QMT Features: September 2009
Metrology for nanotechnology
The development of a micro standards infrastructure is a critical for manufacturers to interchange parts, packaging and designs.  By Richard Leach, Engineering Measurement Division, National Physical Laboratory.

Micro- and nano-scale structures are increasingly playing an exciting part in the manufacturing industries. An example is self-cleaning glass, now widely available, which features a micro pattern engineered onto the surface giving the window enhanced properties. Micro structured surfaces are also used to improve tribological properties in orthopaedics, leading to improved longevity of the implant. This trend is sure to increase and, just as standards played a significant role in the advancement of trade and prosperity in the macro world, the same is true of the micro and nano world. With these benefits, substantial funding is entering these sectors across the globe and commercial applications are becoming increasingly widespread.

A micro standards infrastructure is essential to allow manufacturers to interchange parts, packaging and designs. Such an infrastructure will also help to reduce costs, predict component compatibility and improve quality. This can lead to a significant time saving as developing in house standards can be costly for the manufacturer and their supply chain. The costs of developing such standards are significant, but the rewards of doing so can be vast; not least due to the increased customer confidence when buying something specified to an internationally recognised traceable standard.
Similarly, if interchangeability of parts is to become a reality then manufacturers need to move away from ‘in-house’ standards and move towards measurement standards that are traceable to national or international realisations of the unit of length, the metre. A vital step towards this will be widespread access to equipment that will allow manufacturers to work to these standards.

Recognising the need to overcome these barriers, the UK Government established the Centre of Excellence in Metrology for Micro and Nano Technologies (CEMMNT*), now funded by the Technology Strategy Board.
The National Physical Laboratory (NPL), in partnership with CEMMNT is addressing two major challenges of industry. Firstly, offering open access to a suit of nanometrology instruments including a micro CMM, vibrometers, surface profilometers, and white light interferometers amongst others. Secondly, developing traceable standards in nanometrology and offering open access measurement and characterisation services to organisations that are commercialising new micro and nano products.

With the support of CEMMNT funding, NPL is developing traceable methods to measure the dimensions of micro and nanostructures, which builds on a number of instruments previously developed at NPL. Two important aspects of engineering nanometrology are surface topography and micro co-ordinate metrology, and NPL is working in these areas to provide industry with an accurate, traceable measurement service. The work that is being done in each of these areas is outlined below.

Surface topography
Quantitative surface topography measurement is important in almost all areas of manufacturing, yet there has only been limited standardisation of such measurements at the nano-scale. 3D measurement currently has no infrastructure, and whilst standardisation of stylus instruments is now underway for 3D surface texture, there has been very little attention paid to the corresponding issues for optical instruments.

The topographic properties of a surface can strongly influence its functionality and these properties must be taken into account when designing or manufacturing nano-devices. Structured surfaces are not properly represented by 2D descriptions; 3D measurement is a minimum requirement.

To address these problems, NPL has developed a traceable 3D measuring instrument with a working range of 8 mm x 8 mm x 0.1 mm and corresponding measurement uncertainties of 50 nm x 50 nm x 5 nm, at a confidence level of 95 %. The instrument uses laser interferometers to measure the position of a stylus in three axes and obtains traceability to the metre via the laser sources. The instrument is currently being tested, with a view to launching an areal surface topography measurement service at NPL, in the near future.

To help companies develop their own traceable nano-metrology capabilities, NPL has also developed areal transfer artefacts that can be measured using the NPL areal instrument and then used to calibrate stylus and optical instruments in industry and academia.

Micro co-ordinate metrology
The co-ordinate measurement machine (CMM) revolution has yet to come to the nano-manufacturing area. The shape of key components, features on these components and assemblies of nano-components will need to be measured in three-dimensions. The development of probes and probing systems capable of making accurate, 3D measurements will, therefore, be of vital importance.

In recognition of the need for such measurements to enhance product quality and manufacturing process control, NPL is developing a high accuracy 3D micro-probing system capable of incorporation into commercial micro-CMMs.
With CEMMNT funding, NPL has purchased a Zeiss F25 micro-CMM and is carrying out research to develop a micro-probe system capable of making 3D measurements on miniature components with high aspect ratio features.

The probe element will consist of a flexure structure with integrated sensing and actuating elements, supporting a ball ended probe stylus. To overcome potential problems with surface adhesion that can restrict the performance of small contact probes, the new micro-probe will be designed to vibrate.
The final product will be available for industry to help meet the nano-measurement challenges it faces.

Manufacturers hoping to be part of the nano-revolution need to support and be involved in the development of traceable measurement standards. NPL is currently looking for companies with nano-measurement challenges that we can help solve. This will assist us in identifying the issues facing industry and develop standards traceable to the international realisation of the metre, in this exciting emerging sector. Specifically, NPL is now soliciting case studies that will require no direct funding for NPL from the companies involved.

Nanometrology sets a number of challenges for the future, but looks set to become huge business. It is, therefore, important to get the measurement infrastructure right from the start. NPL is active in this area and our work will help to build and maintain the infrastructure required for commercial development of nanotechnology, and the predicted revolution in manufacturing and life-style that such technologies will bring.
Email: richard.leach@npl.co.uk.

*CEMMNT provides a point of access for world-leading measurement, characterisation and analytical services across multiple industry sectors, enabling companies to innovate in design, optimise product quality and performance, reduce costs and maximise competitive advantage. Its partners are NPL, BAE Systems, QinetiQ, Taylor Hobson and Coventor.

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