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Interferometric In-Situ Determination of Etch Rates in Wet Etch Processes

IP.com Disclosure Number: IPCOM000038752D
Original Publication Date: 1987-Mar-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Kempf, G: AUTHOR [+4]

Abstract

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.

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Interferometric In-Situ Determination of Etch Rates in Wet Etch Processes

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. If required, electrodes 15 may be provided as well as an inlet 16 for an inert sweep gas. In periods of overpressure, the gas bubbles 14 collapse, so that undisturbed interferometric measurement can be carried out. In periods of underpressure, the etch liquid is degassed. Changes in the optical parameters of the etchant, caused, for instance, by pressure changes, can be corrected by periodically switching measuring beam 9 between the etched surface 11 and an unetched second reference surface 13. The proposed method yields a high measurement accuracy and is particularly useful for electroless etch processes where etch rates cannot be determined from c...