, the interconnection 60 corresponcung to the
third wiring layer formed in the memory array is electrically
connected to its corresponding interconnection 53 of the second
wiring layer via a through hole 63 defined in the silicon oxide
film 59, 58 and 57 placed in the layer below the interconnection
60. Further, the interconnection 61 is electrically connected to
its corresponding upper electrode 47 of each information storage
capacitive element C via a through hole 64 defined in the silicon
oxide films 59, 58, 57, 52 and 51 placed in the layer below the
interconnection 61. Namely, the interconnection 61 makes up a
power-supply or feeding interconnection for supplying a
predetermined source of power (e.g., 1/2 Vcc) to the upper
electrode 47 of each information storage capacitive element C.
[0123] The interconnection 62 corresponding to the third wiring
layer formed in a peripheral circuit region is electrically
connected to its corresponding interconnection 54 of the second
wiring layer via a through hole 65 defined in the silicon oxide
films 59, 58 and 57 placed in the layer therebelow. Plugs 66 each
comprised of, for example, the Ti film, TiN film and W film are
embedded inside their corresponding through holes 63 through
65.
[0124] One example of a method of manufacturing the DRAM
constructed in the above-described manner will next be described in
process order with reference to FIGS. 5 through 42.
[0125] As shown in FIG. 5, a device separation groove 6 is defined
in a device separation region of a main or principal surface of a
semiconductor substrate 1 comprised of monocrystal silicon which is
of a p type and whose resistivity is about 10 .OMEGA./cm. The
device separation groove 6 is formed as follows. The surface of the
semiconductor substrate I is etched to define a groove having a
depth which ranges from about 300 to 400 nm. Next, a silicon oxide
film 5 is deposited over the semiconductor substrate 1 including
the groove by the CVD method. Afterwards, the silicon oxide film 5
is polished back and formed by a chemical mechanical polishing
(CMP) method. The silicon oxide film 5 is flattened so that the
surface thereof takes substantially the same height as that of each
active region. Owing to the definition of the device separation
groove 6, active regions L having slender island-shaped patterns
surrounded by the device separation groove 6 are simultaneously
formed in the region (memory array) for forming each memory cell as
shown in FIG. 6. Unillustrated active regions surrounded by the
device separation groove 6 are simultaneously formed even in the
region for forming the peripheral circuit.
[0126] Next, an n-type impurity, e.g., P (phosphorous) is
ion-implanted in the semiconductor substrate 1 of the memory array
to form an n-type semiconductor region 3. Thereafter, a p-type
impurity, e.g., B (boron) is ion-implanted in part (region for
forming each n channel MISFET Qn) of the peripheral circuit of the
memory array to form a p-type well 2. Further, the n-type impurity,
e.g., P (phosphorous) is ion-implanted in the other part (region
for forming each p channel MISET Qp) of the peripheral circuit to
form an n-type well 4.
[0127] Subsequently, an impurity for controlling or adjusting the
threshold voltage of each MISFET, e.g., BF2 (boron fluoride) is
ion-implanted in the p-type well 2 and n-type well 4. Next, the
surfaces of the p-type well 2 and n-type well 4 are cleaned with a
cleaning fluid made up of HF (hydrofluoric acid) Thereafter, the
semiconductor substrate 1 is subjected to wet oxidation to thereby
form a clean gate oxide film 7 over the p-type well 2 and n-type
well 4.
[0128] Next, gate electrodes 8A (word lines WL) and gate electrodes
8B and 8C are formed over the gate oxide film 7 as shown in FIGS. 8
and 9. The gate electrodes 8A (word lines WL) and the gate
electrodes 8B and 8C are formed by depositing a polycrystal silicon
film doped with the n-type impurity such as P (phosphorous) over
the semiconductor substrate 1 by the CVD method, followed by
depositing a WN (tungsten nitride) film and a W film over the
polycrystal silicon film by sputtering, depositing a silicon
nitride film 12 over the WN film and W film by the CVD method, and
thereafter patterning these films with a photoresist film as a
mask. The WN film serves as a barrier layer for preventing the
formation of a high-resistance silicide layer at the interface
between the W film and the polycrystal silicon film by the reaction
between the W film and the polycrystal silicon film upon
high-temperature heat treatment. A WN-film high-meting point metal
nitride film, e.g., TiN (titanium nitride) film may be used for the
barrier layer. Since the gate electrode 8A (word line WL) having a
polymetal structure, which is comprised principally of the
high-melting point metal film and the polycrystal silicon film, is
low in electrical resistance as compared with a gate electrode
composed of a polycrystal silicon film and a polysilicide film
(corresponding to a film obtained by stacking a high-melting point
metal silicide film and a polycrystal silicon film on each other),
it is possible to reduce the signal delay developed in each word
line.
