Demonstration of an Optical Isolator with a Semiconductor Guiding Layer that was Obtained by Use of a Nonreciprocal Phase Shift

We present the experimental study of an optical isolator with a semiconductor guiding layer that was obtained by use of a nonreciprocal phase shift. The isolator is equipped with an optical interferometer composed of tapered couplers, nonreciprocal phase shifters, and a reciprocal phase shifter. The nonreciprocal phase shifter was constructed by wafer direct bonding between the semiconductor guiding layer and the magneto-optic cladding layer. The isolator, designed for the 1.55-mum wavelength, was fabricated to investigate the characteristics of each component. By applying an external magnetic field to the nonreciprocal phase shifter, we achieved an isolation ratio of approximately 4.9 dB in the interferometric isolator.     

Simultaneous order-lot pegging and wafer release planning for semiconductor wafer fabrication facilities

In semiconductor wafer fabrication facilities, order-lot pegging is the process of assigning wafer lots to orders and meeting the due dates of orders is considered one of the most important operational issues. In many cases of order-lot pegging, some orders cannot be fulfilled with the current wafers in the lots being processed, necessitating the release of additional new wafer lots into the wafer fabrication facility. In this paper, we propose a simultaneous decision model for order-lot pegging and wafer release planning in semiconductor wafer fabrication facilities, and develop a Lagrangian heuristic for solving the model. The results of computational experiments conducted using randomly generated problem instances that mimic actual field data from a Korea semiconductor wafer fabrication facility indicate that the performance of the Lagrangian heuristic is superior to that of a practical greedy algorithm for practical-sized problem instances. The results also point to how sensitivity analysis can be used to answer important managerial questions for effective management of the semiconductor wafer fabrication process.     

Electron trajectory control of odd and even order harmonics in high harmonic generation using an orthogonally polarised second harmonic field

We investigate quantum trajectory control in high-order harmonic generation using an additional orthogonally polarised second harmonic field. By controlling the relative phase between this field and the fundamental, we are able to suppress and enhance particular electron trajectories which results in a modulation of the harmonic emission. We observe a phase shift of the modulation between the short and long trajectories that is different for adjacent odd and even harmonics. These results show qualitative agreement with a full propagation calculation where the single atom response was obtained from the strong field approximation and the main results are explained by consideration of a single atom quantum orbit picture.     

Hypothesis of local determinability for five-dimensional strain trajectories

Summary Hypothesis of local determinabilily predicting the behavior of the angles between a stress vector and a Frenet's frame established on a strain trajectory in a five-dimensional vector space of strain deviator is discussed to formulate a plastic constitutive equation of metals under complex loadings. Namely, a set of equations giving the rates of angles at the relevant instant for arbitrary five-dimensional curved strain trajectories is derived first on the basis of the previously reported experiments for the deformation along three-dimensional orthogonal trilinear strain trajectories. Then, a simple constitutive equation is formulated by employing the above equations together with the relation between the magnitude of stress vector and the arc-length of strain trajectory for pure torsion. It is found that the resulting equation reproduced well the above experimental results.With 4 Figures     

4H-SiC晶体中的层错研究

采用物理气相传输法(PVT法)在4英寸(1英寸=25.4 mm)偏<11¯20>方向4°的4H-SiC籽晶的C面生长4H-SiC晶体。用熔融氢氧化钾腐蚀4H-SiC晶体, 并利用光学显微镜研究了晶体中的堆垛层错缺陷的形貌特征和生长过程中氮掺杂对4H-SiC晶体中堆垛层错缺陷的影响。结果显示, 4H-SiC晶片表面的基平面位错缺陷的连线对应于晶体中的堆垛层错, 并且该连线的方向平行于<1¯100>方向。相对于非故意氮掺杂生长的4H-SiC晶体, 氮掺杂生长的4H-SiC晶体中堆垛层错显著偏多。然而, 在氮掺杂生长的4H-SiC晶体的小面区域, 虽然氮浓度高于其他非小面区域, 但是该小面区域并没有堆垛层错缺陷存在, 推测这主要是由于4H-SiC晶体小面区域特有的晶体生长习性导致的。     

