Study on electrical characteristics and reliability of fluorinated HfO2 for HKMG

The dielectric properties and reliability of fluorinated HfO₂ have been studied. The fluorinated HfO₂ dielectric treated by NF₃ plasma showed improved dielectric characteristics but resulted in interfacial layer (IL) regrowth during the fluorine plasma treatment process, which led to an oxide capacitance reduction and poor electrical characteristics. Through the analysis of chemical composition and electrical characteristics, it has been revealed that the Hf-O bonds in HfO₂ layer were converted to Hf-F bonds by the plasma treatment and then the dissociated oxygen diffused to the IL. In order to suppress the IL regrowth, newly fluorinated HfO₂ has been developed. Reliability of fluorinated HfO₂ dielectric was sharply improved without a decrease in the oxide capacitance at fluorine plasma treatment conditions of low power and temperature.     

Effect of RuO2 electrode on laser-MBE prepared HfO2 gate dielectrics

In this paper, we report our recent study of the effect of RuO₂ as an alternative top electrode for pMOS devices to overcome the serious problems of polysilicon (poly-Si) gate depletion, high gate resistance and dopant penetration in the trend of down to 50 nm devices and beyond. The conductive oxide RuO₂, prepared by RF sputtering, was investigated as the gate electrode on the Laser MBE (LMBE) fabricated HfO₂ for pMOS devices. Structural, dielectric and electric properties were investigated. RuO₂/HfO₂/n-Si capacitors showed negligible flatband voltage shift (<10 mV), very strong breakdown strength (>10 MV cm⁻¹). Compared to the SiO₂ dielectric with the same EOT value, RuO₂/HfO₂/n-Si capacitors exhibited at least 4 orders of leakage current density reduction. The work function value of the RuO₂ top electrode was calculated to be about 5.0 eV by two methods, and the effective fixed oxide charge density was determined to be 3.3 × 10¹² cm⁻². All the results above indicate that RuO₂ is a promising alternative gate electrode for LMBE grown HfO₂ gate dielectrics.     

Design and fabrication of a novel high damage threshold HfO2/TiO2/SiO2 multilayer laser mirror

This paper describes a new method to design a laser mirror with high reflectivity, wide reflection bandwidth and high laser-induced damage threshold. The mirror is constructed by three materials of HfO2/TiO2/SiO2 based on electric field and temperature field distribution characteristics of all-dielectric laser high reflector. TiO2/SiO2 stacks act as the high reflector (HR) and broaden the reflection bandwidth, while HfO2/SiO2 stacks are used for increasing the laser resistance. The HfO2/TiO2/SiO2 laser mirror with 34 layers is fabricated by a novel remote plasma sputtering deposition. The damage threshold of zero damage probability for the new mirror is up to 39.6 J/cm2 (1064 nm, 12 ns). The possible laser damage mechanism of the mirror is discussed.     

Atomic-layer-deposited Al2O3 and HfO2 on GaN: A comparative study on interfaces and electrical characteristics

Al₂O₃, HfO₂, and composite HfO₂/Al₂O₃ films were deposited on n-type GaN using atomic layer deposition (ALD). The interfacial layer of GaON and HfON was observed between HfO₂ and GaN, whereas the absence of an interfacial layer at Al₂O₃/GaN was confirmed using X-ray photoelectron spectroscopy and transmission electron microscopy. The dielectric constants of Al₂O₃, HfO₂, and composite HfO₂/Al₂O₃ calculated from the C-V measurement are 9, 16.5, and 13.8, respectively. The Al₂O₃ employed as a template in the composite structure has suppressed the interfacial layer formation during the subsequent ALD-HfO₂ and effectively reduced the gate leakage current. While the dielectric constant of the composite HfO₂/Al₂O₃ film is lower than that of HfO₂, the composite structure provides sharp oxide/GaN interface without interfacial layer, leading to better electrical properties.     

Pseudopotential study of PrO2 and HfO2 in fluorite phase

Praseodymium and hafnium oxides are prospective candidates to subsitute SiO₂ in decanano MOSFET transistors. We report first ab initio pseudopotential band structure calculations for these materials. We find that fluorite phases of PrO₂ and HfO₂ have similar electronic structures. The important difference is a narrow sub-band forming the conduction band bottom in PrO₂ but absent in HfO₂. Electrons in this f-type sub-band have large masses. This explains why ultrathin epitaxial Pr oxide films have low leakage in spite of a relatively small conduction band offset (1 eV) between the oxide and the Si substrate.     

