Diagnosis of electron density and temperature by using collisional radiative model in capacitively coupled Ar plasmas II: two-dimensional distributions

TL;DR

This study uses a collisional radiative model and spatially resolved emission measurements to analyze how radio-frequency power and frequency affect the two-dimensional distributions of electron density and temperature in capacitively coupled argon plasmas.

Contribution

It introduces a method combining emission diagnostics with a collisional radiative model to map 2D electron density and temperature distributions in plasma.

Findings

Lower RF power results in more uniform electron density.

Higher excitation frequency flattens electron temperature profiles.

Mode transition from α to γ mode increases electron density and decreases electron temperature.

Abstract

Effects of radio-frequency power and driven frequency on the two-dimensional (axial and radial) distributions of electron density and temperature were experimentally investigated in low pressure capacitively coupled argon plasmas. The intensity profiles of 696.5 nm and 750.4 nm emission lines were detected by employing a spatially resolved diagnostic system, which consists of a charge coupled device (CCD) and bandpass interference filters. The two-dimensional distributions of electron density and electron temperature were calculated from the spatial distributions of emission intensities via a collisional radiative model (CRM). It is found that the axial and radial distributions of electron density are more uniform at a lower RF power. The axial uniformity of electron density is better at a lower driven frequency, while the radial profiles of electron temperature is flatter at a higher excitation frequency. In all the cases, the electron temperature is extremely uniform in the bulk plasma. Moreover, a mode transition from the {\alpha} to the {\gamma} mode is observed with the increase of input RF power at 13.56 MHz, which causes a significant increase of electron density and an abrupt decrease of electron temperature.