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Organosilane polymers have created widespread interest as precursors for &Sic fibers (1-S), as impregnating agents for strengthening ceramics (6,7), and as dopable semiconductors (4). In the preceding article we described a general synthesis for a variety of very high-molecular-weight organosilane homopolymers (8) :Me I I X t S i j n 1: X = P h 5 : X=n-butyl 2: x =p-tolyl 6: X=n-hexyl 3: X = 0-phenethyl 7 : X = n-dodecyl 4: X = n-propyl 8:We now report unusual ultraviolet (UV) absorption properties of the polyorganosilanes as well as their photolytic degradation under U V (3 13 nm) radiation. Previous investigators have shown that compounds containing catenated Si-Si bonds, such as R'(SiR2),R' (n = 2-24; R = H, Me, Ph; R' = H, Me, Ph, CI), unlike the analogous alkane series, display intense UV absorptions in the region of 200-300 nm, and that the position of the absorption maximum (Amax) and the molar absorptivity increases regularly with increasing chain length (9-13). These intense UV absorptions may be explained as a transition between a usi-si HOMO delocalized over the Si framework and a delocalized u* or 3d nsi-si . Results and Discussion(7) and an aryl-substituted polymer *Because the progression of A, , , approaches a maximum limiting value as n gets very large, reasonable comparisons can be made of the positions of A, , , for different polymers of high molecular weights.Short phenyl-substituted and phenyl-terminated permethyl catenates show similar red shifts of absorption maxima compared with analogous permethyl compounds, which have been ascribed to a stabilization of the LUMO by interaction of the delocalized 3dsi-siMO with the p-n* MOs of the aryl groups (see ref. 16).

Contamination of chemical amplification resists by airborne basic substances can be minimized by reducing the free volume of resist films by annealing. Good annealing requires heating the resist films above their glass transition temperatures. However, it is not usually possible to bake chemical amplification positive resists based on poly(4-hydroxystyrene) above their glass transition temperatures because thermal deprotection typically occurs below their glass transition temperatures. Use of metaisomers to lower glass transition temperatures is described first to prove the validity of our annealing concept. Furthermore, our high temperature bake process of a new thermally and hydrolytically stable positive resist (ESCAP) is reported. The annealing effectively reduces uptake of airborne contaminants by resist films because the diffusivity of small molecules in polymer films is an exponential function of the free volume and thus stabilizes the latent images.

A production-worthy deep UV resist system built on the ESCAP platform is described. The resist consists of a thermally and hydrolytically stable resin and acid generator and thus can be heated at high temperatures for free volume reduction, which provides stabilization toward airborne base contamination. The film densification in conjunction with the use of a bulky acid reduces acid diffusion during postexposure bake, contributing to high lithographic performance. Robust 0.25 µm process latitudes have been demonstrated. Furthermore, the resist has produced excellent 175 nm line/space images with a depth-of-focus of 0.3 p m on a KrF excimer laser stepper with a numerical aperture of 0.60, indicating that the resist allows the use of the current exposure tool in the early 1 Gbit generation.

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