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Copolymers of maleic anhydride with styrene, ethylene, and methyl vinyl ether were modified and
evaluated for use as negative working resist materials in electron beam lithography. The copolymers used
were modified by reaction with an organometallic compound, which resulted in incorporation of tin in the
pendant chains of the copolymers. The polymers were blended with a reactive plasticizer, dipentaerythritol
pentaacrylate (DPEPA), to enhance sensitivity and to improve resolution. The esterified copolymer of
styrene and maleic anhydride was fractionated to obtain fractions with a range of molecular weights and
dispersities. The fractions obtained were used to determine effects of molecular weight and dispersity of the
base polymer on sensitivity and contrast of the resist. The lithographic response of the modified copolymers
was compared with that of the original unmodified base copolymer. Incorporation of tin into the copolymer
resulted in an increase in sensitivity to electron beam. It also improved the dimensional stability of the resist
material. There was a dramatic increase in oxygen reactive ion resistance by incorporation of tin, which was
a result of formation of an etch-resistant passivating barrier. The etch resistance of the tin modified
copolymer containing approximately 20 weight % tin was about twenty fold higher than that of poly(methyl
methacrylate) under identical etching conditions. Blending the polymer with dipentaerythritol pentaacrylate
resulted in a twenty fold increase in electron beam sensitivity over the base copolymer. Tin modified
polymers blended with this plasticizer yielded sensitivities in the range of 0.2 to 1 .5tC/cm2. Fractions of
copolymer obtained were blended with DPEPA and evaluated for lithographic properties. Increase in
molecular weight of the base polymer results in increase in sensitivity of the resist. Monodisperse polymers
yielded higher contrast and better resolution. The effect of molecular weight of base copolymer on contrast
was determined independent of molecular weight distribution.
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