Wafer Inspection Research Articles

Thermal stress induced void formation during 450 mm defect free silicon crystal growth and implications for wafer inspection

When pulling large diameter Si crystals from a melt close to the Voronkov criterion, small changes in pulling speed and thermal gradient can lead to the formation of voids leading to detrimental pits on the polished wafer surface. The creation of voids is mainly due to the lowering of the vacancy formation energy due to increased thermal compressive stress. The small size and low density of the formed voids when pulling crystals close to the Voronkov criterion conditions are a challenge for wafer surface inspection tools and possible solutions are discussed.

Classification and Size Estimation of Wafer Defects by Using Scattered Light Distribution

SUMMARY Usually, wafer inspection is a two-step process. The first step, which is very important, consists of detection of defects on the wafer. The second step classification of the detected defects, which is done after defect detection as necessary. Recently, it has become necessary to perform simultaneous detection and classification of wafer defects in order to reduce the wafer inspection time while maintaining high resolution of inspection. Optical wafer inspection is the most effective method for detecting and classifying defects and estimating their size in a short time. In this method, the scattered light distribution is compared with a database of previous scattered light distributions and pattern matching is used to classify defects and estimate their size. Therefore, to achieve optical wafer inspection based on scattered light distribution, it is necessary to gather scattered light distribution data for many samples of various kinds. The first aim of this study is to develop a defect classification and size estimation method utilizing the scattered light distribution. We propose a method of classifying defects on wafers and estimating their size. The proposed method is based on pattern matching utilizing a parametric eigenspace. The second aim of the paper is to validate the proposed method by applying it to scattered light distribution samples. The light scattering distribution samples were generated by discrete dipole approximation (DDA) simulation. A database of the light scattering distribution is easily created using the simulation.

Photonic nanojet focusing for hollow-core photonic crystal fiber probes

Large-pitch kagome-lattice hollow-core photonic crystal fibers (HC-PCFs) offer appealing optical properties for beam delivery and remote sensing. However, focusing their optical mode on a submicrometer spot can be challenging due to the large mode diameter and low numerical aperture of these fibers. Here, we demonstrate that a 30 μm latex microsphere directly set at the HC-PCF end-face provides an efficient means to focus the fiber mode down to a spot of 540 nm full width at half-maximum thanks to a photonic nanojet effect. The system is used for fluorescence imaging and direct laser writing on a thin absorbing layer. Potential applications include inspection of semiconductor wafers, photolithography, laser surgery, fluorescence sensing, or optical transfection.

Automatic detection of micro-crack in solar wafers and cells: a review

This paper presents a review of the machine detection systems for micro-crack inspection of solar wafers and cells. To-date, there are various methods and procedures that have been developed at various laboratories around the world to inspect solar wafers and solar cells for manufacturing defects. This paper on micro-crack detection offers a comprehensive and an up-to-date review of different detection strategies, describing the main features of each technique together with its strengths as well as weaknesses. This paper will benefit researchers and practitioners, especially those who want to develop automatic inspection systems for inspecting solar wafers or solar cells for micro-cracks.

태양전지 실리콘 웨이퍼의 표면결함 검출을 위한 구조적 하이브리드 조명시스템의 개발 및 최적 조건 선정

본 논문에서 태양전지 실리콘 웨이퍼 검사를 위해 광학스캐닝 메커니즘 기반 검사장비를 개발하였다. 그 중에서 다양한 결함검사 요구와 적절한 조명조건을 만족하는 구조적 하이브리드 조명시스템을 설계하였다. 그 다음으로 실험계획법을 이용하여 구조적 하이브리드 조명시스템의 최적 조명조건을 마스터 유리와 실리콘 웨이퍼에서 선정하였다. 마스터 유리에서 최적 조명조건은 B-강, BG-강, BR-강, BGR-강 이며, 실리콘 웨이퍼에서 최적조건은 R-중-B-중 이다. 이 최적조명조건을 적용하여 실리콘 웨이퍼 표면을 검사한 결과, 핀홀, 스크래치, 치핑 등 다수의 표면결함을 정확하게 검출하였다. 구조적 하이브리드 조명시스템은 태양전지 실리콘 웨이퍼 표면결함 검사에 유용하게 사용될 수 있다.

