Thin Film Coating Apparatus

Abstract

In vacuum deposition apparatus a horizontally disposed rotatable platform supports and orbits a plurality of trays about the axis of rotation. Each tray is rotatable about its own axis and supports a plurality of wafer holder and orbits said holders about the tray axis of rotation. Means rotate each holder about its own axis. The platform, trays and holders are arranged in a generally common plane.

Description

SUMMARY OF THE INVENTION AND STATE OF THE PRIOR ART

The present invention relates to apparatus for coating a plurality of thin wafer-like objects, and more particularly relates to evaporation apparatus for assuring uniform coating of irregular surfaces of a semiconductor wafer by providing, in conjunction with complex motion, a single plane of rotation of the wafer in conjunction with a plurality of material sources, or a single material source depending upon the nature of the product.

The idea of attempting to assure uniform coating of irregular surfaces of objects during a coating operation, wherein the objects are semiconductor wafers, by providing for complex motion of the wafer is clearly taught in the prior art. For example, U.S. Pat. No. 3,598,083 to Dort illustrates thin film coating apparatus having 3.degree. of freedom or rotation wherein the central axis of the substrates of objects being coated is oblique to the axis of the source material crucible. While such apparatus does coat relatively uniformly as compared with a single rotation, dome shaped cage or double rotation dome shaped holders, it has been found that it is difficult if not impossible to achieve uniformity of coating in certain topographies having depressions to be coated where the depression includes an undercut and it is required that the coating layer extend uniformly from the upper surface of the wafer, covering the undercut and the bottomm of the depression. Alternatively, it has been found that where only the bottom of such a depression is desired to be covered so that a surface covering may be removed without removal of the covering on the bottom of the depression (due to adherence to the covering material on the side walls of a depression), such single plane multiple rotation is highly desirable and a uniform coverage of the desired surfaces may be obtained with a central source and a long distance between the source and the object to be coated.

In view of the above, it is the principal object of the present invention to provide apparatus which will more uniformly coat irregular surfaces of a thin member such as a semiconductor wafer.

Another object of the present invention is to provide a complex motion apparatus in which the rotation of the wafer or object to be coated occurs about three axes which are substantially parallel to one another and to the axis of at least one crucible.

Yet another object of the present invention is to provide thin film coating appratus including, in one embodiment, a plurality of source material holders with means to effectively and rapidly shield the holders from the wafers being coated.

Still another object of the present invention is to provide means for uniformly heating the wafers to be coated from the back sides thereof to aid the coating material in adherence to the irregular surface of the wafers.

Still another object of the present invention is to provide in an evaporator, means to adjust the distance between the source material and the wafer holder.

Other objects and a more complete understanding of the invention may be had by referring to the following specification and claims taken in conjunction with the accompanying drawings in which:

Fig. 1 is a fragmentary perspective view of apparatus constructed in accordance with the present invention;

FIG. 2 is an enlarged fragmentary sectional view (foreshortened) of the apparatus illustrated in FIG. 1;

FIG. 3 is an enlarged fragmentary plan view taken along line 3--3 of FIG. 2;

FIG. 4 is an enlarged fragmentary plan view of a portion of the apparatus illustrated in FIG. 3; and

FIG. 5 is a fragmentary sectional view taken along line 5--5 of FIG. 4.

Referring now to the drawing, and especially FIG. 1 thereof, apparatus 10 used for depositing thin films of material on thin objects or workpieces such as semiconductor wafers, is illustrated therein. As shown, the apparatus includes a conventional coating chamber or vacuum envelope 11 housing apparatus 12 constructed in accordance with the present invention. The envelope 11, as is conventional, is connected to a source of vacuum (not shown) to evacuate the chamber in accordance with customary or usual practice.

The apparatus 12 is mounted on a base 13, and comprises a rotatable platform 15 (in the preferred embodiment horizontally disposed) including a plurality of rotatably mounted trays 25 spaced about and mounted on the platform and in the same plane thereof. Each of the trays 25 includes a plurality of rotatably mounted object of wafer holders 35, in the illustrated instance semiconductor wafers, and includes means, hereinafter described, for retaining the wafer with one surface exposed downwardly. Underlying the platform 15 is a material source holder or crucible, in the illustrated instance three such holder cups 45, 46, and 47 which are radially spaced about an axis perpendicular to the platform 15 while being spaced axially therefrom. Drive means 55 (see FIG. 2) serve to effect rotation of the platform 15, the trays 25 and the holders 35 in the same plane wherein the wafers pass through several angles with respect to the source holders or the axes thereof. Overlying the platform 15 is heater means 75 positioned adjacent the platform and substantially parallel thereto for heating the backside of the workpieces.

