Dimensional measurement by use of an SEM

cutting edge of a razor blade
The scanning electron microscope (SEM) is readily used for measurements of length in the range of µm and nm. Especially all kinds of layers and stacks of layers are often measured by means of an SEM. It is important to note though that for precise measurements a calibration of the instrument by a standard length object is absolutely necessary (like you would do it with an optical microscope as well).

* The example to the rigth shows the cutting edge of a standard not yet used razor blade. The radius of the edge should be determined. The radius of the cutting edge is half of the measured distance in the image.

  Image analysis using SEM images
SEM images can also be used as a source of image analysis. Image analysis is every kind of quantitative interpretation of images. The information contained in the image will be reduced to more or less many numbers in order to come to an objektive base for the comparison of different images. Recently this task is done by special software (and suitable hardware of course), that can be programmed to follow strikt rules in the way the image at first will be digitized, then be edited, then features in the image be detected and after all will be calculated the interesting numbers for these features. This succession of tasks can more or less be automized with the help of macro commands, if many images shall be evaluated economically in this way.

In the example to the right the distribution of pore sizes on a filter foil was to be determined. At first a digital image that shows the pores in good contrast has to be created. An image section in the example shows the by their gray value detected pores in the color green. After detection the binary resulting image will be measured. A further section in the example shows some of the counted, measured and numbered pores.

pore analysis

filter In the animation to the left you see a section of the original list of the automatically measured values for all of the pores, and the statistik results calculated from these measurements.

Image analysis will for instance be used for:
* Determination of grain size distribution,
* Determination of grain shape,
* Distribution of pore size
* Analysis of direction (anisotropy)
* Determination of area shares and many more applications.

The image analysis will be used in connection with all methodes that produce any kind of images. We usually work with digitized SEM images. It is still possible for us to work with other images as well, if those images are allready in digital form or can be digitized by us using a scanner. The exserption of valuable results requires knowledge in many different areas: image generation, image edition, statistics a.o.m.. At EMTEC this experience is at hand. For the digitalisation of SEM image information we use the ORION system. For the image analysis itself we use the program "NIH-Image", developted at the "National Instituts of Health / USA" especially for scientific image analysis with MAC`s and later on ported for WINDOWS-PCs. One of our cooperating laboratories uses software developted by the well known company SIS for image analysis. The presentation of results is partly be done using options of the image analysis software, partly also with options of Microsoft Excel e.g..

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