A generalised uncertain decision tree for defect classification of multiple wafer maps

Classification of defect chip patterns is one of the most important tasks in semiconductor manufacturing process. During the final stage of the process just before release, engineers must manually classify and summarise information of defect chips from a number of wafers that can aid in diagnosing the root causes of failures. Traditionally, several learning algorithms have been developed to classify defect patterns on wafer maps. However, most of them focused on a single wafer bin map based on certain features. The objective of this study is to propose a novel approach to classify defect patterns on multiple wafer maps based on uncertain features. To classify distinct defect patterns described by uncertain features on multiple wafer maps, we propose a generalised uncertain decision tree model considering correlations between uncertain features. In addition, we propose an approach to extract uncertain features of multiple wafer maps from the critical fail bit test (FBT) map, defect shape, and location based on a spatial autocorrelation method. Experiments were conducted using real-life DRAM wafers provided by the semiconductor industry. Results show that the proposed approach is much better than any existing methods reported in the literature.     

The Electronic Structures and Magnetism in Al Doped 4H-SiC: The First-Principles Calculation

In the field of a diluted magnetic semiconductor, a nontransition metal doped semiconductor or oxide is a way to avoid the ferromagnetic clusters of secondary phase. Since there is no d electron in such system, the origin of magnetism is a surprise. In this article, first-principles calculations were used to investigate the origin of magnetism in Al doped 4H-SiC. It is found that a hole was introduced into the SiC:Al system, which is located on one C atom adjacent to the Si vacancy. A neutral Si vacancy with a substituting Al lead to the formation of a net moment less than 1.0μ _B, while the Al itself has no contribution to the magnetic moment, but plays a key role to form them. The coupling between such local moments is paramagnetic.     

基于游离磨粒的化学机械抛光材料去除非均匀性形成机制(英文)

本文主要研究硬脆晶体材料化学机械抛光中基片内材料去除非均匀性的形成机理.首先分析了化学机械抛光时抛光机的运动参数对硅片表面上相对速度分布非均匀性、摩擦力分布非均匀性、接触压力分布非均匀性及磨粒运动轨迹密度分布非均匀性的影响规律.然后通过基片内材料去除非均匀性实验,得出了抛光机运动参数对基片表面材料去除非均匀性的影响.通过比较理论分析与实验结果,基片表面上相对速度分布非均匀性、摩擦力分布非均匀性及接触压力分布非均匀性随转速的变化趋势与基片表面材料去除非均匀性的实验结果相差较大,只有磨粒在基片表面上的运动轨迹分布非均匀性与基片表面材料去除非均匀性的实验结果趋势相同.研究结果表明,基片表面材料去除非均匀性是由磨粒在基片表面上的运动轨迹分布非均匀性造成的,充分说明了基片表面材料去除的机械作用主要是磨粒的机械作用.     

A model-based clustering approach to the recognition of the spatial defect patterns produced during semiconductor fabrication

Defects on semiconductor wafers tend to cluster and the spatial defect patterns of these defect clusters contain valuable information about potential problems in the manufacturing processes. This study proposes a model-based clustering algorithm for automatic spatial defect recognition on semiconductor wafers. A mixture model is proposed to model the distributions of defects on wafer surfaces. The proposed algorithm can find the number of defect clusters and identify the pattern of each cluster automatically. It is capable of detecting defect clusters with linear patterns, curvilinear patterns and ellipsoidal patterns. Promising results have been obtained from simulation studies.     

Numerical solution of the anisotropic Poisson equation for SiC semiconductors device simulation

Classically, in semiconductor simulation programs it is assumed that the semiconductor material is isotropic, i.e. dielectric constant, transport parameters such as carrier mobility have no direction dependence. In this work, we propose a numerical study for the Poisson's equation, addressing the anisotropic properties for the hexagonal silicon carbide (SiC) polytype. The implementation uses a vectorized code. Investigation has been conducted for the 4H- and 6H-SiC. Our results have been compared with TCAD-dessis which enables anisotropic simulation, results have shown good agreement.     

