Image sharpness measurement in scanning electron microscopy—part I

Abstract

Summary: This study introduces the idea of the sharpness concept in relationship to the determination of scanning electron microscope (SEM) performance. Scanning electron microscopes are routinely used in many manufacturing environments. Fully automated or semiautomated SEMs as metrology instruments are used in semiconductor production and other forms of manufacturing where the ability to measure small features with the smallest possible errors is essential. It is felt that these automated instruments must be routinely capable of 5 nm (or better) resolution at or below 1 kV accelerating voltage for the measurement of nominal 0.18-0.35 µm size parts of the integrated circuits. Testing and proving on a day-by-day basis that an instrument is performing well is not easy, but, understandably, is an industry need and concern. Furthermore, with the introduction of fully automated inspection and metrology instrumentation, not only does an appropriate, easy to obtain or manufacture sharpness measurement sample have to exist but also an objective and automated algorithm must be developed for its analysis. Both of these have been the object of a study at the National Institute of Standards and Technology (NIST), and the fundamentals are discussed in this paper and the computer-based automated analysis in a companion paper (Part II;Vladár et al. 1998). The method described in these papers is based on the analysis of the frequency domain representation of the SEM image and can also be used to check and optimize two basic parameters-focus and astigmatism-of the primary electron beam as related to a measure of image sharpness. The application of this technique to check regularly the resolution of the SEM in quantitative form will also be discussed.

Rapid detection of microorganisms with nanoparticles and electron microscopy

“…In addition to its dependence on the magnetic electronoptical system which produces the scanning beam, resolution is also limited by the size of the interaction volume, or by the extent to which the material examined interacts with the electron beam (Hermann and Muller, 1991). The SEM characteristics make the instrument best suitable for attaining the highest resolution when using metals (Postek and Vladar, 1998).…”

A novel approach to evaluate spatial resolution of MRI clinical images for optimization and standardization of breast screening protocols

“…Power spectrum analysis (PSA) can be used to assess the spatial frequency content in the Fourier transform of an image, thus characterizing the ability to resolve structures of different size. [11][12][13][14][15] Unlike MTF analysis, PSA takes into account only the spatial frequencies present in the images and can therefore be targeted to a particular clinical protocol.…”

Orientation identification of the power spectrum

“…To this end, one needs on one hand a thorough analysis of the Fourier transform, on the other hand the analysis must be fast. The image's power spectrum -i.e., the square of a modulus of its Fourier transform -is widely used for blind deconvolution procedures [4,28], for defocus and astigmatism correction in Scanning Electron Microscopy (SEM) [17,18,29], as well as in other types of electron microscopes [2,7,10,26,31,32]. Power spectrum is used for automated defocus and astigmatism correction, as well as a visual support for a non-automated correction performed by a human operator.…”