2012 Volume 25 Issue 5 Pages 633-640
This paper describes fundamental studies of the degradation of LER in EUV resists as a function of film thickness. This research focused on the influence of three variables on this LER film thickness problem:
·Substrate interaction (primed silicon vs. organic underlayer)
·Changes in optical density (variations in fluorine content)
·PAG attachment (bound and unbound)
Our experimental approach struck a balance between using resists prepared by commercial resist vendors and using open-source resists with custom-designed polymers to address specific variables listed above. One key feature of this research was our development of a mathematical method for evaluation of the extent of the LER deviation in thin films, called ψLER. Our results showed that the effect of substrate was not significant for two different resists (one commercial and one open source). Additionally, we found that increasing optical density actually made the LER degradation (ψLER) worse-which was contrary to what was predicted by other researchers. Most significant was our demonstration that PAG attachment plays the most important role in the degradation of LER in thinner resist films; polymer-bound PAGs showed a dramatic 3X improvement in ψLER over a similar blended system.
