Avoiding Oxygen Plasma Damage During Hard Mask Etching in Magnetic Tunnel Junction (MTJ) Fabrication Process

A method of etching a magnetic tunnel junction (MTJ) stack of layers, comprising:

• providing a MTJ stack of layers on a first electrode wherein the MTJ stack of layers includes a hard mask (HM) on a first stack of layers, and forming a second stack of layers comprising a dielectric antireflective coating (DARC) on the HM, and a photoresist layer on the DARC wherein the HM is a metal, alloy, or metal nitride having a first thickness;
• forming a pattern with a critical dimension (CD) in the photoresist layer and transferring the pattern through the DARC with a first etch process that is an ion beam etch (IBE) or a reactive ion etch (RIE) wherein the pattern after the first etch process has a sidewall that extends from a top surface of the photoresist layer to a top surface of the HM;
• performing a second etch that is an IBE or RIE wherein the pattern in the DARC is transferred through the HM, and wherein the first thickness is sufficiently large such that the photoresist layer is entirely removed and the sidewall extends to a top surface of the first stack of layers, and wherein the second etch comprises one or more oxidants that passivate the sidewall;
• and
• performing a third (MTJ) etch that is one or both of a RIE or IBE comprised of a noble gas and the one or more oxidants wherein the MTJ etch transfers the pattern through the first stack of layers, and extends the sidewall to a top surface of the first electrode and thereby forms a plurality of MTJ cells.