E. Clayton Teague

Piezodriven 50‐μm range stage with subnanometer resolution

A micropositioning stage has been developed for use with optical and electron microscopes in the accurate measurement of fine lines used by the microelectronics industry and microscopic objects such as biological cells, air pollution particles, and asbestos fibers. The stage combines a piezoelectric driving element and flexure pivoted lever arms to achieve a compact, vacuum compatible device with a resolution of 0.001 μm or less over a range of 50 μm.

Three-dimensional stylus profilometry☆

Abstract Work carried out at the National Bureau of Standards to acquire surface microtopographic data using three-dimensional stylus profilometry and to display the data as intensity variations on a television monitor is described. Images of the data are generated from an array of 512 × 512 8-bit digitized surface height values. The surface slope and wavelength capabilities of stylus instruments are compared with other surface microtopography measurement techniques to highlight their unique high vertical resolution capabilities for low sloped surfaces. Finally, examples of some alternative means for displaying three-dimensional data sets are given for three types of surface irregularities: a discrete feature, a periodic profile surface and a random profile surface. These representations of the topography are also compared with scanning electron micrographs of the same surface irregularities.

Light Scattering from Manufactured Surfaces

We present an evaluation of light scattering theories and experimental techniques for measuring the roughness of manufactured surfaces. Our goal was to define the ultimate capabilities and regions of validity of these methods for deducing surface microtopography. Available theories are evaluated in terms of a heuristic interpretation of direct electromagnetic scattering from surfaces. Experimental methods using specular reflectance, total integrated scatter, angular scattering distribution, and speckle are reviewed in terms of their spatial-bandwidth sampling of surface wavelengths and their roughness amplitude sensitivity and accuracy. Graphs in a slope/relative-wavelength space are used to intercompare the regions of validity of theories, regions of applicability for experimental methods and regions occupied by typical manufactured surfaces. A relatively unknown theory, valid for light scattering from many typical manufactured surfaces but previously unused for this purpose, is briefly described.

Key-Note-PapersLight Scattering from Manufactured Surfaces†

We present an evaluation of light scattering theories and experimental techniques for measuring the roughness of manufactured surfaces. Our goal was to define the ultimate capabilities and regions of validity of these methods for deducing surface microtopography. Available theories are evaluated in terms of a heuristic interpretation of direct electromagnetic scattering from surfaces. Experimental methods using specular reflectance, total integrated scatter, angular scattering distribution, and speckle are reviewed in terms of their spatial-bandwidth sampling of surface wavelengths and their roughness amplitude sensitivity and accuracy. Graphs in a slope/relative-wavelength space are used to intercompare the regions of validity of theories, regions of applicability for experimental methods and regions occupied by typical manufactured surfaces. A relatively unknown theory, valid for light scattering from many typical manufactured surfaces but previously unused for this purpose, is briefly described.

In-Process and On-Line Measurement of Surface Finish

Future trends In surface finish measurement for manufacturing are discussed. It is expected that optical techniques will be used increasingly for measurements of surface roughness and of other parameters as well because these techniques are inherently fast and three-dimensional. Four optical techniques are discussed and evaluated. Stylus techniques, however, will continue to play an important role in research and metrology. Statistical methods for the three dimensional characterization of surfaces are briefly reviewed.

Sinusoidal profile precision roughness specimens

Abstract The design, specifications, fabrication, testing and potential use of a series of sinusoidal profile precision roughness specimens are described. These specimens were designed primarily to provide a means for optimum transfer of an accurate roughness average Ra value from primary to secondary laboratories. However, properties of the specimens also make them very useful for evaluating instrumentation and computational algorithms designed to measure the statistical parameters and functions now being investigated in many laboratories. Specimens with an Ra value of 1.0 μm and spatial wavelengths of 40, 100 and 800 μm are being fabricated. For the wavelength of 100 μm, specimens are also being fabricated with Ra values of 3.0 and 0.3 μm. Fabrication using numerically controlled diamond lathes has produced specimens with very high quality sinusoidal profile waveforms with uniform Ra values across the surfaces and with very low amounts of waviness over a test area of about 2 cm2.

