In-situ optical emission spectroscopic examination of chrome etch for photomasks

In this paper, optical emission spectroscopy is used to characterize and monitor chrome etch processes on the Etec Tetra photomask etch chamber. Changes in process conditions, such as source power, bias power, pressure, and gas flows have been captured by time-averaged optical emission traces. Using multi-wavelength OES data collected during chrome etching, a fingerprint of the plasma was taken. The fingerprint was generated using a principal component analysis (PCA) technique, which detects spectral correlation between multiple wavelengths. The PCA reduces the dimensionality of the multi-wavelength OES and extracts just the most relevant information. The new variables are created as linear combinations of the original variables. The new principal component peaks diminish more than the original peaks, allowing strong endpoint detection for a 1 percent chrome-loaded mask.