Influence of annealing temperature on passivation performance of thermal atomic layer deposition Al_2O_3 films

Chemical and field-effect passivation of atomic layer deposition （ALD） Al2O3 films are investigated, mainly by corona charging measurement. The interface structure and material properties are characterized by transmission electron microscopy （TEM） and X-ray photoelectron spectroscopy （XPS）, respectively. Passivation performance is improved remarkably by annealing at temperatures of 450 ℃ and 500 ℃, while the improvement is quite weak at 600 ℃, which can be attributed to the poor quality of chemical passivation. An increase of fixed negative charge density in the films during annealing can be explained by the Al2O3/Si interface structural change. The Al–OH groups play an important role in chemical passivation, and the Al–OH concentration in an as-deposited film subsequently determines the passivation quality of that film when it is annealed, to a certain degree.     

Fabricating GeO_2 passivation layer by N_2O plasma oxidation for Ge NMOSFETs application

In this paper, oxidation of Ge surface by N2O plasma is presented and experimentally demonstrated. Results show that1.0-nm GeO2is achieved after 120-s N2O plasma oxidation at 300?C. The GeO2/Ge interface is atomically smooth. The interface state density of Ge surface after N2O plasma passivation is about ～ 3 × 1011cm-2·eV-1. With GeO2passivation,the hysteresis of metal–oxide–semiconductor(MOS) capacitor with Al2O3serving as gate dielectric is reduced to ～ 50 mV,compared with ～ 130 mV of the untreated one. The Fermi-level at GeO2/Ge interface is unpinned, and the surface potential is effectively modulated by the gate voltage.     

Fabricating GeO2 passivation layer by N20 plasma oxidation for Ge NMOSFETs application

In this paper, oxidation of Ge surface by N2O plasma is presented and experimentally demonstrated. Results show that 1.0-nm GeO2 is achieved after 120-s N20 plasma oxidation at 300 ℃. The GeO2/Ge interface is atomically smooth. The interface state density of Ge surface after N20 plasma passivation is about - 3 × 1011 cm-2.eV-1. With GeO2 passivation, the hysteresis of metal-oxide-semiconductor （MOS） capacitor with A1203 serving as gate dielectric is reduced to - 50 mV, compared with - 130 mV of the untreated one. The Fermi-level at GeO2/Ge interface is unpinned, and the surface potential is effectively modulated by the gate voltage.     

A model for the thermal conductivity of nanofluids – the effect of interfacial layer

A model for predicting the effective thermal conductivity of nanofluids is proposed. It has been documented that the interfacial layer at the solid (particle)/liquid interface and particle size is one of the major mechanisms for enhancing the thermal conductivity of nanofluids. Comparing with other classical models, the proposed model takes into account some additional effects including volume fraction, thickness, thermal conductivity of the interfacial layer and particle size. The proposed model is found to be better than the existing models since the predicted effective thermal conductivity of different types of nanofluids are closer to the experimental results.     

Influences of different oxidants on characteristics of La_2O_3/Al_2O_3 nanolaminates deposited by atomic layer deposition

A comparative study of two kinds of oxidants(H_2O and O_3) with the combination of two metal precursors(TMA and La(~iPrCp)_3) for atomic layer deposition(ALD) La_2O_3/Al_2O_3 nanolaminates is carried out. The effects of different oxidants on the physical properties and electrical characteristics of La_2O_3/Al_2O_3 nanolaminates are studied. Initial testing results indicate that La_2O_3/Al_2O_3 nanolaminates could avoid moisture absorption in the air after thermal annealing. However, moisture absorption occurs in H_2O-based La_2O_3/Al_2O_3 nanolaminates due to the residue hydroxyl/hydrogen groups during annealing. As a result, roughness enhancement, band offset variation, low dielectric constant and poor electrical characteristics are measured because the properties of H_2O-based La_2O_3/Al_2O_3 nanolaminates are deteriorated. Addition thermal annealing effects on the properties of O_3-based La_2O_3/Al_2O_3 nanolaminates indicate that O_3 is a more appropriate oxidant to deposit La_2O_3/Al_2O_3 nanolaminates for electron devices application.     

