Imaging characteristics of lithography using phase edge type PSM are investigated intensively based on optical image calculations. Even in the absence of aberration, imaging characteristics are very complicated for high coherent illumination. Shape of CD-Focus curve of isolated line varies from concave to convex with increasing dark line, i.e., Cr line width on mask. Hence, in the case that DOF is optimized for smallest Cr width on mask, DOF decreases with increasing image CD. Moreover, CD-Focus characteristics varies with shifter width on mask. As a result, fair CD- Focus characteristics can be obtained for some specific patterns. In contrast with this, under medium coherent illumination, variation of CD-Focus characteristics with changing mask pattern is less significant than that for high coherent illumination. Large DOF can be obtained for wide range of image CD and pattern pitch. However, finest CD with iso-focal characteristics, which is given by zero Cr width mask, is larger for lower coherent illumination.

Date Published: 5 July 2000
PDF: 12 pages
Proc. SPIE 4000, Optical Microlithography XIII, (5 July 2000); doi: 10.1117/12.388967

Published in SPIE Proceedings Vol. 4000:
Optical Microlithography XIII
Christopher J. Progler, Editor(s)