Dissertations / Theses on the topic 'Optical surface profilometer'

The research described here provides the technology and theory to quantify surface quality for a variety of wood and wood-based products. This technology provides a means of monitoring trends in surface quality which can be used to discriminate between Agood@ products and Abad@ products (the methods described in this research are not intended to provide ?grading? of individual workpieces) as well as provide information to the machine operator as to the source of poor quality machined surfaces. The analysis can be done either on-line at industrial speeds or off-line as a periodic quality control tool. Although the surface quality can be quantifiably measured, the determination of the best feature from the surface profile (root mean square, peak amplitude, average wavelength, frequency content, Joint Time and Frequency Analysis (JTFA) and Wavelet Analysis results, etc.) for the quantification of surface Adefects@ is highly dependent on the application. This research consisted of three broad areas: (1) determination of an optimal hardware configuration for both laboratory and industrial surface scans of wood products, (2) determination of the optimal set of surface descriptors as well as the development of advanced signal processing techniques such as the wavelet transform to accurately describe the quality of a surface as well as provide information to the machine operator on the cause of the loss of surface quality, and (3) development of a software interface to distill the advanced signal processing techniques into a readily obtainable and readable format for the machine operator as well as provide assistance for process decisions.

Non-contact surface profilometry techniques, especially the phase-measuring profilometry, have been evolved dramatically over recent years. Besides the simple triangulation configuration with a fringe pattern projection system and digital imaging system, efficient computational surface profilometry techniques have also drawn tremendous attention from both academia and a wide range of applications. In the semiconductor industry, high-precision and high-speed, automated optical inspection systems are urgently needed to ensure high quality of semiconductor devices and yield improvement on the production and assembly line. However, by assuming the measured object to be stationary, conventional approaches are not suitable for surface profilometry of moving objects. Moreover, different sources of error such as the low contrast fringe patterns on the measured object, the unevenness in the illumination and the perspective projection effect from the optics will decrease the performance of surface profilometry. To meet these challenges, we have built fringe pattern projection prototypes with projector and camera arrays for surface profilometry of moving objects along the conveyor belt. This design helps to enlarge the field of view with parallel processing. In addition, we have presented an optimization framework to investigate the sources of the error for surface profilometry and generalize various computational surface profilometry approaches under different scenarios. Under this framework, first, we investigate two important factors determining the precision of surface profilometry, namely, the condition number of the phaseshift matrix and the fringe contrast within the images of the projected fringe patterns. Then, a regularized phase-shift algorithm has been proposed to improve the reconstruction results at the low contrast regions such as on the substrate of the semiconductor devices. Second, we study the intensity fluctuation caused by the uneven illumination for surface profilometry of moving objects. After that, an illumination-reflectivity-focus model has been suggested to describe the unevenness and an illumination-invariant phase-shift algorithm has been developed to handle this uneven illumination effect. Third, the perspective projection effect from the optics also affects the accurate phase-shift estimation for a moving object. Therefore, we propose a general polynomial phase-measuring profilometry model to establish the relationship between the phase-shift and height variation for each measured point. Accordingly, a polynomial phase-shift algorithm with error compensation technique has been put forward to improve the performance of the surface profilometry for moving objects. Both simulation and real experiments from the prototype have been conducted to verify the improvement on the performance of the proposed methodologies. Furthermore, these research results have demonstrated the effectiveness and efficiency of the presented optimization framework for investigating the sources of error for surface profilometry. Moreover, the proposed computational surface profilometry techniques and the corresponding fringe pattern projection systems have been used in automated optical inspection systems for yield improvement on the production line in the semiconductor industry.
published_or_final_version
Electrical and Electronic Engineering
Doctoral
Doctor of Philosophy