[0129] Next, a p-type impurity such as B (boron) is ion-implanted
in the n-type well 4 to form p.sup.--type semiconductor regions 15
in the n-type well 4 on both sides of each gate electrode 8C as
shown in FIG. 10. Further, an n-type impurity, e.g., P
(phosphorous) is ion-implanted in the p-type well 2 to form
n.sup.--type semiconductor regions 9a in the p-type well 2 on both
sides of each gate electrode 8B and to form n.sup.--type
semiconductor regions 14 in the p-type well 2 on both sides of each
gate electrode 8B. Each memory cell selection MISFET Qs is
substantially completed according to the process steps used so
far.
[0130] Next, as shown in FIG. 11, a silicon nitride film 13 is
deposited over the semiconductor substrate 1 by the CVD method and
thereafter the silicon nitride film 13 of the memory array is
covered with a photoresist film (not shown). Further, the silicon
nitride film 13 of the peripheral circuit is subjected to
anisotropic etching, whereby sidewall spacers 13s are respectively
formed over the side walls of the gate electrodes 8B and 8C of the
peripheral circuit. This etching is performed using gas for,
etching the silicon nitride film 13 at a high selection ratio in
order to minimize the amount of cutting of the silicon oxide film 5
embedded in the device separation groove 6 and the gate oxide film
7. In order to minimize the amount of cutting of the silicon
nitride films 12 over the gate electrodes 8B and 8C, the amount of
overetching is allowed to remain fixed to the required minimum.
[0131] Next, as shown in FIG. 12, a p-type impurity, e.g., B
(boron) is ion-implanted in the n-type well 4 of the peripheral
circuit to form p.sup.+-type semiconductor regions 11 (source and
drain) of each p channel MISFET Qp. Further, an n-type impurity,
e.g., As (arsenic) is ion--implanted in the p-type well 2 of the
peripheral circuit to form n.sup.+-type semiconductor regions 10
(source and drain) of each n channel MISFET Qn. The p channel
MISFET Qp and n channel MISFET Qn each having an LDD structure are
substantially completed according to the process steps used so
far.
[0132] Next, as shown in FIG. 13, an SOG film 16 is spin-applied
onto the semiconductor substrate 1 and is subjected to bake
processing in an oxygen atmosphere containing water vapor at about
400.degree. C., followed by heat treatment at 80.degree. C. for
about one minute, thereby densifying the SOG film 16. The SOG film
16 makes use of an inorganic SOG of polysilazane, for example. The
SOG film 16 is high in reflow characteristic as compared with a
glass flow film such as a BPSG film and provides an excellent
gap-filling characteristic of a micro space. Therefore, no void
occurs even if the SOG film is embedded in a space of each gate
electrode 8A (word line WL) miniaturized to the order of a
resolution limit of photolithography. Since the SOG film 16 can
obtain a high reflow characteristic even though a high-temperature
and long-time heat treatment necessary for the BPSG film or the
like is not performed, it is possible to restrain the diffusion of
heat of the impurities implanted in the source and drain of each
memory cell selection MISFET Qs and the source and drain of each
MISFET (n channel MISFET Qn and p channel MISFET Qp) and thereby
achieve a shallow junction. Since the SOG film can restrain the
oxidation of the metal (W film) constituting the gate electrodes 8A
(word lines WL) and gate electrodes 8B and 8C upon heat treatment,
each memory cell selection MISFET Qs and each MISFET of the
peripheral circuit can be enhanced in performance.
[0133] Next, a silicon oxide film 17 is deposited over the SOG film
16 as shown in FIG. 14. The silicon oxide film 17 is then polished
by the CMP method to flatten the surface thereof, and a silicon
oxide film 18 is deposited over the silicon oxide film 17. The
silicon oxide films 17 and 18 are deposited by a plasma CVD method
in which, for example, oxygen (or ozone) and tetra ethoxy silane
(TEOS) are used for a source gas. The silicon oxide film 18
corresponding to the upper layer is deposited to mend or fix micro
flaws on the surface of the silicon oxide film 17 corresponding to
the lower layer, which are produced when it is polished by the CMP
method.
