Method of monitoring emissivity

Abstract

A method for reliably forming polysilicon of a desired surface roughness includes providing a layer of doped or undoped amorphous silicon on a substrate and heating said substrate while monitoring the emission of said substrate and comparing the monitored emission with an expected emission attributable to the heating regime employed. An increase in the monitored emission not attributable to the heating regime signals a transition of the layer of amorphous silicon to rough polysilicon. A decrease in the monitored emission not attributable to the heating regime signals a transition to smooth polysilicon. The increases and decreases in the monitored emission can be used to end the heating regime at the time at which the desired surface roughness of polysilicon is formed, or merely to passively monitor the process. The power supplied to heat the substrate to a desired temperature can also be monitored, in that a drop in required power is indicative of the formation of polysilicon. By selecting the degree of crystallinity of the layer of doped or undoped amorphous silicon on a substrate, the grain size of the resulting HSG polysilicon can be controlled.