Reliability study of carbon-doped GST stack robust against Pb-free soldering reflow

Abstract

In this paper, we investigate the performances of carbon-doped Ge2Sb2Te5 films (named hereafter GST) which have been integrated together with a thin titanium capping layer into Phase-Change Memory devices. We show that the carbon content into GST and the titanium cap layer thickness can be optimized to obtain an Amorphous As-Deposited (A-AD) phase which is stable under both the typical Back End-Of-Line (BEOL) thermal budget (2 min at 400°C) and standard Pb-free soldering reflow process conditions (temperature peak at 260°C). Therefore, the material obtained at fab-out keeps its disordered phase and can be used to precode one state of information stable against the standard soldering reflow (peak at 260°C). We propose to use this high resistance state together with an electrically induced low resistance state to pre-code the memory prior to PCB manufacturing.