Bottom-up approach for traceable calibration of tip geometry of stylus profilometer

Abstract

A novel approach for accurate and traceable calibration of stylus tip geometry is introduced in the paper. The approach consists of several steps. Firstly, the geometry of an AFM tip is calibrated to a kind of line width standard whose geometry is traceably calibrated to the lattice constant of crystal silicon. Then, the stylus tip to be calibrated is measured by the calibrated AFM tip in an AFM, thus its tip geometry can be accurately determined after the contribution of the AFM tip geometry being corrected from the measured AFM image. After being calibrated, the stylus tip can be applied in measurements of vast microstructures and surfaces, where the measurement results can be in turn corrected using the characterized stylus tip geometry. In such a way, the stylus tip geometry and its measurement results can be finally traceable to the lattice constant of silicon, using this bottom-up approach. Detailed experimental examples are illustrated. For a stylus type RFTHB-50 studied in this paper, its tip radius is measured as 1.727 μm with a standard deviation of 0.007 μm. It is significantly smaller than its nominal value of 2 μm, indicating the need of the calibration. The application of calibrated stylus tip in measurements of microspheres is demonstrated. Compared to conventional tip characterization methods based on tip characterizers the proposed method has advantages of (i) no risk of damaging sharp edges of tip characterizers, (ii) capable of directly characterizing the 3D geometry of stylus tip, (iii) high accuracy.