Electron cyclotron resonance plasma enhanced chemical vapour deposition and optical properties of SiO x thin films

Abstract

Silicon–oxygen alloys ranging from amorphous silicon to silicon dioxide have been deposited from electron cyclotron resonance SiH 4/O 2/Ar plasmas onto radio frequency biased substrates at room temperature. Hundred Watt microwave power, a working pressure of 2 mTorr, a total gas flow rate of 20 sccm, and 13.5 Watt radio frequency bias power were used. Refractive indices of 3.8 to 1.48 were measured by ellipsometry at a wavelength of 632.8 nm. Deposition rates for different SiH 4/(SiH 4+O 2) gas flow ratios were between 4.3 and 7.5 nm min −1. Fourier transform infrared spectroscopy revealed a gradual evolution of the chemical composition of the films from amorphous silicon to silicon dioxide with change in gas phase composition. For silicon dioxide films, the centre frequency of the main Si–O stretching band is 1060 cm −1, whereas full width at half maximum is approximately 94 cm −1. Presence of Si–OH bonds is not detectable for any of the films. The amount of hydrogen in the films is considerably less than that in similar layers deposited by radio frequency plasma enhanced chemical vapour deposition, and for amorphous silicon it does not exceed 1.5×10 22 cm −3. The presence of a single band at 486 cm −1 in the Raman spectrum of the a-Si film confirmed its amorphous structure.