U.S. patent application number 11/210607 was filed with the patent office on 2005-12-22 for method for stabilizing high pressure oxidation of a semiconductor device.
Invention is credited to Al-Shareef, Husam N., Chapek, Dave, DeBoer, Scott, Gealy, F. Daniel, Thakur, Randhir.
Application Number | 20050279283 11/210607 |
Document ID | / |
Family ID | 23527741 |
Filed Date | 2005-12-22 |
United States Patent
Application |
20050279283 |
Kind Code |
A1 |
Gealy, F. Daniel ; et
al. |
December 22, 2005 |
Method for stabilizing high pressure oxidation of a semiconductor
device
Abstract
A method and apparatus for preventing N.sub.2O from becoming
super critical during a high pressure oxidation stage within a high
pressure oxidation furnace are disclosed. The method and apparatus
utilize a catalyst to catalytically disassociate N.sub.2O as it
enters the high pressure oxidation furnace. This catalyst is used
in an environment of between five atmospheres and 25 atmospheres
N.sub.2O and a temperature range of 600.degree. to 750.degree. C.,
which are the conditions that lead to the N.sub.2O going super
critical. By preventing the N.sub.2O from becoming super critical,
the reaction is controlled that prevents both temperature and
pressure spikes. The catalyst can be selected from the group of
noble transition metals and their oxides. This group can comprise
palladium, platinum, iridium, rhodium, nickel, silver, and
gold.
Inventors: |
Gealy, F. Daniel; (Kuna,
ID) ; Chapek, Dave; (Merrimack, NH) ; DeBoer,
Scott; (Boise, ID) ; Al-Shareef, Husam N.;
(Tristin, CA) ; Thakur, Randhir; (San Jose,
CA) |
Correspondence
Address: |
TRASK BRITT
P.O. BOX 2550
SALT LAKE CITY
UT
84110
US
|
Family ID: |
23527741 |
Appl. No.: |
11/210607 |
Filed: |
August 23, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11210607 |
Aug 23, 2005 |
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09798445 |
Mar 2, 2001 |
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09798445 |
Mar 2, 2001 |
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09386941 |
Aug 31, 1999 |
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6291364 |
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Current U.S.
Class: |
118/724 ;
257/E21.285; 438/770 |
Current CPC
Class: |
H01L 21/02183 20130101;
H01L 21/28202 20130101; H01L 21/31662 20130101; H01L 21/02271
20130101; H01L 29/518 20130101; Y10S 438/903 20130101; H01L
21/02197 20130101; C30B 33/005 20130101 |
Class at
Publication: |
118/724 ;
438/770 |
International
Class: |
C23C 016/00; H01L
021/31; H01L 021/469 |
Claims
What is claimed is:
1. A furnace comprising: a furnace tube having a length and an
interior surface for processing semiconductor material therein when
operating in a predetermined range of temperature and a range of
pressure; a gas feed coupled to the furnace tube for introducing a
gas into the furnace tube; and a catalyst located within said
furnace tube for contacting the gas introduced into the furnace
tube.
2. The furnace according to claim 1, wherein the predetermined
range of temperature includes 600.degree. C. to 750.degree. C.
3. The furnace according to claim 1, wherein the catalyst matrix
comprises: a tube liner placed along a portion of a length of the
interior surface of the furnace tube, the tube liner including a
plurality of openings therein.
4. The furnace according to claim 3, wherein the tube liner
comprises: a base material having a plurality of openings formed
therein; and a catalyst material covering a portion of the base
material.
5. The furnace according to claim 4, wherein the base material
comprises stainless steel.
6. The furnace according to claim 5, wherein the catalyst material
is selected from a group consisting of lead, platinum, iridium or
palladium.
7. The furnace according to claim 5, wherein the catalyst material
is selected from a group consisting of rhodium, nickel, or
silver.
8. The furnace according to claim 1, wherein the predetermined
range of pressure includes a range of five atmospheres to
twenty-five atmospheres.
9. The furnace according to claim 1, wherein the predetermined
range of pressure is at least five atmospheres.
10. The furnace according to claim 1, further comprising a gas
outlet connected to the furnace tube.
11. A furnace comprising: a furnace tube having a length and an
interior surface for processing semiconductor material therein in a
predetermined range of temperature and a predetermined range of
pressure; a gas feed coupled to the furnace tube for introducing a
gas into the furnace tube; a catalyst matrix located within the
furnace tube for contacting the gas introduced into the furnace
tube; and a gas outlet coupled to the furnace tube for removing gas
therefrom.
