US 3187715 A
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June 1965 c. L. WELLARD MECHANISM FOR EVAPORATION DEPOSITION 2 Sheets-Sheet 1 Filed Oct. 23, 1965 INVENTOR. CHARLES L. WELLARD momnow l u ATTOR NEY June 8, 1965 3,187,715
c. L. WELLARD MECHANISM FOR EVAPORATION DEPOSITION Filed Oct. 25, 1963 2 Sheets-Sheet 2 INVENTOR.
CHARLES L.WELLARD WfM ATTORNEY United States Patent 3,187,715 MECHANLM FQR EVAP'SRATEQN BEPQSHTIQN Qharies IL. Weilard, Wayne, Pm, assignor to American Components, ind, Conshohociren, Pa, a corporation of Pennsylvania Filed Get. 23, 1963, Ser. No. 31%,4-49 7 (Ilaims. (Qt. 118-49) The present application is a continuation-in-part of my copending application entitled Mechanism for Evaporation Deposition, Serial Number 164,900, filed l'anuary 8, 1962, and now abandoned.
This invention relates to evaporated films and more particularly to a mechanism for producing an evaporated electrically-resistive film on substrate elements. At each part of the following specification wherein the continuation information has been included, the specification will be set out in brackets.
The technique of evaporating metal under vacuum is well known. This technique has been employed to some extent in the production of electrically-resistive films on substrate elements to provide electrical resistors. In the course of such a procedure, initially, a strip of a particular metal, which is to be evaporated, is wrapped around a heating element such as tungsten, or a boat is shaped in the tungsten element, and the metal to be evaporated is placed in the boat. Thereafter the heating element is heated under a high vacuum condition and the particular metal melts and evaporates on all exposed surfaces of the substrate elements.
In order to produce a uniform film on the entire surface of each substrate, or resistor blank, there must be a means of uniformly exposing all surfaces thereof. Heretofore the techniques employed to obtain a uniform exposing of all of the surfaces of the substrate elements normally involved some version of the so-called Ferris Wheel Method. Generally in the Ferris Wheel Method the re sistor blanks are fastened by wires to theperiphery of a wheel and the wheel is rotated about a heating element or a source of evaporating metal. In one version of the Ferris Wheel Method the substrates are held fixed in space and get the entire surface exposed by rotating around the fixed heating element. In another version the individual elements are rotated about their own axis as well as around the axis of the wheel.
While this above-mentioned technique has merit, it also has a number of inherent disadvantages. First, since the substrates are fastened to the periphery of the wheel, they are normally tubes which allow a wire to be passed through the center thereof (for fastening purposes) rather than solid ceramic rods. The tubular shaped substrates are more costly than the solid ceramic rods. econdly, the labor for fastening and unfastening the substrates to and from the wheel isanother costly factor. A third disadvantage is that there is little flexibility in changing the distance between the source of evaporating metal and the substrates since the locations on the wheel are fixed. Fourthly, the substrates are subjected to the evaporating metal during their entire 360 excursion around the evaporating metal source and this arrangement gives rise to a shortened evaporation time which, in turn, leads to control problems.
Accordingly, it is an object of the present invention to provide an improved mechanism for producing evaporated film electrical resistors.
It is a further object of the present invention to provide a mechanism for producing evaporated metal film resistors which can readily alter the distance between the ice source of evaporating metal and the substrates to effect a high degree of control.
It is a still further object of the present invention to produce a mechanism for producing evaporated metal film resistors which requires a minimum of handling of the substrates and which enables the substrates to be solid rods rather than tubes.
It is another object of the-present invention to provide a mechanism for producing evaporated metal film resistors, in which there can be a regulation of the speed at which the surfaces of the substrates are exposed to the source of evaporating metal, thereby eifecting a high degree of control.
In accordance with a feature of the present invention there is provided a rotatable chamber having fins therein and an opening on either end, which rotates and causes the substrates to tumble, thereby uniformly exposing all the surfaces of all of the substrates to the evaporating metal.
In accordance with another feature of the present invention, there is provided an adjustable holding mechanism disposed adjacent to said rotatable chamber. Said holding mechanism positions the heating element and the metal to be evaporated at predetermined distances from the substrates in order to efiect desired controls for producing evaporated metal film resistors.
in accordance. with another feature of the present invention there is provided a variable speed drive which rotates the rotatable chamber at predetermined speeds to effect desired controls for producing evaporated metal film resistors.
