U.S. patent application number 12/641064 was filed with the patent office on 2010-04-15 for tailoring nitrogen profile in silicon oxynitride using rapid thermal annealing with ammonia under ultra-low pressure.
Invention is credited to Arnaud Lepert, Gary E. Miner, Pravin K. Narwankar.
Application Number | 20100090294 12/641064 |
Document ID | / |
Family ID | 32850981 |
Filed Date | 2010-04-15 |
United States Patent
Application |
20100090294 |
Kind Code |
A1 |
Narwankar; Pravin K. ; et
al. |
April 15, 2010 |
TAILORING NITROGEN PROFILE IN SILICON OXYNITRIDE USING RAPID
THERMAL ANNEALING WITH AMMONIA UNDER ULTRA-LOW PRESSURE
Abstract
A method of forming a dielectric film that includes nitrogen.
The method includes incorporating nitrogen into a dielectric film
using a nitridation gas and a rapid thermal annealing process,
wherein an ultra-low pressure of equal to or less than about 10
Torr is used for the rapid thermal annealing process.
Inventors: |
Narwankar; Pravin K.;
(Sunnyvale, CA) ; Miner; Gary E.; (Fremont,
CA) ; Lepert; Arnaud; (Belmont, CA) |
Correspondence
Address: |
APPLIED MATERIALS/BSTZ;BLAKELY SOKOLOFF TAYLOR & ZAFMAN LLP
1279 OAKMEAD PARKWAY
SUNNYVALE
CA
94085-4040
US
|
Family ID: |
32850981 |
Appl. No.: |
12/641064 |
Filed: |
December 17, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
10772893 |
Feb 4, 2004 |
7658973 |
|
|
12641064 |
|
|
|
|
60445281 |
Feb 4, 2003 |
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Current U.S.
Class: |
257/411 ;
257/E29.255; 428/220; 501/154 |
Current CPC
Class: |
H01L 21/3105 20130101;
H01L 21/02255 20130101; H01L 29/66181 20130101; H01L 21/02238
20130101; H01L 21/28185 20130101; H01L 21/02337 20130101; H01L
21/3144 20130101; H01L 21/0214 20130101; H01L 29/518 20130101; H01L
21/02332 20130101 |
Class at
Publication: |
257/411 ;
428/220; 501/154; 257/E29.255 |
International
Class: |
H01L 29/78 20060101
H01L029/78; B32B 5/00 20060101 B32B005/00; C04B 35/14 20060101
C04B035/14; C04B 35/597 20060101 C04B035/597 |
Claims
1. A nitrogen-containing dielectric film, comprising: a dielectric
material; and a total amount of nitrogen incorporated into the
dielectric material, the total amount of nitrogen having a
concentration peak occurring at the top surface of the dielectric
film.
2. The nitrogen-containing dielectric film of claim 1, wherein the
total amount of nitrogen incorporated into the dielectric film has
an atomic concentration equal to or greater than 5% of the
nitrogen-containing dielectric film.
3. The nitrogen-containing dielectric film of claim 1, wherein the
dielectric material has a thickness equal to or less than about 12
angstroms.
4. The nitrogen-containing dielectric film of claim 1, wherein the
dielectric material is silicon dioxide (SiO.sub.2).
5. The nitrogen-containing dielectric film of claim 1, wherein the
nitrogen-containing dielectric film is a silicon oxynitride.
6. A gate stack, comprising: a nitrogen-containing dielectric film
comprising a dielectric material and a total amount of nitrogen
incorporated into the dielectric material, the total amount of
nitrogen having a concentration peak occurring at the top surface
of the dielectric film; and a cap layer disposed on the
nitrogen-containing dielectric film.
7. The gate stack of claim 6, wherein the total amount of nitrogen
incorporated into the dielectric film has an atomic concentration
equal to or greater than 5% of the nitrogen-containing dielectric
film.
8. The gate stack of claim 6, wherein the dielectric material has a
thickness equal to or less than about 12 angstroms.
9. The gate stack of claim 6, wherein the dielectric material is
silicon dioxide (SiO.sub.2).
10. The gate stack of claim 6, wherein the nitrogen-containing
dielectric film is a silicon oxynitride.
11. A silicon oxynitride film wherein a nitrogen concentration in
the silicon oxynitride film is greatest at the top surface of the
film and decreasing with depth, and the silicon oxynitride film is
free of unassociated nitrogen.
12. The silicon oxynitride film of claim 11, wherein the nitrogen
concentration is equal to or greater than 5%.
13. The silicon oxynitride film of claim 11, wherein the silicon
oxynitride film has a thickness equal to or less than about 12
angstroms.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 10/772,893 filed Feb. 4, 2004, which claims the benefit of
U.S. Provisional Patent Application No. 60/445,281 filed Feb. 4,
2003, the entire contents of which are hereby incorporated by
reference herein.
BACKGROUND
[0002] 1). Field
[0003] The present invention relates generally to the field of
semiconductor manufacturing. More specifically, the present
invention relates to a method of forming a silicon oxynitride (SiON
or SiO.sub.xN.sub.y) gate dielectric and integrating it into a gate
stack using Rapid Thermal Process (RTP).
