t-BOC maleimide copolymers for thermally stable deep UV resists by chemical amplification.

Four kinds of new t-BOC protected maleimide copolymers P(t-BOCMI/St), P(t-BOCMI/SiSt), P(t-BOCMI/t-BOCSt) and P(t-BOCOPMI/SiSt) were investigated as thermally stable, deep UV resists in high sensitivity. The resist polymers are composed of N-(t-butyloxycarbonyl)maleimide (t-BOCMI) or N-[p-(t-butyloxycarbonyloxy)phenyl]maleimide (t-BOCOPMI) and styrene derivatives (X-St) such as styrene (St), p-(t-butoxycarbonyloxy)styrene (t-BOCSt) and p-trimethylsilylstyrene (SiSt). The t-BOC protected copolymers have alternating structures and are readily deprotected by thermolysis and acidolysis to the corresponding polar maleimide (MI) and phenolic OH functions from t-BOCMI and t-BOC-oxyphenyl, respectively. The deprotected polymers P(MI/St), P(MI/SiSt), P(MI/HOSt) and P(HOPMI/SiSt) exhibit quite high Tg's above 245°C and high oxygen RIE resistance. In particular, the both silicon containing polymers P(MI/SiSt) and P(HOPMI/SiSt) are superior to a novolac photoresist in oxygen RIE resistance. The RIE resistance of the resist polymers in Cl2/He and CHF3/C2F6 gases are found to be comparable to the novolac resist. The three t-BOCMI copolymers have very low absorbance no more than 0.2 per μm at 248nm wavelength. The polymers P(t-BOCMI/St), P(t-BOCMI/SiSt), P(t-BOCMI/t-BOCSt) and P(t-BOCOPMI/SiSt) were compounded with 10wt% of triphenylsulfonium hexafluoroantimonate as a photoacid generator and the resists are named as MIST, MISIX, BMIST and PMISIX, respectively. The resists films were exposed to deep UV or KrF excimer laser and post-exposure baked at 100°C followed by development with aqueous alkaline solutions for positive image-making to get sub-micron patterns.In the case of MISIX and PMISIX resists only negative tone images were possible by organic developing. Thus the t-BOC protected maleimide copolymers combine capability of high resolution with high sensitivity in deep UV region and thermal stability above 200°C along with high oxygen RIE resistance.