Dispersion of magnetostatic waves in a tangentially magnetized ferrite wafer with normal uniaxial anisotropy

A dispersion law is obtained and analyzed for the first time for magnetostatic waves in a tangentially magnetized ferrite wafer with uniaxial anisotropy where the axis is perpendicular to the plane of the wafer and the applied static magnetic field is weaker than the anisotropy field. This model qualitatively describes the dispersion of magnetostatic waves in hexa-and orthoferrite wafers and also in an unsaturated ferrite wafer. Pis’ma Zh. Tekh. Fiz. 25, 73–78 (November 26, 1999)     

Determination of optical birefringence by using off-axis transmission ellipsometry

Utilizing transmission ellipsometry at small angles of incidence, it is shown that c-cut uniaxial samples can be used to determine both the miscut of the optic axis with respect to the plane of incidence as well as very accurate values of the spectroscopic birefringence. For example, wafers of ZnO, LiNbO3, and 6H-SiC single-crystals are examined and the miscut direction and the spectroscopic birefringence are determined. While all materials show strong dispersion in birefringence, ZnO exhibits a distinct isotropic point at 396.8 nm.     

Fabrication of high aspect ratio metal nanotips by nanosecond pulse laser melting

The authors have developed an approach to fabricate sharp and high aspect ratio metal tips using nanosecond pulse laser melting. A quartz wafer covered with a thin chromium (Cr) film was placed on top of a second wafer with a sub-micrometer gap between them and the Cr film facing the second wafer. Then an excimer laser pulse (308?nm wavelength, 20?ns pulse duration) was shone from the back of the quartz wafer and melted the Cr film momentarily (several hundred nanoseconds). It is found that the molten Cr films can self-form discrete metal pillars connecting the two wafers. After separating the two wafers, nanotips were formed at the broken pillar necks. The sharpest tip achieved has an apex diameter 10?nm and height 180?nm. The self-formation of Cr pillars between the two wafers was attributed to the attractive electrostatic force caused by the work function difference of two wafers that were in close proximity. This technique could be extended to other metals, and a periodic uniform tip array could be obtained by pre-patterning the metal into identical isolated mesas and precisely controlling the gap between the two wafers.     

Epitaxial silicon carbide on a 6″ silicon wafer

The results of the growth of silicon-carbide films on silicon wafers with a large diameter of 150 mm (6″) by using a new method of solid-phase epitaxy are presented. A SiC film growing on Si wafers was studied by means of spectral ellipsometry, SEM, X-ray diffraction, and Raman scattering. As follows from the studies, SiC layers are epitaxial over the entire surface of a 150-mm wafer. The wafers have no mechanical stresses, are smooth, and do not have bends. The half-width of the X-ray rocking curve (FWHM_ω?θ) of the wafers varies in the range from 0.7° to 0.8° across the thickness layer of 80–100 nm. The wafers are suitable as templates for the growth of SiC, AlN, GaN, ZnO, and other wide-gap semiconductors on its surface using standard CVD, HVPE, and MBE methods.     

Fiducial markers for increasing the versatility of optical correlation in the measurement of faults on integrated-circuit wafers

A microscope-coherent optical processor is used for the measurement of the registration errors on integrated-circuit wafers. The measurements are obtained from the optical correlation of wafers with reference wafer patterns by use of matched spatial filters. Previously, the intricate pattern of the active circuit area of wafers has been used in the correlation process, and a new matched spatial filter had to be created for each different integrated circuit. Here, the results of using comparatively plain fiducial markers on a wafer for the registration-error measurement are presented, and these show that the measurements can be made independent of the design of the integrated circuit while maintaining the advantages and accuracy of the optical correlation technique.     

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.     

A run-to-run controller for product surface quality improvement

In semiconductor manufacturing, the surface quality of silicon wafers has a significant impact on the subsequent processes that produce devices using the wafers as a component. The surface quality of a wafer is characterised by a two-dimensional (2-D) data structure: the geometric requirement for the wafer surface is smooth and flat and the thickness should fall within certain specification limits. Therefore, both low deviation and high uniformity are desirable for control over the wafer quality. In this work, we develop a run-to-run control algorithm for improving wafer quality. Considering the unique 2-D data structure, we first construct a model that encompasses the spatial correlation of the observations on the wafer surface to link the wafer quality with the process variables, and subsequently develop a recursive algorithm to generate optimal set points for the controllable factors. More specifically, a Gaussian-Kriging model is used to characterise the spatial dependence of the thickness measures of the wafer and a recursive least square method is employed to update the estimates of the model parameters. The performance of the new controller is studied via simulation and compared with existing controllers, which demonstrates that the newly proposed controller can effectively reduce the surface variations of the silicon wafers.     

