US3407783A

US3407783A - Vapor deposition apparatus

Info

Publication number: US3407783A
Application number: US393253A
Authority: US
Inventors: Emil R Capita
Original assignee: Individual
Current assignee: Individual
Priority date: 1964-08-31
Filing date: 1964-08-31
Publication date: 1968-10-29
Anticipated expiration: 1985-10-29

Description

Oct. 29, 1968 Filed Aug. 3l, 1964 E. R. CAPITA VAPOR DEPOS IT ION APPARATUS 3 Sheets-Sheet l L .l S 39 l i 38 INVENTOR.

5 4Sheeos-Sheet 2` E. R. CAPITA VAPOR DEPOSITION APPARATUS Illllllllllgillllll Oct. 29, 1968 Filed Aug.V 3l, 1964 Oct. 29, 1968 E. R. CAPITA VAPOR DEPOSITION APPARATUS 3 Sheets-Sheet I5 Filed Aug.- 3l, 196,4

i .5. T INVENTR.`

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United States Patent O 3,407,783 VAPOR DEPOSITION APPARATUS Emil R. Capita, Hudson, NJ. (7020 Hudson Blvd., North Bergen, NJ. 07047) Filed Aug. 31, 1964, Ser. No. 393,253 Claims. (Cl. 11S-49.5)

The present invention relates to a means for vapor plating and more particularly to an improved vapor coating furnace of the type adapted to form a coating of a precisely controlled and uniform thickness. The present invention is particularly characterized by its improved coating thickness and uniformity, its reduction in any possible contamination, and its improved and more useful structure which simplifies operation and decontamination.

The present invention represents an improvement in this general type of vapor coating apparatus wherein a uniformity of the coating thickness, an improved depth control, and a degree of purity of the coating are obtained which have not been heretofore achieved. In particular, the apparatus of the present invention is an improvement upon my copending application Ser. No. 189,365, tiled Apr. 23, 1962, now Patent No. 3,233,578.

Known vapor deposition coating processes reduce or decompose a volatile compound on the heated surface of the object to be coated. The hydrogen-reduction process, for example, passes hydrogen over a heated liquid metal halide to provide a resulting mixture of hydrogen and the metal halide vapor. The mixture passes into a furnace coating chamber having a controlled pressure where it reacts at the heated surface of the object to be coated and deposits an adherent coating of the nonvolatile reaction product.

An important use of vapor deposition is in applying silicon coatings to silicon discs or slices such as are used in the manufacture of transistors. A silicon slice comprises the N-type and a silicon coating on the slice comprises the P-type. The coating purity, the uniformity of the coating thickness, and the control of the coating depth are of critical importance in transistors. The apparatus of the present invention obtains these results in a simpler and more reliable manufacturing operation to give a better product. The invention will now be described in a silicon coating operation although it is to be understood that it is not limited to such an operation and may be used with other coatings on other objects in a similar way.

Accordingly, an object of the present invention is to provide improvements in vapor plating.

Another object of the present invention is to provide an improved apparatus for vapor plating combining improved coating control and contamination elimination with simplicity of furnace manufacture and operation.

Another object of the present invention is to provide an improved vapor plating furnace which is safely and efficiently operated by relatively inexperienced personnel.

Other and further objects of the invention will be obvious upon an understanding of the illustrative embodiment about to be described, or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice.

A preferred embodiment of the invention has been chosen for purposes of illustration and description and is shown in the accompanying drawings, forming a part of the specification, wherein:

FIG. l is a perspective view partially cut away of a preferred embodiment of the vapor plating furnace of the invention;

FIG. 2 is a vertical sectional view of the vapor plating furnace of FIG. 1 taken along line 2-2 of FIG. l;

FIG. 3 is a top plan view of a Faraday shield for the apparatus;

3,407,783 Patented Oct. 29, 1968 ICC FIG. 4 is a sectional view of the Faraday shield taken along line 4-4 of FIG. 3;

FIG. 5 is a sectional view of a heating coil lead disconnect taken along line 5-5 of FIG. l;

FIG. 6 is an enlarged detailed sectional view of the connection between the rotating article support and the source of gas and vapor;

FIG. 7 is an exploded perspective of the support of FIG. 2;

PIG. 8 is a vertical sectional view of another embodiment of the vapor plating furnace; and

FIG. 9 is a plan View of another embodiment of the furnace of FIG. 8 for polycrystal deposition.