12. The furnace according to claim 11, wherein the predetermined
range of temperature includes 600.degree. C. to 750.degree. C.
13. The furnace according to claim 11, wherein the catalyst matrix
comprises: a tube liner placed along a portion of a length of the
interior surface of the furnace tube, the tube liner including a
plurality of openings therein.
14. The furnace according to claim 13, wherein the tube liner
comprises: a base material having a plurality of openings formed
therein; and a catalyst material covering a portion of the base
material.
15. The furnace according to claim 14, wherein the base material is
formed in a honeycomb configuration.
16. The furnace according to claim 14, wherein the base material is
formed in a hexagonal configuration.
17. The furnace according to claim 14, wherein the base material
comprises stainless steel.
18. The furnace according to claim 14, wherein the base material
comprises a structural ceramic.
19. The furnace according to claim 14, wherein the catalyst
material is selected from a group consisting of lead, platinum,
iridium or palladium.
20. The furnace according to claim 14, wherein the catalyst
material is selected from a group consisting of rhodium, nickel, or
silver.
21. The furnace according to claim 11, wherein the predetermined
range of pressure includes a range of five atmospheres to
twenty-five atmospheres.
22. The furnace according to claim 11, wherein the predetermined
range of pressure is at least five atmospheres.
23. A furnace comprising: a furnace tube having a length and an
interior surface for processing semiconductor material therein in a
predetermined range of temperature and a predetermined range of
pressure; a gas feed coupled to the furnace tube for introducing
N.sub.2O gas into the furnace tube; a catalyst matrix located
within the furnace tube for contacting the N.sub.2O gas introduced
into the furnace tube; and a gas outlet coupled to the furnace tube
for removing the N.sub.2O gas therefrom.
24. The furnace according to claim 23, wherein the predetermined
range of temperature includes 600.degree. C. to 750.degree. C.
25. The furnace according to claim 23, wherein the catalyst matrix
comprises: a tube liner placed along a portion of a length of the
interior surface of the furnace tube, the tube liner including a
plurality of openings therein.
26. The furnace according to claim 25, wherein the tube liner
comprises: a base material having a plurality of openings formed
therein; and a catalyst material covering a portion of the base
material.
27. The furnace according to claim 26, wherein the base material is
formed in a honeycomb configuration.
28. The furnace according to claim 26, wherein the base material is
formed in a hexagonal configuration.
29. The furnace according to claim 26, wherein the base material
comprises at least one of stainless steel and a structural
ceramic.
30. The furnace according to claim 26, wherein the catalyst
material is selected from a group consisting of lead, platinum,
iridium or palladium.
31. The furnace according to claim 26, wherein the catalyst
material is selected from a group consisting of rhodium, nickel, or
silver.
32. The furnace according to claim 23, wherein the predetermined
range of pressure includes a range of five atmospheres to
twenty-five atmospheres.
33. The furnace according to claim 23, wherein the predetermined
range of pressure is at least five atmospheres.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of application Ser. No.
09/798,445, filed Mar. 2, 2001, pending, which is a divisional of
application Ser. No. 09/386,941, filed Aug. 31, 1999, now U.S. Pat.
No. 6,291,364, issued Sep. 18, 2001.
BACKGROUND OF THE INVENTION
[0002] The present invention relates generally to oxidizing a
semiconductor surface during an anneal processing step and, more
particularly, the present invention relates to stabilizing a high
pressure oxidation step using nitrous oxide gas within a
temperature range of 600.degree. to 750.degree. C.
[0003] Advanced semiconductor devices, such as high density dynamic
random access memories ("DRAMs"), impose severe restrictions on the
times, temperatures, and atmospheres of all thermal process steps.
DRAMs are comprised of a plurality of memory cells. Each memory
cell is further comprised of a field effect transistor and a
capacitor. It is well known in the art of semiconductor fabrication
to use planar capacitors within DRAM cells; however, in DRAM cells
that utilize conventional planar capacitors, more integrated
circuit surface area is dedicated to the planar capacitor than to
the field effect transistor.
[0004] As the density of components in integrated circuit memories
increased, the shrinkage of memory cell size resulted in a number
of other problems in addition to the problems associated with a
smaller capacitor. Among the resulting problems was that of dopant
diffusing out of the semiconductor material when forming the
transistors of the memory cells. In order to form transistors,
dopants must be implanted in regions of the semiconductor
materials. The dopant, however, tends to diffuse out of the
transistor regions when the transistors are heated during
subsequent integrated circuit processing steps. For example, dopant
diffuses from the semiconductor material during the reoxidation
anneal of the dielectric layer of the cell capacitor.
