U.S. patent application number 12/202095 was filed with the patent office on 2009-02-05 for nitriding method of gate oxide film.
This patent application is currently assigned to TOKYO ELECTRON LIMITED. Invention is credited to Seijii Matsuyama, Toshio Nakanishi, Shigenori Ozaki, Masaru Sasaki, Takuya Sugawara.
Application Number | 20090035950 12/202095 |
Document ID | / |
Family ID | 29544952 |
Filed Date | 2009-02-05 |
United States Patent
Application |
20090035950 |
Kind Code |
A1 |
Matsuyama; Seijii ; et
al. |
February 5, 2009 |
NITRIDING METHOD OF GATE OXIDE FILM
Abstract
A substrate processing method comprises the step of forming an
oxide film on a silicon substrate surface, and introducing nitrogen
atoms into the oxide film by exposing the oxide film to nitrogen
radicals excited in plasma formed by a microwave introduced via a
planar antenna.
Inventors: |
Matsuyama; Seijii;
(Kyoto-shi, JP) ; Sugawara; Takuya; (Nirasaki-Shi,
JP) ; Ozaki; Shigenori; (Amagasaki-Shi, JP) ;
Nakanishi; Toshio; (Amagasaki-Shi, JP) ; Sasaki;
Masaru; (Amagasaki-Shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
TOKYO ELECTRON LIMITED
Tokyo
JP
|
Family ID: |
29544952 |
Appl. No.: |
12/202095 |
Filed: |
August 29, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11616217 |
Dec 26, 2006 |
7429539 |
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12202095 |
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10988561 |
Nov 16, 2004 |
7232772 |
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11616217 |
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PCT/JP2003/006080 |
May 15, 2003 |
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10988561 |
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Current U.S.
Class: |
438/786 ;
257/E21.266 |
Current CPC
Class: |
H01L 21/31662 20130101;
H01L 21/0234 20130101; H01J 37/32935 20130101; H01L 21/3144
20130101; H01J 37/32082 20130101; H01L 21/02238 20130101; H01L
21/02252 20130101; H01L 21/02332 20130101 |
Class at
Publication: |
438/786 ;
257/E21.266 |
International
Class: |
H01L 21/314 20060101
H01L021/314 |
Foreign Application Data
Date |
Code |
Application Number |
May 16, 2002 |
JP |
2002-141654 |
Claims
1-15. (canceled)
16. A method for nitriding an oxide film, comprising the steps of:
forming an oxide film on a substrate; forming plasma of a mixed gas
of a rare gas and a nitriding gas over said oxide film; and
nitriding a surface of said oxide film by said plasma, said
nitriding step being conducted by said plasma formed under a
pressure of 60 Pa or more, said nitriding step thereby converting
said oxide film into an oxynitride film.
17. The method as claimed in claim 16, wherein said step of forming
said oxide film is conducted by any of a thermal annealing process
of said substrate or oxidation of said substrate by plasma
containing oxygen.
18. The method as claimed in claim 16, wherein said oxide film has
a thickness of 1 nm or more.
19. The method as claimed in claim 16, wherein said step of
nitriding said oxide film is conducted at a process temperature of
550.degree. C. or less.
20. A method for nitriding an oxide film, comprising the steps of:
forming an oxide film on a substrate; forming plasma of a mixed gas
of a rare gas and a nitriding gas on said oxide film; and nitriding
a surface of said oxide film by said plasma, said nitriding step
being conducted by said plasma formed under a pressure of 60-130
Pa, said nitriding step thereby converting said oxide film into an
oxynitride film.
21. The method as claimed in claim 20, wherein said step of forming
said oxide film is conducted by a thermal annealing process of said
substrate or oxidation of said substrate by plasma containing
oxygen.
22. The method as claimed in claim 20, wherein said rare gas is any
of a Kr gas or an Ar gas.
23. The method as claimed in claim 20, wherein said step of
nitriding said oxide film is conducted at a process temperature of
550.degree. C. or less.
24. The method as claimed in claim 20, wherein said nitrogen
concentration is controlled such that no nitrogen is detected at
said interface.
25. A method for nitriding an oxide film, comprising the steps of:
providing a substrate carrying thereon an oxide film; forming
plasma of a mixed gas of a rare gas and a nitriding gas on said
oxide film; and nitriding a surface of said oxide film by said
plasma, said nitriding step being conducted by said plasma formed
under a pressure of 60 Pa or less, said nitriding step thereby
converting said oxide film into an oxynitride film.
