U.S. patent application number 14/880287 was filed with the patent office on 2016-02-04 for semiconductor circuit structure.
The applicant listed for this patent is Powerchip Technology Corporation. Invention is credited to Yi-Shiang Chang, Shu-Cheng Lin, Zih-Song Wang.
Application Number | 20160035733 14/880287 |
Document ID | / |
Family ID | 49291613 |
Filed Date | 2016-02-04 |
United States Patent
Application |
20160035733 |
Kind Code |
A1 |
Lin; Shu-Cheng ; et
al. |
February 4, 2016 |
SEMICONDUCTOR CIRCUIT STRUCTURE
Abstract
A NAND flash circuit structure includes two select gates
disposed on a substrate, and an even number of spaced-apart word
lines disposed between the two select gates. The select gate is
provided with a first portion and a second portion. The thickness
of the first portion and the second portion are different.
Inventors: |
Lin; Shu-Cheng; (Taipei
City, TW) ; Wang; Zih-Song; (Hsinchu City, TW)
; Chang; Yi-Shiang; (Changhua County, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Powerchip Technology Corporation |
Hsinchu |
|
TW |
|
|
Family ID: |
49291613 |
Appl. No.: |
14/880287 |
Filed: |
October 12, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13603426 |
Sep 5, 2012 |
9196623 |
|
|
14880287 |
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Current U.S.
Class: |
257/314 |
Current CPC
Class: |
H01L 27/115 20130101;
H01L 29/66477 20130101; H01L 27/0207 20130101 |
International
Class: |
H01L 27/115 20060101
H01L027/115; H01L 27/02 20060101 H01L027/02 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 6, 2012 |
TW |
101112247 |
Claims
1. A NAND flash circuit structure, comprising: a substrate; two
select gates disposed on said substrate; and an even number of
spaced-apart word lines disposed between said two select gates,
wherein said select gate is provided with a first portion and a
second portion, and the thickness of said first portion and said
second portion are different.
2. The NAND flash circuit structure according to claim 1, wherein
said first portion is the middle portion of said select gate while
said second portion is the bilateral portion of said select
gate.
3. The NAND flash circuit structure according to claim 2, wherein
the thickness of said first portion is larger than the thickness of
said second portion, and said select gate is in reverse-T
shape.
4. The NAND flash circuit structure according to claim 3, wherein
the surface of said first portion of said select gate comprises a
hard mask layer.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of and claims
the benefit of U.S. patent application Ser. No. 13/603,426, filed
Sep. 5, 2012.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to a semiconductor
structure, and more particularly, to a NAND flash circuit
structure.
[0004] 2. Description of the Prior Art
[0005] The principle of a photolithographic process is to transfer
a circuit pattern on a mask to a wafer by a method of exposure and
development, thereby producing specific circuit patterns on the
wafer. However, with the trend towards scaling down the
semiconductor products, the conventional photolithographic
technologies face formidable challenges. Takes mainstream ArF
excimer laser method with wavelength of 193 nm for example, the
reachable minimum half-pitch of a transistor device produced by
this kind of light source during exposure in the photolithographic
process is 65 nm. By incorporating the well-known immersion
lithography technology, the reachable half-pitch maybe further
reduced to 45 nm, which is almost the physical limitation in the
photolithographic processes. For this reason, if the half-pitch of
the semiconductor device need to go under 45 nm, the industry needs
to utilize more advanced a photo-lithographic technology, such as a
double patterning technology, an extreme ultra violet (EUV)
technology, a maskless photolithography (ML2) technology or a
nano-imprint technology, etc.
[0006] Double patterning is one of most mature method in the
aforementioned various advanced photolithography technologies. The
double patterning technology enables the use of current available
photolithographic tool to produce desired finer circuit patterns,
without the requirement of purchasing extremely expensive advanced
photolithography tools thereby avoiding huge investments. As the
double patterning technology and relevant equipment gradually
mature in the industry, the 193 nm immersion lithography technology
once limited by the physical limits can be further applied to the
advanced process nodes of 32 nm, or even 22 nm, thereby becoming
the mainstream photolithographic technology for the next
semiconductor generation.
[0007] The principle of the double patterning technology is to
separate one fine semiconductor circuit pattern into two
alternative or complementary circuit patterns. The two separate
patterns will be transferred respectively by the photolithographic
process and then be combined on the wafer to obtain the final
completed circuit pattern. Among various double patterning
technologies, negative self-aligned double patterning (N-SADP) is
one of mature process already applied in the current NAND flash
process flow. The N-SADP process can produce word lines or bit
lines with intervals smaller than 28 nm, thereby significantly
improving the memory capacity in memory blocks.
