Diagnostics of Electron Energy Distribution Function (EEDF) using Optical Emission Spectroscopy (OES) in CF4/O2 Plasma

As semiconductor devices have become increasingly miniaturized, the ability to control very small Critical Dimensions (CDs) during the etching process has become crucial through controlled plasma processes. Hence, diagnosing plasma and reflecting this in the process to enhance yield is of paramount importance. Typically, a Single Langmuir Probe (SLP) is utilized for plasma diagnostics. While electrical probes offer the advantage of high accuracy, their invasive nature when diagnosing through the viewport can distort the plasma and lead to issues in signal acquisition due to deposition on the probe tip. On the other hand, Optical Emission Spectroscopy (OES), as a non-invasive diagnostic method, does not alter the plasma during measurement, offering a clear advantage over SLP, although it presents challenges in understanding the physical significance of intensity variations across wavelengths. Despite these drawbacks, the accurate measurement of plasma parameters (such as electron temperature Te, electron density ne, Electron Energy Distribution Function EEDF, plasma potential Vp, floating potential Vf, etc.) using SLP is crucial for diagnosing changes in the plasma. Therefore, this study aims to develop a model that can predict plasma parameters measured by SLP using OES measurement data, thereby enabling virtual measurement of plasma. In this research, diagnostic data from OES and SLP are acquired using a 6-inch Inductively Coupled Plasma (ICP) system. Furthermore, by collecting and analyzing data from simultaneous measurements of SLP and OES in a 6-inch ICP etcher, this study seeks to establish a Virtual Measurement (VM) model that can diagnose plasma parameters using OES wavelength-specific intensity and line ratio data as inputs.