Critical aspects of chemical etch patterning of magnetic tunnel junction-based MRAM

This paper describes the development of a novel wet etch process for selective patterning of ferromagnetic freelayers in MRAM magnetic tunnel junction (MTJ) stacks. The method uses a nonadsorbing acid, trifluoromethane sulfonic (TFMSA), as the etchant acid. Freelayer etch selectivity to the alumina tunneling barrier is achieved through the use of long-chain alkane sulfonic acid salts, e.g. sodium 1-tetradecanesulfonate. These inhibitors can increase the alumina barrier etch resistance in the TFMSA solution by up to two orders of magnitude. Also discussed is a means of dramatically lowering lateral etching under the mask using an etch inhibitor. ©The Electrochemical Society.