Persistence length measurements from stochastic single-microtubule trajectories

We present a simple method to determine the persistence length of short submicrometer microtubule ends from their stochastic trajectories on kinesin-coated surfaces. The tangent angle of a microtubule trajectory is similar to a random walk, which is solely determined by the stiffness of the leading tip and the velocity of the microtubule. We demonstrate that even a single-microtubule trajectory suffices to obtain a reliable value of the persistence length. We do this by calculating the variance in the tangent trajectory angle of an individual microtubule. By averaging over many individual microtubule trajectories, we find that the persistence length of microtubule tips is 0.24 +/- 0.03 mm.     

Identification and control of SiC polytypes in PVT method

Raman scattering spectra and transmission electron microscope are applied to 6H-SiC wafers. 15R-SiC polytype inclusion appears in 6H-SiC wafer. The proportion of 15R-SiC polytype inclusion decreases obviously by controlling temperature of growth surface and top powder via adjusting monitored temperature and relative position between the crucible and coils at certain interval in physical vapor transport method. When the temperature is below 2,100 °C, 15R-SiC polytype still exists in the 6H-SiC crystal; when the temperature is up to 2,100–2,300 °C and the relative position of crucible is suitable, there exists almost only 6H-SiC polytype in the whole wafer.     

Screening of metal flux for SiC solution growth by a thin-film combinatorial method

4H-SiC is a wide-bandgap semiconductor with potential applications in power devices. The lack of a liquid phase in SiC hinders conventional crystal growth from the melt; consequently, SiC wafers still have low quality and are nearly 100 times more expensive than Si wafers. To take advantage of the solution growth for improving the quality and reducing the cost of SiC, Ni addition to Si–Ti flux has been investigated. A combinatorial approach was employed to accelerate the screening of metal flux for the SiC solution growth.     

硅晶圆磨削减薄工艺的磨削力模型

硅晶圆磨削减薄是一种有别于传统磨削的材料加工方式。磨削减薄过程中,硅晶圆和砂轮同时绕旋转轴旋转,砂轮沿垂直方向连续进给去除材料,其中磨削力是磨削质量的决定性因素。目前,尚缺少一个用于硅晶圆磨削减薄工艺的磨削力预测模型。为了得到磨削力模型,分析了磨削减薄过程中的硅晶圆材料去除机理,将磨削力分为摩擦力和切屑力,考虑了磨粒运动轨迹,分别计算了单颗磨粒在法向和切向上的摩擦力和切屑力,最后基于有效磨粒总数建立了总磨削力模型。模型综合考虑了磨削参数、砂轮和硅晶圆的几何参数和材料性质对磨削力的影响。讨论了砂轮进给速度、晶圆转速和砂轮转速三个主要磨削参数对磨削力的影响,讨论了硅晶圆上晶向对磨削力的影响,给出了磨削力在硅晶圆面上沿径向的分布情况。     

Effect of pre-strain on the plastic deformation of metals along orthogonal bilinear strain trajectories

The effect of deformation history (expressed by the configuration of strain trajectory in a vector space of strain deviators) on the plastic behavior is examined in the range before the saturation of the effect of pre-strain. For this purpose, experiments were performed on thin-walled tubular mild steel and brass specimens, using orthogonal bilinear strain trajectories with various amounts of pre-strain. These strain trajectories were produced by applying combined loads of axial force and torque. It was found that the effect of pre-strain on the stress-strain curve was saturated for mild steel in the range from 0.8 to 2% of pre-strain, while the saturation was not attained for brass in less than 5% of pre-strain. The delay angle of the direction of stress vector from the tangential direction of the strain trajectory is expressed as a function of arc length after the corner point of the bilinear strain trajectory together with that of total strain trajectory. The hypothesis of local determinability, which asserts that the variation of the delay angle in relation to the arc length can be expressed as a function of the delay angle itself, geometric parameters and the arc length of the trajectory, and a simplified approximation of constitutive relation are discussed by using the expression for the delay angle.     

