Comprehensive spatial mapping of plasma parameters in low-pressure nitrogen plasma by optical emission spectroscopy

Optical emission spectroscopy (OES) has been extensively used for qualitative measurements, such as end-point detection (EPD) and species analysis, in low-pressure plasma processes within the semiconductor industry. In addition, various spectroscopic techniques allow for the determination of further plasma parameters, such as excitation temperature and radical density [1]. Comprehensive plasma analysis can be achieved by combining OES with kinetic modeling, allowing the measurement of crucial parameters like plasma density, and temperature [2].

Although the valuable information of plasma is provided by OES, it has limitations in spatial analysis as it only measures local information at a single point. To obtain spatially-resolved information in plasma, methods such as laser-induced fluorescence and tomography have been suggested [3]. However, these methods are often impractical for industrial applications due to their invasive nature, lengthy measurement times, and complex experimental setups.

In this study, therefore, we investigate a technique to analyze the spatial characteristics of plasma based on emission images captured using a charge-coupled device (CCD). The spectrum of each pixel in 2-dimensional images of plasma was reconstructed using a novel filtering method and numerical simulation of spectra. Moreover, crucial plasma parameters, such as electron temperature and density, were mapped by applying simple kinetic modeling to the reconstructed spectrum.