US2902574A - Source for vapor deposition - Google Patents

Description

Sept. 1, 1959 Filed Feb. 3, 1958 R. A. GUDMUNDSEN ETAL SOURCE FOR VAPOR DEPOSITION 2- Sheets-Sheet l Jon H. Myer, I

Richard A. Gudmundsen, INVENTORS.

A TTORNEY.

p 1959 I R. A. GUDMUNDSEN ETAL 2,902,574

SOURCE FOR VAPOR DEPOSITION Filed Feb. 3, 1958 2 Sheets-Sheet 2 F fg. 6.

Jon H. Myer,

Richard A. Gudmundsen,

INVENTORS.

A T TOR/VE Y United States Patent Office 2,902,574 SOURCE FOR VAPOR DEPOSITION Richard A. Gudmundsen, Rolling Hills, and Jon H. Myer,

Los Angeles, Calif., assigno'r'sto Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Application February 3, 1958, Serial No. 712,913 Claims. :1. 2219-19 This invention relates to vapor deposition and more particularly to an improved source from which a relatively thick layer of molten material may be deposited by evaporation upon a surface to be coated.

In the prior art wherein a layer of molten material is to be deposited upon a surface by evaporation of the material from a source, difliculty has often been encountered when it becomes desirous to deposit relatively thick layers by the methods heretofore known. For example, vapor deposition of materials in the prior art has generally been performed by resistance heating of a wire filament of various configurations. Such a filament works well so long as relatively thin layers of material are deposited. When thick layers of material are required and the amount of material placed upon the wire filament is increased to accomplish this, it has been found that the material to be deposited upon becoming molten tends to fall or drop from the filament prior to evaporation thereof. This, therefore, limits the amount of material which may be placed upon the wire filament and in turn limits the thickness of the moltenlayer of material which may be deposited upon the desired surface. It has also been found in many instances that the thickness of the layer of material deposited upon the desired surface is not uniform.

A further consideration of prior art methodsis that when evaporating from a wire filament or the like the vaporized material leaves the filament in a non-directional manner. Such evaporation tends to coat the interior surface of the chamber within which the evaporation is taking place, thus resulting in a great loss of material.

Accordingly, it is an object of the present invention to provide a source for vapor deposition of relatively thick layers of material upon a desired surface.

It is another object of the present invention to provide a source from which material may be evaporated to provide relatively thick layers thereof upon a desired surface and from which the material to be evaporated will not drop prior to evaporation thereof.

It is still another object of the present invention to provide a source from which material may be evaporated and which is capable of retaining large amounts of material and from which the material may be evaporated evenly over the surface upon which it is to be deposited.

A still further object of the present invention is to provide an improved source from which material may be deposited in substantially thick layers upons urfaces to be coated therewith which is adapted for production processes and which is rugged in construction.

Yet another object of the present invention is to provide a source from which material may be evaporated in a controlled and predetermined direction.

An improved source for vapor deposition of a material upon a surface to be coated therewith in accordance with the present invention comprises a'member of heat conducting material having an orifice in the surface thereof which, is disposed in a predetermined direction, at least one cavity is provided within said member for receiving 2,902,574 I Patented Sept. 1, 19 59 2 a material which is to be deposited, the orifice and the cavity being in communication with each other.

The novel features of the present invention are set forth in the appended claims. Further objects and advantages of the present invention will be better understood from the following description taken in connection with the accompanying drawings in which alternative embodiments of the present invention are illustrated by way of example. It is to be expressly understood however that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of this invention.

Fig. 1 is a schematic diagram partly in cross section of one form of apparatus in which the present invention may be employed.

Fig. 2 is a top view of one embodiment of a container in accordancewith the present invention.

Fig. 3 is a schematic diagram of a cover or cap for the container as shown in Fig. 2. t

Fig. 4 is a cross sectional view of the container as illustrated in Fig. 2 taken about lines 44.

Fig. 5 is 'a schematic diagram partly in cross section illustrating the container as shown in Fig. 2 fully assembled and in operation.

Fig. 6 is a side view partly in cross section of an alternate embodiment of a container in accordance with the present invention.

Fig. 7 is a top view of the container of Fig. 6 illustrating the arrangement of cavities therein.

Fig. 8 is a cross sectional view of the container illustrated in Fig. 6 taken about the lines 88.

Referring now to the drawings wherein like reference characters designate like or corresponding parts throughout the various views, there is shown in Fig. 1 one form of apparatus for depositing a material such as molten metal upon the surface of a semiconductor body which is illustrative of the applicability of the present invention. For example, in forming a P-N junction upon a silicon semiconductor body in accordance with the method disclosed and claimed in Patent No. 2,789,068, issued April 16, 1957, to J. Maserj ian, a silicon body is preheated to a temperature above the eutectic temperature of silicon and aluminum and a molten layer of aluminum is deposited upon the silicon surface. The heating of the body and the evaporation of the aluminum upon the surface thereof is performed in an inert atmosphere or a vacuum. The apparatus as shown in Fig. 1 may also be used to evaporate a metal such as gold upon the surface of a semiconductor body to provide an ohmic connection thereto. Although the applicability of the present invention will be discussed with respect to deposition of metal upon a silicon semiconductor body, it is to be expressly understood that many other materials may be deposited from the source of the present invention. An example of additional materials is compounds or oxides of various material, such as those used in lens coatings, surface protection and shadow casting for electron microscope work.

