Etch characteristics of magnetic tunnel junction materials using H2/NH3 reactive ion beam

Magnetic tunneling junction (MTJ) materials such as CoFeB, Co, Pt, MgO, and the hard mask material such as W and TiN were etched with a reactive ion beam etching (RIBE) system using H2/NH3. By using gas mixtures of H2 and NH3, especially with the H2/NH3( 2:1) ratio, higher etch rates of MTJ related materials and higher etch selectivities over mask materials (>30) could be observed compared to those etching using pure H2( no etching) and NH3. In addition, no significant chemical and physical damages were observed on etched magnetic materials surfaces and, for CoPt and MTJ nanoscale patterns etched by the H2/NH3( 2:1) ion beam, highly anisotropic etch profiles >83° with no sidewall redeposition could be observed. The higher etch rates of magnetic materials such as CoFeB by the H2/NH3( 2:1) ion beam compared to those by H2 ion beam or NH3 ion beam are believed to be related to the formation of volatile metal hydrides (MH, M = Co, Fe, etc) through the reduction of M-NHx( x = 1 ∼ 3) formed in the CoFeB surface by the exposure to NH3 ion beam. It is believed that the H2/NH3 RIBE is a suitable technique in the etching of MTJ materials for the next generation nanoscale spin transfer torque magnetic random access memory (STT-MRAM) devices.

使用H₂/NH₃，利用反应离子束蚀刻（RIBE）系统对诸如CoFeB、Co、Pt、MgO等磁性隧道结（MTJ）材料以及诸如W和TiN等硬掩模材料进行蚀刻。通过使用H₂和NH₃的混合气体，尤其是H₂/NH₃为2∶1的比例，与使用纯H₂（无蚀刻）和NH₃进行蚀刻相比，可以观察到MTJ相关材料具有更高的蚀刻速率，并且对掩模材料具有更高的蚀刻选择性（>30）。此外，在蚀刻后的磁性材料表面未观察到明显的化学和物理损伤，并且对于由H₂/NH₃（2∶1）离子束蚀刻的CoPt和MTJ纳米级图案，可以观察到具有>83°的高度各向异性蚀刻轮廓且无侧壁再沉积。与H₂离子束或NH₃离子束相比，H₂/NH₃（2∶1）离子束对诸如CoFeB等磁性材料具有更高的蚀刻速率，这被认为与通过NH₃离子束暴露在CoFeB表面形成的M - NHₓ（x = 1∼3）被还原而形成挥发性金属氢化物（MH，M = Co、Fe等）有关。据信，H₂/NH₃ RIBE是用于下一代纳米级自旋转移矩磁性随机存取存储器（STT - MRAM）器件的MTJ材料蚀刻的一种合适技术。