Diagnostics of a chemically active, pulsed microwave plasma for deposition of quartz-like films

A remote microwave plasma has been used for the deposition of scratch-resistant quartz-like films. Process gases are argon, oxygen, and hexamethyl-disiloxane. Input power is modulated and the effects on the plasma as well as on the deposition process are studied by means of various diagnostic methods. The film deposition rate is slightly reduced under most conditions but film quality (i.e., cluster size, roughness, scratch resistance) may be improved. A precursor has been identified by mass spectrometric measurements. Its relation to volatile oxides is discussed. The atomic oxygen density and the electron density are determined temporally-resolved. By a suitable choice of the pulse frequency the time-averaged densities of both species can be significantly enhanced as compared to the continuous case. Consideration of the plasma power balance explains how electron density and temperature are influenced by pulsing. It is concluded that the optimum pulse frequency has to be matched to the electron loss rate which mainly depends on the geometrical dimensions of the process chamber.