Secondary Grain Growth in Heavily Doped Polysilicon During Rapid Thermal Annealing

Abstract

To successfully implement Silicon-on-Insulator (SOI) technology using polysilicon-on-oxide, it is necessary to maximize the grain size such that the active devices are entirely within very large single crystal grains. A drastic increase in grain size in polysilicon has been reported due to secondary grain growth in ultra-thin, heavily n-type doped films upon regular furnace annealing. Very little work has been undertaken, however, to study secondary grain growth during Rapid Thermal Annealing (RTA).This paper is a study of the grain growth mechanism in heavily P-doped, amorphous silicon films during RTA. Secondary grains as large as 16 μm have been obtained in 160 nm thick films after a 180 s RTA at 1200 °C, representing a grainsize- to-film-thickness-ratio of 100:1. This is the largest secondary grain size and grain-size-to-film-thickness reported in the literature. A detailed analysis of negatively charged silicon vacancies has also been employed to explain the lower activation energy (1.55 eV) of secondary grain growth compared to that of normal grain growth (2.4 eV).