Defect Detection Sensitivity Research Articles

Simulation of Edge Cracks Using Pulsed Eddy Current Stimulated Thermography

Thermography has proven to be one of the most effective approaches to detect cracks in conductive specimens over a relatively large area. Pulsed eddy current stimulated thermography is an emerging integrative nondestructive approach for the detection and characterization of surface and subsurface cracks. In this paper, heating behaviors of edge cracks, excited by pulsed eddy currents, are examined using numerical simulations. The simulations are performed using COMSOL multiphysics finite element method simulation software using the AC/DC module. The simulation results show that in the early heating stage, the temperature increases more quickly at the crack tip compared with other points on the sample. The results indicate that to maximize sensitivity, the response should be analyzed in the early stages of the heating period, no more than 100 ms for samples in which we are interested. The eddy current density distribution is changed with a variation in inductor orientation, but the crack tips remain the “hottest” points during the excitation period, which can be used for robust quantitative defect evaluation. Signal feature selection, transient temperature profile of the sample, and influence of the inductor orientation on the detection sensitivity for edge cracks are investigated. The work shows that positioning of the inductor, perpendicular to the crack line, results in the highest sensitivity for defect detection and characterization. The crack orientation can be estimated through the rotation of the linear inductor near the sample edge and the crack tips.

EUV pattern defect detection sensitivity based on aerial image linewidth measurements

As the quality of EUV-wavelength mask inspection microscopes improves over time, the image properties and intensity profiles of reflected light can be evaluated in ever-greater detail. The SEMATECH Berkeley Actinic Inspection Tool (AIT) is one such microscope, featuring mask resolution values that match or exceed those available through lithographic printing in current photoresists. In order to evaluate the defect detection sensitivity of the AIT for dense line patterns on typical masks, the authors study the linewidth roughness (LWR) on two masks, as measured in the EUV images. They report the through-focus and pitch dependence of contrast, image log slope, linewidth, and LWR. The AIT currently reaches LWR 3σ values close to 9nm for 175nm half-pitch lines. This value is below 10% linewidth for nearly all lines routinely measured in the AIT. Evidence suggests that this lower level may arise from the mask’s inherent pattern roughness. While the sensitivity limit of the AIT has not yet been established, it is clear that the AIT has the required sensitivity to detect defects that cause 10% linewidth changes in line sizes of 125nm and larger.

Improvement of penetrant-testing methods

A study has been made of the influence of different factors (characteristics of technological stages of testing, roughness of the tested surface, and thermal effects) on the sensitivity and efficiency of nondestructive-penetrant-testing methods. Facilities for quantitative evaluation of the sensitivity of sets of flaw-detector materials and indicator liquids and the technological regime of testing with blowing of the tested surface with warm air, in which the sensitivity and efficiency of flaw detection of penetrant-testing methods increase significantly, have been developed.

Automated visual inspection of imprinted pharmaceutical tablets

This paper is on automated visual inspection of tablets that may, in contrast to manual tablet sorting, provide objective and reproducible tablet quality assurance. Visual inspection of the ever-increasing numbers of produced imprinted tablets, regulatory enforced for unambiguous identification of active ingredients and dosage strength of each tablet, is especially demanding. The problem becomes more tractable by incorporating some a priori knowledge of the imprint shape and/or appearance. For this purpose, we consider two alternative automated tablet defect detection methods. The geometrical method, incorporating geometrical a priori knowledge of the imprint shape, enables specific inspection of the imprinted and non-imprinted tablet surface, while the statistical method exploits statistical a priori knowledge of tablet surface appearance, derived from a training image database. The two methods were evaluated on a large tablet image database, consisting of 3445 images of four types of imprinted tablets, with and without typical production defects. A ‘gold standard’ for testing the performances of the two inspection methods was established by manually classifying the tablets into good and five defective classes. The results, obtained by ROC (receiver operating characteristics) analysis, indicate that the statistical method yields better defect detection sensitivity and specificity than the geometrical method. Both presented image analysis methods are quite general and promising tools for automated visual inspection of imprinted pharmaceutical tablets.

