John M. Zeigler

Picosecond reorientations of the transition dipoles in polysilanes using fluorescence anisotropy

Abstract Time-resolved fluorescence and fluorescence anisotropy measurements have been performed on solutions of high molecular weight polysilane materials. The physical processes responsible for the decay of the anisotropy are discussed.

Two-photon spectroscopy of polysilanes

Abstract We report the first two-photon excited fluorescence excitation spectra for polysilanes in solution, film, and low temperature glass. We discuss band-to-band and exciton models for the optical excitations, in order to explain a strong two-photon resonance 0.9 eV above the first absorption band.

Self-developing polysilane deep-uv resists - photochemistry, photophysics, and submicron lithography

A new class of alkyl silane copolymers with relatively facile self-developing behavior under deep UV exposure has been examined. These materials can reproduce 0.8 μ features by projection lithography with a KrF excimer light source. The mechanism of material removal is primarily photochemical in nature and yields chemically inert volatile siloxanes as the major photoproducts, via a high quantum yield silylene expulsion/oxidation process.

Polysilanes - prototypical σ-conjugated polymers

Abstract Polysilanes constitute the first examples of sp 3 -bonded σ-conjugated high polymers. Their spectroscopic and electronic properties are strongly reminiscent of those of the π-conjugated polymers, but, unlike the π-conjugated polymers, polysilanes are generally fully soluble and airstable. They exhibit molecular weight dependent mid-UV absorption which is polarized along the silicon backbone and strongly thermochromic. The fluorescent emission is narrowed relative to the absorption and vibrationally decoupled, indicative of a highl delocalized singlet state. Consistent with the σ-electron delocalization, the materials are excellent non-dispersive photoconductors, dopable to 0.5 S/cm conductivities, and exhibit large 3rd order optical non-linearities. Their extreme photosensitivity endows some polysilanes with promise as photoresist materials.

Excitation dynamics in polysilanes

Abstract The spectral properties of poly-(di-n-hexyl)-silane, of different molecular weights, dissolved in low temperature glasses are presented and discussed. Laser photolysis produces both narrow holes at the exciting frequency as well as overall changes of the spectrum. The non-local spectral changes reflect the competing processes governing the dynamics of the extended excitations in the linear polymer chain. Numerical modelling of the spectra and the holeburning qualitatively reproduces the observed changes and gives insight in the polymer chain structure and properties.

Lithographic, Photochemical And O 2 RIE Properties Of Three Polysilane Copolymers

Polysilanes are high Si-content polymers containing backbone Si-Si bonds. Their high Si content makes them very resistant to removal by 02 reactive ion etching (RIE) while their Si-Si bonding results in strong transitions in the mid- and deep-UV regions. Mid-UV photolysis causes chain scission, a process used by IBM workers in two lithographic applications: as imaging layers in organometallic bilevel, 02-RIE-developed resistsl and as contrast enhancement materials for imaging with positive photoresists.

Extreme ultraviolet resist and mirror characterization: Studies with a laser plasma source

A monochromatized laser‐produced plasma source of extreme ultraviolet (XUV) radiation has been used to study resists and reflective multilayers for use in projection x‐ray lithography. We report the characterization of near‐edge x‐ray absorption fine structure (NEXAFS) spectra, exposure sensitivity, and contrast of selected polysilane resists at photon energies near 100 eV, where projection x‐ray lithography is being developed. We find absorption resonance features in the NEXAFS spectra which we assign based on ab initio quantum chemical calculations to excitation into Si–Si and Si–C σ* orbitals. Using monochromatized XUV exposures on the Si–Si σ* resonance at 105 eV, followed by solvent dissolution development, we have measured the exposure sensitivity curves of these resists. We find sensitivities in the range of 600–3000 mJ/cm2 and contrasts in the range from 0.5–1.4, depending on the polysilane side chain. Exposure sensitivity measurements have also been performed below the edge at 92 eV where we find...

Chain transfer processes in dichlorosilane reductive polymerization and their control: A simplified route to high molecular weight polysilylenes

Polysilylenes are usually synthesized by a reductive coupling of diorganodichlorosilanes with molten sodium dispersions in an inert solvent, typically neat toluene or toluene mixed with a cosolvent such as heptane. The surface nature of this reaction leads to highly nonstatistical molecular weight distributions which are broad and poorly reproducible in the absence of rigid control over reaction parameters. Because the electronic and physical properties of polysilylenes are sensitive to molecular weight distribution, it is important to understand the factors which influence the molecular weight distribution obtained during preparation. In this work, we have examined the chain transfer processes in the Na-mediated reductive coupling of representative alkyl and aryl diorganodichlorosilanes by comparing rigorously controlled reactions carried out in toluene, a solvent normally thought to be non-chain-transferring in these reactions, to reactions carried out in benzene, which is thermodynamically incapable of undergoing chain transfer via hydrogen abstraction by a terminal polysilyl radical. We have identified for the first time a low-yield back-biting hydrogen abstraction process on the polysilylene side chain C-H bonds which generates an Si-H terminated polysilylene chain and a reactive site alpha to the silicon. The data also suggest the presence of a second back-biting reaction on the polysilylene Si-Si backbone bonds which produces cyclosilane by-products. An outgrowth of the work is a new modification of the Wurtz coupling process which routinely provides very high molecular weight polysilylenes by the safer and more convenient “normal” addition procedure.

Excited states of polysilanes: High-resolution spectroscopy and molecular modeling

High-resolution spectroscopy at low temperatures (1.5–77 K) is used to study the electronic properties of the low-temperature phase of poly-di-n-hexyl-silane in solution. The absorption spectra exhibit an unexpected sensitivity to sample preparation. Experiments probing the energy transfer dynamics are reported and a model for the electronic excitation and the disorder reigning in the polymer is presented.

Mutual Annihilation of Singlet Excitons in [sgrave]-Conjugated Polysilanes

Abstract In previous papers, we have reported that the exciton-exciton annihilation rate constant is very high for singlet excitons in poly(n-propyl methyl silane) and that it is insensitive to temperature. In this paper, we report further that this rate constant is roughly the same magnitude as that found earlier in both poly(phenyl methyl silane) and poly(di-n-hexyl silane), and that it is not affected by the molecular weight of the polymer, at least in poly (di-n-hexyl silane). However, solid films of poly(di-n-hexyl silane) undergo an order-disorder transition near 42°C, and it appears that this transition causes an order of magnitude decrease in the annihilation rate constant.