US 3633537 A
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.
Claims available in
Description (OCR text may contain errors)
United States Patent Inventor William E. Rowe Kokomo, 1nd.
Appl. No. 52,387
Filed July 6, 1970 Patented Jan. 11, 1972 Assignee General Motors Corporation Detroit, Mich.
VAPOR DEPOSITION APPARATUS WITH PLANETARYSUSCEPTOR 2 Claims, 3 Drawing Figs.
U.S. Cl. 118/48, 118/500, 219/1049 Int. Cl C23c 11/00 Field alien-9& 1 181413 495,
References Cited UNITED STATES PATENTS 2,812,846 11/195] Nord quis t.... 118/500 X 3,399,651 9/1968 Forari 1 18/500 3,486,237 12/1969 Sawicki 118/500 X 3,523,517 8/1970 Corbani.... 118/500 3,408,982 I 1/1968 Capita Primary ExaminerMorris Kaplan Attorneys-william S. Pettigrew and R. .1. Wallace 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.
PATENTEUJANHM 3.633537 INVENTOR.
M/Zziazz 5/2 0416 BY ATTORNEY 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 ofany 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 oftheir 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 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 inven- Hon;
FIG. 2 is a sectional view along the line 2-2 of FIG. I 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 0 with a quartz bell jar l0 and a metal baseplate [2. A circular following description of a 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 I8. Quartz pedestal I8 is, in turn, mounted on a stain less 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 late. p 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 l8 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 l0 revolutions per minute, which does not impart much centrifugal force to the slices. For this order of susceptor plate rotation, I prefer a 30 slope on the upper surface of the susceptor plate. However, 25-40 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 l,200l,450 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 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.
1. In an apparatus for growing epitaxial films of highly uniform electronic characteristics on a plurality of semiconductor substrates in a single operation,
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 2540 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.