SUCCESS STORY – Fast, High-Precision 3D Surface Inspection-- Gernot Hamann --Fast, High-Precision 3D Surface Inspection
Piezo Actuators Position Objectives

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 – Fast, High-Precision 3D Surface Inspection-- Gernot Hamann --The best possible positioning accuracy is now essential inmany technical fields. Examples of such fields range fromsemiconductor manufacturing and biotechnology through to
optical metrology, microscopy and other imaging
applications. For such applications, there is no serious
alternative to nanopositioning systems with piezoelectric
drives. These operate with repeatability in the nanometer
range and response times below one millisecond, and withthat they continually conquer new fields of applications.
Often they even drive on technology, as the application in thefield of microscopic metrology described hereafter shows.
With the BW-D501, Nikon Instech. Co. Ltd. has developed anew, high-speed measurement device which facilitates
extremely high height resolution, 1 pico meter observationsin three-dimensional, non-contact and non-destructive
surface control of the most diverse materials (Fig. 1).

Fig. 2

Fast, high-precision 3D surface inspection done with the BWD501 from Nikon (image: Nikon/PI)

Capturing Roughness andContours

Fig. 1

Nikon BW-D501 Super High Vertical Resolution Non-Contact 3D
Surface Profiler (image: Nikon/PI)

The deformation of gel samples or surface coatings whenheated can thus be analyzed; a heating table required for thispurpose is already integrated in the device. The inspection
method is suited for numerous industrial applications since, incontrast to conventional methods, even surfaces with diffuse
reflection characteristics offer no difficulty to themeasurement device. Surface contours as well as theroughness of different surfaces can now be captured,visualized and analyzed with high resolution (Fig. 2).

The camera system of the measurement device initially
examines the surface of the sample with high resolution. To
get the depth of field necessary for a three-dimensional
analysis, the optics is moved gradually in the direction of the Z
axis. Depending on the position of the objective, different
areas of the sample are put in focus. Afterwards, theindividual images can be collated for analysis. Approximately
1000 images are necessary for a detailed, analyzable picture.
The system works with considerable speed: Up to 2000
images are taken per second. To be able to display thedetailed structure as well as the shape, as for example in anelevation map, the system additionally works with white-lightinterferometry. The interference pattern provides
information on the shape of the surface.
The fast and precise positioning of the objectives is animportant requirement for the analysis and for the assemblyof the individual measurement results to meaningful pictures.
For this purpose, a positioning system that moves the entire
revolving nosepiece was directly integrated in the microscope(Fig. 3).

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 – Fast, High-Precision 3D Surface Inspection-- Gernot Hamann --With it the all objectives mounted to the nosepiece can be
moved with high precision in the direction of the Z axis.

In addition, they can accellerate with up to 10g and with thatthey are suited for high frequencies which are necessary forthe real-time measurement of the 3D surface analysis. At thesame time, play-free and high-precision flexure guides
provide high focus stability and extremely straight motion.
This in turn means that travel ranges of up to 100 µm can beachieved in the application described above practicallywithout lateral displacement of the objective. The accuracy ofthe motion of the kinematics is in the nanometer range. The
flexure guides used for the transfer of force and motion
operate without wear as well.

Fig. 3The piezo-based nanopositioning system moves the entire
revolving nosepiece with the different objectives in the directionof the Z axis (image: PI)

All of this can hardly be realized with conventional motordrives. The positioning system therefore is based on piezo
actuators. They are supplied by the company Physik
Instrumente (PI) from Karlsruhe, Germany. There were manyreasons for this particular choice: Piezo actuators (Fig. 4) workwithout wear or friction and with no backlash.

Capacitive sensors, supplied by PI, too, are employed for theprecise measurement of the position while in motion. They
measure the part of the mechanical system that is in motion
directly and without physical contact (direct metrology).Neither friction nor hysteresis affect the measurement.
Combined with the position resolution in the subnanometer
range, very good linearity values can be achieved. With thisthe position of the objective can be matched accurately to thecorresponding image which is a necessary requirement for
high-precision 3D surface inspection.

About Nikon Corporation,Instruments Company
The roots of Nikon Corporation, Instruments Company reachas far back as 1917 when three Japanese companies
amalgamated to one enterprise which developed andproduced high-precision optical glass. In 1925 already, they presented the first microscope which
offered a revolving nosepiece where different objectives
could be interchanged. In the coming decades, the upcoming
enterprise set new standards in microscopy. Today, it is oneof the market leaders in digital imaging applications andconvinces again and again with innovative products. An
example for this is the high-precision and real-time capablesurface analysis, including the powerful and easy to use
software for the analysis, described in this text.

Fig. 4The piezo actuators work without wear or friction and with nobacklash (image: PI)

Typical fields of application for the high-performancemicroscopy can today be found in the industry sector as wellas in biology, medical engineering and materials research.
Nikon has been actively represented on the European market
since 1961.

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 – Fast, High-Precision 3D Surface Inspection-- Gernot Hamann --About 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 the
global leaders for piezo actuator and sensor products.
PI miCos GmbH in Eschbach near Freiburg, Germany, is aspecialist for positioning systems for ultrahigh vacuum
applications as well as parallel-kinematic positioning systems
with six degrees of freedom and custom-made designs.

Author

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

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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