Geller Magnification Calibration Standard MRS-4XY Recalibration in XY

Pattern Design

The MRS-4 is fabricated by using the highest accuracy electron direct write semiconductor manufacturing equipment available today. The pattern is anti reflective chromium (30nm of CrO₂over 70nm of Cr) over quartz. The overall size is 9mm X 9mm X 2.3 mm thick. The size can be modified for special applications (such as for a TEM bulk holder or mounting on a large wafer) to 3mm thick or another custom size. For applications requiring an electrically conductive sample, the MRS-4 is coated with a proprietary material which allows for image observation at any accelerating voltage. A distinct advantage of this coating is that electron beam tracks from contamination are removable by plasma etching. However we do not advise customer cleaning of the contamination, since the coating itself can be very easily removed inadvertently. Applying a fresh coating restores the MRS-4 to like new condition. And when an MRS-4 is submitted for recertification, as part of the package, the top surface is properly cleaned and a new coating applied. If for some reason you do not want this conductive coating present, that would be a special order (but at the same price) but we do have to be told that at the time of order placement.

The geometric design of the MRS-4 has groups of nested squares spanning several orders of magnitude with pitches of ½ µm, 1 µm, 2 µm, 50 µm and 500 µm. Newly incorporated into the standard is a ruler which is 6mm long with 1µm increments. We measure and certify pitch (the distance between repeating parallel lines using center-to-center or edge-to-edge spacing. This is the only type of measurement that can be used to relate measurements from different microscopy techniques (see "Submicrometer Linewidth Metrology in Optical Microscopy", Nyysonen & Larrabee, Journal of the Research of the National Bureau of Standards, Vol. 92, No. 3, 1987). Linewidth measurements (the measurement of a single line or space width) can only be related if the same type of illumination is used as for the calibrating instrument since edge effects lead to uncertainty in the edge locations. Using pitch measurements, errors from edge-to-edge locations cancel as long as like positions are measured. Several examples are given on the illustrations in this resource guide.

Square boxes are used for measuring magnification simultaneously in the X and Y directions. This gives us a measure of image skew, barreling, pincushion and other non-linearities which can have various origins, such as stray magnetic fields. With the MRS-4 we have provided multiple boxes for the ½, 1, and 2 µm pitches.

The largest pattern has an overall dimension of 8mm square. It contains lines and spaces that are nominally 250 µm wide (totaling 500 µm pitch). This can be used to check magnifications from 10X - 100X. The 50 µm pitch patterns are useful from 100X - 1000X. The 2, 1, and ½ µm pitch patterns will allow calibrations up to 200,000X. The "ruler" has an overall length of 6mm in the X and Y directions. The 1µm increments have graphics every 10µm and emphasized lines and graphics every 50 µm and 100 µm.

Included are squares and rectangles from 1 - 31 µm in 1 µm increments, 30 - 75 µm in 5 µm increments, and 70 0 120 µm in 10 µm increments. Also included is an array of 4 repeating patterns of circles with diameters ranging from 2 - 39 µm in 2 µm increments and 40 - 100 µm in 10 µm increments. These patterns are useful for checking the performance and setup of particle size counting systems. From our experience it is very difficult to get the proper size distribution knowing the correct answer. The patterns can also be used for determining imaging and chemical spatial resolution, and chemical mapping. Since the circles and rectangles are not pitch patterns, they cannot be made traceable.

How accurate are the pitch patterns?

Pattern accuracy is now being determined by the National Physical Laboratory in the U.K. Based upon previous MRS measurements the accuracy of the 500 µm pitch pattern was ±0.25 µm, and ±0.02 µm for the 50 µm and 2 µm patterns.

Z-direction calibration:

The step height is 100 nm in the vertical direction. The z-calibration is not useful for light microscopy or SEM but can be very useful for confocal and any type of profilometry.

Classification of the different product forms:

The MRS-4NT is available in three different forms: Just the basic product, as described but without any calibrations, certification or traceability (NT= Not Traceable). This is SPI# 02775-AB. Or as described above but with complete calibration and certification in the X and Y directions (but not the z direction). This is SPI# 02776-AB.

Or as described above but with complete calibration and certification, not just in X and Y but also the Z direction. This is SPI# 02777-AB

What is included in the certification report?

We follow the ISO guidelines for certification and traceability. Included is the unique serial number engraved on the standard, certification date, recertification due date, operator, instrumentation used, and actual pattern measurements along with a measure of accuracy.