High-reflectivity HfO2/SiO2 ultraviolet mirrors

High-reflectivity dense multilayer coatings were produced for the ultraviolet spectral region. Thin-film single layers and UV mirrors were deposited by ion plating and plasma ion-assisted deposition high-energetic technologies. Optical characterizations of HfO2 and SiO2 single layers are made. The optical constants obtained for these two materials are presented. HfO2 and SiO2 mirrors with a reflectance of approximately 99% near 250 nm are reported.     

Tunneling currents through ultra thin HfO2/Al2O3/HfO2 triple layer gate dielectrics for advanced MIS devices

The dramatic scaling down of silicon integrated circuits has led to an intensive study of high dielectric constant materials as an alternative to the conventional insulators currently employed in microelectronics, i.e., silicon dioxide, silicon nitride, or oxynitride, which seem to have reached their physical limit in terms of reduction of thickness due to large leakage gate current. Introducing a physically thicker high-K material can reduce the leakage current to the acceptable limit. There are many potential candidates for high-K gate dielectrics with the K-valves ranging from 9 to 80. These are Al₂O₃, Y₂O₃, La₂O₃, Ta₂O₅, TiO₂, ZrO₂ and HfO₂. It is important to study the various leakage mechanisms in these films with the aim of improving their leakage current characteristics for use in advanced microelectronics devices. A procedure for calculating the tunneling current for stacked dielectrics is developed and subsequently applied to ultra thin films with equivalent oxide thickness (EOT) of 3.0 nm. Tunneling currents have been calculated as a function of gate voltage for different structures. Direct and Fowler-Nordheim tunneling currents through triple layer dielectrics are investigated for substrate injection. Using exact tunneling transmission calculations, current density–gate voltage (J _g?V _g) characteristics for ultra thin single layer gate dielectrics with different thicknesses have been shown to agree well with recently reported experiments. Extensions of this approach demonstrate that tunneling currents in HfO₂/Al₂O₃/HfO₂ structure with equivalent oxide thickness of 3.0 nm can be significantly lower than that through single layer oxides of the same thickness.     

HfO2/SiO2 chirped mirrors manufactured by electron beam evaporation

A HfO2/SiO2 chirped mirror was manufactured by electron beam evaporation to increase the laser resistance. The hybrid monitoring strategy utilizing both monochromatic monitoring and quartz crystal monitoring was applied to the deposition compared to the single optical monitoring method. The coatings were characterized by transmission spectrophotometer and white light interferometry, and the experimental results showed that the chirped mirror monitored with the hybrid strategy possessed high reflectivity (>99.7%) and tolerable group delay dispersion oscillation (-50±20?fs2) in the spectra range of 740-860?nm.     

Laser damage study of nodules in electron-beam-evaporated HfO2/SiO2 high reflectors

A reactive electron beam evaporation process was used to fabricate 1.064?μm HfO2/SiO2 high reflectors. The deposition process was optimized to reduce the nodular density. Cross-sectioning of nodular defects by a focused ion-beam milling instrument showed that the nodule seeds were the residual particles on the substrate and the particulates from the silica source "splitting." After optimizing the substrate preparation procedure and the evaporation process, a low nodular density of 2.7/mm2 was achieved. The laser damage test revealed that the ejection fluences and damage growth behaviors of nodules created from deep or shallow seeds were totally different. A mechanism based on directional plasma scald was proposed to interpret observed damage growth phenomenon.     

Nanostructuring of ultra-thin HfO2 layers for high-k/III-V device application

We report on the nanopatterning by electron beam lithography (EBL) and reactive ion etching (RIE) in a SF6/Ar+ plasma of ultra-thin HfO2 films deposited on GaAs (001) substrates for gate oxide application in next generation III-V metal-oxide-semiconductor field effect transistors (MOSFETs). Characterization of the HfO2/GaAs nanostructured samples by atomic force microscopy (AFM), high-resolution scanning electron microscopy (HRSEM), energy-dispersive X-ray spectroscopy microanalysis (EDX) and transmission electron microscopy (TEM) has shown the formation of well defined HfO2 patterns with nanometre-scale linewidth control and anisotropic profiles. In addition, atomically smooth, stoichiometric and residue-free bottom GaAs etched lines with a lateral dimension of approximately 50 nm have been demonstrated.     

Proton-based total-dose irradiation effects on Cu/HfO2:Cu/Pt ReRAM devices

The resistive switching properties of Cu-doped-HfO(2)-based resistive-random-access-memory (ReRAM) devices are investigated under proton-based irradiations with different high-range total doses of 1.5, 3 and 5 Giga-rad[Si]. The measurement results obtained immediately after irradiation demonstrate that the proton-based total dose will introduce significant variations in the operation voltages and resistance values. These effects are enhanced almost linearly when the dose increases from 1.5 to 5 Giga-rad[Si]. Furthermore, five days after irradiation, the electrical properties of the device rebound, resulting in reduced operation voltages and resistance values. This is consistent with the time-dependent super-recovery behavior observed previously in CMOS gate oxide. These results can be explained by the proton irradiation effect on the electron/hole trap density inside HfO(2) and its impact on ReRAM device metallic filament formation-and-rupture, which is based on electrolyte theory.     

