A silicon nitride layer formed by nitrogen implantation was characterized for VLSI application. Molecular nitrogen was implanted in an energy range of 5 to 60 keV for forming various nitride layers during subsequent annealing at 1000°C in nitrogen. The nitride layers formed were characterized before and after furnace annealing with differential IR, SIMS, and ellipsometry to find a useful implantation condition for a local oxidation mask. The initial IR peak of the implanted nitrogen was 815 cm−1 for the entire implantation energy range. While the position shifted to a higher wave number for the high energy implants after annealing, the low energy implants peak remained very close to 830 cm−1, which is comparable to the LPCVD nitride peak. This finding suggests that the composition of the low energy nitrides is nearly stoichiometric. Annealing shifted the concentration profile toward the surface and increased the peak nitrogen concentration. The nitride profile peaked at the surface or disappeared below 10 keV. The masking properties of these nitrides were tested by growing 5300Å oxide in steam at 1000°C. The nitrides with dosages of ions formed an effective oxidation mask for implantation energy below 40 keV. Under the experimented conditions, the nitride formed with 10 keV appeared to be an effective oxidation masking with adequate etching selectivity to , reducing the “bird's beak” size to one fourth of the conventional LOCOS.