We intentionally introduced excessive Si during the SiOxNy film deposition in order to increase the etch selectivity-to-SiOxNy for advanced self-aligned contact (SAC) etching in sub-0.25 mu m ultralarge scale integration devices. The SiOxNy layer was deposited at a conventional plasma enhanced chemical vapor deposition chamber by using a mixture of SiH4, NH3, N2O, and He. The gas mixing ratio was optimized to get the best etch selectivity and low leakage current. The best result was obtained at 10% Si-SiOxNy. In order to employ SiOxNy film as an insulator as well as a SAC barrier, the leakage current of SiOxNy film was evaluated so that SiOxNy may have the low leakage current characteristics. The leakage current of 10% Si-SiOxNy film was 7 x 10(-9) A/cm(2). Besides, the Si-rich SiOxNy layer excellently played the roles of antireflection coating for word line and bit line photoresist patterning and sidewall spacer to build a metal-oxide-semiconductor transistor as well as a SAC oxide etch barrier. The contact oxide etching with the Si-rich SiOxNy film was done using C4F8/CH2F2/Ar in a dipole ring magnet plasma. As the C4F8 flow rate increases, the oxide etching selectivity-to-SiOxNy increases but etch stop tends to happen. Our optimized contact oxide etch process showed the high selectivity to SiOxNy larger than 25 and a wide process window (greater than or equal to 5 sccm) for the C4F8 flow rate. When the Si-rich SiOxNy SAC process was applied to a gigabit dynamic random access memory of cell array, there was no electrical short failure between conductive layers.