Line-scanning microscopy is a technique with ability to deliver images with an higher acquisition rate than confocal
microscopy. But it is accomplished at expense of the degradation of resolution for details parallel to sensor if slit detectors
are used. With a linear image sensor it is possible to attenuate or even cancel this effect through the use of information
stored in each pixel / light distribution across line pixels of the sensor. In spite of its great potential the use of linear image
sensors and in particular the development of three-dimensional (3D) reconstruction methods that take into account its
specificity is scarce. This led to our motivation to build a laboratory prototype of a bench stage-scanning microscope using
a linear image sensor. We aim at improving lateral resolution isotropy but also image visualization and 3D mesh
reconstruction using different optical setups particularly illumination modes, e.g., widefield and line-illumination. The
versatility of the laboratory prototype namely its software for image acquisition, processing and visualization is important
to attain this goal in the sense that it provides excellent means to develop and test algorithms. Several algorithms for 3D
reconstruction were developed and are presented and discussed in this paper. Results of the application of these 3D
reconstruction methods show the improvements on lateral resolution isotropy and depth discrimination achieved using
algorithms integrating sensor geometry or spatial sampling rate. Also it is evidenced the impact of an insufficient spatial
sampling rate from 3D mesh reconstructions.
This work aims at showing the applicability of a scanning-stage bench-microscope in bright-field reflection mode for wirebonding
inspection of integrated circuits (IC) as well as quality assurance of tracks in printed circuit boards (PCB). The
main issues of our laboratorial prototype arise from the use of a linear image sensor taking advantage of its geometry to
achieve lower acquisition time in comparison to traditional (pinhole) confocal approach. The use of a slit-detector is
normally related to resolution degradation for details parallel to sensor. But an improvement will surely arise using light
distribution along line pixels of the sensor which establishes a great advantage in comparison to (pure) slit detectors. The
versatility of this bench-microscope affords excellent means to develop and test algorithms. Those to improve lateral
resolution isotropy as well as image visualization and 3D mesh reconstruction under different setups namely illumination
modes. Based on the results of these tests tests both wide-field illumination and parallel slit illumination and detection
configurations were used in these two applications. Results from IC wire-bonding show the ability of the system to extract 3D information. A comparison of auto-focus images and 3D profiles obtained using different 3D reconstruction algorithms as well as a method for the determination of the diameter of the bond wire are presented. Measurements of PCB track width and thickness were performed and the comparison of these results from both longitudinal and transverse tracks stress the limitations of a lower spatial sampling rate induced by the resolution of object stage positioners.
The aim of this work is to obtain improved sectioning ability in our slit-scanning microscope. The experimental setup is
based on a linear sensor and different illumination modes were evaluated. MTF measurements from USAF target images
showed the great benefit of using slit illumination in comparison to widefield. Experimental determination of Strehl
ratios of 0.62 and 0.96 for wide-field and slit-illumination configurations, respectively, is depicted. Also MTF
degradation with defocus is fairly established as stated by Strehl ratio decrease from 0.68 to 0.59 in 2 μm defocus using
widefield configuration. Experimental measurement of axial response showed good accordance to numerically simulated
curves modeled for the same parameters as the experimental setup. Linear sensor microscopy shows its advantage in
comparison to simple slit microscopy particularly for slit illumination. Imaging for details running in sensor direction is
accomplished for parallel illumination and detection slits as well as effective axial response for right-angled slits. These
results indicate that linear sensor microscopy should be able to surpass lateral resolution asymmetry of slit microscopy.
Preliminary results from tests to develop a reconstruction method that combine algorithms to improve lateral resolution
isotropy of 2D images and those to build 3D images will be presented.
Linear sensor microscopy as a mode of slit microscopy is faster than confocal microscopy as it eliminates one lateral
scanning but its lateral/axial resolution are lower. Regardless specific image formation characteristics dependent on
illumination mode its circular symmetry is lost therefore lateral resolution anisotropy arises. The purpose of this work is
to evaluate the application of a low-cost scanning-stage bench-microscope in brightfield reflection mode using a linear
sensor for shape and thickness measurements. Firstly we describe overall system architecture emphasizing its
effectiveness to easily accommodate different optical setups. In particular different configurations of scanning
microscopes are briefly described and a comparison of its image formation characteristics is presented giving special
attention to the effect of slit illumination/detection. Results of lateral resolution in both lateral orientations show slit
illumination should be used. A reconstruction method used to build three-dimensional representations from images of 3D
structures results in relief borders shapes equally defined independently of its orientation relative to sensor. Further
results of its application for the measurement of height and thickness of PCB tracks show its inherent ability though a
more robust reconstruction algorithm integrating data from light distribution in sensor is being developed to improve
clearness and measurement accuracy.
