No abstract

The absolute electron density in the downstream region of a 2.45 GHz microwave plasma source has been measured by the plasma oscillation method. In the plasma oscillation method a weak electron beam injected into the plasma excites electrostatic electron waves oscillating at the electron plasma frequency, which is proportional to the square root of the electron density. The plasma source is a slot antenna (SLAN) type, that is the microwave power is coupled from a ring resonator through equidistantly positioned resonant coupling slots into the plasma chamber which is made of quartz. The results of the plasma oscillation method are compared with the results of single and double Langmuir probe (LP) measurements. In Ar and Ar:O 2 mixtures reasonable agreement between the two diagnostic methods is found. However, in depositing plasmas traditional LPs cannot be used with confidence. We studied Ar:O 2 gas mixtures with hexamethyldisiloxane (HMDSO) added downstream for the deposition of quartz-like films. We found that even a small amount of HMDSO in the gas mixture leads to erroneous LP measurements due to probe surface coating, while the plasma oscillation method is still applicable here.

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.