[0004] 2). Description of the Related Art
[0005] Integrated circuits are made up of literally million of
active and passive devices such as transistors, capacitors and
resistors. A transistor 100 generally includes a source 102, a
drain 104, and a gate stack 106. The gate stack (FIG. 1) consists
of a substrate 108 (e.g., typically made of silicon) on top of
which is grown a dielectric 110 (typically made of silicon dioxide
(SiO.sub.2)) and this is capped with an electrode 112 (made with a
conductive material such as polycrystalline silicon).
[0006] In order to provide more computational power, the trend is
to scale down transistors by shrinking device geometry. Moore's law
scaling requires that the gate drive current must increase in order
to increase the speed of the transistor. The gate drive current
give by equation (1) can be increased by increasing the gate
capacitance (C.sub.ox), which in turn (as shown by equation (2))
can be increased by either decreasing the dielectric thickness (d)
or using a dielectric that has higher dielectric constant (k) than
the existing SiO.sub.2 dielectric (k=3.9).
I D ~ .mu. / Lg * C ox ( V DD - V TH ) 2 ( 1 ) C ox = kA d ( 2 )
##EQU00001##
where I.sub.D is the Drive Current; .mu. is the Carrier Mobility,
Lg is the gate length, C.sub.ox is the Gate Capacitance, V.sub.DD
is the Opening Voltage; V.sub.TH is the Threshold Voltage; k is the
dielectric constant, d is the dielectric thickness, and A is the
device area.
[0007] To avoid complex integration and materials handling issues,
device manufacturers would like to scale the device parameters as
much as they can by decreasing the dielectric thickness. However
lowering the SiO.sub.2 thickness below 20 .ANG. results in poor
gate reliability due to increase in tunneling current, increase in
boron penetration into the substrate and poor process control for
very thin oxide. While in theory the alternative of using a higher
k gate dielectric appears very attractive, the material
compatibility with the underlying Si substrate and the polysilicon
gate electrode cannot be matched to what is provided with
SiO.sub.2. Additionally, using SiO.sub.2 eliminates many materials
handling contamination issues that must be dealt with when
introducing rare-earth oxide as gate dielectrics.
[0008] Challenges encountered in extending SiO.sub.2 to 0.1 .mu.m
technology node and beyond, include (1) boron penetration in a
transistor such as a PMOS device with a P+ boron (B) doped gate
electrode into the gate oxide and underlying Si substrate. And, (2)
increasing gate leakage current with decreasing gate oxide
thickness.
[0009] Nitridation of the SiO.sub.2layer to form silicon oxynitride
(SiO.sub.xN.sub.y or alternatively SiON) has evolved as a promising
candidate to scale the SiO.sub.2 dielectric down to 0.1 device
generations. Incorporating nitrogen into the dielectric film blocks
boron as well as increases the dielectric constant of the gate
dielectric. The increase in the dielectric constant means a thicker
dielectric can be used in comparison to pure SiO.sub.2 hence
reducing gate leakage. For the nitrogen (N) doping to be effective
in circumventing the challenges described above in ultra-thin
(e.g., 12 .ANG.) gate dielectrics, it is essential to have high
(.gtoreq.5%) total concentration of nitrogen in the dielectric film
with the peak of the nitrogen concentration profile at the top
surface of the gate dielectric.
[0010] Traditionally, thermal processes have been carried out in
furnaces that process multiple wafers (5-100) at once. The furnaces
have large volumes and it is difficult to pump out this huge
volume. This coupled with the fact that the growth rate of most of
the thermal processes goes down with decrease in process pressure
has resulted in thermal processes usually being carried out at
atmospheric (760 Torr) or slightly below atmospheric (>500 Torr)
pressure.
[0011] Thermally grown silicon oxynitride has been used as gate
dielectrics for several years from the 0.2 .mu.m to 0.13 .mu.m
device generations. As the device technology has advanced from 0.2
.mu.m to 0.1 .mu.m the gate oxide has thinned from >25 .ANG. to
<12 .ANG.. Hence, in order to block boron and reduce gate
leakage the amount of nitrogen in the film has to be increased from
<3% to 5-10%. When nitric oxide (NO) and nitrous dioxide
(N.sub.2O) are used to grow the oxynitride gate dielectric the N
gets incorporated in the dielectric film simultaneously as the
oxynitride grows, hence nitrogen is distributed evenly in the film.
If NO or N.sub.2O are used to form silicon oxynitride by annealing
an existing SiO.sub.2 layer at elevated temperatures, the nitrogen
incorporated by growing SiON at the Si-substrate/Oxide interface.
Hence, nitrogen is incorporated at this interface. The amount of
nitrogen in the later case (<2%) is less than in the former case
(4-5%).
[0012] Silicon oxynitride grown directly with N.sub.2O or formed by
annealing an SiO.sub.2 film with N.sub.2O has been the favored
candidate for higher technology generations (0.2 .mu.m) devices.