Equivalent oxide thickness scaling of Al2O3/Ge metal-oxide-semiconductor capacitors with ozone post oxidation

Aluminum-oxide films deposited as gate dielectrics on germanium （Ge） by atomic layer deposition were post oxidized in an ozone atmosphere. No additional interfacial layer was electron microscopy and X-ray photoelectron spectroscopy detected by the high-resolution cross-sectional transmission measurements made after the ozone post oxidation （OPO） treatment. Decreases in the equivalent oxide thickness of the OPO-treated Al2O3/Ge MOS capacitors were confirmed. Furthermore, a continuous decrease in the gate leakage current was achieved with increasing OPO treatment time. The results can be attributed to the film quality having been improved by the OPO treatment.     

Atomic-layer-deposited Al_2O_3 and HfO_2 on InAlAs: A comparative study of interfacial and electrical characteristics

Al_2O_3 and HfO_2 thin films are separately deposited on n-type InAlAs epitaxial layers by using atomic layer deposition(ALD).The interfacial properties are revealed by angle-resolved x-ray photoelectron spectroscopy(AR-XPS).It is demonstrated that the Al_2O_3 layer can reduce interfacial oxidation and trap charge formation.The gate leakage current densities are 1.37×10~6 A/cm~2 and 3.22×10~6 A/cm~2 at+1V for the Al_2O_3/InAlAs and HfO_2/InAlAs MOS capacitors respectively.Compared with the HfO_2/InAlAs metal-oxide-semiconductor(MOS) capacitor,the Al_2O_3/InAlAS MOS capacitor exhibits good electrical properties in reducing gate leakage current,narrowing down the hysteresis loop,shrinking stretch-out of the C-V characteristics,and significantly reducing the oxide trapped charge(Q_(ot)) value and the interface state density(D_(it)).     

Interface states in Al_2O_3/AlGaN/GaN metal-oxide-semiconductor structure by frequency dependent conductance technique

Frequency dependent conductance measurements are implemented to investigate the interface states in Al2O3/AlGaN/GaN metal-oxide-semiconductor(MOS) structures. Two types of device structures, namely, the recessed gate structure(RGS) and the normal gate structure(NGS), are studied in the experiment. Interface trap parameters including trap density Dit, trap time constant τit, and trap state energy ETin both devices have been determined. Furthermore,the obtained results demonstrate that the gate recess process can induce extra traps with shallower energy levels at the Al2O3/AlGaN interface due to the damage on the surface of the AlGaN barrier layer resulting from reactive ion etching(RIE).     

Influence of strain distribution on the morphology evolution of a Ge/GeO_2 core/shell nanoparticle confined in ultrathin Al_2O_3 thin film by surface oxidation

The influence of strain distribution on morphology evolution of Ge/GeO2 core/shell nanoparticle confined in ultrathin Al2O3 thin film by surface oxidation is investigated. A finite-element simulation is performed to simulate the morphology evolution of the confined Ge/GeO2 core/shell nanoparticle under the influence of the local strain distribution. It indicates that the resultant oxidation-related morphology of Ge/GeO2 core/shell nanoparticle confined in ultrathin film is strongly dependent on the local strain distribution. On the other hand, the strain gradients applied on the confined GeO2 shell can be modified by the formation of polycrystalline GeO2 shell, which has potential application in tailoring the microstructure and morphology evolution of the Ge/GeO2 core/shell nanoparticle.     

蓝宝石Al_2O_3晶体的高压热传导系数研究

对蓝宝石Al2O3晶体在高压下的热传导系数这一在的理论和实验仍处于探索中的问题,本文从较严格的固体理论出发,考虑到晶格声子的最小平均自由程、Debye温度、Gruneisen参数以及冲击温度在冲击压缩状态下的变化,进而对在高压实验中最常用的窗口材料蓝宝石Al2O3晶体的导热系数进行了理论分析,计算结果较好解释了实验结果.     

