U.S. patent application number 13/272457 was filed with the patent office on 2012-02-09 for semiconductor device manufacaturing method and silicon oxide film forming method.
This patent application is currently assigned to Kabushiki Kaisha Toshiba. Invention is credited to Takeshi Hoshi, Kazuaki Iwasawa, Tetsuya Kai, Ryu Kato, Shogo Matsuo, Takashi Nakao, Keisuke Nakazawa, Katsuyuki Sekine.
Application Number | 20120034754 13/272457 |
Document ID | / |
Family ID | 42354485 |
Filed Date | 2012-02-09 |
United States Patent
Application |
20120034754 |
Kind Code |
A1 |
Iwasawa; Kazuaki ; et
al. |
February 9, 2012 |
SEMICONDUCTOR DEVICE MANUFACATURING METHOD AND SILICON OXIDE FILM
FORMING METHOD
Abstract
A semiconductor device manufacturing method has forming element
isolation trenches in a semiconductor substrate, forming a silicon
compound film in insides of the element isolation trenches in order
to embed the element isolation trenches, conducting a first
oxidation processing at a first temperature to reform a surface of
the silicon compound film to a volatile matter emission preventing
layer which permits passage of an oxidizing agent and impurities
and which does not permit passage of a volatile matter containing
silicon atoms, and conducting a second oxidation processing at a
second temperature which is higher than the first temperature to
form a coated silicon oxide film inside the element isolation
trenches.
Inventors: |
Iwasawa; Kazuaki;
(Yokohama-shi, JP) ; Hoshi; Takeshi;
(Yokohama-Shi, JP) ; Nakazawa; Keisuke;
(Yokohama-Shi, JP) ; Matsuo; Shogo; (Yokohama-Shi,
JP) ; Nakao; Takashi; (Yokohama-Shi, JP) ;
Kato; Ryu; (Yokohama-Shi, JP) ; Kai; Tetsuya;
(Yokohama-Shi, JP) ; Sekine; Katsuyuki;
(Yokohama-Shi, JP) |
Assignee: |
Kabushiki Kaisha Toshiba
Tokyo
JP
|
Family ID: |
42354485 |
Appl. No.: |
13/272457 |
Filed: |
October 13, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12691483 |
Jan 21, 2010 |
8080463 |
|
|
13272457 |
|
|
|
|
Current U.S.
Class: |
438/423 ;
257/E21.54 |
Current CPC
Class: |
H01L 21/76229
20130101 |
Class at
Publication: |
438/423 ;
257/E21.54 |
International
Class: |
H01L 21/76 20060101
H01L021/76 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 23, 2009 |
JP |
2009-12736 |
Mar 27, 2009 |
JP |
2009-78525 |
Claims
1.-20. (canceled)
21. A semiconductor device manufacturing method comprising: forming
a gate isolation film on a semiconductor substrate; forming a gate
electrode on the gate isolation film; forming an element isolation
trench in the gate electrode, the gate isolation film and the
semiconductor substrate; forming an impurity diffusion preventing
film in the element isolation trench; forming a silicon compound
film in insides of the element isolation trench in order to embed
the element isolation trench that the impurity diffusion preventing
film is formed; conducting a first oxidation process to reform a
surface of the silicon compound film at a first temperature; and
conducting a second oxidation process to form a coated silicon
oxide film from the silicon compound film at a second temperature,
the second temperature being higher than the first temperature,
wherein the first oxidation process is ozone oxidation.
22. The semiconductor device manufacturing method according to
claim 21, wherein the impurity diffusion preventing film is formed
by using a CVD method.
23. The semiconductor device manufacturing method according to
claim 21, wherein the impurity diffusion preventing film is a
silicon oxide film.
24. The semiconductor device manufacturing method according to
claim 21, further comprising conducting a warm water processing
process between the first oxidation process and the second
oxidation process.
25. The semiconductor device manufacturing method according to
claim 21, further comprising conducting a third oxidation process
after the coated silicon oxide film is formed.
26. The semiconductor device manufacturing method according to
claim 25, wherein the third oxidation process is ozone
oxidation.
27. The semiconductor device manufacturing method according to
claim 21, wherein the second oxidation process is an oxidation
conducted in a steam (H.sub.2) atmosphere or an oxide
atmosphere.
28. The semiconductor device manufacturing method according to
claim 21, wherein the first oxidation process is conducted at a
temperature of 300.degree. C. or less.
29. The semiconductor device manufacturing method according to
claim 21, wherein the silicon compound film is either polysilazane
(polyperhydrosilazane) or hydrogen silses quioxane (HSQ).
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No. 2009-12736,
filed on Jan. 23, 2009, and No. 2009-78525, filed on Mar. 27, 2009,
the entire contents of which are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a method for forming a
silicon oxide film in a semiconductor device manufacturing process,
and a semiconductor device manufacturing method.
[0004] 2. Background Art
[0005] In the semiconductor device development, it is demanded to
improve the speed, reduce the power dissipation, and suppress the
manufacturing cost. For satisfying these requirements, it is
necessary to shrink the size of the semiconductor device and shrink
the area of the semiconductor device. As one of effective means for
it, it is mentioned to shrink the size of an element isolation
region provided to isolate semiconductor elements included in the
semiconductor device.
[0006] In recent years, the shallow trench isolation (STI)
technique has been adopted as the method for manufacturing a minute
element isolation region. According to the shallow trench isolation
(STI) technique, an element isolation region is formed by embedding
an insulation film of silicon oxide in a trench (element isolation
trench) formed by using an anisotropic etching method such as the
reactive ion etching (RIE).
[0007] As a method for forming the insulation film in the trench
while suppressing generation of voids and seams, the spin on glass
(SOG) method is known.
[0008] According to this method, an insulation film of silicon
oxide is formed in the trench by coating a solution of a silicon
compound (for example, polysilazane (polyperhydrosilazane)
[--(SiH.sub.2NH)n--]) serving as a material of silicon oxide by
using the spin coating method and oxidizing the silicon compound.
The silicon oxide film (insulation film) formed by using such a
method is especially called coated silicon oxide film.
[0009] In general, the coated silicon oxide film formed by using
such a method has the following issues.
[0010] (1) The film density is low.
[0011] (2) There are a large number of impurities in the film.
[0012] As a method for solving these issues, there is a method for
oxidizing a silicon compound to form a coated silicon oxide film
and then conducting anneal processing in an atmosphere of nitrogen
or the like. The bond structure of the coated silicon oxide film
can be made more minute by conducting the anneal processing
(heating processing). At the same time, impurities which still
remain in the coated silicon oxide film can be removed. As a
result, the issues of the coated silicon oxide film can be
solved.
[0013] In the process for forming the coated silicon oxide film by
conducting the above-described processing, however, the coated
silicon oxide film contracts and film stress is generated,
resulting in new issues such as occurrence of defects in the coated
silicon oxide film, peeling of the coated silicon oxide film, and
deformation of the element isolation region.
[0014] As the method for solving such a new issue, therefore, the
following proposals have been made.
[0015] According to a proposed method, all insulation films of
silicon oxide in the trench are not formed by using the SOG method,
but a coated silicon oxide film is first formed on the lower half
in the trench by using the SOG method, and in addition an HTO (High
Temperature Oxide) film (silicon oxide film) having a bond
structure which is more minute than that of the coated silicon
oxide film is embedded in the upper half in the trench which is
equivalent to over the coated silicon oxide film (see, for example,
Japanese Patent Laid-Open No. 2000-114362).
[0016] According to another proposed method, a coated silicon oxide
film is formed in the lower half of the trench by using the SOG
method, and in addition a silicon oxide film having a bond
structure which is more minute than that of the coated silicon
oxide film is embedded in the upper half in the trench which is
equivalent to over the coated silicon oxide film by using the high
density plasma chemical vapor deposition (HDP-CVD) method (see, for
example, Japanese Patent Laid-Open No. 2003-31650).
[0017] However, both proposed methods need the CMP (Chemical
Mechanical Polishing) process at least twice. In other words, a
remarkable increase in the number of processes and complicated
processes cause issues such as a lowered process margin.
[0018] According to another proposed method, a silicon oxide film
having a bond structure which is more minute than that of a coated
silicon oxide film is embedded in the lower half in the trench by
using the HDP-CDV method, and in addition, a coated silicon oxide
film is embedded in the upper half in the trench which is
equivalent to over the silicon oxide film (see, for example,
Japanese Patent Laid-Open No. 2003-31650).
[0019] In this method as well, however, the coated silicon oxide
film is embedded in the upper half in the trench. In the coated
silicon oxide film which occupies the upper half of the trench,
therefore, peeling of the coated silicon oxide film or ensuing wet
etching poses a issue that an abnormality of the local shape is
caused in the coated silicon oxide film.
[0020] As the insulation film embedding technique for STI and
PMD
[0021] (Pre Metal Dielectric) advanced in size shrinking, a
plurality of techniques can be mentioned. For example, a technique
for embedding a film having fluidity such as a SOG film and a TEOS
(Tetraethyl Orthosilicate) film formed by using the spin coating
method, and a technique for combining an HDP-CVD silicon oxide film
and the above-described film having fluidity and embedding a
resultant film are considered to become promising.
