U.S. patent application number 13/869208 was filed with the patent office on 2014-02-06 for apparatus and method for selective oxidation at lower temperature using remote plasma source.
The applicant listed for this patent is Christopher S. OLSEN, Heng PAN, Matthew Scott ROGER, Agus S. TJANDRA. Invention is credited to Christopher S. OLSEN, Heng PAN, Matthew Scott ROGER, Agus S. TJANDRA.
Application Number | 20140034632 13/869208 |
Document ID | / |
Family ID | 50024469 |
Filed Date | 2014-02-06 |
United States Patent
Application |
20140034632 |
Kind Code |
A1 |
PAN; Heng ; et al. |
February 6, 2014 |
APPARATUS AND METHOD FOR SELECTIVE OXIDATION AT LOWER TEMPERATURE
USING REMOTE PLASMA SOURCE
Abstract
Devices and methods for selectively oxidizing silicon are
described herein. An apparatus for selective oxidation of exposed
silicon surfaces includes a thermal processing chamber with a
plurality of walls, first inlet connection and a second inlet
connection, wherein the walls define a processing region within the
processing chamber, a substrate support within the processing
chamber, a hydrogen source connected with the first inlet
connection, a heat source connected with the hydrogen source, and a
remote plasma source connected with the second inlet connection and
an oxygen source. A method for selective oxidation of non-metal
surfaces, can include positioning a substrate in a processing
chamber at a temperature less than 800.degree. C., flowing hydrogen
into the processing chamber, generating a remote plasma comprising
oxygen, mixing the remote plasma with the hydrogen gas in the
processing chamber to create an activated processing gas, and
exposing the substrate to the activated gas.
Inventors: |
PAN; Heng; (Santa Clara,
CA) ; ROGER; Matthew Scott; (San Jose, CA) ;
TJANDRA; Agus S.; (San Jose, CA) ; OLSEN; Christopher
S.; (Fremont, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PAN; Heng
ROGER; Matthew Scott
TJANDRA; Agus S.
OLSEN; Christopher S. |
Santa Clara
San Jose
San Jose
Fremont |
CA
CA
CA
CA |
US
US
US
US |
|
|
Family ID: |
50024469 |
Appl. No.: |
13/869208 |
Filed: |
April 24, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61678452 |
Aug 1, 2012 |
|
|
|
Current U.S.
Class: |
219/520 ;
438/768 |
Current CPC
Class: |
H01L 21/02252 20130101;
H01L 21/02164 20130101; H01L 21/02068 20130101; H01L 21/02238
20130101 |
Class at
Publication: |
219/520 ;
438/768 |
International
Class: |
H01L 21/02 20060101
H01L021/02 |
Claims
1. An apparatus for selective oxidation of exposed silicon
surfaces, comprising: a thermal processing chamber with a plurality
of walls having a first inlet connection and a second inlet
connection, wherein the plurality of walls define a processing
region within the processing chamber; a substrate support within
the processing chamber; a hydrogen source in fluid connection with
the first inlet connection of the processing chamber; a heat source
in connection with the hydrogen source; a remote plasma source in
fluid connection with the second inlet connection of the processing
chamber; and an oxygen source in fluid connection with the remote
plasma source.
2. The apparatus of claim 1, wherein the heat source connects the
hydrogen source to the first inlet connection of the processing
chamber.
3. The apparatus of claim 1, wherein the heat source is a resistive
heat source.
4. The apparatus of claim 1, further comprising: a hot wire
apparatus formed in fluid communication between the hydrogen source
and the processing chamber, such that the hydrogen gas is activated
by the hot wire apparatus prior to entering the processing
chamber.
5. The apparatus of claim 1, wherein the fluid connection with the
hydrogen source comprises tubing which comprises an inert
material.
6. A method for selective oxidation of non-metal surfaces,
comprising: positioning a substrate in a processing chamber,
wherein the processing chamber is maintained at a temperature less
than 800.degree. C.; flowing hydrogen into the processing chamber;
generating a remote plasma comprising oxygen; flowing the remote
plasma into the processing chamber, wherein the remote plasma mixes
with the hydrogen gas to create an activated processing gas; and
exposing the substrate to the activated gas.