The <2% nitrogen in the film was sufficient to enhance the
device performance with >25 .ANG. thick gate dielectric. As the
device technology advanced to 0.13 .mu.m, the nitrogen in the film
had to be increased from <2% to 4-5% by using NO direct growth
or NO anneal, in order to reduce the leakage current in comparison
to the undoped SiO.sub.2 and prevent boron from diffusing through
the thinner dielectric into the substrate. The amount of nitrogen
incorporated by either one of these techniques is insufficient and
the nitrogen concentration profile is inappropriate for extending
SiON to 0.1 .mu.m device generation as explained earlier. Lowering
the process pressure would only reduce the rate of nitrogen
incorporation into the film, hence the nitridation processes
continued to be carried out at elevated pressures.
[0013] More recently, plasma nitridation has been used to nitride
(to incorporate nitrogen into) the gate oxide. This technique
results in high nitrogen concentration at the poly gate/oxide
interface, which prevents boron penetration into the oxide
dielectric. At the same time, the bulk of the oxide dielectric gets
lightly doped with unassociated nitrogen during the plasma
nitridation process, which reduces the electrical oxide thickness
(EOT) over the starting oxide. The plasma nitridation process
requires plasma hardware that can among other things cause metal
contamination and plasma damage to the device and is difficult to
maintain as compared to the traditional thermal processing hardware
optimized for the front end processing. The challenges that plasma
nitridation currently faces is scaling of device parameters
Electrical Oxide Thickness (EOT) to <11 .ANG., Mobility
degradation and lowering of Drive Current (Idsat) with ultra-thin
dielectric (starting oxide <10 .ANG.) for high performance
application.
[0014] Another more recently adopted option has been thermal
ammonia (NH.sub.3) anneal which has been demonstrated to
incorporate nitrogen in the excess of 5% and under certain process
conditions can result in higher nitrogen content at the surface of
the dielectric than at the interface. This chemistry however has
not been as popular as the NO or N.sub.2O chemistries for several
reasons. The NH.sub.3 chemistry was production worthy when using
furnaces for the thermal nitridation, as O.sub.2 or moisture
(H.sub.2O) contamination even at the ppm level can prevent the
incorporation of nitrogen in the film or give inconsistent results.
In the case of furnace processing during the loading of wafers,
large volumes of air and moisture enters the furnace which takes
considerable amount of time to be removed resulting in inconsistent
incorporation of nitrogen in the film in the wafers from the edge
of the furnace to the center of the furnace. Unlike the NO and
N.sub.2O chemistries, NH.sub.3 anneal results in hydrogen
incorporation in the dielectric which results in hot electrons and
results in device reliability issues. It has been shown that the
hydrogen in the silicon oxynitride film can be eliminated by a post
nitridation anneal at elevated temperatures for short times in
either inert (N.sub.2 or Ar) or O.sub.2 ambient.
[0015] With the advent of Rapid Thermal Processing (RTP) and its
integration with other process chambers in a cluster type tool, the
NH.sub.3 process has become production worthy since the film can be
efficiently nitrided in a controlled ambient without an O.sub.2 or
H.sub.2O contamination as well as hydrogen in the film can be
eliminated by RTP anneal. However the problems of the interfacial
peak still remain. In the existing art, a base oxide SiO.sub.2 film
(grown in a single wafer RTP chamber or a furnace) is subjected to
ambients containing either pure NH.sub.3 or mixture of NH.sub.3 and
inert gas (N.sub.2 or Ar) at elevated temperatures (>850.degree.
C.) and atmospheric (760 Torr) or sub atmospheric (>500 Torr)
pressures. It has been observed, however, that this results in a
bimodal distribution of nitrogen within the starting SiO.sub.2
film, with one nitrogen peak at the silicon oxynitride surface (or
sometimes at the polysilicon cap/silicon oxynitride interface) and
a second peak at the silicon oxynitride/substrate interface. Such
bimodal distribution has been observed even at reaction pressures
as low as 100 Torr. The first peak is responsible for imparting
good electrical properties to the device such as boron blocking and
increasing the dielectric constant, thereby decreasing the leakage
current in the device as compared to the starting oxide of similar
electrical thickness. The second peak on the other hand imparts
poor interfacial properties to the gate stack resulting in larger
threshold voltage shifts and mobility degradation of charge
carriers in the transistor.
[0016] The kinetics of thermal nitridation of gate oxide with
NH.sub.3 has been studied for 80-100 .ANG. gate oxides. For the
silicon oxynitride dielectric film to be useful in the 0.1 .mu.m
device technology node and beyond the thickness has to be <25
.ANG. in the low leakage transistor devices and <12 .ANG. for
high performance transistors. The high pressure NH.sub.3 process
currently used for the silicon oxynitride formation will cause a
high concentration of nitrogen at the silicon oxynitride/substrate
interface resulting in poor device performance, limiting the
scaling of this process at 0.1 .mu.m technology and beyond.
SUMMARY
[0017] The current method of incorporating nitrogen into a
dielectric film such as SiO.sub.2 is not effective for forming an
ultra-thin silicon oxynitride (SiON or SiO.sub.xN.sub.y) film with
NH.sub.3 and integrating into a gate stack to scale for use in the
advanced technology nodes of 0.1 device and beyond for both high
performance and low leakage applications. As will be apparent from
the below, embodiments of the present invention fulfills this
long-standing need and desire in the art.
[0018] According to an aspect of the invention, a method of forming
a dielectric film includes incorporating nitrogen into a dielectric
film using a nitridation gas and a rapid thermal annealing process.
