单晶硅在氦离子注入前后的力学性能研究

以微机电系统常用的单晶硅材料和经氮离子注入单晶硅后形成的表面改性层为研究对象，在原位纳米力学测试系统上进行微压痕实验，对样品的表面纳米硬度进行了测试。同时，还通过该仪器的原子力成像功能对实验区域扫描成像，在纳米尺度下观察和分析形貌。结果表明：单晶硅在氮离子注入前后的纳米硬度值与载荷有很大关系。通过对微压痕和原子力图像的分析，表明单晶硅在氮离子注入后的纳米硬度值有所降低，其主要原因是氮离子注入后导致晶格抵抗变形的能力降低。     

单晶硅在氮离子注入前后的力学性能研究

以微机电系统常用的单晶硅材料和经氮离子注入单晶硅后形成的表面改性层为研究对象,在原位纳米力学测试系统上进行微压痕实验,对样品的表面纳米硬度进行了测试。同时,还通过该仪器的原子力成像功能对实验区域扫描成像,在纳米尺度下观察和分析形貌。结果表明:单晶硅在氮离子注入前后的纳米硬度值与载荷有很大关系。通过对微压痕和原子力图像的分析,表明单晶硅在氮离子注入后的纳米硬度值有所降低,其主要原因是氮离子注入后导致晶格抵抗变形的能力降低。     

单晶硅各向异性纳米切削分子动力学研究

在293K温度下,通过分子动力学仿真软件LAMMPS建立单晶硅(100)、(110)和(111)不同晶面的纳米切削仿真模型,对样件内部原子之间相互作用选用改进型Tersoff势函数描述,并结合OVITO可视化分析,研究了样件的表面完整性演化规律和亚表层损伤机制.结果 表明:在纳米切削时,材料去除方式主要靠刀具的法向挤压...     

单晶硅纳米级磨削过程的理论研究

对内部无缺陷的单晶硅纳米级磨削过程进行了分子动力学仿真,从磨削过程中瞬间原子位置、磨削力、原子间势能、损伤层深度等角度研究了纳米级磨削加工过程,解释了微观材料去除、表面形成和亚表面损伤机理。研究表明：磨削过程中,单晶硅亚表面损伤的主要形式是非晶结构形式,无明显的位错产生,硅原子间势能的变化是导致单晶硅亚表面损伤的重要原因;另外,发现磨粒原子与硅原子之间有黏附现象发生,这是由于纳米尺度磨粒的表面效应而产生的。提出了原子量级条件下单晶硅亚表面损伤层的概念,并定义其深度为沿磨削深度方向原子发生不规则排列的原子层的最大厚度。     

基于分子动力学的单晶硅纳米压痕过程分析

基于分子动力学角度,本文主要分析了单晶硅的纳米压痕过程,并尝试解释其瞬间原子位置、作用力变化以及其压痕过程等原理。经过笔者试验发现:磨粒的不断压入,会使单晶硅的硅晶格发生变成,且磨粒产生的能量会以应变能的形式存储在晶格之中。同时,随着硅原子势能增加到一定数值时,硅原子键就会以断裂形式变成非晶层堆积在磨粒下方。当磨粒离开单晶硅时,非晶层开始重构,释放能量,达到新的平衡状态。     

采用AFM研究单晶硅纳米加工特性

为获得AFM金刚石微探针在纳米尺度上加工脆性材料的加工特性,在AFM系统上对单晶硅表面进行了刻划、加工实验.实验结果与宏观车削加工结果进行了对比,得出在纳米尺度上进行的加工属塑性域加工.采用AFM金刚石微探针加工硅表面的加工质量主要受材料残留高度和形成的切屑在已加工表面的粘结两个因素影响.验证了AFM作为一种加工工具,受其刻划方向的影响,可以很容易地实现纳米量级材料的去除,得到厚度为数个纳米的切屑.     

应用纳米压痕法测试类金刚石薄膜的力学性能

纳米压痕仪被称为材料机械性质微探针,它借助于加载-卸载过程中压痕对载荷和压入深度的敏感关系,使得测试始终在薄膜材料的弹性限度内,克服了维氏法和努氏法等传统方法引起压痕边缘模糊或者碎裂的缺点,从而正确地、可靠地测试出薄膜材料的硬度和弹性模量等纳米力学性能.试验用微波电子回旋共振等离子体增强化学气相沉积技术,在不同偏压条件下制备三种类金刚石薄膜(DLC膜),用纳米压痕仪测试不同载荷下薄膜的硬度和弹性模量值.试验结果表明,材料的纳米硬度和弹性模量随着载荷的增大而逐渐减小.     

