INVESTIGATIONS OF THE STRUCTURE AND STABILITY OF ALTERNATIVE GATE DIELECTRICS

摘要

We discuss issues in the high-temperature stability of alternative high-k dielectrics grown on silicon, in particular the mechanisms of silicide reaction with Si substrates and polycrystalline Si gate electrodes and phase separation in high-k alloys. We present experimental data showing silicide formation and phase separation. For HfO_2-SiO_2 and ZrO_2-SiO_2 alloys, phase separation is expected for most compositions, although the pathways of microstructure evolution are different for different compositions. Calculations for the ZrO_2-SiO_2 system show that on the silica-rich side of the phase diagram, compositions with less than ～ 90 mol% silica are expected to phase separate at the typical device processing temperature of 1000 ℃. For the pure binary alloys, such as ZrO_2, with oxygen vacancy concentrations greater than about 0.3%, the silicide formation reaction will become thermodynamically favorable.