[0022] As one of its methods, there is a method for embedding a
perhydrosilazane polymer (polysilazane) solution in an STI trench
formed in a semiconductor substrate, oxidizing the semiconductor
substrate in a steam atmosphere in a diffusion furnace or the like,
and thereby forming a silicon oxide film in the STI trench (see,
for example, see, for example, Japanese Patent Laid-Open No.
2004-179614 and Japanese Patent Laid-Open No. 2002-367980).
[0023] In the coated polysilazane film, nitrogen (N) contained in
the raw material and carbon (C) contained in an organic solvent
such as dibutyl ether remain in the film as impurities. For
obtaining a silicon oxide film having a good film quality,
therefore, it is necessary to increase the quantity of oxidation to
remove these impurities.
[0024] For transforming the polysilazane film to a silicon oxide
film having a good quality, annealing is conducted in an atmosphere
of inert gas such as nitrogen to make the polysilazane film
oxidized by, for example, steam oxidation.
[0025] At the time of this annealing, however, film contraction in
the polysilazane film occurs. Stress is applied to the foundation
(semiconductor substrate) by the film contraction, resulting in a
cause of occurrence of crystal defects or the like in the
semiconductor substrate.
SUMMARY OF THE INVENTION
[0026] According to one aspect of the present invention, there is
provided: a semiconductor device manufacturing method
comprising:
[0027] conducting a first oxidation processing to reform a surface
of a silicon compound film; and
[0028] conducting a second oxidation processing to form a coated
silicon oxide film from the silicon compound film.
[0029] According to one aspect of the present invention, there is
provided: a semiconductor device manufacturing method
comprising:
[0030] forming element isolation trenches in a semiconductor
substrate;
[0031] coating a silicon compound solution obtained by dissolving a
silicon compound in a solvent to insides of the element isolation
trenches to embed the element isolation trenches;
[0032] conducting a first oxidation processing at a first
temperature to reform a surface of the silicon compound solution to
a volatile matter emission preventing layer which permits passage
of an oxidizing agent, impurities and the solvent and which does
not permit passage of a volatile matter containing silicon
atoms;
[0033] conducting heating processing to evaporate the solvent via
the volatile matter emission preventing layer and form a silicon
compound film from the silicon compound solution located under the
volatile matter emission preventing layer; and
[0034] conducting a second oxidation processing at a second
temperature which is higher than the first temperature to form a
coated silicon oxide film inside the element isolation
trenches.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] FIG. 1 is a graph showing relations between the thermal
processing temperature and the emission accumulation quantities of
the volatile matter having a molecular weight of 76 from the
polysilazane film;
[0036] FIG. 2 is a schematic plan view (a part) of a semiconductor
device according to a first embodiment of the present
invention;
[0037] FIG. 3 is a schematic process sectional view showing a
manufacturing method of the semiconductor device according to the
first embodiment, the fourth embodiment and the fifth embodiment of
the present invention;
[0038] FIG. 4 is a schematic process sectional view showing a
manufacturing method of the semiconductor device according to the
first embodiment, the fourth embodiment and the fifth embodiment of
the present invention, and is continuous from FIG. 3;
[0039] FIG. 5 is a schematic process sectional view showing a
manufacturing method of the semiconductor device according to the
first embodiment, the fourth embodiment and the fifth embodiment of
the present invention, and is continuous from FIG. 4;
[0040] FIG. 6 is a schematic process sectional view showing a
manufacturing method of the semiconductor device according to the
first embodiment, the fourth embodiment and the fifth embodiment of
the present invention, and is continuous from FIG. 5;
[0041] FIG. 7 is a schematic process sectional view showing a
manufacturing method of the semiconductor device according to the
first embodiment, the fourth embodiment and the fifth embodiment of
the present invention, and is continuous from FIG. 6;
[0042] FIG. 8 is a schematic process sectional view showing a
manufacturing method of the semiconductor device according to the
first embodiment, the fourth embodiment and the fifth embodiment of
the present invention, and is continuous from FIG. 7;
[0043] FIG. 9 is a schematic process sectional view showing a
manufacturing method of the semiconductor device according to the
first embodiment, the fourth embodiment and the fifth embodiment of
the present invention, and is continuous from FIG. 8;
[0044] FIG. 10 is a schematic process sectional view showing a
manufacturing method of semiconductor device according to the
second embodiment of the present invention;
[0045] FIG. 11 is a schematic process sectional view showing a
manufacturing method of the semiconductor device according to the
second embodiment of the present invention, and is continuous from
FIG. 10;
[0046] FIG. 12 is a schematic process sectional view showing a
manufacturing method of the semiconductor device according to the
second embodiment of the present invention, and is continuous from
FIG. 11;
[0047] FIG. 13 is a schematic process sectional view showing a
manufacturing method of the semiconductor device according to the
second embodiment of the present invention, and is continuous from
FIG. 12;
[0048] FIG. 14 is a schematic process sectional view showing a
manufacturing method of the semiconductor device according to the
second embodiment of the present invention, and is continuous from
FIG. 13;
[0049] FIG. 15 is a schematic process sectional view showing a
manufacturing method of the semiconductor device according to the
third embodiment of the present invention;
[0050] FIG. 16 is a schematic process sectional view showing a
manufacturing method of the semiconductor device according to the
third embodiment of the present invention, and is continuous from
FIG. 15;
[0051] FIG. 17 is a schematic process sectional view showing a
manufacturing method of the semiconductor device according to the
third embodiment of the present invention, and is continuous from
FIG. 16;
[0052] FIG. 18 is a sectional view in respective process of a
silicon oxide film forming method according to the sixth embodiment
of the present invention;
[0053] FIG. 19 is a sectional view in respective process of a
silicon oxide film forming method according to the sixth embodiment
of the present invention, and is continuous from FIG. 18;
[0054] FIG. 20 is a sectional view in respective process of a
silicon oxide film forming method according to the sixth embodiment
of the present invention, and is continuous from FIG. 19;
[0055] FIG. 21 is a sectional view in respective process of a
silicon oxide film forming method according to the sixth embodiment
of the present invention, and is continuous from FIG. 20; FIG. 22
is a diagram showing an example of an apparatus which generates
ozone by using UV light and oxidizes the surface of the
polysilazane film on the semiconductor substrate; and
[0056] FIG. 23 is a diagram showing another example of an apparatus
which generates ozone by using UV light and oxidizes the surface of
the polysilazane film on the semiconductor substrate.
DETAILED DESCRIPTION
[0057] Hereafter, a semiconductor device manufacturing method and a
silicon oxide film forming method according to the present
invention will be described more specifically with reference to the
drawings.
[0058] Prior to description of embodiments of the present
invention, a method for forming an insulation film of coated
silicon oxide used by the present inventors heretofore will be
described briefly.
[0059] Herein, "silicon compound film" means a film containing
silicon atoms which becomes the coated silicon oxide film by being
oxidized.
[0060] The case where an insulation film composed of the coated
silicon oxide is formed within a trench (element isolation trench)
of a semiconductor device will now be described as an example.
[0061] A semiconductor film is formed on a semiconductor substrate,
and a plurality of trenches is formed in a part of the
semiconductor substrate and the semiconductor film. Then, a silicon
compound coating solution (silicon compound solution) is made by
dissolving a silicon compound (for example, polysilazane) which
becomes a material of a silicon compound film in a solvent. The
trench is embedded with this silicon compound coating solution.
Pre-baking (heating processing) is conducted to evaporate the
solvent contained in the silicon compound coating solution. In this
way, a silicon compound film is within each of a plurality of
trenches. Then, high temperature oxidation processing is conducted
in an atmosphere such as steam. By doing so, the silicon compound
film is oxidized and the coated silicon oxide film is formed in
each of the trenches. In addition, anneal processing (heating
processing) is conducted in order to make the bond structure of the
coated silicon oxide film more minute.
[0062] Heretofore, the present inventors have formed the coated
silicon oxide film in the trenches by using the method heretofore
described.
[0063] For further improving the performance and the reliability of
the semiconductor device, however, it is necessary to decrease
defects of the coated silicon oxide film in the trenches of the
semiconductor device.
[0064] It is considered that film contraction or film stress is
caused by high temperature oxidation processing or heating
processing at the time when oxidizing the silicon compound film and
forming the coated silicon oxide film and thereby defects are
generated in the coated silicon oxide film.
[0065] First, the present inventors have individually conducted an
analysis about a cause of contraction of the coated silicon oxide
film at the time of the high temperature oxidation processing for
oxidizing the silicon compound film to form the coated silicon
oxide film.
[0066] The present inventors have conducted experiments to know
what kind of phenomenon is occurring in the silicon compound film
at the time of the high temperature oxidation processing. In other
words, the present inventors have measured the thermal desorption
spectroscopy (TDS) in order to know relations among a molecular
weight of a volatile matter emitted from the silicon compound film
during the high temperature oxidation processing, its emitted
quantity, and the temperature of the high temperature oxidation
processing.
[0067] Hereafter, details thereof will be described.
