Browse Prior Art Database

Pre-Liftoff Ash

IP.com Disclosure Number: IPCOM000044612D
Original Publication Date: 1984-Dec-01
Included in the Prior Art Database: 2005-Feb-06
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Geffken, RM: AUTHOR [+4]

Abstract

Pre-liftoff ash, the application of an oxygen plasma (ashing) cleaning step at a crucial point in the standard metal liftoff process, promotes the adhesion between two layers of polyimide by removing process residuals. Resist residuals left on the product during integrated circuit device metallization processing have been shown to cause metal corrosion under temperature and humidity stress. These residuals are byproducts from photoresist exposure to metal pre-clean solutions. When patterned, photoresist is submerged in metal pre-clean solutions where about 1000 angstroms of the resist surface is hardened. The hardened resist is insoluble in 80ŒC N-methyl Pyrrolidone (NMP). During liftoff the hardened resist remains on the wafer.

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Pre-Liftoff Ash

Pre-liftoff ash, the application of an oxygen plasma (ashing) cleaning step at a crucial point in the standard metal liftoff process, promotes the adhesion between two layers of polyimide by removing process residuals. Resist residuals left on the product during integrated circuit device metallization processing have been shown to cause metal corrosion under temperature and humidity stress. These residuals are byproducts from photoresist exposure to metal pre-clean solutions. When patterned, photoresist is submerged in metal pre-clean solutions where about 1000 angstroms of the resist surface is hardened. The hardened resist is insoluble in 80OEC N-methyl Pyrrolidone (NMP). During liftoff the hardened resist remains on the wafer. Electro-spectroscopic chemical analysis (ESCA) of wafers after liftoff shows trace amounts of inorganics in the residual resist on the substrate surface. Further process steps do not selectively remove the residuals left after NMP liftoff. Once hardened resist has been deposited on the wafer, no wet or dry clean has proved effective in removing the 1000-angstrom resist skin. To prevent the hardened resist from redepositing on the wafer, it must be removed before metal liftoff in NMP. Implementation of a low power-density oxygen ash after metal deposition and before liftoff consistently removes the 1000 angstroms of hardened resist. Scanning electron microscopy and ESCA data shows no evidence of resist residuals when an ox...