[0008] The normal N-SADP process is able to produce fine word lines
with identical intervals. However, due to the process nature, the
number of word lines in a single memory block produced through this
process is definitely an odd number. This characteristic cannot
fulfill the current memory standard of an even number of word lines
in one memory block.
[0009] Accordingly, it is necessary for the semiconductor industry
to improve the current double patterning technology in order to
overcome the aforementioned problem.
SUMMARY OF THE INVENTION
[0010] To overcome the above-mentioned drawbacks in prior art, a
novel semiconductor structure is provided in the present invention.
One object of the present invention is to provide a semiconductor
circuit structure comprising a substrate, two select gates disposed
on the substrate and an even number of spaced-apart word lines,
wherein the select gates are provided with a first portion and a
second portion, and the thicknesses of first portion and of the
second portion are different.
[0011] These and other objectives of the present invention will no
doubt become obvious to those of ordinary skill in the art after
reading the following detailed description of the preferred
embodiment that is illustrated in the various figures and
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The accompanying drawings are included to provide a further
understanding of the embodiments, and are incorporated in and
constitute apart of this specification. The drawings illustrate
some of the embodiments and, together with the description, serve
to explain their principles.
In the drawings:
[0013] FIGS. 1-10 are cross-sectional views illustrating a
semiconductor process in accordance with the preferred embodiment
of the present invention; and
[0014] FIG. 11 is a main process flow of the semiconductor process
in the present invention.
[0015] It should be noted that all the figures are diagrammatic.
Relative dimensions and proportions of parts of the drawings have
been shown exaggerated or reduced in size, for the sake of clarity
and convenience in the drawings. The same reference signs are
generally used to refer to corresponding or similar features in
modified and different embodiments.
DETAILED DESCRIPTION
[0016] In the following detailed description of the exemplary
embodiment, reference is made to the accompanying drawings, which
form a part thereof, and in which are illustrated by way of
illustration of specific embodiments in which the invention may be
practiced. These embodiments are described in sufficient details to
allow those skilled in the art to practice the invention. It is to
be understood that other embodiments may be utilized and
structural, logical, or electrical changes may be made without
departing from the scope of the present invention. The following
detailed description is, therefore, not to be taken in a limiting
sense, and the scope of the present inventions is defined only by
the appended claims. Furthermore, certain terms are used throughout
the following descriptions and claims to refer to specific
components. As one skilled in the art will appreciate, consumer
electronic equipment manufacturers may refer to a component by
different names, for example, dielectric layer and insulating
layer. This document does not intend to distinguish between
components that differ in name but not function.
[0017] The exemplary embodiments will now be explained with
reference to the accompanying drawings to provide a better
understanding of the process of the present invention, wherein
FIGS. 1-10 are cross-sectional views illustrating a semiconductor
process in accordance with the preferred embodiment of the present
invention. The method of the present invention is an improved
approach to the conventional negative self-aligned double
patterning (N-SADP) process, wherein the disclosed detailed steps
can solve the problem that common N-SADP process can't produce an
even number of equally-spaced word lines in one memory block.
[0018] Please refer to FIG. 1, a substrate is first provided to
serve as a base for forming semiconductor devices in the structure
of the preferred embodiment. A target layer, for example a
conductive layer 101, and a hard mask layer 102 are sequentially
formed on the substrate 100. The target layer is designed to be
patterned into the components and conductive circuits of various
desired semiconductor devices. In the preferred embodiment, the
conductive layer 101 will be used in later processes to form
conductive circuits, such as word lines, bit lines or select gates,
etc. The hard mask layer 102 will also be patterned in later
processes to serve as the etching mask for forming the conductive
pattern features from the underlying conductive layer. In the
embodiment, the substrate 100 may include a silicon substrate, a
silicon-containing substrate, a GaN-on-silicon (or other material
of Group III-V), a grapheme-on- silicon substrate or a
silicon-on-insulator (SOI) substrate and so on, but not limited to
a semiconductor substrate. The concept of the present invention may
also be applied to other technical fields, such as the field of
display panel. For example, the substrate 100 may be an insulating
glass substrate or a quartz substrate. The material of the
conductive layer 101 may include polycrystalline silicon, amorphous
silicon, salicide or metal material, while the material of the
target layer is, but not limited to, a conductive material, a
semiconductor material or an insulating material. The material of
the hard mask layer 102 may include silicon nitride, silicon oxide,
but not limited to insulating materials. For example, the hard mask
layer 102 may include a metal material such as titanium nitride
(TiN).
