US3583363A

US3583363A - Substrate support apparatus

Info

Publication number: US3583363A
Application number: US804535A
Authority: US
Inventors: Robert Leland Shrader
Original assignee: Air Reduction Co Inc
Current assignee: Airco Inc
Priority date: 1969-03-05
Filing date: 1969-03-05
Publication date: 1971-06-08
Anticipated expiration: 1988-06-08

Abstract

Apparatus is described for supporting a substrate in a vapor flow to produce a variation in the direction of exposure of the substrate to the vapor. A generally spherical structure, which supports the substrate, is supported for rotation about at least two nonparallel axes and is rotated about the two axes simultaneously.

Description

United States Patent m WM mn a t "t nuuue "e nu r.r r. nee e "Hm m m .1 6 Kb Ym a 6 AENKGFG 6723477 5566666 9999999 HHHHHHH 3795 7 7 73752 5352 79 0364 72 70040393 2233333 M YLCR m4an o o -le RC8MJAN m mm e mrmem 1 HAFPA H HUM Primary Examiner-Morris Kaplan [541 SUBSTRATE SUPPORT APPARATUS Altorney-Anderson, Luedeka, Fitch, Even and Tabin 7 Claims, 1 Drawing Fig.

ML /4 8 1 1 0 B m MS l m d m .mF M 55 ABSTRACT: Apparatus is described for supporting a sub- -49.5, 53, 56, 500,503; 18/26 R; 269/58, 55 n the direction f exposure of the substrate to the vapor. A generally spherical strate in a vapor flow to produce a variation i [56] References Cited UNITED STATES PATENTS 8/1940 Henderson...................

structure, which supports the substrate, is supported for rotation about at least two nonparallel axes and is rotated about 18/53 the two axes simultaneously.

SUSSTRATE SUPPORT APPARATUS This invention relates to apparatus for supporting substrates for deposition of vapor thereon. More particularly, the invention relates to apparatus for supporting a substrate in a vapor flow to produce a variation in the direction or angle of exposure of the substrate to the vapor, or to expose a relatively large total substrate surface area to the vapor in a minimal required volume, or both.

Certain manufacturing processes involve the coating of a substrate by condensing a vapor thereon. Due to the nature of the materials or the vaporization process, the deposition of the vapor may be required to be carried out in an evacuated environment. For example, the evaporation of metals or semiconductor materials by bombarding the surface of a molten pool thereof with one or more electron beams requires the maintenance of evacuated conditions.

Typically, the vapor source is relatively small, for example 2 or 3 inches in diameter. Accordingly, where a large number of individual substrates are to be coated, the substrates must be moved individually into and out of the path of the vapor from the source. Moreover, for certain types of materials, the nature of the substrate and the coating material requires that the coating be put on at a plurality of different incidence directions or angles to ensure proper film continuity. For example, in the coating of electrical conducting films on microelectronic integrated circuits, if the coating is not put on at different angles, the film continuity in many cases is not satisfactory.

Apparatus for moving a plurality of individual substrates into and out of the flow of vapor, or for moving substrates in a manner to achieve uniform coating from a plurality of angles or directions, is known in the art. Such apparatus, however, has tended to be costly and elaborate, and has frequently required large containment vessels or vacuum enclosures, adding to the costs of the equipment.

Accordingly, it is an object of the present invention to provide improved apparatus for supporting a substrate in a vapor flow to produce a variation in the angle of exposure of the substrate to the vapor.

Another object of the invention is to provide apparatus for supporting a substrate in a vapor flow which provides a very large substrate mounting surface for a given volume of occupied space.

A further object of the invention is to provide apparatus for supporting a substrate in a vapor flow which is capable of moving the substrate in a generally three-dimensional quasirandom manner.

Other objects of the invention will become apparent to those skilled in the art from the following description, taken in connection with the accompanying drawing wherein the sole FIGURE is a perspective view of apparatus constructed in accordance with the invention.

Very generally, the apparatus of the invention comprises a generally spherical structure 11 including means 12 thereon for supporting the substrate. The structure 11 is supported for rotation about at least two nonparallel axes and is rotated above the two axes simultaneously.

