U.S. patent number 3,633,537 [Application Number 05/052,387] was granted by the patent office on 1972-01-11 for vapor deposition apparatus with planetary susceptor.
This patent grant is currently assigned to General Motors Corporation. Invention is credited to William E. Howe.
United States Patent |
3,633,537 |
Howe |
January 11, 1972 |
VAPOR DEPOSITION APPARATUS WITH PLANETARY SUSCEPTOR
Abstract
An apparatus for uniformly vapor plating circular articles, and
particularly for making highly uniform epitaxial deposits on a
plurality of semiconductor slices simultaneously. A preferred
embodiment of the apparatus includes a susceptor plate mounted for
rotation about a vertical axis. The susceptor plate has a generally
conical upper surface, upon which the circular semiconductor slices
are placed for epitaxial deposition. A stationary noncontiguous
concentric ring is disposed around the outer edge of the susceptor
plate. The edges of the slices overhang the susceptor plate and
contact the stationary ring. Rotation of the susceptor plate
produces planetary rotation of the circular semiconductor
slices.
Inventors: |
Howe; William E. (Kokomo,
IN) |
Assignee: |
General Motors Corporation
(Detroit, MI)
|
Family
ID: |
21977291 |
Appl.
No.: |
05/052,387 |
Filed: |
July 6, 1970 |
Current U.S.
Class: |
118/725; 118/500;
118/730; 118/900; 219/634 |
Current CPC
Class: |
C23C
14/34 (20130101); C23C 16/00 (20130101); Y10S
118/90 (20130101) |
Current International
Class: |
C23C
16/00 (20060101); C23C 14/34 (20060101); C23c
011/00 () |
Field of
Search: |
;118/48-49.5,500,503
;117/106-107.2 ;219/10.49,275 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kaplan; Morris
Claims
I claim:
1. In an apparatus for growing epitaxial films of highly uniform
electronic characteristics on a plurality of semiconductor
substrates in a single operation,
a housing;
a generally circular susceptor plate in said housing supported for
rotation about a vertical axis;
an outwardly declining generally conical upper surface on said
susceptor plate for supporting a plurality of circular slices of
semiconductive material;
means for maintaining said disks mutually spaced about the
circumference of said susceptor plate with their edges overhanging
its outer periphery;
a stationary noncontiguous concentric ring around said susceptor
plate for contact with the overhanging edges of said circular
disks;
means for rotating said susceptor plate about said axis and
relative to said stationary ring to produce planetary rotation of
said circular disks on said generally conical upper surface;
means for introducing a mixture of epitaxial deposition gases into
said chamber through the center of said susceptor plate and flowing
it over the disks thereon; and
induction means for heating said susceptor plate whereby to heat
said disks and to uniformly epitaxially deposit a semiconductive
coating from said gases onto said disks on said susceptor
plate.
2. The apparatus as defined in claim 1 wherein the upper surface of
the susceptor plate has a 25.degree.-40.degree. slope and the means
for circumferentially spacing said disks on said plate includes a
plurality of radially arrayed circular recesses in the upper
surface of said susceptor plate intersecting the periphery of said
susceptor plate, with said recesses being of a larger diameter and
a depth not substantially greater than the thickness of said disks.
Description
BACKGROUND OF THE INVENTION
This invention relates to vapor plating, and more particularly to
epitaxially depositing highly uniform coatings on semiconductor
slices.
It is well recognized that one of the most significant factors
affecting the electronic characteristics of semiconductive
materials is the concentration and distribution of various
impurities within the material. Even very small variations in
impurity content or distribution can drastically affect the
significant electronic characteristics. This is particularly true
with respect to the starting material used to make semiconductive
devices.
Semiconductor slices having doped epitaxial deposits thereon have
become widely used as a starting material for many semiconductor
devices. This is achieved by including a small amount of a selected
impurity vapor, the dopant, with epitaxial deposition vapors. The
amount of dopant, however, must be rigidly controlled and
thoroughly mixed with the deposition vapor. It is difficult enough
to coat one slice at a time, and attain a completely homogeneous
epitaxial deposit which has uniform electronic characteristics
across the face of the slice. However, for commercial production
one must coat a number of slices simultaneously, and still obtain
coating uniformity. Moreover, the slices should be rapidly and
economically produced for commercial production operations.
It has already been appreciated that such uniformity is a function
of the content and distribution of plating vapors within the
deposition chamber. Various devices and techniques have been
proposed to insure that the entire face of each slice is exposed to
the same processing conditions, including vapor composition and
flow rate. One technique involves rotating the susceptor that is
used to support the slices during deposition. However, it has been
found that even when the deposition gases are introduced into the
deposition chamber through the center of the rotating susceptor
plate nonuniformity across the face of each slice frequently
results.
SUMMARY OF THE INVENTION
It is, therefore, a principal object of this invention to provide
an improved apparatus for rapidly and economically epitaxially
coating a plurality of semiconductor slices at one time with each
slice being uniformly coated across its face. It is also an object
of this invention to provide an improved apparatus for
simultaneously highly uniformly vapor plating a plurality of any
circular articles.
These and other objects of the invention are attained in a
vapor-plating apparatus having a generally circular susceptor plate
with an outwardly declining upper surface. A concentric ring is
spaced around the outer periphery of the susceptor plate. Circular
articles to be plated are placed on the upper surface of the
susceptor plate, with their edges overhanging the outer periphery
of the plate. The spaced concentric ring provides a ledge against
which the overhanging edges of the slices abut. As the susceptor
plate is rotated the slices not only rotate about the susceptor
plate axis but roll in planetary fashion on their own axes due to
frictional engagement of their edges with the surrounding ring.