Use of Astronomy Filters in Fluorescence Microscopy

Monochrome astronomy filters are well suited for use as excitation or suppression filters in fluorescence microscopy. Because of their particular optical design, such filters can be combined with standard halogen light sources for excitation in many fluorescent probes. In this "low energy excitation," photobleaching (fading) or other irritations of native specimens are avoided. Photomicrographs can be taken from living motile fluorescent specimens also with a flash so that fluorescence images can be created free from indistinctness caused by movement. Special filter cubes or dichroic mirrors are not needed for our method. By use of suitable astronomy filters, fluorescence microscopy can be carried out with standard laboratory microscopes equipped with condensers for bright-field (BF) and dark-field (DF) illumination in transmitted light. In BF excitation, the background brightness can be modulated in tiny steps up to dark or black. Moreover, standard industry microscopes fitted with a vertical illuminator for examinations of opaque probes in DF or BF illumination based on incident light (wafer inspections, for instance) can also be used for excitation in epi-illumination when adequate astronomy filters are inserted as excitatory and suppression filters in the illuminating and imaging light path. In all variants, transmission bands can be modulated by transmission shift.

Evaluation of extreme ultraviolet mask defect using blank inspection, patterned mask inspection, and wafer inspection

The key challenge before extreme ultraviolet lithography is to make defect-free masks, for which it is important to identify the root cause of defects, and it is also necessary to establish suitable critical mask defect size for the production of ULSI devices. We have been developing extreme ultraviolet (EUV) mask infrastructures such as a full-field actinic blank inspection tool and 199 nm wavelength patterned mask inspection tool in order to support blank/mask supplier in reducing blank/mask defects which impact wafer printing. In this paper, by evaluating the printability of programmed phase defects and absorber defects exposed by full-field scanner EUV1, we demonstrate that defect detection sensitivities of actinic blank inspection and patterned mask inspection are higher than that of wafer inspection in HP32nm. The evaluations were done by comparing the detection sensitivities of full-field actinic blank inspection tool, 199 nm wavelength patterned mask inspection tool, and electron beam (EB) wafer inspection tool. And then, based on the native defect analysis of blank/mask, we ascertained that actinic blank inspection and patterned mask inspection are effective in detecting killer defects both at the main pattern and at the light-shield border area.

Camtek receives a $3 million order for multiple wafer inspection systems

Camtek receives a $3 million order for multiple wafer inspection systems

Micro crack detection of multi‐crystalline silicon solar wafer using machine vision techniques

PurposeThe detection of invisible micro cracks (μ‐cracks) in multi‐crystalline silicon (mc‐si) solar wafers is difficult because of the wafers' heterogeneously textured backgrounds. The difficulty is twofold. First, invisible μ‐cracks must be visualized to imaging devices. Second, an image processing sequence capable of extracting μ‐cracks from the captured images must be developed. The purpose of this paper is to reveal invisible μ‐cracks that lie beneath the surface of mc‐si solar wafers.Design/methodology/approachTo solve the problems, the authors first set up a near infrared (NIR) imaging system to capture images of interior μ‐cracks. After being able to see the invisible μ‐cracks, a region‐growing flaw detection algorithm was then developed to extract μ‐cracks from the captured images.FindingsThe experimental results showed that the proposed μ‐cracks inspection system is effective in detecting μ‐cracks. In addition, the system can also be used for the inspection of silicon solar wafers for stain, pinhole, inclusion and macro cracks. The overall accuracy of the defect detection system is 99.85 percent.Research limitations/implicationsAt present, the developed prototype system can detect μ‐crack down to 13.4 μm. The inspection resolution is high but the speed is low. However, the limitation on inspection speed can easily be lifted by choosing a higher resolution NIR camera.Practical implicationsGenerally, this paper is a great reference for researchers who are interested in developing automatic optical inspection systems for inspecting solar wafer for invisible μ‐cracks.Originality/valueThe research described in this paper makes a step toward developing an effective while low‐cost approach for revealing invisible μ‐crack of mc‐si solar wafers. The advantages provided by the proposed system include excellent crack detection sensitivity, capability of detecting hidden subsurface μ‐cracks, and low cost.

