Scatter method for measuring roughness of very smooth surfaces: an analysis and preliminary results

Romuald Synak

doi:10.1117/12.921665

4 May 2012 Scatter method for measuring roughness of very smooth surfaces: an analysis and preliminary results

Romuald Synak

Proceedings Volume 8430, Optical Micro- and Nanometrology IV; 843015 (2012) https://doi.org/10.1117/12.921665
Event: SPIE Photonics Europe, 2012, Brussels, Belgium

Abstract

A novel method for measuring roughness and reflectance of very smooth surfaces has been presented in the paper. It is based on the measurement of the Total Integrated Scatter (TIS) parameter using a flat photodiode integrator rather than a conventional optical sphere or hemisphere. By that means, one can obtain much less expensive and smaller instruments than the traditional ones that could find their application for surface control purposes in the production area of a wider range of companies. Unfortunately, a decrease of the integrator dimensions could reduce its spatial frequency bandwidth causing measurement errors. Additional errors can occur because of the integrator flatness. Therefore, an analysis of the influence of those factors has been performed. Using the results of the Rayleigh-Rice vector perturbation theory, dependences showing the influence of the range-of-acceptance angle on the TIS value measured have been shown. For the case when very smooth surfaces (e.g. silicon wafers, optical mirrors, precision metal elements) are investigated, the lower limit of the angle range is particularly critical and should be carefully selected. On the other hand, the upper limit can be even smaller than 20-30° which makes it possible to find a compromise while designing the measuring unit. Assuming such a limit, the influence of the integrator flatness is proved to be irrelevant. In the paper, results of measurements of some parameters valuable for the analysis are presented as well as preliminary results of sample measurements in a tentative system. The results obtained confirm the validity of further investigations in this research area. A precise unit for investigating functional properties of the method is under development, and it is planned that the measurement results derived from this unit are to be compared with results of different measurements conducted by means the Ulbricht sphere instruments and by other methods.

Citation Download Citation

Romuald Synak "Scatter method for measuring roughness of very smooth surfaces: an analysis and preliminary results", Proc. SPIE 8430, Optical Micro- and Nanometrology IV, 843015 (4 May 2012); https://doi.org/10.1117/12.921665

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