Pure zyxwvutsrqpo & zyxwvutsrq Appl. zyxwvutsrqpo Chem., Vol. zyxwvutsrq 60, No. 7, pp. 959-972, 1988. Printed in Great Britain. @ 1988 IUPAC Solution photochemistry of poly(dialkylsi1anes): a new class of photoresists zyxw Josef Michl*, John W. Downing*, Takashi Karatsu*, Allan J. McKinley*, Gabriella Poggi*, Gregory M. Wallraff*, Ratnasabapathy SooriyakumaranO and Robert D. Miller' *Center for Structure and Reactivity, Department of Chemistry, The University of Texas at Austin, Texas 78712-1167; OIBM Research Laboratories, Almaden Research Center, San Jose, CA 95120-6099 ABSTRACT polysilanes represent a new class of polymeric materials of considerable theoretical and practical interest. Although formally saturated, they absorb in the near UV and undergo rapid photodegradation. After a review of the present understanding of the electronic structure of poly(dialkylsi1anes) as a function of backbone conformation, we summarize their photophysics and describe recent advances in the understanding of their solution photochemistry. INTRODUCTION Polysilanes (1) are high-molecular weight polymers with a silicon backbone and remarkable properties. (ref 1) Although the structure is formally saturated, they have an intense absorption band in the near UV region, between 300 and 400 nm depending on substitution, and suffer rapid photochemical degradation when irradiated at these wavelengths. Their utility as photoresists has already been demonstrated (ref 2, 3) and continues to be of great interest in the electronics industry, as is the promise of these materials as electron beam and X-ray resists. Free radicals are formed in the UV-radiation induced process, and polysilanes have been proposed for use as polymerization initiators (ref 4). They are also currently under investigation as non-linear optical materials,(ref 5) positive charge conductors,(ref 6,7) and as ceramic precursors.(ref 8) The recent wave of industrial interest in these materials is due tothe advances in the synthesis of soluble polysilanes (ref 9) which can be cast as thin films and otherwise processed. suitable substituents as side-chains: materials containing only methyl or ony phenyl substituents are quite insoluble and intractable. (ref 10) A recent review of polysilanes is availabler and the interested reader is referred there for further detail. (ref 1) This progress was due t o t h e use of Although diary1 and arylalkyl substituted polysilanes are known and exhibit interesting interactions between the conjugated substituent and the silicon backbone, the present survey of recent results from our laboratory will be restricted to dialkyl substituted polysilanes, which have the simplest electronic structure. It shall also be largely restricted to the photochemical behavior of these polysilanes solutions at room temperature. Many of the polysilanes arethermochromic, both in the solid state and in solution, presumably as a result of temperature-induced conformational changes in the polymer backbone. (ref 2/11-14) The relation between conformational changes in solution and the process of aggregation and microcrystallite formation has not yet been fully elucidated, and we shall avoid the issue by concentrating on the behavior of the room temperature conformers in solution. The materials we have investigated have high molecular weightr mostly in excess of a millionr and have been synthesized by standard procedures. 959