| 摘要 |
<p>In the alignment of an optical mask 11 with the pattern of the previous layer on a wafer 15 in the fabrication of an integrated circuit, the mask 11 is formed with a transparent phase reversal zone plate 10 comprising alternate zones of a height relative to the surface of the mask 11 such that their optical path difference differs from adjacent zones for normal incident light by a half- wave. A laser beam is directed perpendicularly to the planes of the mask 11 and wafer 15 and is focussed by the zone plate as a line on the surface of the wafer. The wafer is formed with a line bar 14 and the relative position of the mask and wafer is adjusted until the line is focussed on the bar 14, thus indicating exact alignment. <IMAGE></p> |