26. The method as claimed in claim 25, wherein said oxide film is
an oxide film formed by a thermal annealing process of said
substrate or oxidation of said substrate by plasma containing
oxygen.
27. The method as claimed in claim 25, wherein said oxide film has
a thickness of 1 nm or more.
28. The method as claimed in claim 25, wherein said nitriding step
is conducted with controlled nitrogen concentration such that there
is formed a peak of nitrogen concentration in said oxynitride film
below a top surface of said oxide film but above an interface of
said oxide film and said substrate.
29. A method for nitriding an oxide film, comprising the steps of:
providing a substrate carrying thereon an oxide film; forming
plasma of a mixed gas of a rare gas and a nitriding gas on said
oxide film; and nitriding a surface of said oxide film by said
plasma, said nitriding step being conducted by said plasma formed
under a pressure of 60-130 Pa, said nitriding step thereby
converting said oxide film into an oxynitride film.
30. The method as claimed in claim 29, wherein said oxide film is
an oxide film formed by a thermal annealing process of said
substrate or oxidation of said substrate by plasma containing
oxygen.
31. The method as claimed in claim 29, wherein said oxide film has
a thickness of 1 nm or less.
32. The method as claimed in claim 29, wherein said step of
nitriding said oxide film is conducted at a process temperature of
550.degree. C. or less.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present invention is a continuous-in-part application of
PCT/JP2003/006080 filed on May 15, 2003 based on Japanese Patent
Application 2002-141654 filed on May 16, 2002, the entire contents
of these are incorporated herein as reference.
BACKGROUND OF THE INVENTION
[0002] The present invention generally relates to substrate
processing method and more particularly to a nitriding method of an
oxide film formed on a silicon substrate surface.
[0003] With progress in the art of device miniaturization,
fabrication of ultrafine semiconductor devices having a gate length
of less than 0.1 .mu.m is now becoming possible.
[0004] In order to achieve improvement of operational speed of the
semiconductor device with such ultrafine semiconductor devices by
way of decrease of the gate length, there is a need to decrease the
thickness of the gate insulation film according to scaling law. In
the case of using a conventional thermal oxide film for the gate
insulation film, for example, it is necessary to reduce the
thickness of the gate insulation film to be equal to or smaller
than the conventional thickness of 1.7 nm. However, such a decrease
of thickness of the oxide film invites increase of the gate leakage
current through the oxide film as a result of tunneling effect.
[0005] Thus, there have been studies to use a high-K dielectric
film such as Ta.sub.2O.sub.5 or ZrO.sub.2 for the gate insulation
film in place of the conventional silicon oxide film. However,
these high-K dielectric films have a nature very much different
from that of the silicon oxide film used conventionally in the
semiconductor technology, and there remain numerous problems to be
solved before such high-K dielectric film is used for the gate
insulation film.
[0006] Contrary to this, a silicon nitride film has a material used
conventionally in the semiconductor processes, and is thought as
being a promising material for the gate insulation film of the
next-generation high-speed semiconductor devices in view of its
specific dielectric constant, which is twice as large as that of a
silicon oxide film.
[0007] Conventionally, a silicon nitride film has been formed on an
interlayer insulation film by a plasma CVD process. However, such a
CVD nitride film generally has the feature of large leakage
current, and the use thereof for a gate insulation film has been
inappropriate. In fact, no attempts have been made conventionally
to use a nitride film for a gate insulation film.
[0008] Meanwhile, there have been proposed recently the technology
of nitriding a surface of a silicon oxide film and convert the same
to an oxynitride film by generating N radicals or NH radicals by
introducing a gas containing nitrogen such as a nitrogen gas,
nitrogen and hydrogen gases or an NH.sub.3 gas into
microwave-excited rare gas plasma of Ar, Kr, or the like. The
oxynitride film thus formed has the feature of small oxide-film
equivalent thickness and also the feature of leakage current
characteristics comparable to or even surpassing that of a thermal
oxide film, and thus, the oxynitride film thus formed is thought as
being a promising material for the gate insulation film of the
next-generation high-speed semiconductor devices. Further, the
oxynitride film thus formed is chemically stable, and it is
possible to suppress, in the case a high-K dielectric film is
formed on the oxynitride film, the diffusion of metal elements in
the high-K dielectric film through the oxynitride film and
associated reaction of the high-K dielectric film with the silicon
substrate caused by way of such diffusion. Further, there is
proposed a technology of directly nitriding a silicon substrate
surface by such microwave plasma.
