Patent GB-1100130-A (GB)
Title: Contact printing mask alignment apparatus for semi-conductor wafer geometry
IPC: G03F7/20
Filed: 1965-10-28
Abstract: 1,100,130. Contact printing onto semiconductors. KULICKE & SOFFA MANUFACTURING CO. Oct.28, 1965 [Jan.27, 1965], No.45704/65. Heading G2A. A contact printing apparatus has means for precisely orienting a pattern of geometric indicia on a mask M with respect to geometric indicia on the surface of a semi-conductor wafer W. In fabricating transistor and micro-circuit devices, it is necessary to apply a sequence of separate photo-sensitive resist coatings, each being contact printed with geometric indicia from a succession of master masks. In printing each mask pattern on to the preceding pattern an extremely high order of accuracy of alignment must be maintained. Figs. 7-9 show in diagram form the sequence of alignment operations, the mechanisms of the actual embodiment being described in considerable detail. The initial loading step is shown in Figs. 7 and 13. The mask M is slidably mounted in a holder 90 having a central exposure aperture 92 by means of clips 93, 94, and is held therein by vacuum suction. The holder 90 is itself slidably mounted on a bridge support (80) Fig. 12 (not shown), and similarly held by vacuum suction, the mask being located in a reference plane. The semi-conductor wafer W is vacuum clamped to the top of a ball chuck 70 supported as a universal joint in a carriage 40 (described in detail with reference to Fig. 12 not shown). The carriage is slidable on the horizontal upper surface of a wedge 30 which can be pulled up an inclined trackway 20 (described in detail with reference to Fig. 4 not shown). From the position of Fig. 7, the carriage 40 is pulled up the inclined trackway by a drive assembly H until wafer W abuts the mask M (Fig. 8), so that wafer and mask are in parallel interfacial engagement since the ball chuck is self aligning. A depressor assembly J now automatically retracts the wedge 30 a small distance down the inclined trackway, so that the two surface planes W and M are slightly spaced apart (less than 0À001 inch). The wafer assembly can now be oriented so as to bring the two surface patterns into precise registration by means of a micro-manipulator E, which can adjust the wafer along X and Y axes, and also by rotation about a polar axis (described in detail with reference to Figs. 1 and 3 not shown). During this orienting operation, the surface patterns are viewed through a high power split-image stereo microscope (150) Figs. 1, 2, 4 (not shown). After correct registration has been achieved, the depressor assembly J is released, thereby bringing the wafer and mask back into contact, in readiness for the photographic exposure. The microscope, which is mounted on pivots, can now be swung out of the way by a hand crank, which simultaneously rotates the exposure assembly (G) into position above the mask Figs. 14 and 17 (not shown). Light from the source (254) is collimated by a lens (255) to pass through a tunnel (207), and is reflected downwards by a mirror (206) to fall on the mask assembly. In the path of the light as it passes towards the tunnel is a rotary shutter (260), Fig. 17 (not shown) having a pair of downwardly depending blades (256, 257), rotation of which controls the exposure. Figs. (not shown) 29A and 29B are diagrams of the electrical circuitry by means of which the operation of the apparatus is controlled.