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Downloaded by TUFTS UNIV on November 24, 2016 | http://pubs.acs.org Publication Date: May 5, 1989 | doi: 10.1021/ba-1990-0224.ch039
Synthesis and Lithographic Evaluation of a Poly(acylsilane) 1
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Antoni S. Gozdz, Hans J. Reich, and Michael D. Bowe 1
Bell Communications Research, 331 Newman Springs Road, Red Bank, NJ 07701-7020 S. M. McElvain Laboratories of Organic Chemistry, Department of Chemistry, University of Wisconsin, Madison, WI 53706
2
The polymerization of twoα,β-unsaturatedacyhsilanes, 1-trimethylsilyl-2-propen-1-one (vinyl trimethylsilyl ketone, VTMSK) and 1trimethylsilyl-2-methyl-2-propen-1-one (isopropenyl trimethylsilyl ketone, IPTMSK) was studied. VTMSK polymerized readily under free-radical-initiation conditions to give a well-defined, highly solu ble, high-molecular-weight polymer. Exposure of thinfilmsof this polymer to mid- and deep-UV radiation or heating at 320 nm) sources at the wafer plane were 21 and 7.1 mW/cm2, respectively. The patterns were exposed through chrome-on-quartz masks and developed by spraying with or dipping into 2-propanol, followed by drying. Film thickness was measured with an Alpha-Step 200 (Tencor Instruments) profilometer. Oxygen reactive-ion etching (0 2 RIE) was carried out with a Cooke Vacuum Products (model C71-3) parallel-plate RIE reactor operating at 13.56 MHz. Oxygen pressure andflowrate were 2 Pa and 10 seem (standard cubic centimeters per minute), respectively, and the RF (radiofrequency)power density and self-bias were 0.15 W/cm2 and -350 V, respectively.
Results and Discussion Preparation. Although acylsilanes (I) and a, β-unsaturated acylsilanes (II) have been the subject of numerous synthetic and photochemical studies (14, 15), to the best of our knowledge, no acylsilane polymers have been characterized or reported prior to our recent work (II). Two simple a, β-unsaturated acylsilanes, l-trimethylsilyl-2-propen-lone (HI) and l-trimethylsilyl-2-methyl-2-propen-l-one (IV) were chosen for polymerization studies. The polymerization of the carbon analogues of these a, β-unsaturated acylsilanes, that is, 4,4-dimethyl-2-propen-3-one (vinyl tertbutyl ketone, V) and 2,4,4-trimethyl-2-propen-3-one (isopropenyl tert-butyl ketone, VI) has been studied by Willson et al. (16, 17). These authors re ported that whereas V readily polymerizes under free-radical-polymerization conditions, VI undergoes polymerization only under anionic-initiation con ditions in the presence of a crown ether as a complexing reagent. On the basis of UV and NMR spectroscopic data, Willson et al. (16, 17) ascribed the difference in polymerization behavior to the nonplanar, unconjugated structure of ketone VI brought about by steric hindrance caused by the methyl group at C-2. The a, β-unsaturated acylsilanes III and IV behaved similarly under freeradical-polymerization conditions. VTMSK (IH) polymerized readily even without an added initiator (Table I), but IPTMSK (IV) did not. VTMSK was polymerized in high yield both in bulk and in solution to give high-molecular-weight products. The polymerizations were always car ried out at only slightly elevated temperatures (25-50 °C) to minimize the decomposition of the monomer and polymer. The spectral characteristics and other analytical data obtained for the products were in agreement with those expected for PVTMSK (Figure 1A). However, the separation and purification of PVTMSK were difficult, because the polymer exhibited an unusually high solubility in a range of polar and nonpolar organic solvents, including lower molecular weight alcohols and hexane. Although PVTMSK could be precipitated from chloroform solutions into an excess of methanol, such solutions decomposed rapidly even in the dark and at room tempera-
Zeigler and Fearon; Silicon-Based Polymer Science Advances in Chemistry; American Chemical Society: Washington, DC, 1989.
Downloaded by TUFTS UNIV on November 24, 2016 | http://pubs.acs.org Publication Date: May 5, 1989 | doi: 10.1021/ba-1990-0224.ch039
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GOZDZ ET AL.
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Synthesis and Properties of Poly(acylsilane)s
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Figure 1. IR spectra of poly(acylsilane)s. (A) PVTMSK, (B) product of a freeradical polymerization of IPTMSK, and (C) a copolymer of IPTMSK with methyl methacrylate. The stars denote prominent PMMA hands.
ture. Solutions of PVTMSK in less reactive solvents such as hexane, acetone, and chlorobenzene were stable for several weeks when stored in the freezer. Several attempts at the free-radical (benzene, 1% AIBN, 100 h, 55 °C) and anionic (1:4 THF-benzene, n-butyllithium- 18-crown-6 complex [16, 17], -78 °C) polymerization of IPTMSK afforded only traces (
