Patent GB-1325822-A (GB)
Title: Alignment apparatus
IPC: H01L21/68
Filed: 1971-04-19
Abstract: 1325822 Alignment apparatus INTERNATIONAL BUSINESS MACHINES CORP 19 April 1971 [31 March 1970] 23745/71 Heading H1K Apparatus for aligning a semi-conductor wafer with a mask comprises a base having a chamber within which is mounted a piston having a socket within which rests a gimbal on which the wafer is mounted, means for positioning the mask above the wafer, a fluid supply connected to the socket for floating the gimbal, means for elevating the piston to bring the wafer into contact with the mask, means responsive to increased fluid pressure in the socket for stopping the elevation of the piston, means for locking the gimbal in the socket, means for lowering the piston a predetermined amount to space the wafer from the mask to permit relative adjustment, and means for re-elevating the piston by the same predetermined amount to bring the wafer back into contact with the mask. As shown, Fig. I, the semi-conductor wafer 18 is positioned on a chuck 30 forming a gimbal which rests in a socket 17 of piston 16 centred within a chamber 15 of a base 11 by two annular diaphragms (90A, 91A). The base 11 is arranged in an aperture in a support 12 on which is mounted a carriage 60 which supports the mask 62 above the wafer. In operation the mask is roughly aligned with marks on the wafer, air is supplied to socket 17 through flow gauge 20 and pipe 19 to float the chuck 30 in socket 17 and air is also supplied to chamber 15 by means of a pressure regulator 22 controlled by a stepping motor 23 to elevate the piston 16. When the wafer 18 contacts the mask 62 the gimbal chuck automatically tilts to make the surfaces coplanar. The chuck is pressed down into the socket 17 causing an increase in the pressure and a decrease in the flow rate of the air supplied so that a ball 24 in the flow gauge 20 gradually moves down until it reaches the position illustrated where it operates a proximity detector 25. The electric control system 26 then stops the elevation of the piston and applies a vacuum to the socket 17 to clamp the chuck in position. The pressure applied to the piston is then reduced by a predetermined amount to lower the piston so that fine adjustment of the wafer and mask alignment can be made and the pressure is then increased by the same amount to elevate the wafer into contact with the mask for exposure of a photoresist coating on the wafer. The carriage 60 has a ring 75 supported by springs 77, the mask being held to the ring by a vacuum system. When desired an annular flexible tube (82) may be inflated to depress the ring (75) to bring the mask 62 into contact with the top of the base member. The carriage may be moved away along tracks (63, 64) while the mask is in its raised position to provide access to the chuck for the removal of the exposed wafer and insertion of an unexposed wafer. The carriage is accurately relocated in its position above the wafer by means of two pistons (71) which are elevated into conical recesses (72) in the carriage. An annular ring 130 is provided on the base which when inflated after the accurate alignment step locks the base to the support and seals the space round the wafer which may then be evacuated or filled with an inert gas for the exposure of the photoresist if the meterial used requires this. The apparatus described is also provided with a ring (90), surrounding the piston and chuck, which may be raised to facilitate placing the wafer on the chuck; a stop (37) against which a flat or notch on the wafer may be located, the stop being retracted when a vacuum is applied via line 54A to hold down the wafer; a pair of arms (42, 43) operated by a further vacuum line to push the wafer into contact with the stop; and plungers (56) mounted in the vacuum holddown openings so that application of a positive pressure raises the plungers to lift the wafer from the chuck surface.