Effect of In-situ Capping on Phase Change Memory Device Performance : AEPM: Advance Equipment Processes and Materials

Oxidation of phase-change memory (PCM) materials (e.g. $Ge_{2}Sb_{2}Te_{5}$, GST) has been shown to decrease crystallization temperature and impact film composition, thus impacting analog switching behavior [1], [2]. PCM mushroom-cell devices were engineered on a 14 nm backend test vehicle to compare the electrical switching performance of in-situ and ex-situ capped GST 225. To mitigate the electrical effects from varying top electrode processes between tools, in-situ devices were fabricated with a Ti-TiN cap on GST before exposure to air. The in-situ cap is reduced to a minimal thickness to prevent oxidation of the Ti adhesion layer and the remainder of TiN was deposited matching to the ex-situ top electrode process. TEM of in-situ capped samples were found to have less GST undercut from patterning and have less reduction of the contact area between the GST and top electrode. SET and RESET programming of in-situ capped PCM devices show comparable SET and RESET state resistances to ex-situ processed PCM devices. Current-voltage measurements show that the in-situ PCM can have slightly lower voltage threshold switching but achieves a significantly higher current after threshold switching. The increased current for in-situ capped PCM results in higher power consumption with fixed voltage programming.