Optimized acid release underlayers for 157-nm lithography

As the semiconductor industry moves to sub 193 nm imaging wavelengths the switch to thin film resists with marginal transparency can result in a significant degradation of resist profiles. Tremendous progress has been made recently in lowering the absorbance of 157 nm polymer systems, however etch resistant single layer resists are likely to have absorbance values of 1-2/mm. Current generation EUV resists have even higher absorbance values of 2-3/mm. While the use of thin films mitigates (but does not eliminate) the effect of high resist absorbance the impact of resist footing, notching, and standing waves are exacerbated. Surface effects such as top rounding or surface contamination are also likely to be a significant concern. One way to minimize the effect of non vertical profiles due to high absorbance and/or resist footing is through the use of optimized underlayer/ photoacid generator (PAG) systems. The PAG’s are selected so as to have higher diffusiveness but lower reactivities than the PAGs used in the resist itself in order to have a greater effect on the resist profile. Characterization data will be presented using a high absorbance resist (> 3.0/mm). Lithographic data on this system will be described and imaging data presented showing features down to 90 nm in a resist 120 nm thick.