T. Das

Atomic layer deposited (TiO2)x(Al2O3)1−x/In0.53Ga0.47As gate stacks for III-V based metal-oxide-semiconductor field-effect transistor applications

Atomic layer deposited (ALD) (TiO2)x(Al2O3)1-x(TiAlO) alloy gate dielectrics on In0.47Ga0.53As/InP substrates are shown to produce high quality interfaces between TiAlO and InGaAs. The surface morphology and interfacial reaction of nanolaminate ALD TiAlO on In0.53Ga0.47As are studied using atomic force microscopy and x-ray photoelectron spectroscopy. Measured valence and conduction band offsets are found to be 2.85 ± 0.05 and 1.25 ± 0.05 eV, respectively. Capacitance-voltage characteristics show low frequency dispersion (∼11%), interface state density (∼4.2 × 1011 cm−2eV−1), and hysteresis voltage (∼90 mV). Ga-O and As-O bonding are found to get suppressed in the gate stacks after post deposition annealing. Our experimental results suggest that higher oxidation states of In and Ga at the In0.53Ga0.47As surface and As diffusion in the dielectric are effectively controlled by Ti incorporation in Al2O3.

Charge trapping and reliability characteristics of sputtered Y2O3 high-k dielectrics on N- and S-passivated germanium

We demonstrate the potential of sulfur passivation to improve the interface characteristics between germanium (Ge) and Y2O3 high-k gate dielectric. Effects of nitrogen (N) and sulfur (S) passivation of the Ge surface on the charge trapping and reliability properties of Y2O3/Ge gate stacks are studied in detail and the results are compared. Sulfur passivation of the Ge surface has been performed using both the wet sulfidation technique with aqueous ammonium sulfide and plasma sulfidation with H2S gas. N-passivation of Ge substrates has been performed in NO plasma for comparison. Ultrathin (~15 nm) Y2O3 films are deposited on both the N- and S-passivated p-Ge (1 0 0) wafers. Y2O3 films on the S-passivated Ge surface show low fixed oxide charge and interface state density than what is achieved with N-passivation. The electrical characterization results of MOS capacitors with Y2O3 films reveal the potential of S-passivation for the fabrication of Y2O3/Ge gate stacks for Ge MOSFETs.

An extension of the Curie-von Schweidler law for the leakage current decay in MIS structures including progressive breakdown

Abstract The leakage current decay and progressive breakdown in Al/HfYO x /GaAs and Al/Y 2 O 3 /GaAs structures during constant voltage stress are investigated. It is shown that the Curie-von Schweidler law in combination with series and parallel resistances can describe the observed current decrease in these structures accurately. The circuit model incorporates an additional parallel leakage current path associated with the local degradation of the oxide layer as well. Even though the evolution of the current is remarkably different in HfYO x than in Y 2 O 3 because of the applied stress voltage range and current magnitudes, the proposed model is able to capture the main features exhibited by the current–time characteristic in both cases. Experimental data from other authors are analyzed within the same framework.

Thermal stability of HfOxNy gate dielectrics on p-GaAs substrates

The structural, electrical and interfacial properties of metal-oxide–semiconductor (MOS) capacitors with hafnium-oxynitride (HfOxNy) gate dielectrics on p-GaAs substrates were investigated with post-deposition annealing (PDA). X-ray photoelectron spectra (XPS) show the presence of nitrogen at the interface and the intensity increases with annealing temperatures. Although the defective Ga-oxide increases with temperatures, the presence of nitrogen stabilizes and modulates the interface trap by reducing the oxygen vacancy. The electrical characteristics of GaAs MOS devices with HfOxNy gate dielectric show low interface state density, frequency dispersion and hysteresis voltage even after annealing at 600 °C. The accumulation capacitance decreases with annealing temperatures due to the formation of a stable thick nitride interfacial layer. The leakage current density of ~2.4 × 10−6 A cm−2 at VG = −1 V was achieved after 600 °C annealing for an EOT of 3.9 nm. The thermal stability and charge trapping behavior of the HfOxNy/p-GaAs gate stack at a constant voltage and current stressing have exhibited good interface quality and high dielectric reliability, making the films suitable for GaAs-based complementary metal-oxide–semiconductor technology

