Correlating absolute concentrations of gas-phase species determined by microwave, Fourier transform infrared, and atomic absorption spectroscopies to properties of silicon dioxide films deposited in an electron cyclotron resonance reactor

Three different gas-phase absorption spectroscopies (microwave, FTIR, and silicon atomic absorption) were used simultaneously during the plasma enhanced chemical vapor deposition of SiO₂ and fluorinated SiO ₂ films using an ECR deposition reactor. With these spectroscopic techniques, absolute concentrations of a large number of species present in these deposition plasmas were determined. A new ECR system with multiple diagnostic ports on the same horizontal plane, and incorporating an electrostatic chuck, rf-bias, and He-backside cooling, was constructed to facilitate these studies. Correlations to the quality of the resulting films were made using ellipsometry, FTIR, XPS, and wet etch rate techniques. The systems investigated were SiH ₄/O₂/Ar, SiH₄/SiF₄/O₂ and TEOS/O₂ plasmas. The SiH₄/O₂ plasmas are found to contain less water than previously expected (under our detection limit of 0.1 mTorr). The molecular fragment SiO was monitored as a function of power, pressure, oxygen flow, and argon flow at densities between 3.7 × 109 and 1.3 × 10−11 cm−3 in this system. Silicon atoms were detected at densities between 5.1 × 109 and 5.8 × 1010 cm −3. The decomposition of SiF₄ is investigated and is shown to occur at a constant rate of about 98% in pure SiF₄/O ₂ plasmas. This dissociation rate is enhanced when silane is added. Water and HF are generated in large quantities when SiH₄ and SiF ₄ are both present in the system, and reach their maximum concentrations at the SiF₄/SiH₄ ratio where the film quality appears to be the best. Fluorine incorporation into SiOF films result in a consistent decrease in index of refraction values. No SiO molecules were detected in SiH₄/SiF₄/O₂ chemistries (<5 × 10 9 cm−3). Plasmas employing TEOS/O₂ chemistries show large concentrations of CO, CO₂ and H₂O. Larger organic molecules (ethanol, acetaldehyde, methanol, formaldehyde, and formic acid) are also present in these plasmas, totaling about 9% of the species present under most conditions. Densities of SiO were very close to those found in SiH₄/O₂/Ar plasmas. Results in all plasma conditions indicate a curious depletion of silicon-containing species detectable with these absorption techniques in the plasmas relative to the silicon in-flow.