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

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 degrees 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) similar to 2.1 and extinction coefficient (k) similar to 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 similar to 22nm corresponding to the l minima of the swing curve is sufficient for pattern generation.