MOS devices with tetragonal ZrO2 as gate dielectric formed by annealing ZrO2/Ge/ZrO2 laminate

A Ge-stabilized tetragonal ZrO₂ (t-ZrO₂) film with permittivity (κ) of 36.2 was formed by depositing a ZrO₂/Ge/ZrO₂ laminate and a subsequent annealing at 600 °C, which is a more reliable approach to control the incorporated amount of Ge in ZrO₂. On Si substrates, with thin SiON as an interfacial layer, the SiON/t-ZrO₂ gate stack with equivalent oxide thickness (EOT) of 1.75 nm shows tiny amount of hysteresis and negligible frequency dispersion in capacitance-voltage (C-V) characteristics. By passivating leaky channels derived from grain boundaries with NH₃ plasma, good leakage current of 4.8 × 10⁻⁸ A/cm² at V_g = V_fb − 1 V is achieved and desirable reliability confirmed by positive bias temperature instability (PBTI) test is also obtained.     

A novel thermally-stable zirconium amidinate ALD precursor for ZrO2 thin films

ZrO₂ thin films were deposited by the atomic layer deposition process on Si substrates using tetrakis(N,N′-dimethylacetamidinate) zirconium (Zr-AMD) as a Zr precursor and H₂O as an oxidizing agent. Tetrakis (ethylmethylamino) zirconium (TEMA-Zr) was also evaluated for a comparative study. Physical properties of ALD-derived ZrO₂ thin films were studied using ellipsometry, grazing incidence XRD (GI-XRD), high resolution TEM (HRTEM), and atomic force microscopy (AFM). The ZrO₂ deposited using Zr-AMD showed a better thermal stability at high substrate temperature (>300 °C) compared to that using TEMA-Zr. GI-XRD analysis reveals that after 700 °C anneal both ZrO₂ films enter tetragonal phase. The electrical properties of N₂-annealed ZrO₂ film using Zr-AMD exhibit an EOT of 1.2 nm with leakage current density as low as 2 × 10⁻³ A/cm² (@V_fb−1 V). The new Zr amidinate is a promising ALD precursor for high-k dielectric applications.     

Structural, electrical and optical properties of GZO/HfO2/GZO transparent MIM capacitors

Metal–insulator–metal (MIM) transparent capacitors were prepared by pulsed laser deposition (PLD) on glass substrates. The effect of the thickness of the dielectric layer and oxygen pressure on structural, electrical, and optical properties of these capacitors was investigated. Experimental results show that film thickness and oxygen pressure have no effect on the structural properties. It is also found that the optical properties of the HfO₂ thin films depend strongly on both the film thickness and oxygen pressure. The electrical properties of transparent capacitors were investigated at various thickness of the dielectric layer. The capacitor shows an overall high performance, such as a high dielectric constant of 28 and a low leakage current of 2.03×10⁻⁶ A/cm² at ±5 V. Transmittance above 70% was observed in visible region.     

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.     

Characterization of ZrO2 thin films deposited by MOCVD for high-density 3D capacitors

This work deals with high-density integrated capacitors for output filters in future micro DC–DC converters. To reach high capacitance density, 3D structures were created in silicon with DRIE followed by MOCVD of ZrO₂ (100 nm thick). The step coverage revealed two deposition regimes: a surface reaction controlled regime for cavities aspect ratio lower than 2 and a diffusion-controlled regime for higher aspect ratios. The ZrO₂ films present mostly a cubic/tetragonal structure. The permittivity extracted from the measurement is 26.4. These results are discussed with static dielectric responses calculated in literature.     

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.     

Investigation of Ta2O5/SiO2/4H-SiC MIS capacitors

Tantalum pentoxide (Ta₂O₅) deposited by pulsed DC magnetron sputtering technique as the gate dielectric for 4H-SiC based metal-insulator-semiconductor (MIS) structure has been investigated. A rectifying current-voltage characteristic was observed, with the injection of current occurred when a positive DC bias was applied to the gate electrode with respect to the n type 4H-SiC substrate. This undesirable behavior is attributed to the relatively small band gap of Ta₂O₅ of around 4.3 eV, resulting in a small band offset between the 4H-SiC and Ta₂O₅. To overcome this problem, a thin thermal silicon oxide layer was introduced between Ta₂O₅ and 4H-SiC. This has substantially reduced the leakage current through the MIS structure. Further improvement was obtained by annealing the Ta₂O₅ at 900 °C in oxygen. The annealing has also reduced the effective charge in the dielectric film, as deduced from high frequency C-V measurements of the Ta₂O₅/SiO₂/4H-SiC capacitors.     