In order to support the platform 15 for driving rotation about the central axis thereof, a plurality of adjustable, telescopically engagable stanchions 16 are spaced about the platform and mounted, as by a retaining block 16A on a drive ring 18. At their extended or upper end the stanchions are connected to a platform ring 23 which extends about the periphery of the platform 15. The stanchions 16 are made adjustable in a conventional manner as by pins 16B and apertures 16C so that the height of the platform may be adjusted relative to the source holder cups, depending upon the operation to be performed.

In order to impart driving motion to the drive ring 18, the drive means 55 is frictionally engaged to the ring and effects rotation thereof about the central axis of the apparatus, i.e., substantially perpendicular to the plane of the platform 15. To this end, and referring to FIG. 2, a shaft 56 is connected to the frustoconical, smooth surfaced drive member 57 which mates with a complementary angled surface 58 on the internal periphery of the drive ring 18. As shown, the shaft 56 contains suitable thrust bearings as at 59 to support the structure, there being similar frustoconical smooth surface drive idlers 60 spaced 120.degree. apart from the main drive which serve to support the drive ring 18. As illustrated, the idlers 60 are suitably mounted for rotation on pedestal mounts 61 which are connected to the base 13.

The trays 25 are mounted for rotation in or on the platform 15, the platform and trays serving as a shield, in a manner which will be more fully explained hereinafter, and separate the source material from the heaters 75 mounted on the backside of the platform 15. To this end, the platform 15 comprises a plurality of segments 19, each segment containing a tray 25 and including radially extending expansion joints 20 with overlapping lip termini 21 which serve to shield the heaters 75 from the source material, while allowing for expansion and contraction of the metal segments 19. The expansion joints 20 are connected to braces 22 to the platform ring 23. The trays 25, in turn, are suspended in a cutout 26 in the segment 19 as by a cantilever arm 27, one end of which is connected to the platform ring 23, and the other end of which includes a bushing 28 and shaft 29, the lower end of the shaft 29 being rigidly secured to the tray 25, while the upper end of the shaft is coupled to a driver sprocket 30. An enlarged gear or sprocket 31 is mounted intermediate the bushing 28 and the tray, and connected to the shaft 29 for rotation therewith. A drive sprocket 32 is connected to a shaft 33 which passes through the platform ring 23, the drive sprocket 32 being connected to the driven sprocket 30, and thus the shaft 29 as by a drive belt 34.

In order to impart motion to the trays 25, the shafts 33 are connected as through universal joints 34' to adjustable length drive shafts 62 (see FIG. 2). A second universal joint 63 connects the drive shaft 62 to a stub shaft 64 which is mounted for rotation as by a bearing 65 in the drive ring 18. As shown best in FIG. 2, the stub shaft 64 is connected, at its lower terminal end, to a gear 66 which mates with an internally toothed ring gear 67 rigidly secured as by posts 68 to the base 13. Thus as the drive ring 18 is rotated, the idler gear 66 are forced into rotation by the stationary teeth of the ring gear 67, thereby affecting rotation of the drive shafts 62 and causing the trays 25 in the platform to rotate.

In order to provide further rotation of a wafer, means are provided to effect rotation of the wafer holders, the wafer holders 35 being adapted to retain a wafer in a position where a major surface thereof faces the crucibles or source material holders 45, 46 and 47. To this end, and referring now to FIGS. 3, 4, and 5, the wafer holders 35 comprise a cup having an inwardly projecting circumferentially extending lip portion 36 on the lower portion thereof, and wafer retaining means 37 for retaining a wafer or workpiece 40 on the lower side of the cup, against the lip so as to expose the surface 40A of the wafer to the source material. The wafer retaining means 37 includes a plurality of clip-like retainers 37A, 37B, and 37C, each of which includes a tang 38 which is bent inwardly to overlie the lip 36 of the cup and to capture the wafer 40 and press the wafer against the lip 36. The tang 38 of the clip extends through the peripheral lip 36 of the cup into the interior of the cup where it terminates in an enlarged spade-like section 38A. A spring retainer 39, associated with each of the clips serves to bias the enlarged spade-like section 38 against the wall of the cup thereby forcing the tang section against the periphery of the wafer like workpiece 40. In this manner, when it is desired to remove a wafer from the lip, the spade-like section 38A may be biased away from the wall by a simple purging action.