7. The method of claim 6, wherein hydrogen comprises at least 70
atomic percent as compared to oxygen.
8. The method of claim 7, wherein hydrogen comprises at most 95
atomic percent of the activated processing gas.
9. The method of claim 6, further comprising soaking the substrate
in hydrogen prior to generating a remote plasma comprising
oxygen.
10. The method of claim 9, wherein the soak process is maintained
at a temperature between 600.degree. C. and 800.degree. C. for at
least 45 seconds.
11. The method of claim 9, wherein the flow rates of hydrogen gas
are from about 3.33 sccm/cm.sup.2 to about 16.67 sccm/cm.sup.2.
12. The method of claim 9, wherein the flow rates of hydrogen gas
are from about 3.33 sccm/cm.sup.2 to about 33.33 sccm/cm.sup.2.
13. A method for selective oxidation of non-metal surfaces,
comprising: positioning a substrate in a processing chamber,
wherein the processing chamber is maintained at a temperature less
than 800.degree. C.; flowing hydrogen in proximity to a hot wire
apparatus to generate activated hydrogen; flowing the activated
hydrogen into the processing chamber; generating a remote plasma
comprising oxygen; mixing the remote plasma with the hydrogen gas
in the processing chamber to create an activated processing gas;
exposing the substrate to the activated gas to oxidize a desired
amount of silicon, wherein the activated gas oxidizes silicon
surfaces and reduces metal surfaces; and cooling the substrate.
14. The method of claim 13, wherein hydrogen comprises at least 70
atomic percent as compared to oxygen.
15. The method of claim 14, wherein hydrogen comprises at most 95
atomic percent of the activated processing gas.
16. The method of claim 13, further comprising soaking the
substrate in hydrogen prior to generating a remote plasma
comprising oxygen.
17. The method of claim 16, wherein the soak process is maintained
at a temperature between 600.degree. C. and 800.degree. C. for at
least 45 seconds.
18. The method of claim 13, wherein the flow rates of hydrogen gas
are from about 3.33 sccm/cm.sup.2 to about 16.67 sccm/cm.sup.2.
19. The method of claim 13, wherein the flow rates of hydrogen gas
are from about 3.33 sccm/cm.sup.2 to about 33.33 sccm/cm.sup.2.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit of U.S. Provisional Patent
Application Ser. No. 61/678,452 (APPM/16996L), filed Aug. 1, 2012,
which is herein incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] Embodiments of the present invention generally relate to
apparatus and methods for selectively oxidizing silicon.
[0004] 2. Description of the Related Art
[0005] Oxidation of silicon is a fundamental technology to CMOS
fabrication, dating back to the inception of the integrated
circuit. The most common methods for oxidation of silicon rely on
thermal processes in ambient of O.sub.2, H.sub.2O/H.sub.2,
H.sub.2O/O.sub.2, O.sub.2/H.sub.2 or combinations thereof. The
hardware used to provide the silicon oxidation process in the IC
manufacturing are batch thermal furnaces and RTP. In conventional
oxidation systems and processes, high temperature (above
700.degree. C.) is required to provide the activation energy for
the oxide growth on silicon or poly-silicon.
[0006] Advanced integrated circuit fabrication requires a number of
process steps where thin films of silicon oxide are grown on
silicon or polysilicon structures. For some applications, the
oxidation process must be selective, such that other materials
including tungsten are not oxidized. Currently thermal processing
in either an ambient of O.sub.2, H.sub.2O/H.sub.2, or
H.sub.2O/O.sub.2 at high temperature (greater than 700.degree. C.)
is used to perform this oxidation processes.
