Spin-on silicon-nitride Films for Photo-lithography by RT Cure of Polysilazane

Abstract

Perhydropolysilazane (PHPS) is widely used as high cure temperature pre-ceramic polymer. In this paper, we report the conversion of PHPS films into solvent insoluble amorphous-silicon-nitride at room temperature in an inert atmosphere by vacuum ultra-violet (VUV) exposure. The films were deposited using spin-coating and pre-baked at 80°C for 3 mins before VUV exposure. The FT-IR spectra show an increase in Si-N bonds, a large reduction in Si-H content and complete elimination of N-H on VUV exposure. The refractive index (RI) ∼2.1 and extinction coefficient (k) ∼0.45 at 193nm were calculated using Cauchy fitting of spectroscopic ellipsometry (SE) measurements. The extinction coefficient exhibits a linearly dependence on VUV exposure time, suggestive VUV exposure time can be used a parameter to control the optical parameters of the films. These films could be used as inorganic-BARC (bottom anti-reflection coating) for ArF photolithography and the results are in accordance with the ProLith simulations showing that film of thickness ∼22nm corresponding to the 1st minima of the swing curve is sufficient for pattern generation.