Recent Developments in Electrical Linewidth and Overlay Metrology for Integrated Circuit Fabrication Processes

Electrical linewidth measurements have been extracted from test structures replicated in planar films of monocrystalline silicon that were electrically insulated from the bulk-silicon substrate by a layer of silicon dioxide formed by separation by the implantation of oxygen (SIMOX) processing. Appropriate selection of the surface orientation of the starting material, the design and orientation of the structures features, and patterning by a lattice-plane selective etch provide features with planar, atomically smooth sidewalls and rectangular cross sections. The primary motivation for this approach is to attempt to overcome the serious challenge posed by methods divergence to the certification of linewidth reference-materials for critical-dimension (CD) instrument calibration and related tasks. To enhance the physical robustness of reference features with deep submicrometer linewidths, the new test structure embodies short reference-segment lengths and arbitrarily wide voltage taps. Facilities for reconciliation of measurements extracted from the same feature by all normally practiced techniques are also implemented. In overlay metrology, electrical inspection of two types of hybrid overlay targets allows pixel calibration of, and shift extraction from, the overlay instruments. The overall strategic focus of this research is to resolve methods-divergence issues and possibly to develop universal deep-submicrometer linewidth reference materials for CD instruments and techniques for instrument- and process-specific shift extraction for optical overlay metrology.

Uncertainties in Calibrating a Stylus Type Surface Texture Measuring Instrument with an Interferometrically Measured Step

This paper presents discussion and experimental data to demonstrate that: (1) proper measurement of a step-height with interferometry must include a determination of the geometry of the surfaces on both sides of the step in the neighborhood of the measured area, (2) uncertainty of a step-height measurement with the use of interferometry is determined both by uncertainty in the measurement of fringe displacement and uncertainty produced by the variation of step height measurements with fringe dispersion when specimen geometry is imperfect, (3) when specimen geometry is imperfect, uncertainty in calibrating the stylus instrument is produced by methods divergence between the height values measured with interferometry and with stylus instruments, and (4) uncertainty in assigning a height value to a stylus profile of a step is ultimately limited by and is approximately equal to the root mean square roughness, or the arithmetical average roughness value of the surface texture on both sides of the step.

Toward nanometer accuracy measurements

We at NIST are building a metrology instrument called the Molecular Measuring Machine (MMM) with the goal of performing 2D point-to-point measurements with one nanometer accuracy cover a 50 mm by 50 mm area. The instrument combines a scanning tunneling microscope (STM) to probe the surface and a Michelson interferometer system to measure the probe movement, both with sub-nanometer resolution. The instrument also feature millidegree temperature control at 20 degrees C, an ultra-high vacuum environment with a base pressure below 10-5 Pa, and seismic and acoustic vibration isolation. High-accuracy pitch measurements have been performed on 1D gratings. In one experiment, the MMM STM probe imaged an array of laser-focused, atomically deposited chromium lines over an entire 5 micrometers by 1 mm area. Analysis of the data yielded an average line spacing of 212.69 nm with a 5 pm standard uncertainty. The uncertainty estimate is derived for an analysis of the sources of uncertainty for a 1 mm point-to-point measurement, including the effects of alignment, Abbe offset, motion cross-coupling, and temperature variations. In another measurement, the STM probe continuously tracked a holographically-produced grating surface for 10 mm, counting out 49,996 lines and measuring an average line spacing of 200.011 nm with a 5 pm standard uncertainty.

Model calculations of fields related to near‐field optical scanning of a silver strip on a glass substrate

The vertical energy flux density for the electromagnetic fields near the surface of a silver strip on a glass substrate is computed for an incident plane wave to aid in the measurement of the width of the strip. The dimensions of the strip cross section, e.g., 300 nm by 100 nm, are a fraction of the wavelength of the incident light , 632.8 nm. The flux 1 nm above the surface shows sharp spikes at the edges of the strip. The features of the fields near the surface could be used for accurate determination of the width of the strip by measurements up to about 30 nm above the strip. The effects of other variables are also shown in the figures.