Comparison of metal gate electrodes on MOCVD HfO2

Metal gate electrodes of sputtered aluminum (Al), titanium nitride (TiN) and nickel aluminum nitride (NiAlN) are investigated in this work. They are compared with respect to their compatibility with metal organic chemical vapor deposited (MOCVD) hafnium dioxide (HfO₂) gate dielectrics. TiN, with a midgap work function of 4.65 eV on SiO₂, exhibits promising characteristics as metal gate on HfO₂. In addition, encouraging results are presented for the ternary metal NiAlN, whereas classic Al electrodes are found unstable in conjunction with HfO₂.     

Effects of La2O3 incorporation in HfO2 gated nMOSFETs on low-frequency noise

The effect of La₂O₃ incorporation on the spatial trap distribution in HfO₂ gate dielectrics is investigated. The incorporation of La₂O₃ in HfO₂ dielectric has been found to improve the effective mobility in addition to reduced interface-state density. The trap distribution analysis in the HfO₂ layer extracted by combining the charge pumping (CP) method and the low-frequency noise (LFN) method has revealed significant reduction in the amount of traps at HfO₂/SiO₂-interlayer interface and in the HfO₂ layer by La₂O₃ incorporation.     

Resistive switching effects of HfO2 high-k dielectric

Resistive switching behavior of HfO₂ high-k dielectric has been studied as a promising candidate for emerging non-volatile memory technology. The low resistance ON state and high resistance OFF state can be reversibly altered under a low SET/RESET voltage of ±3 V. The memory device shows stable retention behavior with the resistance ratio between both states maintained greater than 103. The bipolar nature of the voltage-induced hysteretic switching properties suggests changes in film conductivity related to the formation and removal of electronically conducting paths due to the presence of oxygen vacancies induced by the applied electric field. The effect of annealing on the switching behavior was related to changes in compositional and structural properties of the film. A transition from bipolar to unipolar switching behavior was observed upon O₂ annealing which could be related to different natures of defect introduced in the film which changes the film switching parameters. The HfO₂ resistive switching device offers a promising potential for high density and low power memory application with the ease of processing integration.     

Wideband frequency and in situ characterization of ultra thin ZrO2 and HfO2 films for integrated MIM capacitors

High-κ dielectrics are promising candidates to increase capacitor integration densities but their properties depend on manufacturing process and frequency because relaxation and resonance mechanisms occur. Complementary characterization protocols are needed to analyze high-κ insulator behaviour from DC to microwave frequencies. The extraction of Plasma Enhanced Atomic Layer Deposition HfO₂ and ZrO₂ complex permittivity was performed up to 5 GHz using dedicated test vehicles allowing an in situ characterization as a function of dielectric thickness. The measurement procedure was thus validated, highlighting the potentiality of these two dielectrics to cover a wide range of frequencies.     

High-k HfO2-Ta2O5 mixed layers: Electrical characteristics and mechanisms of conductivity

Electrical properties of mixed HfO₂-Ta₂O₅ films (10;15 nm) deposited by rf sputtering on Si have been studied from the view point of their applications as high-k layers, by standard capacitance-voltage and temperature dependent current-voltage characteristics. The effect of HfO₂ addition to the Ta₂O₅ is thickness dependent and the thicker layers exhibit advantages over the pure Ta₂O₅ (higher dielectric constant, enhanced charge storage density and improved interface quality). The process of HfO₂ and Ta₂O₅ mixing introduces negative oxide charge, tends to creates shallow bulk traps and modifies the dominant conduction mechanisms in the stack capacitors as compared to the Ta₂O₅-based one (a contribution of tunneling processes through traps located below the conduction band of mixed layers to the leakage current in the HfO₂-Ta₂O₅ stacks is observed). The traps involved in both Poole-Frenkel and tunneling processes are identified.     

