Igor Krylov

Experimental evidence for the correlation between the weak inversion hump and near midgap states in dielectric/InGaAs interfaces

Temperature dependent capacitance–voltage (C-V) and conductance-voltage (G-V) measurements were performed to obtain activation energies (EA) for weak inversion C-V humps and parallel conductance peaks in Al2O3/InGaAs and Si3N4/InGaAs gate stacks. Values of 0.48 eV (slightly more than half of the band gap of the studied In0.53Ga0.47As) were obtained for EA of both phenomena for both gate dielectrics studied. This indicates an universal InGaAs behavior and shows that both phenomena are due to generation-recombination of minority carriers through near midgap located interface states. The C-V hump correlates with the interface states density (Dit) and can be used as a characterization tool for dielectric/InGaAs systems.

Indium outdiffusion and leakage degradation in metal/Al2O3/In0.53Ga0.47As capacitors

Annealing of Ni/Al2O3/InGaAs structures results in a significant increase of the leakage current. The same treatment of Au/Ti/Al2O3/InGaAs structures results in a slight increase in leakage only. Time of flight secondary ions mass spectrometry measurements detected an annealing induced indium outdiffusion into the dielectric layer. In structures having nickel metallization, the released indium accumulated at the Ni/Al2O3 interface. In structures having Au/Ti metallization, the indium atoms penetrated into the gold layer, and an indium free Al2O3 layer was observed. We attribute the observed different electrical behavior to the different indium diffusion behavior, and eliminate other explanations.

Correlation between Ga-O signature and midgap states at the Al2O3/In0.53Ga0.47As interface

Al2O3/In0.53Ga0.47As gate stacks were fabricated using different concentrations of NH4OH as a pre-deposition treatment. Increased NH4OH concentrations significantly reduced the C-V weak inversion hump and the measured near midgap interface states density (Dit). X-ray photoelectron spectroscopy (XPS) studies revealed that these changes in the electrical properties were accompanied by a reduction in the amount of the Ga-O bonding while As-As dimers as well as other XPS detected InGaAs surface species did not correlate with the observed Dit trend. Possible explanations for these findings are suggested.

The physical origin of dispersion in accumulation in InGaAs based metal oxide semiconductor gate stacks

Dispersion in accumulation is a widely observed phenomenon in technologically important InGaAs gate stacks. Two principal different interface defects were proposed as the physical origin of this phenomenon—disorder induced gap states and border traps. While the gap states are located at the semiconductor side of the interface, the border traps are related to the dielectric side. The study of Al2O3, HfO2, and an intermediate composition of HfxAlyO deposited on InGaAs enabled us to find a correlation between the dispersion and the dielectric/InGaAs band offset. At the same time, no change in the dispersion was observed after applying an effective pre-deposition treatment which results in significant reduction of the interface states. Both observations prove that border traps are the physical origin of the dispersion in accumulation in InGaAs based metal-oxide-semiconductor gate stacks.

Indium out-diffusion in Al2O3/InGaAs stacks during anneal at different ambient conditions

Indium out-diffusion during anneal enhances leakage currents in metal/dielectric/InGaAs gate stacks. In this work, we study the influence of ambient conditions during anneal on indium out-diffusion in Al2O3/InGaAs structures, prior to the gate metal deposition. Using X-ray photoemission spectroscopy and time of flight secondary ions mass spectrometry, we observed much lower indium concentrations in the Al2O3 layer following vacuum and O2 anneals compared to forming gas or nitrogen anneals. The electrical characteristics of the Ni/Al2O3/InGaAs gate stack following these pre-metallization anneals as well as after subsequent post metallization anneals are presented. Possible explanations for the role of the annealing ambient conditions on indium out-diffusion are presented.

