Effects of hydrogen dilution on deposition process of nano-crystalline silicon film by SiCl4/H2 plasma

Abstract

Growth of nano-crystalline silicon (nano-Si) films from hydrogen-diluted SiCl4 by the plasma enhanced chemical vapour deposition technique at 250 °C has been studied through mass spectrometry, Langmuir probe diagnostic techniques and Raman spectra measurements. The effects of the hydrogen dilution ratio on the relative densities of SiCln (n = 0–2) in SiCl4/H2 plasma are investigated. The average electron energy (Ee) and electron density (Ne) in SiCl4/H2 plasma increase with the hydrogen dilution ratio till their maxima at 9.25 eV and 3.7 × 109 cm−3, respectively. A suitable hydrogen dilution ratio R (0.4–0.67) is beneficial for the formation of SiCln (n = 0–2) radicals because Ee and Ne both have maxima in this range. More SiCln (n = 0–2) radicals will improve the deposition rate and film quality. In addition, hydrogen radicals play an important role in the surface reaction process. The reaction of H and SiCln (n = 0–2) on the growing surface is beneficial for creating dangling bond sites and prompting the film growth, and the exothermic reaction exothermic energy of H with Cl on the film-growing surface results in the increase of the effective temperature of the film growth.