Study of buried silicon nitride layers synthesized by ion implantation

Abstract

The formation of buried layers of silicon nitride by nitrogen-ion implantation in single-crystal silicon is studied. He+ backscattering, x-ray diffraction, scanning and transmission electron microscopies, and infrared absorption measurements were used for the physico-chemical characterization; sheet resistivity determination, spreading-resistance profile, and current-voltage characteristics for the electrical characterization. It is shown that, for 180-keV nitrogen ions, a fluence about 1018 N/cm2 must be implanted in order to obtain a continuous layer of silicon nitride and that annealing must be performed at 1200 °C to make it homogeneous and electrically insulating. The Si3N4 layer obtained crystallizes in the α phase and presents properties nearly similar to those of deposited layers. It is demonstrated that the conditions of implantation (energy, substrate temperature, beam intensity) play a fundamental role in the structure of the superficial silicon layer: the substrate must not be amorphized up to the surface during the implantation to obtain, after annealing, a monocrystalline surface layer suitable, for instance, for further epitaxy.