First-principles calculations are performed to investigate the relaxation and electronic properties of SiF$_2$ molecule deposited on surface. The reconstructed Si(001)-p(2 x 2) surface, modeled using density func-tional theory method, forms the basis for our molecule adsorption study. Several adsorption configurations corresponding to different orientations of the molecule have been investigated. Both stable dissociative and non-dissociative adsorption are found. For the most stable configuration, the adsorption takes place without dissociation of the molecule whose silicon atom binds two atoms of the surface. The progressive decomposition process of SiF$_2$ is also explored using the nudged elastic band (NEB) method. An important energy barrier is obtained for the SiF$_2$ molecule decomposition as compared to that of the SiF molecule. This could explain the high percentage of the SiF$_2$ volatile molecule observed experimentally during the fluoride plasma etching process on the specialIntscript surface.