Sub-half-micron deep-UV lithography using wet and dry developable resist schemes

DUV lithography is an emerging technology which promises excellent resolution coupled with an improved depth of focus. Whilst the hardware connected with this technology is rapidly maturing, there remain question marks over the suitablilty of present DUV resists in the fabrication of actual circuits. Two widely differing approaches are typified by Plasmask (DESIRE) which involves surface imaging and dry development and by the wet developable Shipley Megaposit SNR 248-1.0, which utilises acid catalysed chemistry. We have studied both materials using a contact printing system and the ASM-L PAS 5000110 DUV stepper (both at 248 nm wavelength). In particular we have compared the lithographic performance of both resists on a variety of substrates and topographical features, commonly encountered during processing. Practical issues such as the intrinsic adhesion, photospeed, exposure latitude, focus latitude, linearity, thermal resistance and etch resistance are presented. For the Shipley material we have compared its performance under various development conditions, with respect to resolution, photospeed, profile and residues. On the Plasmask material we have investigated the degree of silicon incorporation for various silylation conditions and for various Plasmask formulations. Significant differences have been noted for exposures made with this wavelength (248 nm) and those commonly reported with g and i-line exposure. Finally, the feasibility of using TMDS (1,1,3,3 Tetramethyldisilazane) as a silylating agent is presented.