[0068] A polysilazane film is formed as a silicon compound film
according to the method described earlier by using polysilazane as
the silicon compound and using dibutyl ether as the solvent for
dissolving polysilazane. Then, the polysilazane film is heated
while raising the temperature under the existence of an oxidizing
agent. The molecular weight of the volatile matter emitted from the
polysilazane film and the pressure of the volatile matter for each
molecular weight are measured. The pressure of the volatile matter
is proportionate to the accumulation quantity emitted from the
volatile matter.
[0069] Results of the measurement are shown in FIG. 1. FIG. 1 is a
graph showing relations between the thermal processing temperature
and the emission accumulation quantities of the volatile matter
having a molecular weight of 76 from the polysilazane film.
[0070] A curve B in FIG. 1 indicates the pressure of the volatile
matter having the molecular weight of 76 emitted from the
polysilazane film, i.e., emission accumulation quantity as a
function of the temperature of the oxidation processing (a curve A
in FIG. 1 will be described later). A curve C in FIG. 1 indicates
the background.
[0071] As appreciated from the curve B in FIG. 1, the volatile
matter having the molecular weight of 76 is little emitted from the
polysilazane film when the oxidation processing temperature is
300.degree. C. or less. However, it is appreciated that the
emission quantity of the volatile matter having the molecular
weight of 76 abruptly increases if the temperature of the oxidation
processing exceeds 300.degree. C.
[0072] It is conjectured based on various elements and the molecule
structure contained in the polysilazane film and the solvent
(dibutyl ether) considered to remain slightly in the polysilazane
film that the volatile matter having the molecular weight of 76 is
SiO.sub.3, SiC.sub.4 and CH.sub.4O.sub.2Si. In other words, it is
conjectured that when the temperature of the oxidation processing
exceeds 300.degree. C. a matter having a low molecular weight
containing silicon atoms is volatilizing from the polysilazane
film.
[0073] Based on such results obtained from the measurement, the
present inventors consider the reason why the coated silicon oxide
contracts as hereafter described.
[0074] In other words, the silicon compound film (polysilazane
film) is oxidized, under the presence of an oxidizing agent, by
being subjected to the high temperature oxidation processing at a
high temperature, for example, at 300.degree. C. or more to become
the coated silicon oxide film. At the time of such high temperature
oxidation processing, a volatile matter having a low molecular
weight containing silicon atoms which constitute the silicon
compound film escapes and is emitted. The coated silicon oxide film
during the oxidation processing has a bond structure having
flexibility. Therefore, the coated silicon oxide film causes film
contraction so as to make up for a part from which silicon atoms
have escaped.
[0075] Based on such an individual consideration, the present
inventors have considered that the contraction of the coated
silicon oxide film can be suppressed and consequently defects of
the coated silicon oxide film can be decreased by preventing the
volatile matter having the low molecular weight and containing
silicon atoms from being emitted from the silicon compound film at
the time of high temperature oxidation processing. The present
inventors have considered that this can be attained by conducting
the oxidation processing for oxidizing the silicon compound film at
a low temperature, for example, at a temperature of 300.degree. C.
or less. Even if the surface of the silicon compound film can be
oxidized, however, it is difficult to oxidize up to the inside of
the silicon compound film in such oxidation processing at the low
temperature.
[0076] Therefore, the present inventors have considered that if it
is inevitable to use the method for oxidizing the silicon compound
film at a high temperature a volatile matter emission preventing
layer having the property of preventing passage of a volatile
matter having a low molecular weight and containing silicon atoms
should be formed on the silicon compound film before conducting the
high temperature oxidation processing (second oxidation
processing). Because owing to existence of such a volatile matter
emission preventing layer on the silicon compound film, it is
possible to prevent the volatile matter having the low molecular
weight and containing silicon atoms from being emitted from the
silicon compound film at the time of high temperature oxidation
processing.
[0077] In addition, the present inventors have thought of providing
the volatile matter emission preventing layer with not only the
property of preventing the passage of the volatile matter having
the low molecular weight and containing silicon atoms but also a
property of passing an oxidizing agent such as oxygen, ozone, or
water through it. Because owing to the property of passing the
oxidizing agent through it, it becomes possible for the oxidizing
agent to arrive at the silicon compound film located under the
volatile matter emission preventing layer even after the volatile
matter emission preventing layer is formed and consequently the
silicon compound film can be oxidized.
[0078] Furthermore, the present inventors have thought of providing
the volatile matter emission preventing layer with a property of
passing hydrogen or nitrogen through it in addition to the
properties described heretofore. Because owing to such a property
of the volatile matter emission preventing layer it becomes
possible to evaporate hydrogen, nitrogen or the like which are
impurities in the coated silicon oxide film, from the silicon
compound film and the coated silicon oxide film and remove these
substances from the silicon compound film and the coated silicon
oxide film.
[0079] Therefore, the present inventors have selected to form the
volatile matter emission preventing layer with silicon oxide in
order to provide the volatile matter emission preventing layer with
all properties described above, based on various experiment results
obtained until then and the molecular structure of the volatile
matter having the low molecular weight and containing silicon
atoms.
[0080] In addition, it is also possible to obtain advantages
described below by forming the volatile matter emission preventing
layer of silicon oxide.
[0081] In the case where the volatile matter emission preventing
layer is formed of a substance other than silicon oxide, there is a
possibility that molecules contained in the substance which
constitutes the volatile matter emission preventing layer will
become impurities and contaminate the insulation film (the silicon
oxide film) in the trenches, even if the volatile matter emission
preventing layer is provided with all properties described above.
In addition, if such impurities enter the insulation film in the
trenches and contaminate the insulation film, there is a
possibility that defects will be caused in the insulation film.
[0082] On the other hand, if the volatile matter emission
preventing layer is formed of silicon oxide, it is possible obtain
an advantage that there is no fear of contaminating the insulation
film because the same substance as that of the insulation film (the
silicon oxide film) in the trenches.
[0083] Furthermore, since the volatile matter emission preventing
layer is formed of silicon oxide, it is possible to use reforming
of oxidizing the surface of the silicon compound film formed
already in the trenches to obtain the volatile matter emission
preventing layer. Since it is not necessary to purposely stack a
separate silicon oxide film on the silicon compound film by doing
so, it is possible to obtain an advantage that a remarkable
increase of the number of processes for forming the coated silicon
oxide film can be avoided.
[0084] However, adoption of this method causes the following new
issue.
[0085] If reforming of forming the volatile matter emission
preventing layer is conducted by using high temperature oxidation
processing, which is the conventional oxidation method for the
silicon compound film, then the volatile matter having the low
molecular weight and containing silicon atoms is emitted, resulting
in contraction of the silicon compound film. In addition, an issue
that defects are caused in the silicon compound film by the
contraction of the silicon compound film is posed.
[0086] Therefore, the present inventors have decided to form the
volatile matter emission preventing layer by using reforming of
oxidizing the surface of the silicon compound film (first oxidation
processing) at a low temperature, for example, by using ozone
oxidation processing at a low temperature. As a result, it becomes
possible to modify the surface of the silicon compound film and
form the volatile matter emission preventing layer while avoiding
the emission of the volatile matter having the low molecular weight
and containing silicon atoms.
[0087] In addition, silicon oxide is made to exist on the surface
of the silicon compound film by forming the volatile matter
emission preventing layer of silicon oxide. At the time of the
oxidation processing after the volatile matter emission preventing
layer is formed, oxidation of the silicon compound film is advanced
by using silicon oxide existing on the surface of the silicon
compound film as a base point. This results in an advantage that
oxidation of the whole silicon compound film can be advanced
efficiently.
[0088] Then, the present inventors have conducted experiments to
determine whether emission of the volatile matter from the silicon
compound film is prevented when the volatile matter emission
preventing layer is formed. Results of the confirmation experiments
will now be described with reference to FIG. 1.
[0089] FIG. 1 shows relations between the oxidation processing
temperature and the emission accumulation quantities of the
volatile matter having a molecular weight of 76 emitted from the
polysilazane film (silicon compound film). A curve A in FIG. 1
shows the case where the volatile matter emission preventing layer
is formed on the surface of the polysilazane film. On the other
hand, a curve B in FIG. 1 shows the case where the volatile matter
emission preventing layer is not formed on the surface of the
polysilazane film. A curve C in FIG. 1 indicates the
background.
[0090] As appreciated from FIG. 1, the quantity of the volatile
matter having the molecular weight of 76 emitted from the
polysilazane film having the volatile matter emission preventing
layer abruptly increases if the temperature of the oxidation
processing rises above 300.degree. C. (see the curve B in FIG. 1).
On the other hand, even if the temperature of the oxidation
processing rises, the volatile matter having the molecular weight
of 76 is little emitted from the polysilazane film having the
volatile matter emission preventing layer (see the curve A in FIG.
1). In other words, it has been confirmed that emission of the
volatile matter having the low molecular weight and containing
silicon atoms is prevented by forming the volatile matter emission
preventing layer on the surface of the polysilazane film.
[0091] In addition, it has been determined whether contraction of
the coated silicon oxide film is suppressed by forming the volatile
matter emission preventing layer of silicon oxide on the surface of
the silicon compound film to prevent emission of the volatile
matter.
