Measurement of neutral gas temperature in inductively coupled Ar and Ar/O2 plasmas

In low-temperature inductively coupled radio frequency (rf) plasmas, electrons and ions that gain energy from the electric field can transfer a portion of energy to neutral particles. The resulting radial variation of the neutral gas temperature T-g can significantly influence the radial distributions of reaction rates and radical densities on the substrate, thus affecting the etching/film deposition uniformity. In this work, we perform an experimental study on the dependence of the neutral gas temperature T-g on external parameters (i.e., rf power, pressure, and gas component) in inductively coupled Ar and Ar/O-2 plasmas by using a fiber Bragg grating sensor. To analyze the correlation between T-g and the plasma characteristics, a Langmuir probe is used to measure the electron density n(e), effective electron temperature T-e, and ion density n(i) under the same discharge conditions. It is found that in both Ar and Ar/O-2 plasmas, neutral gas heating is sensitive to plasma density. As the plasma density increases with the pressure/power, the collisions of ions and electrons with neutral particles are enhanced so that T-g increases monotonically. With the increase of O-2 content, n(e) and n(i) are observed to decrease due to enhanced dissociation and excitation of O-2, leading to a decrease in T-g. The radial profile of T-g exhibits a parabolic distribution in pure Ar discharges, whereas it evolves through a center-flat shape into a saddle shape with the increase of O-2 content. The variation of T-g with rf power during the E-to-H mode transition is also presented and discussed. Published under an exclusive license by AIP Publishing.

Automated summary

In this work, an experimental study was conducted to investigate the dependence of the neutral gas temperature T-g on external parameters (rf power, pressure, and gas component) in low-temperature inductively coupled rf plasmas. The results showed that neutral gas heating is sensitive to plasma density in both Ar and Ar/O-2 plasmas. T-g increases with pressure/power and decreases with an increase in O-2 content.