PATTERNING OF X-RAY MASKS USING THE NEGATIVE-ACTING RESIST P(SI-CMS)

The copolymer of trimethylsilylmethyl methacrylate with chloromethylst yrene [P(SI-CMS)] is a negative electron-beam and deep-UV resist which can withstand erosion in O2-containing plasma environments [J. R. Mal donado, J. Electron. Mater. 19, 6699 (1990)]. Manipulation of its comp osition and molecular weight allows control of the etch resistance and radiation sensitivity properties. Methods have been developed to prov ide reproducible synthesis of P(SI-CMS) with molecular weight and comp osition tailored to specific lithographic demands. For x-ray mask patt erning, the copolymer having a 90:10 mole ratio of SI:CMS [P (SI90-CMS 10)] and M(w)BAR between 30 000 and 41 000 g/mol has been found to pro vide an optimal combination of resist sensitivity, dry-etching resista nce, and pattern resolution. P(SI90-CMS10) is used to image the Cr-W-C r metallization layer of a monolithic x-ray mask structure, by subtrac tive etching techniques [G. K. Celler et al., Appl. Phys. Lett. 59, 31 05 ( 1 99 1 ); G. K. Cellar et al., J. Vac. Sci. Technol. B 10, 3186 ( 1992); C. W. Jurgensen et al., J. Vac. Sci. Technol. B 9, 3280 (1991)] . The resist pattern is transferred into chromium with a O2-Cl2 plasma , and then into tungsten with a fluorine-based plasma. Resolution of 0 .15 mum (line-space) in the resist has been achieved with 50 keV elect ron-beam exposure, and 0.20 mum patterns (line-space) have been succes sfully transferred into the tungsten of the x-ray mask.