[0092] Hereafter, details of the confirmation will be
described.
[0093] The contraction of the coated silicon oxide film have been
checked by measuring the film thickness of the polysilazane film
(silicon compound film) and measuring the film thickness of the
coated silicon oxide film obtained by then conducting high
temperature oxidation processing and comparing them with each
other. As an index indicating the contraction, a contraction factor
obtained by finding the difference between the film thickness of
the polysilazane film and the film thickness of the coated silicon
oxide film obtained by then conducting high temperature oxidation
processing and dividing the difference by the film thickness of the
polysilazane film is used.
[0094] When films are fabricated under the same condition, the film
on which the volatile matter emission preventing layer is not
formed is 19% in contraction factor, whereas the film on which the
volatile matter emission preventing layer is formed is limited to
10% in contraction factor. In other words, it has been appreciated
from this result that the contraction of the coated silicon oxide
film can be suppressed by forming the volatile matter emission
preventing layer.
[0095] As heretofore described, it is revealed that there is an
effect that emission of the volatile matter having the low
molecular weight and containing silicon atoms is prevented and the
contraction of the coated silicon oxide film is suppressed at the
time of the high temperature oxidation processing by forming the
volatile matter emission preventing layer of silicon oxide on the
surface of the silicon compound film.
[0096] Even if the volatile matter emission preventing layer and
the coated silicon oxide film are formed in this way, however, the
film stress is still generated in the coated silicon oxide
film.
[0097] Therefore, the present inventors have thought that it is
necessary to suppress the occurrence of the film stress and
consequently further decrease defects in the coated silicon oxide
film in order to make the film quality of the coated silicon oxide
film further better.
[0098] The present inventors have thought that the film stress in
the coated silicon oxide film might be generated at the time of
anneal processing (heating processing). Hereafter, details of the
generation mechanism of the film stress in the coated silicon oxide
film individually thought by the present inventors will be
described.
[0099] First, it is considered that the following change occurs in
the coated silicon oxide film at the time of the anneal
processing.
[0100] Unoxidized parts sometimes exist in the coated silicon oxide
film before the anneal processing. In addition, the coated silicon
oxide film before the anneal processing dose not yet form a firm
bond structure. The Unoxidized part is oxidized by conducting the
anneal processing on such a coated silicon oxide film. At the same
time, the coated silicon oxide film changes so as to form a minute
and firm bond structure.
[0101] In other words, a part of silicon atoms in the bond
structure of the coated silicon oxide film before the anneal
processing remains bonded to hydrogen atoms or nitrogen atoms. In
addition, in the bond structure in the coated silicon oxide film
before the anneal processing, silicon atoms and oxygen atoms do not
bond regularly. By conducting the anneal processing on such a
coated silicon oxide film, hydrogen atoms and nitrogen atoms which
have remained in the bond structure of the coated silicon oxide
film escape and are replaced by oxygen atoms. At the same time, the
coated silicon oxide film is changed so as to have a regular,
minute, firm bond structure in which each silicon atom bonds to
another silicon atom via an oxygen atom.
[0102] In other words, it is considered that the two changes
described heretofore are simultaneously occurring in the coated
silicon oxide film during the anneal processing.
[0103] The present inventors have considered that hydrogen atoms
and nitrogen atoms which have remained in the coated silicon oxide
film escape from the coated silicon oxide film, they are replaced
by oxygen atoms, and a coated silicon oxide film having a minute
and firm bond structure is formed, resulting in a strain in the
bond structure. In addition, the present inventors have considered
that the film stress might be caused by the strain in the bond
structure.
[0104] Therefore, the present inventors have thought that hydrogen
atoms and nitrogen atoms in the coated silicon oxide film should be
removed and replaced by oxygen atoms while preventing the coated
silicon oxide film from forming a minute firm bond structure before
the coated silicon oxide forms a minute firm bond structure, for
suppressing the occurrence of the film stress in the coated silicon
oxide film. In other words, the present inventors have thought that
it suffices to only oxidize the Unoxidized part in the coated
silicon oxide film before conducting the anneal processing.
[0105] As for such a method, the present inventors have thought of
conducting oxidation processing at a low temperature (third
oxidation processing), for example, ozone oxidation at a low
temperature. Because according to this method, the Unoxidized parts
of the coated silicon oxide film can be oxidized without causing
the coated silicon oxide film to have a minute firm bond
structure.
[0106] The present inventors have conducted confirmation to
determine whether generation of the film stress in the coated
silicon oxide film is obstructed by conducting oxidation processing
at a low temperature (the third oxidation processing) before the
anneal processing. To be more precise, the present inventors have
measured the film stress in the coated silicon oxide film by
optically measuring the warp of the semiconductor substrate having
the coated silicon oxide film formed thereon. Hereafter, results of
the measurement will be described.
[0107] A coated silicon oxide film is formed according to the
method described above. In other words, a polysilazane film
(silicon compound film) is subject to high temperature oxidation
processing at 500.degree. C. for 5 minutes in a steam environment.
Then, anneal processing is conducted at 850.degree. C. for 30
minutes in a nitrogen environment to form a coated silicon oxide
film. The coated silicon oxide film thus obtained has a film stress
of 115 MPa.
[0108] On the other hand, a coated silicon oxide film is formed by
using a similar method and further adding the ozone oxidation
processing (the third oxidation processing) at a low temperature
before the anneal processing. The coated silicon oxide film thus
obtained has a film stress of 88 MPa.
[0109] In other words, it is appreciated that the film stress of
the coated silicon oxide film finally obtained is decreased by
adding the oxidation processing at a low temperature (the third
oxidation processing).
[0110] From this result, therefore, it is confirmed that the
generation of the film stress in the coated silicon oxide film is
suppressed by adding the oxidation processing at a low temperature
(the third oxidation processing) before the anneal processing.
[0111] The present invention has been made based on individual
finding of the present inventors described heretofore.
[0112] Hereafter, embodiments of the present invention will be
described by taking a method for manufacturing a NAND flash memory
as an example. However, the present invention is not restricted to
the manufacturing method for the NAND flash memory.
FIRST EMBODIMENT
[0113] FIG. 2 is a schematic plan view (a part) of a semiconductor
device according to a first embodiment of the present invention. To
be more precise, FIG. 2 is a schematic plan view (a part) of a NAND
flash memory. The schematic plan view of the semiconductor device
according to second to fifth embodiments of the present invention
described later also becomes as shown in FIG. 2.
[0114] In the NAND flash memory according to the first embodiment,
a plurality of active areas 101 in the longitudinal direction on
paper as shown in FIG. 2. In addition, the active areas 101 are
arranged at regular intervals in the lateral direction on the paper
and are parallel to each other. Furthermore, a plurality of gate
electrodes 102 is formed so as to be perpendicular to the active
areas 101 when seen as a plane. A plurality of memory cells 60 is
formed in a plurality of parts where the active areas 101 and the
gate electrodes 102 intersect three-dimensionally. In other words,
the memory cells 60 are arranged in a NAND flash memory in a matrix
form. In addition, each pair of memory cells 60 adjacent in the
lateral direction on the paper is arranged with an STI (Shallow
Trench Isolation) 103 between. Each of a plurality of STIs 103 is
formed of a trench (element isolation trench) and an insulation
film (coated silicon oxide film) which occupies the inside of the
trench.
[0115] FIGS. 3 to 9 are schematic process sectional views showing a
manufacturing method of the semiconductor device according to the
first embodiment of the present invention. These views correspond
to a section obtained by cutting along a line A-A' shown in FIG. 2.
Incidentally, schematic process sectional views for a manufacturing
method of the semiconductor device according to fourth and fifth
embodiments of the present invention which will be described later
are also represented by FIGS. 3 to 9 in the same way.
[0116] Hereafter, the manufacturing method for the semiconductor
device according to the first embodiment of the present invention
will be described with reference to FIGS. 3 to 9.
[0117] A gate insulation film (SiON film) 2 having a thickness of 8
nm is formed on a semiconductor substrate (silicon substrate) 1. A
floating gate film (P-doped polycrystalline silicon film) 3 having
a thickness of 80 nm is formed on the gate insulation film 2. A CMP
stopper film (SiN film) 4 for protecting the gate insulation film 2
and the floating gate film 3 from chemical mechanical polishing
(CMP) is formed on the floating gate film 3 so as to have a
thickness of 70 nm. Then, over the whole surface of the
semiconductor substrate 1, a mask material film (silicon oxide) 5
serving as a mask for reactive ion etching (RIE) is formed so as to
cover the CMP stopper film 4 by using the chemical deposition (CMP)
method. In addition, a photoresist film material 6 is applied over
the whole surface of the semiconductor substrate 1 so as to cover
the mask material film 5 by using the spin coating method. As a
result, a photoresist film 16 is formed (see FIG. 3(A)).
[0118] Then, a desired pattern is formed in the photoresist film 16
by using the lithography technique, and a photoresist pattern 26 is
formed (see FIG. 3(B)).
[0119] A pattern is formed in the mask material film 5 by using the
photoresist pattern 26 having the pattern formed therein as a mask
and using the RIE method. As a result, the mask material film 5
becomes a hard mask 15 (see FIG. 4(A)).
