Direct-Viewing Alignment Scheme for Projection Lithography
Original Publication Date: 1983-Dec-01
Included in the Prior Art Database: 2005-Feb-08
In a projection lithography system, wafer alignment is generally accomplished by inserting some alignment optics so that the images of the alignment marks on the mask and the wafer are superimposed through the imaging lens. This leads to complicated optical design, source of alignment errors, low resolving power, and limitation of signal-to-noise ratio. In this publication, a direct viewing scheme is proposed for a class of aligners in which the mask and the wafer can be moved together without changing their relative position. For example, one type of scanning projection aligner mounts the mask and the wafer on a surface of a scanning block, as shown in Fig. 1. Another aligner mounts the mask and the wafer at the opposite sides of the scanning block, as shown in Fig. 2. They are both suitable for direct viewing alignment.