[0019] In the following steps, refer again to FIG. 1, a material
layer 103 is formed on the hard mask layer 102. The material layer
103 is designed to define core bodies for forming the core circuit
pattern. For this purpose, the material layer 103 will be
transformed into a plurality of protruding core bodies on the hard
mask layer 102 in the later process to constitute the desired core
circuit pattern. The detailed description will be explained in the
embodiment hereafter. In this embodiment, the material layer 103
may include silicon nitride, silicon oxide or polycrystalline
silicon, but is not limited thereto. However, the material layer
103 and the hard mask layer 102 must have different etching
selectivity. That is, the material layer 103 and the hard mask
layer 102 will have different etching rate in the same etching
process.
[0020] After forming the material layer 103, please refer to FIG.
2, a photolithographic/etching process is then performed to pattern
the material layer 103. In the preferred embodiment, the material
layer 103 is patterned into a plurality of core bodies with
different sizes through the photolithographic/etching process, like
the group of small core bodies 103a and the group of large core
bodies 103b shown in FIG. 2. When observed from the top, the core
bodies 103a/103b are arranged in spaced-apart line structure and
define a common area referred herein as a feature unit 104. The
surface of the entire substrate 100 may include a plurality of
feature units 104 arranged in an array. Each feature unit 104 may
be considered as a memory block in a common memory structure. The
number of small core bodies 103a is half of the even number of the
necessary word lines. For example, if a number M of word lines is
required in the memory structure, the number of small core bodies
is designed to be M/2. To explicitly describe the steps of present
invention, the following drawings and embodiment will take the
configuration of three small core bodies 103a as an example. The
aforementioned photolithographic/ etching process is a well-known
method in the relevant field of technology, thus the redundant
description is herein omitted.
[0021] With regard to the core bodies 103a/103b, please refer again
to FIG. 2, the widths of the small core bodies 103a and large core
bodies 103b are respectively W1 and W2. The width W2 of the large
core bodies 103b may be several-fold, for example, twice or three
times the width W1 of the small core bodies 103a. The width W2 of
large core bodies 103b must be able to provide a sufficient overlay
budget for the following photolithographic process in order to form
the desired circuit structure, such as a select gate. Furthermore,
the small core bodies 103a are equally-spaced from each other by a
first interval d1, and the large core bodies 103b are
equally-spaced from each other by a second interval d2. Besides,
one side of the group of the small core bodies 103a is spaced apart
from the adjacent large core body 103b by the first interval d1,
while the other side of the group of the small core bodies 103a is
spaced apart from the adjacent large core body 103b by the second
interval d2. In the preferred embodiment, the first interval d1 is
designed to be smaller than the second interval d2. For example,
the first interval d1 may be 3F (ex. 84 nm), which is three times
the size of the interval F (ex. 28 nm) between the desired final
circuit structure (ex. word lines). The second interval d2 may be
5F (ex. 140 nm), which is five times the size of the interval F. In
the embodiment, the design of a relatively smaller first interval
d1 and a larger second interval d2 may achieve the purpose of
forming a mask structure with different widths at the opposite
sides of the group of the small core bodies 103a in the later
N-SADP process, thereby producing the desired circuit structure,
such as the equally-spaced word lines and the select gate structure
at the opposite sides of the word line. The aforementioned
configuration is one of the essential features of the present
invention. Detailed description will be explained in following
embodiment.
[0022] After the sizes of small core bodies 103a and of the large
core bodies 103b are defined, please refer to FIG. 3, a deposition
process is performed to form a spacer material layer 105 on the
substrate 100. The spacer material layer 105 is formed conformally
on the surface of the hard mask layer 102 and core bodies
103a/103b, with the same thickness throughout the substrate 100. In
this manner, a plurality of recesses 106 are formed between the
core bodies 103a/103b. The recesses are spaced-apart on the
substrate in a fashion similar as the core body 103a/103b. In this
embodiment, the material of the spacer material layer 105 may be,
but not limited to, silicon nitride, silicon oxide or
polycrystalline silicon, etc. However, the spacer material layer
105, the material layer 103 and the hard mask layer 102 must have
different etching selectivities. That is, the spacer material layer
105, the material layer 103 and the hard mask layer 102 will have
different etching rates under the same etching process. This may
facilitate the removing of predetermined portion of the material
layer 103 through the following anisotropic etching process with
specific etching selectivity.