[0009] Conventionally, it has been known to introduce nitrogen into
an oxide film by a thermal annealing process conducted in nitrogen
ambient or by an implantation of nitrogen ions. On the other hand,
it is known that the nitrogen atoms introduced according to such a
process predominantly concentrate in the vicinity of the interface
between the silicon substrate and the oxide film. As a result, in
the case such a conventional oxynitride film is used for the gate
insulation film of a MOS transistor, there are caused problems such
as variation of the threshold voltage or degradation of mobility
caused by formation of the interface states.
[0010] Because of similar reasons, there can be caused
deterioration of semiconductor device characteristics also in the
case of an oxynitride film processed by N radicals or NH radicals
is used, instead of the desired improvement of semiconductor device
characteristics, unless the distribution of the nitrogen atoms in
the film is controlled appropriately.
SUMMARY OF THE INVENTION
[0011] Accordingly, it is a general object of the present invention
to provide a novel and useful substrate processing method wherein
the foregoing problems are eliminated.
[0012] Another object of the present invention is to provide a
nitridation method of an oxide film capable of optimizing
distribution of nitrogen atoms in the film.
[0013] Another object of the present invention is to provide a
substrate processing method, characterized by the steps of:
[0014] forming an oxide film on a silicon substrate surface;
[0015] introducing nitrogen atoms into said oxide film by exposing
said oxide film to nitrogen radicals or nitrogen ions excited in
microwave plasma.
[0016] According to the present invention, it becomes possible to
obtain an oxynitride film having optimum characteristics including
the leakage current characteristics by choosing processing pressure
according to an initial film thickness of the oxide film at the
time of nitriding an oxide film by microwave-excited nitrogen
radicals.
[0017] Other objects and further features of the present invention
will become apparent from the following detailed description when
read in conjunction with the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIGS. 1A and 1B are diagrams showing the construction of a
microwave plasma processing apparatus used with the present
invention;
[0019] FIGS. 2A-2C are diagrams showing the oxidation processing of
a silicon substrate and nitridation processing of an oxide film
conducted by the substrate processing apparatus of FIGS. 1A and 1B
according to a first embodiment of the present invention;
[0020] FIG. 3 is a diagram showing the distribution of the nitrogen
atoms in the oxynitride film obtained with an embodiment of the
present invention;
[0021] FIG. 4 is a diagram showing the time-dependent change of the
nitrogen atom distribution in the oxynitride film of FIG. 3;
[0022] FIG. 5 is a diagram showing the relationship between the
leakage current and the oxide-film equivalent thickness of the
oxide film associated with the nitridation process of the present
embodiment;
[0023] FIG. 6 is another diagram showing the relationship between
the leakage current and the oxide-film equivalent thickness of the
oxide film associated with the nitridation process of the present
embodiment;
[0024] FIGS. 7A-7C are diagrams showing the oxidation processing of
a silicon substrate and nitridation processing of an oxide film
according to a second embodiment of the present invention;
[0025] FIGS. 8A and 8B are diagrams respectively showing the
overall construction of the substrate processing system according
to a third embodiment of the present invention including the
substrate processing apparatus of FIGS. 1A and 1B and used with the
present invention for substrate processing and the construction of
a computer used for controlling the substrate processing system of
FIG. 8A;
[0026] FIG. 9 is a flowchart of the computer-controlled processing
according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0027] In the investigation constituting the foundation of the
present invention, the inventor of the present invention has
discovered, in the experiments of nitriding an oxide film by
nitrogen radicals excited by Ar gas plasma, that the distribution
of the nitrogen atoms in the film changes significantly depending
on the nitridation processing condition, especially the processing
pressure and processing time.
[0028] Thus the object of the present invention is to provide,
based on the foregoing knowledge, a nitridation method of an oxide
film capable of optimizing the distribution of the nitrogen atoms
in the film.
First Embodiment
[0029] FIG. 1A shows the schematic construction of a plasma
processing apparatus 10 used with the present invention.