[0005] Silicon nitride is used as a dielectric layer because it has
less desirable leakage current properties than silicon dioxide.
Further, a thin oxide layer is grown upon the dielectric layer by
reoxidizing a layer of silicon nitride enough to form this oxide
layer to further reduce the leakage current of the silicon nitride
film.
[0006] Once the proper amount of silicon oxide and nitride oxide
have been grown upon the surface to form the dielectric layer, a
reoxidation anneal step is necessary to reduce the imperfections
typically occurring during the initial reoxidation growth
stages.
[0007] One method to provide the silicon dioxide film is to perform
a high pressure chemical vapor deposition (HPCVD) process step on
the semiconductor device. The formation of the cell dielectric, as
well as transistor gate oxides and reoxidation steps in other
processing application steps, is subjected to high pressures in
excess of one atmosphere, typically between five (5) atmospheres to
twenty-five (25) atmospheres, where an atmosphere is represented as
a pressure of 760 Torr. An atmosphere of pure N.sub.2O is
introduced under such pressures in a temperature range of
600.degree. C. to 800.degree. C. The desired reaction is:
N.sub.2O.fwdarw.N.sub.2+O.sup.-; 2N.sub.2O.fwdarw.2NO+N.sub.2
[0008] This allows the oxygen to react with the silicon surface,
forming the silicon dioxide layer.
[0009] Unfortunately, as the N.sub.2O reaction proceeds, it can
become uncontrollable under certain circumstances; specifically,
the N.sub.2O reaction can become supercritical, which gives rise to
high pressure spikes within the high pressure oxidation furnace.
These high pressure spikes abort the high pressure furnace runs and
prevent the furnaces from operating in pure N.sub.2O in the
temperature range of 600.degree. C. to 750.degree. C. As the
concentration of unreacted N.sub.2O builds up in the high pressure
oxidation furnace, it reaches a critical point where the
disassociation reaction is self-propitiating. This reaction goes
from
2N.sub.2O.fwdarw.2NO+N.sub.2
[0010] Once the concentration of unreacted N.sub.2O exceeds this
critical point, the uncontrolled reaction occurs and generates
pressure spikes that may explode a furnace tube of the high
pressure oxidation furnace. An exploding furnace tube results in
ruined product as well as dangerous working environment conditions
for personnel.
[0011] Accordingly, a method and apparatus are needed that reduce,
if not prevent, the unreacted N.sub.2O from becoming super critical
to ensure the uniform processing of the semiconductor wafers.
BRIEF SUMMARY OF THE INVENTION
[0012] According to the present invention, a method and apparatus
for preventing N.sub.2O from becoming super critical during a high
pressure oxidation stage within a high pressure oxidation furnace
are disclosed. The method and apparatus utilize a catalyst to
catalytically disassociate N.sub.2O as it enters the high pressure
oxidation furnace. This catalyst is used in an environment of
between five (5) atmospheres to twenty-five (25) atmospheres
N.sub.2O and a temperature range of 600.degree. to 750.degree. C.,
which are the conditions that lead to the N.sub.2O going super
critical. By preventing the N.sub.2O from becoming super critical,
the reaction is controlled such that it prevents both temperature
and pressure spikes. The catalyst can be selected from the group of
noble transition metals and their oxides. This group can comprise
Palladium, Platinum, Iridium, Rhodium, Nickel, Silver, and
Gold.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 depicts a block diagram of a high-pressure furnace
with a catalytic matrix sleeve inserted therein;
[0014] FIG. 2 depicts a grid arrangement of the catalytic matrix
sleeve used in FIG. 1; and
[0015] FIG. 3 depicts a high pressure furnace that uses a catalytic
matrix screen in an alternative embodiment.
DETAILED DESCRIPTION OF THE INVENTION
[0016] With reference to drawing FIG. 1, a high pressure furnace 10
for chemical vapor deposition is illustrated. The furnace 10
comprises a reactor vessel or furnace tube 12 and a front and rear
flange assembly 14 and 16, respectively. Wafers are positioned
within furnace tube 12. Front flange assembly 14 includes various
gas inlets. The gas inlets terminate right at the flange assembly.
Gas is injected into furnace tube 12 and immediately adjacent the
inlet flange. An exhaust port 18 connects to a suitable pump for
exhausting gases from furnace tube 12. Placed within furnace tube
12 is a catalyst matrix liner 20 that is comprised of a catalyst
element that catalyzes N.sub.2O gas dissociation as the gas enters
the furnace tube 12.
[0017] Furnace 10 operates under high pressure and temperatures.
