Logo of the Physikalisch-Technische Bundesanstalt
symbolic picture: scientific-technical publications

PTB-Reports Optik (Opt)

Publication single view


Multi-wavelength VIS/UV optical diffractometer for high-accuracy calibration of nano-scale pitch standards

Author(s): Egbert Buhr and Alexander Diener
Editor: Bodermann, Bernd; 4.2, Bild- und Wellenoptik, PTB-Braunschweig
Buhr, Egbert; 4.2, Bild- und Wellenoptik, PTB-Braunschweig
Report type: PTB-Report
Year: 2009
ISBN: ISBN 978-3-86918-032-8
Abstract: This talk will describe an optical diffractometer which has been developed and set up at the Physikalisch-Technische Bundesanstalt (PTB). The device offers the possibility of traceable high-accuracy calibrations of the lateral period of gratings (pitch) in the micro- and nanometer scale. The measurement principle is based on a modified Littrow configuration, where the incident and the diffracted laser beams are almost collinear. The grating is mounted on a rotary table, and a high-precision rotary encoder is used to measure its angular positions. The profiles of the diffracted laser beams are recorded by means of a line array image detector. To determine the centre positions of the imaged laser beam profiles, different analysis methods can be applied. A variety of laser wavelengths, ranging from 266 nm to 633 nm, can be used. Due to the optional UV wavelength, the smallest measurable pitch is about 144 nm. Depending on the quality of the sample, the measurement uncertainty can be smaller than 10 pm. For two-dimensional gratings the pitch of the two main and the diagonal directions can be measured and thus, also the angle between the two main grating orientations can be determined.
The performance of the diffractometer instrument has been verified by two international comparisons with other national metrology institutes (NMIs). One of these comparisons dealt with the calibration of 1D gratings with a pitch of 700 nm and 4 µm, and the other with the calibration of 2D gratings with a pitch of 300 nm and 1000 nm. Both comparisons were accepted as supplementary comparisons by the Bureau International des Poids and Mesures (BIPM).
Note: Scatterometry and ellipsometry on structured surfaces : Beiträge des 245. PTB-Seminars am 18. und 19. März 2009 ; (PTB-Bericht PTB-Opt-71)

Back to the list view