Manufacturing of precise structures in MEMS, semiconductors, optics and other fields requires high standards in manufacturing and quality control. Appropriate surface topography measurement technologies should therefore deliver nm accuracy in the axial dimension under typical industrial conditions. This work shows the characterization of a dispersion-encoded low-coherence interferometer for the purpose of fast and robust surface topography measurements. The key component of the interferometer is an element with known dispersion. This dispersive element delivers a controlled phase variation in relation to the surface height variation which can be detected in the spectral domain. A laboratory setup equipped with a broadband light source (200 - 1100 nm) was established. Experiments have been carried out on a silicon-based standard with height steps of 100 nm under different thermal conditions such as 293.15 K and 303.15 K. Additionally, the stability of the setup was studied over periods of 5 hours (with constant temperature) and 15 hours (with linear increasing temperature). The analyzed data showed that a height measurement of 97.99 ± 4:9nm for 293.15 K and of 101.43 ± 3:3nm for 303.15 K was possible. The time-resolved measurements revealed that the developed setup is highly stable against small thermal uctuations and shows a linear behaviour under increasing thermal load. Calibration data for the mathmatical corrections under different thermal conditions was obtained.

The subject of this dissertation is the development of three-dimensional (3D) surface profilers for semiconductor back-end inspection. The value of this study is: 1) to provide a new phase-to-height relationship for Fourier Transform Profilometry (FTP) that is universal as it allows alternate FTP system architectures for a micrometer scale object measurement, and 2) to provide a new method for full field substrate warpage and ball grid array (BGA) coplanarity inspection using machine vision. The desire to increase electronic device performance has resulted in denser and smaller IC packaging. As the dimensions of the devices decrease, the requirements for substrate flatness and surface quality become critical in avoiding device failure. For a high yield production, there is an increasing demand in the requirement for the dimensional verification of height, which requires 3D inspection. Based on the current demands from the semiconductor industry, this dissertation addresses the development of fast in-line surface profilers for large volume IC package inspection. Specifically, this dissertation studies two noncontact surface profilers. The first profiler is based on FTP for measuring the IC package front surface, the silicon die and the epoxy underfill profile. The second profiler is based on stereovision and it is intended for inspecting the BGA coplanarity and the substrate warpage. A geometrical shape based matching algorithm is also developed for finding point correspondences between IC package images. The FTP profiler provides a 1 σRMS error of about 4 μm for an IC package sample in an area of 14 mm x 6.5 mm with a 0.13 second data acquisition time. For evaluating the performance of the stereovision system, the linearity between our system and a confocal microscope is studied by measuring a particular IC sample with an area of 38 mm x 28.5 mm. The correlation coefficient is 0.965 and the 2σdifference in the two methods is 26.9 μm for the warpage measurement. For BGA coplanarity inspection the correlation coefficient is 0.952 and the 2difference is 31.2 μm. Data acquisition takes about 0.2 seconds for full field measurements.

Of the wide variety of existing optical techniques for non-contact 3D surface mapping, Fourier Transform Interferometry (FTI) is the method that most elegantly combines simplicity with high speed and high resolution. FTI generates continuous-phase surface maps from a projected optical interference pattern, which is generated with a simple double-pinhole source and collected in a single snapshot using conventional digital camera technology. For enhanced stability and reduced system size, the fringe source can be made from a fiber optic coupler. Unfortunately, many applications require mapping of surfaces that contain challenging features not ideally suited for reconstruction using FTI. Rough and discontinuous surfaces, commonly seen in applications requiring imaging of rock particles, present a unique set of obstacles that cannot be overcome using existing FTI techniques. This work is based on an original analysis of the limitations of FTI and the means in which errors are generated by the particular features encountered in the aggregate mapping application. Several innovative solutions have been developed to enable the use of FTI on rough and discontinuous surfaces. Through filter optimization and development of a novel phase unwrapping and referencing technique, the Method of Multiple References (MoMR), this work has enabled surface error correction and simultaneous imaging of multiple particles using FTI. A complete aggregate profilometry system has been constructed, including a MoMR-FTI software package and graphical user interface, to implement these concepts. The system achieves better than 22µm z-axis resolution, and comprehensive testing has proven it capable to handle a wide variety of particle surfaces. A range of additional features have been developed, such as error correction, particle boundary mapping, and automatic data quality windowing, to enhance the usefulness of the system in its intended application. Because of its high accuracy, high speed and ability to map varied particles, the developed system is ideally suited for large-scale aggregate characterization in highway research laboratories. Additionally, the techniques developed in this work are potentially useful in a large number of applications in which surface roughness or discontinuities pose a challenge.
Ph. D.