Comparative study of AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors with Al2O3 and HfO2 gate oxide

AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOSHFETs) with Al₂O₃ gate oxide which was deposited by atomic layer deposition (ALD) were fabricated and their performance was then compared with that of AlGaN/GaN MOSHFETs with HfO₂ gate oxide. The capacitance (C)-voltage (V) curve of the Al₂O₃/GaN MOS diodes showed a lower hysteresis and lower interface state density than the C-V curve of the HfO₂/GaN diodes, indicating better quality of the Al₂O₃/GaN interface. The saturation of drain current in the I_D-V_GS relation of the Al₂O₃ AlGaN/GaN MOSHFETs was not as pronounced as that of the HfO₂ AlGaN/GaN MOSHFETs. The gate leakage current of the Al₂O₃ MOSHFET was five to eight orders of magnitude smaller than that of the HfO₂ MOSHFETs.     

Electrical and interfacial characteristics of nanolaminate (Al2O3/ZrO2/Al2O3) gate stack on fully depleted SiGe-on-insulator

The structural and electrical characteristics of a novel nanolaminate Al₂O₃/ZrO₂/Al₂O₃ high-k gate stack together with the interfacial layer (IL) formed on SiGe-on-insulator (SGOI) substrate have been investigated. A clear layered Al₂O₃ (2.5 nm)/ZrO₂ (4.5 nm)/Al₂O₃ (2.5 nm) structure and an IL (2.5 nm) are observed by high-resolution transmission electron microscopy. X-ray photoelectron spectroscopy measurements indicate that the IL contains Al-silicate without Ge atom incorporation. A well-behaved C–V behavior with no hysteresis shows the absence of Ge pileup or Ge segregation at the gate stack/SiGe interface.     

Charge trapping and interface characteristics in normally-off Al2O3/GaN-MOSFETs

Normally-off GaN-MOSFETs with Al₂O₃ gate dielectric have been fabricated and characterized. The Al₂O₃ layer is deposited by ALD and annealed under various temperatures. The saturation drain current of 330 mA/mm and the maximum transconductance of 32 mS/mm in the saturation region are not significantly modified after annealing. The subthreshold slope and the low-field mobility value are improved from 642 to 347 mV/dec and from 50 to 55 cm² V⁻¹ s⁻¹, respectively. The I_D-V_G curve shows hysteresis due to oxide trapped charge in the Al₂O₃ before annealing. The amount of hysteresis reduces with the increase of annealing temperature up to 750 °C. The Al₂O₃ layer starts to crystallize at a temperature of 850 °C and its insulating property deteriorates.     

Plasma-enhanced flexible metal-insulator-metal capacitor using high-k ZrO2 film as gate dielectric with improved reliability

We demonstrate a new flexible metal-insulator-metal capacitor using 9.5-nm-thick ZrO₂ film on a plastic polyimide substrate based on a simple and low-cost sol-gel precursor spin-coating process. The surface morphology of the ZrO₂ film was investigated using scan electron microscope and atomic force microscope. The as-deposited ZrO₂ film under suitable treatment of oxygen (O₂) plasma and then subsequent annealing at 250 °C exhibits superior low leakage current density of 9.0 × 10⁻⁹ A/cm² at applied voltage of 5 V and maximum capacitance density of 13.3 fF/μm² at 1 MHz. The as-deposited sol-gel film was completely oxidized when we employed O₂ plasma at relatively low temperature and power (30 W), hence enhancing the electrical performance of the capacitor. The shift (Zr 3d from 184.1 eV to 184.64 eV) in X-ray photoelectron spectroscopy of the binding energy of the electrons towards higher binding energy; clearly indicates that the O₂ plasma reaction was most effective process for the complete oxidation of the sol-gel precursor at relatively low processing temperature.     

Electrical characterization of high-k gate dielectrics fabricated using plasma oxidation and post-deposition annealing of a Hf/SiO2/Si structure

High permittivity (high-k) gate dielectrics were fabricated using the plasma oxidation of Hf metal/SiO₂/Si followed by the post-deposition annealing (PDA), which induced a solid-phase reaction between HfO_x and SiO₂. The oxidation time and PDA temperature affected the equivalent oxide thickness (EOT) and the leakage current density of the high-k dielectric films. The interfacial structure of the high-k dielectric film/Si was transformed from HfO_x/SiO₂/Si to HfSi_xO_y/Si after the PDA, which led to a reduction in EOT to 1.15 nm due to a decrease in the thickness of SiO₂. These high-k dielectric film structures were investigated by X-ray photoelectron spectroscopy. The leakage current density of high-k dielectric film was approximately four orders of magnitude lower than that of SiO₂.     

