抄録
This paper describes a mask-to-wafer alignment technique for submicron X-ray lithography which utilizes single and dual gratings. A single grating method is proposed to avoid the influence of lateral displacement on the gap detection signal. The single grating method utilizes a flat surface without a grating acting as the wafer mark. Both+1-order diffracted light beams, which are reflected from a mask grating and wafer surface, produce an interference signal. By using the linear part of this signal, a resolution of 0.02μm in the gap servo-control is achieved. Moreover, the envelope signal of the interference signal makes it possible to detect the absolute gap. Next, dual grating method with an intensity difference between +1-and 1-order diffracted light beams is applied to detect the lateral displacement. It is found that the lateral displacement signal is highly sensitive and stable when the gap has a specific value and the mask grating aperture ratio is slightly larger than 0.5. By combining the single and dual grating methods, an alignment value is achieved where the lateral displacement is detected within a resolution of 100 A and the gap is set to an accuracy of ±0.5μm.
