Abstract
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 trapping occurs in stress-induced traps increasing the shift of VFB towards positive bias. The overall results clearly show that the improvement of the high-k dielectric/InGaAs interface by introducing N into the Al-oxide does not necessarily mean an increase in the reliability of the MOS stack.
Highlights
The analysis of the degradation characteristics of metal gate (MG)/high-k dielectric/InGaAs stacks with Al2O3/AlON in comparison to Al2O3 only gate dielectrics is performed under constant voltage stresses (CVS).The addition of N is not applied to the InGaAs interface by NH3 treatment as in Ref. 10, but rather by creating with ALD an N-enriched AlOx inner layer; NH4OH was used as a chemical passivation step for both samples prior to the ALD
The influence of the addition of N to alumina-based gate oxide was studied by the comparison of the degradation characteristics of MOS stacks with Al2O3/ AlON and Al2O3 as dielectric layers
The degradation is dominated by the generation of positive charge in the gate oxide, and the accumulated charge is larger for MOS stacks with Al2O3/AlON as dielectric
Summary
InGaAs is an attractive candidate to be used as a channel material for the extension of CMOS (Complementary MetalOxide-Semiconductor) technology beyond Si due to its high electron mobility. Lacking a good native oxide interface, a major challenge is the reduction of the density of interface states (Dit) at the semiconductor interface. High Dit values lead to inefficient Fermi level response, degrade the control of charge concentration in the channel, decrease the subthreshold slopes, and reduce the drive current of metal-oxide-semiconductor field effect transistors (MOSFETs). High Dit values are manifested in the capacitance-voltage (C-V) measurements as a hump at the weak inversion regime, a phenomenon that is almost always observed in InGaAsbased gate stacks at room temperature. Krylov et al have shown that an ammonia (NH4OH) pretreatment of the InGaAs surface improved the C-V characteristics of alumina-based MOS capacitors, and reduced the mid-gap Dit. Surface treatment with NH4OH shows a better quality of the interface in terms of interface states; it contributes to generation of charge on the dielectric layer. Since the suppression of the Ga-O bonds by the treatment with NH4OH only occurs after the annealing in N2, it opens the question about the role of N in the generation of defects/charge in the gate oxide. The analysis of the degradation characteristics of metal gate (MG)/high-k dielectric/InGaAs stacks with Al2O3/AlON in comparison to Al2O3 only gate dielectrics is performed under constant voltage stresses (CVS).The addition of N is not applied to the InGaAs interface by NH3 treatment as in Ref. 10, but rather by creating with ALD (atomic layer deposition) an N-enriched AlOx inner layer; NH4OH was used as a chemical passivation step for both samples prior to the ALD. The dynamics of degradation of the flat band voltage (VFB) and the generation of defects at interfaces of the stack
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