[0007] The high temperatures are necessary to obtain the oxide
growth rate to make the process practical and in some cases are
required for oxide quality. However, many of the next generation
devices will undergo serious damage at the point in the process
flow where the oxide growth is required, if exposed to the
combination of high temperature and an oxidizing environment. Thus,
there is a need in the art for methods and apparatus which allow
for low temperature selective oxidation of silicon without
oxidizing other surface materials.
SUMMARY OF THE INVENTION
[0008] Embodiments of the present invention generally relate to
methods of selective oxidation of silicon. In one embodiment, an
apparatus for selective oxidation of exposed silicon surfaces can
include a thermal processing chamber with a plurality of walls
having a first inlet connection and a second inlet connection,
wherein the plurality of walls define a processing region within
the processing chamber, a substrate support within the processing
chamber, a hydrogen source in fluid connection with the first inlet
connection of the processing chamber, a heat source in connection
with the hydrogen source, a remote plasma source in fluid
connection with the second inlet connection of the processing
chamber, and an oxygen source in fluid connection with the remote
plasma source. In some embodiments, the fluid connection can
comprise tubing which comprises an inert material.
[0009] In another embodiment, a method for selective oxidation of
non-metal surfaces, can include positioning a substrate in a
processing chamber, wherein the processing chamber is maintained at
a temperature less than 800.degree. C., flowing hydrogen into the
processing chamber, generating a remote plasma comprising oxygen,
flowing the remote plasma into the processing chamber, wherein the
remote plasma mixes with the hydrogen gas to create an activated
processing gas, and exposing the substrate to the activated
gas.
[0010] In another embodiment, a method for selective oxidation of
non-metal surfaces can include positioning a substrate in a
processing chamber, wherein the processing chamber is maintained at
a temperature less than 800.degree. C., flowing hydrogen in
proximity to a hot wire apparatus to generate activated hydrogen,
flowing the activated hydrogen into the processing chamber,
generating a remote plasma comprising oxygen, mixing the remote
plasma with the hydrogen gas in the processing chamber to create an
activated processing gas, exposing the substrate to the activated
gas to oxidize a desired amount of silicon, wherein the activated
gas oxidizes silicon surfaces and reduces metal surfaces, and
cooling the substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] So that the manner in which the above recited features of
the present invention can be understood in detail, a more
particular description of the invention, briefly summarized above,
may be had by reference to embodiments, some of which are
illustrated in the appended drawings. It is to be noted, however,
that the appended drawings illustrate only typical embodiments of
this invention and are therefore not to be considered limiting of
its scope, for the invention may admit to other equally effective
embodiments.
[0012] FIG. 1 is a schematic representation of a thermal processing
chamber with a remote plasma source according to one
embodiment.
[0013] FIG. 2 is a block diagram of a method of selective oxidation
according to one embodiment.
[0014] FIGS. 3A and 3B are graphical representations of selective
oxidation and reduction achieved both with and without
pre-baking.
[0015] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures. It is contemplated that elements
disclosed in one embodiment may be beneficially utilized on other
embodiments without specific recitation.
DETAILED DESCRIPTION
[0016] Embodiments of the present invention generally relate to
methods of selective oxidation of silicon. Embodiments more
specifically relate to the selective oxidation of silicon and the
selective reduction of tungsten to remove native oxides.
[0017] The selective oxidation of Si over tungsten is an important
process to repair silicon oxide damage caused by ion implantation
or reactive ion etching (RIE) around tungsten gate electrodes on
SiO.sub.2 dielectric in the advanced CMOS devices. The embodiments
described here can be employed to selectively oxidize silicon over
non-metals in a rapid thermal processing (RTP) chamber or thermal
furnace by using a combination of remote plasma and thermal
processing.
[0018] Without intending to be bound by theory, the induced Gibbs
free energy change during the oxidation of silicon is more than
that during oxidation of tungsten, therefore resulting in selective
oxidation of silicon over tungsten. In related art oxidation
processes, the reaction involves water vapor or combustion of
hydrogen and oxygen delivered to the substrate at a high
temperature and pressure. High temperature can cause tungsten
whiskering, which is the formation of long crystalline structures
from the tungsten which can be detrimental to device performance.