[0030] Referring to FIG. 1A, the plasma substrate processing
apparatus 10 includes a processing vessel 11 in which a processing
space 11A is formed such that a stage 12 holding a substrate W to
be processed thereon is formed in the processing space 11A, wherein
the processing vessel 11 is evacuated by an evacuation system 11E
at an evacuation port 11C via a space 11B surrounding the stage 12
and an adaptive pressure controller 11D.
[0031] The stage 12 is provided with a heater 12A, wherein the
heater 12A is driven by a power source 12C via a line 12B.
[0032] Further, the processing vessel 11 is provided with a
substrate in/out opening 11g and a gate valve 11G cooperating
therewith for loading and unloading of the substrate W to be
processed to and from the processing vessel 11.
[0033] On the processing vessel 11, there is formed an opening in
correspondence to the substrate W to be processed on the stage 12,
and the opening is closed by a top plate 13 of quartz or a low-loss
ceramic such as alumina or AlN. Further, underneath the top plate
13, there are formed a gas ring 14 formed with a gas inlet path and
a large number of nozzle openings communicating therewith such that
the gas ring 14 faces the substrate W to be processed.
[0034] It should be noted that the cover plate 13 forms a microwave
window, and a flat microwave antenna 15 of a radial line slot
antenna or a horn antenna is provided on the top part of the top
plate 13.
[0035] In the illustrated example, a radial line slot antenna is
used for the flat microwave antenna 15, wherein it should be noted
that the radial line slot antenna includes a flat antenna main part
15A and a radiation plate 15C, wherein the radiation plate 15C is
provided at the opening part of the flat antenna main part 15A via
a retardation plate 15B of quartz or alumina.
[0036] The radiation plate 15C is provided with a large number of
slots 15a and 15b as will be explained with reference to FIG. 1B,
wherein the radial line slot antenna 15 is connected to a coaxial
waveguide 16 having an outer conductor 16A connected to the antenna
main part 15A of the radial line slot antenna 15 and a central
conductor 16B connected to the radiation plate 15C through the
retardation plate 15B. The coaxial waveguide 16 is connected to a
rectangular waveguide 110B via a mode conversion part 110A, wherein
the rectangular waveguide 110B is connected to a microwave source
112 via an impedance matcher 111. Thereby, the microwave source 112
supplies a microwave to the radial line slot antenna 15 via the
rectangular waveguide 110B and the coaxial waveguide 16.
[0037] FIG. 1B shows the construction of the radial line slot
antenna.
[0038] Referring to FIG. 1B showing the radiation plate 15C in a
plan view, it can be seen that the slots 15a and 15b are formed in
a concentric relationship in such a manner that a slot 15a and an
adjacent slot 15b form an angle of 90 degrees.
[0039] Thereby, the microwave supplied from the coaxial waveguide
16 spreads in the radial direction in the radial line slot antenna
15 with wavelength compression caused by the retardation plate 15B.
Thereby, the microwave is emitted from the slits 15a and 15b
generally in the direction perpendicular to the plane of the
radiation plate 15C in the form of a circular polarized
microwave.
[0040] Further, as shown in FIG. 1A, a rare gas source 101A such as
an Ar gas source and a nitrogen gas source 101B are connected to
the gas ring 14 via respective mass flow controllers 103A and 103N
and via respective corresponding valves 104A, 104N, 105A, 105N and
a common valve 106. As noted before, the gas ring 14 is provided
with a large number of gas inlet ports around the stage 12
uniformly, and the rare gas and the nitrogen gas supplied to the
gas ring 14 are introduced into the processing space 14A inside the
processing vessel 11 uniformly. In addition, an oxygen gas source
101O is connected to the gas ring 14 via a mass flow controller
103O and valves 104O and 105O in the illustrated example for
supplying oxygen to the processing vessel 11.
[0041] In operation, the processing space inside the processing
vessel 11 is set to a predetermined pressure by evacuating through
the evacuation port 11C, and an oxidizing gas or a nitriding gas is
introduced from the gas ring 14 together with an inert gas such as
Ar, Kr, Xe, Ne, Ne (rare gas) and the like.