[0120] The photoresist pattern 26 is removed by usher processing
and etching using a mixed solution of sulfuric acid and hydrogen
peroxide water (see FIG. 4(B)).
[0121] Then, the CMP stopper film 4, the floating gate film 3 and
the gate insulation film 2 are successively etched by using the
hard mask 15 as a mask and using the RIE method. In addition, the
semiconductor substrate 1 is etched until the etching depth becomes
220 nm as compared with the thickness of the semiconductor
substrate 1. As a result, a plurality of trenches (element
isolation trenches) 50 extending from the CMP stopper film 4 to the
semiconductor substrate 1 are formed. For example, the trench 50
formed between one pair of adjacent memory cells 60 has a width of
30 nm, and each of the trenches in a peripheral circuit in which a
plurality of control transistors are arranged has a width of at
least 100 nm (see FIG. 5(A)).
[0122] Then, a silicon compound solution 8 is applied over the
whole semiconductor substrate 1 having the trenches 50 formed
therein.
[0123] To be more precise, the silicon compound is, for example,
polysilazane (polyperhydrosilazane) [--(SiH.sub.2NH)n--], hydrogen
silses quioxane (HSQ) [--(HSiO.sub.3/2)n--], or the like, and it is
a silicon compound which is finally oxidized to become silicon
oxide (coated silicon oxide). In addition, the silicon compound
solution 8 is obtained by dissolving such a silicon compound in an
organic solvent such as dibutyl ether or xylene.
[0124] Here, a solution obtained by dissolving polyperhydrosilazane
having an average molecular weight in the range of 2,000 to 6,000
in dibutyl ether which is an organic solvent is used as the silicon
compound solution 8. Therefore, it is supposed in the ensuing
description that the polysilazane solution is used as the silicon
compound solution 8.
[0125] The polysilazane solution 8 is applied so as to cover the
whole surface of the semiconductor substrate 1 and occupy the whole
trenches 50. By doing so, the polysilazane solution 8 having a
thickness in the range of approximately 400 to 600 nm with
reference to the top surface of the hard mask 15 and taking the
shape of a film is formed over the semiconductor substrate 1 (see
FIG. 5(B)).
[0126] Subsequently, pre-baking (heating processing) is conducted
on the polysilazane solution 8 by using a hot plate under the
condition of 150.degree. C. and three minutes. As a result, dibutyl
ether (solvent) is evaporated from the polysilazane solution 8,
which exists as a film over the semiconductor substrate 1 and in
the trenches 50, and a polysilazane film (silicon compound film) 18
is formed over the semiconductor substrate 1 and in the trenches
50. In this stage, the polysilazane film 18 contains a very small
amount of the organic solvent, and its composition is close to a
composition of the SiN film having a low crystalline density (see
FIG. 6(A)).
[0127] Then, reforming (the first oxidation processing) is
conducted on the polysilazane film 18 by exposing the polysilazane
film 18 to an ozone atmosphere at a temperature (first temperature)
which is lower than a temperature (second temperature) of ensuing
high temperature oxidation processing (second oxidation
processing), to be more precise, at a temperature of 300.degree. C.
or less and oxidizing the surface of the polysilazane film 18. In
other words, the surface of the polysilazane film 18 is formed as a
volatile matter emission preventing layer (silicon oxide film) 28
through which an oxidizing agent such as oxygen, ozone, or water
and impurities such as nitrogen or hydrogen can pass and a volatile
matter containing silicon atoms cannot pass. To be more precise, a
part of the polysilazane film 18 located at depths in the range of
approximately 40 to 50 nm from the surface of the polysilazane film
18 is oxidized and reformed to form the volatile matter emission
preventing layer (silicon oxide film) 28 (see FIG. 6(B)).
[0128] This reforming (the first oxidation processing) is conducted
by, for example, irradiating the polysilazane film 18 with light
from excimer UV lamp in the air at the room temperature for several
minutes. By doing so, oxygen contained in the air by approximately
20% is changed to ozone by the UV light. This ozone functions as
the oxidizing agent and conducts reforming of oxidizing the surface
of the polysilazane film 18. In addition, the surface of the
polysilazane film 18 can be oxidized by using an alternative
method, for example, by heating the whole semiconductor substrate 1
on the hot plate at a temperature of 300.degree. C. or less for ten
minutes to one hour while exposing the whole semiconductor
substrate 1 to an ozone atmosphere (with an ozone concentration of
at least 200 g/m.sup.3).
[0129] Then, in order to oxidize up to the inside of the
polysilazane film 18 and form a coated silicon oxide film
(insulation film) 38 integrated with the volatile matter emission
preventing layer, high temperature oxidation processing (the second
oxidation processing) is conducted on the polysilazane film 18. For
example, heating in the range of 300 to 1,000.degree. C. is
conducted in an atmosphere such as H.sub.2O, O.sub.2 or N.sub.2 as
the high temperature oxidation processing. In an alternative
method, for example, heat treatment is conducted at 500.degree. C.
in a steam (H.sub.2O) atmosphere for five minutes. Incidentally,
conditions such as the temperature of the high temperature
oxidation processing depend upon desired performance of the element
to be fabricated. By doing so, the coated silicon oxide film 38 is
formed (see FIG. 7(A)).
[0130] Then, ozone oxidation processing (the third oxidation
processing) is conducted to expose the coated silicon oxide film 38
to an ozone atmosphere at a temperature (third temperature) which
is lower than a temperature of ensuing annealing (heating
processing), to be more precise, at a temperature of 300.degree. or
less. As a result, an unoxidized part in the coated silicon oxide
film 38 is oxidized without making the bond structure of the coated
silicon oxide film 38 firm as described earlier. To be more
precise, hydrogen and nitrogen remaining in the coated silicon
oxide film 38 are removed and replaced by oxygen without making the
bond structure of the coated silicon oxide film 38 firm.
[0131] In this process as well, a method similar to the method used
in forming the volatile matter emission preventing layer 28 can be
used. In other words, in the air at the room temperature, the
method for irradiating the coated silicon oxide film 38 with UV
light from an excimer UV lamp for approximately several minutes can
be used. Alternatively, the whole semiconductor substrate 1 may be
heated on the hot plate at 300.degree. C. or less for a time period
in the range of ten minutes to one hour while exposing the whole
semiconductor substrate 1 to an ozone atmosphere (with an ozone
concentration of at least 200 g/m.sup.3).
[0132] Then, anneal processing (heating processing) is conducted on
the coated silicon oxide film 38 in a nitrogen atmosphere at
850.degree. C. for 30 minutes. By doing so, the coated silicon
oxide film 38 embedded in trenches 50 has a firm bond
structure.
[0133] Then, planarization processing is conducted to planarize the
coated silicon oxide film 38 by using the CMP stopper film 4 and
the CMP method. At this time, extra coated silicon oxide film 38 on
the surface of the semiconductor substrate 1, i.e., a part of the
coated silicon oxide film 38 which is not embedded in the trenches
50 is removed by the planarization using the CMP method. At this
time, the hard mask 15 is also removed simultaneously (see FIG.
7(B)).
[0134] In addition, the coated silicon oxide film 38 embedded in
the trenches 50 is etched (etched back) by 120 nm in the thickness
direction of the semiconductor substrate 1 by using the RIE method.
By doing so, the top surface of the coated silicon oxide film 38
embedded in the trenches 50 is located in a middle position of the
thickness of the floating gate film 3 of each memory cell 60
disposed on both sides of each trench 50 so as to have the trench
50 between (see FIG. 8(A)).
[0135] Then, the CMP stopper film 4 is removed by using phosphoric
acid heated to 150.degree. C. (see FIG. 8(B)).
[0136] Then, an ONO (silicon oxide film--silicon nitride
film--silicon oxide film) film 9 which becomes an inter-electrode
insulation film (IPD) is formed as a single layer so as to cover
the top surface of the coated silicon oxide film 38 and the top
surface and parts of side walls of the floating gate film 3 in the
memory cell 50. Then, a control gate electrode film (P-doped
polycrystal Si film) 10 is formed on the ONO film 9. A WSi film 11
is formed on the control gate electrode film 10. A SiN film 12 is
formed on the WSi film 11. In addition, the SiN film 12, the WSi
film 11, the control gate electrode film 10, the ONO film 9 and the
floating gate film 3 are successively processed to have a desired
shape by using the known lithography technique and the RIE method
(see FIG. 9).
[0137] Thereafter, a process for forming an interlayer insulation
film (PMD) and interconnections and other processes are executed.
Finally, a NAND flash memory is completed.
[0138] As a modification of the present embodiment, warm water
processing can also be added to improve electrical characteristics
of the coated silicon oxide film. Hereafter, details thereof will
be described.