We aim at establishing a bench-microscope based on a linear sensor as a versatile research tool for the development and
assessment of image reconstruction algorithms. Therefore we built a laboratory prototype of a scanning-stage bright-field
microscope. It is epi-illuminated with a white-light source. The detector is a linear CMOS image sensor. A stand-alone
sensor readout module has been developed and integrated in this
low-cost bench-microscope. Through lateral scanning
along one axis it acquires two-dimensional (2D) images of the specimen that suffer from substantial contributions from
out-of-focus portions. This haze in the optical slices will be removed or significantly diminished using computational
methods. As the output performance of these methods is extremely dependent on the imaging quality of the microscope
prototype, two types of measurement to assess it are described. Axial discrimination will be evaluated along with the
development of computational methods. Nevertheless a plane reflector was scanned along z-axis to measure intrinsic
axial response of this microscope arrangement. Results of overall system resolution and contrast are presented. At last,
preliminary results of three-dimensional (3D) image reconstruction using a simple algorithm to find the best-in-focus
image through the determination of maximum intensity are presented. Raw bright-field images from wire bond of an
integrated circuit (IC) were used.
Several microscope techniques namely confocal microscopy have a huge number of applications in metrology reported in literature. Although they are essentially imaging techniques metrology and particularly profilometry is a very attractive field of application owing to their ability to obtain depth discrimination. In recent years there has been a growth of three dimensional microscopy methods namely those based on structured incoherent illumination. In spite of different implementation approaches they are based on the fact that the optical transfer function (OTF) of the imaging system attenuates with defocus for every spatial frequency with the exception of zero-frequency. In this way it is able to get depth information through the projection of a grid structure so it is suitable for application in profilometry. The purpose of this work is to develop and test a profilometer based on a low-cost bench microscope. The optical layout is an epi-illuminated configuration of scanning-stage type for reflection microscopy. Tests with structured incoherent illumination in this case line-illumination are being carried out in order to achieve depth discrimination using a linear image sensor of CMOS type as detector. This paper presents a description of the optical arrangement as well as the acquisition and control system. Preliminary results are shown that were obtained using a plane mirror to measure its axial resolution and a micromachined component to test the application of this bench microscope in profilometry.
KEYWORDS: Sensors, Image sensors, Confocal microscopy, Microscopy, Microscopes, 3D image processing, 3D acquisition, Image acquisition, Signal to noise ratio, Lamps
Three-dimensional (3D) microscopy is a huge field that includes several microscopy techniques. Among these techniques the confocal microscopy is widely known and used due to its improved axial resolution or optical sectioning ability. However its high cost and image acquisition time as well as low signal-to-noise ratio are important drawbacks. Other techniques use wide-field structured illumination to get depth information from the sample. The detectors in commercial microscopes are normally of the point detector type (PMTs) in confocal and area sensors (CCDs) in wide-field microscopy. Examples of microscopes that take advantage of lower cost and faster readout cycles of linear image sensors are very uncommon. The purpose of this work is to develop a low-cost microscopy technique for obtaining 3D images with lower acquisition time and higher signal-to-noise ratio (SNR) than in classical confocal microcopy. It uses a linear CMOS image sensor and specific reconstruction algorithms will be able to extract 3D information from the distribution of light intensity collected. The sensor readout circuitry has been developed and tests are currently running in a laboratory prototype in reflection mode with an epi-illuminated configuration of scanning-stage type. The light source is a commercial incandescent lamp with regulated intensity. For the development, test and optimization of the reconstruction algorithms the object is mounted on a 3-axis translation stage to scan the object in three perpendicular directions. Contrast and resolution results obtained using a resolution test slide and preliminary images of integrated circuit (IC) bonding are presented.
The aim of this work is to establish a laboratory system, that embraces different areas such as optics, electronics, signal processing and software, to make possible the application of a linear sensor as detector in a scanning optical microscope (SOM) and to evaluate the application of different signal processing techniques on axial and lateral resolution. Thus a low-cost SOM laboratory prototype with reflection epi-illuminated configuration was assembled and a stage scanning type was selected to minimize the aberrations because low-cost optical components were employed. The line illumination was achieved using a low-cost anamorphic optical lens. In this paper a discription of the optical arrangement is presented. Also the acquisition system is reported regarding the circuitry developed with a microcontroller from PIC family to readout data from a linear sensor. A brief discription of the acquisition and
visualization software running in microcontroller and personal computer (PC), respectively, is also included. The preliminary results presented in this paper were attained using plane mirror object mounted in a translation stage. A Matlab program was developed to implement different routines to estimate the axial resolution and evaluate its validity for the achievement of better depth discrimination.
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