Electron energy distribution measurement in an inductively coupled plasma with a cryogenic temperature substrate

Abstract

The impact of substrate cooling on electron energy probability function is investigated in an inductively coupled plasma. For Ar plasma, the electron density triples at 60 mTorr as the substrate temperature decreases. The dependence is observed over a wide temperature range from 200 K (cryogenic) to 330 K (above room temperature). The electron density enhancement is attributed to a decrease in neutral gas temperature, which increases gas density and subsequently enhances electron-neutral collisions, promoting ionization. The effect is more pronounced at higher pressures, and the impact of substrate temperature varies with the gas species (Ar, He, N2, and O2). In molecular gas plasma, the electron density enhancement is suppressed. These results demonstrate that substrate temperature serves as a primary determinant of plasma characteristics in cryogenic etching processes, offering a fundamental basis for optimizing cryogenic processes in semiconductor manufacturing applications.