The improved coating apparatus or furnace will first be described generally with particular reference to FIGS. 1 and 2. As discussed above, the process will be described in connection with the formation of a silicon coating upon silicon slices in the manufacture of P-N type transistor elements wherein the slices comprise the N-type and the silicon coating comprises the P-type. The silicon slices to be coated are illustrated at 1 arranged in spaced relation on the top of a susceptor 12 on a rotatable support 2.

An air-tight chamber is provided surrounding the support 2 and comprising a removable cover 4 formed of a heat and corrosion resistant quartz. The cover 4 is removably mounted by means of an air-tight seal 5 on a hollow and air-tight base 6. The gases used in the process to purge the air-tight chamber and the vapor plating mixture are admitted to the chamber through a gas and power coupling 7 in base 6 and an exhaust outlet 8 (FIG. l) is provided to evacuate 'the enclosure and to withdraw the purging gases and the spent gases of the vapor coating mixture from the furnace.

The slices 1 are raised to the reaction. temperature before the vapor plating operation by a pancake-type induction heating coil 9 mounted beneath the susceptor 12 and coupled to a high frequency power source through the coupling 10 in the base 6. The ring-like susceptor 12 is preferably formed of molybdenum or pure graphite which is heated by the field of the induction heating coil 9 and which transfers the heat energy to the slices 1. During the heating and the plating operations, the entire support 2 including the susceptor 12 is rotated. The support 2 includes a hollow support shaft 11 having an upper flanged portion 13 and a lower drive portion 14.

The coating mixture of gas and vapor is directed upwardly through the hollow shaft 11 so that it flows radially outwardly over the slices 1 which are being rotated on the susceptor 12 of the support 2. While the coating mixture may be passed directly out of the flared outlet at the top of the upper shaft portion 13, a preferred embodiment is illustrated in FIG. 2 wherein a feed tube 13 is mounted in the upper portion 13 of the shaft 11 having a anged outlet at its top so that the coating mixture is released centrally but above the slices 1.. The uniformity of the coating thickness has been found to be improved by the use of a rounded dome 16 positioned on support 2 below the feed tube 13. This dome 16' is also formed of a heat resistant material such as quartz and a preferred embodiment as illustrated is made up of an inner and outer shell. As illustrated in FIG. 2, the ring-like susceptor 12 is removably held in place on a quartz support plate 15 and is held down on the support plate by a quartz hold-down plate 16. As seen in FIG. 7, these

plates

15 and 16 preferably have a generally triangular shape to further facilitate the even flow of the coating mixture about the slices 1.

In order to further insure the uniform heating of the slices 1, the induction heating coil 9 is mounted on an adjustable support plate 17 of a suitable heat resistant insulating material such as quartz. The relative position of the coil 9 with respect to the rotating support 2 is adjusted by changing the lengths of the supports 18 which connect the coil support plate 17 to the base 6.

It will be seen that a tine adjustment can bemade of the length of each of the supports by rotating the nut portion 19 on the threaded portion 20. The slice heating may be controlled by this adjustment of the spacing between the coil 9 and the susceptor 12 through a suitable adjustment of the length of the supports 18. In order to prevent corrosion and contamination Within the chamber, the heating coil 9 and the connecting leads 21 and 22 between the coil 9 and the coupling 10 are silver or silver coated. Both the

leads

21 and 22 and the coil 9 are hollow tubes to permit a coolant to be passed through them during the coating or epitaxial deposition operation.

The upper portion 13 of the shaft 11 for the support 2 is preferably made of a material which is heat resistant and corrosion resistant such as quartz. This upper portion 13 is threadedly coupled and sealed with an O-ring to a lower shaft 14 which also has a hollow center 24 communicating with the hollow center of the upper portion 13 and which communicates with the coupling 7 through bearing 26 as will be further described below. The rotatable shaft 11 is supported by thrust bearing 26 and axial bearing 25.

In order to insure an absolutely tight furnace chamber for the coating operation and to maintain a contamination-free coating zone by preventing the entrance of impurities, a novel coupling plan for the detachable shaft 11 is provided in the improved furnace as is illustrated in detail in FIG. 6. The inlet `line 27 for the coating vapor is welded to the bottom of the furnace chamber at a suitable aperture 28 as illustrated at 29. This stationary vapor inlet line 27 has the lower portion 30 of the coupling magnet 31 rotatably mounted thereon on a suitable bearing 32. The radial ange portion 33 of the thrust bearing 26 supports the weight of the support 2 together with bearing and fixes the height of support 2 in respect to the heating coils 9. In order to transmit the rotational drive of the lower magnet portion to the support 2 and to simultaneously provide a hold-down force to improve the seal of the thrust bearing the upper portion 34 of the magnet 31 is flxedly attached to the support shaft 11 by the gripping nuts 36 and 37. The lower portion 30 of the magnet 31 is coupled to a variable speed drive motor through the reduction box 38 and gear train 39 illustrated in FIG. l so that this portion of the magnet rotates about the stationary vapor inlet 27 at a predetermined speed. This motion is transmitted to the support 2 by the magnetic coupling between the upper and lower portions of the magnet 30 as the upper portion 34 rotates in synchronization with the lower portion 30.

