Sensitive plasma etching endpoint detection using tunable diode laser absorption spectroscopy

We report the use of a tunable diode laser locked to a molecular vibrational absorption line as a sensitive plasma etching endpoint detector. Measurements were made on multilayer silicon wafers etched in a SF₆ plasma discharge. We show that polycrystalline silicon to silicon dioxide endpoint transitions on wafers with exposed area as small as 33 mm² should be observable by detecting the etch end product SiF₄. The method shows considerable potential as an endpoint detection technique for applications such as contact hole etching wherein very small areas are being etched.