Chemical etching of MRAM permalloy soft layers: ROLE of passive films

Chemical etching was used 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 a, 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.