[0042] Further, a microwave having the frequency of several GHz
such as 2.45 GHz is introduced from the microwave source 112 via
the antenna 15, and there is excited high-density microwave plasma
in the processing vessel 11 at the surface of the substrate W to be
processed with a plasma density of 10.sup.11-10.sup.13/cm.sup.3. By
exciting the plasma by the microwave introduced via the antenna,
the plasma has low electron temperature of 0.7-2 eV or less,
preferable 1.5 eV or less, with the substrate processing apparatus
of FIG. 1A, and damaging of the substrate W or the inner wall of
the processing vessel is avoided. Further, the radicals thus formed
are caused to flow in the radial direction along the surface of the
substrate W to be processed and are evacuated promptly. Thereby,
recombination of the radicals is suppressed, and an extremely
uniform and efficient substrate processing is realized at the low
temperature of 550.degree. C. or less.
[0043] FIGS. 2A-2C show the substrate processing process according
to an embodiment of the present invention that uses the substrate
processing apparatus 10 of FIGS. 1A and 1B.
[0044] Referring to FIG. 2A, a silicon substrate 21 is introduced
into the processing vessel 11 of the substrate processing apparatus
10 as a substrate W to be processed, and a mixed gas of Kr and
oxygen is introduced from the gas ring 14. Further, atomic state
oxygen O* (oxygen radial) is formed by exciting the same with
microwave-plasma. As a result of processing of the surface of the
silicon substrate 21 with such atomic state oxygen O*, there is
formed a silicon oxide film 22 on the surface of the silicon
substrate 21 with the thickness of 1.6 nm as shown in FIG. 2B. The
silicon oxide film 22 thus formed has a leakage current
characteristic comparable with that of a thermal oxide film formed
at a high temperature of 700.degree. C. or more, in spite of the
fact that it is formed at a very low temperature of about
400.degree. C. Alternatively, the silicon oxide film 22 may be a
thermal oxide film.
[0045] Next, in the step of FIG. 2C, a mixed gas of Ar and nitrogen
is introduced into the processing vessel 11 in the substrate
processing apparatus 10 of FIGS. 1A and 1B, and excitation of
plasma is made by supplying a microwave power while setting the
substrate temperature to about 400.degree. C.
[0046] In the step of FIG. 2C, it should be noted that the internal
pressure of the processing vessel 11 is set to 5-7 Pa and the Ar
gas is supplied with the flow rate of 1000 SCCM, for example.
Further, the nitrogen gas is supplied with the flow rate of 40
SCCM, for example. As a result, the surface of the silicon oxide
film 22 is nitrided and is converted to a silicon oxynitride film
22A.
[0047] FIG. 3 shows the SIMS profile showing the distribution of
the oxygen atoms and nitrogen atoms (continuous line A) in the
oxynitride film 22A thus processed with the nitridation
processing.
[0048] Referring to FIG. 3, the interface between the oxynitride
film 22A and the silicon substrate 21 is located at the depth of
about 1.6 nm, and it can be seen that there appears a maximum
concentration of the nitrogen atoms at the central part of the
oxynitride film 22A in the thickness direction. Further, the result
of FIG. 3 indicates that the nitrogen atoms distribute generally in
the entirety of the oxynitride film 22A except for the film surface
and the region right underneath the film surface, while this also
means that there exits substantial amount of nitrogen atoms also in
the vicinity of the interface between the oxynitride film 22A and
the silicon substrate 21.
[0049] FIG. 3 also shows the distribution of the nitrogen atoms in
the oxynitride film 22A for the case the processing of FIG. 2C is
conducted under the same condition except that the processing
pressure is changed to 60-130 Pa by a broken line B.
[0050] Referring to FIG. 3 again, it will be noted that the number
of the nitrogen atoms incorporated into the oxynitride film 22A is
decreased in the case the nitridation processing of FIG. 2C is
conducted under such a high processing pressure, as compared with
the case the processing pressure is low, and associated with this,
the nitrogen concentration in the film is reduced also.
Particularly, in the case the nitridation processing is conducted
under such a high processing pressure, it will be noted that the
nitrogen concentration in the vicinity of the interface between the
oxynitride film 22A and the silicon substrate 21 is below the
detection limit and that there exist little nitrogen in such a
part.
[0051] Thus, by conducting the nitridation processing of the oxide
film of FIG. 2C at high processing pressure, it becomes possible to
restrict the distribution of the nitrogen atoms in the oxynitride
film 22A at the shallow part thereof. By using such an oxynitride
film 22A for the gate insulation film of a MOS transistor, it
becomes possible to eliminate the problem of degradation of the
carrier mobility or variation of the threshold voltage caused by
the existence of the nitrogen atoms in the vicinity of the
interface between the oxynitride film 22A and the silicon
substrate.
