Selective Etching of Magnetic Tunnel Junction Materials Using CO/NH3 Gas Mixture in Radio Frequency Pulse-Biased Inductively Coupled Plasmas

Abstract

The etch characteristics of magnetic tunneling junction (MTJ) materials and the etch selectivity over W have been investigated using RF pulse-biased conditions in addition to the continuous wave (CW) bias condition with a CO/NH3 gas combination in an inductively coupled plasma system. By using a time-averaged substrate DC bias voltage condition for the RF pulse biasing, the etch rates of MTJ materials for the RF pulse-biased conditions were generally similar to those etched using the CW RF bias condition even though the etch rates were slightly decreased with decreasing the duty percentage of the RF pulse biasing. However, the use of the RF pulse biasing improved the etch selectivity of the MTJ materials over mask materials such as W. When the surface roughness and the residual thickness remaining on the etched surface of the MTJ material such as CoFeB were investigated by using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS), respectively, it was clear that the use of the RF pulse biasing instead of CW RF biasing also decreased the residual thickness and the surface roughness. This is believed to be related to the formation of a more uniform chemically reacted layer on the etch CoFeB surface during the RF pulse-biased etching condition.