Referring now more particularly to Fig. l, the apparatus for carrying out a process as described above is shown and comprises a vacuum chamber 11 defined by a bell jar 12, and a base 13, a port 14 communicates with the vacuum chamber 11 and is attached to a vacuum pump 15. A resistance heating platform 16 is sup ported within chamber 11 by any means known to the art, not shown for purposes of clarity. Platform 16 is connected outside the vacuum chamber to a source of electrical energy 20 by means of leads 17 and 18. The source of electrical energy 20 maybe any type presently known to the art which is controllable for supplying a predetermined amount ofelectrical energy to platform 16 and is preferably of a type to supply a low-current at high voltage. It may, for example, include an 3 auto-transformer which is connectable across a 110 volt alternating current source.

Positioned within vacuum chamber 11 is a container 21 constructed in accordance with the present invention. Container 21 is connected to another source of electrical energy 2%), which is preferably of a type to supply a high current at low voltage, by means of leads 22 and 23. As illustrated in Fig. 1, container 21 comprises a resistance heated container. It is, however, to be expressly understood that container 21 may be heated indirectly as well as by means of passing an electrical current therethrough.

Container 21 in its presently preferred embodiment, as shown in Fig. 2, comprises a member of heat conducting material, a recess 31 is provided along a portion of the surface thereof which is adapted to receive a cover or cap 32 as illustrated in Fig. 3. Slideable clamps 33 are provided for retaining cover 32 in place as hereinafter more fully described. The surface of container 21 defines an orifice therein as shown at 34 in Fig. 2. Orifice 34 extends from the recessed portion 31 through the opposite side of container 21 as more clearly shown in Fig. 4. Also provided within container 21 is a plurality of cavities 35 spaced along the length of the container. The number of cavities is determined by the amount of material to be deposited and the surface area to be covered and, therefore, may be as few as one, there being no upper limit. Web 36 separating the cavities from the orifice is recessed along the top surface thereof as more clearly shown in Fig. 4 to provide direct communication between each cavity and the orifice 34. Although it is not deemed necessary, a rib 37 is Provided between the outer wall of container 21 and the interior thereof in order to provide structural strength to con tainer 21, thereby making it more rugged in construction and thus better adapted for utilization in production techniques.

In order to further illustrate the utility of the present invention, the operation of the apparatus of Fig. 1 will be further described in conjunction with the formation of an ohmic contact by depositing a layer of molten gold upon a semiconductor body. With the bell jar 12 removed, a semiconductor body 45 is placed upon resistance heating platform 16, particles of gold 41 and 42 are placed within cavities 35 of container 21 as shown in Fig. 5. In a typical example for providing an ohmic contact to a silicon crystal a container having twelve cavities distributed along its length may be used. About 2.7 grams of gold would be distributed evenly in each of the twelve cavities. The specific amount of material to be used in any particular application is dependent upon the surface area to be coated and the thickness of material to be deposited. Cover 32 is then placed within recess 31 and clamps 33 are positioned so as to retain cover 32 in place. Container 21 is then placed within chamber 11 and electrical connection made thereto. In the presently preferred embodiment of the apparatus as shown in Fig. 1, container 21 may be held in place by clamps which also provide the electrical connection and at the same time allow container 21 to be adjusted in such a manner that the orifice is disposed in a downward direction towards semiconductor body 45. Container 21 is positioned above the upper surface of the body 45 as shown in Fig. 1. The distance between the upper surface of body 45 and container 21 is not critical and may vary depending upon the particular design considerations involved in each application.

Bell jar 12 is then placed upon base 13 and the chamber 11 sealed by means of gaskets 24 and chamber 11 is then evacuated. Current is applied to resistance heating platform 16 from source of electrical energy 24) to raise it to the necessary temperature. After the heating platform has attained the required temperature current is passed through container 21 to raise it to a temperature suflicient to melt and evaporate the gold as shown in Fig. 5. In practice using a container 21 made of carbon approximately /8 inch in diameter, approximately 300 amperes of current are passed through container 21 until the surface thereof between clamps 33 appears to be bright yellow in color indicating a probable temperature for the container of more than 1250 C. At such a temperature the gold will become molten and will then pass into the vapor state thus leaving the cavities and being projected through the orifice as shown at 42 in Fig. 5 upon the surface of semiconductor body 45. The temperature is maintained for a time sufficient to evaporate the desired amount of gold upon the surface of body 45, utilizing the material and container above referred to. If the temperature is maintained for approximately 10 minutes, it has been found that approximately milligrams of gold per square inch of surface area will be deposited. When the gold evaporates and is deposited upon the surface of semiconductor body 45 to the desired depth, the semiconductor body is cooled to form the ohmic connection thereto.

