A Practical Interferometric Technique for Mask/Wafer Alignment During Proximity Printing,
NAVAL OCEAN SYSTEMS CENTER SAN DIEGO CA
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A new automated technique for sensing translationalrotational mask-to-wafer alignment will be presented that is useful with proximity printing processes such as masked ion beam or x-ray lithography. The technique is based on computer interpretation of fringe patterns created by laser beams diffracted from unique grating structures on both the mask and the wafer. It requires no moving parts and features a simple optical configuration that uses a dielectric cube beamsplitter to the novel grating structure and fringe analysis provides a capture range in excess of 20 um. Additional key features of the technique are that it is insensitive to variations in the gap between mask and wafer and that its performance does not degrade with changes in surface reflectivity or topography as device wafers are processed. A single channel of the grating alignment technique has been implemented and tested in a laboratory bench fixture. The required mathematics, computer code, and experimental results will be discussed.
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