Special Issue on Measurement and Quality Control

It has now been recognized that prompt scientific and technological measures should be taken against the rapidly expanding globalization of common issues such as ecology, economy, energy, food, and safety. Measurements are the key to progress in the natural sciences and the major requirement for technological innovation. This special issue reviews manufacturing metrology and quality management evolution, where applications now range from macro- to micro- and nanoengineering. The articles presented point out their implications for science, engineering, and industry and highlight the latest in research, development, and potential applications of promising measurement and quality control techniques. These include specific applications in aerospace, automotive and transport, semiconductor devices, photonics, and manufacturing. Measurement and quality control are essential to industrial technology, as shown in cases of quality control of optical devices, the measurement of metal parts in the automotive industry, silicon wafer inspection in the semiconductor industry, and the study of biomedical chips. The developments in such main fields of interests as dimensional metrology in production engineering, laser metrology for precision measurement, and quality management methodology are enabling us to extend applications in emerging basic technologies. In most industrial applications, measurement of dimensional, geometrical, and mechanical quantities in the manufacturing process have changed significantly and globally due to an increasing demand for precision arising from the introduction of new manufacturing technologies and requirements for parts functionality. The requirements of precision engineering made it inevitable to establish traceable metrology supporting the international exchange of goods and the development of precise manufacturing processes. I am certain that this special issue will further strengthen the ongoing effort for attaining excellence inmeasurement science and technology and quality control. I sincerely hope this special issue will give many beginning and established researchers a chance to share 21st Century technology. Lastly, I thank the authors, reviewers, and editors for their invaluable advice, strong backup, and continuing cooperation that have helped ensure the success of this issue.

Camtek receives order for multiple wafer inspection systems

Camtek receives order for multiple wafer inspection systems

High Precision Defect Inspection & Binning

Wafer inspection and defect classification have been traditionally done in Fab solely using wafer level data. For processes as 45 nm and beyond, device performance has become very sensitive to process variations that include litho conditions and process-induced pattern fidelity. For example a slight mismatch in process chamber can have a drastic impact to yield. Also evaluation of OPC treatment on wafer is becoming more difficult when subtle pattern failures can be hidden in high volume of defect data. Certain defect type such as incomplete contact hole cannot be detected before etch and the occurrences can be intermittent, making it virtually impossible to detect them using random sampling [1]. In addition, Foundry Fabs need to meet the challenge of fast device characterization and quick ramp. Design-Aware inspection delivers new capability that allows Fabs to characterize device and process with higher dimension that were not possible before using the traditional approaches.

Quantitative measurement of voltage contrast in scanning electron microscope images for in-line resistance inspection of wafers

We develope an in-line inspection method for partial-electrical measurement of defect resistance, which is quantitatively estimated from the voltage contrast formed in a scanning electron microscopy (SEM) image of an incomplete-contact defect. We first manufacture standard calibration wafers for the voltage-contrast calibration. The contact resistance of systematically formed defects varied from 108 to 1017 . Then, we quantitatively analyze the gray scales of these defect images captured using a review SEM. As a result, calibration curves for estimating the contact resistance of the incomplete-contact defect are obtained at a probe current of 60 pA and a charging voltage of 4 V. The estimated contact resistance is between 107 and 1012 . Finally, this inspection method is applied to wafers manufactured for a static random access memory device. Accordingly, the gray scales of defective plugs formed for shared contact patterns are classified into two levels. The resistances of these defects are estimated from the calibration curve. The estimated resistances of the lower contrast defects (with an accuracy of about one order of magnitude) agree well with the resistances measured using a nanoprober. The resistances of the higher contrast defects are estimated as well, although they are too high to be measured using a nanoprober.

Development of Piezo Driven Inchworm Micro X-Y Stage and Hemispherical Tilting Positioner with Microscope Head

This paper deals with small piezo driven inchworm X-Y stage for a cell-manipulation in SEM chamber. Generally the electric noise from the moto causes the image destorsion in SEM operation. Thus the piezo driven inchworm small X-Y stage has been designed and fabricated as well as another tilting mechanism has been developed so that a micro pipettee can be implemented onto this tilting stage and manipulate such bio cell samples. Here we also developed a manipulation tool with micro force indicating system by using acoustic modulation technique since the microscopic operation in SEM without tactile information is difficult for the operator to control the tool precisely. On the other hand, a self-walking wafer inspection system is also described. The unique system is composed of the hemispherical manipulator and a self-walking piezo driven stage. This small walking mechanism can move on the glass plate that covers on the micro patterned plate. The hemispherical ball with microscope lens that can be rotated by the manner of stick-slip with three point contact piezo actuators is mounted on this self-walking stage so that the microscope lens can be focused onto the target sample to investigate the defect of micro patterns on the printed plate.