AFM的纳米硬度测试与分析

基于原子力显微镜(AFM)和金刚石针尖建立了一套纳米压痕测量系统。通过向系统发送控制电压使金刚石针尖在完成加载和卸载全过程的同时进行实时的数据采集并直接绘出载荷-压深曲线。利用该系统,对单晶铝和单晶铜薄膜材料进行了单点压痕实验,用美国Hysitron公司的纳米原位测量仪(TriboIndenter)做了验证试验。实验结果表明,该系统适合测量较软材料的纳米硬度。分析了基体材料对薄膜硬度和弹性模量的影响,在薄膜厚度低于5~10倍压入深度时,基体对薄膜材料的力学性能影响很大;并根据获得的载荷－压深曲线分析得出由于尺度效应的影响,随着压痕深度的减小,薄膜的硬度值呈明显的上升趋势,弹性模量没有这个趋势。     

单晶硅微桥式梁力学性能的弯曲测试

微梁是微电子机械系统(M EM S)中常见的结构,单晶硅是M EM S最基本、最常用的材料之一,其材料力学性能需要精确的评价。应用光刻等技术加工了六组不同尺寸的微桥式梁试件,并进行了弯曲测试,梯形截面的试件可代表矩形、方形等截面的常见微梁。弯曲测试选用的纳米压痕法适用于弹塑性材料,且可同时获取弹性模量、硬度和弯曲强度等多种力学性能参数。实验测得单晶硅的平均弹性模量为(170.295±2.4850)GPa,没有呈现尺寸效应;弯曲强度在3.24~10.15GPa范围内变化,有较强的尺寸效应,平均硬度为(9.4967±1.7533)GPa,尺寸效应不太明显。     

基于分子动力学的单晶硅压痕过程计算机仿真研究

对单晶Si的压痕过程进行了分子动力学模拟。采用Morse势函数描述原子间的相互作用,以牛顿方程建立力学运动方程,使用改进后的Verlet算法解子运动轨迹,通过对MD仿真结果的分析研究,将压痕过程分为三个特征阶段,即初期弹性变形阶段,中期塑性变形阶段及非晶层形成阶段。并从原子角度分析了压痕过程中原子间势能,磨削力的变化,应力状态,磨削温度等特征,解释了微观材料的去除和表面形成机理。     

Study of EDM cutting of single crystal silicon carbide

Electrical discharge machining (EDM) is developing as a new alternative method for slicing single crystal silicon carbide (SiC) ingots into thin wafers. Aiming to improve the performance of EDM slicing of SiC wafers, the fundamental characteristics of EDM of SiC single crystal were experimentally investigated in this paper and compared to those of steel. Furthermore, EDM cutting of SiC ingot by utilizing copper foil electrodes was proposed and its performance was investigated. It is found that the EDM characteristics of SiC are very different from those of steel. The EDM machining rate of SiC is higher and the tool wear ratio is lower compared to those of steel, despite SiC having a higher thermal conductivity and melting point. Thermal cracks caused by the thermal shock of electrical discharges and the Joule heating effect due to the higher electrical resistivity are considered to be the main reasons for the higher material removal rate of SiC. It is concluded that the new EDM cutting method utilizing a foil electrode instead of a wire electrode has potential for slicing SiC wafers in the future.     

A simple approach to fabricate amorphous silicon pattern on single crystal silicon

Scratch tests on single crystal silicon under dry sliding and pentadecane lubrication are performed on a commercially available nano-scratch tester. Loads range of elastic, elasto-plastic deformation and fracture are classified according to depth-load curves. A fully plastic removal of single crystal silicon below critical load for fracture is observed under pentadecane lubrication, which is quite different from that under dry sliding. Raman micro-spectra indicate that the phase compositions of the scratched track under dry sliding consist of a number of phases, including Si-I, Si-III, Si-XII and a-Si, while the phase composition of the track under pentadecane lubrication consists of single a-Si. Based on the results obtained, a simple approach to fabricate amorphous silicon pattern on single crystal silicon is introduced and discussed.     

单晶蓝宝石的延性研磨加工

为实现单晶蓝宝石的延性研磨加工,采用纳米压痕和划痕法测试并分析了单晶蓝宝石(0001)面的微纳力学特性,建立了单颗圆锥状磨粒的压入模型并计算了延性研磨加工的受力临界条件,分析了金刚石磨粒嵌入合成锡研磨盘表面的效果.对单晶蓝宝石进行了延性研磨加工试验,采用NT9800白光干涉仪、扫描电子显微镜(SEM)和透射电子显微镜(TEM)等方法分析了单晶蓝宝石的延性研磨表面特征.试验结果表明:采用纳米压痕和划痕法可以为单晶蓝宝石的延性研磨加工提供工艺参数,单晶蓝宝石的延性堆积的极限深度为100 nm,金刚石磨粒的嵌入及在适当载荷下可以实现蓝宝石的延性研磨加工,实验条件下的最佳载荷为21 kPa,延性研磨后单晶蓝宝石表面划痕深度的分布情况较好,分散性小,研磨后的表面发生了位错滑移变形.     