Influence of the metal electrode on the characteristics of thermal Ta2O5 capacitors

The effect of various electrodes (Al, W, TiN) deposited by evaporation (Al) and sputtering (W, TiN) on the electrical characteristics of thermal thin film (15-35 nm) Ta₂O₅ capacitors has been investigated. The absolute level of leakage currents, breakdown fields, mechanism of conductivity, dielectric constant values are discussed in the terms of possible reactions between Ta₂O₅ and electrode material as well as electrode deposition process-induced defects acting as electrically active centers. The dielectric constant values are in the range 12-26 in dependence on both Ta₂O₅ thickness and gate material. The results show that during deposition of TiN and Al a reaction that worsens the properties of Ta₂O₅ occurs while there is not an indication for detectable reduction of Ta₂O₅ when top electrode is W, and the leakage current is 5-7 orders of magnitude lower as compared to Al and TiN-electroded capacitors. The high level of leakage current for TiN and Al gate capacitors are related to the radiation defects generated in Ta₂O₅ during sputtering of TiN, and damaged interface at the electrode due to a reaction between Al and Ta₂O₅, respectively. It is demonstrated that the quality of the top electrode affects the electrical characteristics of the capacitors and the sputtered W is found to be the best. The sputtered W gate provides Ta₂O₅ capacitors with a good quality: the current density <7 × 10⁻¹⁰ A/cm² at 1 V (0.7 MV/cm, 15 nm thick Ta₂O₅). W deposition is not accompanied by an introduction of a detectable damage leading to a change of the properties of the initial as-grown Ta₂O₅ as in the case of TiN electrode. Damage introduced during TiN sputtering is responsible for current deterioration (high leakage current) and poor breakdown characteristics. It is concluded that the sputtered W top electrode is a good candidate as a top electrode of storage capacitors in dynamic random access memories giving a stable contact with Ta₂O₅, but sputtering technique is less suitable (favorable) for deposition of TiN as a metal electrode due to the introduction of radiation defects causing both deterioration of leakage current and poor breakdown characteristics.     

Optimization of electric properties of high-k zirconium dioxide by varying deposition and annealing conditions

ZrO₂ thin films with a smooth surface were synthesized on silicon by atomic vapor deposition™ using Zr[OC(CH₃)₃]₄ as precursor. The maximum growth rate (7 nm min⁻¹) and strongest crystalline phase were obtained at 400 °C. The increase of the deposition temperature reduced the deposition rate to 0.5 nm min⁻¹ and changed the crystalline ZrO₂ phase from cubic/tetragonal to monoclinic. These films showed no enhancement of the dominating monoclinic phase by annealing. The values of the dielectric constant (up to 32) and leakage current density (down to 1.2×10⁻⁶ A cm⁻² at 1×10⁶ V cm⁻¹) varied depending on the deposition temperature and film thickness. The midgap density of interface states was N_it=5×10¹¹ eV⁻¹ cm⁻². The leakage current and the density of interface states were lowered by the annealing to 10⁻⁷ A cm⁻² at 1×10⁶ V cm⁻¹ and to 10¹⁰ eV⁻¹ cm⁻², respectively. However, this also led to a decrease of the dielectric constant.     

On the etching mechanism of ZrO2 thin films in inductively coupled BCl3/Ar plasma

The etching mechanism of ZrO₂ thin films in BCl₃/Ar plasma was investigated using a combination of experimental and modeling methods. It was found that an increase in the Ar mixing ratio causes the non-monotonic behavior of the ZrO₂ etch rate which reaches a maximum of 41.4 nm/min at about 30-35% Ar. Langmuir probe measurements and plasma modeling indicated the noticeable influence of a BCl₃/Ar mixture composition on plasma parameters and active species kinetics that results in non-linear changes of both densities and fluxes for Cl, BCl₂ and . From the model-based analysis of surface kinetics, it was shown that the non-monotonic behavior of the ZrO₂ etch rate can be associated with the concurrence of chemical and physical pathways in ion-assisted chemical reaction.     

