Stability of Advanced Gate Stack Devices

Abstract

The stability of poly-Si gated HfO 2 ͑ϳ1.2 nm equivalent oxide thickness, EOT͒ and Y 2 O 3 ͑ϳ3.1 nm EOT͒ n-channel metal oxide semiconductor field effect transistor devices were assessed after constant current stressing of the gate. The changes in threshold voltage and transconductance were measured as a function of stress time and stress current over the range of 10 Ϫ3 to 10 5 C of injected charge per square centimeter. With forming gas annealed HfO 2 , positive shifts in the threshold voltage exhibited a powerlaw dependence. Under high stressing conditions, a power-law dependence of degradation of threshold voltage on the injected charge (ϳQ 0.1 ) was observed. Stressing at high current was seen to generate traps. Stressing at low current revealed a saturation of the threshold voltage after modest stressing times. Stressing on deuterium annealed sample showed less V t and g m shift ͑under high injection conditions͒, which is attributed to the effectiveness of heavier D 2 in preventing trap generation under high stressing conditions. With Y 2 O 3 , stressed at similar electric fields, the threshold voltage shifted negatively and the transconductance increased.