Paramagnetic defects and charge trapping in TaYOx gate dielectrics on strained-Si

Charge trapping kinetics and chemical nature of defects present in Al/TaYOx/strained-Si/Si0.8Ge0.2 MIS capacitors have been studied using internal photoemission and magnetic resonance. Reliability characteristics have been studied using CVS and CCS techniques. Results of electron paramagnetic resonance (EPR) and internal photoemission (IPE) studies on the charge trapping behavior are reported.

Study of the spatial distribution of breakdown spots in MOS devices in case of important edge effect anomalies

The breakdown spots spatial distribution in metal gate/high-K/III-V semiconductor capacitors caused by severe electrical stress is investigated. The spots appear as a random point pattern on the top electrode and are the consequence of important thermal effects occurring at the very moment of the formation of filamentary leakage current paths across the gate oxide stack. The damage is permanent, easily detectable without any image or sample treatment and accumulates with the application of successive stresses. It is shown using spatial statistics techniques that despite the distribution of spots is anomalous in the periphery of the devices, they follow a Poisson process within the structure far from the edges.

Reliability behavior of TaAlOx Metal-Insulator-Metal capacitors

Reliability characteristics of TaAlO<inf>x</inf> high-k dielectric MIM capacitors are reported. TaAlO<inf>x</inf> films have been deposited by RF co-sputtering of Ta<inf>2</inf>O<inf>5</inf> and Al<inf>2</inf>O<inf>3</inf> targets at a low substrate temperature. A high capacitance density and a low value of VCC (voltage coefficients of capacitance) have been achieved. Degradation kinetics in TaAlO<inf>x</inf>-based MIM capacitors have been studied under constant current stressing (CCS: 20 to 60 nA) and constant voltage stressing (CVS: 3 to 7 V). A dielectric breakdown voltage in the range of ∼ 4.2 – 5.4 MV/cm was found for TaAlO<inf>x</inf> films.

Characterization of RF sputter deposited HfAlOx dielectrics for MIM capacitor applications

Advanced metal-insulator-metal (MIM) capacitors with ultra-thin (EOT~2.1-4.9nm) RF sputter-deposited HfAlOx dielectric layers having excellent electrical properties have been fabricated. The capacitance density is found to increase with the decrease in thickness of insulator film. MIM capacitors show little voltage and frequency dependence along with low dissipation and leakage current. Our experimental observations indicate the high potential of HfAlOx for MIM capacitor applications.

Studies on Lattice vibration, impurity and defects in MIS structures using Hf-based dielectrics on Si and SiGe substrates

Lattice dynamics, molecular vibrations as well as defects and traps in ultra-thin Hf-based gate dielectrics on Si and strained-SiGe layers have been studied using inelastic tunneling spectroscopy (IETS). Molecular vibrations, phonons, defects and trap-features are identified from IETS of the samples for comparing and analyzing different interface qualities.

Electrical and charge trapping properties of HfO 2 /Al 2 O 3 bilayer gate dielectrics on In 0.53 Ga 0.47 As substrates

Electrical properties and reliability of bilayer HfO₂ (~7nm)/Al₂O₃ (~3nm) high-k dielectric films prepared by RF sputtering have been studied in detail. It is observed that the bilayer dielectric reduces the frequency dispersion, hysteresis, interface trap charge density (D_it) and gate leakage current density when compared to single layer HfO₂. In order to study the degradation mechanisms in Al/HfO₂/Al₂O₃/p-In_0.53Ga_0.47As and Al/HfO₂/p-In_0.53Ga_0.47As structures as a function of different stress conditions, trapped charge distribution were determined after constant voltage stressing at different bias levels. HfO₂/Al₂O₃ gate stacks exhibited superior electrical performance in terms of trap induced flatband voltage instability and trap charge generation compared to directly deposited HfO₂ films on p-In_0.53Ga_0.47As.