Progressive Breakdown on Bi-Layered Gate Oxide Stacks

Using different proportions of A1
₂
O
₃
and HfO
₂
dielectrics on a 10 nm thick gate insulator, this work studies the influence of each layer on the breakdown transients of metal-oxide-semiconductor (MOS) capacitors. The MOS structures are subjected to a constant voltage stress to determine the breakdown current and the degradation rate. Using an electromigration-based model to explain the current growth through the stack during progressive breakdown, a clear increase in the applied voltage that results in a certain degradation rate is observed as the A1
₂
O
₃
thickness is increased. This can be linked to a strong contribution of the higher thermal conductivity of A1
₂
O
₃
to the overall degradation dynamics of the stack. Results suggest that a small increase of the effective oxide thickness can be traded-off for longer lifetimes in future MOS stacks.