<i>In situ</i> measurement of fluorocarbon polymer thickness deposited on viewport window of dry etching chamber wall using plasma emission spectrum analysis

The deposition of fluorocarbon layers on chamber walls during plasma processes and the resulting interference patterns in optical emission spectroscopy (OES) were investigated. The thickness of these films significantly influences factors related to etching characteristics, such as the reactive sticking coefficients of radicals and ion fluxes to the wafer. Additionally, this deposition alters OES signal intensity by distorting the transmittance of quartz or sapphire viewport windows. This study proposes an algorithm for in situ polymer film thickness measurement during plasma processes through the analysis of interference patterns in OES. The algorithm identifies successive constructive and destructive interference orders over time by analyzing oscillatory patterns across multiple wavelengths, enabling in situ absolute thickness measurement. Thickness measurements derived from the algorithm exhibit strong agreement with ex situ spectroscopic ellipsometer (SE) measurements. As a result of analyzing the chemical states and bonding structure of the film deposited on the viewport window using x-ray photoelectron spectroscopy, it was confirmed that the film possesses a plasma-polymerized fluorocarbon structure. This technology demonstrates significant potential for in situ, noninvasive monitoring of chamber walls during etching processes that primarily utilize fluorocarbon-based process gases. It is anticipated that this approach can be applied not only to chamber seasoning monitoring and cleaning process optimization but also to virtual metrology for predicting process results.