[0023] In the concept of present invention, the function of the
spacer material layer 105 is to reduce the intervals between the
core bodies 103a/103b. With regard to the N-SADP process, the
thickness W3 of the spacer material layer 105 is designed to be the
interval between the desired final circuit structures, such as a
plurality of equally-spaced word lines. In one preferred
embodiment, the thickness of the deposited spacer material layer
105 is designed to be half the exposure limit value of the
photolithographic tool used in the process. For example, in the
condition that ArF excimer laser stepper (with an exposure
wavelength of 193 nm) is utilized as the photolithographic tool,
the exposure limit value will be 56 nm, so the thickness of spacer
material layer 105 must be designed to be the value of 28 nm.
Alternatively, the thickness W3 of spacer material layer 105 may be
designed to be one-third of the first interval dl between the small
core bodies 103a or to be one-fifth of the second interval d2
between the large core bodies 103b. The configuration of the
predetermined and designed thickness for the deposited spacer
material layer 105 may facilitate the formation of equally-spaced
and equi-width word lines in later processes. Detailed description
will be explained in following embodiment.
[0024] After the spacer material layer 105 is formed, please refer
to FIG. 4, the recesses 106 are then filled up with a filling
material, thereby forming a plurality of small filling bodies 107a
and large filling bodies 107b with different widths. In the present
invention, the function of the filling bodies 107a/107b is to serve
as parts of the etching mask for the following processes, in order
to obtain the desired circuit pattern. The material of the filling
bodies 107a/107b may be silicon nitride, silicon oxide or
polycrystalline silicon. However, the filling bodies 107a/107b, the
surrounding spacer material layer 105, the material layer 103 and
the hard mask layer 102 must have different etching selectivity, so
that the filling bodies 107a/107b can be kept when undergoing the
following etching process for removing the spacer material layer
105.
[0025] In one preferred embodiment of the present invention, the
width W4 (ex. 28 nm) of the small filling body 107a is designed to
be the same as the width of desired final circuit structure (ex.
word lines). The width W5 of large filling body 107b is three times
the width W4 of the small filling body 107a, 84 nm for example.
Optionally, depending on the process requirement, a chemical
mechanical polishing process or an etching back process may be
performed to planarize the surface of the deposited filling
material, thereby obtaining the structure as shown in FIG. 4.
[0026] Please now refer to FIG. 5. An anisotropic (first) etching
process is performed after the forming of the filling bodies
107a/107b. The first etching process has a different etching
selectivity to the spacer material layer 105, the filling bodies
107a/107b and the material layer 103 so that the exposed spacer
material layer 105 is etched away and the core bodies 103a/103b and
filling bodies 107a/107b remain on the surface. The aforementioned
remained core bodies 103a/103b and filling bodies 107a/107b may
serve as a mask in following etching processes to obtain desired
pattern. After the first etching process, a plurality of recesses
108 are formed between the core bodies 103a/103b and the filling
bodies 107a/107b on the surface of the substrate 100 and expose the
underlying hard mask layer 102. Since the recess 108 in the
embodiment is formed by etching away the spacer material layer 105,
the width of the recess 108 is the same as the thickness W3 of the
originally-deposited spacer material layer 105, and each recess 108
has the same width.
[0027] After the spacer material layer 105 is removed by the first
etching process, please refer again to FIG. 5, the remained core
bodies 103a/103b and filling bodies 107a/107 are used as a mask to
perform a second etching process. The hard mask layer 102 exposed
from the recesses 108 will be etched away by the second etching
process, so that the feature pattern of the core bodies 103a/103b
and the filling bodies 107a/107b once presented on the substrate is
transferred to the hard mask layer 102. The core bodies 103a/103b
and filling bodies 107a/107b will be removed after the
aforementioned etching process to obtain the structure as shown in
FIG. 6. The patterned hard mask layer 102 is provided with a
plurality of mask bodies with different sizes, as the group of
small hard mask bodies 102a and the group of large hard mask bodies
102b shown in FIG. 6. The hard mask bodies 102a/102b formed by the
process of the present invention will have the same interval (ex.
W3), and the number of the small hard mask bodies 102a must be even
and is twice the number of the small core bodies 103a defined in
previous processes. For example, the number of the small hard mask
bodies 102a is preferably 2n, wherein n is a positive integer.
