Tj. Dalton et al., INTERFEROMETRIC REAL-TIME MEASUREMENT OF UNIFORMITY FOR PLASMA-ETCHING, Journal of the Electrochemical Society, 141(7), 1994, pp. 1893-1900
A new technique has been developed to measure etch rate uniformity in
situ using a charge coupled device (CCD) camera which views the wafer
during plasma processing. The technique records the temporal modulatio
n of plasma emission or laser illumination reflected from the wafer; t
his modulation is caused by interferometry as thin films are etched or
deposited. The measured etching rates compared very well with those d
etermined by helium-neon laser interferometry. This technique is capab
le of measuring etch rates across 100 nun or larger wafers. It can res
olve etch rate variations across a wafer or within a die. The CCD meas
urement technique is a valuable tool for process development and has p
otential use as a real-time diagnostic for process control.