An ultra-low pressure of equal to or less than about 10 Torr is
used for the rapid thermal annealing process.
[0019] According to another aspect of the invention, a method of
forming a gate stack includes forming a silicon dioxide film on a
substrate. Nitrogen is then incorporated into a silicon dioxide
film using a rapid thermal annealing process and a nitridation gas,
wherein the rapid thermal annealing process occurs at about or less
than about 10 Torr. After the nitrogen is incorporated, the silicon
dioxide film becomes a silicon oxynitride film. The rapid thermal
annealing process is continued with the nitridation gas for a
sufficient amount of time for nitrogen to be incorporated into the
silicon dioxide film to form the silicon oxynitride with a nitrogen
concentration of about or more than 5%. A cap layer is formed on
the silicon oxynitride.
[0020] According to another aspect of the invention, a method of
forming a gate stack includes incorporating nitrogen into a silicon
dioxide film using a nitridation gas and a rapid thermal annealing
process. An ultra-low pressure of equal to or less than about 10
Torr is used for the rapid thermal annealing process. The
incorporating of nitrogen into the dielectric film forms a silicon
oxynitride film. The silicon oxynitride film is post-annealed after
a sufficient amount of nitrogen is incorporated into the silicon
dioxide film for form the silicon oxynitride.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Embodiments of the present invention is illustrated by way
of examples and not limitations in the figures of the accompanying
drawings, in which like references indicate similar elements and in
which:
[0022] Table 1 compares various ways of incorporating nitrogen into
a silicon dioxide film;
[0023] FIG. 1 illustrates an exemplary transistor;
[0024] FIG. 2 illustrates a nitrogen concentration profile when a
silicon oxynitride film is formed by a rapid thermal annealing
(RTA) process in the presence of ammonia (NH.sub.3) and high
pressure (e.g., about 100 Torr and above);
[0025] FIGS. 3A-3E illustrate the effect of reducing pressure on a
nitrogen concentration profile when a silicon oxynitride film is
formed by a rapid thermal annealing (RTA) process in the presence
of ammonia (NH.sub.3);
[0026] FIGS. 4A-4C illustrate the effect of processing temperature
on a nitrogen concentration profile when a silicon oxynitride film
is formed by a rapid thermal annealing (RTA) process in the
presence of ammonia (NH.sub.3) and ultra-low pressure (e.g., about
less than or equal to 10 Torr);
[0027] FIG. 5A-5C compares the nitrogen concentration profile of a
silicon oxynitride film formed by using plasma nitridation and by
using RTA with NH.sub.3; and
[0028] FIG. 6 illustrates cluster tool that can be used for some of
the embodiments of the present invention.
DETAILED DESCRIPTION
[0029] Embodiments of the present invention includes a novel method
of forming a dielectric film that includes nitrogen, such as SiON
or SiO.sub.xN.sub.y, using a rapid thermal annealing process with
ammonia and an ultra-low processing pressure (e.g., about equal to
or less than 10 Torr). In the following description, for purposes
of explanation, numerous specific details are set forth in order to
provide a thorough understanding of the present invention. It will
be evident, however, to one skilled in the art that the present
invention may be practiced without these specific details. In other
instances, specific apparatus structures and methods have not been
described so as not to obscure the present invention. The following
description and drawings are illustrative of the invention and are
not to be construed as limiting the invention.
[0030] In one embodiment, there is provided a method of forming a
silicon oxynitride dielectric film using a rapid thermal annealing
process with the presence of NH.sub.3 referred to herein as
RTA-NH.sub.3. The processing pressure for forming the silicon
oxynitride film is an ultra-low pressure (about equal to or less
than 10 Torr). In addition, varying the processing pressure allows
for the tailoring of the amount and distribution of nitrogen in the
silicon oxynitride film.
[0031] In another embodiment, there is provided a method of
integrating the silicon oxynitride film, (SiON film or
SiO.sub.xN.sub.y film) formed using the RTA-NH.sub.3 process into a
gate stack for forming a transistor.
[0032] In one embodiment, a substrate having a silicon dioxide
(SiO.sub.2) film formed there on is subjected to ammonia gas in a
single wafer rapid thermal processing (RTP) chamber configured to
carry out the rapid thermal annealing (RTA) process. The substrate
can be a monocrystalline silicon wafer or a silicon wafer typically
used in the art for making semiconductor devices. The SiO.sub.2
film may have a thickness about less than 30 .ANG. in one
embodiment. In one embodiment, the ammonia gas flow into the RTP
chamber ranges from about 100 sccm to 5 slm. It is to be
appreciated that the gas flow may vary depending on the size of the
processing chamber. For instance, the gas flows mentioned above are
for a 200 mm single wafer reactor chamber. The gas flows may be
proportionately increased for a 300 mm single wafer reactor chamber
owing to the increase in the reactor volume. In one embodiment, the
processing temperature ranges from 900-1100.degree. C. and the
processing pressure is about equal to or less than 10 Torr, or
alternatively, may ranges from 0.010 Torr to about 10 Torr. The
process uses either pure ammonia or ammonia diluted with an inert
gas such as Argon or Nitrogen. An SiON or SiO.sub.xN.sub.y is
formed as a result.