[0052] FIG. 4 is a diagram showing the time-dependent change of the
distribution of the nitrogen atoms in the film for the case the
nitridation processing of FIG. 2C is conducted at a high pressure
of 60-130 Pa (broken line) and the case in which the nitridation
processing is conducted at a low processing pressure (continuous
line).
[0053] Referring to FIG. 4, it will be noted that the depth of
penetration of the nitrogen atoms in the oxynitride film 22A is
limited in the case the processing pressure is high, and thus, it
is concluded that the nitridation processing conducted at a high
processing pressure exceeding 60 Pa is suited for introducing
nitrogen only to a part of an extremely thin oxide film such as the
one having the thickness of 1 nm or less. On the other hand, in the
case the processing pressure is low, the nitrogen atoms distribute
over the entirety of the oxide film, and thus, the nitridation
processing under low processing pressure of 60 Pa or less is
suitable for uniformly nitriding an oxynitride film of relatively
large thickness such as the one having the thickness of 1 nm or
more.
[0054] It is believed that the results of FIGS. 3 and 4 reflect the
situation that, in the case the processing pressure is increased in
the nitridation processing of FIG. 2C, there is caused a decrease
of electron temperature and the nitrogen ions formed in the plasma
are less susceptible for acceleration in the direction toward the
substrate. Thereby, the nitrogen ions are deactivated before they
reach the substrate and cause nitridation therein. In the case the
processing pressure is set low, on the other hand, there occurs
increase of electron temperature, and the nitrogen ions are
accelerated toward the substrate. Thereby, the nitrogen ions reach
the substrate in the active state and facilitate the nitridation
therein.
[0055] FIG. 5 shows the leakage characteristics of an N-type MOS
capacitor in which the oxynitride film formed according to the
method of the present invention is used for the gate insulation
film. In FIG. 5, it should be noted that the oxynitride film is
formed by two methods, the first being the one conducting the
nitridation processing of FIG. 2C for the oxide film having the
thickness of 1.6 nm under a high processing pressure of 60-130 Pa
for various processing durations and the second being the one
conducting the nitridation processing of FIG. 2C for the oxide film
having the thickness of 1.6 nm under a low pressure of 5-7 Pa,
wherein the vertical axis represents the gate leakage current
density Jg for the case a gate voltage of -1.8V is applied, while
the horizontal axis represents the oxide-film equivalent thickness
Tox.
[0056] In FIG. 5, the broken line shows the results for the case of
using the high processing pressure, while the continuous line
represents the case of using the low processing pressure.
[0057] Referring to FIG. 5, it will be noted that there is caused a
decrease in the oxide-film equivalent thickness Tox when the
nitridation processing of FIG. 2C is conducted under the foregoing
low processing pressure to about 1.4 nm as a result of penetration
of the nitrogen atoms into the oxide film, and there is also
achieved suppression of increase of the leakage current. On the
other hand, when the nitridation processing is continues for a long
time, there is caused a turn-around phenomenon, and the leakage
current starts to decrease, while this decrease of the leakage
current is accompanied with increase of the oxide-film equivalent
thickness Tox. It is believed that this reflects the situation
that, with extensive invasion of the nitrogen atoms into the oxide
film 12 at the time of formation of the oxynitride film 12A, the
oxygen atoms in the film start to invade into the silicon
substrate, resulting in the increase of the physical thickness of
the oxynitride film 12A. It should be noted that such invasion of
the oxygen atoms into the silicon substrate causes deterioration in
the interface between the oxynitride film 12A and the silicon
substrate 12. Thus, at the time of forming the oxynitride film 12A
by introducing nitrogen into the oxide film 12 in the step of FIG.
2C, it becomes possible to minimize the oxide-film equivalent
thickness Tox of the oxynitride film 12A without deteriorating the
film quality, by realizing the state immediately before the
turn-around.
[0058] In the case the nitridation processing of FIG. 2C is
conducted under the high processing pressure, on the other hand,
the amount of the nitrogen atoms incorporated into the film is
small, and thus, the decrease of the oxide-film equivalent
thickness is small as represented in FIG. 5 by the broken line. On
the other hand, the increase of the leakage current associated with
the decrease of the oxide film equivalent thickness is suppressed
further. Thus, it should be noted that the gradient of the curve
shown in FIG. 5 is smaller than the gradient of the curve
represented by the continuous line.
