Impact of thin resist processes on post-etch LER

Abstract

While evaluating 193 nm, and early versions of 157 nm and EUV resists, the lithography community has focused on post-develop LER values derived from image analysis of top-down SEM micrographs. These numbers, however, do not capture the tendency of a resist to facet and roughen during plasma etching processes. They also do not convey any information about the role of the anti-reflective coatings/hard masks in the transfer of resist roughness into the underlying substrate. From a manufacturing perspective, it is the "LER" of the final etched substrate that is more important. This paper systematically studies the impact of resist polymer platform and thickness, etching conditions, and presence of organic and inorganic anti-reflective coatings/hard masks on substrate roughening. An AFM technique, previously developed by Reynolds and Taylor1, is used to measure the feature sidewall roughness as a function of etch depth. This technique enables us to calculate the sidewall roughness of the resist, ARC/hard mask and substrate surfaces simultaneously, and determine correlations that may exist between these values. The paper identifies and demonstrates patterning methodologies that can be used to achieve "smooth" substrate surfaces even when the resist is "thin".