[0033] In one embodiment, a commercially available reduced pressure
RTP chamber hardware such as XE, XE Plus or Radiance made by
Applied Materials, Inc. is used to carry out the RTA-NH.sub.3
process to form the SiON or SiO.sub.xN.sub.y film. Such reduced
pressure RTP chamber provides an ultra-low processing pressure
(e.g., 1 Torr or less than 10 Torr) for the forming of the SiON or
SiO.sub.xN.sub.y using RTA-NH.sub.3. In one embodiment, a turbo
pump can be connected or added to the RTP chamber to assist in
lowering the total pressure of the RTP chamber to about 0.010 Torr
(or 10 mTorr).
[0034] It is observed that when the SiON or SiO.sub.xN.sub.y film
is formed by RTA in the presence of ammonia and at high pressure
(e.g., 100 Torr), the nitrogen concentration profile in the SiON or
SiO.sub.xN.sub.y film as determined by a method called
Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) indicates
that the nitrogen concentration profile has two peaks 202 and 204
as shown in FIG. 2. The first peak 204 indicates that the nitrogen
concentration is high (about 4.times.10.sup.21 units) at the oxide
surface and the second peak 202 indicates that there is also a
significant amount of nitrogen concentration (about
4.times.10.sup.21 units) at the substrate interface.
[0035] It is discovered by the inventors that changing the process
condition such as processing pressure, temperature, and time can
change the ratio of the intensities of these two peaks 204 and 202.
As shown in FIGS. 3A-3E, the process pressure has a high impact on
the ratio of the peak 202 and 204 intensities. As shown in FIGS.
3A-3E, when the pressure is reduced from 100 Torr to 0.250 Torr at
a fixed temperature of 1000.degree. C., the second peak 202 at the
substrate interface disappears completely. As can be seen from FIG.
3A, when the SiON or SiO.sub.xN.sub.y film is formed using
RTA-NH.sub.3 with a pressure at about 100 Torr, two peaks 202 and
204 are present. In FIG. 3B, when the SiON or SiO.sub.xN.sub.y film
is formed using RTA-NH.sub.3 with a pressure at about 10 Torr, the
peak 202 is decreasing indicating that the nitrogen concentration
at the substrate interface is decreasing. Similarly, as shown in
FIGS. 3C-3E, the peak 202 is decreasing until it is substantially
eliminated at a process pressure of about 0.25 Torr.
[0036] Additionally, increasing temperature while forming the SiON
or SiO.sub.xN.sub.y film at an ultra-low pressure (e.g., about
equal to or less than 10 Torr) enhances the nitrogen concentration
peak 204 at the surface as shown in FIGS. 4A-4C. For instance, in
FIG. 3B, when the nitridation used to form the SiON or
SiO.sub.xN.sub.y film is done using the RTA-NH3 at about 10 Torr
and about 1000.degree. C., the peak 204 is at about
3.2.times.10.sup.21 concentration units. In FIG. 4C, when the
nitridation used to form the SiON or SiO.sub.xN.sub.y film is done
using the RTA-NH3 at about 10 Torr and about 1100.degree. C.
(100.degree. C. higher) the peak 204 is at about 6.times.10.sup.21
concentration units.
[0037] Thus, it is optimal to form the SiON or SiO.sub.xN.sub.y
film at an ultra-low pressure (about .ltoreq.10 Torr) and high
temperature (.gtoreq.1000-1100.degree. C.). Having a high nitrogen
concentration at the first peak 204 (at the surface of the SiON or
SiO.sub.xN.sub.y film) and a low or substantially minimal nitrogen
concentration at the substrate interface provides an ideal profile
for an ultra-thin gate dielectric for advanced .ltoreq.0.1 .mu.m
technology nodes.
[0038] At low pressure, the nitrogen concentration dose in the SiON
or SiO.sub.xN.sub.y film can also be adjusted by changing the
temperature or alternatively, by changing the process time while
keeping the processing temperature fixed. For example, a similar
quality SiON or SiO.sub.xN.sub.y film is formed by nitridating a 6
.ANG. silicon dioxide using the RTA-NH.sub.3 process either at
about 1000.degree. C., 10 Torr, for 10 second or at about
1000.degree. C., 1 Torr, for 45 second. Thus, lowering the pressure
at a constant temperature requires increasing the time to achieve
the same nitrogen dose in a film of equivalent thickness.
