Electrical behaviour of Ti-doped Ta₂O₅on N₂O- and NH₃-nitrided Si

Abstract

The influence of process parameters: doping approach, Si surface nitridation ambient (NH 3 and N 2 O), type of the gate (Al and W) and its technology of deposition on the electrical characteristics (capacitance-voltage, temperature-dependent current-voltage curves), and the mechanism of conductivity of Ti-doped stacks (6 nm) have been investigated. Among the three factors studied, the surface engineering appears to be with the greatest impact on the film permittivity and stack charges. It is shown that the Ti incorporation through the surface of Ta 2 O 5 deposited on NH 3 -rapid thermally nitrided Si is effective in achieving films with high permittivity. The interface metal/doped high-k layer is a critical factor in leakage current behaviour. The evaporated Al is a good candidate as a top electrode of Ti-doped stacks giving satisfactory level of leakage current while radiation defects introduced in the stack during W sputtering cause current deterioration, making sputtered W less favourable as a metal electrode of Ta 2 O 5 -based capacitors. The conduction mechanism in Ti-doped Ta 2 O 5 stacks is controlled by the gate electrode processing rather than by both the substrate nitridation and the doping approach. The energy levels of the traps responsible for the current transport are estimated.

Gate oxide thickness dependence of the leakage current mechanism in Ru/Ta2O5/SiON/Si structures

“…We now turn our attention to identification of the nature of 0.7 eV deep trap level extracted from the I-V-T characteristics. Similar trap level has been reported in rf-sputtered Ta 2 O 5 (0.6-0.75 eV) [20,27] as well as Ti-doped Ta 2 O 5 (0.62-0.72 eV) [28] and attributed to H-related bond in Ta 2 O 5 [27]. As our samples received standard forming gas annealing in H 2 /N 2 atmosphere, H-related defects throughout the whole gate stack may be responsible for the trap level involved in conduction mechanisms.…”

Consideration of conduction mechanisms in high-k dielectric stacks as a tool to study electrically active defects

“…The analysis of the temperature dependence of the current in Ti:Ta 2 O 5 layers [48] reveal that the energy levels of the defects participating in the conduction are in the range of 0.6-0.7 eV and do not depend on the method of Ti incorporation.…”

Time-dependent dielectric breakdown in pure and lightly Al-doped Ta2O5stacks

“…Rapid thermal nitridation of the Si surface in NH 3 at 700 • C for 20 s before deposition of high-k layer was done in order to improve the permittivity of the interface layer. Our previous study [33] showed that this nitridation causes an increase of the dielectric constant of the stack and improves its electrical performance through formation of SiON interface layer (with a thickness of 1 nm) instead of SiO 2 -like layer. Using these substrates the following two sets of samples were prepared: MIS capacitors with pure and with lightly Al-doped Ta 2 O 5 , respectively.…”