Space-Time-Resolved Measurement of Electronegativity in Inductively Coupled Ar/O₂ Plasmas

Pulsed low temperature inductively coupled plasmas (ICPs) are widely used in the microelectronics industry for etching and deposition. The processing discharges frequently use a mixture of argon with various 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 can be run in steady state, or a pulsed mode 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. Langmuir probe (LP) assisted laser photo-detachment is used to map out the negative ion density, while a hairpin probe and an RF compensated LP are used for electron measurement. Temporal evolution and spatial distribution of the negative ion density, electron density, electron temperature and induced EM fields are reported and compared for varying ratios of Ar:O₂ concentrations. The comparisons with 2D calculations will be presented.