A novel organosiloxane-vapor-annealing method has been developed forimproving the mechanical strength of porous silica films with a lowdielectric constant. Treatment of a porous silica film with1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS) under atmospheric nitrogenabove 350 °C significantly enhanced the mechanical strength (i.e., elasticmodulus and hardness) of the film. Results of Fourier transform infraredspectroscopy (FT-IR) and thermal desorption spectroscopy (TDS) suggested theformation of cross-linked poly(TMCTS) network on the porous silica internalwall surfaces by the TMCTS treatment. Such TMCTS cross-linked network isthought to enhance the mechanical strength of the low-k film.