The role of the substrate on the dispersion in accumulation in III-V compound semiconductor based metal-oxide-semiconductor gate stacks

Dispersion in accumulation is a widely observed phenomenon in metal-oxide-semiconductor gate stacks based on III-V compound semiconductors. The physical origin of this phenomenon is attributed to border traps located in the dielectric material adjacent to the semiconductor. Here, we study the role of the semiconductor substrate on the electrical quality of the first layers at atomic layer deposited (ALD) dielectrics. For this purpose, either Al2O3 or HfO2 dielectrics with variable thicknesses were deposited simultaneously on two technology important semiconductors—InGaAs and InP. Significantly larger dispersion was observed in InP based gate stacks compared to those based on InGaAs. The observed difference is attributed to a higher border trap density in dielectrics deposited on InP compared to those deposited on InGaAs. We therefore conclude that the substrate plays an important role in the determination of the electrical quality of the first dielectric monolayers deposited by ALD. An additional observat...

Elimination of the weak inversion hump in Si3N4/InGaAs (001) gate stacks using an in situ NH3 pre-treatment

Silicon nitride thin films were deposited by plasma enhanced chemical vapor deposition on In0.53Ga0.47As (001) surfaces with and without NH3 pre-deposition treatments. The influence of the NH3 pre-deposition treatments on the electrical properties of the Si3N4/In0.53Ga0.47As interface was investigated by frequency dependent capacitance-voltage and conductance-voltage measurements. A fully unpinned C-V behavior was obtained for all samples. Samples that underwent NH3 pre-deposition treatment exhibited electrical characteristics with no evidence of the midgap interface states (Dit) effects in weak inversion, which are reported in the literature on In0.53Ga0.47As capacitors.

Fermi level pinning in metal/Al2O3/InGaAs gate stack after post metallization annealing

The effect of post metal deposition annealing on the effective work function in metal/Al2O3/InGaAs gate stacks was investigated. The effective work functions of different metal gates (Al, Au, and Pt) were measured. Flat band voltage shifts for these and other metals studied suggest that their Fermi levels become pinned after the post-metallization vacuum annealing. Moreover, there is a difference between the measured effective work functions of Al and Pt, and the reported vacuum work function of these metals after annealing. We propose that this phenomenon is caused by charging of indium and gallium induced traps at the annealed metal/Al2O3 interface.

Comparison of the degradation characteristics of AlON/InGaAs and Al2O3/InGaAs stacks

In this paper, the degradation characteristics of MOS (Metal-Oxide-Semiconductor) stacks with Al2O3/AlON or Al2O3 only as dielectric layers on InGaAs were studied. The dielectric nitrides are proposed as possible passivation layers to prevent InGaAs oxidation. At negative bias, it has been found out that the main contribution to the overall degradation of the gate oxide is dominated by the generation of positive charge in the gate oxide. This effect is pronounced in MOS stacks with Al2O3/AlON as dielectric, where we think the positive charge is mainly generated in the AlON interlayer. At positive bias, the degradation is dominated by buildup of negative charge due to electron trapping in pre-existing or stress-induced traps. For stress biases where the leakage currents are low, the changes in the electrical characteristics are dominated by electron-trapping into traps located in energy levels in the upper part of the semiconductor gap. For stress biases with higher leakage current levels, the electron tra...

A comparison between HfO2/Al2O3 nano-laminates and ternary HfxAlyO compound as the dielectric material in InGaAs based metal-oxide-semiconductor (MOS) capacitors

We compare the electrical properties of HfO2/Al2O3 nano-laminates with those of the ternary HfxAlyO compound in metal oxide semiconductor (MOS) capacitors. The dielectrics were deposited by atomic layer deposition on InGaAs. Water, ozone, and oxygen plasma were tested as oxygen precursors, and best results were obtained using water. The total dielectric thickness was kept constant in our experiments. It was found that the effective dielectric constant increased and the leakage current decreased with the number of periods. Best results were obtained for the ternary compound. The effect of the sublayer thicknesses on the electrical properties of the interface was carefully investigated, as well as the role of post-metallization annealing. Possible explanations for the observed trends are provided. We conclude that the ternary HfxAlyO compound is more favorable than the nano-laminates approach for InGaAs based MOS transistor applications.