SENSITIVE PLASMA-ETCHING END-POINT DETECTION USING TUNABLE DIODE-LASER ABSORPTION-SPECTROSCOPY

We report the use of a tunable diode laser locked to a molecular vibra tional 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 diox ide endpoint transitions on wafers with exposed area as small as 33 mm 2 should be observable by detecting the etch end product SiF4. The met hod shows considerable potential as an endpoint detection technique fo r applications such as contact hole etching wherein very small areas a re being etched.