3D capability for nanometrology POSIT IONING & METROLOGY

1 | 2011 Laser+Photonics 1

ENRICO LANGLOTZDENYS DONTSOVWALTER SCHOTT

The ability to perform nanometer-precision metrology is becomingincreasingly influential throughout

all phases of product development andmanufacture, from engineering develop-

ment, through prototyping and manufac-turing, to quality control, process analysisand final inspection of components andworkpieces. In particular, advances in theminiaturization of components, such asmicrodrives or injection nozzles andextrusion dies, all having extremely smalldimensions and subject to stringenttolerances, has driven the need to measure

three-dimensional shapes with nanometerprecision. Exact machining of press tools,molding dies and optical components withnanometer precision and optical finish hasalso led to demands for high-precisionmetrological systems, as accurate infor-mation on the dimensions and shape ofprocessing tools, components and work-pieces is needed in those areas as well.

3D capability for nanopositioning and nanometrologyPRECISION, FLEXIBLE, BROAD-RANGE MEASUREMENT OF THREE-DIMENSIONAL OBJECTS

Many branches of industry and fields of research require tactile 3D coordinate measurement

systems with sub-nanometer resolution for proofing high-precision, fine-mechanical and optical

components as well as for manufactured elements and for tooling used for manufacturing

microlenses. In order to meet these requirements, nanopositioning and nanomeasuring machines

have been upgraded by incorporating 3D functionality and tactile 3D microprobes.

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3D capability for nanometrology POSIT IONING & METROLOGY

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The ›NMM-1‹ nanomeasuring machine,developed at the Technical University ofIlmenau’s Institute for Process Measure-ment and Sensor Technology and pro-duced by Sios Messtechnik, provides theopportunity for conducting many differenttypes of measurements (Figure 1 and 2).The NNM-1 exhibits 0.1 nm resolution in ameasurement volume of 25x25x5 mm3

and can be equipped with various types oftactile microprobes.

Engineering design features

The NMM-1 is composed of xyz guidanceand drive systems, upon which a cornermirror is mounted that serves as thereflector for three fiberoptic-coupledlaser interferometers. The laser interfero-meters are mounted on a thermallystable, metrology frame. The basis for itshigh precision is the arrangement of thethree laser interferometers used forpositional measurements. Their threemeasurement beams intersect at a singlepoint that coincides with the probesystem’s contact point. The object beingmeasured is attached to the corner mirrorand moves with it – compliance with theprinciple that forms the basis for theoperation of an Abbe comparator will bemaintained on all three axes at all times,as the object being measured and thecomponent utilized for determining itsdimensions are colinearly arranged, thusminimizing the effects of systematicerrors in the guidance system and anyresulting misalignment of the cornermirror. In order to provide for ultraprecisemeasurements, tilting of the cornermirror is measured by a pair of anglesensors and corrected for by the z-axisdrive via a closed-loop regulation circuit.This approach avoids any remainingresidual errors (Figure 3).

Within the NMM-1, the probe systemacts as a zero-point indicator. Widelyvarying types of sensors and processingsystems may be readily incorporated,thanks to the open interface. Non-contacting metrological systems, such asfocus sensors or white light interfero-meters, as well as scanning force micro-scopes or tactile 3D microprobes exertinglow tactile forces, are currently beingemployed (Figure 4).

The NMM-1 thus has various applica-tion areas, such as positioning, manipu-lation, processing and measurement of

microelectronic, micromechanical, opti-cal and microsystem objects (such asmicrolenses or membranes) as well as thehigh-precision calibration of ring gauges,

lateral displacement standards and step-height standards. Measurement precisionin the subnanometer range is attainable,although the overall measurable range

1 The nanopositioning and nanomeasurering machine NMM-1

2 Comparison of the measurement ranges for the NMM-1 with alternative methods

3D capability for nanometrology POSIT IONING & METROLOGY

1 | 2011 Laser+Photonics 3

can be vastly expanded when used incombination with a scanning probe mi-croscope. The employment of laser inter-ferometers for the positional measure-ments also allows tracing measurementsback to reference objects for calibrationpurposes.

Extended 3D functionality

The concept on which the NMM-1 iscurrently based permits using just the z-axis as the tactile-probing direction,which means that precisely one heightmeasurement will be correlated to everypoint on the xy-plane. Such measure-ments are termed ›2.5D‹ surface measure-ments. The NMM-1’s excellent metrologi-cal characteristics are being exploited forcalibrating transfer standards, such asstep-height standards, one-dimensionaland two-dimensional lateral-displacementstandards, planarity standards and rough-ness standards, at several governmentinstitutions around the world. Severalround-robin comparative measurementshave demonstrated its potential.

