Self-aligned n-channel GaAs metal-oxide-semiconductor field-effect transistors (MOSFETs) using HfO2 and silicon interface passivation layer: Post-metal annealing optimization

In this work, using Si interface passivation layer (IPL), we demonstrate n-MOSFET on p-type GaAs by varying physical-vapor-deposition (PVD) Si IPL thickness, S/D ion implantation condition, and different substrate doping concentration and post-metal annealing (PMA) condition. Using the optimized process, TaN/HfO₂/GaAs n-MOSFETs made on p-GaAs substrates exhibit good electrical characteristics, equivalent oxide thickness (EOT) (∼3.7 nm), frequency dispersion (∼8%) and high maximum mobility (420 cm²/V s) with high temperature PMA (950 °C, 1 min) and good inversion.     

Post deposition UV-induced O2 annealing of HfO2 thin films

UV-assisted annealing processes for thin oxide films is an alternative to conventional thermal annealing and has shown many advantages such as low annealing temperature, reducing annealing time and easy to control. We report in this work the deposition of ultra-thin HfO₂ films on silicon substrate by two CVD techniques, namely thermal CVD and photo-induced CVD using 222 nm excimer lamps at 400 °C. As-deposited films of around 10 nm in thickness with refractive indices from 1.72 to 1.80 were grown. The deposition rate measured by ellipsometry was found to be about 2 nm/min by UV-CVD, while the deposition rate by thermal CVD is 20% less than that by UV-CVD. XRD showed that the as-deposited HfO₂ films were amorphous. This work focuses on the effect of post deposition UV annealing in oxygen on the structural, optical and electrical properties of the HfO₂ films at low temperature (400 °C). Investigation of the interfacial layer by FTIR revealed that thickness of the interfacial SiO₂ layer slightly increases with the UV-annealing time and UV annealing can convert sub-oxides at the interface into stoichiometric SiO₂, leading to improved interfacial qualities. The permittivity ranges in 8–16, are lower than theoretical values. However, the post deposition UV O₂ annealing results in an improvement in effective breakdown field and calculated permittivity, and a reduction in leakage current density for the HfO₂ films.     

退火温度对ZrO_2高介电薄膜电学性能的影响

利用反应磁控溅射法沉积了ZrO2介电薄膜,研究了退火温度对ZrO2介电薄膜电学性能的影响,并对漏电流最小的样品的漏电流机制进行了分析。结果表明,随着退火温度的升高,漏电流先减小后增大,退火温度为300℃时所制备薄膜的漏电流最小,当所加电压为–1.4 V时,漏电流密度为8.32×10–4 A/cm2。当所加正偏压为0-0.8 V和0.8-4.0 V时,该样品的漏电流主导机制分别为肖特基发射和直接隧穿电流;当所加负偏压为–1.7-0 V和–4.0-–1.7 V时,其主导机制分别为肖特基发射和空间电荷限制电流。     

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.     

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.     

介质前后双重臭氧处理实现锗/氧化铪间界面钝化

The physical and electrical properties of a Ge/GeO₂/HfO₂/Al gate stack are investigated.A thin interfacial GeO₂ layer（ 1 nm） is formed between Ge and HfO₂ by dual ozone treatments,which passivates the Ge/high-k interface.Capacitors on p-type Ge substrates show very promising capacitance-voltage（C-V） characteristics by using in situ pre-gate ozone passivation and ozone ambient annealing after high-k deposition,indicating efficient passivation of the Ge/HfO₂ interface.It is shown that the mid-gap interface state density at the Ge/GeO₂ interface is 6.4×10¹¹ cm^-2·eV^-1.In addition,the gate leakage current density of the Ge/GeO₂/HfO₂/Al gate stack passivated by the dual ozone treatments is reduced by about three orders of magnitude compared to that of a Ge/HfO₂/Al gate stack without interface passivation.     

Electrical properties of Ge metal–oxide–semiconductor capacitors with high-k La2O3 gate dielectric incorporated by N or/and Ti

LaON, LaTiO and LaTiON films are deposited as gate dielectrics by incorporating N or/and Ti into La2O3 using the sputtering method to fabricate Ge MOS capacitors, and the electrical properties of the devices are carefully examined. LaON/Ge capacitors exhibit the best interface quality, gate leakage property and device reliability, but a smaller k value (14.9). LaTiO/Ge capacitors exhibit a higher k value (22.7), but a deteriorated interface quality, gate leakage property and device reliability. LaTiON/Ge capacitors exhibit the highest k value (24.6), and a relatively better interface quality (3.1E11 eV^-1cm^-2), gate leakage property (3.6E3 A/cm^2 at Vg = 1 V + Vfb) and device reliability. Therefore, LaTiON is more suitable for high performance Ge MOS devices as a gate dielectric than LaON and LaTiO materials.     

