Method of and spinning head for spin coating resist onto a wafer

Abstract

 This invention relates to a method of spin coating resist onto a wafer 72 and to a spinning head for coating the wafer: The spinning head has a chuck 10 to be rotated by a spinner motor shaft 14.
The resist is coated onto the wafer 72 through a hole 82 in the centre of an interchangeable top clamp plate 78. The piate 78 is tapered to a knife-edge 86 to seal the top of the wafer and fuide the resist, during spinning, up the tapered surface and off the head. The plate 78 allows certain areas on the wafer, such as areas containing registration marks, to be protected from resist coating

Description

[0001] The present invention relates to a method of spin coating resist onto a wafer. The invention also relates to a spinning head for spin coating resist onto a wafer.

[0002] In known techniques employed to spin coat a resist onto a wafer by means of a spinning head, the wafers are baked after having been spin coated and are subsequently exposed to ultraviolet radiation to clear an outer ring around the edge of the wafer. After development, the resist is removed and the ring is used to make electrical contact for electroplating. The provision of the outer ring has required exposure and development steps.

[0003] In addition, it has been observed that in spin coating a resist onto a wafer there is an unwanted build-up of resist at the edge of the wafer especially when thick resist solutions are cast onto the wafer.

[0004] The present invention now provides a method of spin coating resist onto a wafer, the method incorporating the steps of mounting the wafer onto a rotatable wafer platform, spinning the wafer by means of the platform and applying the resist onto the wafer. In order to provide an area of the wafer clear of the resist, the method is characterised in that the wafer is clamped onto the platform by means of a plate which is tapered into a knife edge at the wafer surface to seal the top of the wafer in contact with the plate and to allow the resist to flow up over the clamping plate and off the spinning head.

[0005] The invention also provides a spinning head for spin coating resist onto a wafer, the head incorporating a base to be driven by a spin motor shaft, and a wafer platform mounted on the base to receive a wafer to be spin coated characterised in that the wafer platform has a clamp plate to clamp a wafer to be coated onto the platform, the clamp plate having a flat lower surface to engage and seal off a portion of a wafer to be coated and an upper surface tapered to meet the lower surface at a knife edge to allow resist to flow up over the clamp plate and off the head.

[0006] The clamp plate is preferably of circular ring configuration. Preferably, the clamp plate has means for attachment to the base and the wafer platform is supported by a spring and ball joint interposed between the wafer platform and the base to enable the wafer platform to be depressed and to swivel relative to the base to accommodate a wafer between the clamp plate and the wafer platform.

[0007] The invention will now be further described by way of example with reference to the drawings in which:-

FIGURE 1 shows an assembled wafer spinning head embodying the present invention;

FIGURE 2 shows a sectional exploded view of the head of Figure 1;

FIGURE 3 shows a spring and ball support sub-assembly included in the head of Figure 1;

FIGURE 4 shows an exploded view of the sub-assembly of Figure 3;

FIGURE 5 shows an exploded view of a ring spinner and bayonet lock ring sub-assembly included in the head of Figure 1; and

FIGURE 6 shows in plan'a wafer after having been resist coated using the head of the previous Figures.

[0008] Referring to Figures 1 and 2, a wafer spinner chuck 10 includes a base 12 adapted to be attached to a spinner motor shaft 14, by a set screw 16 which holds the motor shaft 14 in place in the hub 18 of base 12.

[0009] Base 12 has a notched portion 20A and 20B on opposite sides of the raised shoulder portion 22 such that the arms 24A and 24B of a bayonet lock ring 26 cooperate in the respective notched portions 20A and 20B. A retainer ring 28 has a central opening 30 for accommodating the central portion 32 of the lock ring 26. During assembly, the retainer ring 28 is attached, such as by screw means 34, to the base 12 with the lock ring 26 interposed between such members 12 and 28 and the bayonet arms 24A and 24B extending through the slots formed by the notches 20A and 20B and the retainer ring 28. The base 12, ring 26 and retainer ring 28 continue to form a bayonet lock ring assembly 36.