Referring now more particularly to the drawing, the apparatus of the invention includes a fixed ring 13 adapted for mounting within an evacuated enclosure. In the illustrated embodiment, the fixed ring is shown supported by three legs l4, l and 16 which, inturn, bear upon the floor of the evacuated enclosure. The

legs

14, 15 and 16 are positioned around the source, not shown, of vapor to be deposited and support the ring 13 directly above the vapor source.

The fixed ring 13 supports a pair of bearings 17, only one of which is visible in the drawing. A first movable ring 18 is supported for rotation about a diametrical axis by the bearings 17, only one of which is visible in the drawing. The diameter or axis of rotation of the first movable ring 18 coincides with a diameter of the fixed ring 13. The outer diameter of the ring 18 is small enough that sufficient clearance exists between the ring 18 and the ring 13 as to allow a full 360 of rotation of the ring 18 within the ring 13. The ring 18 is supported in the bearings 17 by a pair of aligned stub shafts, only one of which, indicated at 19, is visible in the drawing. The shaft 19 extends a farther distance from the ring 18 than the corresponding unillustrated diametrically aligned shaft for reasons which will be explained below.

A pair of

bearings

21 and 22 are supported in suitable notches in the ring 18 aligned on a diameter displaced from the diameter or axis of rotation of the ring 18. A second movable ring 23 is supported by aligned stub shafts24 and 26 in the

bearings

21 and 22, respectively. The stub shafts on the ring 23, as well as the stub shafts on the ring 18, may be mounted on the respective ring by the provision of a suitable notch or slot extending from one end of the stub shaft for accommodating the ring to which the shaft is attached. The shaft may then be welded to the ring. The ring 23 is therefore free to rotate with respect to the ring 18 about a diameter which is perpendicular to the diameter of rotation of the ring 18 in a gimbal type of arrangement. The outer diameter of the ring 23 is of a size to provide sufficient clearance to permit a full 360 rotation of the ring 23 with respect to the ring 18.

A pair of bearings 27, only one of which is visible, are supported in suitable notches in the second ring 23. The bearings 27 are axially aligned on a diameter of the ring 23 and support a rotary axle 29 correspondingly aligned. The generally spherical structure 11 is supported on the axle 29 and rotates therewith. The spherical structure 11 includes a plurality of annular bands 31 arranged as meridians with the axle 29 on a diameter of each band and extending through the poles of the generally spherical structure 11. The bands are arrayed at uniformly spaced intervals around the axle. The bands, at the region of their juncture with the axle, are supported by support discs 32 and 33 toward respective ends of the axle 29. The annular bands may be broken in continuity at the disc and welded thereto for rigid support. Angular spacing of the bands 31 with respect to each other is maintained by an equitorial band 34, crossing each of the annular bands 31 at the mid points of their span between the discs 32 and 33. Any number of bands may be utilized, depending upon the particular requirements of the substrates to be supported.

Any suitable means may be utilized for attaching the substrates to be coated to the generally spherical structure 11, depending upon the nature of the substrates. In the illustrated embodiment, the means 12 for supporting the substrates consist of a plurality of discs, suitably secured to the annular bands 31. One suitable means of securing the discs is by the utilization of an L-shaped clip (not shown) welded to the disc and secured to the band by a setscrew. This enables the discs to be moved to any convenient position on the outer surface of the generally spherical structure 11. Although illustrated in connection with only one of the discs 12, each of the discs may be provided with suitable means for holding a substrate on the disc, such as a wire clip 37. A particular use for the described configuration is in holding semiconductor wafers of approximately 8-mils thickness for coating with a conducting film.

