A STUDY OF THE MORPHOLOGY AND MICROSTRUCTURE OF LPCVD POLYSILICON

The morphology and microstructure of polysilicon films deposited by low-pressure chemical vapour deposition (LPCVD) have been investigated as a function of deposition conditions. The deposition temperature was varied from 540-640-degrees-C. As-deposited polysilicon films had a rough surface with (1 1 0) textured columnar grain structure, while as-deposited amorphous films had a smooth surface. The polysilicon film deposited at the amorphous to polycrystalline transition temperature had an extra-rough, rugged surface with (3 1 1) texture. At the transition temperature, the grain structure tended to shift from the polycrystalline to the amorphous state with increasing deposition pressure and film thickness. It was found that nucleation of amorphous film during in situ annealing at the transition temperature without breaking the vacuum began to occur from surface silicon atom migration, in contrast to a heterogeneous nucleation during film deposition.