Defect detection in thin plates by ultrasonic lamb wave techniques

In the present study, the ability of ultrasonic lamb wave testing for defect detection and sizing in a thin aluminium plate (2mm in thickness) was investigated. The numerical methods were applied for drawing the dispersion and displacement curves of lamb waves in order to adopt mode selection. Two ultrasonic lamb wave techniques, pulse-echo (a1 mode as emitter) and emission (s1 mode as emitter), were applied for interpretation of notch defects with depths of 10, 30 and 60% of plate thickness. It was observed that these techniques are sensitive enough to evaluate notch defects, especially in short probe to defect distances. Defect location and defect length were proposed to be determined in the manner similar to common ultrasonic testing methods. Also, a Distance-Amplitude-Correction (DAC) curve was proposed for defect sizing which showed that amplitude analysis can give some qualitative information about defect depth but results were not always repeatable. The pulse-echo method showed better sensitivity for defect detection and sizing.

63.2: New-Generation Electro-Optic Modulator for TFT Array Inspection

A new generation of electro-optic (EO) modulator has been developed for thin film transistor (TFT) array inspection with improved defect detection sensitivity and reliability. The new modulators are made of solvent-based polymer dispersed liquid crystal (PDLC) and by a simple spin coating and a vacuum lamination process.

Detection of Small Convex and Concave Defects on Optical Films by Patterned Illumination (3rd Report)

This paper describes an optimum designing method of optical system for convex and concave defect detection, which uses patterned illumination. “Reaching Range of the Ray(RRR)”, which is calculated numerically based on the defect shape, is defined. RRR indicates width of effective area on the patterned illumination that contributes to observation of the defect. It is used as guidance for sensitivity of defect detection. Determination method of illumination pattern and optical alignment by using detection sensitivity based on RRR is shown. This paper also described an estimation method of observation images of defects and a selection method of defect detection algorithm for various shapes of defects.

Multiple-parameter CMOS IC testing with increased sensitivity for I/sub DDQ/

Technology scaling challenges the effectiveness of current-based test techniques such as I/sub DDQ/. Furthermore, existing leakage reduction techniques are not as effective in aggressively scaled technologies. We exploited intrinsic dependencies of transistor and circuit leakage on clock frequency, temperature, and reverse body bias (RBB) to discriminate fast ICs from defective ones. Transistor and circuit parameters were measured and correlated to demonstrate leakage-based testing solutions with improved sensitivity. We used a test IC with available body terminals for our experimental measurements. Our data suggest adopting a sensitive multiple-parameter test solution. For high performance IC applications, we propose a new test technique, I/sub DDQ/ versus F/sub MAX/ (maximum operating frequency), in conjunction with using temperature (or RBB) to improve the defect detection sensitivity. For cost sensitive applications, I/sub DDQ/ versus temperature test can be deployed. Our data show that temperature (cooling from 110/spl deg/C to room) improved sensitivity of I/sub DDQ/ versus F/sub MAX/ two-parameter test by more than an order of magnitude (13.8/spl times/). The sensitivity can also be tuned by proper selection of a temperature range to match a required defect per million (DPM) level.

Science and technology of non-destructive testing, evaluation and characterisation

The quality of life available to the majority of citizens of any country is a direct measure of its state of economy. India has shown the quality consciousness through its rich tradition, heritage, monuments and idols. From the heritage to the atomic, space and information age, India has matured as a nation endowed with expertise in relevant and critical technologies. In India there has been a sustained and comprehensive approach to the development of industries for production of precision, strategic and heavy components of high quality through the application of non-destructive evaluation (NDE) techniques and procedures. A large number of non-destructive testing techniques have been developed in India by strategic and core sectors for in-house requirements. Academic institutes have played a key role in nurturing excellence in the area. The knowledge base is made available to the needy industries. With the availability of these techniques, together with the advent of advanced electronics, innovations in sensor technology, availability of computers and signal and image processing methodologies, improvement in detection sensitivity and quantitative characterisation of defects and assessment of microstructural degradation have taken place. The outcome of these developments is the improvement in fitness for purpose of fabricated components and their performance in service with a possibility for their life extension. An example is the front line research carried out and the expertise developed at IGCAR in the area of NDT&E in the last two decades. The expertise has been effectively utilised for finding reliable, comprehensive and cost-effective solutions for many unique and challenging problems in strategic (nuclear, space, and defence) and core (power, chemical and petrochemical) sectors. In this paper an overview of the authors' experience in the developments and applications of advanced NDE methodologies for a variety of applications has been given.

A New Inspection Method for Phase-Shift Mask (PSM) on Deep-UV Inspection Light Source

As the mask pattern becomes smaller and more complex, the demand for a highly precise mask inspection system with high detection sensitivity and few false defects increases. In regard to inspection systems using a deep-UV wavelength, some issues have been encountered concerning inspection of an ArF-halftone (ArF-HT) mask, which is now entering practically used. In this paper, we report the defect detection sensitivity of Cr and KrF-HT masks, and discuss the issues concerning ArF-HT mask inspection and countermeasures to deal with them.