In order to provide uniform heating of the workpiece by the heater 75 which is superimposed of the platform 15, a removable disk 41 of heat conductive material is provided intermediate the wafer and the heater. The disk 41 is dimensioned to rest in the cup 35 against the inner surface of the lip 36 in close proximity to the wafer like workpiece 40. In the preferred embodiment, it has been found that a material such as copper obtains a uniform heat relatively quickly and therefore is a relatively inexpensive and yet excellent medium for heat transmission to insure such uniformity of heating of the semiconductor wafer.

In order to drive the cup, so that it rotates not only with the tray 25 but also about its own central axis, the rim of the cup 35 is provided with a plurality of teeth 42 which mesh with the teeth of the sprocket or gear 31 so that upon rotation of the sprocket, the teeth 42 of the cups in engagement with the sprocket effect rotation of the cups. As shown, the cups may be nested in a plurality of shouldered cutouts 42' in the tray 25 and held in position to ensure rotation of the cups as by stub posts 43 projecting upwardly from the tray and engaging the wall of the holders. The shouldered cutouts also serve to prevent the source material from impinging on the heater 75.

In circumstances where it is desirable to obtain maximum coverage and uniform distribution not only of the surface of the wafer, but of any undercuts in recesses in the surface of the wafer, it is desirable that a multiplicity of sources such as the sources 45, 46 and 47, which are radially spaced from the central axis of the platform while being axially spaced therefrom, are provided. As shown best in FIG. 1, the source material holders or crucibles 45-47 are each mounted on a separate post 48 with a common conductive plate 49, joining in the illustrated instance, carbon electrodes 50 and 51. Insulators 52 through which suitable wiring may pass join the common plate 49 to the carbon electrodes which serves to heat the source material in the cricibles, located inside of the shields 45A, etc. It should be recognized, however, that the source material may be heated in any conventional manner as by low or high frequency induction heating or even E beam heating depending upon the source material. Thus the resistance heating scheme illustrated is not critical to the operation of the apparatus as above described.

In accordance with one feature of the invention, means are provided to shade and expose the wafers from and to the source holding cups so that the wafers are exposed to the source material when desired. To this end and referring now to FIGS. 1 and 2, a focal plane shutter assembly 80 is positioned intermediate the source holders and the wafer holders, the shutter assembly being movable between a first position, wherein the source holders are shielded from the wafer holders, and a second position wherein a line of sight is provided between the waafer holders and the source holders. As illustrated, the shutter assembly comprises a plurality of plates, in the present instance three designated 81, 82 and 83 for purposes of identification, the plates being generally arcuate in form and supported from a center shaft 87 as by radially extending arms 85 which are connected to a hub 86. A central shaft 87, connected to the hub, extends through a sleeve bearing and the like 88 which is mounted on a brace or support 89 suitably connected as by arms 90 to upstanding pillow blocks 91 which are mounted on the base 13. In order to rotate the shutter assembly between its first position wherein the source holders are shielded from the wafer holders and a second position where a line of sight is provided between the wafer holders and the source holders, the center shaft 87 is connected through the brace or support 89 to a drive plate 92, the drive plate having a plurality of pins or projections 93 depending therefrom which are engagable by a pawl 94 operatively connected as through an arm 95 to an actuator shaft 96. As desired, the pawl may be energized through the shaft 96 by either air or electric solenoid control causing engagement of the pawl against the pins and therefore rotation of the drive plate 92.

In instances where the maximum edge coverage is desired of depressions in the workpiece, the maximum angle of the source material with respect to the rotating wafers is when the platform 15 lies closely adjacent the source holders 45, 46 and 47 thereby assuring maximum exposure of any undercuts in the surface of the wafer of the boiling source material. However, in instances where the operation to be performed is one utilizing, for example, a lift off process, that is where only surface coverage of the depression or of the exposed surface is to be covered so that a peeling operation may take place and the metal or other material deposited from the source holder is in the bottom of the recess or depression in the semiconductor wafer, it is desirable to have the platform 15 spaced farther from the source holder or holders. To this end, the stanchions 16 as well as the drive 62, inasmuch as they are adjustable, may be positioned so as to space the wafer holders in a remote position with regard to the source material holders. Additionally, if minimum vertical wall (relative to the depressions or recesses in the wafer) coverage is desired, a central source material holder may be employed, and a more conventional type centrally located shutter assembly may be employed.

