SEM Performance Standard

U1011A SEM PERFORMANCE STANDARD Click here to view SEM image

Introducing a reliable test and performance sample for your scanning electron microscope. This specimen is vapor deposited aluminum on a silicon substrate, photo lithographed and etched, with sufficient information to do at least ten important measurements and tests.

1) Magnification calibration is straightforward. Specimen dimensions are specified in microns so magnification can be measured directly from photomicrographs in millimeters. Keep in mind the possibility of camera reduction ratios. It will be necessary to use large spot size for good definition at low magnifications.

2) The layout of this device is easy to remember. Start by using the sales brochure as a map. Simple stage maneuvers will allow the next area of interest to be placed in the field of view quickly.

3) The eight point star in the upper right hand corner of the specimen makes it possible to visualize where magnification center and scan rotation center occurs.

4) Pin cushion or barrel distortion can easily be visualized by selecting any of the grid areas. The squares in these areas have reasonable edges. A straight edge placed upon a micrograph should easily touch all grid boundaries within the accuracy of the etching process. Any evidence of bowing would be considered distortion. Checking at various magnifications will verify if these conditions exist in the optics. Measuring along the X and Y or the X plus Y-axis will show geometry errors.

5) Depth of field measurements can be done with any of the grids however the ten micron grid may be most useful. Tilting the specimen to 89 degrees and looking across the bars will give calibrated measurements away from focus.

6) Tilt correction is best done using the circles, since perfect corrections is not available, circles will allow you to visualize the best position of scan rotation vs. tilt correction for given KV and working distance.

7) Dynamic focus performance is best done in conjunction with tilt correction calibration. This will assure Y scan alignment along the vertical axis.

8) Orthagonality and linearity tests use the eight-point star. The intersecting angles of this device are 45 degrees. They should remain at that regardless of scan rotation or scan speed settings. Any deviation between the 90 degree intersection of the X and Y lines on the star should be interpreted as orthagonality errors usually due to the column scan coils, the display scan coils or an electronic problem in the deflection amplifiers or their power supplies.

9) Stage motion tests are accomplished using either the eight point star, or for more critical tests use an appropriate set of cross hairs.

10) Video performance can be measured by placing the 5 micron squares in the center of the field of view and reducing the magnification until all detail on this area disappears. This will be the lower limit of the display definition. Changing scan speed during this test will show if the video electronics have the capability to produce an equal quality image at fast visual scan rates as well as slow record rates. Remember the faster the scan the more demand on the video electronics. Moving the squares to the edge of the screen and repeating this test will prove the quality of the cathode ray tubes. Astigmatism on CRTs is most noticeable at high deflection angles and there the definition will be the poorest.

11) Video loop stability is defined as any variation of the entire image formation system and the test is accomplished this way. Select the 10 micron squares, specimen tilt 0 degrees, place a silicon window of the specimen in the center of the scanned raster at 100x adjust the focus to the point that a noticeable defocus occurs, set the magnification to 100Kx, adjust signal and gain to produce a gray raster. Photograph this raster, it should show uniform gray form top to bottom, any variation is some sort of electron image system instability. If noticeable bands or lines occur, turn off the electron gun supply, readjust the brightness for the record CRT and photograph another blank raster. If variation still remains, problems in the video detector though the display amplifiers is indicated. If the variation disappears, problems exist in the electron optic system. These could possibly be: poor specimen condition, a non grounded x-ray culminator or something similar in the immediate specimen area, contamination in the optics or electron gun, instability in the alignment circuits or lenses, or contamination in the electron collector. These are general suggestions to aid in the diagnosis of problems and do not necessarily cover all video instability that could be encountered.

12) Additional information can be gained about the scanning system such as: do the spaces between the squares show any distortion at TV or other fast scanning speeds, which would indicate a miss match between the scan and display system or the inability of one or more of the deflection amplifiers to perform at high repetition rates. Circles should remain round with 360 degrees of scan rotation; if the specimen is perpendicular to the beam, if not, this would indicated a gain error in one or more axis of the scan systems. If instead there is center wobble, this would indicate and improper zero condition in one or more of the column scan amplifiers.

This specimen, the U1011A, was designed to be an all around performance standard for SEMs. It was built to exacting specifications, using photolithography techniques; it must be realized that due to the manufacturing process, absolute accuracy at higher magnifications is not possible. Secondary Images believes that all information contained on this specimen is as nearly correct a possible, however we decline; to accept any legal responsibility for the accuracy portrayed on this device. We would like to suggest NIST as a source for calibration standards.

NIST compared samples are available, at additional cost.