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In evaporating material to be vapor deposited on a workpiece, either directly or through holes in a pattern, the material to be evaporated may be deposited in the dished out portion of an evaporation boat. The boat may be made of refractory, high-resistance material which is very brittle. The boat is heated to material evaporation temperature by passing a current therethrough, clamps being provided to connect an electrical source to the ends of the boat. The clamps must be tightly fixed to the ends of the boat to prevent electrical arcing between the clamps and the boat because the arcing causes the material of the boat or of the clamps to be vaporized whereby the workpiece will be coated with contaminated material. The boat must be allowed to expand and contract without great enough confinement thereof or without sufficient twisting or bending thereof to cause the boat to break. Otherwise, the brittle boat will be destroyed. As will be understood, these two requirements that the electrical leads to the boat be tightly connected thereto and that the boat be allowed to expand and contract freely and without restriction are inconsistent requirements.
In accordance with the prior art, the electrical clamps to the boat have been tightly fixed thereto but the clamps have comprised parts in electrical contact with each other through which the heating current flows, these parts being allowed to slide with respect to each other to permit expansion and contraction of the boat. Such prior art support and heating means for the boat has been unacceptable since it is impossible to eliminate all arcing between the sliding contacts. Other prior art supports and heating means have included rigid electrical clamps to the boat mounted on a flexible support. However, the expansion and contraction of the boat has caused the flexible support to bend, causing a bending motion to be applied to the brittle boat, causing breakage thereof, making this type of support also unacceptable.
It is an object of this invention to provide means for clamping electrical connections to a boat in a nonarcing manner and to support the boat in a manner to permit its expansion and contraction and yet not to break or damage the boat due to motion caused by the expansion and contraction thereof.
In accordance with this invention, clamping means are provided that may be tightly clamped to the ends of a boat to make electrical connections to the ends of the boat, said clamping means being linearly slideably supported, whereby said boat may be heated by electrical currents passing therethrough and no, or very little, confining or twisting or bending force is applied to the boat.
The invention will be better understood upon reading the following description in connection with the accompanying drawing in which
FIG. 1 shows a boat, including the clamping means of this invention, arranged to evaporate a material which is to be plated on a workpiece,
FIG. 2 is an elevational view of the boat and boat guards which are applied to said boat and which are shown in FIG. 1,
FIG. 3 is an end view of the boat and boat guards of FIG. 2,
FIG. 4 is a section of FIG. 1 on line 4--4 thereof showing a feature of the clamping means of this invention, and
FIG. 5 is an end elevational view of the guide block of FIG. 1 comprising a portion of the clamping means thereof.
Turning first to FIG. 1, a chamber 10 is arranged to be evacuated. The chamber 10 comprises a cylindrical portion 12 and end portions 14 which can be removed to allow access to the cylindrical portion 12. In the cylindrical portion 12, a boat 16 is supported in a manner to be described. The boat 16 is made of high-resistance, highly refractive material such as Union Carbide Aluminide Boride Intermetallic boat material. The boat is of rectangular parallelopiped shape and it is dished out to provide a trough 18 to receive material to be evaporated. Boat guards 20 are fitted on the boat beyond the ends of the trough 18 from the middle thereof. These boat guards 20 may be of any refractory material such as graphite, may have rectangular outer outline and have a central hole through which the boat fits.
In the operation of the equipment of FIG. 1, after the material to be evaporated is placed in the trough 18 and the chamber 10 is either evacuated or is filled with a neutral atmosphere, the boat 16 is raised to the evacuation temperature of the material to be evaporated. This is done by passing electrical currents through the boat 16. An electrical conductive clamp 22 is provided for each end of the boat 16. The clamp 22 comprises an upper plate 24 and a lower plate 26, each of which is conductive. A bolt 28 passes through one, the upper plate 24, and is threaded into the other, the lower plate 26. A spacer comprising a bolt 30 is threaded into the upper plate 24 and bears against the lower plate 26. By adjustment of the bolt 30, the plates 24 and 26 may be made parallel to the boat 16. By adjustment of the bolt 28, the plates 24 and 26 may be so tightly clamped to the boat 16 as to prevent any chance of arcing between the plates 24 and 26 and the boat 16. Two clamps 22 are provided, one for each end of the boat 16. In a known manner, a flexible electrical cable 32 is connected to each plate 24 and 26 and current is caused to flow through the boat 16 by connecting a supply of current to the cables 32 in a known manner.
As the boat 16 heats up, it expands. Since the clamps 22 tightly fit the boat 16, they must move as the boat expands and contracts as it is heated and cooled. The contraction and expansion of the boat must not be so confined or opposed as to break or damage the brittle boat. Supports 34 and their connections to the clamps 22 are provided to permit expansion and contraction of the boat without causing breakage thereof.
The support 34 may be U-shaped having parallel top and bottom arms and a vertical arm. The top arm 36 is slotted at 38, see FIG. 4. A bolt 40 extends through the top and bottom plates 24 and 26 and through a guide block 42. The guide block 42, as shown in FIG. 5, has a lower restricted portion 44 which slideably fits into the slot 38 in the top arm 36 and an upper enlarged portion which bears on the arm 36 on each side of the slot 38. The bolt 40 also extends through the block 42 and through the slot 38 and into a nut 46. Therefore, the clamps 22 can move towards and away from each other as the boat 16 contracts and expands but they cannot twist or turn or move other than in a straight line. Therefore, the boat 16 is so supported on the U-shaped members 34 that there can be no arc between the boat and the electrical connections thereto and also there is little or no confining or bending force applied to the boat by the clamps 22 or by the means for support of the clamps 22 including the U-shaped members 34. Therefore, no arcing takes place between any electrical connections and the boat and, at the same time, the boat is allowed to contract and expand as required in the use thereof.
As is noted above, the system of FIG. 1 is used for evaporative plating of a workpiece. The workpiece 46 may be one or more semiconductive bodies and the workpiece 46 may be supported on a mask 48 having holes provided therethrough to provide a pattern through which evaporative material may flow to be deposited on the workpiece 46 in accordance with the pattern of the mask 48.
The boat guards 20, which are here described for completion of the disclosure, are described and claimed in an application filed in the name of the inventor Philip J. Fox and assigned to the assignee of this application.