Diameter is one of the most fundamental and important parameters that characterize the optical properties of a tapered fiber, so it is necessary to accurately measure its diameter. In this study, we proposed a method for measuring the diameter in the sub-1 µm diameter region of a tapered fiber by measuring the spatial period of the standing wave formed by counter-propagating light waves incident from its both sides. We used a scanning near-field optical microscopy (SNOM) probe fabricated from an optical fiber to measure the standing wave intensity distribution along the tapered fiber axial direction and its spatial period, from which the tapered fiber diameter can be estimated.
The significant development of terahertz wave technology requires precise measurement of terahertz optical devices such as diffractive gratings with micrometer-scale periodicity. We propose a new measurement method for fast, robust and precise shape measurement of micro-periodic structures, which can be regarded as a scan-less version of the deflectometry. Whereas the deflectometry demands the scanning of the beam spot in order to collect the tilt angle information from various different position on the sample surface, the proposed method simultaneously obtains it from a single diffraction image, then reconstructs the sample shape based on a light reflection model called ray reflection model. In comparison to the interferometry, the proposed method is principally robust to the mechanical vibration because the diffraction image is hardly affected by the displacement of the sample. The limitation of the proposed method is also discussed, and the mathematical expression of the constraint conditions required for the shape reconstruction is clarified. The numerical experiment based on the electromagnetic simulation with rigorous coupled-wave analysis (RCWA) demonstrates the possible accuracy on the order of 10 nm and the effectiveness of the use of the incoherent light. The physical experiment is also conducted by the constructed optical system, and the fundamental validity of the measurement result of the proposed method is confirmed.
KEYWORDS: Finite-difference time-domain method, Super resolution, Near field, Near field optics, Microscopy, Waveguides, Reflection, Reconstruction algorithms, Diffraction, Light scattering
The optical-based super-resolution, non-invasive method is preferred for the inspection of surfaces with massive
microstructures widely applied in functional surfaces. The Structured Illumination Microscopy (SIM) uses standing-wave
illumination to reach optical super-resolution. Recently, coherent SIM is being studied. It can obtain both the super-resolved
intensity distribution and the phase and amplitude distribution from the sample surface. By analysis of the phase-depth
dependency, the depth measurement for microgroove structures with coherent SIM is expected. FDTD analysis is applied
for observing the near-field response of microgroove narrower than the diffraction limit under the standing-wave
illumination. The near-field phase shows depth dependency in this analysis.
Tapered fibers with a diameter of sub-micrometer to several micrometer show various optical characteristics, and the diameter is the most important parameter. To guarantee their functions, it is necessary to measure the fiber diameter with high precision during manufacturing. In this research, we propose an in-process measurement method of the diameter of sub-micro-optical fiber. The proposed technique is based on analyzing optically scattered light generated by standing wave illumination. First, we show the scattering characteristics of sub-microfibers using numerical simulation based on finite element method (FEM). From the result of simulation, it was revealed that the optical fiber of 100 nm in diameter can be evaluated with the standing wave illumination.
As represented by "Lab on a Tip" using microchannels, the miniaturization of manufacturing and inspection processes attracts widespread interest. Therefore, many micro-tool fabrication techniques using optical tweezers have been reported. Most reported methods focus on assembling trapped microbeads, and it was necessary to have a photocurable resin phase and surface modification process to assemble solid beads. However, because many procedures such as dispersion of microbeads and removal from the resin solution were required, flexible one-step fabrication is difficult with previous methods. This study proposed a direct adhesion and assembly of the photocurable resin droplets dispersed in the aqueous solution. Since the photocurable droplets work as both base material and an adhesive, a flexible one-step fabrication of micro-tools can be achieved. It was experimentally found that the morphology of emulsion droplets in contact significantly affects the adhesion. Generally, oil-in-water emulsion droplets are stabilized by a surfactant, and adhesion between droplets can be disturbed by a surfactant bilayer. By controlling the contact angle between the droplets, the optically trapped droplets successfully adhered together with photopolymerization. Furthermore, combining the various diameter and materials of emulsion droplets using microfluidic channels, more functional and complex microtools can be expected.