With consideration of tungsten whiskering, using a lower
temperature selective oxidation would be more favorable to overall
device performance.
[0019] Embodiments of the present invention are described more
clearly with reference to the figure below.
[0020] FIG. 1 is a RTP chamber with a remote plasma source
according to one embodiment. The RTP chamber employed with
embodiments of the present invention may be of any type which can
heat and cool a substrate while maintaining atmospheric conditions
around the substrate, such as the Centura thermal processing system
or the Vantage RTP system, available from Applied Materials, Inc.
located in Santa Clara, Calif. It is envisioned that other thermal
processing chambers, including chambers from other manufacturers,
may be employed with embodiments of the present invention without
diverging from the scope of the present invention.
[0021] The RTP chamber can employ heating from resistive heat, such
as a resistive heating element formed in a substrate support, from
radiant heat, such as from a heat lamp, or from radiant energy,
such as from a laser annealing system.
[0022] The processing chamber 100 generally comprises a chamber
body 101 defining a processing area 110 in which a substrate 102
may be thermally processed. The substrate 102 is positioned on a
substrate support 112 which can help define the processing area
110. An energy source 103 is configured to direct radiant energy
105 towards the processing area 110. A sensor 108 is disposed in
position to measure an attribute of components in the interior of
the chamber body 101. In one embodiment, the sensor 108 is
configured to measure temperature of the substrate 102 by obtaining
and measuring radiant energy from the substrate 102. The sensor 108
may be connected to a system controller 109, which may be used to
adjust the energy source 103 according to the measurement from the
sensor 108.
[0023] Connected with the processing chamber 100 is a remote plasma
source 120. The remote plasma source employed with embodiments of
the present invention may be of any type which can be used to form
a remote plasma comprising at least oxygen, such as a R*evolution
III Remote RF Plasma Source available from MKS Instruments located
in Andover, Mass. It is envisioned that other remote plasma
chambers, including chambers from other manufacturers, may be
employed with embodiments of the present invention without
diverging from the scope of the present invention.
[0024] A remote plasma source 120 is fluidly coupled to the
processing chamber 100 through a first tubing 122, which can be a
line of sight tubing. An oxygen gas source 126 is also fluidly
coupled to the remote plasma source 120, such as an inductively
coupled remote plasma source. Further embodiments can include an
inert gas source 128 coupled with the remote plasma source 120 so
as to create an oxygen/inert gas plasma which can be delivered to
the processing area 110 of the processing chamber 100.
[0025] The first tubing 122 fluidly couples the remote plasma
source 120 to the processing chamber 100. The term "line of sight"
used herein is meant to convey a short distance between the remote
plasma source 120 and the processing chamber 100 so as to minimize
the possibility of radical recombination or adsorption onto the
surface of the tubing. The first tubing 122 can comprise an inert
material, such as sapphire, quartz, or other ceramic material, to
prevent adsorption and/or recombination of the oxygen radicals
provided by the remote plasma source 120. The first tubing 122 can
be configured to provide a direct, short path for oxygen radicals
generated in the remote plasma source 120 into the processing
chamber 100.
[0026] A hydrogen gas source 124 is connected to the processing
chamber 100. The hydrogen gas source 124 delivers hydrogen gas to
the processing area 110 where the hydrogen gas will be activated by
the remote plasma comprising oxygen delivered from the remote
plasma source 120. A hot wire apparatus 130 can optionally be
positioned between the hydrogen gas source 124 and the processing
chamber 100. In embodiments with the hot wire apparatus 130, the
hydrogen gas can be flowed over a hot filament of the hot wire
apparatus 130 which activates the hydrogen prior to delivering the
hydrogen into the chamber. Further, the hot wire apparatus 130 can
be be connected to the processing chamber using a second tubing
132, such as a line of sight tubing. The composition and parameters
for the first tubing 122 can be used for the second tubing 132.