[0039] FIG. 5 compares the nitrogen concentration profile for SiON
or SiO.sub.xN.sub.y film manufactured using a plasma nitridation
process with RTA-NH.sub.3 process. In one embodiment, the plasma
nitridation process used is Decoupled Plasma Nitridation (DPN)
which is known in the art. DPN is a technology using inductive
coupling to generate nitrogen plasma and incorporate a high level
of nitrogen onto an oxide film. DPN allows formation of the silicon
oxynitride film with less nitrogen at the oxide/substrate interface
and higher nitrogen concentration at the oxide surface. In DPN, a
surface, e.g., an SiO.sub.2 film, is bombarded with nitrogen ions
which break the SiO.sub.2 film and bond the nitrogen ions to the
SiO.sub.2 film forming an SiON or SiO.sub.xN.sub.y film. The
SiO.sub.2 film is thus exposed to decoupled nitrogen plasma. In one
embodiment, DPN is performed in a chamber with pressure ranging
from about 5-20 mTorr or less than 10 Torr, in the presence of
nitrogen gas with a flow rate ranging from about 100-200 sccm and
plasma power of about 300 Watt. The DPN process parameters can be
modified depending on the chamber size and volume thickness of the
dielectric film as is known in the art. The PDN yields an SiON or
SiO.sub.xN.sub.y film that does not have a second peak 202 at the
substrate interface. In addition, in both processes, the DPN and
the RTA-NH.sub.3 processes, the SiON or SiO.sub.xN.sub.y film is
characterized by having the greatest concentration of nitrogen
(N.sub.y) at the top surface of the dielectric film, with "y"
decreasing with depth. However, the tail of the nitrogen
concentration profile for the DPN process seems to be extended
closer to the Si substrate than the RTA-NH.sub.3 process carried
out at an ultra low processing pressure as shown in FIGS. 5B-5C.
This will be reflected in the increased drive current of the device
that incorporates the SiON or SiO.sub.xN.sub.y film formed using
the RTA-NH.sub.3 process than that of the SiON or SiO.sub.xN.sub.y
film formed using the plasma nitridation process. In addition, the
SiON or SiO.sub.xN.sub.y film formed using the RTA-NH.sub.3 process
will also be free of unassociated nitrogen. Another advantage of
the RTA-NH.sub.3 process over the DPN process is that is uses the
same RTP reactor that has been developed and optimized for the
front end anneals and SiO.sub.2 growth. The RTP chamber has been
optimized for ultra low metal contamination and issues that would
eliminate or minimize any impact to the device integrity and
reliability.
[0040] In one embodiment, the gate stack containing the
RTA-NH.sub.3 processed SiON or SiO.sub.xN.sub.y film is
manufactured in a cluster tool, such as an integrated Gate Stack
Centura made by Applied Materials, Inc., is used to form a gate
that has the SiON or SiO.sub.xN.sub.y film formed as previously
described for improved device performance. An example of cluster
tool is shown in FIG. 6.
[0041] FIG. 6 illustrates a cluster tool 600, which comprises
several processing chambers, e.g., loadlock chambers 602 and 604,
RTP chambers 606, 608, 610, a deposition chamber 612 (e.g., for
depositing a polysilicon film), and a cool down chamber 614. The
cluster tool 600 also includes a wafer-handling tool 616 used to
transfer a substrate 618 (e.g., wafer) in and out of particular
processing chamber. The wafer-handling tool 616 is typically
located in a transfer chamber that can communicate to all of the
processing chambers. The loadlock chambers 602 and 604 house
substrates (e.g., wafers) to be processed. The deposition chamber
612 can be conventional chemical or physical vapor deposition that
can be used to form a film or a layer as is known in the art. In
one embodiment, the deposition chamber 612 is a deposition chamber
that can be configured to form a polysilicon film or other
electrode film. The chambers 606, 608, and 610 are chambers that
can be configured to run a rapid thermal annealing (RTA) process at
a reduced or ultra-low pressure (e.g., about equal to or less than
10 Torr). Any one of the chambers 606, 608, and 610 can be used to
perform the RTA-NH.sub.3 process previously described to form an
SiON or an SiO.sub.xN.sub.y film.
[0042] In one embodiment, an SiO.sub.2 dielectric film with a
physical thickness of about 4-15 .ANG. is grown using a reduced
pressure RTP chamber such as the RTP chamber 606 of the cluster
tool 600 (FIG. 6). The SiO.sub.2 dielectric film can be formed by a
rapid thermal oxidation which is an oxidation process where the
chamber uses lamp(s) to quickly heat and dry a substrate surface to
form an oxidized layer in the presence of oxygen. The rapid thermal
oxidation of a silicon substrate (or a wafer) can be carried out
using a dry process rapid thermal oxidation with the presence of
O.sub.2, O.sub.2+N.sub.2, O.sub.2+Ar, N.sub.2O, or N.sub.2O+N.sub.2
gas mixtures. The gas or gas mixtures can have a total flow rate of
about 1-5 slm. Alternatively, the rapid thermal oxidation of a
silicon substrate can be carried out using a wet process such as
In-Situ Steam Generation (ISSG) with the presence of
O.sub.2+H.sub.2, O.sub.2+H.sub.2+N.sub.2, or N.sub.2O+H.sub.2
having, for example, a total flow rate of about 1-5 slm with 1-13%
H.sub.2. In one embodiment, the rapid thermal oxidation process to
form the SiO.sub.2 dielectric film is formed at a processing
temperature of about 800-1000.degree. C. and a processing pressure
of about 0.5-50 Torr for about 5-90 seconds which results in a
SiO.sub.2 dielectric film having a thickness in the range of 4-15
.ANG..
