Dimensional measurements from secondary electron (SE) images were compared with those from backscattered electron (BSE) and low-loss electron (LLE) images. With the commonly used 50% threshold criterion, the lines consistently appeared larger in the SE images. As the images were acquired simultaneously by an instrument with the capability to operate detectors for both signals at the same time, the differences cannot be explained by the assumption that contamination or drift between images affected the SE, BSE, or LLE images differently. Simulations with JMONSEL, an electron microscope simulator, indicate that the nanometer-scale differences observed on this sample can be explained by the different convolution effects of a beam with finite size on signals with different symmetry (the SE signal’s characteristic peak versus the BSE or LLE signal’s characteristic step). This effect is too small to explain the >100 nm discrepancies that were observed in earlier work on different samples. Additional modeling indicates that those discrepancies can be explained by the much larger sidewall angles of the earlier samples, coupled with the different response of SE versus BSE/LLE profiles to such wall angles.

In this article, a new scanning electron microscopy (SEM) image composition technique is described, which can significantly reduce drift related image corruptions. Drift distortion commonly causes blur and distortions in the SEM images. Such corruption ordinarily appears when conventional image-acquisition methods, i.e., “slow scan” and “fast scan,” are applied. The damage is often very significant; it may render images unusable for metrology applications, especially where subnanometer accuracy is required. The described correction technique works with a large number of quickly taken frames, which are properly aligned and then composed into a single image. Such image contains much less noise than the individual frames, while the blur and deformation is minimized. This technique also provides useful information about changes of the sample position in time, which may be applied to investigate the drift properties of the instrument without a need of additional equipment.

All forms of microscopy are being pushed to the limit by nanotechnology. This is especially true for high-resolution scanning electron and helium ion microscopes, which are proving to be extremely useful for nanometer-scale imaging, characterization, and dimensional measurements. Excellent resolution is essential for imaging nanomaterials. Hence, there is a relentless quest to achieve better and better resolution with various electron and ion microscopes and to monitor and maintain these instruments to achieve the best possible performance levels.

The ability to resolve fine details with a microscope has greatly improved over the past 20 years. The resolution achievable with the newest scanning electron microscopes (SEMs) can now be at or below 0.4 nm and for the scanning helium ion microscope (HeIM), 0.24 nm has been reported. To put this into perspective, the {111} crystal plane in silicon (Si) has 0.32 nm lattice spacing, so one cubic nanometer in the Si crystal contains only a few atoms. Therefore, an instrument must be performing at the highest level possible to resolve routinely the finest structures. Clearly, the instrument operator must also be functioning at a high level as well to achieve the best resolution and to prove that the instrument is capable of doing the work.

SEM Instrument calibration is something most people don't always realize they need to do. Images look about right so the magnification seems close enough. Today, measurements are being done in specialized scanned beam metrology instruments everyday, so correct magnification calibration is very important. Calibration is probably more acknowledged from the point of the transmission electron microscope than for the scanning microscope. But, it still needs to be done. Today, people can buy SEM's that cost around $100,000 (refurbished ones somewhat less) to $2.5M with one instrument model from one manufacturer costing about $8M. Believe it or not, often the instrument buyer thinks that as soon as they get the instrument into their facility (since it is new and they paid a lot of money for it) that it is perfect and everything is correct.

One of the missions of the NIST Manufacturing Engineering Laboratory (MEL) is to improve and advance length metrology in aid of U.S. Industry. This responsibility is found within the Precision Engineering Division (PED). The successful development of a “Collaboratory” for TelePresence Microscopy provides an important new tool to promote technology transfer in the area of length metrology and measurement technology. NIST and Texas Instruments, under the auspices of the National Advanced Manufacturing Testbed (NAMT) and in collaboration with the University of Illinois are developing a microscopy collaboratory testbed. This facility is designed to demonstrate the value of telepresence microscopy within a large distributed manufacturing facility such as Texas Instruments and between organizations such as NIST, Texas Instruments and Universities.

Telepresence Microscopy is an application of the state-of-the-art Internet based technology to long-distance scientific endeavors.