Plasma enhanced chemical vapor deposition Si-rich silicon oxynitride films for advanced self-aligned contact oxide etching in sub-0.25 μm ultralarge scale integration technology and beyond

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 μm 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 $7×10−9 A/cm2.$ 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 (⩾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.