室温下单晶硅压痕微裂纹的形成与扩展

用透射电镜定位观察研究了在室温下高纯单晶硅显微压痕表面radial脆性微裂纹的纳观形变 ,阐述了塑性变形对微裂纹形核、扩展及开裂的影响。发现 :室温下单晶硅的压痕前沿经历了极复杂的非线性演化 :前沿区的位错发射与运动 (Kcleave>Kemit时 )、解理微纹形核与扩展 (σ塞 >σth 时 )。观察到压痕前沿发生塑性诱导解理和解理胚不连续形核与扩展的过程     

籽晶粘接工艺对SiC单晶生长质量的影响

空洞等缺陷是SiC晶体生长中常见的缺陷之一。通过改进SiC籽晶粘接工艺,在SiC籽晶和籽晶托之间形成致密层,有效抑制了空洞缺陷的产生,改善了SiC晶体的结晶质量。采用该工艺生长的SiC晶体内已观察不到空洞缺陷,微管密度也得到抑制,晶体半峰宽40″,结晶质量良好。     

W/Al双层膜系的纳米压痕实验及有限元仿真

采用磁控溅射法在CAT.No.7101玻璃基底上沉积了W/Al双层金属膜,并对其进行纳米压痕实验。利用非线性有限元法对压痕过程进行仿真,分析了膜基体系的应力分布。结果表明:磁控溅射法制备的薄膜组织均匀、力学性能好。W/Al双层金属膜系中的W薄膜的弹性模量与硬度平均值分别为75.4335GPa、6.206GPa,其值与块状W材料的相应参数差别较大。仿真曲线与实验结果基本相符,能够反映出膜基体系的力学状态以及应力分布规律。     

单晶SiC电化学腐蚀及化学机械抛光

通过电化学工作站对4英寸(1英寸=2.54 cm)n型单晶SiC(4H-SiC)进行电化学腐蚀特性研究,采用36GPAW-TD单面抛光机对其Si面和C面进行了化学机械抛光(CMP)。结果表明,采用H2O2和NaClO作为氧化剂,均可促进SiC的电化学腐蚀并提高其抛光去除速率,其促进作用与氧化剂浓度和抛光液的pH值密切相关。选择含体积分数5%的H2O2、pH值为12的SiO2抛光液对SiC进行CMP,得到的Si面抛光速率可以达到285.7 nm/h。在含H2O2抛光液中引入适量的NaNO3和十二烷基硫酸钠,SiC表现出较高的腐蚀电位绝对值和去除速率。在H2O2和NaClO抛光液体系中,SiC的去除速率与其腐蚀电位的绝对值正相关,该结果对实际应用有一定的借鉴意义。     

SiC单晶生长界面形状计算机模型的建立及验证

利用多物理场耦合模拟软件研究了3英寸(1英寸=2.54 cm)碳化硅(SiC)单晶生长中感应线圈位置对单晶生长系统温度场的影响.分析了感应线圈位置变化对晶体表面径向温度、晶体内部轴向温度以及晶体生长界面形状的影响.同时分析了不同生长时期晶体的界面形状和各向温差的变化规律,建立了3英寸SiC单晶生长界面形状计算机模型,进而将计算机模拟得到的晶体界面形状与单晶生长对照实验获得晶体的界面形状相对比,验证了该模型的可靠性.以此为依据,优化了单晶生长工艺参数,获得了理想的适合3英寸SiC单晶生长的温度场,并成功获得了高质量的3英寸SiC单晶.     

SiC籽晶上生长AlN单晶的断裂特性研究

通过扫描电镜(SEM)观察了SiC籽晶上生长AlN单晶的断裂面形貌。模拟了SiC籽晶与AlN晶体之间的应力分布。通过计算不同晶面的面间距,确定了六方晶系的AlN晶体中m面为解理面。拉曼光谱仪对不同晶面的特性进行了表征。结果表明,断裂面为m面,即裂纹扩展并沿m面解理形成断裂面。切割面为c面,AlN沿垂直于c方向生长。拉曼光谱中波数为656.2 cm-1的（E2(high)声子模为AlN单晶中的特征拉曼峰） 声子模式的半高宽为6.5 cm-1,晶体质量高。残余的张应力是裂纹产生的主要原因。     

