Charged particle densities and energy distributions in a multipolar electron cyclotron resonant plasma etching source

Abstract

The discharge downstream from a 9 cm i.d. multipolar electron cyclotron resonant (ECR) plasma was characterized in terms of positive ion density, electron energy distribution functions (EEDFs), ion energies incident on a biased conducting substrate, and silicon etching performance. Ion density in the process chamber was found to decrease exponentially away from the plasma source with a peak density of 6×1011 cm−3 in 1 mTorr argon with 250 W of microwave power. While EEDFs are non-Maxwellian, no evidence of high-energy ECR electrons was observed in the process chamber. The ion flux to a conducting substrate diverges by approximately 15° from normal but the ion incidence energy is easily controllable with a dc bias to the substrate. Despite the divergent ion flux from the ECR source, anisotropic etching of silicon was possible with etch rates of 300 nm/min. Uniform etching of silicon over 7.6 cm (3 in.) diam wafers was attained 8 cm below the plasma source.