Redistribution of in situ doped or ion-implanted nitrogen in polysilicon

This article reports a secondary ion mass spectroscopy analysis of the redistribution of in situ doped or implanted nitrogen in polysilicon and the segregation of nitrogen at the polysilicon/SiO2 interfaces during heat treatment at 700-1000 degrees C. When nitrogen-doped polysilicon is subjected to heat treatment at a temperature above 800 degrees C. When nitrogen diffuses to the poly-Si/SiO2 interface and surface, and piles up there. Some of the nitrogen is immobile when the concentration is above a particular threshold concentration. This immobile nitrogen becomes mobile and diffuses during annealing. The threshold concentration for nitrogen diffusion depends on the grain size. There is a limit to how much nitrogen segregates to the interface. The limit depends not on the initial amount of nitrogen in the polysilicon, but only on the annealing temperature. A comparison of data for polysilicon films with data for bulk silicon suggests that the redistribution of nitrogen in the polysilicon films is limited by the transformation process by which immobile nitrogen becomes mobile. (C) 1996 American Institute of Physics.