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.