It will be appreciated that, in the illustrated embodiment, the spherical structure may be rotated about three different axes simultaneously. These axes correspond to the axle 29, the shafts 24 and 26 extending from the ring 23, and the shaft 19 and its corresponding unillustrated shaft extending from the ring 18. In order to effect rotation of the generally spherical structure 11 about the three axes simultaneously, rotating means are provided. Such rotating means include a power source or motor 41 supported on a plate 42 which depends from the ring 13 and is supported thereby. The motor 41 includes a drive shaft 43 upon which a drive sprocket 44 is mounted. The sprocket 44 is coupled to a sprocket 46 mounted on the outer end of the shaft 19 by means of a drive chain 47. A pulley 48 is mounted on the shaft 19 between the bearing 17 and the ring 18. A pulley 49 is mounted on the end of the shaft 26 projecting beyond the bearing 22. The pulley 48 is coupled to transfer torque to the pulley 49 by means of a drive belt 51. The drive belt St is guided by two pairs of guide pulleys 53 and 54. The guide pulleys 53 are mounted for rotation on a shaft 56 mounted in the ring 18 perpendicular to the plane in which the circumference of the ring lies. The pulleys 54 are mounted on an idler shaft 57 secured to the ring l8 and parallel with the shaft 56. The drive belt 51 comprises a coil spring which is preferably lnconel (International Nickel Co.) or other suitable high-temperature alloy. Any other suitable torque transferring means may be utilized, such as a chain and sprocket drive or a rigid drive shaft with appropriately angled gears. The spring belt, however, eliminates thermal expansion problems and is easily cleaned and disassembled. Moreover, spring belts allow slippage to enable manual positioning of the spherical structure for loading and unloading substrates without disconnecting the drive.

When the motor 41 is energized, the shaft 19 is rotated, transferring torque to the shaft 26 through the belt 51. Accordingly, as the ring is rotated the ring 23 is also rotated.

In order to rotate the spherical structure 11 within the ring 23, a pulley 611 is provided on the shaft 24 between the bearing 21 and the ring 23. A similar pulley 62 is provided on the end of the axle 29 which projects through the bearing 27. A drive belt 63 transfers torque (between the pulley 61 and the pulley 62) produced due to rotation of the ring 23 on the shafts 24 and 24. A pair of idler pulleys 64 are provided near the drive pulley 61 and are mounted on a shaft 66 secured in the ring 23. The shaft 66 is perpendicular to the plane of the circumference of the ring 23. A similar pair of pulleys 67 are mounted on a shaft 68 to guide the belt 63 near the drive pulley 62. The idler shaft 67 is mounted to the ring 23 parallel with the shaft 66. When the pulley 61 is rotated upon rotation of the ring 23, torque is transferred through the belt 63 to the pulley 62 which rotates the axle 29. Accordingly, rotation of the spherical structure 11 is effected. The drive belt 63 is of similar construction to the drive belt 51, but may be any of the suggested alternatives.

The described illustrated embodiment consisting basically of two gimbals and a sphere, is operated so that the various elements are rotated about their three respective axes of rotation. This has the effect of rotating the spherical structure 11 about three nonparallel axes. The ensuing motion of the sphere relative to the fixed ring 13 is quasi-random, that is, although the motion of any given point on the outer surface of the sphere may be predicted mathematically, drive ratios may be utilized in which a motion of a given point approaches randomness. Thus, any given point on a moving outer surface of the spherical structure ill may be made to pass, eventually, by any given stationary point. By choosing different drive ratios between the three rotating axes, by appropriate selection of pulley diameters in the illustrated embodiment, the motion of the spherical structure 111 can be made to vary so that combinations of the frequency with which various points on the outer surface of the spherical structure passby a given stationary point can be changed. Thus, a substrate mounted on the outer surface of the spherical structure is exposed to vapor flow with a variety of exposure angles. Moreover, although the cross-sectional area of the vapor flow may be small, the spherical nature of the substrate mounting surface, together with the motion above described, makes a relatively large surface available for exposure to the vapor. The vapor flow then impinges uniformly over the entire surface of the sphere after a period of time sufficient to approach randomness and will strike every area on the surface of the sphere from a wide number of directions and angles of incidence, assuring maximum coverage on substrates that have irregular surfaces.

The actual motion of the spherical structure 11 is not known. The driving mechanism of the spherical structure superimposes three separate periodic motions of the structure about three different axes at not necessarily equiangular speeds. Accordingly, a point on the spherical structure follows a complicated trajectory so that every surface element is exposed to the vapor.

Although the motion of the spherical structure is complex, a qualitative understanding may be obtained by considering a two-dimensional planar analogue. For mathematical purposes, a vapor source may be considered as projecting a point on the surface of a planar substrate, though in actuality, typical vapor deposition consists of a central spot area of high density and uniform intensity, and a lower intensity penumbra in which the coating thickness falls off in accordance with the cosine law. If the spherical structure were to rotate about two axes at right angles to each other, the two-dimensional planar analogue consists of the combination of two simple harmonic motions at right angles to each other. Two simple harmonic motions at right angles to each other and having the same amplitudes but different frequencies, w and wl idporrespond to two different angular speeds of rotation about two orthogonal axes of the sphere. in the two-dimensional planar analogue, therefore, the motion of a point on a planar Area A is described by the two equations:

x=A cos wt This assumes that the time counting is started when the two vibrations are in phase.