Dependence of electrical properties on interfacial layer of Ta2O5 films

The change in the thickness and chemical states of the interfacial layer and the related electrical properties in Ta₂O₅ films with different annealing temperatures were investigated. The high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy analyses revealed that the 700 °C-annealed Ta₂O₅ film remained to be amorphous and had the thinnest interfacial layer which was caused by Ta-silicate decomposition to Ta₂O₅ and SiO₂. In addition, the electrical properties were improved after annealing treatments. Our results suggest that an annealing treatment at 700 °C results in the highest capacitance and the lowest leakage current in Ta₂O₅ films due to the thinnest interfacial layer and non-crystallization.     

Structural and electrical properties of HfO2 with topnitrogen incorporated layer

A novel technique to control the nitrogen profile in HfO₂ gate dielectric was developed using a reactive sputtering method. The incorporation of nitrogen in the upper layer of HfO₂ was achieved by sputter depositing a thin Hf_xN_y layer on HfO₂, followed by reoxidation. This technique resulted in an improved output characteristics compared to the control sample. Leakage current density was significantly reduced by two orders of magnitude. The thermal stability in terms of structural and electrical properties was also enhanced, indicating that the nitrogen-doped process is effective in preventing oxygen diffusion through HfO₂. Boron penetration immunity was also improved by nitrogen-incorporation. It is concluded that the nitrogen-incorporation process is a promising technique to obtain high-k dielectric with thin equivalent oxide thickness and good interfacial quality     

Comparison of interfacial and electrical properties between Al2O3 and ZnO as interface passivation layer of GaAs MOS device with HfTiO gate dielectric

GaAs metal–oxide–semiconductor(MOS) capacitors with HfTiO as the gate dielectric and Al2O3 or ZnO as the interface passivation layer(IPL) are fabricated. X-ray photoelectron spectroscopy reveals that the Al2O3 IPL is more effective in suppressing the formation of native oxides and As diffusion than the ZnO IPL. Consequently, experimental results show that the device with Al2O3 IPL exhibits better interfacial and electrical properties than the device with ZnO IPL: lower interface-state density(7.21012 eV1cm2/, lower leakage current density(3.60107A/cm2 at Vg D1 V) and good C–V behavior.     

Influences of bottom electrode TaN on electrical characteristics for metal–HfO2–metal capacitors

For TaN–HfO₂–TaN_x capacitors, the effects of bottom electrode TaN_x with different nitrogen contents on electrical characteristics are exhibited. An obvious oxygen deficiency can be found in HfO₂ film by AES analysis for the sample with bottom electrode TaN_x sputtered at a N₂/(N₂ + Ar) flow ratio of 10%. The bottom electrode TaN_x films with different nitrogen contents apparently affect HfO₂/TaN_x interfacial property and electrical characteristic of follow-up deposited HfO₂ film. Experimental results reveal that the more defective TaN_x structure can induce more oxygen vacancies in subsequently deposited HfO₂ film and result in a higher leakage current density and a worse breakdown electric field. Two factors affect these electrical characteristics including interfacial stress and oxygen vacancy. It indicates that interfacial stress due to various stochiometric TaN_x structure dominates the voltage linearity property of capacitance, but more leak paths and local field breakdown defects can be induced by interfacial stress and oxygen vacancy. Better electrical characteristics can be attained for the sample with bottom electrode TaN_x sputtered at a N₂/(N₂ + Ar) flow ratio of 20%.     

The effect of blocking layer of Al2O3 on thermal stability and electrical properties of HfO2 dielectric films deposited on SiGe layer

HfO₂ dielectric films with a blocking layer (BL) of Al₂O₃ on Si_0.8Ge_0.2 were treated with rapid thermal annealing process. The effect of BL on thermal stability and electrical properties was reported. X-ray photoelectron spectroscopy suggested that BL could suppress the further growth of the interfacial layer composed of SiO_x and GeO_x, and lead to the decomposition of GeO_x and the saturation of O vacancy in SiO_x structure. High-resolution transmission electron microscopy indicated that BL would keep HfO₂ amorphous after annealed treatment. Electrical measurements indicated that there was no stretch-out in capacitance-voltage curves, the accumulation region was flat, and leakage current was reduced for the sample with BL.     

