Use of NH₃ etchant for voids suppression to enhance set cycles in CGeSbTe-based phase change memory devices

As the cell size of phase change memory devices decreases to less than 100 nm, the dry etch used for cell patterning becomes extremely critical because of its impact on the properties of memory cells. HBr gas has been known as the etchant that can minimize surface etching damage to GeSbTe-based phase change materials. However, the findings reported herein show that the HBr etch of CGeSbTe (CGST) films causes voids after annealing at temperatures below 400 °C due to the vaporization of volatile bromides (GeBr₄, SbBr₂, and TeBr₂) that form when bromine diffuses during the etch. In this investigation, we report on the use of NH₃ etchants to suppress the formation of volatile compounds and thereby eliminate void formation in CGST materials. The properties of NH₃ etchants were compared to those of HBr etchants as a function of both etch rate and profiles. The effects of void suppression as observed in transmission electron microscopy images of as-etched CGST film after annealing indicate that phase change memory devices etched using an NH₃ exhibited enhanced set cycles that were over 10⁸ superior to results of HBr etchants by 2 orders of magnitude.