[0027] Temperature control is important to the formation of silicon
oxide while simultaneously not forming whisker structures on
tungsten. As such, the RTP chamber used in embodiments described
herein should be able to control temperature between the ranges of
500.degree. C. and 1100.degree. C. with fast heating and cooling of
the substrate in the chamber. Such heating and cooling may be
performed using structures, such as heating elements and/or coolant
ports in the substrate support.
[0028] FIG. 2 is a block diagram of a method of selective oxidation
according to one embodiment. The method 200 can include positioning
the substrate in a thermal processing chamber, wherein the
substrate is maintained at a temperature less than 800.degree. C.,
as in step 202. At temperatures above 800.degree. C., tungsten
whiskers may form on tungsten features deposited on the surface of
a substrate. As the tungsten whiskers grow, they can contact nearby
features as well as creating a non-uniform surface of the
substrate. Further, maintaining temperatures below about
800.degree. C. is beneficial for applications with a low thermal
budget. Therefore, maintenance of the substrate at temperatures
below about 800.degree. C., and preferably at or below about
700.degree. C., can be beneficial to the overall functionality of
the semiconductor device.
[0029] The method 200 can further include flowing hydrogen into the
processing chamber, as in step 204. Silicon is difficult to oxidize
by conventional thermal oxidation in O.sub.2 or H.sub.2O, usually
requiring a very high temperature and long time. It is known to
oxidize in atomic oxygen, including species generated by an oxygen
plasma. The use of O.sub.2 and H.sub.2 mixtures, including O.sub.2
activated by a plasma may also allow oxidation of silicon, while
also changing the rate and/or the relative rates of oxidation of
silicon and other materials, such as tungsten.
[0030] For a 300 mm substrate in an appropriately sized chamber,
the flow rates of H.sub.2 can be from about 1 slm to about 10 slm
(from about 3.33 sccm/cm.sup.2 to about 33.33 sccm/cm.sup.2). The
hydrogen can be flowed into the chamber to maintain an overall
chamber pressure of between 1 Torr and 2 Torr, such as 1.5 Torr.
The temperature of the substrate can be ramped down to between
about 550.degree. C. and about 650.degree. C., such as a substrate
which is ramped down to about 600.degree. C. In some embodiments,
the chamber can be maintained at the same temperature as the
substrate.
[0031] A further embodiment may include a pre-soak/pre-bake
process. In one embodiment, hydrogen (H.sub.2) is flowed into a
processing chamber with a substrate located therein. The substrate
is then soaked in between about 450 Torr and about 550 Torr of
H.sub.2, for example 530 Torr, while maintaining the substrate at
about 700.degree. C. The substrate then remains in the H.sub.2 soak
for a short period of time, such as between about 45 and about 75
seconds, such as 60 seconds. Related data shows that a pre-soak in
H.sub.2 may benefit the formation of silicon oxide while
simultaneously reducing the native oxide formed on the surface of
the tungsten.
[0032] Yet further embodiments can include the use of hot wire
activation of the H.sub.2 prior to flowing the H.sub.2 into the
chamber. In this embodiment, H.sub.2 is flowed over a hot filament.
The filament can be composed of a corrosion resistant metal or
alloy, such as tungsten or ruthenium-tungsten. The hot filament can
activate the hydrogen without forming a plasma, thereby preventing
some of the more deleterious effects which can be seen when using
hydrogen as a plasma. The activated hydrogen, which will comprise
H.sub.2 and ionized hydrogen, is flowed into the processing chamber
where the activated hydrogen can both extract oxygen from the
native oxides formed on the surface of exposed metals, such as
tungsten, and deposit oxygen onto the silicon. The reduction of
tungsten has been seen from 70 atomic % to 95 atomic %
hydrogen.
[0033] The method 200 can further include generating a remote
plasma comprising oxygen, as in step 206. There are a number of
issues regarding the formation of H.sub.2 as a remote plasma. First
and foremost, H.sub.2, when converted to a plasma, can attack the
source and other chamber components, such as components composed of
anodized aluminum, quartz and sapphire. This reaction can lead to
premature source failure. Further, the reaction with H.sub.2 can
create deposition precursors such as metal hydrides, which can
deposit on the substrate. By forming a remote plasma of the oxygen
alone, activated species of oxygen can be formed with minimal
damage to the substrate and without having the deleterious effects
of hydrogen plasma when contacting other portions of the chamber.