Full-band tunneling in high-κ dielectric MOS structures

High-κ oxides such as ZrO₂ and HfO₂ have attracted great interest, due to their physical properties, suitable to replacement of SiO₂ as gate dielectric materials. In this work, we investigate the tunneling properties of ZrO₂ and HfO₂ high-κ oxides, by applying quantum mechanical methods that include the full-band structure of Si and oxide materials. Semiempirical sp³s*d tight-binding parameters have been determined to reproduce ab initio band dispersions. Transmission coefficients and tunneling current have been calculated for Si/ZrO₂/Si and Si/HfO₂/Si MOS structures, showing a very low gate leakage current in comparison to SiO₂-based structures with equivalent oxide thickness.     

Structural and electrical characteristics of RF-sputtered HfO2 high-k based MOS capacitors

The HfO₂ high-k thin films have been deposited on p-type (1 0 0) silicon wafer using RF magnetron sputtering technique. The XRD, AFM and Ellipsometric characterizations have been performed for crystal structure, surface morphology and thickness measurements respectively. The monoclinic structured, smooth surface HfO₂ thin films with 9.45 nm thickness have been used for Al/HfO₂/p-Si metal-oxide-semiconductor (MOS) structures fabrication. The fabricated Al/HfO2/Si structure have been used for extracting electrical properties viz dielectric constant, EOT, barrier height, doping concentration and interface trap density through capacitance voltage and current-voltage measurements. The dielectric constant, EOT, barrier height, effective charge carriers, interface trap density and leakage current density are determined are 22.47, 1.64 nm, 1.28 eV, 0.93 × 10¹⁰, 9.25 × 10¹¹ cm⁻² eV⁻¹ and 9.12 × 10⁻⁶ A/cm² respectively for annealed HfO₂ thin films.     

Electrical reliability aspects of HfO2 high-k gate dielectrics with TaN metal gate electrodes under constant voltage stress

The dielectric breakdown property of ultrathin 2.5 and 5.0 nm hafnium oxide (HfO₂) gate dielectric layers with metal nitride (TaN) gate electrodes for metal oxide semiconductor (MOS) structure has been investigated. Reliability studies were performed with constant voltage stressing to verify the processing condition effects (film thicknesses and post metal annealing temperatures) on times to breakdown. The leakage current characteristics are improved with post metal annealing temperatures (PMA) for both 2.5 and 5.0 nm HfO₂ physical thicknesses. However, it is more prominent (2 orders of magnitudes) for 2.5 nm HfO₂ film thickness. The values of oxide-trapped charge density and interface-state density are also improved for 2.5 nm HfO₂ film. The different stages of charge-trapping behaviors, i.e., stress-induced leakage current, soft and hard breakdown mechanisms have been detected. During constant voltage stress of the MOS capacitors, an increase in the time-dependent gate current is observed, followed by the occurrence of several fluctuations. The amplitude of the fluctuations is much larger in the 5.0 nm HfO₂ gate dielectric layer compared to the 2.5 nm HfO₂ layer. After the occurrence of such fluctuations, the current–voltage characteristics exhibited an increased in gate current compared to the fresh (unstressed) devices.     

Characterization of the annealing impact on La2O3/HfO2 and HfO2/La2O3 stacks for MOS applications

The impact of various rapid thermal annealing used during the integration on the La₂O₃/HfO₂ and HfO₂/La₂O₃ stacks deposited by Atomic Layer deposition was analyzed. The consequences of lanthanum localization in such stacks on the evolution of the films during the rapid thermal annealing are investigated in term of morphology, crystalline structure, silicate formation and film homogeneity as a function of the depth. It appeared that the La₂O₃ location has an impact on the temperature of the quadratic phase formation which could be linked to the formation of SiOHfLa silicate and the resistance of the films to dissolution in HF 0.05 wt%.     

Modeling growth rate of HfO2 thin films grown by metal-organic molecular beam epitaxy

HfO₂ dielectric layers were grown on the p-type Si (100) substrate by metal-organic molecular beam epitaxy (MOMBE). Hafnium-tetra-butoxide, Hf(O·t-C₄H₉)₄ was used as a Hf precursor and Argon gas was used as a carrier gas. The thickness of the HfO₂ film and intermediate SiO₂ layer were measured by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The properties of the HfO₂ layers were evaluated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high frequency (HF) capacitance-voltage (C-V) measurement, and current-voltage (I-V) measurement. C-V and I-V measurements have shown that HfO₂ layer grown by MOMBE has a high dielectric constant (k) of 20-22 and a low-level of leakage current density. The growth rate is affected by various process variables such as substrate temperature, bubbler temperature, Ar and O₂ gas flows and growth time. Since the ratio of O₂ and Ar gas flows are closely correlated, the effect of variations in O₂/Ar flow ratio on growth rate is also investigated using statistical modeling methodology.     