[0134] Next, as shown in FIG. 15, the silicon oxide films 18 and 17
over the n.sup.--type semiconductor region (source and drain) of
each memory cell selection MISFET Qs are removed by dry etching
with the photoresist film 27 as a mask. This etching is performed
using gas for etching the silicon oxide film 17 at a high selection
ratio in order to prevent the silicon nitride film 13 placed in the
layer below the silicon oxide film 17 from being removed.
[0135] Next, as shown in FIG. 16, the silicon nitride film 13 over
the n.sup.--type semiconductor regions (source and drain) 9a is
removed by dry etching using the photoresist film 27 as the mask,
followed by removal of the thin gate oxide film 7 placed in the
layer below the silicon nitride-film 13, whereby a contact hole 19
is defined above one of the n.sup.--type semiconductor regions
(source and drain) and contact holes 20 are defined above the
others thereof. As shown in FIG. 17, each contact hole 19 (contact
hole over the n-type semiconductor region 9 shared by the two
memory cell selection MISFET Qs) is formed in such a slender
pattern that the diameter thereof in the Y direction becomes about
twice the diameter thereof in the X direction.
[0136] An n-type semiconductor layer may be formed in the p-type
well 2 lying in the region deeper than the source and drain of each
memory cell selection MISFET Qs by ion-implanting the n-type
impurity (e.g. phosphorous) in the p-type well 2 through the
contact holes 19 and 20 after the contact holes 19 and 20 have been
defined. Since the n-type semiconductor layer has the effect of
reducing electric fields which concentrate on the ends of the
source and drain, leakage current at the ends of the source and
drain can be reduced so as to improve a refresh characteristic of
each memory cell.
[0137] The etching of the silicon nitride film 13 is performed
using gas for etching the silicon nitride film 13 at a high
selection ratio in order to minimize the amount of cutting of the
semiconductor substrate 1 and the device separation groove 6.
Further, the present etching is done under such a condition as to
anisotropically etch the silicon nitride film 13 and the silicon
nitride film 13 is left on each side wall of the gate electrode 8A
(word line WL). Thus, the minute contact holes 19 and 20 whose
X-direction diameters are less than or equal to the resolution
limit of the photolithography, can be formed in self-alignment with
the gate electrodes 8A (word lines WL).
[0138] Next, plugs 21 are formed inside the contact holes 19 and 20
as shown in FIG. 18. The plugs 21 are formed by depositing a
polycrystal silicon film doped with the n-type impurity (e.g., As
(Arsenic)) over the silicon oxide film 18 by the CVD.method and
thereafter polishing the polycrystal silicon film by the CMP method
to thereby leave it inside the contact holes 19 and 20.
[0139] Next, as shown in FIG. 19, a silicon oxide film 28 is
deposited over the silicon oxide film 18 and thereafter the
semiconductor substrate 1 is heat-treated in an atmosphere of a
nitrogen gas. The silicon oxide film 28 is deposited by the plasma
CVD method in which, for example, the oxygen (or ozone) and tetra
ethoxy silane are used for the source gas. The n-type impurity in
the polycrystal silicon film constituting the plugs 21 is diffused
from the bottoms of the contact holes 19 and 20 to the n.sup.--type
semiconductor regions 9a of the memory cell selection MISFETs Qs,
so that n-type semiconductor regions (source and drain) 9 low in
resistance are formed.
[0140] Next, as shown in FIG. 20, the silicon oxide film 28
provided over each contact hole 19 is removed by dry etching using
a photoresist film (not shown) as a mask, so that a through hole 22
is defined. Each through hole 22 is placed above the device
separation groove 6 which falls outside each active region L (see
FIG. 4).
[0141] As shown in FIG. 21, the silicon oxide films 28, 18, 17, SOG
film 16 and gate oxide film 7 in the peripheral circuit are then
removed by dry etching using a photoresist film (not shown) as a
mask, whereby contact holes 30 and 31 are defined above the
n.sup.+-type semiconductor regions 10 (source and drain) of each n
channel MISFET Qn, and contact holes 32 and 33 are defined above
the p.sup.+-type semiconductor regions 11 (source and drain) of
each p channel MISFET Qp. Simultaneously at this time, a contact
hole 34 is defined in a portion above the gate electrode 8C of each
p channel MISFET Qp and an unillustrated contact hole is defined in
a portion above the gate electrode 8B of each n channel MISFET
Qn.