The pressure is above one atmosphere and ranges from five (5)
atmospheres to twenty-five (25) atmospheres. The temperature range
is from 600.degree. C. to 750.degree. C. These pressures and
temperatures can be greater or less, with a transition through the
stated temperature range. The importance of using catalyst matrix
liner 20 is to protect against pressure and temperature spiking
occurring within the furnace tube 12 of the furnace 10 during such
pressure and temperature ranges of operation of the furnace 10.
[0018] Catalyst matrix liner 20, which is also shown in drawing
FIG. 2, is comprised of a catalyzing agent that causes the N.sub.2O
gas in the furnace 10 to react to form the base components of
nitrogen and oxygen of the N.sub.2O gas according to the following
reaction:
N.sub.2O.fwdarw.N.sub.2+O.sup.-+Catalyst
[0019] The use of a catalyst constrains the chemical reaction from
running away or becoming uncontrollable, which would cause a
pressure and temperature surge within the furnace 10. Such surges
must be avoided as they destroy the semiconductor materials under
fabrication within the furnace 10 as well as cause the possible
destruction of the furnace tube 12.
[0020] Catalyst materials are selected from the group consisting of
Palladium, Platinum, Iridium, Rhodium, Nickel, and Silver. Gold
also can be used as a catalyst, but should be avoided as gold
contaminates the silicon used in the wafers on which semiconductor
devices are formed. Additional catalysts include perovskites,
CaTiO.sub.3, a natural or synthetic crystalline mineral composed of
calcium dioxide and titanium dioxide. When using a Tantalum
compound to form the gate oxide or the cell dielectric for the
transistors of a semiconductor device, a tantalum oxide is produced
in the N.sub.2O atmosphere in the furnace 10. The oxygen from the
N.sub.2O combines with the tantalum oxide according to the
following reaction:
2TaO.sub.x+O.sub.2.fwdarw.Ta.sub.2O.sub.5+Catalyst
[0021] The use of the catalyst material helps to drive this
reaction nearly to full stoichiometry. When used with a Barium
Strontium Titanate compound, the catalyst allows the oxidation to
produce:
Ba.sub.xSr.sub.1-xTiO.sub.3
[0022] which is driven to a full stoichiometry reaction as
well.
[0023] The catalyst matrix liner 20 of drawing FIG. 2 is shown to
be in a honeycomb or hexagonal geometry. This particular geometry
is used because of its ease of manufacture and its strength and
stability. Other geometric shapes are also possible, such as, for
example, circles, ovals, rectangles, diamonds, and other various
types of polygonal shapes. Referring to drawing FIG. 3, illustrated
is an alternative embodiment of catalyst matrix liner 20 with
respect to its location within furnace 10. In this embodiment,
catalyst matrix liner 20 is placed next to the gas inlets of front
flange assembly 14. This position allows for the nitrous oxide to
strike the catalyst matrix liner 20 as the gas enters the furnace
chamber or tube 12 of furnace 10. Again, as stated previously, the
contents of furnace 10 in drawing FIG. 3 are under high pressure
and temperatures as described herein.
[0024] The catalyst matrix liner 20 can be made having a honeycomb
or hexagonal base or supporting material base from a material, such
as stainless steel, which is subsequently plated with the desired
catalytic material as described herein. Other well known materials
may be used for the honeycomb or hexagonal catalyst matrix liner
that are suitable for such use as a substitute for stainless steel
include aluminum oxide, or other suitable structural ceramics where
the catalyst is embedded therein.
[0025] The furnace 10 is useful during gate oxidation in growing
either a nitride layer or an oxide layer, or both. Further, cell
dielectric layers can also be oxidized under safe conditions using
the furnace 10. Additionally, reoxidation can be performed safely
under the desired temperature and pressure constraints as described
herein within the furnace 10. The advantages of using high
pressures within the stated temperature range is that the
semiconductor material is not subjected to the high heat loads of
temperature in excess of 800.degree. C., which can warp and damage
the wafers as well as inhibit the oxide growth layer. Additionally,
the reactions within the furnace 10 can be easily controlled during
operation without undesired reactions occurring. Additionally, the
high pressure oxidation process minimizes the time the wafers are
subjected to high temperatures and helps to minimize any
undesirable diffusion of dopants whose rate of diffusion increases
with increases in temperature.
[0026] While the preferred embodiments of the present invention
have been described above, the invention defined by the appended
claims is not to be limited by particular details set forth in the
above description, as many apparent variations thereof are possible
without departing from the spirit or scope thereof.
* * * * *