Diagnostics of a Chemically Active, Pulsed Microwave Plasma for Deposition of Quartz‐like Films

Abstract

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.

Plasma polymerization of hexamethyldisiloxane: Revisited

“…[ 90 ] At higher pressure (40−70 Pa) and lower T e (clearly below 2 eV), on the contrary, no deposition rate could be observed in an HMDSO remote plasma of an MW plasma source. [ 91,92 ] Activation reactions with oxygen were required to initiate film growth when ion bombardment was negligible.…”

“…[ 100 ] Likewise, no deposition was achieved with Ar/HMDSO in a microwave remote plasma at 40−70 Pa, primarily yielding CH 3 abstraction from HMDSO at low T e . [ 91,92 ] It should be noted that the observed energy threshold for the lumped activation reaction of 14 ± 1 eV lies in between the (average energy loss‐weighted) Ar excitation and ionization energies with 12.14 and 15.76 eV, respectively. The observed exponential increase in k a for T e < ~2 eV, thus, appears to be consistent.…”

Investigation of a pulsed oxygen microwave plasma by time-resolved two-photon allowed laser-induced fluorescence

“…Parallel to the experiment described in this paper, we performed a deposition experiment using hexamethyldisiloxane (HMDSO) in pulsed oxygen plasmas generated by the same type of plasma source. As reported in [2], film properties like homogeneity and roughness can be controlled by a variation of pulse frequency. In some qualitative considerations on the deposition process, it is suggested that atomic oxygen plays a role in two ways: on the one hand, it is used for the formation of precursors; on the other hand, it oxidizes hydrocarbon compounds which otherwise would be integrated into the growing film.…”

“…a 23 stands for the branching ratio of the fluorescence transition. σ (2) is the cross section of the two-photon transition, whereas g( ω)…”

“…To achieve such an agreement, it has been necessary to assume a very low electron density in the downstream zone of the discharge at the order of 1 × 10 8 cm −3 . Electron densities have been extensively measured with Langmuir probes and with a microwave interferometer [2]. However, most of that study was devoted to pulsed argon plasmas yielding downstream electron densities around 10 10 cm −3 .…”