The effect of cryogenic substrate cooling on electron energy distribution in inductively coupled plasma

Cryogenic etching processes employing substrate cooling below -100°C exhibit distinct plasma characteristics compared to conventional conditions. This study investigates electron energy probability function (EEPF) transitions in inductively coupled plasma (ICP) under cryogenic substrate cooling by single Langmuir probe measurement. While pressure-dependent EEPF transitions from bi-Maxwellian to Maxwellian distributions are observed at 40°C, EEPFs at -100°C show suppression of this transition at -100°C. Substrate cooling induces cooling of neutral gas, increasing electron-neutral collisions and preventing formation of bi-Maxwellian distributions. Measurements across 2–90 mTorr reveal persistent Maxwellian EEPFs under cryogenic conditions, contrasting with pressure-driven transitions observed at 40°C. This effect is also observed in ICP E-mode which is a capacitively discharged dominant regime.

Variations of electron density and electron temperature confirm the EEPF distribution changes. These findings suggest that substrate temperature control represents an additional parameter for manipulating plasma characteristics in plasma processing environments.