[In accordance with another feature of the present invention, there is provided an adjustable shield with an aperture included therein which directs and limits the amount of evaporant being deposited on the substrates when resistors having high ohmic values are being produced] The foregoing and other objects and features of this invention will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawing, wherein:
FIG. 1 is a pictorial-schematic of the present mechanism for producing evaporated metal film resistors;
FIG. 2 is a pictorial view of a heating element with a boat shaped therein;
[FIG. 3 is a sectional schematic of the rotatable chamber of FIG. 1 showing the adjustable shield] Consider FIG. 1 which shows the mechanism mounted on a double table having a first table surface 11 and a second table surface 13. The rotatable chamber 15 is supported by four friction drive wheels 17, two of which can be seen in FIG. 1. Two other identical friction drive wheeis support the rotatable chamber 15 on the side which is not shown in FIG. 1. Although the rotatable chamber 15 is depicted as being friction driven by the wheels 17, it should be readily understood that other ways of driving the chamber 15 could be employed.
The friction drive wheels 17 are secured to the axle 19 which is supported by two bars 21. The support bars 21 are bolted to the table 11. Fastened to the end of each axle 19 is a primary drive wheel 23. Looping the primary drive wheels 23, over the central drive 25, is a belt 29. Although a belt drive is shown in FIG. I, obviously a chain drive or gear chain drive could be used.
As the motor 31 drives the shaft wheel 27, the gear28 moves to engage and drive the gear 39. Gear 30 is pinned to shaft 32 which is further pinned to the central drive wheel'25. The shaft 32 is supported by bracket 34. The shaft 27 passes through table surface 11 by means of a vacuum sealed sleeve 36. As' the central drive wheel 25 turns, the primary drive wheels 23 also turn and the chamber is rotated by the friction drive of Wheels 17. Since motor 31 is a variable speed motor, the
speed of rotation of the chamber 15 can be varied uccording to any desired evaporation control which is required.
Although it was mentioned earlier that other types of drive sysems can be used, the simple friction drive depicted in FIG. 1 does provide advantages for unloading substrates from the chamber 15 and cleaning the chamber 15. Since the rotatable chamber, 15 is simply'supported by the friction drive wheels 17 it can be easily removed by lifting, and held on end to enable the substrates to be dumped out. Other types of drives would entail disengaging some mechanism.
It should be noted that the flanges 33 limit the forward and backward movement of the chamber 15. As the chamber-15 moves forward or backward the flanges 33 bump into the friction wheels and terminate such. horizontal movement.
Through the end opening 35 of the rotatable chamber 15 there can be seen depicted two fins 37 and 39. Actually such fins aredisposed around the entire inside surface of the chamber 15. The fin 37 is disposed at an angle such that the substrates 41 tumble and/or roll toward the front of the chamber 15 as the chamber is rota-ting clockwise. The fin 39 is disposed at an angle such that the blanks 41 tumble and/or roll toward the rear of the rotatable chamber 15 as it rotates clockwise. By virtue of this tumbling effect the surfaces of each of the substrates is fully exposed to the source of evaporating metal. Fins or'agitating members of other shapes can readily be employed.
Actually the substrates are loaded in the bottom portion of the chamber 15 with some substrates piled on top of others. The tumbling effect just described causes the substrates on the top to move to the bottom of the pile and the substrates on the bottom to work their way to the top of the pile. This churning or cyclical movement of the substrates within the pile insuresthat each resistor blank gets its fair share of metal evaporated thereon. In addition the substrates in the piletend to shield one another and this extends the time of evaporation for a batch, which provides better end products, as will be more fully discussed below.
As shown in FIG. 1, the heating element 43 is mounted by the variable positioning device 45.. The adjustment screw 47 is unscrewed to allow the upper portion 49 of the positioning device 45 to be moved up and down. When the correct position for mounting the heating element 43 is attained, the adjustment screw 47 is tightened thereby holding the upper portion 49 in place.v
In order to mount the element 43 in place the adjustment screw 51 is unscrewed or loosened. The halves of the upper portion 49 (which are permanently bonded together along the lower portion) are spread and the heating element 43 is inserted therein. Subsequently the adjustment screw 51- is tightened to hold the heating element-43 secure. On theend of the heating element 43 there is an insulation sleeve 53 which keeps the electrical current which is connected to .the heating element, through clamp 55, from being by-passed to other parts of the machine.
In a preferred embodiment a second positioning device is located at the back end of the chamber 15 adjacent to the opening at that end. The second positioning device also holds the heating element 43 as does front positioning device 45. While a second positioning device is. employed in a preferred embodiment, it has been found that the mechanism will successfully operate with only one positioning device.
The electrical current needed to cause the heating element to produce heat, is supplied from the alternating current source 57. A complete circuit is provided by the wire 59, through the clamp 55,. through heating element 43, through a clamp identical to clamp 55 on the back end of element 43, and through wire 61 to source 57. The wires 59 and 61 pass through vacuum sealed holes in table surface 11. When alternating electrical current is passed through the circuit just described, the heating element 43 produces heat which melts the metal to be evaporated and drives it off in metal-vapor form.
