Fredric Scire

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.

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.

Measurements of stylus radii

Abstract In stylus measurements of surface texture the measured results for roughness depend on the stylus radius. Therefore it is important to determine the stylus radius. Since stylus tips are not perfectly spherical, the local radius of curvature varies significantly over the surface which makes the determination of an effective radius difficult. Both the techniques used to generate stylus profiles and the subsequent algorithms used to derive an effective radius are discussed. Comparisons are made between three techniques: sharp-edge traces, optical microscopy and scanning electron microscopy. Several algorithms, including that prescribed by the American National Standard ANSI B46-1, are discussed. It is concluded that the radius scale method is accurate, unambiguous and easy to use for routine measurements in the laboratory.

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.

Grating Pitch Measurements With the Molecular Measuring Machine

At the National Institute of Standards and Technology, we are building a metrology instrument called the Molecular Measuring Machine (M3) with the goal of performing nanometer- accuracy two-dimensional feature placement measurements over a 50 mm by 50 mm area. The instrument uses a scanning tunneling microscope to probe the surface and an interferometer system to measure the lateral probe movement, both having sub-nanometer resolution. The continuous vertical measurement range is 5 micrometer, and up to 2 mm can be covered by stitching overlapping ranges. The instrument includes temperature control with millikelvin stability, an ultra-high vacuum environment with a base pressure below 10-5 Pa, and seismic and acoustic vibration isolation. Pitch measurements were performed on gratings made by holographic exposure of photoresist and on gratings made by laser-focused atomic deposition of Cr. The line pitch for these gratings ranged from 200 nm to 400 nm with an estimated standard uncertainty of the average pitch of 25 X 10-6. This fractional uncertainty is derived from 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. These grating pitch measurements are uniquely accomplished on M3 because of the combination of probe resolution and long-range interferometer-controlled stage. This instrument could uniquely address certain dimensional metrology needs in the data storage industry.

Para‐flex stage for microtopographic mapping

The design and performance of a high‐precision X–Y stage which uses a unique type of flexure pivots is described. Performance achieved with a symmetrical arrangement of four arm/pivots for each axis is such that pitch, roll, and yaw is less than one arcsecond for 1×1‐mm stage motion. Vertical vibration during stage motion is less than 2.5 nm peak to valley, with the major limitation being insufficient decoupling from the drive mechanism. Also described is the application of the stage for performing microtopographic mapping with a stylus transducer.

Surface Roughness Metrology By Angular Distributions Of Scattered Light

On-line industrial inspection of batch manufactured parts requires fast measurement techniques for surface finish quality. In order to develop the measurement basis for these techniques, a system has been built to determine surface roughness by measuring the angular distributions of scattered light. The system incorporates data gathered from the angular distribution instrument and traditional surface stylus instruments. These data are used both as input and as comparison data in order to test various mathematical models of optical scattering phenomena. The object is to develop a mathematical model that uses the angular distribution of scattered light to deduce surface roughness parameters such as Ra and surface wavelength. This paper describes the results of an experiment in which angular scattered data from surfaces with sinusoidal profiles was used to compute the surface R and wavelength. Stylus measurements of these parameters were made separately. A comparative table is given of the computed and measured values. Estimates of uncertainties are also given.

Optical Roughness Measurements Of Industrial Surfaces

This paper reviews our efforts to develop the theory and instrumentation needed to measure surface roughness of manufactured surfaces by optical scattering methods. We are addressing three key problems: developing a valid and sufficient optical scattering theory for this roughness range, applying appropriate mathematical inversion techniques so that practical roughness parameters can be calculated from scattering distributions, and finally evaluating a compact commercial instrument for a wide variety of problems. Recent results from our group suggest that the simple phase screen approximation model of optical scattering validly describes light scattering from machined metal surfaces with a predominant surface lay in the 0.01 pm R to 3.0 pm R range. A model for scattering in the entire farr-field hemisphere and obsera vations on our r approach to the inverse problem is given.

Method to characterize overlay tool misalignments and distortions

A new optical alignment artifact under development at NIST is described. This artifact, referred to as a stepped microcone, is designed to assist users and manufacturers of overlay metrology tools in the reduction of tool-induced measurement errors. We outline the design criteria and diamond turning lathe techniques used for manufacturing this structure. The alignment methods using this artifact allow the separation of error components associated with the optical system or the mechanical positioning systems as encountered when performing measurements in different focal planes.Although some difficulties have been encountered when performing measurements in different focal planes. Although some difficulties have been encountered in the actual diamond turning process,the data presented show some improvements with the more recent prototypes which indicate that this method of fabrication will be useful. Photometer scan data and CCD image acquisition hardware show a significant optical response at the step edges from these structures. Initial analysis of the optical response of these edges shows sensitivity to the material used and the details of the manufacturing processes.