Controlling surface chemical states for selective patterning of CoFeB

Abstract

Controlling the surface chemical states of CoFeB thin films was employed to create a chemical contrast between the modified surface and the underlying intermetallic thin film, thereby enabling a selective etching process. The oxidation states of Co and Fe were tailored by reacting the CoFeB surface to chlorine or oxygen plasmas. This modified surface resulted in an enhanced etch rate as well as selectivity in an etchant such as H2 plasma or an organic vapor such as formic acid. Hydrogen plasma was found to be effective in removing metal chlorides and restoring the magnetic properties of CoFeB. For a halogen-free process, the formic acid vapor was found to be most effective in removing oxidized CoFeB. To realize atomic layer etch, a cyclical process was developed with alternating cycles of oxygen plasma with a −100 V substrate bias and formic acid vapor, resulting in a controlled etch rate at 1.8 nm/cycle and extremely high selectivity to the underlying intermetallic CoFeB.

Recent Progress of Atomic Layer Technology in Spintronics: Mechanism, Materials and Prospects

“…It is anticipated that when the ALE technique is used to this end, there will be a significant improvement. For the etching of the CoFeB film, Altieri et al published a paper in 2019 reporting an etching rate of 1.8 nm/cycle, achieved by using an alternating cycle of oxygen plasma with a −100 V substrate bias and formic acid vapor [163]. Most recently, Konh et al employed a continuous dosage of chlorine and 2,4-pentanedione (acetylacetone, acacH) to etch a CoFeB alloy film, and achieved an etching rate of 0.15 nm/cycle using the thermal dry etching method.…”