Polysilanes for microlithography

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Abstract
We have recently reported the formation of scum-free micron images in a bilayer composed of a thin (1500 angstrom) imaging layer of poly(cyclohexylmethylsilane) coated over a thick planarizing layer of a hardbaked diazoquinone-novalac type photoresist using deep UV exposure. Although excellent resolution was achieved (< 0.5 micrometers ) in this process, the exposure doses required (125-150 mJ/cm2) were higher than desirable for commercial DUV imaging tools. We have addressed this problem using two approaches: (i) the synthesis of new polysilanes which are intrinsically more sensitive to photodegradation in the solid state and (ii) the incorporation of additives which enhance the photosensitivity. Regarding the former, a number of aryl substituted polysilane homopolymers which are significantly more photolabile than the standard poly (methylphenylsilane), as assayed by the rate of spectral photobleaching upon exposure to DUV radiation, have been prepared and tested. In addition, a number of small molecule additives which quantitatively quench the polymer fluorescence in the solid state have been identified. Some of the additives which efficiently quench the polymer fluorescence in the solid state also accelerate the rate of photodegradation. The combination of the new polysilane materials with sensitizing additives has allowed submicron DUV imaging at exposure doses as low as 20 mJ/cm2 or less in a bilayer configuration employing O2-RIE for image transfer of the wet-developed images.

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