[0043] In one embodiment, after the SiO.sub.2 dielectric film is
formed in the RTP chamber 606, the substrate is transferred to
another RTP chamber, e.g., the RTP chamber 608 of the cluster tool
600 under an inert (e.g., N.sub.2 or Ar) environment with the
transfer chamber pressure being less than or about 10 Torr to
incorporate nitrogen into the SiO.sub.2 dielectric film to form an
SiON or SiO.sub.xN.sub.y film. The RTP chamber 608 can be a reduced
pressure chamber reactor such as an Applied Material reactor XE, XE
Plus, or Radiance. The RTP chamber 608 is configured to have
NH.sub.3, N.sub.2, or Ar gases plumbed to it to form an SiON or
SiO.sub.xN.sub.y as previous discussed. In one embodiment, the
substrate with the SiO.sub.2 dielectric film is heated to an
elevated temperature of about 900-1100.degree. C. with a flow of
pure NH.sub.3 or NH.sub.3+Inert gas (e.g., N.sub.2 or Ar) into the
processing chamber, e.g., the RTP chamber 608. The pressure in the
chamber is reduced to less than or about equal to 10 Torr. The SiON
or SiO.sub.xN.sub.y formed under this condition can have a profile
similar to those shown in FIGS. 3C-3D. The SiON or SiO.sub.xN.sub.y
has a nitrogen concentration equal to or great than 5%. The peak
concentration of the nitrogen within the SiO.sub.2 film occurs at
the top surface of the SiO.sub.2 film.
[0044] In one embodiment, the SiON or SiO.sub.xN.sub.y film is
subjected to a post nitridation annealing (PNA) process in another
RTP chamber such as the RTP chamber 610 of the cluster tool 600
(FIG. 6). The PNA process chemistry can either be pure N.sub.2 or
O.sub.2+N.sub.2 gas mixtures. In the event of a pure N.sub.2
chemistry, the PNA can be carried out in the same RTP chamber,
(e.g., the RTP chamber 600) as the RTA-NH.sub.3 process that is
used to form the SiON or SiO.sub.xN.sub.y film. In one embodiment,
the PNA includes heating up the substrate having the SiON or the
SiO.sub.xN.sub.y film to an elevated temperature of
1000-1100.degree. C. at less than or equal to about 5 Torr total
pressure. In one embodiment, pure N.sub.2 gas of about 1 slm is
flown into the RTP chamber (e.g., the RTP chamber 608 or 610) for
about 60 seconds. Follow the N.sub.2 flow, O.sub.2 or
O.sub.2+N.sub.2 gas mixture at about 1 slm total flow rate is flown
into the RTP chamber for about 15 seconds. It is to be appreciated
the flow rates mentioned are examples only for a particular reactor
or processing chamber size (e.g., a 200 mm reactor). The flow rates
are proportionately adjusted (increased or decreased) for other
size reactors owing to the difference in volume.
[0045] In one embodiment, following the PNA process, the nitrogen
containing gate dielectric (the SiON or SiO.sub.xN.sub.y) film is
capped with a conductive layer such as a polysilicon film. The
polysilicon film can be formed in a deposition chamber such as the
deposition chamber 612 of the cluster tool 600 (FIG. 6). This
completes the formation of the gate stack. The substrate can then
be transferred to a cool down chamber such as the cool down chamber
614 and then be transferred to a storage area such as the loadlock
614 for further processing, testing, or other processes as known in
the art.
[0046] It is to be appreciated that the gate stack that includes
the gate dielectric film and the polysilicon cap film can be formed
in one processing chamber or several processing chambers besides
the cluster tool 600 previously described. For instance, the
SiO.sub.2 dielectric film can be formed first in one chamber. Then,
the same chamber is adjusted for the rapid thermal annealing at the
ultra low pressure to perform the nitridation process to form the
SiON or SiO.sub.xN.sub.y film. Then the same chamber can be
adjusted to perform the PNA for the SiON or the SiO.sub.xN.sub.y
film. And, the polysilicon film is formed over SiON or
SiO.sub.xN.sub.y film in the same chamber.
[0047] A transistor formed with the gate stack as described herein
has optimized performance due to the continuous and uniform
processing environment or ambient owing to the use of the cluster
tool 600, in one embodiment. The processing of the gate stack is
formed without a break between any of the processes. Thus, better
scaling in terms of reduced Electrical Oxide Thickness, leakage, or
Drive Current can be achieved as compared to processes with breaks
in between various processes.
[0048] Table 1 summarizes the various processes of incorporating
nitrogen into an SiO.sub.2 film including conventional processes as
well as process of the exemplary embodiments of the present
invention. Table 1 illustrates that incorporating nitrogen into the
SiO.sub.2 film using exemplary embodiments of the present invention
gives superior nitrogen concentration profile. In addition, as
mentioned above, the exemplary embodiments of the present invention
allow one to tailor the nitrogen concentration profile to achieve
an optimum SiON or SiO.sub.xN.sub.y film for a particular
application.
[0049] As shown in Table 1, when the nitridation process is carried
out using NO or NO+O.sub.2 gas mixture using a mixture growth
process to thermally grow the SiON or SiO.sub.xN.sub.y film. The
nitrogen concentration ([N]) profile is incorporated throughout the
SiO.sub.2 film with a high nitrogen concentration at the substrate
interface. When the nitridation process is carried out using
N.sub.2O anneal using a conventional process, the nitrogen is
incorporated close to the Si substrate-SiO.sub.2 interface.