The effects of corrosion inhibitors on water quality and the distribution system were studied. This dissertation investigates the effect of inhibitors on iron surface roughness, copper surface roughness, and copper release. Corrosion inhibitors included blended poly/ortho phosphate, sodium orthophosphate, zinc orthophosphate, and sodium silicate. These inhibitors were added to a blend of surface water, groundwater, and desalinated brackish water. Surface roughness of galvanized iron, unlined cast iron, lined cast iron, and polyvinyl chloride was measured using pipe coupons exposed for three months. Roughness of each pipe coupon was measured with an optical surface profiler before and after exposure to inhibitors. For most materials, inhibitor did not have a significant effect on surface roughness; instead, the most significant factor determining the final surface roughness was the initial surface roughness. Coupons with low initial surface roughness tended to have an increase in surface roughness during exposure, and vice versa, implying that surface roughness tended to regress towards an average or equilibrium value. For unlined cast iron, increased alkalinity and increased temperature tended to correspond with increases in surface roughness. Unlined cast iron coupons receiving phosphate inhibitors were more likely to have a significant change in surface roughness, suggesting that phosphate inhibitors affect stability of iron pipe scales. Similar roughness data collected with new copper coupons showed that elevated orthophosphate, alkalinity, and temperature were all factors associated with increased copper surface roughness. The greatest increases in surface roughness were observed with copper coupons receiving phosphate inhibitors. Smaller increases were observed with copper coupons receiving silicate inhibitor or no inhibitor. With phosphate inhibitors, elevated temperature and alkalinity were associated with larger increases in surface roughness and blue-green copper (II) scales.. Otherwise a compact, dull red copper (I) scale was observed. These data suggest that phosphate inhibitor addition corresponds with changes in surface morphology, and surface composition, including the oxidation state of copper solids. The effects of corrosion inhibitors on copper surface chemistry and cuprosolvency were investigated. Most copper scales had X-ray photoelectron spectroscopy binding energies consistent with a mixture of Cu2O, CuO, Cu(OH)2, and other copper (II) salts. Orthophosphate and silica were detected on copper surfaces exposed to each inhibitor. All phosphate and silicate inhibitors reduced copper release relative to the no inhibitor treatments, keeping total copper below the 1.3 mg/L MCLG for all water quality blends. All three kinds of phosphate inhibitors, when added at 1 mg/L as P, corresponded with a 60% reduction in copper release relative to the no inhibitor control. On average, this percent reduction was consistent across varying water quality conditions in all four phases. Similarly when silicate inhibitor was added at 6 mg/L as SiO2, this corresponded with a 25-40% reduction in copper release relative to the no inhibitor control. Hence, on average, for the given inhibitors and doses, phosphate inhibitors provided more predictable control of copper release across changing water quality conditions. A plot of cupric ion concentration versus orthophosphate concentration showed a decrease in copper release consistent with mechanistic control by either cupric phosphate solubility or a diffusion limiting phosphate film. Thermodynamic models were developed to identify feasible controlling solids. For the no inhibitor treatment, Cu(OH)2 provided the closest prediction of copper release. With phosphate inhibitors both Cu(OH)2 and Cu(PO4)·2H2O models provided plausible predictions. Similarly, with silicate inhibitor, the Cu(OH)2 and CuSiO3·H2O models provided plausible predictions.
Ph.D.
Department of Civil and Environmental Engineering
Engineering and Computer Science
Environmental Engineering PhD

Etude d'un profilometre optique base sur la defocalisation d'un faisceau de lumiere blanche. Etude de deux dispositifs optonumeriques d'analyse statistique utilisant les techniques de fourier optiques: un analyseur de particules et un dispositif de classement automatique des surfaces non polies

This work introduces a modified low-coherence interferometry approach for nanometer surface-profilometry. The key component of the interferometer is an element with known dispersion which defines the measurement range as well as the resolution. This dispersive element delivers a controlled phase variation which can be detected in the spectral domain and used to reconstruct height differences on a sample. In the chosen setup, both axial resolution and measurement range are tunable by the choice of the dispersive element. The basic working principle was demonstrated by a laboratory setup equipped with a supercontinuum light source (Δλ = 400 ̶ 1700 nm). Initial experiments were carried out to characterize steps of 101 nm on a silicon height standard. The results showed that the system delivers an accuracy of about 11.8 nm. These measurements also served as a calibration for the second set of measurements. The second experiment consisted of the measurement of the bevel of a silicon wafer. The modified low-coherence interferometer could be utilized to reproduce the slope on the edge within the previously estimated accuracy. The main advantage of the proposed measurement approach is the possibility to collect data without the need for mechanically moving parts.

