Impact of nitrogen incorporation on interface states in (100)Si/HfO2

TL;DR

This study investigates how nitrogen incorporation affects interface states in (100)Si/HfO2 systems, revealing that nitrogen increases trap density in certain energy ranges but can also enable effective passivation of traps with proper processing.

Contribution

It provides detailed analysis of nitrogen's dual role in trap formation and passivation in Si/HfO2 interfaces, highlighting optimal conditions for minimal defect density.

Findings

Nitrogen increases trap density in the upper Si band gap.

Efficient passivation of fast traps occurs with thin nitrogen interlayers.

Lowest defect density achieved after specific annealing and hydrogen passivation.

Abstract

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.