单晶硅纳米压痕过程的有限元模拟与实验验证

采用商用有限元软件ABAQUS建立了单晶硅纳米压痕过程的2D轴对称模型,通过分析模拟得到载荷-位移曲线,讨论了压头尖端半径、压头与样品间的摩擦系数对压痕过程的影响规律。为了验证模拟结果的有效性,用美国Hysitron公司的Triboindenter纳米压痕仪进行了实验。由仿真结果可知,在固定压深的条件下,增大压头尖端半径,所需施加的载荷增加,弹性回复程度增加。而摩擦系数的改变对压痕过程影响不大,可以在模拟中忽略不计。对比仿真曲线和实验曲线,实验曲线在卸载段55nm处出现了一明显拐点,使得其弹性回复程度远大于模拟的结果。这是由于高压诱导的相变导致了单晶硅纳米压痕过程中出现了复杂的本构关系,而有限元软件中还没有如此复杂的本构关系模型。     

基于纳米压痕法的SnBi-xNi钎料的塑性比较

借助纳米压痕的方法,采用压痕形成过程中塑性应变与总应变的比值来表征钎料塑性。对Sn Bi-x Ni(x=0,0.05,0.1,0.15和0.2)成分钎料的硬度、弹性模量及塑性进行了对比。结果表明:Sn58Bi钎料合金加入Ni元素后,钎料硬度和弹性模量升高。当Sn58Bi-x Ni钎料中Ni含量的质量分数为0.1%时,其硬度及弹性模量最大。当Ni质量分数超过0.1%时,钎料的硬度与弹性模量有所下降。当添加Ni元素质量分数为0.05%~0.1%时,钎料合金的组织得到了细化,钎料合金的塑性提高;当Ni质量分数大于0.15%时,钎料的塑性降低。     

含有空位缺陷的单晶锗纳米切削过程分子动力学仿真

针对含有空位缺陷的单晶锗纳米切削过程展开研究,利用分子动力学仿真软件构建了含有空位缺陷的单晶锗切削模型并进行了分子动力学仿真切削。文中从原子角度考虑了切削过程中系统势能的变化、切削力的变化,解释了材料的去除过程和切屑的形成机理,并分析了空位缺陷对切削的影响。结果显示在切削过程中,单晶锗晶体所含空位数越多则基础系统势能越大,且随着切削的进行系统势能逐渐增大。该结果表明空位缺陷的增加会加剧系统的不稳定性。     

纳米压痕和划痕法测定氧化硅薄膜材料的力学特性

为了研究不同制备工艺对材料力学性能的影响,选择了热氧化、LPCVD和PECVD三种典型工艺,在硅片上制备1μm氧化硅薄膜.通过纳米压痕和划痕检测可知,热氧化工艺制备的SiO2薄膜的硬度和模量最大,LPCVD制备的样品界面结合强度高于PECVD.纳米压痕和划痕技术为此提供了丰富的近表面弹塑性变形和断裂等的信息,是评价微米薄膜力学性能的有效手段.     

杂质对单晶硅材料硬度的作用

室温下使用维氏硬度计研究了硅单晶表面的接触损伤及硅单晶中杂质对表面损伤的影响 .实验发现 ,硅单晶的硬度不仅与晶体的本身特性——晶向有关 ,还与所掺入杂质的种类和浓度有关 .损伤造成的裂纹倾向于沿着〈1 1 0〉晶向扩展 ,而且 { 1 1 1 }面上的硬度要大于 { 1 0 0 }面 .重掺 n型单晶由于能带结构的变化而使硬度下降 ;相反 ,重掺 p型和掺氮单晶的硬度则由于掺入原子对位错的钉扎作用加强而有所提高     

Characterization of Epitaxial Indium Nitride Interlayers for Ohmic Contacts to Silicon Carbide

Ohmic contacts to n-type 4H- and 6H-SiC without postdeposition annealing were achieved using an interlayer of epitaxial InN beneath a layer of Ti. The InN films were grown by reactive dc magnetron sputtering at 450°C, whereas the Ti films were deposited by electron-beam evaporation at room temperature. The InN films were characterized by x-ray diffraction (XRD), secondary electron microscopy (SEM), cross-sectional transmission electron microscopy (TEM), and Hall-effect measurements. Both XRD and TEM observations revealed that the Ti and InN films have epitaxial relationships with the 6H-SiC substrate as follows: (0001)[]_Ti∥(0001)[]_InN∥(0001)[]_6H-SiC. The Ti/InN/SiC contacts displayed ohmic behavior, whereas Ti/SiC contacts (without an InN interlayer) were nonohmic. These results suggest that InN reduces the Schottky barrier height at the SiC surface via a small conduction-band offset and support previous reports of an electron accumulation layer at the surface of InN.     