[0139] The polysilazane film 18 is formed by coating the
polysilazane solution 8 to the semiconductor substrate 1 and
conducting pre-baking (heating processing) on the polysilazane
solution 8. In addition, the volatile matter emission preventing
layer 28 is formed by exposing the polysilazane film 18 to an ozone
atmosphere of 300.degree. C. or less (the first oxidation
processing). Then, warm water processing is executed on the
polysilazane film 18 (details such as conditions will be described
later). Water is made to penetrate into the polysilazane film 18
via the volatile matter emission preventing layer 28 by the warm
water processing. Then, high temperature oxidation processing (the
second oxidation processing) is conducted at a temperature in the
range of 300 to 1,000.degree. C. under the presence of an oxidizing
agent to form the coated silicon oxide film 38. In addition, the
coated silicon oxide film 38 is exposed to an ozone atmosphere of
300.degree. C. or less (the third oxidation processing) in the same
way as the embodiment described earlier, and then anneal processing
(heating processing) is conducted on the coated silicon oxide film
38 in a N.sub.2 atmosphere. Ensuing processes are the same as those
in the embodiment described earlier.
[0140] To be more precise, this warm water processing is conducted
by immersing the polysilazane film 18 in pure water kept at a
temperature in the range of 50.degree. C. to 70.degree. C. for
several minutes to approximately one hour.
[0141] In addition, the oxidation processing (the second oxidation
processing) in the range of 300.degree. C. to 1,000.degree. C.
under the presence of the oxidizing agent may be conducted a
plurality of times as another modification of the present
embodiment. In addition, if oxidation processing is thus conducted
a plurality of times, ozone processing (the third oxidation
processing) of exposing the coated silicon oxide film 38 to an
ozone atmosphere of 300.degree. C. or less may be conducted a
plurality of times in the intervals of oxidation processing.
[0142] According to the first embodiment of the present invention,
it is possible to obtain an insulation film of coated silicon oxide
having few defects and a good quality by preventing contraction of
the coated silicon oxide film and suppressing the generation of the
film stress in the coated silicon oxide film as heretofore
described.
SECOND EMBODIMENT
[0143] According to a second embodiment, an impurity diffusion
preventing film (silicon oxide film) 7 is formed after the trenches
(element isolation trenches) 50 are formed and before the
polysilazane solution 8 is applied to the whole surface of the
semiconductor substrate 1. Since the impurity diffusion preventing
film 7 is formed so as to cover side walls of each memory cell 60
and side walls of each trench 50, it is possible to obtain an
effect that a very small amount of impurities contained in the
coated silicon oxide film 38 are prevented from the coated silicon
oxide film 38 to the memory cells 60 located on both sides of the
coated silicon oxide film 38 and in addition adhesion force between
the coated silicon oxide film 38 and the side walls of the trench
50 is improved resulting in an increased mechanical strength of the
NAND flash memory.
[0144] As described earlier, a schematic plan view of the
semiconductor device according to the second embodiment is shown in
FIG. 2. Description of FIG. 2 will not be given here.
[0145] FIGS. 10 to 14 are schematic process sectional views showing
a manufacturing method of the semiconductor device according to the
second embodiment of the present invention. These views correspond
to a section obtained by cutting the semiconductor device according
to the embodiment of the present invention along a line A-A' shown
in FIG. 2.
[0146] Hereafter, the second embodiment will be described with
reference to FIGS. 10 to 14.
[0147] A gate insulation film 2 is formed on a semiconductor
substrate 1. A floating gate film 3, a CMP stopper film 4, a mask
material film 5, and a photoresist film 16 are formed successively
over the semiconductor substrate 1 according to a method similar to
that in the first embodiment. Then, a desired pattern is formed in
the photoresist film 16 as a photoresist pattern 26. In addition, a
pattern is formed in the mask material film 5 by using the
photoresist pattern 26 as a mask. As a result, a hard mask 15 is
formed. Then, the photoresist pattern 26 is removed. Then, the CMP
stopper film 4, the floating gate film 3, the gate insulation film
2 and the semiconductor substrate 1 are successively etched by
using the hard mask 15 as a mask and using the RIE method. As a
result, a plurality of trenches (element isolation trenches) 50 is
formed in the semiconductor substrate 1 (see FIG. 10(A)).
[0148] Then, the impurity diffusion preventing film 7 is formed. A
layer of silicon oxide having a thickness of 10 nm is formed so as
to cover the whole semiconductor substrate 1, to be more precise,
so as to cover the top surface and the side faces of the hard mask
15, the side faces of the CMP stopper film 4, the side faces of the
floating gate film 3, the side faces of the gate insulation film 2,
and the side walls and the bottom part of the trench 50, by using
silane gas (dichlorosilane or monosilane) and N.sub.2O as raw
materials and using the CVD method (see FIG. 10(B)).
[0149] Then, the polysilazane solution (silicon compound solution)
8 is applied according to the same method as that of the first
embodiment. At this time, the top surface of the semiconductor
substrate 1 is covered by the polysilazane solution 8, and insides
of the trenches 50 are filled with the polysilazane solution 8 (see
FIG. 11(A)).
[0150] Then, a polysilazane film (silicon compound film) 18 is
formed according to a method similar to that of the first
embodiment as shown in FIG. 11(B). In addition, a volatile matter
emission preventing layer 28 is formed as shown in FIG. 12(A)
(first oxidation processing). Then, a coated silicon oxide film 38
is formed as shown in FIG. 12(B) (second oxidation processing).
[0151] Then, processes shown in FIGS. 13(A), 13(B) and 14 are
executed by using the same method as that in the first embodiment.
Finally, a NAND flash memory is completed.
[0152] According to the second embodiment of the present invention,
it is possible to obtain an insulation film of coated silicon oxide
having few defects and a good quality by preventing contraction of
the coated silicon oxide film and suppressing the generation of the
film stress in the coated silicon oxide film in the same way as the
first embodiment as heretofore described. In addition, it is
possible to prevent a very small amount of impurities contained in
the coated silicon oxide film 38 from spreading to films included
in the memory cell 60.
THIRD EMBODIMENT
[0153] In the first embodiment described earlier, the reforming
(the first oxidation processing) for forming the volatile matter
emission preventing layer (the silicon oxide film) 28 is conducted
after the polysilazane solution (the silicon compound solution) 8
is pre-baked (subjected to the heating processing). In a third
embodiment, the volatile matter emission preventing layer 28 is
formed before pre-baking the polysilazane solution 8.
[0154] Even if the order of processes for forming the volatile
matter emission preventing layer 28 is thus changed, the same
effects as those of the first embodiment can be obtained. Because
the volatile matter emission preventing layer 28 formed of silicon
oxide has a property of preventing a volatile matter containing
silicon atoms from being emitted, passing an oxidizing agent such
as oxygen and impurities such as nitrogen through it, and passing a
solvent contained in the polysilazane solution 8 through it.
[0155] A semiconductor device according to the third embodiment
also has the same configuration as that of the semiconductor device
according to the first embodiment described earlier. As described
earlier, a schematic plan view of the semiconductor device
according to the third embodiment becomes the same as FIG. 2.
Description of FIG. 2 will not be given here.
[0156] FIGS. 15 to 17 are schematic process sectional views showing
a main manufacturing method of the semiconductor device according
to the third embodiment. FIGS. 15 to 17 correspond to a section
obtained by cutting the semiconductor device according to the third
embodiment along a line A-A' in FIG. 2.
[0157] Hereafter, a main manufacturing method in the third
embodiment will be described with reference to FIGS. 15 to 17. As
for the same processes as those in the first embodiment,
description will not be repeated.
[0158] A gate insulation film 2 is formed on a semiconductor
substrate 1. A floating gate film 3, a CMP stopper film 4, a mask
material film 5, and a photoresist film 16 are formed successively
over the semiconductor substrate 1 according to a method similar to
that in the first embodiment. In addition, a plurality of trenches
50 is formed in the semiconductor substrate 1 (see FIG. 15(A)).
[0159] Then, a polysilazane solution (silicon compound solution) 8
obtained by dissolving, for example, polysilazane in an organic
solvent (for example, dibutyl ether or the like) is applied to the
top face of the semiconductor substrate 1 and insides of the
trenches (element isolation trenches) 50. By doing so, a
film-shaped polysilazane solution 8 is formed on the top face of
the semiconductor substrate 1 and inside the trenches 50 (see FIG.
15(B)).
[0160] Then, reforming (the first oxidation processing) for
oxidizing the surface of the polysilazane solution 8 is conducted
by exposing the polysilazane solution 8 to an ozone atmosphere of
300.degree. C. or less, and a volatile matter emission preventing
layer (silicon oxide) 28 is formed on the surface of the
polysilazane solution 8 (see FIG. 16(A)). Incidentally, the
polysilazane solution 8 may be exposed to an oxygen or steam
atmosphere instead of being exposed to the ozone atmosphere.
[0161] In addition, pre-baking (heating processing) is conducted on
the polysilazane solution 8 by using a hot plate under the
condition of 150.degree. C. and three minutes. As a result, an
organic solvent is evaporated from the film-shaped polysilazane
solution 8 located under the volatile matter emission preventing
layer 28 via the volatile matter emission preventing layer 28, and
a polysilazane film (silicon compound film) 18 is formed under the
volatile matter emission preventing layer 28 and on the top face of
the semiconductor substrate 1 and inside the trenches 50 (see FIG.
16(B)).