Although a carbon filament was illustrated in connection with the apparatus of Fig. 1 for evaporating gold upon the semiconductor body, it will be apparent to those skilled in the art that many other materials may be utilized for the container as illustrated. The considerations which must be made in choosing a material for the container are as follows: the melting point of the container material must be greater than the melting point of the material to be deposited upon the desired surface and in some applications, such as evaporation of metal upon the surface of semiconductor bodies, the material of the container must be chosen so as to prevent the intro duction of undesired contaminants into chamber 11.

It should be further understood that many modifications of the internal structure of container 21 may be made without variation from the scope of the present invention. As an example, an alternative embodiment of a container in accordance with the present invention is illustrated in Figs. 6 through 8.

Referring now more particularly to Fig. 6 there is shown a container 51 having cavities 52 disposed therein. A cap 53 retained by clamps 54 is utilized to cover cavities 52 during the evaporation of material therefrom. Communicating with cavities 52 is an orifice 55 more clearly illustrated in Fig. 7. As shown in Fig. 7, cavities 52 may be disposed on opposite sides of orifice 55 and in staggered relationship with each other. As more clearly shown in Fig. 8, cavities 52 are disposed at an angle with respect to orifice 55. In practice particles 56 of metal to be vapor deposited upon a desired surface are placed within cavities 52 as shown in Fig. 8. Cap 53 is then placed upon container 51 and clamps 54 positioned to retain it firmly in place. As hereinabove described, the temperature of container 51 is raised first above the melting point of the material to be evaporated and maintained there until the material within cavities 52 becomes molten. The temperature of the container is thereafter raised above the evaporation temperature of the material to thus evaporate material 56 causing it to pass from the cavities 52 and through the orifice 55 com municating therewith in a downward direction upon the surface of the material to be coated.

There has thus been described a container for evaporat ing material in relatively thick and uniform layers upon a surface to be coated therewith which is capable of retaining large amounts of the materials to be evaporated and of depositing said material in a predetermined direction upon the surface to be coated while at the same time eliminating dropping of the molten material prior to evaporation thereof.

What is claimed is:

1. In a system for evaporating a material upon the surface of a body to be coated therewith, a container for vaporizing said material and directing it toward said body, said container comprising; an elongated member of heat conducting material, a slot provided laterally in and extending through said member to thereby provide first and second opposed openings in the surface of said member, a cavity within said member adjacent said slot and providing a third opening within the surface of said member and adjacent said second opening, said cavity communicating with said slot, and means for substantially sealing said second and third openings.

2. In a system for evaporating a material upon the surface of a body to be coated therewith, a container for vaporizing said material and directing it toward said body, said container comprising; an elongated member of heat conducting material, a plurality of cavities disposed within and longitudinally along said member and adapted to receive said material, each of said cavities forming a first opening Within a surface of said member, a slot provided laterally in and extending through said member to thereby provide second and third opposed openings within a surface of said member, each of said cavities communicating directly with said slot, and means for substantially sealing said first and second openings.

3. In a system for depositing a metallic material upon at least one surface of a semiconductor body, a container for vaporizing said material and directing it toward said semiconductor body, said container comprising; an elongated member of electrical and heat conducting material, a plurality of cavities disposed within and longitudinally of said member and adapted to receive and to retain said material prior to evaporation thereof, a slot disposed within and extending through said member to provide first and second openings therein and communicating directly with said cavities, and a cover for substantially sealing said cavities and said first opening, said second opening being positioned toward said body, whereby said material upon vaporizing is directed through said second opening and toward said semiconductor body.

4. In an evacuated system for depositing a metallic material upon a semiconductor body, a container for vaporizing said material and directing it toward said semiconductor body, said container comprising; an elongated substantially cylindrical electrically and thermally conductive member, a plurality of cavities within and disposed along the length of said member and adapted to receive and retain said metallic material prior to vaporization thereof, a slot within and extending through said member to thereby provide first and second openings in said members, said first opening being adjacent said cavities, said slot communicating directly with said cavities, and means for substantially sealing said cavities and said first opening, whereby said metallic material upon vaporizing passes from said cavities through said slot and away from said member toward said body.

5. In an evacuated system for depositing a metallic material upon a semiconductor body, a container for vaporizing said material and directing it toward said semiconductor body, said container comprising; an elongated carbon bar, a plurality of cavities disposed within said bar and tandemly along the length thereof for-retaining said material prior to the vaporization thereof, a laterally disposed slot extending through and providing first and second opposed openings in said bar, said first opening being disposed adjacent to said cavities and communicating therewith, a cover adapted to substantially seal said first opening of said slot and said cavities to direct said material upon vaporizing through said second opening of said slot in a downward direction toward said body, means operable for retaining said cover over said cavities and first opening, and means disposed upon said bar for providing electrical connection thereto.

References Cited in the file of this patent UNITED STATES PATENTS 2,439,983 Morgan et a1 Apr. 20, 1948 2,447,789 Barr Aug. 24, 1948 2,479,541 Osterberg Aug. 16, 1949 2,730,986 Patton Jan. 17, 1956 2,793,609 Shen et a1. May 28, 1957 2,812,411 Moles Nov. 5, 1957

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