A STUDY OF THE MORPHOLOGY AND MICROSTRUCTURE OF LPCVD POLYSILICON

The morphology and microstructure of polysilicon films deposited by lo w-pressure chemical vapour deposition (LPCVD) have been investigated a s a function of deposition conditions. The deposition temperature was varied from 540-640-degrees-C. As-deposited polysilicon films had a ro ugh surface with (1 1 0) textured columnar grain structure, while as-d eposited amorphous films had a smooth surface. The polysilicon film de posited at the amorphous to polycrystalline transition temperature had an extra-rough, rugged surface with (3 1 1) texture. At the transitio n temperature, the grain structure tended to shift from the polycrysta lline to the amorphous state with increasing deposition pressure and f ilm thickness. It was found that nucleation of amorphous film during i n situ annealing at the transition temperature without breaking the va cuum began to occur from surface silicon atom migration, in contrast t o a heterogeneous nucleation during film deposition.