HfO2薄膜的反应离子刻蚀特性研究

研究了HfO2薄膜在CHF3/Ar和SF6/Ar等气体中的反应离子刻蚀机理.结果表明刻蚀气体的组分和射频偏压对刻蚀速率有较大影响,而气体流量影响不大.CHF3和SF6与HfO2的反应产物具有较好的挥发性,Ar的引入不仅可以打破分子之间的键合促进刻蚀产物的形成,而且通过轰击加快产物从材料表面解吸,从而提高HfO2刻蚀速率.AFM测量结果表明刻蚀降低了HfO2表面粗糙度,显示刻蚀工艺对材料的低损伤.     

Optical properties of the Al2O3/SiO2 and Al2O3/HfO2/SiO2 antireflective coatings

Investigations of bilayer and trilayer Al₂O₃/SiO₂ and Al₂O₃/HfO₂/SiO₂ antireflective coatings are presented in this paper. The oxide films were deposited on a heated quartz glass by e-gun evaporation in a vacuum of 5 × 10^?3 [Pa] in the presence of oxygen. Depositions were performed at three different temperatures of the substrates: 100 °C, 200 °C and 300 °C. The coatings were deposited onto optical quartz glass (Corning HPFS). The thickness and deposition rate were controlled with Inficon XTC/2 thickness measuring system. Deposition rate was equal to 0.6 nm/s for Al₂O₃, 0.6 nm ? 0.8 nm/s for HfO₂ and 0.6 nm/s for SiO₂. Simulations leading to optimization of the thin film thickness and the experimental results of optical measurements, which were carried out during and after the deposition process, have been presented. The optical thickness values, obtained from the measurements performed during the deposition process were as follows: 78 nm/78 nm for Al₂O₃/SiO₂ and 78 nm/156 nm/78 nm for Al₂O₃/HfO₂/SiO₂. The results were then checked by ellipsometric technique. Reflectance of the films depended on the substrate temperature during the deposition process. Starting from 240 nm to the beginning of visible region, the average reflectance of the trilayer system was below 1 % and for the bilayer, minima of the reflectance were equal to 1.6 %, 1.15 % and 0.8 % for deposition temperatures of 100 °C, 200 °C and 300 °C, respectively.     

Elastic properties of partially-stabilized HfO2 compositions

The effect of metastable tetragonal HfO₂ on the elastic properties of partially stabilized HfO₂ doped with Er₂O₃, Y₂O₃ or Eu₂O₃ was studied using a sonic resonance technique. The elastic moduli were monitored at elevated temperatures to follow the effect of the tetragonal-monoclinic phase transformation. Elastic moduli were also determined as a function of porosity and found to follow linear relations. The non-linear modulus versus temperature relations from room temperature to 500° C are explained in terms of the oxygen vacancies present in the fluorite type phase.     

Atomic layer deposition of HfO2 thin films and nanolayered HfO2–Al2O3–Nb2O5 dielectrics

Smooth, 4–6-nm thick hafnium oxide films were grown by atomic layer deposition from HfI₄ or HfCl₄ and H₂O on SiO₂/Si(1 0 0) substrates at 300 °C. Non-uniform films were obtained on hydrogen-terminated Si(1 0 0). The stoichiometry of the films corresponded to that of HfO₂. The films contained small amounts of residual chlorine and iodine. The films deposited on SiO₂/Si(1 0 0) were amorphous, but crystallized upon annealing at 1000 °C. In order to decrease the conductivity, the HfO₂ films were mixed with Al₂O₃, and to increase the capacitance, the films were mixed with Nb₂O₅. The capacitance–voltage curves of the Hf–Al–O mixture films showed hysteresis. The capacitance–voltage curves of HfO₂ films and mixtures of Hf–Al–Nb–O were hysteresis free.     

Preparation of ZrO2-CeO2 and HfO2-CeO2 nanopowders

We prepared weakly agglomerated powders of ZrO₂-CeO₂ and HfO₂-CeO₂ solid solutions 5–8 nm in particle size, consisting of monoclinic and tetragonal phases. After heat treatment at 1200°C, the crystallite size was 30 and 14 nm, respectively. We also examined the effect of precipitate freeze drying on the crystallization of hafnia-based solid solutions containing up to 20 mol % CeO₂.     

Contact size-dependent switching instabilities in HfO2 RRAM

Journal of Materials Science: Materials in Electronics - A comprehensive understanding of the resistive switching mechanisms that activate REDOX-based random access memory devices is necessary to...     