[0142] The execution of the etching for forming the through hole 22
and the etching for forming the contact holes 30 through 34 in the
different processes as described above allows prevention of a
problem that the plug 21 exposed at the bottom of the shallow
through hole 22 of the memory array is cut deep when the deep
contact holes 30 through 34 in the peripheral circuit are defined.
Incidentally, the formation of the through hole 22 and the
formation of the contact holes 30 through 34 may be carried out in
the order opposite to the above.
[0143] Next, a Ti film 36 is deposited over the silicon oxide film
28 including the interior of the contact holes 30 through 34 and
through hole 22 as shown in FIG. 22. The Ti film 36 is deposited by
using a high-oriented sputtering method such as collimation
sputtering, ionization sputtering or the like so that it is
deposited even over the bottoms of the contact holes 30 through 34
large in aspect ratio with a given degree of thickness.
[0144] The Ti film 36 is then heat-treated in an atmosphere of an
inert gas such as Ar (Argon) without being subjected to the
atmosphere. An Si substrate at the bottoms of the contact holes 30
through 33 and the Ti film 36 react with each other due to the heat
treatment, whereby TiSi.sub.2 layers 37 are formed over the
surfaces of the n.sup.+-type semiconductor regions 10 (source and
drain) of each n channel MISFET Qn and the surfaces of the
p.sup.+-type semiconductor regions 11 (source and drain) of each p
channel MISFET Qp as shown in FIG. 23. At this time, the TiSi.sub.2
layer 37 is formed even over the surface of the plug 21 at the
bottom of each through hole 22 by the reaction between the
polycrystal silicon film constituting the plug 21 and the Ti film
36.
[0145] Owing to the formation of the TiSi.sub.2 layers 37 at the
bottoms of the contact holes 30 through 33, portions where plugs 35
formed inside the contact holes 30 through 33 in the next process
make contact with the sources and drains (n.sup.+-type
semiconductor regions 10 and p.sup.+-type semiconductor regions 11)
of the MISFETs in the peripheral circuit, can be reduced in contact
resistance. Therefore, the high-speed operation of the peripheral
circuit such as the sense amplifier SA, the word driver WD or the
like is accelerated. Silicide layers at the bottoms of the contact
holes 30 through 33 may also be formed of a high-melting point
metal silicide other than TiSi such as COSi.sub.2 (cobalt
silicide), TaSi.sub.2 (tantalum silicide), MOSi.sub.2 (molybdenum
silicide) or the like.
[0146] Next, a TiN film 40 is deposited over the TiN film 36 by the
CVD method as shown in FIG. 24. Since the CVD method provides good
step coverage as compared with sputtering, the TiN film 40 having a
thickness of the same degree as that of the flattened portion can
be deposited over the bottoms of the contact holes 30 through 34
large in aspect ratio. A W film 41 is then deposited over the TiN
film 40 by a CVD method in which tungsten hexafluoride (WF.sub.6),
hydrogen and monosilane (SiH.sub.4) are used for a source gas, so
that the W film 41 is completely embedded into the contact holes 30
through 34 and through hole 22.
[0147] Next, the W film 41, TiN film 40 and Ti film 36 over the
silicon oxide film 28 are removed (polished back) using the CMP
method as shown in FIG. 25, so that the plugs 35 composed of the W
film 41, TiN film 40 and Ti film 36 are formed inside the contact
holes 30 through 34 and through hole 22.
[0148] Incidentally, the plugs 35 may be formed by removing
(etching back) the W film 41, TiN film 40 and Ti film 36 over the
silicon oxide film 28 by dry etching. Further, the plugs 35 may be
composed principally of the TiN film 40 without using the W film
41. Namely, the plugs 35 may be formed by embedding the TiN film 40
to a large thickness into the contact holes 30 through 34 and
through hole 22. In this case, the plugs 35 increase in resistance
to some extent as compared with the case in which they are composed
principally of the W film 41. Since, however, the TiN film 40
serves as an etching stopper when a W film 42 deposited over the
silicon oxide film 28 is dry-etched in the next process to form
each bit line BL and wires or interconnections 23 through 26
corresponding to a first wiring layer, of the peripheral circuit,
margins of displacements in alignment of the interconnections 23
through 26 with the contact holes 30 through 34 can be remarkably
improved and the degree of freedom of the layout of the
interconnections 23 through 26 is greatly improved.