热激发效应对界面摩擦的影响

论文主要从微观角度研究摩擦热产生的机理及摩擦热对摩擦性能的影响. 依据固体物理学中原子热振动理论, 以界面摩擦为研究对象, 从分析界面原子的受迫振动出发, 得出界面摩擦过程中原子的振动实际上是自激振动和受迫振动的叠加, 界面原子在非平衡状态下的热振动将导致声子的激发和湮灭, 进而导致摩擦热的产生, 摩擦界面的温度升高. 然后, 从温度对界面原子能级分布和跃迁的影响角度探讨了热激发效应对界面摩擦的影响, 分析得出如下结论: 温度低时, 界面原子处在激发态的概率随着温度的升高而增加, 导致摩擦系数随温度增加而增加; 温度在100 K附近界面原子处在激发态的概率出现峰值, 导致摩擦系数出现峰值; 当温度高于临界值后, 摩擦系数随温度的升高反而会降低. 最后将本文的理论分析的结果与他人的实验结果对比, 显示两者的趋势一致, 表明本文提出的理论和方法可行.     

反应溅射法制备Y_2O_3种子层研究

采用直流磁控反应溅射法在双轴织构的镍钨合金(Ni-5%W)基带上生长Y2O3种子层。研究了由于水分压导致的金属靶材的氧化问题而引起反应溅射的迟滞效应,在其他最优工艺条件下通过水分压系列的试验,通过试验得出溅射电压和水分压的关系和溅射电流和水分压平衡点Pb的关系,以及水分压平衡点为反应溅射法制备Y2O3种子层薄膜的水分压最优化条件。在优化工艺条件下,反应溅射法可以制得C轴单一取向的Y2O3种子层,其面内外半高宽可达到3.874°和4.914°。     

热原子层沉积氧化铝对硅的钝化性能及热稳定性

原子层沉积氧化铝已经成为应用于钝化发射极和背面点接触（PERC）型晶硅太阳能电池优异的钝化材料．对于基于丝网印刷技术的太阳能电池,钝化材料的钝化效果及其热稳定性是非常重要的．本文在太阳能级硅片上用热原子层沉积设备制备了20nm和30nm的氧化铝,少子寿命测试结果显示初始沉积的氧化铝薄膜具有一定的钝化效果,在退火后可达到100μs以上,相当于硅表面复合速度小于100cm／s．经过制备传统晶硅太阳能电池的烧结炉后,少子寿命能够保持在烧结前的一半以上,可应用于工业PERC型电池的制备．通过电子显微镜观察到了较厚的氧化铝薄膜有气泡,解释了30nm氧化铝比20nm氧化铝钝化性能和稳定性更差的异常表现．     

Performance and reliability improvement of La_2O_3/Al_2O_3 nanolaminates using ultraviolet ozone post treatment

La-based binary or ternary compounds have recently attracted a great deal of attention as a potential candidate to replace the currently used Hf-based dielectrics in future transistor and capacitor devices for sub-22 generation. However, the hygroscopic nature of La₂O₃ hampers its application as dielectrics in electron devices. To cope with this challenge, ultraviolet (UV) ozone post treatment is proposed to suppress the moisture absorption in the H₂O-based atomic layer deposition (ALD) La₂O₃/Al₂O₃ nanolaminates which is related to the residual hydroxyl/hydrogen groups after annealing. The x-ray photoelectron spectroscopy (XPS) and conductive atomic force microscopy (AFM) results indicate that the moisture absorption of the H₂O-based ALD La₂O₃/Al₂O₃ nanolaminates is efficiently suppressed after 600 ℃ annealing, and the electrical characteristics are greatly improved.     

Impact of thermostat on interfacial thermal conductance prediction from non-equilibrium molecular dynamics simulations

The knowledge of interfacial thermal conductance (ITC) is key to understand thermal transport in nanostructures. The non-equilibrium molecular dynamics (NEMD) simulation is a useful tool to calculate the ITC. In this study, we investigate the impact of thermostat on the prediction of the ITC. The Langevin thermostat is found to result in larger ITC than the Nose-Hoover thermostat. In addition, the results from NEMD simulations with the Nose-Hoover thermostat exhibit strong size effect of thermal reservoirs. Detailed spectral heat flux decomposition and modal temperature calculation reveal that the acoustic phonons in hot and cold thermal reservoirs are of smaller temperature difference than optical phonons when using the Nose-Hoover thermostat, while phonons in the Langevin thermostat are of identical temperatures. Such a non-equilibrium state of phonons in the case of the Nose-Hoover thermostat reduces the heat flux of low-to-middle-frequency phonons. We also discuss how enlarging the reservoirs or adding an epitaxial rough wall to the reservoirs affects the predicted ITC, and find that these attempts could help to thermalize the phonons, but still underestimate the heat flux from low-frequency phonons.     