KEYWORDS: Optics manufacturing, Near field optics, Near field scanning optical microscopy, Optical testing, Fusion energy, Remote sensing, Diffraction, Free space optics, Control systems, Spatial resolution
In the nano/micro manufacturing, in-process optical inspection plays one of the most important roles for producing the advanced products with high reliability, because it has several practical advantages typified by nondestructiveness, high-throughput characteristics, and so on. Optical measurement methods, however, essentially restrict its spatial resolution due to the diffraction limit, which means that finer structures less than half of the wavelength of optical wave from the objects to be inspected, cannot be observed. This resolution limit of the optical measurement method is a critical problem especially for the nano/micro manufacturing process, where the features of submicrometer fine structures should generate special functions. This critical limit about spatial resolution can be physically explained by focusing on light energy localization property. As shown in Table1, light energy can be mainly classified into the following three types of localizations: (1) Evanescent light generated under the total internal reflection. (2) Near-field light existing in the vicinity of tips of the near-field optical probe. (3) Interference intensity distribution of standing wave (mainly generated with two beam interference) and focusing beam (generated with multiple-beam interference), both of which consist of free-space propagating light (freely propagating light) waves. Physical principles for spatial resolution improvement are essentially different based on these types of light energy localization. In order to develop the effective optical inspection beyond the diffraction limit, it is important to recognize their super resolution property depending on their light localization. Evanescent light is known as effective near-field light illumination for surface, which can be applied to near-field scanning optical microscopic inspections.
In the next generation SAOP (Self-aligned Octuplet patterning) process, the line width and LWR (Line Width Roughness) measurement of lines with sub-10 nm is required. We have already proposed a novel method of line width and LWR measurement with sub-nanometer uncertainty by using FIB (Focused Ion Beam) processing, and TEM (Transmission Electron Microscope) images as reference metrology. In the previous report, we applied the method to SAQP features. A specimen of the SAQP FinFET line and space device is coated with carbon and cut horizontally into a thin planar sample by the FIB sampling system. The thin sample is observed by using planar-TEM. The average PSD of LWR of SAQP FinFET sample at the upper and lower positions calculated from planar-TEM images.
In this article, we apply the methodology to line width and roughness measurement of advanced features by SAOP process. The features are vertically or horizontally sliced as a thin specimen by FIB micro sampling system. LWR is calculated from the edges positions, and PSD (Power Spectrum Density) is analyzed for the reference metrology.
KEYWORDS: Line width roughness, Extreme ultraviolet, Fin field effect transistors, Edge detection, Semiconductors, Metrology, Ion beams, Electron microscopes, Line edge roughness, Transmission electron microscopy
Line edge roughness (LER) and linewidth roughness (LWR) of a semiconductor device are important measures for evaluating its performance. Conventionally, LER and LWR have been evaluated from critical dimension scanning electron microscope (CD-SEM) images. However, the problem with CD-SEM measurement is that the high-frequency image noise is large, and the resolution is not sufficiently high. In order to overcome the problem of image noise in CD-SEM measurement, some techniques have been proposed. In these methods, it is necessary to set the parameters for the model and processing, and it is required to verify the correctness of these parameters using reference metrology. We have already proposed a reference metrology using the focused ion beam process and planar transmission electron microscope (planar-TEM) method. In this study, we apply the proposed method to three new samples, namely self-aligned quadruple patterning fin-shaped field-effect transistor device, extreme ultraviolet lithography (EUV) conventional resist, and EUV new material resist. The LWR and the power spectral density (PSD) of LWR are calculated from the edge positions on planar-TEM images. We confirm that the LWR and the PSD of LWR can be measured with high accuracy and evaluate the difference between PSD by the proposed method and that by CD-SEM images. Furthermore, from comparisons with the PSD of the same sample obtained using CD-SEM, the validity of measurement of PSD and LWR by CD-SEM is verified.