Improvement of EDM efficiency of silicon single crystal through ohmic contact

This paper describes the improvement of the machining rate of electrical discharge machining (EDM) for silicon single crystals by reducing the contact resistance between the silicon single crystal and metal electric feeder. To decrease the resistance of the rectifying contact between a p-type silicon wafer and the metal feeder, attempts to achieve ohmic contact were made by plating the contact surface of the silicon wafer with aluminum by vacuum evaporation, followed by the diffusion process. To accomplish an ohmic contact between n-type silicon and metal, gold–antimony alloy was used in place of aluminum. The influence of polarity on the machining rate is also discussed from the viewpoint of the rectifying nature of the interface between the arc plasma and silicon single crystal.     

基于AFM的压痕硬度自动检测算法的研究

由纳米硬度计可测得载荷-压深曲线,并由原子力显微镜可以扫描得到压痕图.在对单晶硅压痕硬度的检测试验中,用Matlab软件对获得的数据进行处理,编制了利用压痕边长法、直接面积法、Oliver-Pharr法和压痕功法等计算压痕硬度方法的程序,可以自动计算压痕的面积和体积并计算得到单晶硅的硬度值.     

Dynamic measurements of damage generation in single crystal silicon due to sliding contact with a spherical diamond

Single or multiple linear unidirectional scratches were made on (111) n-type single crystal silicon surfaces, at room temperature, by a dead-loaded spherical diamond indenter translated in the [110] direction at a speed of 5 cm s⁻¹. The damage was measured with a simulated four-point probe technique consisting of a voltage detector designed and fabricated on the silicon wafer. The scratches were made between four electrical pads of the detector through which the electrical resistance of the damage region can be recorded in real time by a data acquisition system. The relative change in voltage, between 3 and 10%, was correlated to the time for the diamond to move past the probes and depended on dead load on the diamond, and the silicon properties. This measurement technique is used to develop a model for subsurface crack generation and propagation. If subsurface damage is modeled as a Hertzian crack then a measure of the voltage provides an estimate of the crack size. This relationship between the measured relative change in voltage and load on a pyramid diamond can be expressed as M(%) P^4/3.     

Multi-discharge EDM coring of single crystal SiC ingot by electrostatic induction feeding method

A new technique of EDM coring of single crystal silicon carbide (SiC) ingot was proposed in this paper. Currently single crystal SiC devices are still of high cost due to the high cost of bulk crystal SiC material and the difficulty in the fabrication process of SiC. In the manufacturing process of SiC ingot/wafer, localized cracks or defects occasionally occur due to thermal or mechanical causes resulted from fabrication processes which may waste the whole piece of material. To save the part of ingot without defects and maximize the material utilization, the authors proposed EDM coring method to cut out a no defect ingot from a larger diameter ingot which has localized defects. A special experimental setup was developed for EDM coring of SiC ingot in this study and its feasibility and machining performance were investigated. Meanwhile, in order to improve the machining rate, a novel multi-discharge EDM coring method by electrostatic induction feeding was established, which can realize multiple discharges in single pulse duration. Experimental results make it clear that EDM coring of SiC ingot can be carried out stably using the developed experimental setup. Taking advantage of the newly developed multi-discharge EDM method, both the machining speed and surface integrity can be improved.     

Fundamental investigation of subsurface damage in single crystalline silicon caused by diamond machining

Single crystalline silicon was plunge-cut using diamond tools at a low speed. Cross-sectional transmission electron microscopy and laser micro-Raman spectroscopy were used to examine the subsurface structure of the machined sample. The results showed that the thickness of the machining-induced amorphous layer strongly depends on the tool rake angle and depth of cut, and fluctuates synchronously with surface waviness. Dislocation activity was observed below the amorphous layers in all instances, where the dislocation density depended on the cutting conditions. The machining pressure was estimated from the micro-cutting forces, and a subsurface damage model was proposed by considering the phase transformation and dislocation behavior of silicon under high-pressure conditions.     

Nano‐scratch study of molecular deposition films on silicon wafers using nano‐indentation

Experiments on molecular deposition (MD) films with and without alkyl terminal groups deposited on silicon wafers were conducted using nano‐indentation. It was found that MD films and alkyl‐terminated MD films exhibit a higher critical load and a lower coefficient of friction than the silicon substrate. The critical load increases with the number of layers, and the coefficients of friction of MD films with alkyl terminal groups are lower than those of the corresponding MD films with the same number of layers but without alkyl terminal groups.     

The crystallographic change in sub-surface layer of the silicon single crystal polished by chemical mechanical polishing

The effect of the contact nominal pressure on the surface roughness and sub-surface deformation in chemical mechanical polishing (CMP) process has been investigated. The experimental results show that a better surface quality can be obtained at the lower pressure, and the thickness of sub-surface deformation layer increases with the increase of the pressure. In CMP process, polishing not only introduces amorphous transformation but also brings a silicon oxide layer with a thickness of 2–3 nm on the top surface. The atomic structure of the material inside the damage layer changes with the normal pressure. Under a higher pressure (125 kPa), there are a few crystal grain packets surrounded by the amorphous region in which the lattice is distorted, and a narrow heavy amorphous deformation band appears on the deformation region side of the interface. Under a lower pressure, however, an amorphous layer can only be observed.