Guidelines to improve mobility performances and BTI reliability of advanced high-k/metal gate stacks

A systematic study of mobility performances and BTI reliability was done in advanced dielectrics stacks. By reducing the oxide films thicknesses T_HKles2.5 nm, PBTI becomes generally very low and associated lifetimes are always over 10 years. By studying a large variety of dielectric stacks we also clearly demonstrate that mobility performances, interface defects Nit and NBTI reliability are strongly correlated. All are affected by nitrogen species N which is clearly identified as the main mobility killer when it reaches unintentionally the Si interface during the deposition of nitrided gates or the nitridation steps. However, by optimizing the gate stacks, excellent mobility performances, up to 100% universal mobility at Eeff=1 MV/cm, and reliability can be achieved.