Anomalous acid diffusion in a triphenylene molecular resist with melamine crosslinker

Next generation lithography will require next generation resists. Molecular resists, based on small nonpolymeric
molecules, promise improvements in line width roughness and resolution control for high resolution
lithographic patterns. However, these materials are generally not sensitive enough for commercial
application. We have investigated the application of a common chemical amplification scheme to
molecular resists. The triphenylene derivative C5/C0 (symmetrical 2,6,11-trihydroxy-3,7,11-tris(pentyloxy)
triphenylene), mixed with the crosslinker hexamethoxymethyl melamine and the photoacid generator
triphenylsulfonium triflate shows a substantial sensitivity enhancement, requiring a dose of only
5 lC/cm2 compared with the pure triphenylene sensitivity of 6500 lC/cm2 at 20 keV. Previous work
has indicated that the acid diffusion length of the photoacid generator used here is around 350 nm
and that the diffusion length decreases with film thickness. However, in this molecular resist system
anomalous levels of acid diffusion were observed, indicating that previous results for polymeric systems
may not hold true for these new materials. Initial results indicate that the acid diffusion length in this
system may be on the order of microns. Furthermore, there is some evidence that the excessive diffusion
is occurring in the surface layers of the resist or at the air: resist interface itself.