Effects of underlayer absorption coefficient on bridging risk in chemically amplified resist process for extreme ultraviolet lithography

The suppression of stochastically generated bridges is an important issue in the chemically amplified resist process for EUV lithography. The additional supply of secondary electrons from an underlayer may be required for the suppression of bridging. In this study, the secondary electron dynamics in a resist-underlayer system was calculated assuming line-and-space resist patterns to assess the effects of the underlayer absorption coefficient alpha(u) on the bridging risk R-b. The bridging risk decreased with increasing underlayer absorption coefficient. In particular, the effect of the underlayer absorption coefficient on the bridging risk dlnR(b)/d alpha(u) for alpha(u) > 6 mu m(-1) was larger than that for alpha(u) < 6 mu m(-1). However, the vertical profile of the protected unit distribution was significantly degraded owing to the excessive supply of secondary electrons for alpha(u) > 8 mu m(-1). alpha(u) of 6-8 mu m(-1) is considered to be the target value for suppressing the bridging risk when the resist absorption coefficient was 4 mu m(-1).