Comparative lyophilized platelet-rich plasma wafer and powder for wound-healing enhancement: formulation,in vitro and in vivo studies

Platelet-rich plasma (PRP) accelerates wound healing, as it is an excellent source of growth factors. PRP was separated from whole human blood by centrifugation. PRP powder and wafers were prepared by lyophilization, with the wafers prepared using sodium carboxymethylcellulose (Na CMC). The PRP wafers showed porous structures, as indicated by scanning electron microscopy (SEM) images, and the ability of the wafer to absorb exudates and thus promote wound healing was tested with the hydration capacity test. The platelet count was tested and indicated that the presence of PRP in the wafers had no effect on the platelet count. An antimicrobial activity test was carried out, showing that PRP had antibacterial activity against Gram-negative bacteria. Compared with lyophilized PRP powder and PRP-free wafers, PRP wafers showed the highest percent of wound size reduction on induced wounds in rats. Histopathological examination of rat skin showed that the PRP wafers achieved the shortest healing time, followed by the lyophilized PRP powder and finally the PRP-free wafers. The present study revealed that PRP can be formulated as a wafer, which is a promising pharmaceutical delivery system that can be used for enhanced wound-healing activity and improved the ease of application compared to lyophilized PRP powder.     

Nondestructive evaluation of large-area PZN-8%PT single crystal wafers for medical ultrasound imaging probe applications

A nondestructive quality evaluation and control procedure for large-area, (001)-cut PZN-8%PT wafers is described. The crystals were grown by the flux technique engineered to promote (001) layer growth of the crystals. The wafers were sliced parallel to the (001) layer growth plane. Curie temperature (Tc) variations, measured with matching arrays of dot electrodes (of 5.0 mm in center-to-center spacing), were found to be better than +/- 4.0 degrees C both within wafers and from wafer to wafer. After selective dicing to give final wafers of narrower Tc distributions (e.g., +/- 3.0 degrees C or better), the wafers were coated with complete electrodes and poled at room temperature at 0.7-0.9 kV/mm. Typical overall properties of the poled wafers were: K3T = 5,200 (+/- 10% from wafer to wafer), tan delta < 0.01 (all wafers), and kt = 0.55 (+/- 5%) (all percentage variations are in relative percentages). Then, the distributions of K3S, tan delta, and kt were measured by the array dot electrode technique. The variations in K3S (hence K3T) and kt within individual wafers were found to be within +/- 10% and +/- 5%, respectively. The dielectric loss values, measured at 1 kHz, were consistently low, being < 0.01 throughout the wafers. The kt values determined by the dot electrodes were found to be about 5% smaller than those obtained with the complete electrodes, which can be attributed to an increase in capacitance ratio due to the partial electroding. The k33 values, deduced using the relation K3S approximately (1 - k33(2))K3T, from the mean K3S and overall K3T values, average 0.94 (+/- 2%). The present work shows that the distribution of Tc within wafers can be used as a convenient check for the uniformity in composition and electromechanical properties of PZN-8%PT single crystal wafers. Our results show that, to control deltaK3T and deltakt within individual wafer to < or = 10% and 5%, respectively, the variation in Tc within the wafer should be kept within +/- 3.0 degrees C or better.     

大型硅晶片平面度精密纳米计量技术

描述了一种基于斜率传感器的大型硅晶片平面度扫描测量系统．采用二维斜率传感器对晶片表面扫描，以获得表面绕X和Y轴的倾斜度．斜率传感器装在X向滑板上，而晶片固定在可绕Z轴转动的主轴上．对斜率传感器Y向的输出积分，得到晶片表面各个同心圆上轮廓截面高度．对斜率传感器X向的输出积分，得到晶片表面沿X向的截面轮廓，从而获得各同心圆轮廓之间的关系．构建了一个包括基于自准直原理的小型斜率传感器、气浮主轴、气浮导轨的实验系统，提出一种斜率传感器现场标定方法，用此系统测量了直径300mm的硅晶片平面度。     