Thermo-optical modulation of ultrasonic surface waves for NDE

The well-known thermo-elastic effect of laser irradiation can be exploited to produce strong localized stresses when an expanded, long pulse, low-intensity laser beam is used to irradiate the specimen. These stresses will produce a parametric modulation of the received ultrasonic signals, that is somewhat similar to the acousto-elastic effect often used in nonlinear ultrasonic studies. It is shown in this paper that otherwise hidden small cracks in fatigue-damaged aluminum and titanium specimens can be readily detected by exploiting this optically induced thermo-elastic modulation during ultrasonic surface wave inspection since they are susceptible to crack closure and therefore exhibit strong parametric modulation. The temporal and spatial variations of the ultrasonic signals due to laser irradiation were evaluated numerically and experimentally. Based on these results, the direct temperature modulation of the ultrasonic velocity can be separated from the thermo-elastic stress modulation present only in cracked specimens. It was found that this method can be used to selectively increase the sensitivity of ultrasonic flaw detection to small fatigue cracks by more than one order of magnitude.

Evaluation of eddy current probes based on local field excitation

The paper deals with the eddy current testing by means of a technique based on local field excitation, with the objective to enhance sensitivity and spatial resolution of flaw detection. Two modifications of innovative eddy current probes are presented. Results of the application of the probes for an examination of thin Inconel plate specimens with small artificial defects on the opposite surface are compared. The criteria for comparison are signal-to-noise ratios and spatial resolution of the responses obtained. Performance of the probes is analyzed on the basis of the study of the distribution of their excitation fields with application of magneto-optic sensors and finite element modeling. The decrease of the local extent of the excitation field has been found to be the main cause of sensitivity decrease of the probes to detect opposite-surface defects.

Improving Sensitivity and Reliability of Magnetic-Induction Flaw Detection Based on Dynamic Parametric Spectral Analysis

The paper describes a novel technique for pipe testing based on visualization of parametric pseudo-spectral characteristics of segmented signals from a magnetic-induction flaw detector. As compared with the method of fast spectral Fourier analysis, the new approach provides higher sensitivity and reliability of flaw detection in the presence of notable structural and signal noise. Results of experimental tests of the technique are given.

Guided wave nuances for ultrasonic nondestructive evaluation

Recent developments in guided wave generation, reception, and mode control show that increased penetration power and sensitivity are possible. A tone burst function generator and appropriate signal processing are generally used. Variable angle beam and comb-type transducers are the key to this effort. Problems in tubing, piping, hidden corrosion detection in aging aircraft, adhesive and diffusion bonding, and ice detection are discussed. Additionally, sample configurations, inspection objectives, and logic are being developed for such sample problems as defect detection and analysis in lap splice joints, tear straps, cracks in a second layer, hidden corrosion in multiple layers, cracks from rivet holes, transverse cracking in a beam, and cracks in landing gear assembly. Theoretical and experimental aspects of guided wave analysis include phase velocity, group velocity, and attenuation dispersion curves; boundary element model analysis for reflection and transmission factor analysis; use of wave structure for defect detection sensitivity; source influence on the phase velocity spectrum, and the use of angle beam and comb transducer technology. Probe design and modeling considerations are being explored. Utilization of in-plane and out-of-plane displacement patterns on the surface and longitudinal power distribution across the structural cross-section are considered for improved sensitivity, penetration power, and resolution in nondestructive evaluation. Methods of controlling the phase velocity spectrum for mode and frequency selection are available. Such features as group velocity change, mode cut-off measurements, mode conversion, amplitude ratios of transmission, and reflection factors of specific mode and frequency as input will be introduced for their ability to be used in flaw and material characterization analysis.

Backside Analysis: Developments in SEI and TIVA

Abstract Recent developments in two relatively new failure analysis techniques, Seebeck effect imaging (SEI) and thermally-induced voltage alteration (TIVA), have greatly improved their defect detection sensitivity and image acquisition times for localizing open and shorted interconnections. This article presents several examples demonstrating the enhanced capabilities of these two methods.