Although the invention has been described with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts and the mode of operation may be made without departing from the spirit and the scope of the invention as hereinafter claimed.

Claims

What is claimed is:

1. In an apparatus for providing multiple rotation of a plurality of semiconductor wafers about three parallel axes, said apparatus comprising: a rotatable platform; a rotatably mounted plurality of trays spaced about and mounted on said platform and in the same plane as said platform; each tray including a plurality of rotatably mounted semiconductor wafer holders; said wafer holders comprising a cup, an inwardly projecting lip extending about the periphery of said cup, and wafer retaining means on said lip for receiving a wafer therein and holding said wafer against said lip; said retaining means comprising a clip including a radially projecting tang, resilient means connected to said tang, and means actuable interiorally of said cup for biasing said tank to maintain said tang in firm engagement with a wafer held on said lip; a plurality of source material holders radially spaced about an axis perpendicular to said platform and spaced axially therefrom; and means to effect rotation of said platform, said trays and said holders in the same plane wherein said wafers pass through several angles with respect to said sources.

2. In an apparatus in accordance with claim 1, including means to adjustably position the axial distance between said platform and said source material holders.

3. In an apparatus in accordance with claim 1 wherein said platform is in a substantially horizontal plane.

4. In an apparatus in accordance with claim 3 including heating means adjacent said platform on the side thereof opposite the side exposed to said source material holders, to heat said semiconductor wafers.

5. In an apparatus in accordance with claim 1 including a focal plane shutter assembly intermediate said source holders and said wafer holders, said shutter assembly being movable between a first position wherein said source holders are shielded from said wafer holders and a second position wherein a line of sight is provided between said wafer holders and said source holders.

6. In an apparatus in accordance with claim 1 including heating means disposed on the side opposite said platform to said source holders, to heat said wafers held by said wafer holders.

7. Apparatus in accordance with claim 1 including a removable disk of heat conductive material, said disk being dimensioned to be retained within said cup, and against said lip.

8. In an apparatus in accordance with claim 7 including a plurality of teeth on the rim of said cup, and sprocket means mounted on said tray for engaging the teeth on said rim of said cup.

9. Apparatus for providing multiple rotation of a plurality of thin workpieces in a common plane, said apparatus comprising: a housing; a rotatably mounted platform in said housing, a plurality of trays spaced about and mounted on said platform and for rotation with respect thereto; a plurality of workpiece holders rotatably mounted in each of said trays, said wafer holders comprising a cup, inwardly projecting lip extending about the periphery of said cup, and wafer retaining means on said lip for receiving a wafer therein and holding said wafer against said lip; said retaining means comprising a clip including a radially projecting tang, resilient means connected to said tang, and means actuable interiorally of said cup for biasing said tang to maintain said tang in firm engagement with a wafer held on said lip; a plurality of source material holders spaced from said platform and in a plane substantially parallel to said platform; means to provide a source of heat to said workpiece holders, said means being positioned on the opposite side of said platform as said source material holders; and shutter means operative to shield, as desired, said source material holders from said wafer holders; and means to effect rotation of said platform, said trays and said holders in the same plane whereby wafers held by said holders pass through several angles with respect to said sources.

10. Apparatus for providing a deposition of material on a workpiece and for providing multiple rotation of a plurality of workpieces about three parallel axes, said apparatus comprising: a rotatable platform; a rotatably mounted plurality of trays spaced about and mounted on said platform and in the same plane as said platform; each tray including a plurality of rotatably mounted workpiece holders, said wafer holders comprising a cup, an inwardly projecting lip extending about the periphery of said cup, and wafer retaining means on said lip for receiving a wafer therein and holding said wafer against said lip; said retaining means comprising a clip including a radially projecting tang, resilient means connected to said tang, and means actuable interiorally of said cup for biasing said tang to maintain said tang in firm engagement with a wafer held on said lip; at least one source material holder spaced from said workpiece holders and having an axis substantially perpendicular to the plane of said platform; and means to effect rotation of said platform, said trays and said holders in the same plane wherein said wafers pass through several angles with respect to said source holder.

11. Apparatus in accordance with claim 10 including means for altering the distance between said source holder and said platform.

12. Apparatus in accordance with claim 11 including means for raising and lowering said platform.

13. Apparatus in accordance with claim 10 including a plurality of source material holders radially spaced about an axis perpendicular to said platform.

14. Apparatus in accordance with claim 10 wherein said platform is positioned in a horizontal plane, and heating means substantially parallel to said platform and positioned on the side opposite said platform as said source holders.