A method and apparatus for thermally growing stable silicon dioxide layers on silicon is disclosed. A previously etched and baked silicon nitride tube placed in a furnace is used to grow the silicon dioxide. First, pure oxygen is allowed to flow through the tube to initially coat the inside surface of the tube with a thin layer of silicon dioxide. After the tube is coated with the thin layer of silicon dioxide, the silicon is oxidized thermally in a normal fashion. If the tube becomes contaminated, the silicon dioxide is etched off thereby exposing clean silicon nitride and then the inside of the tube is recoated with silicon dioxide. As is disclosed, the silicon nitride tube can also be used as the ambient for the pyrolytic decomposition of silane and ammonia to form thin layers of clean silicon nitride

Cohen, R. A.

Wheeler, R. K.

English

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LAIESS ON SILICON GROWN IN SILICON
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https://ntrs.nasa.gov/search.jsp?R=19740011656 2020-03-17T14:47:34+00:00Z
March 12, 1974
 R A COHEN ETAL 3,796,592
METHOD AND APPARATUS FOR STABLE SILICON DIOXIDE LAYERS
ON SILICON GROWN IN SILICON NITRIDE AMBIENT
Filed Sept. 9. 1969
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INVENTORS
RONALD A. COHEN &
ROY K. WHEELER
BY
ATTORNEYS
United States Patent Office 3,796,592Patented Mar. 12, 1974
3,796,592
METHOD AND APPARATUS FOR STABLE SILICON
DIOXIDE LAYERS ON SILICON GROWN IN
SILICON NITRIDE AMBIENT
Ronald A. Cohen, South Acton, and Roy K. Wheeler,
Littleton, Mass., assignors to the United States of
America as represented by the Administrator of the
National Aeronautics and Space Administration
Filed Sept. 9,1969, Ser. No. 856,253
Int. O. BOSb 13/06; C23c 11/00
U.S. a. 117—95 2 Claims
ABSTRACT OF THE DISCLOSURE
A method and apparatus for thermally growing stable
silicon dioxide layers on silicon is disclosed. A previously
etched and baked silicon nitride tube placed in a furnace
is used to grow the silicon dioxide. First, pure oxygen is
allowed to flow through the tube to initially coat the inside
surface of the tube with a thin layer of silicon dioxide.
After the tube is coated with the thin layer of silicon di-
oxide, the silicon is oxidized thermally in a normal fash-
ion. If the tube becomes contaminated, the silicon dioxide
is etched off thereby exposing clean silicon nitride and
then the inside of the tube is recoated with silicon di-
oxide. As is disclosed, the silicon nitride tube can also
be used as the ambient for the pyrolytic decomposition of
silane and ammonia to form thin layers of clean silicon
nitride.
ORIGIN OF THE INVENTION
The invention described herein was made by employees
of the United States Government and may be manu-
factured and used by or for the Government for govern-
mental purposes without the payment of any royalities
thereon or therefor.
BACKGROUND OF THE INVENTION
This invention relates to the growing of silicon dioxide
layers on silicon, arid more specifically, to the growing of
stable silicon dioxide layers on silicon in a silicon nitride
ambient and also relates to the pyrolytic decomposition of
silane and ammonia in a silicon nitride ambient to grow
clean layers of silicon nitride.
Silicon dioxide layers and silicon nitride layers have
widespread use as passivation and dielectric layers for
semiconductor devices such as integrated circuits, insu-
lated gate field effect transistors, etc.
Stable layers are needed because unstable layers may
cause circuit failure or system malfunction due to the fact
that unstable layers produce poor parameters such as high
leakage current, low Beta and high threshold voltages. In
addition, unstable layers result in a poor yield caused by
high failure rate with subsequent increase in cost and most
important to space applications poor reliability.
Prior art methods of thermally growing stable silicon
dioxide on silicon generally require ultraclean conditions.
One such prior art method involves the use of pure quartz
tubes and pure alumina liners. This prior art method re-
quires that ultraclean processing techniques be utilized be-
cause quartz is no barrier to mobile ions. At best it is
difficult to obtain and maintain the degree of cleanliness