[0059] Thus, in the case the allowable leakage current is 1
A/cm.sup.2 for the applied voltage of -1.8V as shown in FIG. 6, it
will be noted that this allowable leakage current is exceeded when
the nitrogen atoms are introduced with the nitridation processing
at 5-7 Pa, provided that the oxide film has the initial thickness
of 1.45 nm in the state of FIG. 2B, as represented by an arrow
A.
[0060] In the example of FIG. 6, it will be noted that, in the case
the oxide film 12 has the initial thickness of about 1.6 nm as
shown by the arrow B, the leakage current density immediately
before the turn around point is generally equal to the allowable
limit value, provided that the foregoing nitridation processing is
conducted at the low pressure of 5-7 Pa. From this, it is concluded
that the leakage current exceeds the allowable limit in the case
the nitridation processing is conducted under the low pressure of
5-7 Pa for the oxide film 12 having the initial thickness of 1.6 nm
or less and that it is preferable to conduct the foregoing
nitridation processing under the high pressure of 60-130 Pa, not
with the foregoing low pressure.
[0061] In the case the nitridation processing is conducted in the
pressure range of 60-130 Pa, the proportion of increase of the
leakage current associated with the decrease of the equivalent
thickness is small, and thus, the requirement of the leakage
current value of 1 A/cm.sup.2 is satisfied even in the case the
initial thickness if less than 1.6 nm.
[0062] On the other hand, when the initial thickness of the oxide
film exceeds 1.6 nm, it is preferable to set the processing
pressure of the nitridation processing of FIG. 2C to be less than
30 Pa, preferably 5-7 Pa.
[0063] Thus, according to the present invention, it becomes
possible to achieve, at the time of nitridation processing of an
oxide film, the leakage current of the obtained oxynitride film to
fall within a desired allowable range, by choosing the processing
pressure of the nitridation processing in response to the thickness
of the initial film thickness of the oxide film.
Second Embodiment
[0064] FIGS. 7A-7C show the substrate processing process according
to second embodiment of the present invention that uses the
substrate processing apparatus 10 of FIGS. 1A and 1B.
[0065] Referring to FIG. 7A, a silicon substrate 41 is processed
with a so-called wet oxidation process by processing the silicon
substrate 41 in a furnace supplied with H.sub.2O (moisture).
[0066] With such a wet oxidation processing, there is formed a
silicon oxide film 42 on the surface of the silicon substrate 41
with the thickness of about 1 nm as shown in FIG. 7B.
[0067] Further, in the step of FIG. 7C, a mixed gas of Ar and
nitrogen is introduced into the processing vessel 11 in the
substrate processing apparatus 10 of FIGS. 1A and 1B, and
excitation of plasma is made by supplying a microwave while setting
the substrate temperature to about 400.degree. C.
[0068] In the step of FIG. 4C, the internal pressure of the
processing vessel 11 is set to 5-7 Pa, and the Ar gas is supplied
with the flow rate of 1000 SCCM, for example. Further, the nitrogen
gas is supplied with the flow rate of 40 SCCMM, for example. As a
result, the surface of the oxide film 42 is nitrided and is
converted to a silicon oxynitride film 42A, similarly to the
process of FIG. 2C.
Third Embodiment
[0069] FIG. 8A shows the construction of an overall substrate
processing system 100 that includes the substrate processing
apparatus 10 of FIGS. 1A and 1B and used for the nitridation
processing of the oxide film of the present invention, while FIG.
7B shows a computer used for controlling the substrate processing
apparatus 10 of FIGS. 1A and 1B in the system of FIG. 8A.
[0070] Referring to FIG. BA, the system 100 includes the Ar gas
source 101A, the nitrogen gas source 101B and the oxygen gas source
101O, wherein the Ar gas source 101A supplies an Ar gas to the gas
ring 14 of the substrate processing apparatus 10 via the mass flow
controller 103A and via the valves 104A and 105A and further via
the valve 106, while the nitrogen gas source 101B supplies a
nitrogen gas to the gas ring 14 via the mass flow controller 103N
and via the valves 104N and 105N and further via the valve 106
coupled to the gas ring 14 commonly to the gas supply path of the
Ar gas and the gas supply path of the nitrogen gas. Further, the
oxygen gas source 101O supplies an oxygen gas to the gas ring of
the substrate processing apparatus 10 via the mass flow controller
103O and the valves 104O, 105O and the valve 106.
