H Han Haitjema

Modeling and verifying non-linearities in heterodyne displacement interferometry

The non-linearities in a heterodyne laser interferometer system occurring from the phase measurement system of the interferometer and from non-ideal polarization effects of the optics are modeled into one analytical expression which includes the initial polarization state of the laser source, the rotational alignment of the beam splitter along with different transmission coefficients for polarization states and the rotational misalignment of the receiving polarizer. The model is verified using a Babinet Soleil Compensator allowing a common path for both polarization states and thereby reducing the influence of the refractive index of air. The verification shows an agreement of the model with measurements with a standard deviation of 0.2 nm. With the use of the model it is confirmed that the mean of two polarizer receivers can reduce the effect of non-linearity. However, depending on the accuracy of the polarizer angles, a second-order non-linearity remains. Also the effect of rotational misalignment of the beam splitter can not be reduced in this way.

Development of a Silicon-based Nanoprobe System for 3-D Measurements

Abstract A small 3-D probe system was developed based on sensing the bending of elastic hinges carrying the probe stylus. The stylus platform and elastic hinges are etched in silicon. On the elastic hinges, piezoresistive straingages are integrated, including the necessary wiring. The 3-D measurement range is about one hundred micrometres in each direction and the repeatability is at the nanometre level. Several prototypes of these MEMS-type probe were realised in IC-technology successfully. Calibrations with a displacement generator based on laser interferometry reveal typical repeatabilities in the nanometre level and a 3-D uncertainty of the order of 25 nm.

Bandwidth characteristics and comparisons of surface texture measuring instruments

In this review we will discuss many of the problems that are encountered when designing and carrying out comparisons of surface texture measuring instruments. Previous comparisons are discussed to highlight some of the key issues. The limitations of stylus and optical instruments are identified with a focus on the spatial bandwidths in which they operate. Guidance is given on how to design comparisons to avoid variations in the results that are due to the operating principles and bandwidth limitations of the instruments involved. Methods for matching the bandwidths of different instruments are presented and some examples are given that highlight potential problems. The software aspects of instrument comparisons are also discussed. Finally, some advice is given on how to compare profile and areal surface texture measurements.

Deformation and wear of pyramidal, silicon-nitride AFM tips scanning micrometre-size features in contact mode

An experimental study was carried out, in order to investigate the deformation and wear taking place on pyramidal silicon-nitride AFM tips. The study focuses on the contact mode scanning of silicon features of micrometre-size. First the deformation and the mechanisms of wear of the tip during scanning are discussed. After that the results of an experiment showing both phenomena on a used AFM tip are presented. Both the damaged and the unused tip are shown on AFM and SEM images. Using these images the actual mechanisms of wear are determined. It is shown that adhesive wear, low cycle fatigue and plastic deformation take place on the tip.

Calibration of displacement sensors up to 300 µm with nanometre accuracy and direct traceability to a primary standard of length

A new class of sensor has recently appeared: nanometre sensors. These sensors are characterized by nanometre or sub-nanometre resolution and an uncertainty of a few nanometres over a range of at least several micrometres. Instruments such as capacitive or inductive sensors, laser interferometers, holographic scales, and scanning probe microscopes belong to the class of nanometre sensors. Linearity errors and drift in the mechanical and electronic system limit the accuracy of all these sensors. In order to determine these errors in a traceable way, the instrumentation described in this paper was developed. The heart of the system consists of a Fabry-Perot cavity. One mirror of this cavity generates the required displacement. A so-called slave laser is stabilized to the cavity length. The frequency of this slave laser is compared with the frequency of a primary length standard. In this way the displacement is measured with a resolution of a few picometres, a range of 300 µm and an uncertainty of about 1 nm. Experiments confirm the performance of this instrument and show typical deviations of the probe systems investigated.

Dynamic probe calibration in the μm region with nanometric accuracy

Abstract This paper describes a system that enables a traceable dynamic calibration of probes of roughness testers and roundness testers, for example. The system is based on a digital piezo translator (DPT). For the calibration of the DPT itself, an interferometric technique was used. After calibration by laser interferometry, the DPT is used as a transfer standard that can be driven by signals of various, but exactly known, form. This time-displacement form can range from square to sinusoidal or quasi-random with a maximum displacement of 15 ,μm and a maximum frequency of about 300 Hz. From a practical calibration of a roughness tester, it is shown that, depending upon the profile, roughness parameters can be measured with an uncertainty ranging from a few nm to 1%.

Virtual CMM using Monte Carlo methods based on frequency content of the error signal

In coordinate measurement metrology, assessment of the measurement uncertainty of a particular measurement is not a straight forward task. A feasible way for calculation of the measurement uncertainty seems to be the use of a Monte Carlo method. In recent years, a number of Monte Carlo methods have been developed for this purpose, we have developed a Monte Carlo method that can be used on CMMs that takes into account, among other factors, the auto correlation of the error signal. We have separated the errors in linearity errors, rotational errors, straightness errors and squareness errors. Special measurement tools have been developed and applied to measure the required parameters. The short-wave as well as the long-wave behavior of the errors of a specific machine have been calibrated. A machine model that takes these effects into account is presented here. The relevant errors of a Zeiss Prismo were measured, and these data were used to calculate the measurement uncertainty of a measurement of a ring gauge. These calculations were compared to real measurements.

Uncertainty analysis of roughness standard calibration using stylus instruments

A stylus instrument was characterized and calibrated, including a dynamic calibration of the probe. This stylus instrument was used to calibrate ten roughness standards for six surface roughness parameters. The sensitivity of each parameter of each standard to such measurement conditions as stylus geometry, measurement force, cut-off wavelength, and so forth was determined experimentally. These results were used for an uncertainty evaluation of each parameter for each roughness standard. It is shown that the manufacturers’ specification for the stylus instrument (2% uncertainty in roughness parameters) is approximately correct for the most commonly used samples and parameters, but the uncertainty may range from 0.03% (for sinusoidal profiles) to 100% (for very fine surfaces), depending upon the standard and parameter to be calibrated.

A silicon-etched probe for 3-D coordinate measurements with an uncertainty below 0.1 /spl mu/m

The increasing demand for accurate coordinate measurements on products demands new concepts of probe design. Results of some realized designs are given. One of the most promising utilizes microtechnology and etching in silicon in order to realize the necessary dimensional design with flexure hinges. Microtechnology is also used for the detection system; strain gages are integrated in the probe. Results for two probes are given and possible future developments are discussed.

Design and calibration of a parallel-moving displacement generator for nano-metrology

A displacement generator is realized which enables the calibration of a wide variety of displacement-measuring probes, such as probes of roundness testers, roughness testers and stand-alone type scanning probe microscopes (SPMs), in the range of with a standard uncertainty below 1 nm. A digital piezo translator (DPT) drives a flat mirror which serves as the calibration platform. This mirror is locked to an elastic, hysteresis-free, monolithic parallel guide. Calibration of the platform displacement is carried out by various methods including tunable and stabilized lasers, Fabry-Perot interferometry and laser interferometry. The system is calibrated with a standard uncertainty of about 0.1 nm using three independent methods. As an example the calibration of an SPM using generated steps is shown.