[0162] Then, oxidation processing (second oxidation processing) for
oxidizing the polysilazane film 18 is conducted in the same way as
the first embodiment. By doing so, the polysilazane film 18 is
oxidized and integrated with the volatile matter emission
preventing layer 28, resulting in a coated silicon oxide film 38
(see FIG. 17).
[0163] Since ensuing processes are the same as those in the first
embodiment, description of them will not be repeated. In the same
way as the first embodiment, the processes shown in FIGS. 7(A),
7(B), 8(A), 8(B), and 9 are executed, and finally a NAND flash
memory is completed.
[0164] According to the third embodiment of the present invention,
it is possible to obtain an insulation film of coated silicon oxide
having few defects and a good quality by preventing contraction of
the coated silicon oxide film and suppressing the generation of the
film stress in the coated silicon oxide film in the same way as the
first embodiment as heretofore described.
FOURTH EMBODIMENT
[0165] In the embodiments heretofore described, the volatile matter
emission preventing layer (silicon oxide film) 28 is formed by
using ozone oxidation as the first oxidation processing. In a
fourth embodiment, the volatile matter emission preventing layer 28
is formed by using a method different from that in the embodiments
heretofore described. To be more precise, the volatile matter
emission preventing layer 28 of the oxide silicon is formed on the
surface of the polysilazane film 18 by irradiating the polysilazane
film (silicon compound film) 18 with oxygen radicals and thereby
oxidizing the surface of the polysilazane film 18.
[0166] A semiconductor device according to the fourth embodiment
also has the same configuration as that of the semiconductor device
according to the first embodiment described earlier. As described
earlier, a schematic plan view of the semiconductor device
according to the fourth embodiment becomes the same as FIG. 2.
Description of FIG. 2 will not be given here.
[0167] Schematic process sectional views showing a manufacturing
method of the semiconductor device according to the fourth
embodiment become the same as FIGS. 3 to 9.
[0168] Hereafter, the fourth embodiment will be described with
reference to FIGS. 3 to 9. As for the same processes as those in
the first embodiment, description will not be repeated.
[0169] A gate insulation film 2 is formed on a semiconductor
substrate 1. A floating gate film 3, a CMP stopper film 4, a mask
material film 5, and a photoresist film 16 are formed successively
over the semiconductor substrate 1 according to a method similar to
that in the first embodiment (see FIG. 3(A)). In addition, a
plurality of trenches (element isolation trenches) 50 are formed in
the semiconductor substrate 1 via the processes shown in FIGS. 3(B)
to 4(B) (see FIG. 5(A)). Then, a polysilazane film (silicon
compound film) 18 is formed on the top face of the semiconductor
substrate 1 and inside the trenches 50 via the process shown in
FIG. 5(B) (see FIG. 6(A)).
[0170] Then, the polysilazane film 18 is irradiated with oxygen
radicals. The oxygen radicals can be generated by irradiating a
mixed gas of oxygen and argon gas with a microwave. To be more
precise, it is desirable to set oxygen contained in the mixed gas
equal to at least 5% and more desirable to set it equal to 25%. The
polysilazane film 18 is irradiated with the oxygen radicals thus
generated for at least one minute to conduct reforming for
oxidizing the surface of the polysilazane film 18. The volatile
matter emission preventing layer of silicon oxide (silicon oxide
film) 28 is formed on the surface of the polysilazane film 18 by
the reforming (see FIG. 6(B)).
[0171] In addition, high temperature oxidation processing (second
oxidation processing) for oxidizing the polysilazane film 18 is
conducted in the same way as the embodiments heretofore described.
By doing so, the polysilazane film 18 is oxidized and integrated
with the volatile matter emission preventing layer 28, resulting in
a coated silicon oxide film 38 (see FIG. 7(A)).
[0172] Since ensuing processes are the same as those in the first
embodiment, description of them will not be repeated. In the same
way as the first embodiment, the processes shown in FIGS. 7(B),
8(A) 8(B), and 9 are executed, and finally a NAND flash memory is
completed.
[0173] As a modification of the fourth embodiment, a method for
irradiating the polysilazane film 18 with OH radicals concurrently
with the oxygen radicals can be mentioned. Oxidation of the
polysilazane film 18 can be further promoted by irradiating the
polysilazane film 18 with the OH radicals concurrently with the
oxygen radicals. To be more precise, the OH radicals can be
generated concurrently with the oxygen radicals by further mixing
hydrogen gas with the mixed gas for generating the oxygen radicals
and irradiating a resultant mixed gas with a microwave. The
polysilazane film 18 is irradiated with the oxygen radicals and the
OH radicals thus generated. Other processes are the same as those
in the embodiments described earlier.
[0174] According to the fourth embodiment of the present invention,
it is possible to obtain an insulation film of coated silicon oxide
having few defects and a good quality by preventing contraction of
the coated silicon oxide film and suppressing the generation of the
film stress in the coated silicon oxide film in the same way as the
other embodiments heretofore described.
FIFTH EMBODIMENT
[0175] In the embodiments heretofore described, the volatile matter
emission preventing layer (silicon oxide film) 28 is formed by
using the ozone oxidation or oxygen radical irradiation as the
first oxidation processing. In a fifth embodiment, the volatile
matter emission preventing layer 28 is formed by using a method
different from that in the embodiments heretofore described. To be
more precise, reforming (first oxidation processing) of oxidizing
the surface of the polysilazane film 18 is conducted by implanting
oxygen ions in the polysilazane film (silicon compound film) 18,
and the volatile matter emission preventing layer 28 is formed. The
fifth embodiment has an advantage that the thickness of the formed
volatile matter emission preventing layer 28 can be controlled
easily by changing implantation conditions to be used when
implanting oxygen ions.
[0176] A semiconductor device according to the fifth embodiment
also has the same configuration as that of the semiconductor device
according to the first embodiment described earlier. A schematic
plan view of the semiconductor device according to the fifth
embodiment becomes the same as FIG. 2. Description of FIG. 2 will
not be given here.
[0177] Schematic process sectional views showing a manufacturing
method of the semiconductor device according to the fifth
embodiment become the same as FIGS. 3 to 9. Hereafter, the fifth
embodiment will be described with reference to FIGS. 3 to 9. As for
the same processes as those in the first embodiment, description
will not be repeated.
[0178] A gate insulation film 2 is formed on a semiconductor
substrate 1. A floating gate film 3, a CMP stopper film 4, a mask
material film 5, and a photoresist film 16 are formed successively
over the semiconductor substrate 1 according to a method similar to
that in the first embodiment (see FIG. 3(A)). In addition, a
plurality of trenches (element isolation trenches) 50 are formed in
the semiconductor substrate 1 via the processes shown in FIGS. 3(B)
to 4(B) (see FIG. 5(A)). Then, a polysilazane film (silicon
compound film) 18 is formed on the top face of the semiconductor
substrate 1 and inside the trenches 50 via the process shown in
FIG. 5(B) (see FIG. 6(A)).
[0179] Then, oxygen ions are implanted in the polysilazane film 18.
The film thickness of the volatile matter emission preventing layer
28 formed on the surface of the polysilazane film 18 can be
controlled according to the oxygen ion implantation condition at
this time. For example, oxygen ions are implanted in the
polysilazane film 18 under the condition that the oxygen ion
implantation energy is 10 keV and the oxygen ion implantation
quantity is 1.0.times.10.sup.14/cm.sup.2. By doing so, reforming
(first oxidation processing) of oxidizing the surface of the
polysilazane film 18 is conducted and a volatile matter emission
preventing layer (silicon oxide film) 28 of silicon oxide is formed
on the surface of the polysilazane film 18 (see FIG. 6(B)).
[0180] Then, high temperature oxidation processing (second
oxidation processing) is conducted to oxidize the whole
polysilazane film 18 in the same way as the embodiments heretofore
described. By conducting this processing, the polysilazane film 18
is oxidized and integrated with the volatile matter preventing
layer 28, resulting in a coated silicon oxide film 38 (see FIG.
7(A)).
[0181] Since ensuing processes are the same as those in the first
embodiment, description of them will not be repeated. The processes
shown in FIGS. 7(B), 8(A), 8(B), and 9 are executed, and finally a
NAND flash memory is completed.
[0182] According to the fifth embodiment of the present invention,
it is possible to obtain an insulation film of coated silicon oxide
having few defects and a good quality by preventing contraction of
the coated silicon oxide film and suppressing the generation of the
film stress in the coated silicon oxide film in the same way as the
other embodiments heretofore described. In addition, the thickness
of the formed volatile matter emission preventing layer 28 can be
controlled easily by changing the implantation condition used when
implanting oxygen ions.
SIXTH EMBODIMENT
[0183] In the conventional art already described, annealing is
conducted in an atmosphere of inert gas such as nitrogen in order
to transform the polysilazane film to a good quality silicon oxide
film, for example, in order to make a polysilazane film oxidized by
steam oxidation minuter.
[0184] As already described, film contraction occurs in the
polysilazane film at the time of this annealing. Therefore, stress
is applied to the foundation, and it becomes a cause of generation
of crystal defects in the semiconductor substrate.
[0185] If the surface of the applied polysilazane film is oxidized
by, for example, ozone (O.sub.3) generated by illuminance of UV
light from a UV lamp, then the film contraction of the polysilazane
film can be suppressed at the time of later annealing.
