Multi-alicyclic polymers for application in 193 nm lithography

Abstract

Fully multi-alicylic polymers designed for use as 193nm photoresist materials are obtained by vinyl addition polymerization of tetracarbocyclic norbornene derivatives,t-butyl tetracyclo$[4.4.0.1.^{2,5} 1^{7,10}]$dodec-8-ene-3-carboxylate (t-BDN) and 3-acetoxytetracyclo$[4.4.0.1.^{2,5} 1^{7,10}]$dodec-8-ene (AcODN). The alicyclic polymer backbones of these polymers provide plasma etch resistance, good mechanical properties,and stability toward radiation. For the lithographic applications were provided by carefully tailored two kinds of pendant groups: t-butyl carboxylate group as a carboxylic acid functionality masked by a protecting group. The protecting group undergoes acid-catalyzed thermolysis. The acetoxy polar group influences adhesion, wettability and solubility properties of the polymers. The polymer showed an acceptable high transmittance at 193nm and good adhesion property. The plasma etch rates of the copolymer poly(t-BDN-co-AcODN) (85:15) by $CF_4/CHF_3$ mixed gas were 1.01 times with respect to a novolac based resist. 0.2-㎛ line-and-space patterns were obtained at a dose of $45 mJ cm^{-2}$ using KrF excimer laser stepper. The low UV absorption by the polymer at 193nm and its high resistance to reactive ion etching along with alkaline developability make these copolymers an attractive resist system for 193nm lithography.