Electrical behaviour of Ti-doped Ta_2O_5 on N_2O- and NH_3-nitrided Si

摘要

The influence of process parameters: doping approach, Si surface nitridation ambient (NH_3 and N_2O), 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_2O_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_2O_5-based capacitors. The conduction mechanism in Ti-doped Ta_2O_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.