Screening of metal flux for SiC solution growth by a thin-film combinatorial method

Abstract

4H-SiC is a wide-bandgap semiconductor with potential applications in power devices. The lack of a liquid phase in SiC hinders conventional crystal growth from the melt; consequently, SiC wafers still have low quality and are nearly 100 times more expensive than Si wafers. To take advantage of the solution growth for improving the quality and reducing the cost of SiC, Ni addition to Si–Ti flux has been investigated. A combinatorial approach was employed to accelerate the screening of metal flux for the SiC solution growth.     

A visualization tool of patent topic evolution using a growing cell structure neural network

This research used a cell structure map to visualize technological evolution and showed the developmental trend in a technological field. The basic concept was to organize patents into a map produced by growing cell structures. The map was then disassembled into clusters with similar contexts using the Girvan–Newman algorithm. Next, the continuity between clusters in two snapshots was identified and used as the base for establishing a trajectory in the technology. An analysis of patents in the flaw detection field found that the field was composed of several technological trajectories. Among them, ultrasonic flaw detection, wafer inspection and substrate inspection were relatively larger and more continuing technologies, while infrared thermography defect inspection has been an emerging topic in recent years. It is to be hoped that the map of technology constructed in this research provides insights into the history of technological evolution and helps explain the transition patterns through changes in cluster continuity. This can serve a reference point by experts who attempt to visualize the mapping of technological development or identify the latest focus of attention.     

拉曼面扫描表征氮掺杂6H-SiC晶体多型分布

采用物理气相传输法(Physical Vapor Transport, PVT)沿[0001]方向生长了一个直径为2英寸的氮掺杂6H-SiC晶体. 采用拉曼面扫描方法对晶体中多型的分布进行了细致表征, 研究了SiC晶体生长过程中多型的产生和演化. 在6H-SiC晶体中观察到了15R-SiC和4H-SiC两种多型. 在拉曼面扫描得到的晶体多型分布图上观察到了两类次多型结构区域, 一类是继承其生长界面上对应的次多型结构形成的次多型结构区; 另一类是由温度、压力等生长条件波动导致在6H-SiC主多型中出现的15R-SiC多型结构区. 第一类次多型结构区中掺入的氮元素较多, 载流子浓度较高, 并且随着晶体生长不断扩大; 第二类次多型结构区对晶体结晶质量的影响较小, 且提高生长温度可以抑制15R-SiC多型结构.     

Scheduling of wafer test processes in semiconductor manufacturing

This research focuses on solving a common wafer test scheduling problem in semiconductor manufacturing. During wafer testing, a series of test processes are conducted on wafers using computer-controlled test stations at various temperatures. The test processes are conducted in a specified order on a wafer lot, resulting in precedence constraints for the schedule. Furthermore, the assignment of the wafer lots to test stations and the sequence in which they are processed affects the time required to set up the test operations. Thus, the set-up times are sequence dependent. Four heuristics are developed to solve the test scheduling problem with the aim of minimizing the makespan required to test all wafers on a set of test stations. The heuristics generate a sorted list of wafer lots as a dispatching sequence and then schedule the wafer lots on test stations in order of appearance on the list. An experimental analysis and two case studies are presented to validate the proposed solution approaches. In the case studies, the heuristics are applied to actual data from a semiconductor manufacturing facility. For both case studies, the proposed solution approaches decrease the makespan by 23–45% compared with the makespan of the actual schedule executed in the manufacturing facility.     

A novel hybrid resampling for semiconductor wafer defect bin classification

Generally, defective dies on semiconductor wafer maps tend to form spatial clusters in distinguishable patterns which contain crucial information on specific problems of equipment or process, thus it is highly important to identify and classify diverse defect patterns accurately. However, in practice, there exists a serious class imbalance problem, that is, the number of the defective dies on semiconductor wafer maps is usually much smaller than that of the non-defective dies. In various machine learning applications, a typical classification algorithm is, however, developed under the assumption that the number of instances for each class is nearly balanced. If the conventional classification algorithm is applied to a class imbalanced dataset, it may lead to incorrect classification results and degrade the reliability of the classification algorithm. In this research, we consider the semiconductor wafer defect bin data combined with wafer warpage information and propose a new hybrid resampling algorithm to improve performance of classifiers. From the experimental analysis, we show that the proposed algorithm provides better classification performance compared to other data preprocessing methods regardless of classification models.