2D Spatial Distribution of Negative Ions in Inductively Coupled Ar/O₂ Plasmas

Pulsed low temperature inductively coupled plasmas (ICPs) have wide applications in the microelectronics industry. The processing discharges frequently use a mixture of electropositive and electronegative gases, which adds complexity to the study of these plasmas. A thorough investigation on the local electronegativity is critical to higher etch efficiency and the understanding of the electronegative plasmas properties. We conducted time-space-resolved 3D measurements of the negative ion density in an industrial ICP tool. The stovetop coil plasma source is pulsed at 2 MHz and customizable duty cycle without an impedance matching network. The bottom wafer can be biased up to 1.2 kV peak-to-peak and pulsed at 1MHz, separately from the source coil. Plasmas are sustained in tens of mTorr Ar/O₂ mixtures at any mixing ratio. A 3D probe drive system allows measurement throughout the plasma volume. DC biased langmuir probe techniques and hairpin probe assisted laser photo-detachment is used to measure the negative ion density. Electron density is measured by a frequency swept hairpin probe, while other plasma parameters are provided by an RF compensated langmuir probe. Temporal evolution and spatial distribution of the negative ion density, along with electron density, electron temperature and the subsequent effect on power deposition, are reported and compared for varying operating conditions. The comparisons with 2D calculations will be presented.