[0149] Next, as shown in FIG. 26, the W film 42 is deposited over
the silicon oxide film 28 by sputtering. Thereafter, the W film 42
is dry-etched with a photoresist film (not shown). formed over the
W film 42 as a mask to thereby form each bit line BL in the memory
array and form the interconnections 23 through 26 corresponding to
the first wiring layer in the peripheral circuit. Incidentally,
there may be a case in which, since the W film 4-2 is high in light
reflectivity, the photoresist film causes halation upon exposure to
thereby reduce the dimensional accuracy of the patterns (width and
space). In order to prevent this, a reflection preventive film is
deposited over the W film 42 and the photoresist film may be
applied thereto. An organic material or a metal material (e.g., TiN
film) low in light reflectivity is used for the reflection
preventive film.
[0150] Next, as shown in FIG. 27, a silicon oxide film 38 is
deposited over each bit line BL and the interconnections 23 through
26 corresponding to the first wiring layer, and a silicon oxide
film 39 is then deposited over the silicon oxide film 38.
Thereafter, the surface of the silicon oxide film 39 is flattened
by the CMP method. The silicon oxide films 38 and 39 are deposited
by the plasma CVD method in which, for example, the oxygen (or
ozone) and tetra ethoxy silane are used for the source gas.
[0151] Next, a polycrystal silicon film 70 is deposited over the
silicon oxide film 39 by the CVD method as shown in FIG. 28.
Thereafter, the polycrystal silicon film 70 is dry-etched using a
photoresist film (not shown) as a mask to thereby define grooves
71a above the contact holes 20.
[0152] Sidewall spacers 72 composed of the polycrystal silicon film
are next formed over the side walls of the grooves 71a as shown in
FIG. 29. The sidewall spacers 72 are formed by depositing a
polycrystal silicon film (not shown) over the polycrystal silicon
film 70 including the interior of the grooves 71a by the CVD method
and thereafter anisotropically etching the polycrystal silicon film
to thereby leave it on the side walls of the grooves 71a owing to
the formation of the sidewall spacers 72, the internal diameter of
each groove 71a can be set smaller than the minimum processing size
by the lithography.
[0153] Next, the silicon oxide films 38 and 28 at the bottoms of
the grooves 71a are dry-etched using the polycrystal silicon film
70 and the sidewall spacers 72 as masks as shown in FIG. 30,
thereby defining through holes 48 which extend through space
regions for one bit line BL and another bit line BL adjacent
thereto so as to reach the contact holes 20. Since each through
hole 48 is defined by etching, using each sidewall spacer 72 on the
side wall of each groove 71a as a mask, the internal diameter of
each through hole 48 can be set smaller than the minimum processing
size by the lithography. Thus, since a margin of the alignment of
the space region for each bit line BL with each through hole 48 can
be sufficiently ensured, plugs 49 respectively embedded into the
through holes 48 in the next process or process step can be
prevented from causing a malfunction or trouble, such as a short to
each bit line BL or the plug 35 placed therebelow.
[0154] Next, as shown in FIG. 31, a silicon nitride film 44 is
deposited over the silicon oxide film 39 by the CVD method after
the plugs 49 comprised of the polycrystal silicon film have been
formed inside the through holes 48. The plugs 49 are formed by
depositing a polycrystal silicon film (not shown) doped with the
n-type impurity (e.g., P (phosphorous)) over the polycrystal
silicon film 70 in the interior of, the through holes 48 and
thereafter etching back the polycrystal silicon film together with
the polycrystal silicon film 70 and the sidewall spacers 72.
[0155] Next, as shown in FIG. 32, a silicon oxide film 50 is
deposited over the silicon nitride film 44 and thereafter the
silicon oxide film 50 and the silicon nitride film 44 placed
therebelow are dry-etched using a photoresist (not shown) as a
mask, whereby grooves 73 are define(d above the through holes 48.
Since a lower electrode 45 of each information storage capacitive
element C is formed along the inner walls of the grooves 73, it is
necessary to deposit the silicon oxide film 50 with a large film
thickness (e.g., of about 1.3 gm) for the purpose of increasing the
surface area of the lower electrode 45 to thereby increase the
quantity of storage charge. The silicon oxide film 50 is deposited
by the plasma CVD method in which, for example, oxygen (or ozone)
and tetra ethoxy silane are used for the source gas.
[0156] Next, an amorphous silicon film 45A doped with the n-type
impurity (e.g., P (phosphorus)) is deposited over the silicon oxide
film 50 in the interior of each groove 73 by the CVD method as
shown in FIG. 33.
