We report a method to detect signed differences in two similar data sets representing 3-dimensional intensity profiles
recorded by optical wide-field microscopes. The signed differences describe missing or unexpected intensity values,
defined as defects. In technical applications like wafer and mask inspection, data sets often represent surfaces. The
reported method is able to describe the size and position especially in relation to the neighboring surface and is called
Three-Dimension-Aberration (TDA)-Technology. To increase the tool performance and to handle different sizes of
defects a scaled bottom-up method is implemented and started with high reduced data sets for the search of large defects.
Each analysis contains three steps. The first step is a correlation to calculate the displacement vector between the similar
data sets. In the second step a new data set is created. The new data set consists of intensity differences. Extreme values
in the data set represent the position of defects. By the use of linear and non-linear filters the stability of detection can be
improved. If all differences are below a threshold the bottom-up method starts with the next larger scaled data set. In the
other case it is assumed that the defect is detected and step three starts with the detection of the convex hull of the defect
and the search of the neighboring surface. As a result the defect is described by a parameter set including the relative
position. Because of the layered structure of the data set and the bottom-up technique the method is suitable for multi-core
processor architectures.
A high-speed image processing has been created. Distributed computing is used to get the necessary resources. Controlling a high-resolution microscope, the image processing system grabs thousands of single images from different XYZ-positions. The system can get all available optical information from a greater microscopical structure like a complete chip on a wafer. Image pre-processing functions are used to eliminate optical effects like shading. A digital contrast enhancement is also available to get a better image quality. The scanning process can take several hours if a high-aperture objective lens is used. At the end we have a complex cluster image structure, and after the image post-processing the creation of the mosaic image can be started. The post-processing functions reduce the 3D data to 2D data. Best focus images can be defined or extended depth of focus images can be created. XY-neighboring images have overlapped areas. In two runs a correlation function define offset values. In a XY-run all available offset values define the final offset values. The result can be checked and manual changes are possible before writing the final mosaic image file.
A small depth of focus is very often a problem in the conventional high resolution light microscopy, because the objects are higher than the depth of focus. The connections of conventional light microscopes, video techniques and computers open new fields of applications for microscopy. It is possible to generate an image containing focused areas from a series of images of different focus- or z-positions. In this way it is possible to extend the depth of focus without a physical limitation of the numerical aperture (NA) of the objective lens. The connection of microscope, video and PC opens also the field of high resolution low light color applications, like fluorescence in situ hybridization (FISH). Image processing technology enables the enhancement of contrast for objects with a very low contrast. And such a system opens also the way to view objects with small motions, like processes of growing of biological objects. It is also the elimination of the limits in the X/Y-direction by a full color mosaics (patchwork mode) with a resolution up to 4500 by 3500 pixels. The last step in the development of the system was the generation of short movies of different 2D projections of the 3D data cube showing the spatial structure of the objects. It is possible to display up to 15 true color RGB-images per sec with a resolution of 664 by 512 pixels. Now the system is a powerful tool to generate image you never can see through the eyepieces.
The development of microscopes is nearly fixed since the introduction of confocal microscopy. The credit-point of confocal microscopy is the low depth of focus. But a small depth of focus is very often a problem in conventional light microscopy, because the objects are higher than the depth of focus. There is a physical limitation based on the numerical aperture (NA) of the objective lens of the microscope. The connection of the conventional light microscope, video technique and computers open new fields of applications for the microscopy. It is possible to generate an image containing focused areas from series of images of different focus- or z- positions. In this way it is possible to extend the depth of focus without a physical limitation by the NA of the objective lens. The connection of microscope, video and PC also opens the field of high resolution low light color applications, like fluorescence in situ hybridization (FISH). Image processing technology enables the enhancement of contrast for objects with a very low contrast. And such a system also opens the way for a view to objects with small motion, like processes of growing of biological objects.
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