KEYWORDS: Line width roughness, Extreme ultraviolet, Fin field effect transistors, Transmission electron microscopy, Edge detection, Metrology, Line edge roughness, Semiconductors, Denoising
LER (Line Edge Roughness) and LWR (Line Width Roughness) of the semiconductor device are an important evaluation scale of the performance of the device. Conventionally, LER and LWR is evaluated from CD-SEM (Critical Dimension Scanning Electron Microscope) images. However, CD-SEM measurement has a problem that high frequency random noise is large, and resolution is not sufficiently high. For random noise of CD-SEM measurement, some techniques are proposed. In these methods, it is necessary to set parameters for model and processing, and it is necessary to verify the correctness of these parameters using reference metrology. We have already proposed a novel reference metrology using FIB (Focused Ion Beam) process and planar-TEM (Transmission Electron Microscope) method. In this study, we applied the proposed method to three new samples such as SAQP (Self-Aligned Quadruple Patterning) FinFET device, EUV (Extreme Ultraviolet Lithography) conventional resist, and EUV new material resist. LWR and PSD (Power Spectral Density) of LWR are calculated from the edge positions on planar-TEM images. We confirmed that LWR and PSD of LWR can be measured with high accuracy and evaluated the difference by the proposed method. Furthermore, from comparisons with PSD of the same sample by CD-SEM, the validity of measurement of PSD and LWR by CD-SEM can be verified.
We propose a laser trapping-based scanning dimensional measurement method for free-form surfaces. We previously developed a laser trapping-based microprobe for three-dimensional coordinate metrology. This probe performs two types of measurements: a tactile coordinate and a scanning measurement in the same coordinate system. The proposed scanning measurement exploits optical interference. A standing-wave field is generated between the laser-trapped microsphere and the measured surface because of the interference from the retroreflected light. The standing-wave field produces an effective length scale, and the trapped microsphere acts as a sensor to read this scale. A horizontal scan of the trapped microsphere produces a phase shift of the standing wave according to the surface topography. This shift can be measured from the change in the microsphere position. The dynamics of the trapped microsphere within the standing-wave field was estimated using a harmonic model, from which the measured surface can be reconstructed. A spherical lens was measured experimentally, yielding a radius of curvature of 2.59 mm, in agreement with the nominal specification (2.60 mm). The difference between the measured points and a spherical fitted curve was 96 nm, which demonstrates the scanning function of the laser trapping-based microprobe for free-form surfaces.
KEYWORDS: CMOS sensors, Coating, 3D metrology, Scanning transmission electron microscopy, Metrology, Transmission electron microscopy, Line width roughness, Semiconducting wafers, Semiconductors
A novel method of sub-nanometer uncertainty for the 3D-profile measurement and LWR (Line Width Roughness) measurement by using FIB (Focused Ion Beam) processing, and TEM (Transmission Electron Microscope) and CD-SEM (Critical Dimension Scanning Electron Microscope) images measurement is proposed to standardize 3D-profile measurement through reference metrology. In this article, we apply the methodology to line profile measurements and roughness measurement of advanced FinFET (Fin-shaped Field-Effect Transistor) features. The FinFET features are horizontally sliced as a thin specimen by FIB micro sampling system. Horizontally images of the specimens are obtained then by a planar TEM. LWR is calculated from the edges positions on TEM images. Moreover, we already have demonstrated the novel on-wafer 3D-profile metrology as "FIB-to-CDSEM method" with FIB slope cut and CD-SEM measuring. Using the method, a few micrometers wide on a wafer is coated and cut by 45-degree slope using FIB tool. Then, the wafer is transferred to CD-SEM to measure the cross section image by top down CD-SEM measurement. We applied FIB-to-CDSEM method to a CMOS image sensor feature. The 45-degree slope cut surface is observed using AFM. The surface profile of slope cut surface and line profiles are analyzed for improving the accuracy of FIB-to-CDSEM method.