necessary to obtain a stable oxide by this prior art method.
Mobile ions may be present on the slice surface before
the oxide is grown or mobile ions may be introduced from
the ambient during oxidation.
SUMMARY OF THE INVENTION
This invention relates to a method and apparatus that
permits the thermal growing of clean stable silicon di-
oxides without the cost of maintaining the ultraclean en-
vironment required by the prior art methods. In accord-
ance with this invention, a silicon nitride tube is cleaned
by etching in hydrofluoric acid, rinsed in distilled deion-
ized water, baked dry in a furnace, and then the silicon
nitride tube is placed in a furnace or other suitable heating
5 device and the inside of the tube is coated with a layer of
silicon dioxide by permitting pure oxygen to flow through
the tube. Silicon dioxide is then thermally grown on a
silicon slice housed inside the tube. If the silicon dioxide
layer on the inside of the tube becomes contaminated, it
10 is etched off and a clean layer is again formed on the in-
side of the tube.
The silicon nitride tube can also be used as an ambient
for the pyrolytic decomposition of silane and ammonia to
form thin layers of clean silicon nitride. This method of
15 forming thin layers of clean Si3N4 avoids the problem of
mobile ions that is encountered in the prior art method of
epitaxial deposition of Si3N4 in quartz tubes, because tubes
can contain and also transmit mobile ions.
It is therefore an object of this invention to provide a
20 method for growing stable silicon dioxide layers on silicon.
It is another object of this invention to grow stable
silicon dioxide layers on silicon.
It is a further object of this invention to provide the
apparatus for the thermal growing of stable silicon dioxide
25 layers on silicon.
A still further object of this invention is to provide a
method for forming thin layers of silicon nitride.
And a still further object of this invention is to provide
the apparatus for forming thin layers of silicon nitride.
30
 BRIEF DESCRIPTION OF THE DRAWINGS
The above objects and others will become apparent
from the following detailed description of the invention
when read in conjunction with the annexed drawings in
35 which:
FIG. 1 is a pictorial view of the apparatus for growing
stable silicon dioxide layers on silicon in accordance with
the invention;
FIG. 2 is a pictorial view of the apparatus for forming
40 thin layers of silicon nitride in accordance with the inven-
tion; and
FIG. 3 is a pictorial view of the tube sectioned showing
the silicon dioxide layer and the silicon slice.
45 DESCRIPTION OF THE INVENTION
Referring now to FIG. 1, a silicon nitride tube 1 pass-
ing through a furnace or a heat chamber 2 is shown. The
furnace 2 is shown in cross-section to more clearly show
the silicon nitride tube 1. A flexible tube 5 is attached to
one end of the tube 1. The tube 5 can be made of any
suitable material such as Teflon. The other end of the
tube 5 is connected to a needle valve 6 which may be an
oxygen singlestage regulator valve such as is made by
Airco. A tank of liquid oxygen (gas withdrawal) 7 is con-
nected to the valve 6 by means of a second section of
tubing 10. A wafer or a slice of silicon 3 is housed on a
platform 4 inside the silicon nitride tube 1. The platform
4 can be made of any suitable material that will not con-
taminate the silicon slice 3 or the silicon nitride tube 1;
for example, Si3N4 platform, SiC, or ultrapure quartz.
Of course, the silicon slice 3 could be placed directly in-
side the tube 1 without any platform if the ambient tem-
perature is on the order of 1000° C. Prior to the first
usage, the silicon nitride tube is cleaned by etching with
24% hydrofluoric acid, rinsed in distilled, deionized water,
and baked dry (at 1000" C.).
Silicon dioxide is thermally grown on the silicon wafer
3 in the following manner: The valve 6 is opened per-
mitting pure gaseous oxygen from the tank 7 to flow
'" through the silicon nitride tube 1 with the furnace 2 at a
temperature of 1000° to 1200° C. Under these conditions
a thin coating of silicon dioxide is formed on the inside of
65
3,796,592
the silicon nitride tube 1. Silicon dioxide is then thermal-
ly grown on the silicon wafer 3 in a normal fashsion. The
silicon wafer 3 having been placed inside the tube 1
