Silylated poly(4‐hydroxystyrene)s as negative electron beam resists

Abstract

Silylated poly(4-hydroxystyrene)s and radical polymerized 4-tert-butyldimethylsilyloxystyrene (TBDMSOSt) were examined as electron beam resists. Commercial poly(4-hydroxystyrene) (PHS) with M w ϭ 1.69 ϫ 10 4 and M w /M n ϭ 5.41 was silylated with 1-(trimethylsilyl)imidazole and tert-butylchlorodimethylsilane. Both silylation reactions proceeded quantitatively to afford trimethylsilylated PHS with M w ϭ 3.93 ϫ 10 4 and M w /M n ϭ 4.91, and tert-butyldimethylsilylated PHS with M w ϭ 4.08 ϫ 10 4 and M w /M n ϭ 3.81. These 2 silyl ether polymers acted as a negative working resist to electron beam (EB) exposure. Sensitivity and contrast of tertbutyldimethylsilylated PHS were not affected by prebake temperature around its T g of 97°C, while those of PHS were dependent on prebake temperature around its T g of 160°C. At a prebake temperature of 125°C, the sensitivity parameter D g 0.5 and the contrast ␥ value were obtained as follows: 3.93 ϫ 10 Ϫ4 C cm Ϫ2 and 0.91 for PHS; 1.49 ϫ 10 Ϫ4 C cm Ϫ2 and 1.06 for trimethylsilylated PHS; 1.84 ϫ 10 Ϫ4 C cm Ϫ2 and 1.44 for tert-butyldimethylsilylated PHS. The silylation procedures obviously improved the sensitivity of PHS. TBDMSOSt was polymerized in bulk at 60°C with 2,2Ј-azobisisobutyronitrile (AIBN) as an initiator. The resultant poly(TBDMSOSt) possessed M w ϭ 3.01 ϫ 10 5 and M w /M n ϭ 1.92 and exhibited a sensitivity D g 0.5 of 1.60 ϫ 10 Ϫ5 C cm Ϫ2 and a ␥ value of 1.47. More than 10 times enhancement of sensitivity was observed compared with tert-butyldimethylsilylated PHS. Such a high sensitivity is probably due to the high molecular weight of the bulk polymerized material. Poly(TBDMSOSt) resolved an isolated line of 0.20 m width and 0.5 m line and space patterns.