Enhanced grain growth of polycrystalline silicon at low temperature by dopant redistribution

Abstract

It has been recently reported that the redistribution of dopant during titanium silicide formation enhances the grain growth of polycrystalline silicon at a temperature lower than it normally occurs. The mechanism which is responsible for the enhanced grain growth has been proposed to be dopant diffusion induced grain-boundary migration. We have carried out a detailed study to clarify the mechanism. The results show that the effect of phosphorus dopant alone has a small influence on the grain growth of polycrystalline silicon around 900°C. However, much enhanced grain growth of polycrystalline silicon accompanied by titanium silicide formation was observed at 700°C in medium doped and heavily doped conditions as compared to those without silicide formation. On the other hand, no enhanced grain growth was observed in lightly doped and undoped situations regardless of titanium silicide formation. By correlating these observations with depth profiling of dopant distribution, it is concluded that the formation of titanium silicide serves as a sink for the out-diffusion of dopant. The out-diffusion of dopant, preferentially through grain boundaries, leads to a reduction of 30%-50% of dopant from the implanted levels. The depletion of dopant induces grain boundaries to migrate, and therefore enhances the grain growth.