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 α to the γ 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.

New plasma sources with high density and low energy are required to process material surfaces in nanometers. In this study, an electrode integrated with a hollow cathode (HC) and capacitively coupled plasma (CCP) was developed. With the tool, a novel capacitively coupled plasma driven by the hollow cathode radio-frequency discharges (HC-CCP) was observed experimentally, and its properties in the center of the chamber were investigated by a Langmuir probe. The results demonstrated that the HC-CCP presents wide ranges of electron density (ne), between 10^9 and 10^10 cm^-3, and electron energy (Te), 3.5 – 6.7 eV. And their distributions can be controlled by the modulation of radio-frequency source power and frequency, work pressure, and bias voltage. Therefore, this plasma source can be applied to a new generation of material processing.