[0157] Next, the amorphous silicon film 45A provided over the
silicon oxide film 50 is etched back and thereby removed as shown
in FIG. 34. Thereafter, the surface of the amorphous silicon film
45A left inside each groove 73 is cleaned with an etchant of
hydrofluoric acid. Subsequently, the surface of each amorphous
silicon film 45A is supplied with monosilane in an atmosphere under
reduced pressure and thereafter the semiconductor substrate 1 is
heat-treated to polycrystallize the amorphous silicon film 45A and
grow silicon particles over the surface thereof, whereby each lower
electrode 45 comprised of the polycrystal silicon film whose
surface has been roughened is formed as shown in FIG. 35. The lower
electrode 45 may be composed of a conductive material other than
the polycrystalline silicon, e.g., a high-melting point metal such
as W, Ru (ruthenium), or conductive metallic oxide such as RuO
(ruthenium oxide), IrO (iridium oxide).
[0158] Next, as shown in FIG. 36, a Ta.sub.2O5 film 46 is deposited
over the lower electrode 45 and is heat-treated in an oxidative
atmosphere to thereby improve the quality of the film. Thereafter,
a TiN film (not shown) is deposited over the Ta.sub.2O.sub.5 film
46, and the TiN film and Ta.sub.2O.sub.5 film 46 are patterned by
dry etching using a photoresist film (not shown) as a mask, whereby
each information storage capacitive element C comprised of the
upper electrode 47 composed of the TiN film, the capacitive
insulating film composed of the Ta.sub.2O.sub.5 film 46, and the
lower electrode 45 is formed. The Ta.sub.2O.sub.5 film 46 is
deposited by a CVD method in which penta ethoxy tantalum
(Ta(OC.sub.2H.sub.5).sub.5 is used for a source gas. The TiN film
is deposited by utilizing the CVD method and sputtering in
combination.
[0159] Each memory cell comprised of the memory cell selection
MISFET Qs and the information storage capacitive element C
electrically series-connected thereto is completed according to the
process steps used so far. Incidentally, the capacitive insulating
film of each information storage capacitive element C may be
comprised of a ferroelectric film or a film (high
dielectric-constant film) having a high dielectric constant, which
is composed of metallic oxides such as BST, STO, BaTiO.sub.3
(barium titanate), PbTiO.sub.3 (lead titanate), PZT
(PbZr.sub.xTi.sub.1-xXO.sub.3), PLT (PbLa.sub.xTi.sub.1-xO.sub.3),
PLZT. Further, the upper electrode 47 may be composed of a
conductive film other than the TiN film, e.g., a W film or the
like.
[0160] Next, as shown in FIG. 37, a silicon oxide film 51 is
deposited over each information storage capacitive element C. The
silicon oxide film 51 is then polished by the CMP method to flatten
the surface thereof. Afterwards, a silicon oxide film 52 is
deposited over the silicon oiide film 51. The silicon oxide films
51 and 52 are deposited by the plasma CVD method in which, for
example, oxygen (or ozone) and tetra ethoxy silane are used for the
source gas. The upper silicon oxide film 52 is deposited to mend or
fix micro flaws on the surface of the lower silicon oxide film 51,
which are produced when it is polished by the CMP method.
[0161] Next, the silicon oxide films 52, 51 and 50, silicon nitride
film 44 and silicon oxide films 39 and 38 in the peripheral circuit
region are etched using a photoresist film (not shown) as a mask as
shown in FIG. 38. Thus, a through hole 55 is defined in the portion
above the interconnection 26 corresponding to the first wiring
layer and thereafter a plug 56 is formed inside the through hole
55. Since the through hole 55 is defined so as to extend through
the insulating films corresponding to a plurality of layers
containing the silicon oxide film 50 formed with the large film
thickness, the aspect ratio thereof increases extremely. The plug
56 is formed by, for example, depositing a Ti film over the silicon
oxide film 52 by sputtering, depositing a TiN film and a W film
thereon by the CVD method and thereafter etching back these films
to thereby leave the deposited film inside the through hole 55.
[0162] Next, wires or interconnections 53 and 54 corresponding to a
second wiring layer are formed over the silicon oxide film 52 as
shown in FIG. 39. Of the interconnections 53 and 54 corresponding
to the second wiring layer, the interconnection 54 formed in the
peripheral circuit region is electrically connected to the
interconnection 26 of the first wiring layer via the through hole
55. The interconnections 53 and 54 of the second wiring layer are
formed by, for example, sequentially depositing a TiN film, an Al
(Aluminum) alloy film, a Ti film and a TiN film over the silicon
oxide film 52 by sputtering and thereafter patterning these films
by dry etching using a photoresist film as a mask.