Fabrication and characterization of Zr-rich Zr-aluminate films for high-κ gate dielectric applications

Two kinds of Zr-rich Zr-aluminate films for high-κ gate dielectric applications with the nominal composition of (ZrO₂)_0.8(Al₂O₃)_0.2 and (ZrO₂)_0.9(Al₂O₃)_0.1, were deposited on n-type silicon wafer by pulsed laser deposition (PLD) technique at different deposition conditions. X-ray diffraction (XRD) reveals that the (ZrO₂)_0.8(Al₂O₃)_0.2 film could remain amorphous after being rapid thermal annealed (RTA) at the temperature above 800 °C, while the other one displays some crystalline peaks at 700 °C. The energy gap calculated from optical transmittance spectrum of (ZrO₂)_0.8(Al₂O₃)_0.2 film on quartz is about 6.0 eV. Sputtering depth profile of X-ray photoelectron spectroscopy and Auger electron spectroscopy indicate that a Zr-Si-O interfacial layer was formed at the near surface of the silicon substrate. The dielectric constant of the (ZrO₂)_0.8(Al₂ O₃)_0.2 film has been determined to be 22.1 by measuring a Pt/(ZrO₂)_0.8(Al₂ O₃)_0.2/Pt MIM structure. An EOT of 1.76 nm with a leakage current density of 51.5 mA/cm² at 1 V gate voltage for the film deposited in N₂ were obtained. Two different pre-treatments of Si substrates prior to depositions were also carried out and compared. The results indicate that a surface-nitrided Si substrate can lead to a lower leakage current density. The amorphous Zr-rich Zr-aluminate films fabricated by PLD have promising structure and dielectric properties required for a candidate material for high-κ gate dielectric applications.     

电子束辐照下的石墨烯上的原子层沉积Al2O3介质层

为了研究石墨烯与高k介质的结合,使用原子层沉积氧化铝在石墨衬底上。沉积前使用电子束辐照,观测到了氧化铝明显改善的形貌。归因于电子束辐照过程中的石墨层的无定形变化过程。     

New dielectric material system of Nd(Mg1/2Ti1/2)O3–CaTiO3 at microwave frequency

The microwave dielectric properties of (1 − x)CaTiO₃–xNd(Mg_1/2Ti_1/2)O₃ (0.1  x  1.0) ceramics prepared by the conventional solid state method have been investigated. The system forms a solid solution throughout the entire compositional range. The dielectric constant decreases from 152 to 27 as x varies from 0.1 to 1.0. In the (1 − x)CaTiO₃–xNd(Mg_1/2Ti_1/2)O₃ system, the microwave dielectric properties can be effectively controlled by varying the x value. At 1400 °C, 0.1CaTiO₃–0.9Nd(Mg_1/2Ti_1/2)O₃ has a dielectric constant (ε_r) of 42, a Q × f value of 35 000 GHz and a temperature coefficient of resonant frequency (τ_f) of −10 ppm/°C. As the content of Nd(Mg_1/2Ti_1/2)O₃ increases, the highest Q × f value of 43 000 GHz for x = 0.9 is achieved at the sintering temperature 1500 °C.     

Reducing Cu diffusion in SiCOH low-k films by O2 plasma treatment

This work investigates the Cu diffusion in SiCOH low dielectric constant films treated by O₂ plasma. By capacitance–voltage and current-voltage measurement, and thermal stress analysis, it is found that the O₂ plasma surface treatment of SiCOH films can lead to the decrease of flatband voltage shift ΔV_FB, the increase of activation energy E_a, and the decrease of leakage current. The small ΔV_FB and lower leakage current indicate the weak Cu diffusion. The increase of active energy means the reducing of fast Cu ions surface diffusion through the interconnected pores structure of the film. Hence, the Cu diffusion in SiCOH films can be reduced by O₂ plasma treatment. By FTIR and AFM analysis on the bonding configuration and microstructure, the reduce of Cu diffusion is related to the increase of Si-O cages and networks, which makes more open pores sealed at the surface of SiCOH films.     

Influence of oxidation temperature on the microstructure and electrical properties of Ta2O5 on Si

The effect of the oxidation temperature (673-873 K) on the microstructural and electrical properties of thermal Ta₂O₅ thin films on Si has been studied. Auger electron spectroscopy and X-ray photoelectron spectroscopy results revealed that the films are non-stoichiometric in the depth; an interfacial transition layer between tantalum oxide and Si substrate, containing presumably SiO₂ was detected. It has been found by X-ray diffraction that the amorphous state of Ta₂O₅ depends on both the oxidation temperature and the thickness of the films—the combination of high oxidation temperature (>823 K) and thickness smaller than 50 nm is critical for the appearance of a crystal phase. The Ta₂O₅ layers crystallize to the monoclinic phase and the temperature of the phase transition is between 773 and 823 K for the thinner layers (<50 nm) and very close to 873 K for the thicker ones. The electrical characterization (current/voltage; capacitance/voltage) reveals that the optimal oxidation temperature for achieving the highest dielectric constant (∼32) and the lowest leakage current (10⁻⁸ A/cm² at 1 MV/cm applied field) is 873 K. The results imply that the poor oxidation related defects are rather the dominant factor in the leakage current than the crystallization effects.