However, vertical surfaces can beneither detected nor analyzed using 2.5Dprofile measurements. Problems can alsoarise at steep surface gradients thatexceed a certain angle, for example as

present on the curved surfaces of lensesor press tools. In order to meet all of the demands imposed on high-precisionmeasurements of microcomponents, theNMM-1 was upgraded by adding 3Dfunctionality. In large part, this essen-tially meant modifications to the firm-ware (also developed by the TechnicalUniversity of Ilmenau) by incorporatingmany commands from the I++/DME spec-ification (a non-proprietary interface

between metrological software andmetrological instrumentation).

Open-loop scan commands allowdriving the probe sensor to approach andcontact the surface of the object beingmeasured and subsequently translatingthe table along a defined trajectory. Theprobe system will then be deflected bysurface irregularities. Closed-loop scancommands allow translating the tablealong a straight line in space, or around

3 Schematic of the NMM-1

4 Probe sensors for the NMM-1

3D capability for nanometrology POSIT IONING & METROLOGY

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a circular path in a predefined direction,where the probe sensor’s scanning forcewill be held constant at all times duringscanning. Various options for conductingfree-form measurements utilizing probesensors that have responsivities on allthree spatial axes have been incorpo-rated, where the scanning direction willbe computed based on the signals re-ceived from the sensor. Commands formaking single point measurements havealso been incorporated. Additional com-mands (that are not part of the I++/DMEspecification) have also been incorpo-rated in order to allow employment ofprobe systems, such as white lightinterferometers and other types of sur-face sensors that provide no feedbacksignal for regulating positioning.

Probe systems having responsivitieson all three spatial axes are essential in making measurements on three-dimen-sional objects. The ›Gannen XP‹ micro-tactile-probe system supplied by ExpressEngineering has been incorporated intothe NMM-1. The basis for this system is a silicon membrane, incorporating twelvepiezoresistive elements arranged ingroups of four, and with the groups

spaced evenly (every 120°) around theprobe tip. Each group is connected to aWheatstone bridge and provides ameasurement signal. The probe tip isattached directly to the membrane sothat this assembly can be replaced as aunit (the manufacturer offers a choice ofvarious probe tip diameters and mem-brane stiffnesses). However, the threesignals from the membrane vary with theprobe’s orientation within the NMM-1,which is why probe signals must berecalibrated whenever a membrane isreplaced. A small cube is usually em-ployed for this purpose, the probe tipbeing scanned over the cube in bothdirections along all three spatial axes andthe resultant signals recorded. Calibra-tion factors obtained in this manner may be used to compute a coefficientmatrix that, together with the specificspringiness of any one membrane, may beused to compute the probe’s force vector.High-precision, free-form surface meas-urements and three-dimensional scan-ning and tactile measurements on micro-components are thus possible (Figure 5).

Summary

The NMM-1’s extended 3D functionalityrepresents an effective tool for manu-facturing, quality assurance and re-search and development. Ultraprecise,quantitative, dimensional measure-ments over a 25x25x5 mm3 work-space can be made with a resolution of0.1 nm. By equipping the NNM-1 with

5 Measurement of a spherical surface

C O N TA C T

SIOS Meßtechnik GmbH 98693 Ilmenau, Germany Tel. +49 (0)3677 64470 info@sios.de www.sios.de

different probe sensors, it is capable ofhandling various 2D and 3D metrologi-cal tasks.

LITERATURE 1 G. Jäger et al: “Nanomeasuring and nanopositioning

engineering”, XVII. IMEKO World Congress, Sept. 17-

22, 2006, Rio de Janeiro, Brasil, Book of Summeries,

p.148

2 G. Jäger et al: “Precision mechatronics based on

high precision measuring and positioning systems and

machines”, SPIE International Symposium Optical

Metrology, June 18-22, 2007, Munich, Proceedings Vol.

6616, S. 661621-1 bis 661621-10

3 G. Jäger et al: ”High precision metrological nano

measuring machine“, mst news 01/09, 2009

D. Dontsov, E. Langlotz: “Dem Nanometer auf der Spur”,

QZ 10/09, 2009

4 T. Hausotte; B. Percle; G. Jäger: “Advanced three-

dimensional scan methods in the nanopositioning and

nanomeasuring machine”, 2009 Meas. Sci. Technol. 20

084004

5 G. Dai et al: “Accurate and traceable measurement

of nano- and microstructures“, 2006 Meas. Sci. Technol.

17 545

6 E.J.C. Bos; P.H.J. Schellekens; A.H. Dietzel:

“Aspects of tactile probing on a micro scale“, Euspen

9th International Conference; San Sebastian, Spain,

June 2-5, 2009

AUTHORS Dipl.-Ing. ENRICO LANGLOTZ is a development engineer

in the field of nanometrology and nanopositioning at

Sios Messtechnik. Dr.-Ing. DENYS DONTSOV is head of

R&Dt and Dr.-Ing. WALTER SCHOTT is the Managing

Director at Sios Messtechnik, based in Ilmenau,

Germany.

© Carl Hanser Verlag, München 2011. All rights including reprinting, photographic reproduction and translation reserved by the publishers.