Breakdown, steady-state, and decay regimes in pulsed oxygen helicon diffusion plasmas

Abstract

Continuous and pulsed oxygen plasmas have been created in a helicon diffusion reactor used for the deposition of silicon dioxide films. An energy selective mass spectrometer and a Langmuir probe attached to the wall of the silica-covered aluminum diffusion chamber below the source have been used to characterize the plasma [ion energy distribution function (IEDF), plasma potential, floating potential, plasma density]. The ion flux can be significantly modified by pulsing the discharge. In the continuous case, the IEDF of the O+2 ions escaping from the plasma to the sidewalls of the chamber consists of a single peak at an energy corresponding to the plasma potential in the chamber (≊32 V). In the pulsed case, the IEDF exhibits two additional peaks at high (≊60 eV) and low (≊15 eV) energy as a result of different states of the plasma during the pulse period: three regimes corresponding to the plasma breakdown, steady state, and decay have been observed and characterized. The time decay of the fundamental mode of diffusion in the post-discharge was measured and calculated (about 1 ms). The breakdown regime is highly dependent on the state of the plasma at the end of the post-discharge.