Effects of Al particles and thin layer on thermal expansion and conductivity of Al-Y_2Mo_3O_(12) cermets

Low thermal expansion composites are difficult to obtain by using Al with larger positive thermal expansion coefficient(TEC) and the materials with smaller negative TECs. In this investigation, Y_2Mo_3O_(12) with larger negative TEC is used to combine with Al to obtain a low thermal expansion composite with high conductivity. The TEC of Al is reduced by 19%for a ratio Al:Y_2Mo_3O_(12) of 0.3118. When the mass ratio of Al:Y_2Mo_3O_(12) increases to 2.0000, the conductivity of the composite increases so much that a transformation from capacitance to pure resistance appears. The results suggest that Y_2Mo_3O_(12) plays a dominant role in the composite for low content of Al(presenting isolate particles), while the content of Al increases enough to contact each other, the composite presents mainly the property of Al. For the effect of high content Al, it is considered that Al is squeezed out of the cermets during the uniaxial pressure process to form a thin layer on the surface.     

Effect of patterning on thermal agglomeration of ultrathin silicon-on-insulator layer

Effect of patterning on thermal agglomeration of ultrathin silicon-on-insulator (SOI) layer has been studied. A square-shaped 12 nm thick SOI layer was patterned by lithography and by selective etching with a KOH solution. The structural change by ultrahigh vacuum annealing in a temperature range of 900–1100 °C was observed by atomic force microscopy. The agglomeration takes place preferentially from the pattern edges at a lower annealing temperature than that for the unpatterned layer, indicating enhanced diffusion of Si atoms at the edges. Additionally, the patterning causes formation of smaller islands than those for the unpatterned layer, reflecting that the patterning limits the amount of Si atoms supplied for the island formation.     

基于Al2O3/Pt纳米晶/HfO2叠层的MOS电容存储效应研究

采用电子束蒸发Pt和后快速热退火的方法,研究了退火条件对Pt纳米晶的生长特性的影响,结果显示Pt纳米晶的密度随退火温度的升高和退火时间的延长均表现出先增大后减小的趋势.在800℃下退火20 s能得到分布均匀的、密度为30×10¹¹ cm^-2的Pt纳米晶.进一步研究了基于Al₂O₃/Pt纳米晶/HfO₂叠层的MOS电容结构的存储效应,表明其在-3—+8 V扫描电压范围下C-V< 关键词： Pt纳米晶 快速热退火 原子层淀积 存储效应     

循环氧化/退火制备GeOI薄膜材料及其性质研究

采用超高真空化学气相淀积系统在SOI(绝缘体上硅)衬底上生长了Si_0.82Ge_0.18外延层,通过循环氧化/退火工艺,制备出Ge组分从0.24到1的绝缘体上锗硅(SGOI)材料.采用高分辨透射电镜、拉曼散射光谱和光致发光谱表征了其结构及光学性质,对氧化过程中SiGe层中的Ge组分和应变的演变进行了分析.最后制备出11 nm厚的绝缘体上Ge材料(GeOI),具有完整的晶格结构和平整的界面.室温下观测到绝缘体上Ge直接带跃迁光致发光,发光峰值位于1540 nm,发光 关键词： GeOI 氧化 退火 光致发光谱     

Ultraviolet detectors based on ZnO films by thermal oxidation of Zn metallic films

Metallic Zn films were deposited on glass substrates by electron-beam evaporation. ZnO films were synthesized by thermal oxidation of Zn metallic films in air. At the annealing temperature of 550 °C, ZnO nanowires appeared on the surface, which mainly result from the decrease of oxidation rate. A ZnO ultraviolet photodetector was fabricated based on a metal-semiconductor-metal planar structure. The detector showed a large UV photoresponse with an increase of two orders of magnitude. It is concluded that promising UV detectors can be obtained on ZnO films by thermal oxidation of Zn metallic films. The ways of performing spectral response measurements for polycrystalline ZnO films are also discussed.