[0071] Further, the system 100 includes the microwave power source
112 that supplies the microwave power to the radial line slot
antenna 15 via an impedance matcher 111.
[0072] Further, the heating mechanism 12A is provided in the stage
12 for temperature control of the substrate W to be processed.
[0073] Further, the system 100 includes the evacuation system 11E
coupled to the evacuation port 11C via the adaptive pressure
controller 11D.
[0074] Further, the system 100 includes the gate valve 11G
cooperating with the substrate in/out opening 11g provided on the
processing vessel 11 for loading and unloading the substrate W to
be processed to and from the processing vessel 11.
[0075] Further, it should be noted that there is provided a system
controller 100C that controls the mass flow controllers 103A, 103B,
and 103O, valves 104A, 104N, 104O, 105A, 105N, 105O and 106, the
heating mechanism 12H, an evacuation pump not illustrated, and
further the gate valve 11G according to the program held therein,
and the substrate processing apparatus 10 performs the foregoing
nitridation processing or oxidation processing and nitridation
processing of the oxide film under control of the controller
100C.
[0076] FIG. 8B shows the construction of the controller 100C.
[0077] Referring to FIG. 8B, the controller 100C is a general
purpose computer and includes a CPU 1001, a memory 1002 holding a
program and data, an interface unit 1003 connected to the system
100, and an I/O interface 1005 connected with each other by a
system bus 1004, wherein the computer 100C is provided with the
control program of the substrate processing system 100 from a
recording medium 1006 such as an optical disk or a floppy disk or
from a network 1007 and controls the substrate processing system
100 of FIG. 19A including the substrate processing apparatus 10 via
the interface unit 1003.
[0078] Thus, the present invention also includes such a computer
configured by the program code means recorded on a
processor-readable medium and also the processor readable medium
that carries such a program code.
[0079] FIG. 9 shows a nitridation processing corresponding to FIG.
2C or FIG. 7C conducted with the plasma substrate processing
apparatus 10 of FIGS. 1A and 1B under the control of the system
controller 101C.
[0080] Referring to FIG. 8, the processing vessel 11 is evacuated
in the step 1 by controlling the evacuation system 11E and the
adaptive pressure controller 11D, and the substrate W to be
processed is introduced into the processing vessel 11.
[0081] Next, in the step 2, the substrate W held on the stage 12 is
heated to a predetermined temperature by energizing the heater 12
via the power source 12C.
[0082] Next, in the step 3, the rare gas such as Ar is introduced
into the processing vessel 11 from the gas source 101A by
controlling the valves 104A, 105A and 106 and the mass flow
controller 103A, and the pressure inside the processing vessel 11
is controlled to a predetermined pressure by controlling the
adaptive pressure controller 11D.
[0083] Next, in the step 5, the microwave source 112 and the
impedance matcher 111 are controlled, and plasma is ignited in the
processing vessel 11A in correspondence to the processing space
11A.
[0084] Next, in the step 6, the nitrogen gas in the gas source 101N
is introduced into the processing vessel 11 by controlling the
valves 104N, 105N and 106 and further the mass flow controller
103N.
[0085] After the nitridation process, the plasma is deenergized in
the step 7 by controlling the microwave source 112 and the
impedance matcher 111, and the supply of the plasma gas and the
nitrogen gas is stopped by controlling the valves 104A, 104N, 105A,
105N, 106 and the mass flow controllers 103A and 1036B.
[0086] Further, in the step 9, the adaptive pressure controller 11D
and the evacuation system 11E are controlled and the pressure
inside the processing vessel 11 is controlled to a predetermined
pressure for taking out the substrate W thus processed.
[0087] Further, while the present invention has been described with
regard to preferable embodiments, it should be noted that the
present invention is not limited to such specific embodiments but
various variations and modifications may be made without departing
from the scope of the invention described in the claims.
[0088] According to the present invention, it becomes possible to
obtain an oxynitride film by a nitridation processing of an oxide
film that uses nitrogen radicals excited by a microwave introduced
by a planar antenna, such that the oxynitride film has optimum
characteristics including the leakage current characteristics, by
choosing the processing pressure in response to the initial
thickness of the oxide film.
* * * * *