Mechanical Strength of Silicon Wafers Cut by Loose Abrasive Slurry and Fixed Abrasive Diamond Wire Sawing

This paper reports on the mechanical strength of polycrystalline silicon wafers cut by loose abrasive slurry and fixed abrasive diamond wire sawing processes. Four line bending and biaxial flexure tests are used to evaluate the fracture strength of the wafers. Fracture strength of the wafers depends on the location, size, and orientation of microcracks in the silicon wafer and the distribution and magnitude of applied stresses. Measurement of microcracks at the wafer edge and center shows that edge cracks are typically larger than center cracks. Fixed abrasive diamond wire sawn wafers are found to have a higher crack density but smaller average crack length. Wafer fracture in four line bending is found to be primarily due to the propagation of edge cracks while center cracks are found to be the primary cause of wafer failure in biaxial flexure tests. Fracture mechanics based analyses demonstrate that crack orientation plays a significant role in four line bending, but not in biaxial flexure. Correlations of the wafer fracture strength and critical crack length agree well with microcrack measurements. The fracture strength of diamond cut wafers is found to be comparable or superior to the strength of slurry cut wafers.     

Anisotropic incoherent reflection model for spectroscopic ellipsometry of a thick semitransparent anisotropic substrate

An anisotropic incoherent reflection model for the Mueller matrix elements of an optically thick uniaxial anisotropic semitransparent substrate with its anisotropy axis along its surface normal is developed. The Mueller matrix elements are measured by phase-modulated spectroscopic ellipsometry (SE) and compared with incoherent reflection model simulations. In the case of a sapphire substrate the oscillations observed are accurately modeled, and, in addition, the oscillating degree of polarization is correctly predicted. A straightforward generalization of the optical model, in the case of an arbitrary stack of layers containing a thick anisotropic semitransparent substrate, is also proposed and experimentally validated. The model is further applied to study the anisotropic dielectric function of a semi-insulating 4H-SiC wafer. An approximation based on a simple variation in the optical transition element is proposed to model the SiC birefringence. In conclusion, SE is shown to be a powerful alternative for investigating and predicting the behavior of optically thick birefringent materials.     

A new cost effective method of planarisation for multiple metal layers in the sub-100 nm-region

The availability of multiple metal layers has become essential for high-density layouts and economic chip size. The presented paper describes an efficient and low-cost alternative to Chemical-Mechanical-Polishing (CMP). The method uses an auxiliary wafer as a sort of plunger. Starting with a preprocessed wafer, for example from a Complementary-Metal-Oxide-Semiconductor (CMOS) technology, a spin-on glass is applied before the deposition of the first metal layer. Afterwards a second silicon wafer will be covered homogeneously with photo resist and subsequentially coated with aluminum or titanium. This wafer serves as a plunger, while the metal layer protects the photo resist against impression. Whilst the plunger is pressed down on the spin-on glass, the first wafer is cooled down bonding the two wafers together. Separation of the wafers is accomplished by removing the photo resist layer. After the separation step any remaining photo resist as well as the aluminum layer are removed by etching. This process results in a planar surface which is optimally suited for the deposition and structuring of further metal layers which lead to more freedom concerning the complex interconnects in modern analog and digital circuits.     

Residual stress in piezoelectric poly(vinylidene-fluoride-co-trifluoroethylene) thin films deposited on silicon substrates

The residual stress and its evolution with time in poly(vinylidene-fluoride-co-trifluoroethylene) (P(VDF-TrFE) (72/28)) piezoelectric polymer thin films deposited on silicon wafers were investigated using the wafer curvature method. Double-side polished silicon wafers with minimized initial wafer warpage were used to replace single-side polished silicon wafers to obtain significantly improved reliability for the measurement of the low residual stress in the P(VDF-TrFE) polymer thin films. Our measurement results showed that all the P(VDF-TrFE) films possessed a tensile residual stress, and the residual stress slowly decreased with time. Our analysis further indicates that the tensile stress could arise from the thermal mismatch between the P(VDF-TrFE) film and the silicon substrate. Besides possible viscoelastic creep mechanism in thermoplastic P(VDF-TrFE) films, microcracks with widths in the range of tens of nanometers appeared to release the tensile residual stress.     