KEYWORDS: Scanning transmission electron microscopy, Semiconducting wafers, Transmission electron microscopy, CMOS sensors, Metrology, Semiconductors, Edge detection, 3D metrology, Electron microscopes
A method of sub-nanometer uncertainty for the 3D-profile measurement using TEM (Transmission Electron Microscope) images is proposed to standardize 3D-profile measurement through reference metrology. The proposed method has been validated for profiles of Si lines, photoresist features and advanced-FinFET (Fin-shaped Field-Effect Transistor) features in our previous investigations. However, efficiency of 3D-profile measurement using TEM is limited by measurement time including processing of the sample. In this article, we demonstrate a novel on-wafer 3D-profile metrology as "FIB-to-CDSEM method" with FIB (Focused Ion Beam) slope cut and CD-SEM (Critical Dimension Secondary Electron Microscope) measuring. Using the method, a few micrometer wide on a wafer is coated and cut by 45 degree slope using FIB tool. Then, the wafer is transferred to CD-SEM to measure the cross section image by top down CD-SEM measurement. We apply FIB-to-CDSEM method to CMOS sensor device. 3D-profile and 3D-profile parameters such as top line width and side wall angles of CMOS sensor device are evaluated. The 3D-profile parameters also are measured by TEM images as reference metrology. We compare the 3D-profile parameters by TEM method and FIB-to-CDSEM method. The average values and correlations on the wafer are agreed well between TEM and FIB-to- CDSEM methods.
A novel method of sub-nanometer uncertainty for the line profile measurement using TEM (Transmission Electron Microscope) images is proposed to calibrate CD-SEM (Critical Dimension Scanning Electron Microscope) line width measurement and to standardize line profile measurement through reference metrology. The proposed method has been validated for profile of Si line and photoresist features in our previous investigations. In this article, we apply the methodology to line profile measurements of advanced-FinFET (Fin-shaped Field-Effect Transistor) features. The FinFET features are sliced as thin specimens of 100 nm thickness by FIB (Focused Ion Beam) micro sampling system. Cross-sectional images of the specimens are obtained then by TEM. The profiles of fin, hardmask and dummy gate of FinFET features are evaluated using TEM images. The width of fin, the length of hardmask, and the length of dummy gate of FinFET features are measured and compared to CD-SEM measurement. The TEM results will be used to implement CD-SEM and CD-AFM reference metrology.
The novel method of sub-nanometer uncertainty for the line width measurement and the line profile measurement using STEM (Scanning Transmission Electron Microscope) images is proposed to calibrate CD-SEM line width measurement and the standardization of line profile measurement as reference metrology. In accordance with the proposed method, we already have established the methodology of profile of Si line and photoresist feature for reference metrology. In this article, we applied the proposed method to the sidewall roughness measurement of photoresist features and line profile measurement of finFET features. Using the proposed method, specimens of photoresist feature and finFET feature are sliced as thin specimens of 100 nm thickness by FIB (Focused Ion Beam) micro sampling system. Then the cross-sectional images of the specimens are obtained by STEM and TEM. The sidewall roughness of photoresist features is estimated by the maximum slope of the image intensity graph at the edge. Then, the sidewall roughness is also measured by CD-AFM (Critical Dimension Atomic Force Microscope); we compared the results by STEM image and CD-AFM. Moreover, the line profile of finFET features is defined using TEM images for reference metrology. We compared the line width of fin measured by the proposed method and CD value by CD-SEM measurement.
The novel method of sub-nanometer uncertainty for the line width measurement and line profile measurement using STEM (Scanning Transmission Electron Microscope) images is proposed to calibrate CD-SEM line width measurement and standardization of line profile measurement as reference metrology. In accordance with the proposed method, we already have established the methodology of Si line profile and line width measurement for reference metrology. In this article, we applied the proposed method to edge determination methodology of the photoresist feature. Using the proposed method, a specimen of photoresist feature is coated with metal, and then it is sliced as a thin specimen of 100 nm thickness by FIB (Focused Ion Beam) micro sampling system. Then the dark-field cross-sectional images of the specimen are obtained by STEM. The edge position of the photoresist is defined at the distance of half metal coating thickness from the peak positions of metal coating area. Then the detected line profiles are compared with the measurement results by CD-AFM. From series of analyses, we established the edge detection methodology of photoresist feature for reference metrology.
