  The influence of nitrogen incorporation on the energy distribution of
interface states in the (100)Si/HfO2 system and their passivation by hydrogen
have been studied. The results are compared to those of nominally N-free
samples. The nitrogen in the (100)Si/HfO2 entity is found to increase the trap
density, most significantly, in the upper part of Si band gap, in which energy
range nitrogen incorporation prevents passivation of interface traps by
hydrogen. At the same time, passivation of fast interface traps in the lower
part of the band gap proceeds efficiently, provided the thickness of the
nitrogen containing interlayer is kept within a few monolayers. The minimal
interface trap density below the midgap achieved after passivation in H2 is
dominated by the presence of slow N-related states, likely located in the
insulator. As inferred from capacitance-voltage and ac conductance analysis,
the lowest density of electrically active defects [(8-9)x10 10 eV-1cm-2 at
0.4-0.5 eV from the top of the Si valence band edge] is achieved both in the
N-free and N-containing (100)Si/HfO2 structuresafter post-deposition anneal at
800C in (N2+5%O2) followed by passivation in molecular hydrogen at 400C for 30
min.
