SUCCESS STORY – Accurate Profile Reproduction of the Finest Structures Thanks to Piezo Technology and Confocal Technology-- Gernot Hamann --Accurate Profile Reproduction of the Finest Structures Thanks toPiezo Technology and Confocal Technology
Optical 3D Surface Measuring Technology for Industry and ResearchPhysik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.ws, www.pi.ws

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SUCCESS STORY – Accurate Profile Reproduction of the Finest Structures Thanks to Piezo Technology and Confocal Technology-- Gernot Hamann --Optical 3D Surface Measuring
TechnologyFor surface inspections that are indispensable in many of
today's industries, the trend is heading toward smaller andsmaller structures that must be reproduced or resolved
accurately at nanometer level. Optical measurement
processes as contact-free and destruction-free analysis andtest methods are chosen for many applications because they
can be applied to almost all materials and are also suitable forsensitive samples. Highly precise, confocal reproduction
principles can present the sample topography and roughness
structures not only qualitatively, but also correspondingly
quantitatively using matching tactile measurement methods
that are described in many industry standards. Piezo-based
positioning systems are making considerable contributions inthis field.

NanoFocus AG, located in Oberhausen, Germany, has been
considered for many years as a pioneer in optical-confocal 3D
surface measuring technology. Different product lines covervarious areas of application, from fast inline production
inspection to flexible, customer-specific solutions and evenhigh-precision µsurf systems (Fig. 1).

Fig. 2The optical 3D surface inspection is ideal both for the lab as well
as demanding industrial use, e.g. for checking paint appearance
in the automotive industry (Image: NanoFocus)

For rapid wide-area measurements these µsurf systems workwith vertical resolutions up to 1 nm, laterally up to 300 nm.
This means they are suitable both for the lab as well as fordemanding industrial use (Fig. 2), such as three-dimensionalsurface measurements in medical technology, thesemiconductor industry, forensics, electronics, theautomobile industry, materials management and the steelindustry.

Fig. 1

Here is the new product “µsurf expert” which will be launched inspring 2014 (Image: NanoFocus)

The measurement principle works reliably on bothtransparent and metallic surfaces and on rough or polishedsurfaces. Furthermore, layer thicknesses of partiallytransparent surfaces can be analyzed using special algorithms.

Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.ws, www.pi.ws

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SUCCESS STORY – Accurate Profile Reproduction of the Finest Structures Thanks to Piezo Technology and Confocal Technology-- Gernot Hamann --Extremely Low-Scatter and Robust
Signaling
The core of each of these µsurf systems is the integrated
confocal-optical filter unit that is combined with a highly
precise and fast focusing module.
The patented multi-pinhole disc (MPD) is used as an opticalfilter of reflected light rays (Fig. 3) and distinguishes itself
through extremely low scatter light intensity as well as robust
signaling with a high light yield. The objective focuses lightfrom a high-performance LED source through the multipinhole disc onto the surface. Only the portion of the lightthat is reflected from one point of the surface and which lies
precisely in the focal distance of the objective can pass thepoint openings of the MPD. In contrast, light that is reflectedby a sample area that is not within the focal plane of theobjective, is blocked. By rotating the MPD, the entire sample
surface can be quickly and completely scanned.
By moving the objective vertical to the sample surface, allcontour lines of the sample are focused one after the other.
The CCD camera used stores the brightness values of thevisual field for each objective position. Points with maximum
brightness are located on one contour line. Each confocal
image is a horizontal cross-section through the surface
topography of the sample. The 3D structure of the sample canbe determined from the total number of images at different
height intervals, this is called the image stack. This stackconsists of an average 200 to 400 individual images that arerecorded in a few seconds and are converted by themeasurement software into a 3D topography representation(Fig. 4), accurate to within a few nanometers.

Fig. 4

Fig. 3LED light source (1), multi-pinhole disc (2), sample surface (3),mirror (4) and CCD camera (5) (Image: NanoFocus)

200 to 400 individual 2D images are converted into a 3D image
by the measurement software. (Image: NanoFocus)

Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.ws, www.pi.ws

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SUCCESS STORY – Accurate Profile Reproduction of the Finest Structures Thanks to Piezo Technology and Confocal Technology-- Gernot Hamann --Piezo Positioning System for theObjective
In order to achieve such a high measurement resolution, theobjective must be moved in the direction of the z axis withgreat precision. “This is almost impossible using conventional
motor drives,” explains Dr. Georg Wiora (Image 5),responsible for strategic development and innovation
management at NanoFocus. “The positioning system for ourobjective is therefore based on piezo actuators. They work
free of wear and friction with zero play and they are suitablefor high recording frequencies due to their dynamics.” Zeroplay and highly precise flexure guides together ensure highfocus stability.
This is how travel of up to 500 µm is achieved in the described
application; the position accuracy of the kinematics thus liesin the nanometer range.

