Application Of Halogenated Polymethylstyrenes To X-Ray Resists

Abstract

A series of chlorinated polymethylstyrenes (CPMSs) and brominated polymethylstyrenes (BPMSs) were synthesized by anionic polymerization of methylstyrene followed by radical halogenation. Radiation chemistry of CPMSs and BPMSs were investigated using RhLa X-rays as a radiation source. Resist sensitivity of CPMSs and BPMSs increases with increases in molecular weight and halogen content up to 90 unit% of halogenation. In addition, CPMSs have higher sensitivity than BPMSs toward RhLa X-rays. Infrared spectroscopic studies of radiation induced chemical reactions of the polymers showed that X-ray radiation caused the dissociation of C-X (Cl or Br) bonds and that the dissociation was much faster for CPMSs than BPMSs in spite of lower mass absorption coefficients of CPMSs. CPMS-5 (Mw=49x104, Cl cont.=92 unit%) exhibits the highest sensitivity of 15 mJ/cm2 (Dg) while maintaining high contrast value of 1.3. The patterning tests of CPMS-5 were done with a MICRONIX MX-15 which had a palladium source. As a result, 0.6 μm resist patterns were obtained despite its penumbral blurring being 0.35 μm. It is confirmed that CPMS-5 is one of the best X-ray resists from a practical point of view.