Since the vapor inlet 27 is welded to the furnace base 6, itis clear that the only possible source of vapor leakage in this gland is around the surfaces of the thrust bearing 26. This leakage is eliminated or effectively minimized due to the weight of the support 2 and the magnetic force which holds this bearing in place in the furnace base 6. Any leakage that does occur, however, will be seen to pass the vapor into the furnace enclosure rather than into the surrounding atmosphere. Since this inlet is located in the lower portion of the furnace enclosure adjacent to the vapor outlet 8, the vapor pressure on the inside of the bearing and within the shaft 11 will be greater than the pressure surrounding the outside of the coupling 7 so that any leakage which does occur will be outwardly so that there is no entry of vapor through the bearing 26 to the center of the hollow shaft 11. It is thus clear that the above described vapor entry and drive coupling provide an absolutely leak proof and contamination proof vapor and power coupling for the furnace.

The top of the base 6 is cooled by the inlet 41 which connects a source of coolant to cooling channel 42 and cooling tube 43 at the outer edge of the base 6. The channel 42 and tube 43 connect to outlet 44.

As described above, the support 2 is continuously rotated during the vapor plating operation. The variable 4 speed drive motor 40 is adjusted during the vapor plating operation to rotate the support 2 at speeds of from about 5 to 30 r.p.rn. depending upon the thickness of the coating being applied and other operating conditions.

The quartz jar 4 is preferably shielded by a Faraday shield 45 which is cooled by the tube 46 coupled to a coolant source by inlet 47 and outlet 48, FIG. 3. The shield 4S is clamped to the jar 4 by an insulated and open circuited ring-like clamp 49 (FIGS. 1 and 2).

Preferably, a cover 50 is positioned between the heating coil 9 and the support 2. This cover 50 which is formed of a heat resistant nonconducting material such as quartz reduces heat transfer from the susceptor 12 to the water cooled heating coil and prevents the deposition of silicon on the heating coil 9.

The base 6 and lower portion 14 of the shaft 11 are preferably made of corrosion resistant metal such as stainless steel.

In the vapor coating process described above it is particularly important that absolute purity be maintained for the slices 1 prior to the coating operation as well as for the surrounding elements of the furnace and it is equally important that this purity be maintained in the vapor coating formed during the coating process. The above described structure accomplishes this result with a high degree of eiciency, however, it has been found essential also to periodically perform a thorough clean-out of the interior of the furnace and of the various elements therein.

The improved furnace of my present invention has a novel arrangement of its elements to permit such a decontamination including the provision of readily removable supporting elements for the electrical coils and for the support elements for the slices including the vapor distributing and directing elements.

Referring to FIG. 2, the jar 4 is removably maintained on the base 6 with its lower edge engaging the air tight seal 5. The jar or cover 4 is tightly clamped in this position by a movable top clamp 51. When the clamp 51 is removed, the jar 4 together with its Faraday shield 45 is lifted off so that the interior of the furnace is exposed. The supporting and vapor distributing support 2 is now easily removed since, as described above, this support 2 is rotatably mounted in the furnace with the vertical shaft 11 supported in the base 6 by the two

bearings

25 and 26. The support 2 may therefore be removed by being simply lifted vertically from the

bearings

25 and 26. The top plate 52 of the base 6 is lifted from the furnace at the same time by removing the spaced disconnect bolts 53 which hold the plate 52 onto the lower portion of the base 6. The support 2 and the base 6 may be removed as a unit. If it is desired to further disassemble these elements, the threaded couplings between the upper and lower portions of the column 11 and the threaded connection between the top magnet portion 34 and the lower portion of the shaft 11 may be disconnected. Prior to the lifting off of the plate 52 the heat cover 50 for the induction heating coil 9 may be lifted from its supports by the temporary raising of the support 2 and the heating coils 9 themselves are detached at the two disconnect couplings 53' (FIG. 5). As indicated above both the slices 1, the susceptor 12 and the related hold-down weight 16 are readily removable since they are held in place only by gravity in their normal operating positions.