The novel method of sub-nanometer accuracy (uncertainty) for the line width measurement and line edge detection using
STEM (Scanning Transmission Electron Microscope) images is proposed to calibrate CD-SEM line width measurement
and standardization of line edge detection. In accordance with the proposed method, the traceability and reference
metrology are established using Si lattice structures and edge detection of Si line with metal coating. First, the interface
of SiO2-Air is defined using image intensity of STEM dark field images after metal coating. Second, an image
magnification is calculated using 2D Fourier analysis of the images. Third, the edge positions are detected. Using the
proposed method, the expanded uncertainty (3 sigma) less than 0.3 nm for the line width of 50 nm is established.
Large aspheric optical mirrors and lens are wildly used in high-tech industry such as huge telescopes and synchrotron radiation facilities. The measurement uncertainty of the surfaces is needed to be under several tens of nanometers. Current methods such as interferometry method are not available for measuring aspheric surface with departure over hundreds of wavelength. In this paper, we proposed a new method called improved 3D deflectometry method. Rotatable optical devices are applied to enlarge the measuring range of autocollimator with highly accuracy but small measuring range. Data processing methods are also proposed to improve the measurement uncertainty. Experimental setup is designed based on proposed method. Spherical concave mirror with curvature radius of 5000 mm is measured successfully. The repeatability (mean standard deviation) of 10 times measurement is less than 10 nanometers.
We described a multi-probe system comprising three laser interferometers and one autocollimator to measure a flat bar
mirror profile with nanometer accuracy. The simulation and pre-experiment of multi-probe system have been conducted
on an X-Y linear stage which is composed of a ball bearing slider and a stepping motor. The two standard deviation of
the flat bar mirror profile is mainly fitting the range of simulation results (±20 nm). Comparison of our measured data
with the results measured by ZYGO white light interferometer system showed agreement to within approximately ±30
nm, excluding some points at the edge of the mirror. From the pre-experiment results, we conclude that the systematic
error caused by accuracy of the moving stage can't be ignored. To eliminate this systematic error, the multi-probe system
has been implemented on a high-precision micro-coordinate measuring machine (M-CMM) that has been built at the
Advanced Industrial Science and Technology (AIST).
The novel method of sub-nanometer accuracy (uncertainty) for the line width and line profile measurement using STEM
(Scanning Transmission Electron Microscope) images is proposed to calibrate CD-SEM line width measurement. In
accordance with the proposed method, the traceability and reference metrology of line width measurements are
established using Si lattice structures. First, we define two interfaces of Si-SiO2 and Si-Air. The interface of Si-SiO2 is
defined as the end of Si lattice structure, and the interface of SiO2-Air is defined using image intensity of STEM image
after metal coating. Second, an image magnification is calculated using 2D Fourier analysis of a STEM image. Third, the
edge positions of the line are detected by Si lattice patterns and image intensity. Using the proposed method, the
estimated accuracy less than 0.5 nm for the line width of 50 nm is established.
The resolving power in optical imaging is limited not only by optical diffraction but also by the sampling size, which in
turn is determined by the optical magnification and pixel size of the imaging devices such as CCD or CMOS. In order to
exceed these limits, we propose a method for improving the optical resolving power by using structured illumination
shift and multiple image reconstruction. Theoretical and experimental verifications reveal that the use of structured light
illumination together with successive approximation (which provides the extrapolation effect) causes the resolving
power of the proposed method to exceed the optical diffraction limit. Furthermore, we focused on subpixel sampling
using the structured illumination shift method. Subpixel image processing can improve the resolving power without
narrowing the visual field of the imaging optics. In addition, the proposed method can provide subpixel resolving power
without necessitating the mechanical displacement of the CCD camera. We investigated the relationship between the
CCD pixel size and the resolving power provided by the proposed method. We found that the subpixel spatial shift of the
structured illumination not only improves the optical resolving power but also enables sub-pixel sampling for optical
imaging.
