A MASK-TO-WAFER FINE GAP SETTING METHOD

This paper describes a mask-to wafer gap setting method for an X-ray s tepper. A capacitance micrometer on the wafer chuck and those on the m ask chuck are used in this method. The mask and wafer surfaces are pos itioned parallel to the travel plane of the wafer x-y stage so that th e gap does not vary with the step and repeat motion of the wafer stage . Therefore, gap setting is required only once for each wafer, and the throughput becomes better. This method has the following two addition al merits. A complex gap measurement optics is not required and the se tting value of the gap is variable. The gap setting error caused by ma sk unflatness, wafer unflatness and travel error of the wafer x-y stag e was analyzed. Experiments were carried out using mask and wafer stag es both with six axes. A gap setting accuracy better than +/- 1.5 mu m at the exposure positions of 5 wafers has been achieved for 30 mu m a nd 20 mu m gaps.