Plasma-based PH 3 passivation technique is extensively studied for the surface passivation of InGaAs substrate prior to high-k deposition. The comparative analysis reveals that the striking improvement is achieved when a stable covalent-bond P x N y layer forms at the interface during plasma PH 3 -passivation. We report that P x N y passivation layer improves thermal stability of high-k/InGaAs gate stack up to 750 o C, which enables successful implementation of InGaAs MOSFETs by self-aligned gate-first process. By adopting P x N y passivation on InGaAs with MOCVD HfAlO and metal gate stack, we achieved subthreshold slope of 98mV/dec, G m =378mS/mm at V d =1V, and effective mobility of 2557cm 2 /Vs at E eff =0.24MV/cm.
To realize high electron mobility metal-oxide-semiconductor field effect transistors ͑MOSFETs͒ on In 0.53 Ga 0.47 As with unpinned Fermi level, a PH 3 -N 2 plasma treatment is proposed and preliminarily studied as a novel interface engineering technique, which passivates the InGaAs surface by depositing a phosphorus nitride ͑P x N y ͒ layer to suppress AsO x and free As. Comparative X-ray photoelectron spectroscopy and atomic force microscopy studies reveal that a low pressure PH 3 -N 2 plasma treatment of In 0.53 Ga 0.47 As results in a smooth and atomically thin ͑ϳ1 monolayer͒ P x N y film as a main product, with a P-for-As anion exchanged layer found beneath the P x N y layer in a practically wide range of process window. The process conditions affect the stoichiometry of the P x N y layer, the amount of phosphorus and nitrogen atoms incorporated, and the degree of the P-for-As exchange reaction. MOSFET devices integrated with metalorganic chemical vapor deposited HfO 2 /TaN metal gate on the passivated In 0.53 Ga 0.47 As substrates have been fabricated by the conventional self-aligned gate-first process and compared to nonpassivated MOSFETs. The excellent interface quality of P x N y passivated In 0.53 Ga 0.47 As/HfO 2 /TaN gate stack has been proven showing suppressed frequency dispersion in inversion capacitance by 82-94% compared to the nonpassivated device and a low subthreshold slope approaching the theoretical value of 60 mV/dec.
Gate leakage mechanism of the HfAlO plasma-PH3 passivated and non-passivated In0.53Ga0.47As N-channel metal–oxide–semiconductor field-effect transistors (N-MOSFETs) have been evaluated, in order to correlate the quality of the oxide deposited with the gate leakage mechanisms observed. At temperatures higher than 300 K, trap-free space charge limited conduction (SCLC) mechanism dominates the gate leakage of passivated device but non-passivated device consists of exponentially distributed SCLC mechanism at low electric field and Frenkel–Poole emission at high electric field. This Frenkel–Poole emission is associated with energy trap levels of ∼0.95 to 1.3 eV and is responsible for the increased gate leakage of non-passivated device. In addition, the electrical properties of the non-passivated device has also been extracted from the SCLC mechanism, with the average trap concentration of the shallow traps given as 1.3×1019 cm-3 and the average activation energy given as ∼0.22 to 0.27 eV. The existence of these defect levels in non-passivated device can be attributed to the interdiffusion of Ga/As/O elements across the HfAlO/In0.53Ga0.47As interface. On the other hand, passivated device does not contain Frenkel–Poole emission nor exponentially distributed SCLC mechanism, indicating a reduction in traps in the bulk of the oxide. In addition, the temperature dependent characteristics of off-state leakage have also been evaluated to provide insight into the off-state mechanism. The off-state leakage of both passivated and non-passivated device is determined by junction leakage, with Shockley–Read–Hall mechanism being its main contributor, and has activation energy of 0.38 eV for passivated device and 0.4 eV for non-passivated device. From I
d∝T
-0.37 observed for passivated device, in comparison to I
d∝T
-0.18 for non-passivated device, we have further confirmed the phonon scattering dominance of the passivated device at high electric field.
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