A structural and topographical study of low-pressure chemical-vapor-deposited polysilicon by scanning probe microscopy

Abstract

The surface topography and structure of low-pressure chemical vapor deposited silicon films on thermal oxide grown on (100) silicon substrates have been investigated after different processing steps. Atomic force microscopy topographic measurements are performed on undoped as-grown samples and after ex situ phosphorous doping from a POCl3 source. In addition, topographies of the doped films are obtained using constant current scanning tunneling microscopy on hydrofluoric acid passivated surfaces under high vacuum. As a result we have found that surface topography and roughness are mainly determined by the deposition process. Roughness of films deposited at 620 °C is related to the grain structure represented by hillocks with typical lateral dimensions between 50 and 150 nm in the images. Doping by high temperature diffusion and subsequent annealing causes a complete recrystallisation of the film, leading to typical lateral grain sizes between 200 and 600 nm. However, the surface topography of the doped films still remains determined by the hillocks formed by the deposition process. Values of the surface roughness are between 7 and 14 nm depending on the process step.