Design, Synthesis, and Characterization of Poly(trimethylsilylmethyl methaciylate-co-chloromethyl styrene) for 193 nm Exposure

Requirements of materials for lithography at 193 am limit single layer resist candidates to those with high optical transmission. A random copolymer of trimethylsilymethyl methacrylate (SI) and chloromethyl styrene (CMS), [P(SI-CMS)], has been shown to be highly sensitive negative 193 nm resist in both bi-layer and single layer modes. Such resists show maximum sensitivity with an optical absorbance of the coating oflog10e, or 0.434. Through control of the mole ratio of the monomers in the P(SI-CMS) copolymer, absorbance values have been optimized for film thicknesses of0.2 - 0.3 micrometers for 90: 10 SI:CMS, 0.35 - 0.45 m for 95:5 SI:CMS and 0.55 -0.65 pm for 98:2 SI:CMS. Optical absorbance ofthe CMS is at a maximum in the 190 to 205 nm range, allowing the copolymer to be tailored for a large degree of crosslinking at a relatively low CMS concentration. Spray development of these materials is performed with ethanol, followed by a two step methanol I isopropanol-water rinse. Sensitivities are on the order of 4 to 20 mj/cm^2 at M near 40 000 g/mol. Furthermore, these ratios have been found to produce optimum 02 etch resistance