Seminar on Dimensional Metrology at PTB to support Optical Fabrications

Date: 28 Mar 2011 - 28 Mar 2011

Venue: SIMTech Training Room

The objective of this seminar is to provide technical vision on dimensional metrology developed at Physikalisch-Technische Bundesanstalt (PTB) in Germany. This seminar will cover the key aspects of the two optical methods, namely the optical deflectometric method and the traceable multi-sensor system (TMS) highly relevant to researchers in the fields of precision measurements, optical engineering, surface characterisation, precision manufacturing and testing.

With the increasing demands for smaller, faster and more highly integrated optical and electronic devices, many challenging issues exist in fabricating optical parts, for instance, large size, high numerical apertures, large aspheric departures, tight manufacturing tolerance, ultra fine surface roughness, and complex surface structures. Dimensional metrology is the enabling technology required not only for ensuring the quality of the optical products but also for monitoring the manufacturing processes. In this paper, dimensional metrologies at the Physikalisch-Technische Bundesanstalt (PTB) to support optical fabrications will be introduced. In modern diffractive and nano optics, various micro and nanostructures are applied for realising optical functions. Dimensional metrology of these micro and nanostructures (for instance, the layer thickness, and the height, width, 3D shape, roughness and positions of structures) is a crucial task, since it usually defines the optical functions. With a brief overview of techniques such as scatterometry, optical microscopy and scanning electron microscopy, the presentation will focus on atomic force microscopy (AFM), which is capable of measuring micro and nanostructures directly, accurately, (almost) non-destructively and in 3D. Several AFMs developed at PTB will be detailed, for instance a metrological large range AFM with a capable measurement volume of 25 mm x 25 mm x 5 mm (x,y,z) coupled with homodyne laser interferometers for traceable nanoscale dimensional metrology. A newly developed 3D-AFM which is capable of performing true 3D measurements of nano structures by applying flared AFM tips. In addition, a novel AFM probe, referred to as the assembled cantilever probe (ACP) will also be introduced. It is capable of performing measurements at the sidewalls of micro and nanostructures directly. Versatile measurement examples will be demonstrated. Form metrology of optical lenses and mirrors is another challenging issue for satisfying critical demands raised from, for instance, lithographic devices, objectives and large telescopes. Form metrology of flat, spherical, aspherical and free form surfaces is involved.
The seminar will begin with a brief overview of interferometric form measurement techniques and (optical and stylus) profile methods. The two optical methods will be featured. One is the optical deflectometric method, whereby the direct and the difference deflectometric principle (also called extended shear angle difference (ESAD)) in two new deflectometric reference systems are used. The measurement systems can measure flat surfaces up to 1 m size. The principle is based on scanning the specimen with a pentaprism and measure the deflection angle with a highly accurate autocollimator. The other is a traceable multi sensor system (TMS), which is able to measure curved surfaces accurately. Finally, the limitations of optical and stylus techniques in measuring strongly curved surface and introduce the coordinate measuring machines (CMM) for form metrology will be discussed. 

About the Speaker
Dr Dai Gaoliang is currently a Principal Research Scientist and has been leading the working group on mask metrology at the Physikalisch-TechnischeBundesanstalt (PTB). His main areas of research cover the dimensional metrology of micro- and nanostructures. He is responsible for developing the high accurate metrological SFM, metrological large range SFM, 3D-AFM and micro/nano CMM at PTB. Gaoliang holds a Bachelor's Degree, a Master's Degree and a Doctorate in Optical Engineering from Tsinghua University, China. He was an R&D Engineer at the Physik Instrument (PI) GmbH & Co till the year 2001. He has authored more than 70 technical publications in the field of micro- and nano-metrology.  

9.00 am     Registration
9.20am      Welcome & Introduction         
9.30am      Presentation on dimensional metrology by Dr Dai Gaoliang
10.30am    End of Seminar

Who Should Attend
Industry professionals, R&D managers, researchers, academic staff and students.

Registration for this lecture is free of charge. Seats are available on a first-come, first-served basis. To reserve a place, please register online. 

Contact Us
For technical enquiries: Dr Zhao Liping, Email:
For general enquiries: Alice Koh, Email: