Interferometric In-Situ Determination of Etch Rates in Wet Etch Processes
Original Publication Date: 1987-Mar-01
Included in the Prior Art Database: 2005-Feb-01
Chemical wet etch processes often develop gas bubbles on the etched surface which disturb the phase of optical beams in an interferometric measurement set-up. To overcome this difficulty, a closed etch tank 1 with a safety valve 2 in its cover 3 and comprising an optical window 4 is provided with a device 5, such as a piston, to apply periodic pressure changes to etch liquid 6. A laser beam 7 is split by a birefringent crystal 8 into a measuring beam 9 which is directed through the window onto the etched surface 11 and into a reference beam 10 impinging on a non-etched reference surface 12. Both beams are reflected, recombined in crystal 8, and fed to a known phase-sensitive detector 17 which determines their relative optical phase difference.