Development of Random Micro-roughness Measuring Apparatus Based on Fraunhofer Diffraction. Subnanometer Measurements by the New Error Calibration Method.

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  • Ｆｒａｕｎｈｏｆｅｒ回析による超精密加工表面粗さ測定装置の開発研究　光学系誤差の補正法
  • Fraunhofer カイセツ ニ ヨル チョウ セイミツ カコウ ヒョウメン
  • Subnanometer Measurements by the New Error Calibration Method
  • 光学系誤差の補正法

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Abstract

In this paper, we propose a new optical measuring method which can be applied to in-process measurement of root mean square roughness (Rrms) of ultra-fine finished surface with an accuracy of sub-nanometer. The principle of our method is based on the Fraunhofer diffraction theory with taking account of Gaussian laser beam propagation. The automated random micro-roughness measuring system is developed based on the principle. Practically, the optical parts composing optical system in which laser beam propagates are taken as the diffractive and scattering body, so the systematic error which is defined as optical system roughness is occurred. In order to enable more accurate measurement by eliminating this error, calibration method based on theoretical analysis is introduced. This method is performed by using a reference surface of which surface roughness is measured by using the traditional stylus method with high reliability. The measurements of the ultra-fine polished silicon wafers with the micro-roughness of sub-nanometer order are carried out by using the developed measuring system of which optical system roughness is calibrated. And the silicon wafers are measured by using the ZYGO profiling instrument for checking surface roughnesses. It is shown that the developed measuring sensor which is calibrated is valid for measuring random micro-roughness within a nanometer.

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