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All integrated circuits require several levels of lithography. The alignment process ensures
that each succeeding pattern accurately overlays the preceding ones. Alignment is carried out in
current semiconductor processing tools by using electron beams to locate fiduciary marks placed
on the wafer and or using laser interference methods. Preliminary measurements carried out in
our laboratory on materials relevant to semiconductor processing indicate that the use of positron
beams can lead to enhanced contrast from signals not available when using electron beams.
However, positron beams have never before been used in alignment processes. Here it is
proposed, for the first time, to perform research to determine if the unique contrast mechanisms
available to positrons can be exploited in developing faster, more accurate, and more economic
alignment methods for the semiconductor industry.
Backscattered positrons will be studied to determine which materials result in the best
combination of signal strength and contrast for use in different aspects of the alignment process.
After the initial contrast studies are performed, it is proposed to build a new apparatus
specifically designed to develop positron beam alignment techniques in actual semiconductor
lithographic processes.
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