Preferably, recesses are provided in the susceptor plate surface to
receive the slices being treated.
BRIEF DESCRIPTION OF THE DRAWING
Other objects, features and advantages of the invention will become
more apparent from the following description of a preferred
embodiment thereof and from the drawings, in which:
FIG. 1 is a cross-sectional view schematically showing a
vapor-plating apparatus having a susceptor plate and surrounding
stationary ring made in accordance with the invention;
FIG. 2 is a sectional view along the line 2--2 of FIG. 1 showing
the top of the susceptor plate; and
FIG. 3 is an isometric drawing showing the susceptor plate in the
apparatus of FIGS. 1 and 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The drawing shows a vapor-plating apparatus suitable for use in
epitaxial deposition. It includes a closed housing formed with a
quartz bell jar 10 and a metal baseplate 12. A circular graphite
susceptor plate 14 having a frustoconical upper surface 16 is
disposed in the upper portion of the bell jar 10. The susceptor
plate 14 rests on the flange 17 of hollow quartz pedestal 18.
Quartz pedestal 18 is, in turn, mounted on a stainless steel
rotation tube 20 to provide means for rotating susceptor plate 14
about a vertical axis. Rotation tube 20 is, in turn, preferably
attached to any suitable mechanism (not shown) that automatically
rotates it about its longitudinal axis. A pancake water-cooled
induction heater 22 is supported on another quartz pedestal 24,
that is located beneath susceptor plate 14.
A quartz umbrella 26 having a depending skirt portion 28 lies on
top of the pancake induction heater 22, between the heater and the
susceptor plate 14. A concentric stationary graphite ring 30 rests
on quartz umbrella 26 noncontiguously circumferentially surrounding
the susceptor plate 14. The plate 14 and ring 30, while described
as being of graphite, can be made of any other suitable
high-temperature material, such as quartz, silicon carbide,
molybdenum or the like. Analogously, the various other parts of the
apparatus can be made of materials other than those described.
The upper surface 16 of the susceptor plate has a plurality of
circular recesses 32 therein. The recesses 32 have a flat bottom
and a depth that is preferably not substantially greater than the
slices 34 upon which the epitaxial deposit is to be made. Also, the
recesses 32 are of a slightly larger diameter than the slices 34
and intersect the outer periphery of the susceptor plate. Hence,
slices 34 loosely nest within the recesses and partly overhang the
susceptor plate. The overhanging edges of the slices abut the
adjacent side of stationary ring 30. The ring 30 is, of course,
spaced sufficiently from the susceptor plate to allow free rotation
of the susceptor plate and yet not so far away that the slices 34
can fall in between. Means (not shown) can be used to secure ring
30 to quartz umbrella 26 should this be desired. It should be
recognized that planetary rotation can also be achieved by
modifications of the apparatus described. For example, the slices
need only overhang a shoulder on the susceptor plate and contact a
concentric ring spaced above the outer periphery of the susceptor
plate.
Vapor deposition gases are introduced into the housing through
hollow rotation tube 20 and hollow quartz pedestal 18. They exit
the upper end of the pedestal 18 and enter the top of the bell jar
10 through the center of susceptor plate 14. Since most vapor
depositions are provided at about atmospheric pressure, exhaust
ports 36 are provided in the baseplate to permit spent gases to
exit the bell jar 10 during the deposition process. Skirt 28 on the
quartz umbrella 26 provides means for maintaining the desired
positive pressure of reaction gases over the slices in the
susceptor plate. Means can be employed, if desired, to direct these
spent gases from the exhaust ports 36 to a suitable vent stack for
safety reasons.
The slope on the upper surface of the susceptor plate can vary, so
long as one maintains the slices in sufficient engagement with the
surrounding stationary ring to cause them to rotate in planetary
fashion. The rate of susceptor plate rotation, if high, can even
eliminate the need for any slope at all. However, I prefer to
rotate the susceptor plate at about 10 revolutions per minute,
which does not impart much centrifugal force to the slices. For
this order of susceptor plate rotation, I prefer a 30.degree. slope
on the upper surface of the susceptor plate. However,
25.degree.-40.degree. slopes can readily be used at such speeds.
Higher slopes tend to limit the speed of plate rotation and lower
slopes tend to require higher rotation speeds. Also, ring 30 need
not be stationary, so long as it rotates at a different speed than
the susceptor plate. However, rotation of ring 30 is not
preferred.
My apparatus is otherwise used in the normal and accepted manner
for vapor plating generally or for epitaxial deposition of
semiconductive materials. The deposition gases are initially
flushed through the chamber for a sufficient duration to normalize
the environment. After this the induction heater is energized to
raise the temperature of the susceptor plate, which in turn heats
the slices to the desired deposition temperature. The deposition
gases can be a mixture with hydrogen functioning as a carrier gas
for silicon tetrachloride vapor and trace amounts of a selected
impurity such as antimony or boron can be used. After the
deposition chamber has been sufficiently flushed with this gaseous
mixture, the induction heater is energized to raise the temperature
of the slices to about 1,200.degree.-1,450.degree. C. A positive
pressure is continuously maintained in the upper part of the
chamber during the deposition to maintain a downward flow of gases
around skirt 28 and out through exit ports 36. Rotation of tube 20
is started at least by the time the induction heater is energized.
This action rotates the susceptor plate, causing planetary rotation
of the slices 34 within the recesses 32. After a sufficient coating
thickness has been deposited on the slices, induction heating is
discontinued. When the slices have sufficiently cooled, flow of the
gaseous mixture and rotation of the susceptor plate can be
discontinued.
It is to be understood that although this invention has been
described in connection with certain specific examples thereof no
limitation is intended thereby except as defined in the appended
claims.
* * * * *