Kazumasa Saito

Ladder Structure Silicone Resist PVSS

A novel ladder structure silicone resist, silylated polyvinylsilsesquioxane (PVSS), was developed as a negative bi-level electron-beam or UV resist, showing high sensitivity, half micron resolution and an excellent oxygen reactive-ion etching (02-RIE) resistance. PVSS was prepared by hydrolyzing vinyltrichlorosilane and subsequent polycondensation and silylating active silanol groups. PVSS has vinyl functional groups as a side chain, making it highly-sensitive to electron beams. High resolution PVSS resist with a narrow molecular weight distribution was prepared by fractional precipitation. PVSS patterns are not etched and softened during the 02-RIE due to the large amount of silicon atoms and. high melting temperature. The 02-RIE etching rate of PVSS is about 100 times smaller than that of the planarizing layer and PVSS melting temperature after electron-beam exposure is above 2001. A 0.5 μm line-and-space pattern can be delineated at a dose of 7.6μC/cm using PVSS bi-level resist with molecular weight of 1.1 X 104 and dispersivity of 1.5. Also due to vinyl functional groups, PVSS resist to which adequate photoinitiator has been added is sensitive to UV light. PVSS resist is sensitive to the Ng lamp i-line(365.nm) when 2.6- bis-(4-azidobenzal)-4-methylcyclohexanone is added. It is sensitive to deep UV light when 2,2- dimethoxy-2-phenylacetophenone is added. PVSS UV resist has a 0.5 μm pattern resolution at a 1:1 contact exposure. Synthesis, molecular weight precipitation, and lithographic characteristics of PVSS are discussed in the sections that follow.