Highly doped p-type microcrystalline silicon thin films fabricated by a low-frequency inductively coupled plasma at a low temperature

Abstract

Highly doped p-type microcrystalline silicon thin films are fabricated by a low-frequency inductively coupled plasma at a low temperature of 150 °C. The effects of radio frequency power on the microstructures of thin films such as x-ray diffraction patterns, crystalline volume fraction, grain size and surface morphology are investigated. The deposition rate of the thin films increases from 22 to 35 nm min−1 when the power increases from 1200 to 2000 W. The optical properties of the thin films are studied using UV–VIS–near IR spectroscopy. The Hall effect measurements show that the fabricated thin films present a high doping concentration from 1.2 × 1019 to 1.3 × 1020 cm−3 with increasing power from 1200 to 2000 W. The effect of power on these properties of thin films, especially for high doping, is understood from the impact of power on the plasma properties of the species in the chamber such as the electron energy distribution function (EEDF), electron density and Debye length. The EEDF presents an evolution with increasing power accompanying an increase in electron density and a decrease in Debye length. It is found that the higher the electron density, the higher is the doping concentration. This shows that high electron density is favourable for heavy doping. In fact, the high electron density is determined by the electromagnetic (H) mode of the low-frequency inductively coupled plasma.