Study of Polycrystalline and Amorphous LPCVD Silicon Films by Atomic Force Microscopy

Abstract

The surface topography and structure of low-pressure chemical vapour-deposited silicon films grown on the thermal oxide of (100) silicon substrates have been investigated using atomic force microscopy. The measurements have been performed on undoped as-grown samples with deposition temperatures between 550 and 630°C and after ex situ phosphorus doping for samples deposited at 620°C. The transition from amorphous to polycrystalline deposition of the silicon film takes place in the temperature range 570-600°C. At 570°C a small number of crystallites are embedded in an amorphous matrix. With increasing temperature the number of crystallites grows rapidly and at 600°C the deposited film is polycrystalline. Doping from a POCl 3 source and subsequent annealing of films deposited at 620°C causes complete recrystallization. For the first time it has been possible to investigate the topography and the grain structure of polycrystalline silicon films using a scanning probe technique only. Our clear distinction between these two features allows controversial results from different characterization methods to be clarified.