Remote plasma-enhanced chemical vapor deposition of SiO2 using Ar/N2O and SiH4

Remote plasma-enhanced chemical vapor deposition of SiO2 using a radio-frequency (rf) Ar/N2O plasma and downstream-injected SiH4 was investigated. The deposition rate at 20 W rf power was measured as a function of pressure, temperature, and SiH4 flow rate. The SiO2 deposition rate at 300 degrees C and 300 mTorr depends linearly on the SiH4 flow rate. The deposition rate is independent of N2O flow rate for N2O/SiH4 ratios much greater than 1, consistent with oxygen saturation of the growth surface. The deposition rate increases linearly with pressure up to 400 mTorr. A plateau in the deposition rate is observed above 400 mTorr, and is ascribed to the onset of parasitic gas-phase reactions leading to particle formation. Negative apparent activation energies are observed at pressures less than or equal to 400 mTorr, suggesting that adsorption of Si-bearing species is the rate-limiting step in SiO2 deposition. The deposition chemistry was probed using real-time quadrupole mass spectrometry (QMS) and optical emission spectroscopy(OES). The H-2(+) and H2O+ QMS signal intensities increase monotonically with SiH4 flow rate; approximately 0.67 moles of H-2 and 1.33 moles of H2O are produced per mole of SiH4 consumed. OES evidences the presence of Ar metastables, N-2 metastables, excited NO molecules, and atomic O in the plasma. Fourier transform infrared spectroscopy of thick SiO2 films demonstrated that Si-H and Si-OH groups are present at very low concentrations (<1 atom %). Single-wavelength ellipsometry indicated that films deposited under typical O-rich conditions have an average refractive index of 1.464.