Improving etch selectivity and stability of novolak based negative resists by fluorine plasma treatment

Fluorine plasma treatment is applied to cross-link a novolak based negative tone optical resist (maN-2400) to achieve increased dry etching selectivity. Furthermore, fluorine plasma treatment is used to strengthen the same resist to keep it in place during a second lithography step on top of the first one. Using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, cross-linking and passivation of the resist during plasma treatment is demonstrated. In contrast to the application of a baking process after resist development, AFM images show that fluorine plasma treatment preserves the intrinsic structure of the resist.