Chemical Vapor Deposition of Silicon Carbide Epitaxial Films and Their Defect Characterization

A chemical vapor deposition (CVD) system was designed and fabricated in our laboratory and SiC homo-epitaxial layers were grown in the CVD process using silicon tetrachloride and propane precursors with hydrogen as a carrier gas. The temperature field was generated using numerical modeling. Gas flow rates, temperature field, and the gradients are found to influence the growth rates of the epitaxial layers. Growth rates were found to increase as the temperature increased at high carrier gas flow rate, while at lower carrier gas flow rate, growth rates were observed to decrease as the temperature increased. Based on the equilibrium model, “thermodynamically controlled growth” accounts for the growth rate reduction. The grown epitaxial layers were characterized using various techniques. Reduction in the threading screw dislocation (SD) density in the epilayers was observed. Suitable models were developed for explaining the reduction in the SD density as well as the conversion of basal plane dislocations (BPDs) into threading edge dislocations (TEDs).     

Nd:YAG固体激光铣削单晶硅表面形貌研究

利用体视显微镜和扫描电子显微镜观察Nd:YAG固体脉冲激光铣削的单晶硅表面形貌,利用能谱分析仪EDAX对铣削表面进行成分分析。不同功率密度的激光铣削的单晶硅表面形貌差别比较大,其表面化学成分也存在较大差别。     

硅基单电子晶体管的制备

硅基单电子晶体管是一种极具潜力的新型量子器件。大多数硅基单电子晶体管的制备方法可以很好地与主流的CMOS工艺兼容。介绍了硅基单电子晶体管一些典型的具体制备工艺和方法以及该领域近年来的研究热点。     

坩埚在线圈中位置对大直径SiC单晶温度场影响

利用Virtual Reactor模拟软件研究了大直径SiC晶体生长中坩埚在感应线圈内不同位置对坩埚内整体温度场、生长腔以及料源内温度场的影响。分析比较了生长腔内径向温度梯度以及轴向温度梯度的变化规律以及坩埚内部整体温度场的分布规律。以此为依据,优化了坩埚设计,获得了理想的适合大直径SiC单晶生长的温场,并成功生长出高...     

直拉单晶硅中埚跟比的精确计算研究

在直拉单晶硅生长过程中,埚跟比（即坩埚上升速度与晶体提拉速度的比值）的设置非常重要,它直接决定了液面位置的稳定性。其不但影响单晶硅成品的质量,而且不合理的埚跟比设置可能会在直拉单晶硅生长过程中出现变晶断苞,导致单晶生长失败。目前国内大多数光伏单晶硅生产商仅仅依靠人工经验来设置埚跟比,其准确性很难保证。采用体积元积分的方...     

Investigation of the Surface Removal Process of Silicon Carbide in Elastic Emission Machining

Elastic emission machining (EEM) is a precise surface preparation technique, which uses chemical reactions between the surfaces of the workpiece and fine powder particles. The purpose of this study is to clarify the surface removal process of silicon carbide (SiC) in EEM. A SiC sample with a periodic step-bunched structure was prepared as the initial surface and was flattened by EEM. Optical interferometer and atomic force microscopy (AFM) observations show that the topmost areas on the periodic step-bunched structure in contact with the powder particles are preferentially removed and surface protrusion is gradually reduced as removal depth increases. Moreover, power spectral density analyses reveal that the surface is smoothed in the spatial wavelength range from 0.07 μm to 10 μm.     

In Situ Study of Size and Temperature Dependent Brittle‐to‐Ductile Transition in Single Crystal Silicon

Silicon based micro‐ and nanometer scale devices operating at various temperatures are ubiquitous today. However, thermo‐mechanical properties of silicon at the small scale and their underlying mechanisms remain elusive. The brittle‐to‐ductile transition (BDT) is one such property relevant to these devises. Materials can be brittle or ductile depending on temperature. The BDT occurs over a small temperature range. For bulk silicon, the BDT is about 545 °C. It is speculated that the BDT temperature of silicon may decrease with size at the nanoscale. However, recent experimental and computational studies have provided inconclusive evidence, and are often contradictory. Potential reasons for the controversy might originate from the lack of an in situ methodology that allows variation of both temperature and sample size. This controversy is resolved in the present study by carrying out in situ thermo‐mechanical bending tests on single crystal silicon samples with concurrent control of these two key parameters. It is unambiguously shown that the BDT temperature reduces with sample size. For example, the BDT temperature decreases to 293 °C for a sample size 720 nm. A mechanism‐based model is proposed to interpret the experimental observations.