Effects of Plasticizing Additives on Performance of 193 nm Chemically Amplified Positive Resists.

Abstract

The effects of plasticizing additives on lithographic performance, PEB temperature dependence, and environmental stability were investigated in 193nm chemically amplified resists based on norbornene t-butyl ester/maleic anhydride copolymer. Tert-butyl (t-Bu) cholate was used as a plasticizing additive to control the glass transition temperatures (Tg) of the resists. The resist softening temperature was decreased from>180°C to 150°C by the addition of t-Bu cholate. The resist sensitivity and resolution were almost unchanged, when post-exposure bake (PEB) temperatures were below the resist softening temperature. The resolution capability was degraded as the PEB temperature increased to above the resist softening temperature. High environmental stability of 60min was achieved by optimizing the resist softening temperature, because soft baking at around the resist softening temperature reduced the amount of residual solvent, and thus made the resist absorb basic airborne contaminants less readily. How ver, the environmental stability was deteriorated at lower PEB temperature. Strict optimization of the PEB temperature is required, for both the resolution capability and environmental stability. The environmental stability of the optimized resist at adequate PEB temperature was almost the same as that of 248nm acetal type resist, and it was sufficient for practical use.