Further, the activated oxygen can be used to activate the hydrogen
in the presence of the substrate so as to limit the effects of the
ionized/radicalized hydrogen to the substrate.
[0034] The oxygen gas is flowed into the remote plasma source at
from about 1 slm to about 5 slm for a 300 cm.sup.2 substrate (from
about 3.33 sccm/cm.sup.2 to about 16.67 sccm/cm.sup.2). The oxygen
gas can be mixed with an inert gas to form an oxygen gas mixture.
The inert gas can include gases such as argon, helium or krypton.
Either the oxygen gas or the mixture can then be converted to a
plasma using an energy source. The energy source can be a
capacitive, inductive or microwave energy source.
[0035] The method 200 can further include flowing the remote plasma
into the processing chamber, wherein the remote plasma mixes with
the hydrogen gas to create an activated processing gas, as in step
208. The plasma can be either allowed to quench before flowing or
flowed as a plasma into the chamber through the line of sight tube.
The plasma is mixed with the hydrogen over the substrate, creating
H, O and OH molecules. The temperature of the substrate is
maintained between 550.degree. C. and 650.degree. C., such as at
600.degree. C., to benefit the formation of silicon oxides.
[0036] In one embodiment, the hydrogen which was flowed into the
chamber in the pre-bake step may be reused as the hydrogen gas for
the activated processing gas. Further embodiments can include
clearing the chamber with an inert gas or hydrogen gas prior to
flowing in hydrogen to create the activated gas. These steps can
occur simultaneously with the formation of the oxygen plasma. As
well, the hydrogen may be flowed into the chamber before the oxygen
plasma is flowed from the remote plasma source or flowed
simultaneously to mix with the oxygen plasma over the
substrate.
[0037] The method 200 can further include exposing the substrate to
activated gas to oxidize the silicon and reduce exposed metals,
such as tungsten, as in step 210. Plasma oxidation of silicon
generally obeys an Arrhenius-like dependence with temperature, but
with a much lower activation energy than thermal oxidation owing to
the presence of oxygen radicals formed in the plasma. Due to the
activation of the oxygen and subsequent or concurrent activation of
the hydrogen, the silicon is oxidized. Further, the activated
species of hydrogen and oxygen can lead to the reduction of
tungsten under the same conditions.
[0038] FIG. 3A is experimental data showing increased silicon oxide
growth on silicon substrates. All data was collected from 300 mm
bare silicon substrates. The substrates were initially heated to
700.degree. C., followed by an optional pre-bake step. The optional
pre-bake step includes a soak for 60 seconds in H.sub.2 at a
pressure of 530 Torr. After the pre-bake step, the temperature was
ramped down to 600.degree. C. and the pressure was ramped to 1.5
Torr. During the selective oxidation portion, the temperature was
maintained at 600.degree. C. Remote plasma was produced from oxygen
with source power fixed at 3000 W for 60 seconds and then flowed
into the chamber where it was mixed with H.sub.2 which is flowed
separately in the chamber. The total pressure of H.sub.2 and
O.sub.2 in the chamber was 1.5 Torr.
[0039] The graphical representation shows silicon oxide thickness
from 80 atomic % to 100 atomic % H.sub.2. Silicon growth was higher
between 80 atomic % and 90 atomic % hydrogen (with 20 atomic % and
10 atomic % oxygen respectively). As discovered in further similar
experimentation (not shown here), between 70 atomic % and 95 atomic
% hydrogen (with 30 atomic % and 5 atomic % oxygen respectively)
provides optimal oxide growth on silicon. Silicon oxide thickness
is consistently higher for pre-baked silicon substrates over the
unbaked silicon substrate providing between 0.2 A and 0.8 A of
increased thickness without the need for increased temperatures.