[0010] A spring mount and ball support sub-assembly 40 shown in further detail in Figures 3 and 4 includes a spring mounting cylinder 41 having a first recess 42 for retaining a spring 44, and a second recess 46 for accommodating a retainer ring lock 48 which embraces a groove 50 of a ball support shaft 52 that passes through spring 44, recess 42, an interconnecting passage 54, and into clearance recess 46 for retainer ring 48 installation. Passage 54 has a smaller diameter relative to the recesses 42 and 46 to secure the ball support shaft 52 such that the latter is spring loaded when secured by retainer ring 48. Attached to the ball support shaft 52 is a ball support platform 55 having a circular detent 56 for receiving a ball 58.

[0011] The spring mount and ball support subassembly 40 is connected to the base 12 by screws 60A and threaded holes 60B in the spring mounting cylinder 41. A wafer platform 62 is coupled to the ball support platform 55 via the ball 58 which rides in both its detent 56 and a matching detent 64 in the underside of wafer platform 62 as shown. The wafer platform 62 has a circular internal recess 66 at its underside with a shoulder 68 for receiving and retaining a rim 70 on the outer diameter of the ball support platform 55. The height of recess 66 is greater than the height of the rim 70 to permit a swivel action of wafer platform 62 relative to the ball support platform 55 as indicated by arrows 71 in Figure 3.

[0012] A wafer 72 is placed on the smooth polished surface 74 of the wafer platform 62. The spring mount and ball support sub-assembly 40 permits the wafer platform 62 to swivel and compress downward so that the knife-edge ring can conform to irregularities in the wafer surface, thus creating a seal, and accommodating wafers of various thicknesses. Also, the spring mount and ball support sub-assembly maintains an alignment of the top wafer surface perpendicular to the spinning axis. The wafer 72 is held down by a ring spinner top 76 on which an interchangeable top plate 78 is mounted, such as by screw means 80A and 80B. The hole 82 in the centre of this top plate 78.determines the area of the wafer 72 on which resist will be coated. One feature of the wafer spinner chuck is that the inner edge of the top plate 78 is tapered as shown at 84 on the top side to a knife-edge 86 which seals the top of the wafer and does not allow any resist to flow under the plate. Instead, the resist is guided, during spinning by the tapered top surface 84 to edge of the plate and off the head.

[0013] 

Claims

1. A method of spin coating resist onto a wafer, the method incorporating the steps of mounting the wafer 72 onto a spinning head 10 incorporating a rotatable wafer platform 62, spinning the wafer 72 by means of the platform 62 and applying the resist onto the wafer 72, characterised in that the wafer 72 is clamped onto the platform 62 by means of a plate 78 which is tapered into a knife edge 86 at the wafer surface to seal the top of the wafer 72 in contact with the plate 78 and to allow the resist to flow up over the clamping plate 78 and off the spinning head 10.

2. A spinning head 10 for spin coating resist onto a wafer 72, the head incorporating a base 12 to be driven by a spin motor shaft 14, and a wafer platform 62 mounted on the base 12 to receive a wafer 72 to be spin coated characterised in that the wafer platform 62 has a clamp plate 78 to clamp a wafer 72 to be coated onto the platform 62, the clamp plate 78 having a flat lower surface to engage and seal off a portion of a wafer 72 to be coated and an upper surface tapered to meet the lower surface at a knife edge 86 to allow resist to flow up over the clamp plate 78 and off the head 10.

A spinning head according to claim 2, wherein the lamp plate 78 is of circular ring configuration.

A spinning head according to claim 2 or 3, wherein the clamp 78 plate has means 76 for attachment to the base the wafer platform is supported by a spring and ball joint interposed between the wafer platform and the base to enable the wafer platform to be depressed and to swivel relative to the base to accommodate a wafer between the clamp plate and the wafer platform.

Drawing