A Volumetric Measurement on Fields and Densities in an Inductively Coupled AR/O2 Plasma - Experiment

Abstract

Electronegative inductively coupled plasmas sustained in halogen gases are used in the microelectronics industry for etching and passivation. Pulsing is a primary control strategy for optimizing results. We report on time dependent measurements of electric and magnetic field, plasma current, and densities of different species in pulsed ICPs. Plasma are sustained in tens of mTorr Ar/O2 mixtures with the oxygen being a surrogate electronegative gas, with and without wafer bias. The stovetop coil of the ICP source can be run in steady state or a pulsed mode, 2 MHz source which does not require an impedance matching network. The RF bias to the chuck can also be pulsed with a typical bias voltage of 1 kV. A 3D probe drive system allows measurement of magnetic field and ion and electron densities throughout the plasma volume. The time evolution of electron density distributions is measured using a hairpin probe. An RF compensated Langmuir probe, calibrated against a microwave interferometer, is used to measure electron and positive ion densities and electric potential. Negative ion density is inferred from spectroscopic measurements, as well from combined laser photo-detachment and probe measurements. Results are reported for varying ratios of argon to oxygen concentrations. The comparisons with 2D calculations will be presented.