制备工艺条件对HfO_2薄膜结构和性能的影响

用电子束蒸发、离子束辅助、反应磁控溅射三种方法在石英衬底上制备了氧化铪薄膜.利用掠角X射线衍射和扫描电镜分析了不同制备工艺条件下氧化铪薄膜的晶体结构和显微结构,用紫外.可见分光光度计、椭偏仪、和纳米硬度计分别测试了不同制备工艺条件下氧化铪薄膜的可见透射光谱、光学常数和硬度.结果表明薄膜的晶体结构、显微结构、光学性能和硬度等都与制备工艺有着密切的关系,电子束蒸发制备的薄膜为非晶相,而离子束辅助和反应磁控溅射制备的薄膜为多晶相,三种方法制备的氧化铪薄膜都为柱状结构,电子束蒸发和离子束辅助制备的薄膜色散严重,但反应磁控溅射制备的薄膜吸收较大,反应磁控溅射制备薄膜的硬度远大于电子束蒸发和离子束辅助制备薄膜的硬度.并分别用薄膜成核长大热力学原理和薄膜结构区域模型解释了不同工艺条件下氧化铪薄膜晶体结构和显微结构不同的原因.     

50-nm fully depleted SOI CMOS technology with HfO/sub 2/ gate dielectric and TiN gate

In this paper, we demonstrate for the first time CMOS thin-film metal gate FDSOI devices using HfO/sub 2/ gate dielectric at the 50-nm physical gate length. Symmetric V/sub T/ is achieved for long-channel nMOS and pMOS devices using midgap TiN single metal gate with undoped channel and high-k dielectric. The devices show excellent performance with a I/sub on/=500 /spl mu/A//spl mu/m and I/sub off/=10 nA//spl mu/m at V/sub DD/=1.2 V for nMOSFET and I/sub on/=212 /spl mu/A//spl mu/m and I/sub off/=44 pA//spl mu/m at V/sub DD/=-1.2 V for pMOSFET, with a CET=30 /spl Aring/ and a gate length of 50 nm. DIBL and SS values as low as 70 mV/V nand 77 mV/dec, respectively, are obtained with a silicon film thickness of 14 nm. Ring oscillators with 15 ps stage delay at V/sub DD/=1.2 V are also realized.     

Annealing effect on the formation of high-k dielectric in the W/ultrathin HfO2/Si-substrate system

Using a method of high-frequency magnetron sputtering, the structures W(150 nm)/HfO₂(5 nm)/Si(100) were prepared and were further annealed either at 500°C in vacuum for 30 min or in an atmosphere of argon at 950°C for 12 s. Study of the capacitance-voltage characteristics of these structures showed that high-temperature annealing leads to a decrease in the maximum specific capacitance in accumulation (from 4.8 × 10^?6 to 3.2 × 10^?6 F/cm²) and dielectric constant (from 27 to 23). Using time-of-flight secondary-ion mass spectrometry, it is established that growth of a WO _x phase at the W/HfO₂ interface and a HfSi _x O _y silicate phase at the HfO₂/Si (100) interface occurs during annealing. In addition, the total thickness of the intermediate oxide layer exceeds the thickness of the initial HfO₂ film by 30%.     

O2/Ar气体流量比对射频磁控溅射HfO2薄膜的影响

采用射频磁控溅射法,以HfO2陶瓷作为靶材,在石英衬底上制备了HfO2薄膜.通过椭圆偏振光谱仪(SE)、X射线衍射(XRD)、场发射扫描电子显微镜(FE-SEM)研究了不同O2/Ar气体流量比对薄膜沉积速率、结构、形貌等的影响.结果表明,随着O2/Ar气体流量比从0增加到0.50,薄膜的沉积速率逐渐下降.O2/Ar气体...     

Amorphous InGaZnO thin film transistors with SiO2/HfO2 double-layer gate dielectric fabricated at low temperature

Amorphous InGaZnO (a-IGZO) thin film transistors (TFTs) with double-layer gate dielectric were fabricated at low temperature and characterized. A stacked 150 nm-thick SiO₂/50 nm-thick HfO₂ dielectric layer was employed to improve the capacitance and leakage characteristics of the gate oxide. The SiO₂/HfO₂ showed a higher capacitance of 35 nF/cm² and a lower leakage current density of 4.6 nA/cm² than 200 nm-thick SiO₂. The obtained saturation mobility (μ_sat), threshold voltage (V_th), and subthreshold swing (S) of the fabricated TFTs were 18.8 cm² V^?1 s^?1, 0.88 V, and 0.48 V/decade, respectively. Furthermore, it was found that oxygen pressure during the IGZO channel layer deposition had a great influence on the performance of the TFTs.     

HfO2薄膜的制备与光学性能

采用射频磁控反应溅射法，以高纯热压HfO2陶瓷为靶材，在Si衬底上成功制备出HfO2薄膜。系统研究了工艺参数对薄膜沉积速率的影响规律，并对薄膜的光学性能进行了研究。结果表明，射频功率对薄膜沉积速率的影响最为明显，O2／Ar流量比和衬底温度对沉积速率的作用不明显，所制备薄膜的折射率较高在近红外波段趋于1．95，在500-1650nm波段范围内薄膜几乎无吸收，透过率较高。     

Demonstration of synaptic and resistive switching characteristics in W/TiO2/HfO2/TaN memristor crossbar array for bioinspired neuromorphic computing

In this study,resistive random-access memory (RRAM)-based crossbar arrays with a memristor W/TiO2/HfO2/TaN structure were fabricated through atomic layer deposi...