[0163] A silicon oxide film 57 is next deposited over the
interconnections 53 and 54 corresponding to the second wiring layer
as shown in FIG. 40. Since the interconnections 53 and 54 of the
second wiring layer are formed with a large film thickness (of 400
nm or more, for example) as compared with the interconnections 23
through 26 of the first wiring layer, it is difficult to bury
spaces defined between the interconnections in a dense region (not
shown) of the interconnections of the second wiring layer when the
silicon oxide film is deposited by the above-described plasma CVD
method, for example. Thus, in the present embodiment, the silicon
oxide film 57 is deposited by using a high-density plasma CVD
method in which monosilane, oxygen and Ar (Argon) are used for a
source gas. Since the silicon oxide film 57 deposited by the
high-density plasma CVD method is excellent in gap-filling
characteristic, the silicon oxide film can be sufficiently embedded
into the spaces defined between the interconnections even in the
dense region of the interconnections corresponding to the second
wiring layer.
[0164] Next, silicon oxide films 58 and 59 are deposited over the
silicon oxide film 57 as shown in FIG. 41. The silicon oxide films
58 and 59 are deposited by the plasma CVD method in which, for
example, the oxygen (or ozone) and tetra ethoxy silane are used for
the source gas. The silicon oxide film 57 is excellent in
gap-filling characteristic but poor in film flatness. Therefore, it
is desirable that in order to reduce a grounding step-like offset
or difference between interconnections 60, 61 and 62 corresponding
to a third wiring layer, the silicon oxide film 58 is deposited
over the silicon oxide film 57 and the surface thereof is flattened
by the CMP method. The silicon oxide film 59 is deposited to mend
or fix micro flaws on the surface of the silicon oxide film 58,
which are produced when polished by the CMP method.
[0165] Next, the silicon oxide films 59, 58, 57, 52 and 51 are
etched using a photoresist (not shown) as a mask as shown in FIG.
42. As a result, a through hole 64 is defined in a portion above
the upper electrode 47 of each information storage capacitive
element C. Simultaneously at this time, the silicon oxide films 59,
58 and 57 are etched to define a through hole 63 above the
interconnection 53 of the second wiring layer formed in the memory
array and define a through hole 65 above the interconnection 54 of
the second wiring layer formed in the peripheral circuit
region.
[0166] Since the through hole 64 defined above the upper electrode
47 is formed as shown in FIG. 42 by etching the silicon oxide films
(59, 58, 57, 52 and 51) corresponding to five layers, the through
hole 64 is different in aspect ratio from the through holes 63 and
65 defined by etching the silicon oxide films (59, 58 and 57)
corresponding to three layers. Since, however, the interconnections
53 and 54 corresponding to the second wiring layer are respectively
formed at the bottoms of the through holes 63 and 65 and these
interconnections 53 and 54 serve as etching stoppers, the bottoms
of the through holes 63 and 65, which are smaller than the through
hole 64 in aspect ratio, are not cut even when the through holes
63, 64 and 65 having a different aspect ratio are simultaneously
defined.
[0167] Thereafter, plugs 66 are formed inside the through holes 63,
64 and 65. Afterwards, the interconnections 60, 61 and 62
corresponding to the third wiring layer are formed over the silicon
oxide film 59, whereby the DRAM shown in FIG. 3 is substantially
completed.
[0168] The plugs 66 are formed by, for example, depositing a Ti
film over the silicon oxide film 59 by sputtering, depositing a TiN
film and a W film over the Ti film by the CVD method and etching
back these films to thereby leave the same inside the through holes
63, 64 and 65. Further, the interconnections 63, 64 and 65
corresponding to the third wiring layer are formed by, for example,
successively depositing a TiN film, an Al alloy film, a Ti film and
a TiN film over the silicon oxide film 59 by sputtering and
thereafter patterning these films by dry etching using a
photoresist film as a mask.
[0169] A predetermined source of power is supplied to the upper
electrode 47 of each information storage capacitive element C from
the interconnection (feeding interconnection) 61 of the third
wiring layer via the through hole 64. The interconnection 60
corresponding to the third wiring layer formed in the memory array
is electrically connected to the interconnection 53 of the second
wiring layer via the through hole 63, and the interconnection 54 of
the third wiring layer formed in the peripheral circuit region is
electrically connected to the interconnection 54 of the second
wiring layer via the through hole 65.
