A new general approach for solving the self-calibration problem on large area 2D ultra-precision coordinate measurement machines
2014 (English)In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 25, no 5, 055001- p.Article in journal (Refereed) Published
The manufacturing of flat panel displays requires a number of photomasks for the placement of pixel patterns and supporting transistor arrays. For large area photomasks, dedicated ultra-precision writers have been developed for the production of these chromium patterns on glass or quartz plates. The dimensional tolerances in X and Y for absolute pattern placement on these plates, with areas measured in square meters, are in the range of 200-300 nm (3 sigma). To verify these photomasks, 2D ultra-precision coordinate measurement machines are used having even tighter tolerance requirements. This paper will present how the world standard metrology tool used for verifying large masks, the Micronic Mydata MMS15000, is calibrated without any other references than the wavelength of the interferometers in an extremely well-controlled temperature environment. This process is called self-calibration and is the only way to calibrate the metrology tool, as no square-meter-sized large area 2D traceable artifact is available. The only parameter that cannot be found using self-calibration is the absolute length scale. To make the MMS15000 traceable, a 1D reference rod, calibrated at a national metrology lab, is used. The reference plates used in the calibration of the MMS15000 may have sizes up to 1 m(2) and a weight of 50 kg. Therefore, standard methods for self-calibration on a small scale with exact placements cannot be used in the large area case. A new, more general method had to be developed for the purpose of calibrating the MMS15000. Using this method, it is possible to calibrate the measurement tool down to an uncertainty level of <90 nm (3 sigma) over an area of (0.8 x 0.8) m(2). The method used, which is based on the concept of iteration, does not introduce any more noise than the random noise introduced by the measurements, resulting in the lowest possible noise level that can be achieved by any self-calibration method.
Place, publisher, year, edition, pages
2014. Vol. 25, no 5, 055001- p.
self-calibration, algorithm, metrology, large area, ultra-precision, mask, CMM
Production Engineering, Human Work Science and Ergonomics Reliability and Maintenance
IdentifiersURN: urn:nbn:se:kth:diva-122271DOI: 10.1088/0957-0233/25/5/055001ISI: 000334352000001ScopusID: 2-s2.0-84898464161OAI: oai:DiVA.org:kth-122271DiVA: diva2:621650
QC 20140610. Updated from submitted to published.2013-05-162013-05-162014-06-10Bibliographically approved