The novel calibration method of sub-nanometer accuracy for the line width measurement using STEM images is
proposed to calibrate CD-SEM line width measurements. In accordance with the proposed method, the traceability and
reference metrology of line width standards are established using Si lattice structures. First, we define the edge of a line
as the end of Si lattice structure as the interface between Si lattice and oxide film. Second, an image magnification and
inclination angles are calculated using 2D Fourier analysis of a STEM image. Third, the edge positions of the line are
detected after the novel noise reduction method using averaging by Si lattice patterns. Then, the uncertainty of the line
width measurement is evaluated with the uncertainty contributors of pixel size, edge detections and repeatability. Using
the proposed method, the expanded uncertainty less than 0.5 nm for the line width of 45 nm is established.
The interference measurement using the femtosecond optical frequency comb (FOFC) is in progress at present. We
analyzed the temporal coherence function (TCF) of an FOFC since which is the fundamental description of the
interference phenomenon. As a result, it has been understood that the same high coherence peak exists during the time
which is equal to the repetitions interval in the traveling direction of the FOFC. The theoretical derivation has been used
to model the TCF of an FOFC and shows good agreement with experimental measurements which is taken with a
combination of an ordinary Michelson interferometer and an unbalanced optical-path Michelson interferometer.
Semiconductor design rules and process windows continue to shrink, so we face many challenges in developing new
processes such as 300mm wafer, copper line and low-k dielectrics. The challenges have become more difficult because
we must solve problems on patterned and un-patterned wafers. The problems include physical defects, electrical defects,
and even macro defects, which can ruin an entire wafer rather than just a die. The optics and electron beam have been
mainly used for detecting of the critical defects, but both technologies have disadvantages. The optical inspection is
generally not enough sensitive for defects at 100nm geometries and below, while the SEM inspection has low throughput
because it takes long time in preparing a vacuum and scanning 300mm. In order to find a solution to these problems, we
propose the novel optical inspecting method for the critical defects on the semiconductor wafer. It is expected that the
inspection system's resolution exceed the Rayleigh limit by the method. Additionally the method is optical one, so we
can expect to develop high throughput inspection system. In the research, we developed the experimental equipment for
the super-resolution optical inspection system. The system includes standing wave illumination shift with the
piezoelectric actuator, dark-field imaging and super-resolution-post-processing of images. And then, as the fundamental
verification of the super-resolution method, we performed basic experiments for scattered light detection from standard
particles.
Semiconductor design rules and process windows continue to shrink, so we face many challenges in developing new processes such as 300mm wafer, copper line and low-k dielectrics. The challenges have become more difficult because we must solve problems on patterned and un-patterned wafers. The problems include physical defects, electrical defects, and even macro defects, which can ruin an entire wafer rather than just a die. The optics and electron beam have been
mainly used for detecting of the critical defects, but both technologies have disadvantages. The optical inspection is generally not enough sensitive for defects at 100nm geometries and below, while the SEM inspection has low throughput because it takes long time in preparing a vacuum and scanning 300mm. In order to find a solution to these problems, we propose the novel optical inspecting method for the critical defects using standing wave shift. This method is based on a super-resolution algorism in which the inspection system's resolution exceeds the diffraction limit by shifting standing wave with the piezoelectric actuator. Additionally this method is optical one, so we can expect to develop high throughput inspection system. In this report, we performed theoretical discussions and computer
simulations the defect detection on a patterned wafer. As a result, we succeeded in detecting the critical defects in the sub-90nm line and space interconnections.
In order to realize high accuracy and high speed for measuring the surface profile of soft thin film such as photo resist materials for semiconductor process, we proposed the method of using a multi-ball-cantilever AFM, which has more than one cantilever for wide area and high speed in measurement and each cantilever has the ball stylus with diameter to avoid the plastic deformation of measured surfaces. Therefore, in this research, we investigated the profiles of resist material and influence of the AFM stylus on the resist surface. Then, to verify the feasibility of this method, we performed the computer simulation that reflects the relationship between the shape, size and load of the indenter and the deformation of resist surface with FEM (Finite Element Method), and discussed the influence from the force-displacement curve. The fundamental experiments were carried out using the multi-ball-cantilever AFM and we confirmed the feasibility for measuring the surface of soft thin film with high speed.
