Nitrogen implantation for local oxidation (NILO) of silicon

Abstract

Complete physical and electrical characterisation of nitrogen implantation for local oxidation (NILO) of silicon technology is detailed. Nitrogen implantation is performed at 20 keV through 25 nm of thermal oxide with doses within the range of 5 × 10 16–1.5 × 10 17 cm −2. Physical characterisation of the sealed nitride films is performed using secondary ion mass spectroscopy, transmission electron microscopy, nuclear reaction analysis and X-ray photoelectron spectroscopy. Nitrogen implantation in silicon can provide sealed nitride films of thicknesses around 20–25 nm, capable of masking a 550 nm field oxidation. Physical characterisation shows that implanted nitride films are composed of elemental Si-Si 4 bonds, silicon oxynitride and diffused oxygen. The nitrogen concentration in such films is lower than that of a stoichiometric nitride. “Bird's beak” lengths as short as 0.08 μm can be obtained. For a 950° C field oxide temperature, dislocations are observed at the edge of the nitride mask. At a higher temperature (1050° C) no dislocations are observed; on the other hand, stacking faults with a density of 0.05 faults per μm of mask length are observed at the edge of the nitride mask. Because of the presence of the stacking faults, high leakage currents are measured on n + p diodes.