Interface composition of atomic layer deposited HfO2 and Al2O3 thin films on InAs studied by X-ray photoemission spectroscopy

We present a synchrotron-based XPS investigation on the interface between InAs and Al₂O₃ or HfO₂ layers, deposited by ALD at different temperatures, for InAs substrates with different surface orientations as well as for InAs nanowires. We reveal the composition of the native Oxide and how the high-κ layer deposition reduces Oxide components. We demonstrate some of the advantages in using synchrotron radiation revealing the variation in Oxide composition as a function of depth into the subsurface region and how we can indentify Oxides even on nanowires covering only a small fraction of the surface.     

Grain boundary mediated leakage current in polycrystalline HfO2 films

In this work, we combine conductive atomic force microscopy (CAFM) and first principles calculations to investigate leakage current in thin polycrystalline HfO₂ films. A clear correlation between the presence of grain boundaries and increased leakage current through the film is demonstrated. The effect is a result of a number of related factors, including local reduction in the oxide film thickness near grain boundaries, the intrinsic electronic properties of grain boundaries which enhance direct tunnelling relative to the bulk, and segregation of oxygen vacancy defects which increase trap assisted tunnelling currents. These results highlight the important role of grain boundaries in determining the electrical properties of polycrystalline HfO₂ films with relevance to applications in advanced logic and memory devices.     

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.     

Improvement on low-temperature deposited HfO2 film and interfacial layer by high-pressure oxygen treatment

In this study, high-pressure oxygen (O₂ and O₂ + UV light) technologies were employed to effectively improve the properties of low-temperature-deposited metal oxide dielectric films and interfacial layer. In this work, 13 nm HfO₂ thin films were deposited by sputtering method at room temperature. Then, the oxygen treatments with a high-pressure of 1500 psi at 150 °C were performed to replace the conventional high temperature annealing. According to the XPS analyses, integration area of the absorption peaks of O-Hf and O-Hf-Si bonding energies apparently raise and the quantity of oxygen in deposited thin films also increases from XPS measurement. In addition, the leakage current density of standard HfO₂ film after O₂ and O₂ + UV light treatments can be improved from 3.12 × 10⁻⁶ A/cm² to 6.27 × 10⁻⁷ and 1.3 × 10⁻⁸ A/cm² at |Vg| = 3 V. The proposed low-temperature and high pressure O₂ or O₂ + UV light treatment for improving high-k dielectric films is applicable for the future flexible electronics.     

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.     

Influence of post deposition annealing on Y2O3-gated GaAs MOS capacitors and their reliability issues

The feasibility of employing yttrium oxide (Y₂O₃) as high-k gate dielectrics for GaAs metal-oxide-semiconductor (MOS) devices has been investigated. MOS capacitors were fabricated using RF-sputtered deposited Y₂O₃ films on NH₄OH treated n-GaAs substrate. Indeed high-k (Y₂O₃)/GaAs MOS capacitors exhibiting fairly good electrical characteristics, for instance, especially low leakage current density, low hysteresis and allowable density of interface states, have been achieved. The effects of several annealing treatments on Y₂O₃-gated GaAs MOS capacitors have been investigated in order to optimize the process conditions. A decrease in accumulation capacitance (C_acc) following PDA effectively increases the equivalent oxide thickness (EOT), which is predicted to be correlated with the growth and continuous increase in the physical thickness of a lower-k inter-layer sandwiched between Y₂O₃ and GaAs. However, leakage currents and interface trap densities are reduced with higher values of annealing temperature. The variation of current density with an equivalent oxide thickness (EOT) has also been investigated.     

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%.     

Improving electrical characteristics of W/HfO2/In0.53Ga0.47As gate stacks by altering deposition techniques

The effects of controlling InGaAs substrate temperature during electron beam deposition of HfO₂ on electrical characteristics of W/HfO₂/n-In_0.53Ga_0.47As capacitors are investigated. It is found that by depositing a thin HfO₂ layer at the interface when substrate temperature is raised to 300 °C, frequency dispersion at depletion and accumulation conditions is reduced and interface state density is lowered regardless of the HfO₂ thickness. Cross-sectional transmission electron microscopy images have revealed that the formation of mesoscopic voids in the InGaAs substrate near the interface is suppressed with HfO₂deposition at 300 °C at the interface. A band diagram with an additional bulk trap energy level has been proposed to explain the frequency dispersion and conductance peaks at accumulation condition.