[0028] In following process, please refer to FIG. 7, the group of
small hard mask bodies 102a and the adjacent group of several hard
mask bodies 102b at two opposite sides of the group of the small
hard mask bodies 102a are covered with a photoresist 109. In this
embodiment, the purpose of covering the photoresist 109 is to keep
the necessary pattern feature, such as word lines, bit lines or
select gates, in a single feature unit 104. The photoresist 109 may
be used as a mask to perform an etching process for removing the
unnecessary pattern features outside the circuit pattern, such as
the group of large hard mask bodies 102c shown in FIG. 7. Finally,
as shown in FIG. 8, the photoresist 109 is removed to keep only the
group of small hard mask bodies 102a and the group of large hard
mask bodies 102b adjacent to the small hard mask bodies 102a on the
substrate. Please note that the photoresist 109 shown in FIG. 7
only covers the two large hard mask bodies 102b at the opposite
sides of the small hard mask bodies 102a. However, in other
embodiments, the photoresist 109 may cover a wider area, for
example, more than two large hard mask bodies 102b adjacent to the
two opposite sides of the small hard mask bodies 102a, depending on
the size of the circuit pattern (ex. a select gate) defined at the
opposite sides of the small hard mask bodies 102a. The present
invention takes two adjacent large hard mask bodies 102b as an
exemplary embodiment.
[0029] After removing the unnecessary pattern features in the hard
mask layer 102, as shown in FIG. 9, a photoresist 110 is covered on
the remained large hard mask bodies 102b. The purpose of covering
photoresist 110 is to mask the gap between two adjacent large mask
bodies 102b. In this manner, the adjacent large mask bodies 102b
may be considered as a single hard mask body to produce desired
circuit structure (ex. a select gate) in following processes. In
the embodiment, as aforementioned, since the width W2 of the formed
large hard mask bodies 102b (especially the one nearest to the
small hard mask bodies 102a) is several times the width W1 of the
small hard mask bodies 102a, the photoresist 110 will be provided
with a sufficient overlay budget for covering the two large hard
mask bodies 102b in the photolithographic process without alignment
shift to the area beyond the two hard mask bodies 102b and without
impacting the circuit pattern formed in the following
processes.
[0030] Finally, please refer to FIG. 10, the small hard mask bodies
102a, the large hard mask bodies 102b and the photoresist 110 are
used as a mask to etch the conductive layer 101 after covering the
photoresist 110. In this manner, an even number of spaced-apart
word lines 111 and select gates at two opposite sides may be
obtained in a memory block (i.e. feature unit 104). Since the hard
mask bodies 102a/102b are gradually removed during the etching
process, the portion of the select gate 112 (ex. the middle
portion) defined by the hard mask area covered by the photoresist
110 is thicker, which is referred herein as the first portion 112a,
while the portion of the select gate 112 (ex. the outer portion)
defined by the hard mask area not covered by the photoresist 110 is
thinner, which is referred herein as the second portion 112b.
Therefore, the select gate 112 is in a reverse-T shape with a
thicker middle portion and thinner outer portion. Furthermore,
parts of the large hard mask bodies 102b covered by the photoresist
110 remain on the surface of the select gate 112.
[0031] In conclusion, the process flow shown in FIG. 11 summarizes
the semiconductor process of the present invention. The steps of
the process flow may sequentially includes: providing a substrate
having a conductive layer and a hard mask layer (S1), forming
patterned large and small core bodies on the hard mask layer (S2),
forming a spacer material layer conformally on the substrate and
the core bodies (S3), forming a plurality of filling bodies in the
recesses of the spacer material layer (S4), performing a first
etching process to remove exposed spacer material layer (S5), using
the core bodies and the filling bodies as a mask to perform a
second etching process for patterning the hard mask layer (S6), and
using the patterned hard mask layer as a mask to perform a third
etching process for patterning the conductive layer (S7).
[0032] The essential feature of the aforementioned process claimed
in the present invention is that: by the design of a larger
interval between one side of the group of the small core bodies and
the adjacent large core body and a smaller interval between the
other side of the group of the small core bodies and the adjacent
large core body, the outermost one of the odd number spaced-apart
small circuit feature naturally produced by N-SADP process may be
transformed to a larger circuit feature. In this manner, by further
merging the transformed larger circuit feature with the adjacent
large circuit feature, the desired pattern structure of an even
number of equally-spaced small circuit patterns, which may serve as
word lines, and large circuit patterns, which may serve as select
gates, at the opposite sides may be obtained. This method solves
the problem of the conventional negative self-aligned double
patterning (N-SADP) process that can only produce an odd number of
equally-spaced small circuit patterns (ex. word lines).
[0033] Those skilled in the art will readily observe that numerous
modifications and alterations of the device and method may be made
while retaining the teachings of the invention. Accordingly, the
above disclosure should be construed as limited only by the metes
and bounds of the appended claims.
* * * * *