Atomic Layer Etching of Metals for Microelectronics

As microelectronics evolves more and more metals are being used. Deposition techniques like atomic layer deposition (ALD) are not always available. As a result, precise, selective etching methods are becoming more and more important. For example, magnetoresistive random-access-memory (MRAM) is a leading option for non-volatile digital data storage and depends upon precise stacking of a variety of magnetic metals. Atomic layer etching (ALE), as a time reversed ALD method, has potential for accurately etching nearly all materials, particularly those that cannot be deposited with precision. Herein, we demonstrate the etching of some transition metals used in MRAM applications, Co, Fe, and CoFeB where the tunneling barrier (MgO) acts as an etch stop. The etch is conducted using a thermal approach (versus plasma), where the film is etched by sequential dosing with to two different chemical moieties, chlorine and acetylacetone (acac). Thus, optimizing kinetic factors to overcome thermodynamic limitations, thereby developing a controlled etch driving towards one atomic layer at a time. Similar techniques demonstrate that Cu is etched under comparatively mild conditions, whereas Pt requires more aggressive temperatures and pressures to facilitate the etch. Etching of candidates for lowermost level metallizations will also be discussed.