The main issue for fabricating a conventional Cr mask with e-beam exposure system is a resolution limitation. Required minimum critical dimension (CD) goes down to below 1.0 micrometer on 4X reticle, sometimes down to below 0.5 micrometer for OPC pattern. The resist which is widely used in e-beam lithography is positive tone PBS. PBS has been used in wet chrome etching process with spin spray or dip methods, due to its lack of resistance to dry etch durability. However, the isotropic process of wet chrome etching results in undercutting of the chrome. Thus, undercut causes the differences of CD between after development and final mask image. The purpose of this study is to decrease undercutting so that CD error can be minimized and a lot of rooms for overdevelopment margin can be obtained. CD linearity in case of below 1.0 micrometer was also investigated in detail. For this study, the chrome thickness coated on 6 by 6 by 250 mil PBS chrome plates was reduced. As a result of our study, we found that overdevelopment is marginal for the same final CD when using the thinner Cr, due to undercutting reduction. Good CD uniformity has also been achieved with good CD linearity.

Date Published: 24 July 1996
PDF: 8 pages
Proc. SPIE 2793, Photomask and X-Ray Mask Technology III, (24 July 1996); doi: 10.1117/12.245238

Published in SPIE Proceedings Vol. 2793:
Photomask and X-Ray Mask Technology III
Hideo Yoshihara, Editor(s)