Within this work a scan-free, low-coherence interferometry approach for surface profilometry with nm-precision is presented. The basic setup consist of a Michelson-type interferometer which is powered by a supercontinuum light-source (Δλ = 400 - 1700 nm). The introduction of an element with known dispersion delivers a controlled phase variation which can be detected in the spectral domain and used to reconstruct height differences on a sample. In order to enable scan-free measurements, the interference signal is spectrally decomposed with a grating and imaged onto a two-dimensional detector. One dimension of this detector records spectral, and therefore height information, while the other dimension stores the spatial position of the corresponding height values. In experiments on a height standard, it could be shown that the setup is capable of recording multiple height steps of 101 nm over a range of 500 µm with an accuracy of about 11.5 nm. Further experiments on conductive paths of a micro-electro-mechanical systems (MEMS) pressure sensor demonstrated that the approach is also suitable to precisely characterize nanometer-sized structures on production-relevant components. The main advantage of the proposed measurement approach is the possibility to collect precise height information over a line on a surface without the need for scanning. This feature makes it interesting for a production-accompanying metrology.

碩士
國立虎尾科技大學
光電與材料科技研究所
100
The proposed profilometer with a ten nanometer vertical resolution is based on common-path heterodyne interferometry and the surface plasmon resonance (SPR) angular sensor . The measurement range is proportional to the inverse of the numerical aperture value. Based on the geometrical optics, when the transmitted light from a lens is incident upon a specimen which is located at the focal plane, the reflection beam back to and after the lens, the light will converges or diverges because of the surface height variations, and then deflects a small angle from the optic axis . Let the beam pass through a SPR angular sensor, the small angle change causes the phase difference change between the test beam and reference signal. So, we can use the heterodyne interferometry to measure this phase value, and transfer it to a surface height. The method has some merits, such as, non-contact, non-destructive, and real-time measurement. The lateral resolution is about several tens μm and the vertical resolution is better than 10nm . We can use it to measure a step height or the thickenss of a film in real-time

碩士
國立臺北科技大學
自動化科技研究所
95
A simultaneous confocal full field 3-D surface profilometer using digital structured fringe projection is presented in the article. Using digital micromirror device (DMD) moiré projection, a digital fringe pattern is developed for lateral scanning with high spatial resolution and measurement efficiency. Four conjugate image sensing modules are configured at four different designated focusing positions, which are controlled by glass plate of different thickness. A depth-focus response curve can be established by achieving simultaneous vertical scanning of full-field surface profilometry. A standard step height has been measured to attest the measurement accuracy and feasibility of the developed approach. The depth measurement resolution can reach up to 0.15µm and the maximum measurement error was verified to be within 3% of the overall measuring height size. The measurement efficiency can be significantly improved for on-line automatic optical inspection (AOI).

碩士
國立臺北科技大學
自動化科技研究所
100
This article presents a modified band-pass filter which is used to improve the accuracy of three-dimensional surface reconstruction. Fourier Transform Profilometry (FTP) uses an image to obtain the profile information of a 3D surface. The aim of this approach is to achieve high-speed measurement. However, When projection a structure light onto a complex shape object, the slope will over the measurement limit. There is a phenomenon for the fundamental frequency and first-order overlapping in the spectrum, lead to very difficult for extracting beneficial information. Therefore, the accuracy of measurement results is influenced by collecting the correct surface information in the frequency domain using band-pass filter. So far, the ellipse filter results better than the circle filter. However, after extraction by using the ellipse band-pass filter, the reconstruction of three-dimensional shape error causes by much redundant information was extracted. Accordingly, we present the optimal band-pass filter for extracting useful information in the spectrum.