Aspects of the controlled chemical etching of thin metal films, in particular multilayer type

Abstract

This paper first discusses an application of chemical etching for selective patterning of magnetic soft (or free) layers, principally Permalloy, in MRAM stacks. Passive films formed in the prior cap layer patterning step played a critical role in the etching behavior of the magnetic layers. The novel use of a sulfur-based additive to inhibit Permalloy passivation, thus enabling selective etching in weak acid etchants, was demonstrated. Aqueous etch solutions of α, ω-dicarboxylic acids were found to etch Permalloy films whose surfaces contained a chemisorbed, sulfur-based, passivation inhibitor, but left the alumina tunnel barrier intact, High values of array quality factors for magnetic switching were demonstrated for chemically etched arrays of Permalloy elements. In the second part of the paper, a discussion of self-assembled monolayers as masks for chemical etching is presented, and the paper concludes with a brief review of the role of passive films in chemical mechanical planarization.