Poly(3-Butenyltrimethylsilane Sulfone): A Sensitive Positive Electron-Beam Resist For Two-Layer Systems

Abstract

The synthesis, properties and lithographic performance of poly(3-butenyltrimethylsilane sulfone) (PRTMSS) as an imaging and pattern transfer layer for two-layer resist systems is reported. 3-Rutenyltrimethylsilane (BTMS) was copolymerized with sulfur dioxide over a wide range of temperatures in the presence of a variety of free radical initiators to give a high-molecular-weight product (Mn = (4-9).105; M_w/M_n = 2-2.8), soluble in many common organic solvents. PRTMSS is thermally stahle in air up to 170-180°C and has a Tg of 120°C. It is chemically stable and resistant to hydrolysis. PRTMSS films spun from solution in cyclopentanone or chlorobenzene on top of hard-baked Novolac-type photoresist used as a planarizing layer were exposed to a 20 keV electron beam and developed in 2- butanol at 14 to 16°C. Sensitivity of the resist was 1.0-1.5 μC/cm² and contrast was 1.3-2.5. Half-micron gratings were transferred into the thick, planarizing layer by oxygen reactive ion etching (0₂ RIE). The processing latitude of PRTMSS is considerably wider than that of poly(NTMS butene sulfone), although careful control of the processing parameters is required. The degradation and passivation mechanisms of PRTMSS in 02 RIE have been studied by several surface-sensitive analytical techniques and their results are briefly discussed.