Photo-stereolithography is one of the most typical rapid prototyping and manufacturing technologies which enables to fabricate 3D objects easily, quickly and automatically from CAD drawings. For these advantages, it has been expected of application to the micromachining. But the conventional method is not suitable for such usage. Because it is based on the so-called laser scanning and laminating process that can’t achieve high accuracy and rapidness together.
We propose a new photo-stereolithography method using a liquid crystal display (LCD) as the live-motion mask. Simultaneous exposure using the LCD live-motion mask makes it possible to precisely fabricate each layer at high speed without scanning. A complex 3D structure is fabricated by the continuous laminating of thin layers. Ideally, this method realizes the nonlaminate fabrication.
In order to verify a feasibility of proposed method, we performed the fundamental experiments. As a result, the lateral resolution reached 5 μm. We fabricated the pyramidal shape and the bevel gear shape with both lateral and vertical resolution of 5 μm. Although the size was a few mm order, it took only about 20 minutes to finish fabricating. These experimental results show that the LCD live-motion mask method corresponding to the continuous laminating satisfies the two requirements of accuracy and rapidness.
Measurement techniques of processed micro surface profiles have been increasingly required in the production of microstructures. Especially the demands on evaluating the dimensional characteristics ofmicrostructure components by in-situ and inprocess measurement are quite high. In this paper, we propose an optical measurement method that can be applied to the inprocess measurement of micro surface profile with an accuracy in the nanometer order. Surface profiles are reconstructed by measuring two intensity images, Fraunhofer diffraction pattern of coherently illuminated work surface and an optical microscope image. In this method, the whole illuminated surface can be measured at one time and no scanning process is imposed, and measurement is not likely to be affected by vibration and tilt of work. Such features are advantageous for in-process measurements. Numerical simulations based on Maxwell's equations and the theory ofFourier optics were performed for the verification ofthe proposed method. The results obtained here demonstrate that nanometer accuracy is achievable. An instrument is designed and developed, and an example of experimentally measured Fraunhofer diffraction intensity of an ultra precision grid plate standard which has rectangular pockets 44nm deep at intervals of lOim is presented.
The 3D laser inverse scattering phase method offers the advantage of measuring a 3D microprofile within the whole area illuminated by laser beam at one time. No scanning process is required as you see in SPM (Scanning Probe Microscope). So, this method finds application where the in-process measurement of a 3D microprofile with accuracy in the nanometer order is required for the process error evaluation. The work reported in this paper deals with development of a new iterative Fourier phase retrieval algorithm based on practical object-domain constraints and actual measurements of a NIST traceable surface topography reference with rectangular pockets 44nm deep at intervals of 10micrometers . The results obtained in the measurements show the validity of the newly developed laser inverse scattering phase method.
As the micromachining techniques are developed, in-process measurement and evaluation technique for the 3D micro- profile in the microparts production system are required. In this paper, we propose a new optical measuring method which can be applied to in-process measurement of 3D micro-profile with an accuracy of nanometer order. The laser inverse scattering method has a possibility to measure 3D micro- profile in the whole area of a workpiece which is illuminated by the laser beam simultaneously without scanning. The 3D micro-profile is reconstructed by measuring only Fraunhofer diffraction intensities. The principle of measurement is based on the optical Fourier transform and phase-retrieval technique. The hybrid phase-retrieval algorithm as a fusion of the logarithmic Hilbert transform with the Fourier series expansion and the iterative algorithm is developed. We proposed the process error evaluation system by employing the laser inverse scattering method with introducing design model based scheme and the computer simulation system of measurement procedure is built up. In order to verify the validity of the proposed method, the computer simulations for the 3D profile such as microparts fabricated by photolithography process are performed. We show that the proposed method is effective for evaluating defective 3D micro-profile result from process error.
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