Further, the nitrogen concentration incorporated is insufficient to
block boron into the dielectric film or reduce leakage in 0.1 .mu.m
devices. When the nitration process is carried out using NO anneal
using a conventional process, the nitrogen is incorporated at the
Si substrate-SiO.sub.2 interface with the nitrogen concentration
being slightly higher compared to the N.sub.2O anneal process.
However, it has been observed that boron tends to be trapped inside
the SiO.sub.2 film resulting in poor interfacial properties and not
significant reduction in current leakage.
[0050] When the nitridation process is carried out using an
NH.sub.3 annealing process at high pressure that is equal to or
greater than 100 Torr as is currently practiced in the art, the
nitrogen is incorporated into the SiO.sub.2 film with a bimodal
nitrogen concentration distribution. As previously discussed, the
nitrogen concentration profile includes a nitrogen peak at the
surface of the film and a nitrogen peak at the substrate-SiO.sub.2
interface. The nitrogen concentration is higher in the NH.sub.3
annealing process at high pressure than the NO annealing process.
Nitrogen at the surface of the film tends to trap boron but
nitrogen at the substrate SiO.sub.2 interface causes poor
interfacial properties resulting in larger threshold voltage shifts
and mobility degradation of charge carriers in the transistor. When
the nitridation process is carried out using plasma nitridation, as
acceptable nitrogen concentration profile is produced. High
nitrogen concentration occurs at the surface of the SiO.sub.2 film.
Nitrogen at the surface can block the boron. Plasma nitridation
allows for ultra-thin dielectric film forming (<10 .ANG.) but is
shown to cause drive current to degrade at such ultra-thin
film.
[0051] When the nitridation process is carried out using an RTA
NH.sub.3 process at ultra-low pressure (e.g., Torr), of the
exemplary embodiments of the present invention, the nitrogen
concentration profile has high nitrogen concentration at the
surface of the SiO.sub.2 film and no bimodal distribution. Also,
the RTA-NH.sub.3 process at the ultra-low pressure allows for
Electrical Oxide Thickness scaling to less than 11 .ANG..
[0052] Although it has been describe that ammonia (NH.sub.3) is
used in many of the exemplary embodiments, it is to be appreciated
that any nitrodizing or nitridation gas can be used or substituted
for ammonia. For example, NO or N.sub.2O can be used to form the
SiON or SiO.sub.xN.sub.y using a rapid thermal annealing process at
an ultra-low pressure (e.g., equal to or less than about 10 Torr).
The discussion of the features of the embodiments using the
RTA-NH.sub.3 at ultra-low pressure is thus similarly applicable for
nitridation process using other suitable nitrodizing or nitridation
agents (e.g., NO and N.sub.2O ) using RTA at ultra-low
pressure.
[0053] While certain exemplary embodiments have been described and
shown in the accompanying drawings, it is to be understood that
such embodiments are merely illustrative and not restrictive of the
current invention, and that this invention is not restricted to the
specific construction and arrangements shown and described since
modification may occur to those ordinary skilled in the art.
[0054] In one embodiment, the entire gate stack from the gate oxide
formation to the N doping of the dielectric layer and gate
electrode formation is manufactured within as single tool with
multiple chambers (e.g., the cluster tool) without breaking vacuum.
Advance technology nodes (.ltoreq.0.1 .mu.m) will have a few
monolayers of oxide film as gate dielectric. Processing the gate
stack within a single tool with controlled ambient without vacuum
break and human handling/interference will eliminate any compromise
to the device integrity as a result of contamination or damage from
exposure to the processing ambient and handling of the wafer
multiple times.
[0055] While certain exemplary embodiments have been described and
shown in the accompanying drawings, it is to be understood that
such embodiments are merely illustrative and not restrictive of the
current invention, and that this invention is not restricted to the
specific constructions and arrangements shown and described since
modifications may occur to those ordinarily skilled in the art.
TABLE-US-00001 TABLE 1 Nitridation [N] Explanation of Process
Profile the profile Comments NO or NO + O.sub.2 Mixture Growth
##STR00001## N Incorporated throughout the film Poor device
performance due to high [N] at the substrate interface N.sub.2O
Anneal ##STR00002## N close to Si/SiO.sub.2 interface [N] Content
insufficient to block Boron or reduce leakage in 0.1 .mu.m devices
NO Anneal ##STR00003## N at the Si/SiO2 interface [N] higher than
N.sub.2O anneal. Traps B inside SiO.sub.2. Poor interfacial
properties and not significant reduction in leakage current
NH.sub.3 Anneal (High Pressure .gtoreq.100 Torr) ##STR00004##
Bimodal [N] distribution. N at the surface & substrate
interface [N] higher than NO anneal. N at surface traps Boron. Poor
interfacial properties Plasma Nitridation ##STR00005## High [N] at
the poly/oxide interface [N] at the surface blocks the Boron. Drive
current degrades for ultra-thin dielectrics (<10.ANG.) NH3
Anneal (Low Pressure .ltoreq.10 Torr) ##STR00006## Ideal profile.
High [N] at the poly/oxide interface High Drive current than plasma
nitridation. Allows EOT scaling <11.ANG..
* * * * *