From the two above equations, there can be derived the equation of an ellipse with major and minor axes which change with time, running from zero to Z EA. The resulting trajectory described by the motion of a point in accordance with such an equation is called a Lissajou figure, such being well known in mathematical literature. Depending on the magnitude of d, the difference between the frequencies of the two motions, the trajectory will cover the planar area to different degrees of denseness. The smaller the d, the more dense the coverage will be but it will always remain discrete, since we are assuming a point projection. From this result, it may be shown that the total time T taken by the projected point to pass through all its phases is given by the equation T=21r/d. Accordingly, the smaller the d, the longer it takes to cover the entire planar area. These results may be applied qualitatively to the case of a rotating sphere. From the foregoing analysis, it may be determined that quasi-randomness may be achieved by selecting drive ratios which are relatively close to each other, but as a practical matter, the ratios should be not so close as to render excessive the time for a complete cycle.

The material of which the apparatus is comprised may be of any suitable type to withstand structural damage at the temperatures of deposition. The suggested materials for the drive belts 51! and 63, previously set forth, minimize clogging of the springs to impede torque transfer. During a typical production run, the apparatus of the invention may become severely coated with condensate. However, under most instances, the advantages of the larger available substrate mounting area, together with the angular variation provided, more than offset the problems of cleaning the apparatus subsequent to deposition operations. Under some circumstances, it may be possible to heat critical parts, such as pulleys and bearings, by means of electrical resistance or radiant heaters to avoid excessive condensation of vapor thereon. The bearings and motor, of course, should be resilient to relatively high temperatures. Bearings and motors operable at such high temperatures are available commercially.

It may therefore be seen that the invention provides improved apparatus for supporting a substrate in a vapor flow. The apparatus produces a variation in the angle of exposure of the substrate to the vapor, and provides an extremely large mounting area for substrates with respect to the volume occupied. The apparatus is versatile and is of particular advantage in assuring maximum coverage of deposition vapors on substrates that have irregular surfaces. Although the invention has been described in connection with three axes of rotation, it may be possible in some circumstances to approach the desired degree of randomness by utilizing only two axes of rotation (e.g., by eliminating the intermediate ring 23 in the illustrated embodiment).

Various modifications of the invention, in addition to those shown and described herein, will become apparent to those skilled in the art from the foregoing description and accompanying drawing. Such modifications are intended to fall within the scope of the appended claims.

What I claim is:

1. Apparatus for supporting a substrate in a vapor flow, comprising, a generally spherical structure including means thereon for supporting the substrate, a fixed ring surrounding said spherical structure, a movable ring surrounding said spherical structure and mounted for rotation about a diameter of said fixed ring within said fixed ring, means mounting said spherical structure to said movable ring for rotation about at least one axis with respect thereto, said one axis being nonparallel with respect to the axis of rotation of said movable ring, and means for rotating said structure about the two axes simultaneously.

2. Apparatus according to claim 1 including a second movable ring mounted for rotation about a diameter of said first named movable ring within said first movable ring, and means mounting said structure for rotation about a diameter of said second movable ring.

3. Apparatus according to claim 2 wherein said rotating means comprise first drive means coupling said first movable ring to said second movable ring, second drive means coupling said second movable ring to said structure, and a power source coupled to said first movable ring for rotating same, whereby torque is transferred from said power source through said first and second drive means to said first and second rings and said structure.

4. Apparatus according to claim 3 wherein said first and second drive means each comprise a pulley and flexible belt system.

5. Apparatus according to claim 4 wherein said belts each comprise a coil spring.

6. Apparatus according to claim 2 wherein said rotating means rotate said first and second movable rings and said structure about their axes simultaneously and with uneven ratios to produce a quasi-random movement of the substrate.

7. Apparatus according to claim 1 wherein said spherical structure comprises a plurality of annular bands arrayed at spaced intervals on a common diameter, and an axle supporting said bands and extending coextensive with the common diameter thereof.