Out-of-plane ellipsometry measurements of nanoparticles on surfaces for thin film coated wafer inspection

Measurements of the diameter and size distribution of nanoparticles on wafers are critical parameters in the semiconductor industry, essential to control transistor quality and increase production rate. A goniometric optical scatter instrument (GOSI) has been developed that employs polarized light scattering to make measurements of the diameter and size distribution of nanoparticles on bare and thin film coated wafers. This scatter instrument is capable of distinguishing various types of optical scattering characteristics, which correspond to the diameters of the nanoparticles and thin film thickness, on or near the surfaces using the Mueller matrix calculation in Bobbert and Vlieger (1986) [1]. The experimental results of the GOSI system show good agreement with theoretical predictions for nanoparticles of diameter 100, 200, and 300 nm on wafers coated with thin films of 2, 5, and 10 nm thickness. These results demonstrate that the polarization of light scattered by nanoparticles can be used to determine the size of particulate contaminants on bare and thin film coated silicon wafers.

Development of micro assembly processes for further miniaturization in electronics production

Steady increase of functionality and concurrent reduction of the package size are one of the key driving forces in electronics production. In this paper we will present solutions developed at the institute for the automated assembly of highly miniaturized flip-chips with pitches down to 100 μm. In particular the present and future influences of miniaturization on the main process steps wafer bumping, component placement, reflow soldering and inspection are examined as well as the influences on complementary materials used. Results regarding the achievable yield after assembly and the reliability of the structures will be presented in addition to an analysis of the failure mechanisms.

Reducing Particle Contamination During Pump-down in Load Lock Chamber

Reducing both pump-down time and particle contamination in load lock chambers is important for the vacuum apparatus to improve productivity in semiconductor device manufacturing. In this study, particles that became detached from the chamber wall and flew up in the chamber during pump-down were observed with an in-situ particle monitor. Particles attached to a wafer surface were also counted using a wafer inspection system. The dependence of the number of flying particles on pump-down time constant τ agreed with the dependence of the number of particles attached to the wafer surface on τ. Thus, it was deduced that the in-situ particle monitor was useful for determining a suitable pump-down speed. Furthermore, when the pump-down speed was increased, fast particles were generated, which damaged the fine photoresist patterns.

Nanometer Metrology of Periodic Structures With Ultrafast Optoacoustics

AbstractWe present an optoacoustic method to non-destructively measure the average dimensions of a periodic array of simple structures with aspect ratios greater than 10:1, which are inaccessible to AFM techniques. The technique that we describe could be used as the basis of an inline metrology tool for wafer inspection. The samples examined were test structures with high precision lithographically defined lines of silicon dioxide deposited on a silicon substrate. The thickness of the silicon dioxide was around 400 nm, and the gaps between the lines ranged from 100 nm down to smaller than 40 nm. A drop of water was placed on the sample, and an optoacoustic transducer was placed on top; measurements were taken with a water thickness less than 1 micron between the optoacoustic transducer and the sample. The water filled the spaces between the lines due to the hydrophilic nature of the sample surface. Using the picosecond ultrasonics technique, acoustic pulses are generated in a special optoacoustic transducer, transmitted through a coupling fluid (water), scattered off of the sample being examined and then return to the transducer. The returning acoustic signal shows nanometer sensitivity to the height of the lines and the specific details of their profile.

Wafer defect inspection by neural analysis of region features

Wafer defect inspection is an important process that is performed before die packaging. Conventional wafer inspections are usually performed using human visual judgment. A large number of people visually inspect wafers and hand-mark the defective regions. This requires considerable personnel resources and misjudgment may be introduced due to human fatigue. In order to overcome these shortcomings, this study develops an automatic inspection system that can recognize defective LED dies. An artificial neural network is adopted in the inspection. Actual data obtained from a semiconductor manufacturing company in Taiwan were used in the experiments. The results show that the proposed approach successfully identified the defective dies on LED wafers. Personnel costs and misjudgment due to human fatigue can be reduced using the proposed approach.

Characterization of crystalline defects in silicon for SOI applications by means of light scattering tomography

AbstractCapabilities of LST technique to study defects in silicon wafers for SOI applications are reviewed. Hardware modifications required for quantitative defect size analysis are presented together with novel calibration procedure based on HF inspection of SOI wafers. Examples of LST sensitivity to different types of the defects are demonstrated. Theoretical predictions of dislocation light scattering dependence on polarization have been confirmed allowing determination of dislocation's Burger's vector from LST measurements. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)