[0170] While a passivation film comprised of, for example, a film
or the like obtained by laminating the silicon oxide film and the
silicon nitride film deposited by the CVD method is formed over the
interconnections 63, 64 and 65 corresponding to the third wiring
layer, it is omitted from the drawing. Bonding pads are formed by
an electric conductor film identical in layer to the
interconnection of the third wiring layer. Openings for
respectively exposing the bonding pads are defined in the
passivation film.
[0171] According to the above-described embodiments, since the
silicon oxide film 57, which is deposited by the high-density
plasma CVD method and possessing a feature in that it has an
excellent gap-filling characteristic, whereas it is easy to develop
charge-up according to electrical charges in a plasma, is formed
before the formation of the feeding interconnection 61, the
charged-up electrical charge is transferred to each upper electrode
47 via the feeding interconnection 61 and the through hole 64.
Thus, no damage to each information storage capacitive element C
occurs.
[0172] While the invention made by the present inventors has been
described specifically with reference to an embodiment of the
invention, the present invention is not limited thereto. It is
needless to say that various changes can be made thereto within the
scope not departing from the substance of the invention.
[0173] The power may be supplied to the upper electrode of each
information storage capacitive element through an interconnection
corresponding to a fourth wiring layer or an interconnection formed
in a layer thereabove, for example.
[0174] Effects obtained by a typical one of the features disclosed
in the present application will briefly be described as
follows:
[0175] According to the present invention, when a through hole is
defined in an insulating film between a feeding interconnection for
supplying power to an upper electrode of each information storage
capacitive element and the upper electrode, it is possible to
prevent the bottom of the through hole from extending through the
upper electrode. It is therefore possible to improve the connection
reliability of the feeding interconnection.
[0176] According to the present invention as well, the formation of
an insulating film which is easy to produce charge-up before the
formation of the feeding interconnection allows prevention of
electric breakdown of each information storage capacitive element,
which is caused by the charge-up of the insulating film.
[0177] According to the present invention, since each information
storage capacitive element and a second wiring layer are
electrically insulated from each other when an insulating film easy
to produce charge-up is formed over the second wiring layer, an
electrical charge supplied to the second wiring layer is not
transferred to the capacitive element, and electrical breakdown of
the information storage capacitive element, which is caused by the
charge-up, can be prevented.
[0178] The above-described effect can be achieved even when the
information storage capacitive element and the second wiring layer
are electrically connected to each other through a third wiring
layer after the formation of the insulating film which is easy to
produce charge-up formed over the second wiring layer, for
example.
[0179] When each MISFET sufficiently acts as a charge barrier, the
above-mentioned effect can be achieved even when the second wiring
layer is electrically connected to the information storage
capacitive element through the MISFET.
[0180] According to the present invention, a process step for
defining a first through hole in an insulating film provided
between a feeding interconnection for supplying a predetermined
potential to an upper electrode of each information storage
capacitive element and the upper electrode, and a process step for
defining a second through hole in an insulating film provided
between a first interconnection and a second interconnection in a
peripheral circuit region are separately performed. It is thus
possible to prevent the first through hole from extending through
or penetrating the upper electrode of each information storage
capacitive element, thereby to improve the connection reliability
of the feeding interconnection.
[0181] Further, the process step for defining the first through
hole in the insulating film provided between the feeding
interconnection for supplying the predetermined potential to the
upper electrode of each information storage capacitive element and
the upper electrode, and a process step for defining a third
through hole in an insulating film provided between a second
interconnection and a third interconnection in the peripheral
circuit region are performed in the same process step, thereby
making it possible to achieve a reduction in the number of process
steps.
[0182] Furthermore, since the first and third through holes are
defined in a configuration in which the first through hole is
deeper than the third through hole, the first through hole can be
completely opened and the upper electrode of each information
storage capacitive element can be set to such an etching condition
as not to be extremely over-etched. It is thus possible to prevent
the first through hole from penetrating the upper electrode of each
information storage capacitive element, thereby to improve the
connection reliability of the feeding interconnection.
[0183] Since the depth of the third through hole is shallower than
that of the first through hole, the second interconnection is
over-etched in the third through hole. However, the problems such
as the penetration of the second interconnection, etc. can be
avoided by sufficiently ensuring an etching selection ratio between
the insulating film on the second interconnection and the second
interconnection. Since the second interconnection is thicker than
the upper electrode, a problem concerning the reliability of the
connection to the third interconnection does not occur even if it
is slightly over-etched.
* * * * *