Mechanisms of Peeling Failures of Bonds During Ultrasonic Wedge Bonding

The metallization of wire bonding pads on Si-based integrated circuits (ICs) contains Ti, TiN, and Al layers with vertical W-plugs located through the Ti and TiN layers. One percent Si-Al wire (32 µm in diameter) was bonded on the pads by an ultrasonic transducer using a wire bonding machine. Peeling failures occurred during the ultrasonic bonding process. The peeling fractures were examined using a scanning electron microscope (SEM) with an energy-dispersive spectroscopy (EDS) system. The results showed that bonds peeled off from the interface between the Al layer and the top surface of the W-plugs or from the interface between the Si-base and the bottom surface of the W-plugs. The distribution of W-plugs also affected the bond peeling from the top or bottom surfaces of the W-plugs. Mechanisms giving rise to the peeling failure of bonds were analyzed based on the acoustic impedance of materials, which determined the amount of ultrasonic energy transmitted from one material to another. Two different paths of ultrasonic energy transmission occurred during the bonding process due to the different acoustic impedances of the materials. One is from the Al layer, through the TiN and Ti layers, to the IC. The other is from the Al layer, through the W-plugs, to the IC. The different distributions of ultrasonic energy at the positions with W-plugs and without W-plugs caused stress concentrations around the top or bottom surfaces of the W-plugs, which resulted in peeling failures of the bonds.     

Redesign of the scanning electron microscope for parallel energy spectral acquisition

This paper presents a scanning electron microscope (SEM) design that is compatible with parallel electron energy spectrum acquisition. The SEM should in principle be capable of capturing the energy spectrum of all scattered electrons simultaneously, from low energy secondary electrons to elastic backscattered electrons. Preliminary simulation results predict that the beam separator spectrometer will have a relatively high transmission-energy resolution performance, comparable or better than the cylindrical mirror analyzer (CMA), while at the same time being able to capture the entire energy range of scattered electrons.     

Preservation and fluorescence of the microfossils from Neoproterozoic Doushantuo formation

The phosphatized microfossils from Doushantuo Formation, Southeast China show us the biodiversity about 600 million years ago, which is a unique window for the evolution of the early life on earth. However, the process of phosphatic fossilization in detail still remains unknown. Here we report our study on the preservation state of the fossils by using confocal laser scanning microscopy. We found that fluorescent signal of the fossil could reflect the preservation state when compared with the transmission light microscopy. First, we found the fluorescent signal of the decayed cells of the fossil was weaker than that of the nondecayed part. Second, we found that the three-dimensional reconstruction of the fluorescent signals could help to judge the degree of mineralization of the fossil cells, compared with the observation by transmission light microscope. Third, we found that almost all of the fossil specimens we observed could fluoresce more or less when excited by laser light. Therefore, the fluorescent microscopy provides a useful method for the study of the preservation state of the phosphatic fossil cells.     

用STM研究电化学阳极氧化制备的多孔硅

本文利用扫描隧道显微镜（ＳＴＭ）并辅以快速富立叶变换（ＦＦＴ）和数据拟合等数学方法对电化学极氧化法制备的多孔硅（ＰＳ）的微结构及形貌进行了研究。同时研究了多孔硅的微结构与其发生性质和电化学性质的相互关系。研究表明，在其他条件不变情况下，随阳极氧化电流密度的增大，所形成的多孔硅的微孔向纵深延伸，多孔硅层增厚，微孔相连后形成的硅柱变细，发光强度增大，发光峰位明显蓝移，与单晶硅相比，多孔硅电极的平带电位     

异丙烯膦酸-丙烯酸共聚物对硫酸钙的阻垢性能研究

本文研究了异丙烯膦酸-丙烯酸共聚物对硫酸钙的阻垢性能，探讨了共聚物浓度，钙离子浓度，硫酸根浓度，pH值，温度等因素对硫酸钙阻垢性能的影响，并用扫描电镜研究了不同共聚物用量下硫酸钙的结晶形态，在共聚物浓度为20mg/L时，硫酸钙晶体产生了严重的畸变；结果表明该共聚物对硫酸钙具有良好的阻垢性能。     

外加电场对云母表面纳尺度摩擦行为的影响

利用原子力显微镜（AFM）研究了施加恒定外电场时,AFM针尖与云母表面间的摩擦力变化情况．结果表明,对样品基底施加一定偏压后,由于针尖与云母表面间的静电作用增强,使得针尖与样品间的总相互作用势增加,从而导致针尖与云母间的摩擦力比未施加偏压时大,且摩擦力大小随电压升高而增大．尤其是施加负偏压时,摩擦力增加更为显著,且大于正偏压时的摩擦力．     

油酸钠为稳定剂合成CdS（CdSe）纳米粒子及表征

针对CdS（CdSe）等半导体纳米粒子制备过程中使用的有机溶剂难回收、成本高、难以实现工业化等问题,以油酸钠为稳定剂,乙醇为溶剂,乙酸镉和硫脲（或硒氢化钠）为前驱物,制备了CdS和CdSe纳米粒子.采用紫外-可见吸收光谱、荧光光谱、广角x射线衍射和透射电子显微分析等方法,对CdS和CdSe纳米粒子的光学性质、晶体结构、形貌及尺寸等进行了表征.结果表明,当以油酸钠为稳定剂,乙醇为溶剂时,通过控制一定的前驱物浓度、反应温度和反应时间,在温和的反应条件下,可以得到尺寸分布均匀的CdS和CdSe纳米粒子,从而为在环境友好条件下合成CdS和CdSe半导体纳米粒子提供了一种新途径.     

Roundness error evaluation by minimum zone circle via microscope inspection

Utilizing the convex hull theory, a novel minimum zone circle (MZC) method, named improved minimum zone circle (IMZC) was developed in this paper. There were three steps for IMZC to evaluate the roundness error. Firstly, with the convex hull algorithm, data points on the circle contour were categorized into two sets to determine two concentric circles which contained all points of the contour. Secondly, vertexes of the minimum circumscribed circle and the maximum inscribed circle were found out from the previously determined two sets, and then four tangent points for determining the two concentric circles were also found out. Lastly, according to the evaluation using the MZC method, the roundness error was figured out. In this paper, IMZC was used to evaluate roundness errors of some micro parts. The evaluation results showed that the measurement precision using the IMZC method was higher than the least squared circle (LSC) method for the same set of data points, and IMZC had the same accuracy as the traditional MZC but dramatically shortened computation time. The computation time of IMZC was 6.89% of the traditional MZC.     

Nonlinear control techniques for an atomic force microscope system

Two nonlinear control techniques are proposed for an atomic force microscope system.Initially,a learning-based control algorithm is developed for the microcantilever-sample system that achieves asymptotic cantilever tip tracking for periodic trajectories.Specifically,the control approach utilizes a learning-based feedforward term to compensate for periodic dynamics and high-gain terms to account for non-periodic dynamics.An adaptive control algorithm is then developed to achieve asymptotic cantilever tip tracking for bounded tip trajectories despite uncertainty throughout the system parameters.Simulation results are provided to illustrate the efficacy and performance of the control strategies.     

Si基ZnO缓冲层溅射Ga2O3氨化反应生长GaN薄膜

利用射频磁控溅射法在Si（111）衬底上先溅射ZnO缓冲层,再溅射Ga2O3薄膜,然后在开管炉中分别以850℃,900℃,950℃和1 000℃等温度及常压下通氨气进行氨化,反应生长GaN薄膜.利用该方法制备的GaN薄膜是沿c轴方向择优生长的六角纤锌矿多晶结构,并且随着氨化温度的升高,GaN向棒状和线状形态生长.