prior to the initial step of forming a coating of silicon di-
oxide on the inside of the silicon nitride tube 1. The state-
 5
ment that silicon dioxide is grown on the cleaned silicon
wafer 3 in a normal manner means that the silicon dioxide
is grown on the silicon wafer 3 by any suitable well kown
prior art method such as described in the review article
entitled "The Si—SiO2 Solid-Solid Interface System," ]0
A. G. Reveze and K.H. Zawinger, RCA Review pp. 22-
76, March 1968.
•FIG. 2 shows the apparatus of the invention for form-
ing thin layers of silicon nitride. The apparatus of FIG.
2 is identical to the apparatus of FIG. 1 except that the 15
liquid oxygen tank 7 of FIG. 1 has been replaced by a
first tank 9 containing ammonia and a second tank 9
containing silane has also been connected to the valve
6 by means of a section of tubing 11. Also, a nitrogen
tank 12 has been added for flushing purpose and a hydro- 20
gen chloride and/or hydrogen tank can be added for
optional in situ cleaning of the silicon wafer. In addition,
the wafer or slice 3 can be made of any suitable materal
including silicon, germanium, gallium arsenide, etc. Wafer
3 serves as a substrate upon which the silicon nitride is 25
formed.
In the apparatus of FIG. 2, the inside of the silicon ni-
tride tube 1 is initially coated with a thin layer of silicon
dioxide. In order-to form the silicon nitride layer, the
valve 6 is turned on permitting the silane and ammonia 30 3,472,689
to flow through the tube 1 with the furnace 2 at a tem-
perature of 800° C. to 1200° C. A layer of silicon nitride
is formed on the substrate 3 by the pyrolytic decomposi-
tion of the ammonia an'd silane.
The relative positions of the elements inside the silicon 35
nitride tube 1 are clearly shown in FIG. 3. As shown, the
inside of the silicon nitride tube 1 is coated with a layer
of silicon dioxide 13. The platform or boat 4 is generally .
What is claimed is:
1. A method for growing stable silicon dioxide layers
on a silicon substrate comprising the steps of:
placing said substrate in a silicon nitride tube;
heating said tube to a temperature in the range of
1000° C. to 1200° C.;
flowing pure oxygen through said tube when heated to
said temperature range to thereby provide a coating
of silicon dioxide on the inside surface of said silicon
nitride tube; and
thermally growing a layer of silicon dioxide on the
silicon wafer inside said tube by thermal oxidation.
2. A method for growing thin films of silicon nitride
on a substrate comprising the steps of:
placing the substrate in a silicon nitride tube;
heating said tube to a temperature in the range of
1000° C. to 1200° C.;
flowing pure oxygen through said tube when in said
temperature range to thereby provide a coating of
silicon dioxide on the inside surface of said tube;
flowing a mixture of silane and ammonia through said
tube when maintained in a temperature range of
800° C. to 1200° C. to thereby form a layer of sili-
con nitride on said substrate by the pyrolytic de-
composition of the ammonia and silane.
References Cited
UNITED STATES PATENTS
11/1970 Scott 117—Nitride Dig.
FOREIGN PATENTS
10/1959 France 117—Nitride1,190,308
OTHER REFERENCES
Sage and Histed: Application of Silicon Nitride,
Powder Metallurgy, 1961, No. 8, pp. 210-211.
B. E. Deal: "Electrochemical Society, Extended
centrally located inside the tube 1 and the substrate 3
 Abstract» Fall Meeting Oct. 5-10, 1968 pp. 260-261
which is shown as being a silicon slice m this figure is 4U ^ , _ . - _ ^ ^ T-..__.,. ^ . . ,~A,«n
seated on the boat 4.
.While the invention has been described with reference
to specific embodiments, it will be obvious to those skilled
in the art that various changes and modifications can be
made. For example, the silicon nitride container can be 45
used as a noncontaminating environment for other chemi-
cal reactions, such as deposited alumina, A12O3 and as a
tube for sintering aluminum contacts to silicon integrated
circuits.
Translation of French Pat. 1,190,308.
ALFRED L. LEAVITT, Primary Examiner
M. F. ESPOSITO, Assistant Examiner
U.S. Cl. X.R.
117-106 R, 106 A, 201, Digest 12


Method and apparatus for stable silicon dioxide layers on silicon grown in silicon nitride ambient

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