FIG. 8 illustrates another embodiment of the improved vapor coating furnace, In the embodiment already described above, the vapors used in the coating operation are distributed in an outwardly aring pattern from the hollow center 15 of the rotating support 2. The embodiment illustrated in FIG. 8 has a similar furnace enclosure or jar 60 with a pancake-type induction heating coil 61 and an annular susceptor 62 mounted on the rirn of a rotating support member 63,"In this embodiment, however, which is effective for extremely thin coatings the incoming vapor is applied to the moving slices from a stationary. vapor .distributor 64 having a vapor directing nozzle 65 positioned directly above one portion of the circular path of the moving slices 1. Y

The slices 1 are continuously heated by moving in circular path immediately above the circular induction heating coil 61. The slices 1 pass directly beneath an intense concentration of the coating vapor during a portion onlyof their rotation as they move beneath the vapor distributing nozzle 65.

The interior of the coating furnace is kept tight and secure against contamination by 'having tight seals for the entry of the electrical conduits 6 6 and the vapor conduit 64 and by using a magnetic clutch 67 to transmit power to the rotating slice support 63.

A typical operating cycle for the above described coating apparatus of FIGS. 1-7 will now be described.

With the quartz jar 4 removed from the base 6 by releasing clamp 51, the silicon slices 1 which are to be coated are rst carefully placed on a cleaned susceptor 12 and the susceptor 12 is placed on the support 2 and held down by the plate 16. The quartz jar 4 is now placed on the seal 5 on the base 6 and is clamped into position by clamp 51 to form an air-tight chamber. A vacuum is now drawn in the air-tight chamber surrounding the slices 1 of the order of about one micron. The chamber is next purged with nitrogen or an inert gas such as argon, neon, helium and the like by passing it through the chamber between the coupling 7 and the outlet 8.

A high frequency voltage source is connected to the induction heating coil 9 ranging from about 10 k.c. to about 450 k.c. adjusted to provide power in the range required for the various coating processes. A typical temperature range for applying silicon coatings is about 1190" C. to l450 C. The induction heating coil 9 now heats the molybdenum or graphite susceptor 12 and the silicon slices 1 arranged around the edges of the susceptor 12. The temperature of the slices 1 is observed by means of an optical pyrometer through a viewing surface 70 provided on the jar 4. During the heating, the support 2 is rotated at speeds of from 5 to 30` r.p.m. or higher to insure a uniform heating of the several silicon slices 1 and pure hydrogen is passed through the chamber between coupling 7 and outlet 8. A continuous supply of coolant is passed through the coil 9 and the cooling channel 42 and

tubes

43 and 46 for the base and the Faraday shield 45 during the operation of the induction heating coil 9. When the silicon slices 1 have reached a temperature of between 1190 and 1450 degrees C. the vapor plating is commenced by the admission of hydrogen gas containing silicon tetrachloride vapor through coupling 7. This mixture enters through the above described conduits to the center of the rotating shaft 11 and it then ows outwardly and over the heated slices 1 on the rotating susceptor 12 in a uniform pattern. When the mixture of hydrogen and silicon tetrachloride vapor contacts the heated surfaces of the slices 1, it reacts at the heated surface to deposit an adherent coating of silicon on each of the slices 1. In a typical silicon coating operation, the pressure in the chamber at the slices 1 is maintained at about 1 to 2, p.s.i. above atmospheric pressure and the spent gases flow downwardly through the jar 4 to an exhaust zone within the base 6 adjacent to outlet 8 which is kept at about atmospheric pressure by the continuous evacuation of the Spent gases through the exhaust outlet 8 to the atmosphere. This provides for a continuous ow of the mixture past the heated slices 1. The thickness of the silicon coating on the discs is controlled by controlling the pressure and the flow rates of an incoming mixture as well as the proportions of hydrogen and silicon tetrachloride in the mixture and by continuing the flow of mixture for a predetermined time. When this time period has elapsed, the supply of the vapor mixture and the current to the heating coil 9 is cut off and the chamber is again purged with nitrogen or argon or another inert gas and is opened by the removal of the jar 4 to provide access tothe coated discs 1 after a suitable cooling period.

The embodiment illustrated in FIG. 8 and described above is operated in a generally similar manner including the loading and purging steps. During the actual coating process itself, however, the vapor is directeddownwardly onto the moving slices 1 in a concentrated zone determined by the vapor nozzle 65. The heated slices 1 move in a circular path above the induction heating coil 61 and continually pass through this area of concentrated vapor at a constant speed as they turn on the rotating support 63. i

As described above, the coating is done with various mixtures of vapors and gases with the composition depending upon the coating being applied. FIG. 9 illustrates another embodiment of the general type of furnace illustrated in FIG. 8 which differs by having a plurality of nozzles 70 positioned at the edge of a susceptor plate 71 for coating slices 72. Different vapors or gases may be applied from the various nozzles 70 in performing a coating operation known as polycrystal deposition. This furnace thus provides a further degree of llexibility of operation by permitting this control of gas or vapor control through the various spaced nozzles 70 in addition to the slice temperature and rotational speed control as described above. While three nozzles 70 are illustrated in FIG. 9, it is clear that any number of two or more may be used as required -for particular coatings.