[0186] However, the applied polysilazane film is hardened by heat
which is generated by illumination of UV light from the UV
lamp.
[0187] The present inventors have found that even if the later
steam oxidation and annealing are conducted in the case where
hardening of the polysilazane film is caused the polysilazane film
is not oxidized sufficiently and a silicon oxide film having
desired characteristics cannot be formed.
[0188] Therefore, the present inventors propose a method for
forming a silicon oxide film which improves the film quality of the
silicon oxide film while suppressing occurrence of crystal defects
in the semiconductor substrate.
[0189] Hereafter, a sixth embodiment according to the present
invention will be described with reference to drawings. Hereafter,
the case where a polysilazane solution is used as a solution
containing silicon will be described as an example. In this case, a
silicon oxide film is formed by conducting oxidation processing on
a polysilazane film (a film containing silicon or a silicon
compound film) obtained by volatilizing a solvent in the
solution.
[0190] As the solution containing silicon, however, a solution such
as a polysilane solution or a hydrosiloxane solution may be used.
In this case, a silicon oxide film is formed by conducting
oxidation processing on a polysilane film or a hydrosiloxane film,
which is a film containing silicon (a silicon compound film)
obtained by volatilizing the solvent in the solution.
[0191] In the sixth embodiment, especially an example of the case
where a silicon oxide film is embedded in STI trenches formed on
the semiconductor substrate will be described.
[0192] FIGS. 18 to 21 are sectional views in respective processes
of a silicon oxide film forming method according to the sixth
embodiment of the present invention. FIG. 22 is a diagram showing
an example of an apparatus which generates ozone by using UV light
and oxidizes the surface of the polysilazane film on the
semiconductor substrate. FIG. 23 is a diagram showing another
example of an apparatus which generates ozone by using UV light and
oxidizes the surface of the polysilazane film on the semiconductor
substrate.
[0193] First, a thermal oxidized film 602 having a thickness of,
for example, approximately 5 nm is formed on a semiconductor
substrate 601 by using the thermal oxidation method. And a silicon
nitride film 603 which becomes a polishing stopper film for later
CMP (Chemical Mechanical Polishing) is formed on the thermal
oxidized film 602 so as to have a thickness of, for example,
approximately 150 nm.
[0194] Then, a mask film (not illustrated) such as a silicon oxide
film which becomes a hard mask for RIE (Reactive Ion Etching) is
formed over the whole surface of the semiconductor substrate 601 by
using the CVD (Chemical Vapor Deposition) method. In addition, a
photoresist film (not illustrated) is applied onto this mask
film.
[0195] Then, the photoresist film is processed by using the
ordinary lithography technique. And the mask film is processed by
using the photoresist film as a mask and using RIE. Then, the
photoresist film is removed by etching using usher and a mixed
solution of sulfuric acid and hydrogen peroxide water.
[0196] Then, the silicon nitride film 603, the thermal oxidized
film 602 and the semiconductor substrate 601 are successively
processed by using the mask film as a hard mask and using RIE. As a
result, trenches having an etching depth of 300 nm are formed in
the semiconductor substrate 601 by using the spin coating
method.
[0197] Then, the mask film is removed selectively by using, for
example, hydrogen fluoride vapor. Subsequently, the inside face of
the trenches is subjected to thermal oxidation to form a thermal
oxidized film 604 having a thickness of 4 nm.
[0198] As a result, STI trenches 605 for STI are formed in the
semiconductor substrate 601 (FIG. 18).
[0199] Then, a polysilazane film 606 is formed over the whole
surface of the semiconductor substrate 601 having the STI trenches
formed therein (FIG. 19). To be more precise, the polysilazane film
606 is formed as described hereafter.
[0200] For example, a perhydrosilazane polymer
[(SiH.sub.2NH).sub.n] is scattered in xylene, dibutyl ether, or the
like to generate a perhydrosilazane polymer solution (polysilazane
solution). This perhydrosilazane polymer solution (solution
containing silicon) is applied onto the surface of the
semiconductor substrate 601.
[0201] The perhydrosilazane polymer is embedded inside the trenches
having a high aspect ratio without generating voids (unfilled) and
seams (seam-like unfilled parts) by coating the perhydrosilazane
polymer solution as described above.
[0202] A solvent in the applied perhydrosilazane polymer solution
is volatilized by heating processing to form a polysilazane film (a
film containing silicon) from the perhydrosilazane polymer on the
surface of the semiconductor substrate 601.
[0203] In other words, for example, the semiconductor substrate
having the applied film formed therein is heated to, for example,
150.degree. C. on a hot plate, and baked for several minutes. As a
result, the solvent in the perhydrosilazane polymer solution is
volatilized.
[0204] As heretofore described, the polysilazane film 606 is formed
over the semiconductor substrate 601 (FIG. 19).
[0205] Then, an apparatus shown in FIG. 22 brings the polysilazane
film 606 formed over the semiconductor substrate 601 which is
supported by a support part 63 into a state in which the
polysilazane film 606 is prevented from being hardened by heat from
a UV lamp 61. In this state, the UV lamp 61 is made to emit UV
light in an atmosphere containing oxygen (O.sub.2). As a result,
ozone (O.sub.3) is generated in the atmosphere. The surface of the
polysilazane film 606 is oxidized by the generated ozone.
[0206] In the present embodiment, a screening plate 64 is disposed
between the UV lamp 61 and the surface of the semiconductor
substrate 601 having the polysilazane film 606 formed thereon to
screen heat generated when the UV lamp 61 emits UV light as shown
in FIG. 22. As a result, the heat from the UV lamp 61 is screened
by the screening plate 64 to prevent the polysilazane film 606 from
being hardened by heat from the UV lamp 61. The UV lamp 61 includes
a cover 62 to determine the irradiation direction of the UV light,
and irradiation of the UV light is directed toward the screening
plate 64.
[0207] In the case where the UV lamp 61 emits UV light, the
irradiation direction of the UV lamp may be made parallel to the
surface of the semiconductor substrate 601 by the cover 62 as shown
in FIG. 23. As a result, heat from the UV lamp 61 is screened by
the cover 62, and the polysilazane film 606 can be prevented from
being hardened by heat from the UV lamp 61.
[0208] The UV lamp 61 may be disposed at a predetermined distance
from the semiconductor substrate 601 so as to prevent the
polysilazane film 606 from being hardened by heat from the UV lamp
61.
[0209] The atmosphere containing oxygen needs only to contain at
least oxygen (O.sub.2). For example, the atmosphere containing
oxygen may be the air or an atmosphere which is higher than the air
in oxygen concentration.
[0210] The ozone generated by emission of UV light from the UV lamp
61 may be made to flow as far as the vicinity of the surface of the
polysilazane film 606 by, for example, reducing the pressure in the
vicinity of the semiconductor substrate 601. As a result, the
surface of the polysilazane film 606 can be oxidized more
efficiently.
[0211] Then, impurities in the polysilazane film are removed by,
for example, steam-oxidizing the polysilazane film 606 with a
diffusion furnace.
[0212] Then, the polysilazane film 606 is annealed with the object
of making the film more minute. The annealing is conducted in dry
oxygen for 30 minutes under the condition that the heating
temperature is 900.degree. C. As a result, the polysilazane film
606 is changed (reformed) to a silicon oxide film 606a (FIG.
20).
[0213] Then, the silicon oxide film 606a is polished by using the
CMP technique and using the silicon nitride film 603 as a stopper.
As a result, the silicon nitride film 606a is made to remain only
within the STI trenches 605 (FIG. 21).
[0214] Thereafter, processes such as a process for removing the
silicon nitride film 603 in hot phosphoric acid and forming
elements like transistors follow.
[0215] Owing to the processes heretofore described, the film
quality of the silicon oxide film formed in the STI trenches can be
improved while suppressing occurrence of crystal defects in the
semiconductor substrate.
[0216] According to the silicon oxide film forming method in the
present embodiment, the film quality of the silicon oxide film can
be improved while suppressing occurrence of crystal defects in the
semiconductor substrate.
[0217] In the sixth embodiment, the case where the silicon oxide
film embedded in the STI trenches is formed has been described.
However, the present invention may also be applied to the case
where the silicon oxide film is formed as an interlayer insulation
film.
[0218] In the sixth embodiment, an example in which the
polysilazane film is used singly as the embedded film has been
described. However, similar operation effects can be brought about
even if, for example, a silicon oxide film is formed in STI
trenches by using the CVD method and then a polysilazane film is
formed by using the spin coating method.
[0219] In the sixth embodiment, the case where the polysilazane
solution is used as a solution containing silicon has been
described. In this case, a silicon oxide film is formed by
conducting oxidation processing on a polysilazane film (a film
containing silicon) obtained by volatilizing the solvent in the
solution.
[0220] However, a solution such as a polysilane solution or a
hydrosiloxane solution may be used. In this case as well, oxidation
processing is conducted on a polysilane film or a hydrosiloxane
film, which is a film containing silicon obtained by volatilizing
the solvent in the solution. As a result, a silicon oxide film is
formed.
* * * * *