Modeling for flaw sizing potential with guided waves

Guided waves have demonstrated their value in flaw detection in a variety of different and unusual circumstances, including inspection over long distances with just 1 or 2 probes and inspection under coatings, fluids, and insulation. Via mode control and phase velocity and frequency tuning, defect detection sensitivity can be superb. The problem of going beyond detection to defect classification and sizing, however, is extremely difficult. By way of boundary element modeling, some new approaches to classification and sizing are introduced. A theoretical presentation illustrates some trends and features that might be useful in sizing analysis. Parametric studies and analysis showing amplitude versus frequency profiles for various mode input and mode conversion output via through transmission are presented. A few basic flaw shapes of different size are studied in an attempt to shed some light onto the difficult classification and sizing process.

High-sensitivity Defect Evaluation by a New Preferential Etching Technique for Highly As-doped Si Crystals

A high-sensitivity preferential etching technique is presented to evaluate crystal defects in a highly As-doped silicon crystal with a resistivity lower than 0.01 Ω· cm. For highly doped n-type Si, a conventional preferential etching technique, such as Secco etching, Wright etching or Dash etching becomes less useful because of a significant decrease in defect detection sensitivity. The new method is quite sensitive to dislocations, stacking faults and oxygen precipitates in highly As-doped crystals with a surface of either (111) or (100). In this method, copper is first decorated at the defect site, then the defect is preferentially etched by a dilute alkaline solution. The technique thus offers us a sensitive and Cr-free method, attractive from an environmental aspect. A correlation between the laser scattering method is also obtained for the oxygen precipitate density.

Detection and Sizing of Defects in Control Rod Drive Mechanism Penetrations Using Eddy Current and Ultrasonics

Over the last two years, concern has been generated about the capabilities of performing nondestructive evaluation (NDE) of the closure-head penetrations in nuclear-reactor pressure vessels. These penetrations are primarily for instrumentation and control rod drive mechanisms (CRDMs) and are usually thick-walled Inconel tubes, which are shrink-fttted into the steel closure head. The penetrations are then welded between the outside surface of the penetration and the inside surface of the closure head. Stress corrosion cracks initiating at the inner surface of the penetration have been reported at several plants. Through-wall cracks in the CRDM penetration or CRDM weld could lead to loss of coolant in the reactor vessel. The CRDM penetration presents a complex inspection geometry for conventional NDE techniques. A thermal sleeve, through which pass the mechanical linkages for operating the control rods, is inserted into the penetration in such a way that only a small annulus (nominally 3 mm) exists between the thermal sleeve and inside surface of the penetration. Ultrasonic (UT) and eddy current testing (ET) techniques that could be used to provide defect detection and sizing capability were investigated. NDE techniques that could be applied inside and outside the annulus were investigated, but the major goal was to provide high defect-detection sensitivity without requiring removal of the thermal sleeve. As a result of this investigation, both ET and UT techniques for the CRDM penetrations have been developed and evaluated. Long, thin probes were designed to fit into the annulus to carry both eddy current coils and irrigated ultrasonic transducers into the region of interest. The eddy current probes were used primarily to detect cracks in the penetration while the ultrasonic transducers were used to provide an estimate of the remaining wall thickness. This paper describes the ET and UT techniques, the probes developed, and the results obtained using these probes and techniques on CRDM penetration mock-ups.

A sensitive technique for detecting low concentrations of deep level traps: Current-source deep level transient spectroscopy

A defect characterization method is presented that promises to provide improved defect detection sensitivity. The new technique involves the use of current-source biasing of a pn diode. Under current-source bias the junction voltage is transient, whereas standard deep level transient spectroscopy typically involves voltage-source bias with either capacitance or current transients. Computer simulations predict voltage transients of 5 mV from samples that, under identical trap capture and emission conditions, yield capacitance and current transients of only 0.2 fF and 0.7 pA. The new approach can tolerate large leakage currents, and the voltage transient amplitude is independent of device area.

Enhancement of acoustic imaging of polymers by cooling

A low temperature acoustic imaging technique is proposed to enhance the sensitivity of defect detection in materials with highly temperature dependent acoustic properties. An acoustic imaging device has been developed where the sample temperature is precisely controlled between 30 and −94°C using a methanol coupler. To illustrate both the feasibility and advantages of this method, a bonded structure using bisphenol ether type epoxy resin was observed; and defects and non-uniform structure not visible at ambient temperature became apparent in 25 MHz acoustic images when the sample was cooled to −30°C. From measurements of velocity and attenuation, this improvement was ascribed primarily to a decrease in the attenuation loss within the epoxy resin. The use of phased arrays and non-destructive evaluation of fibre-reinforced plastics are also discussed.