FIG. 9 also illustrates double rings of slices 72 being coated on the susceptor 71 and one nozzle 70 is positioned over each ring and the third nozzle 70 is positioned in an intermediate position between the two rings of circularly arranged slices 72. This provides a coating means of even greater capacity and exibility of operation.

It will be seen that significant improvements have been provided in a means for vapor plating whereby a unique coupling is provided for the entry of vapor and for the rotational forces which cooperate with the article heating elements to provide for a uniform and pure vapor coating of objects. The elements of the improved furnace are combined in a particularly effective and novel manner to provide for improved coating characteristics combined with an improved overall coating operation wherein the decontamination, loading and purging steps, which are an important part of the overall process, are made more eficient and more easily performed,

As various changes may be made in the form, construction and arrangement of the parts herein. without departing from the spirit and scope of the invention and without sacrificing any of its advantages, it is to be understood that all matter herein is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. Apparatus for vapor plating articles comprising the combination of a sealed chamber; an induction heating coil in said chamber; an electrically conductive article supporting susceptor mounted on a rotatable hollow shaft adjacent said coil, said sha-ft adapted for connection to a source of said vapor located externally of said chamber and having a vapor outlet disposed substantially equidistant yfrom and above said susceptor; a vapor guide member disposed uniformly about said hollow shaft and, from a location intermediate the vapor outlet and the article supporting surface of the susceptor, having a uniform wall portion extending from said shaft, downwardly and outwardly to said susceptor surface; a vertical thrust bearing for said shaft within said sealed chamber for supporting the shaft, and a non-conducting heat resistant shield member intermediate said coil and said support.

2. The apparatus as claimed in claim 1 in which said susceptor comprises a ring-like member, said susceptor being removably mounted on said shaft intermediate a support plate and a hold down plate, and :said plates being shaped to permit the passage of a portion of the vapor downwardly through the center of the ring-like susceptor.

3. The apparatus as claimed in claim 1 which further comprises a Faraday shield at least partially surrounding said chamber.

4. The apparatus as claimed in claim 3 in which said shield includes liquid cooling means.

5. The apparatus as claimed in claim 1 wherein means to drive said hollow shaft comprises a magnetic couple.

References Cited UNITED STATES PATENTS 8 Van Leer et al. 118-49.1 X Goetzel et al.

Tassara 11,8-49 Theodoseau et al. A

117-107.1 X Auzolle 118-49 Spitzer et al 11S-48X Reuschel 11S-49.5 X Capita 118-49.1

CHARLES A. WILLMUTH, Primary Examiner.

MORRIS KAPLAN, Assistant Examiner.

Claims

1. APPARATUS FOR VAPOR PLATING ARTICLES COMPRISING THE COMBINATION OF A SEALED CHAMBER; AN INDUCTION HEATING COIL IN SAID CHAMBER; AN ELECTRICALLY CONDUCTIVE ARTICLE SUPPORTING SUSCEPTOR MOUNTED ON A ROTATABLE HOLLOW SHAFT ADJACENT SAID COIL, SAID SHAFT ADAPTED FOR CONNECTION TO A SOURCE OF SAID VAPOR LOCATED EXTERNALLY OF SAID CHAMBER AND HAVING A VAPOR OUTLET DISPOSED SUBSTANTIALLY EQUIDISTANT FROM AND ABOVE SAID SUSCEPTOR; A VAPOR GUIDE MEMBER DISPOSED UNIFORMLY ABOUT SAID HOLLOW SHAFT AND, FROM A LOCATION INTERMEDIATE THE VAPOR OUTLET AND THE ARTICLE SUPPORTING SURFACE OF THE SUSCEPTOR, HAVING A UNIFORM WALL PORTION EXTENDING FROM SAID SHAFT, DOWNWARDLY AND OUTWARDLY TO SAID SUSCEPTOR SURFACE; A VERTICAL THRUST BEARING FOR SAID SHAFT WITHIN SAID SEALED CHAMBER FOR SUPPORTING THE SHAFT, AND A NON-CONDUCTING HEAT RESISTANT SHIELD MEMBER INTERMEDIATE SAID COIL AND SAID SUPPORT.