Etch stop improvement using a roof mask structure in a magnetic material etched by CO/NH3 plasma

Abstract

The etching rate difference of magnetic materials with respect to the aspect ratio (AR) has been investigated using CO/NH3 plasma with a Ta mask for high-density integration of magnetic random access memory devices. The etching depth difference of magnetic stack films as a function of etching times reveals that the etching rate is suddenly reduced at AR > 0.7, and the occurrence of etch stop has been confirmed. From the scanning transmission electron microscope–energy dispersive x-ray spectroscopy results, Ta deposition, which proceeds from the Ta mask to the bottom space of the pattern, induces this etch stop. The roof mask structure, which has a concavity directly under the Ta mask to reduce the amount of Ta deposition, can improve the etch stop, and a fine magnetic stack film pattern with AR = 2.3 can be fabricated.