Fig. 5

Dr. Georg Wiora, head of strategic development and innovation
management at NanoFocus (Image: NanoFocus)

The piezo-based, single-axis positioning system (Fig. 5) used inthe µsurf system originates from the comprehensive productportfolio of Physik Instrumente (PI). It was adapted toprecisely meet the application requirements, was able to beeasily integrated into the objective holder thanks to its
compact dimensions and moves the objective at a constant
speed.
The measurement is performed on the fly. That is why thecore requirement of the positioning system is a high velocity
constancy in the nanometer range. This is the only way
absolutely accurate (down to a few nanometers) roughness
measurements can be taken that are compatible with tactile
processes and meet the requirements of the corresponding
industrial norms. Repeatability is just as important when
positioning the objective, so as to prevent a height offset
when assessing the stack of individual images.

Fig. 6

The piezo-based single-axis positioning system was adapted toprecisely meet the company's application requirements. It fits
easily into the objectiveholder due to its compact dimensions(Image: PI)

High-Resolution Measuring
Process and Application-SpecificController
Repeatability and linearity in highly dynamic and highresolution positioning systems are inconceivable without theuse of measurement processes with the highest possible
resolution. Position accuracies of just a few nanometers orlower require precise position measurement methods thatare able to detect motion in this range.
In the described application, capacitive sensors ensure thishighly precise actual value recording. The high sensor
bandwidth also allows closed-loop control in dynamic
applications. The capacitive sensors are generally suitable formeasurement ranges up to 1000 µm, for resolutions down to0.01 nm. The repeatability and absolute positioning accuracyof the objective are therefore guaranteed.
A controller with an integrated piezo amplifier analyzes thesensor data and controls the positioning system's piezo
actuator. The compact customized electronics can beintegrated into the NanoFocus control system seamlessly,
both in terms of hardware dimensions as well as electricalinterfaces. “In this area, too, Physik Instrumente (PI) has
proven to be a competent partner that has contributed
decisively to our success,” explains Dr. Wiora. Piezo-based
positioning systems have therefore shown once again thatthey can drive technology.

Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.ws, www.pi.ws

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SUCCESS STORY – Accurate Profile Reproduction of the Finest Structures Thanks to Piezo Technology and Confocal Technology-- Gernot Hamann --About NanoFocus

AuthorAs early as 1994, NanoFocus AG has been developing,producing and selling high-precision optical 3D measuringsystems and software to measure industrial surfaces. Itsinnovative systems make it possible to measure 3D
topography extremely quickly, contact free and easily withresolutions in the micro- and nanometer range.
The product families µsurf, µscan and µsprint offer reliable
and repeatable measurement accuracy for different areas ofapplication. This ideal and intuitive software is available formeasurement, analysis and control. It delivers industry
standard-compliant results, comprehensive measurement
reports and the option to automate measurement sequences.
With high measurement and analysis speeds, the systems areideal both for the test lab as well as for production-related
use and inline control. Typical areas of application include
medical technology, the semiconductor industry, forensics,
electronics and the automobile industry, materials scienceand the steel industry.

Dipl.-Physiker Gernot Hamann, Head of Key AccountManagement at PI (Physik Instrumente)

About Physik Instrumente (PI)In the past four decades, PI (Physik Instrumente) with
headquarters in Karlsruhe, Germany has become the leading
manufacturer of nanopositioning systems with accuracies in
the nanometer range. With four company sites in Germany
and fifteen sales and service offices abroad, the privately
managed company operates globally.
Over 850 highly qualified employees around the world enable
the PI Group to meet almost any requirement in the field ofinnovative precision positioning technology. All key
technologies are developed in-house. This allows thecompany to control every step of the process, from design
right down to shipment: precision mechanics and electronics
as well as position sensors.
The required piezoceramic elements are manufactured by its
subsidiary PI Ceramic in Lederhose, Germany, one of theglobal leaders for piezo actuator and sensor products.
PI miCos GmbH in Eschbach near Freiburg, Germany, is a
specialist for positioning systems for ultrahigh vacuum
applications as well as parallel-kinematic positioning systemswith six degrees of freedom and custom-made designs.

Physik Instrumente (PI) GmbH & Co. KG, Auf der Roemerstrasse 1, 76228 Karlsruhe, Germany
Phone +49 721 4846-0, Fax +49 721 4846-1019, Email info@pi.ws, www.pi.ws

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