Hafnium oxide thin films deposited by high pressure reactive sputtering in atmosphere formed with different Ar/O2 ratios

The physical and electrical properties of hafnium oxide (HfO₂) thin films deposited by high pressure reactive sputtering (HPRS) have been studied as a function of the Ar/O₂ ratio in the sputtering gas mixture. Transmission electron microscopy shows that the HfO₂ films are polycrystalline, except the films deposited in pure Ar, which are amorphous. According to heavy ion elastic recoil detection analysis, the films deposited without using O₂ are stoichiometric, which means that the composition of the HfO₂ target is conserved in the deposition films. The use of O₂ for reactive sputtering results in slightly oxygen-rich films. Metal-Oxide-Semiconductor (MOS) devices were fabricated to determine the deposited HfO₂ dielectric constant and the trap density at the HfO₂/Si interface (D_it) using the high–low frequency capacitance method. Poor capacitance–voltage (CV) characteristics and high values of D_it are observed in the polycrystalline HfO₂ films. However, a great improvement of the electrical properties was observed in the amorphous HfO₂ films, showing dielectric constant values close to 17 and a minimum D_it of 2×10¹¹ eV⁻¹ cm⁻².     

Integration of HfxTayN metal gate with SiO2 and HfOxNy gate dielectrics for MOS device applications

Interaction of Hf_xTa_yN metal gate with SiO₂ and HfO_xN_y gate dielectrics has been extensively studied. Metal-oxide-semiconductor (MOS) device formed with SiO₂ gate dielectric and Hf_xTa_yN metal gate shows satisfactory thermal stability. Time-of-flight secondary ion mass spectroscopy (TOF-SIMS) analysis results show that the diffusion depths of Hf and Ta are less significant in SiO₂ gate dielectric than that in HfO_xN_y. Compared to HfO_xN_y gate dielectric, SiO₂ shows better electrical properties, such as leakage current, hysteresis, interface trap density and stress-induced flat-band voltage shift. With an increase in post metallization annealing (PMA) temperature, the electrical characteristics of the MOS device with SiO₂ gate dielectric remain almost unchanged, indicating its superior thermal and electrical stability.     

Novel high-K inverse silver oxide phases of , , , and their alloys

The recently reported inverse silver oxide phase of SiO₂ possesses a high dielectric constant as well as lattice constant compatibility to Si. We explore the closely related oxides, GeO₂, SnO₂ with the same inverse silver oxide structure using ab initio density functional theory within the local density approximation (LDA). According to the phonon dispersion curves, both these structures are computed to be unstable. On the other hand, their alloys Si_0.5Ge_0.5O₂, Si_0.5Sn_0.5O₂, and Ge_0.5Sn_0.5O₂ are stable with higher dielectric constants than that of SiO₂ in the same phase. Their first-principles elastic constants, electronic band structures and phonon dispersion curves have been obtained with high precision.     

Breakdown spots of ultra-thin (EOT < 1.5 nm) HfO2/SiO2 stacks observed with enhanced—CAFM

In this work, the (gate) current versus (gate) voltage (I–V) characteristics and the dielectric breakdown (BD) of an ultra-thin HfO₂/SiO₂ stack is studied by enhanced conductive atomic force microscopy (ECAFM). The ECAFM is a CAFM with extended electrical performance. Using this new set up, different conduction modes have been observed before BD. The study of the BD spots has revealed that, as for SiO₂, the BD of the stack leads to modifications in the topography images and high conductive spots in the current images. The height of the hillocks observed in the topography images has been considered an indicator of structural damage.     

Pre- and post-BD electrical conduction of stressed HfO2/SiO2 MOS gate stacks observed at the nanoscale

In this work, the electrical properties of fresh and stressed HfO₂/SiO₂ gate stacks have been studied using a prototype of Conductive Atomic Force Microscope with enhanced electrical performance (ECAFM). The nanometer resolution of the technique and the extended current dynamic range of the ECAFM has allowed to separately investigate the effect of the electrical stress on the SiO₂ and the HfO₂ layer of the high-k gate stack. In particular, we have investigated this effect on both layers when the structures where subjected to low and high field stresses.