As was suggested earlier, a strip of the evaporant or the metal to be evaporated can be wound around the heating element 43, or the heating element 43 can be formed into a boat to hold the metal to be evaporated. FIG. 2 shows a boat-shaped heating element 43a. The metal to be evaporated, or the evaporant, is inserted in the hollow 63 of the boat-shaped element. The heating element is heated with the hollow 63 facing upward until the metal melts and flows over the sides. of the boat. The melted metal adheres to the element 43a and then the element can be repositionedpwith the hollow 63 facing the bottom of the chamber 15 wherein the substrates are located. The element 43a is reheated to high temperature to drive the metal off in vapor form. Either the use of the boat-formed element 43a, or wrapping a strip of metal around the heating element 43 (FIG. 1) is satisfactory.
In FIG. 1 there is shown in phantom a bell jar 65. After the substrates have been loaded in the chamber 15 and the heating element 43 is properly positioned by adjusting the holding device 45, the bell jar 65 is placed over the entire mechanismyas shown. The pump 67 is connected through the table surface 11 to evacuate the bell jar 65 by means of the hose 69. When the bell jar 65 has been evacuated by the pump 67 the metal evaporation process described above can take place.
The speed of rotation of the chamber. 15 must be varied to accommodate the size of'the substratesand the number of the substrates if mixing is to be optimum. For instance, the larger the substrate element the faster the chamber 15 is rotated.
The location of the heating element 43 can be varied to theextent of the diameter of the hole 35. The variable positioning of the heating element 43 is very important to effect controls for the evaporation process, since the evaporation intensity varies inversely as the square of the distance between the source of evaporating metal and the substrates. It has been found that if the evaporation process is of relatively low intensity the uniformity of the thin film is excellent and hence the characteristics of the resistors are very satisfactory. It has been found that there is a correlation between low intensity evaporation of the metal and long stability of the resistors. However,
the evaporation process cannot be unduly prolonged because it also has been found that excessive heat (long tune heat) leads to unnecessary control problems. By being able to adjust the location of element 43, the proper evaporation intensity (within the limits of overheating time) can be maintained. Since the intensity of evaporation can be held on the low side of the continuumfthe evaporatlon inertia is not as detrimental when employing the present system as it is in other systems. In other words, after the heat is turned off very little evaporating metal forms on the substrates.
[When a resistor having a high ohmic value is to be produced, the conductive .film must be made very thin. However, since there is a practical limit of thickness below which a thin film cannot be effectively mass produced and still provide uniform resistance characteristics, such high ohmic valued resistors are often produced by helically cutting or grooving the thin conductive film.
A helical cut provides a current path which is physi-' uniformly distributed over the substrate, so that the resistance does not vary from one part of the spiral path to the next. The requirement of uniformity for a helically cut resistor is more critical than for a full substrate surface resistor because in the latter there is room for balancing out the non-uniformity since the whole surface is used.
In order to produce an extremely thin conductive film, with good uniformity, the shield 75 of FIG. 3 is employed. Within the shield '75 of HG. 3 there is provided an aperture 77. The size of the aperture 77 can be varied by adjusting the two sides of the shield 75. As the evaporant travels from the boat 63a, it can only effect the substrates 79 by passing through the aperture 77.
It is to be understood that the mechanism of FIG. 3 is included with and in addition to the mechanism shown in PEG. 1. For simplicity of explanation, the components of the device in FIG. 1 are not shown, but in actual practice the entire device is used with the shield 75' of FIG. 3.
The shield 75 can be made of material which has a minimum of out-gassing or some suitable refractory material and is mounted by two holders 81 and 83. Holder 81 has a pair of relatively tight swivel joints 85 and 87, while holder 83 has a pair of relatively tight swivel joints 8? and 91. The swivel joints enable the shield 75 to have its two halves positioned so as to adjust the aperture 77. The holders 81 and 83 can be securely fastened to the table 11 by means of the holder bases 93 and 95.
By forcing the effective evaporant through the aperture 77, the amount of time that any individual substrate is exposed to the evaporant by any part of its surface is quite limited. Obviously by varying the size of the aperture, the amount of time can be varied to accommodate different thicknesses of evaporation on the substrates. The time control of exposure of the substrates to the evaporating evaporant is a most important feature of the shield device. Hence for any small surface area the layer of evaporant deposited is thin. The procedure enables the substrates to work their Way back to the top of the batch and thereat to expose a fresh small surface whereon the thin film will again be deposited. In this way the amount of evaporant deposited around the entire surface is thin and uniform.