Integrated color defect detection method for polysilicon wafers using machine vision

For the typical color defects of polysilicon wafers,i.e.,edge discoloration,color inaccuracy and color non-uniformity,a new integrated machine vision detection method is proposed based on an HSV color model.By transforming RGB image into three-channel HSV images,the HSV model can efficiently reduce the disturbances of complex wafer textures.A fuzzy color clustering method is used to detect edge discoloration by defining membership function for each channel image.The mean-value classifying method and region growing method are used to identify the other two defects,respectively.A vision detection system is developed and applied in the production of polysilicon wafers.     

Determination of the compensation band due to birefringence with dispersion and large phase differences

The simple measurement of birefringence by means of a tilting compensator becomes difficult and unreliable when large phase differences must be compensated in samples in which dispersion of birefringence differs from that of the compensator. The problem is treated experimentally and theoretically. The result is a simple correction formula with only one parameter. A method to obtain this parameter is presented. Measurements on polycarbonate, polyethylene and polyurethane support the assumptions of the theoretical calculations.     

Excess Heat Capacity in NTD Ge Thermistors

Neutron Transmutation Doped (NTD) germanium thermistors, cut from metallized wafers, are useful in bolometry. The rise time of a bolometer depends on its heat capacity. We report measurements on the heat capacity of two NTD Ge wafers down to 24 mK temperatures. Both wafers were neutron irradiated and annealed, one of them had in addition undergone a boron implantation and metallization process. For the non-metallized wafer we found a Sommerfeld constant γ = 7.52·10⁻⁷ J K⁻² cm⁻³. A comparison between the two wafers showed an excess heat capacity in the metallized wafer. For example, at 24 mK temperature, the specific heat of the metallized afer is more than twice the value of the non-metallized one.     

Automatic vision-based grain optimization and analysis of multi-crystalline solar wafers using hierarchical region growing

Solar power has become an attractive alternative source of energy. The multi-crystalline solar cell has been widely accepted in the market because it has a relatively low manufacturing cost. Multi-crystalline solar wafers with larger grain sizes and fewer grain boundaries are higher quality and convert energy more efficiently than mono-crystalline solar cells. In this article, a new image processing method is proposed for assessing the wafer quality. An adaptive segmentation algorithm based on region growing is developed to separate the closed regions of individual grains. Using the proposed method, the shape and size of each grain in the wafer image can be precisely evaluated. Two measures of average grain size are taken from the literature and modified to estimate the average grain size. The resulting average grain size estimate dictates the quality of the crystalline solar wafers and can be considered a viable quantitative indicator of conversion efficiency.     

Modelling the deformation of a confectionery wafer as a non-uniform sandwich structure

The aim of this research was to model the mechanical behaviour of wafers found in various confectionery products in order to optimise the manufacturing stage. Compression and bending tests showed that the mechanical behaviour of the wafer was characteristic of a brittle foam. The internal microstructure of the wafer sheet was examined with an optical microscope which showed that the wafer possessed a sandwich structure with a porous core between two denser skins. An analytical model was developed to calculate the individual moduli of the wafer core and skin sections. These modulus values were used in a finite element (FE) model which consisted of a simple repetitive geometry. The FE model simulated the linear deformation of the wafer under compression and bending. The predictions from the analytical and numerical models were compared. They were found to agree in compression but deviated under bending due to the large mismatch of the core and skin moduli.     

A hierarchical model for characterising spatial wafer variations

Silicon wafers are commonly used materials in the semiconductor manufacturing industry. Their geometric quality directly affects the production cost and yield. Therefore, improvement in the quality of wafers is critical for meeting the current competitive market needs. Conventional summary metrics such as total thickness variation, bow and warp can neither fully reflect the local variability within each wafer nor provide useful insight for root cause diagnosis and quality improvement. The advancement of sensing technology enables two-dimensional (2D) data mapping to characterise the geometric shapes of wafers, which provides more information than summary metrics. The objective of this research is to develop a statistical model to characterise the thickness variation of wafers based on 2D data maps. Specifically, the thickness variation of wafers is decomposed into macro-scale and micro-scale variations, which are modelled as a cubic curve and a first-order intrinsic Gaussian Markov random field, respectively. The models can successfully capture both the macro-scale mean trend and the micro-scale local variation, with important engineering implications for process monitoring, fault diagnosis and run-to-run control. A practical case study from a wafer manufacturing process is performed to show the effectiveness of the proposed methodology.