The pre-bake silicon oxide is significantly higher in the 100%
H.sub.2 sample which may be oxide growth from sequestered oxygen
redistributed by hydrogen in the presence of native oxides.
[0040] FIG. 3B is experimental data showing reduction of native
tungsten oxides. All data was collected from 300 mm silicon
substrates with deposited tungsten by CVD processes. The substrates
were initially heated to 700.degree. C., followed by an optional
pre-bake step. The optional pre-bake step includes a soak for 60
seconds in H.sub.2 at a pressure of 530 Torr. After the pre-bake
step, the temperature was ramped down to 600.degree. C. and the
pressure was ramped to 1.5 Torr. During the selective oxidation
portion, the temperature was maintained at 600.degree. C. Remote
plasma was produced from oxygen with source power fixed at 3000 W
for 60 seconds and then flowed into the chamber where it was mixed
with H.sub.2 which is flowed separately in the chamber. The total
pressure of H.sub.2 and O.sub.2 in the chamber was 1.5 Torr.
[0041] The graphical representation shows a general decrease in
native tungsten oxide thickness in the presence of both hydrogen
and oxygen, as compared to no oxygen. Oxide concentration was
measured using X-ray photoelectron spectroscopy (XPS). The XPS
measurement shows 38-39% Oxygen % in as-deposited tungsten (native
WO.sub.x). The decrease in native WO.sub.x content was higher
between 80 atomic % and 90 atomic % hydrogen (with 20 atomic % and
10 atomic % oxygen respectively). As discovered in further similar
experimentation (not shown here), between 70 atomic % and 95 atomic
% hydrogen (with 30 atomic % and 5 atomic % oxygen respectively)
can be used for reduction of native WO.sub.x. Related to silicon
oxide thickness, native WO.sub.x is consistently lower for
pre-baked tungsten coated substrates over the unbaked tungsten
coated substrates, providing between 2% and 3% of oxide reduction
without the need for increased temperatures. The pre-bake native
WO.sub.x is lower in the 100% H.sub.2 sample which evidences a
benefit to the pre-bake process in overall native WO.sub.N
reduction that behaves synergistically with the oxygen
treatment.
[0042] Though discussed previously, tungsten can form oxides by
contact with the atmosphere, such as during transfer between
chambers. These oxides can degrade the functionality and shorten
the life of tungsten features formed on a substrate. As such, it is
important to remove these defects. Therefore, the benefits of
decreased native WO.sub.x formation can be achieved using the same
process and conditions as are taught for low temperature silicon
oxide production. Further, it is believed that the combination of
reducing tungsten and oxidizing silicon by the same process may be
further synergistic by sequestering oxygen from the native WO.sub.x
layer and forming silicon oxide on the exposed silicon.
[0043] With hydrogen concentrations higher than 80%, XPS measured
0% in the tungsten film has dropped to 31% to 33% as result of
reduction depending on temperature, pre-bake condition and RP
power. It is therefore concluded that selective oxidation can be
realized with hydrogen concentration in the chamber of at least 80
atomic % at 600.degree. C. The experimental parameters described
here are not intended to be limiting, as other temperatures,
pressures, flow rates and device parameters as described above may
provide the same benefits as disclosed here.
[0044] Embodiments described herein relate to an apparatus and
method of selectively oxidizing exposed silicon while reducing
native WO.sub.x. During processing of substrates, such as during
the formation of NAND flash devices, the silicon oxide layer may be
damaged by processes such as etching. Further, as shown above,
as-deposited metals, such as tungsten, contain native oxides which
may be detrimental to device performance. The apparatus and methods
described above can both reduce native oxide on the deposited
metals while simultaneously forming silicon oxide from the exposed
silicon, without temperatures over 800.degree. C.
[0045] While the foregoing is directed to embodiments of the
present invention, other and further embodiments of the invention
may be devised without departing from the basic scope thereof, and
the scope thereof is determined by the claims that follow.
* * * * *