In addition the shield serves to prevent a great deal of direct heat radiation, from the heating element, striking the substrates which as mentioned earlier is related to the problem of control from prolonged heat. I have found that the temperature coefficient, developed in resistors which are metallized on a relatively cold substrate, is constant and controllable, whereas when the substrates tend toward becoming hot the temperature is not defined and the temperature coefficient in the end product becomes variable. The shield provides enough butfer action between the heating element and the substrates to keep them relatively cool and therefore enable the production of a resistor having a constant temperature coefficient.
E-mpirically I have found that when the shield is used with the remainder of the equipment of PEG. 1, the thin film resistors that are produced enable a helical cut to be made and the resultant spiral shaped resistor provides a uniform resistance value along the entire path] The resistors produced in this mechanism have been resistors with high stability and in the range from 2 ohms per square to 10,000 ohms per square. By encapsulating these resistors in epoxy they have been found to withstand continuous operation at 175 C.
While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.
What is claimed is:
1. A thin film deposition device arrangement comprising in combination: a rotatable chamber to hold substrate elements which are to have thin films deposited thereon, said rotatable chamber having its inside wall formed in such a manner as to cause said substrate-elements to tumble as said chamber rotates; friction drive means supporting said rotatable chamber and adapted to cause said chamber to rotate; variable positioning means adapted to hold heating means in any one of a plurality of positions so that at one extreme of said positions said heating means can be in close proximity to all of said substrate-elements and at the other extreme of said positions said heating means is relatively far from all of said substrateelements; heating means held and positioned by said variable positioning means within said rotatable chamber; said heating means adapted to hold an evaporant and provide heat thereto to cause the evaporation thereof; and air evacuation means covering said deposition device to create a vacuum surrounding said deposition device.
2. A thin film deposition device arrangement comprising in combination: a rotatable chamber to hold substrate-elements which are to have thin films deposited thereon; a plurality of fins disposed within said rotatable chamber to tumble said substrate-elements; friction drive means supporting said rotatable chamber and adapted to cause said chamber to rotate; variable positioning means adapted to hold heating means in any one of a plurality of positions so that at one extreme of said positions said heating means can be in close proximity to all of said substrate-elements and at the other extreme of said positions said heating m ans is relatively far from all of said substrate-elements; heating means held and positionedby said variable positioning means within said rotatable chamber; said heating means adapted to hold an evap orant and provide heat thereto to cause the evaporation thereof; and air evacuation means covering said deposition device to create a vacuum surrounding said deposition device.
3. A thin film deposition arrangement according to claim 2 wherein said heating means is a tungsten element partially shaped like a boat to hold the evaporant in the hollow thereof.
4. A thin film deposition arrangement according to claim 2 wherein there is further included a strip of the evaporant wound around said heating means.
5. [A thin film deposition device comprising in combination: a rotatable chamber to hold substrate-elements which are to have thin films deposited thereon; drive means coupled to said chamber to cause said chamber to rotate; variable positioning means adapted to hold an evaporant within said rotatable chamber and further adapted to position said evaporant in any one of a plurality of positions so that at one extreme of said positions said evaporant can be in close proximity to all substrateelements and at the other extreme of said positions said evaporant can be relatively far from all of said substrateelements; heating means disposed relative to said evaporant to cause the evaporation thereof; and shielding means disposed within said rotatable chamber including an aperture therein which directs the evaporating evaporant to said substrate-elements.
6. A thin film deposition device according to claim 5 wherein said shielding means is adjustable thereby enabling said aperture therein to be adjustable.
7. A thin film deposition device according to claim 2 wherein there is further included a shielding means disposed within said rotatable chamber including an aperture therein, and further including adjustable means holding said shielding means in order to be adjusted and thereby to vary the size of the aperture therein, said shielding means in conjunction with said aperture directing the evaporating evaporaht to said substrate-elements] (References on following page) 7 8 References Cite-:1 by the Examiner 2,847,325 8/58 Riseman et a1. 1'17-107.1
UNITED STATES PATENTS 2,902,574 9/59 Gudmundsen et 31 219*19 3/26 Meurer 3,036,549 5/6'2 Iwata et a1 117-107.1 12/31 Bleecker 118504 5 FOREIGN PATENTS 2/441 Sukumlyn 118-49 869 825 3/53 G 9/50 Johnson et a1. 11s 49 3 54 steinfeld 117 107 1 881,550 11/61 7 Great Bntam.
5/57 Dunn 117-1072 5/57 ostmfsky et aL 117 1O72 10 CHARLES A. WILLMUTH, Primary Exammer.
8/58 Baer et a1. 118-49 RICHARD DJNEVIUS, Examiner.