Measurement of microstructures to super resolution by focus probe Kuang-Chao Fan, Liang-Chia Chen Department of Mechanical Engineering National Taiwan University 1, Sec. 4, Roosevelt Rd., Taipei, 10617, Taiwan Tel.: + 886 [2] 2362-0032 Fax: +886 [2] 2364-1186 E-mail: fan@ntu.edu.tw Abstract The edge detection of microstructures by microscopes is poor in resolution due to the effect of diffraction limit. This paper proposes a new technique by using the focus probe in association with a nanopositioning stage. The edge is detected by the total energy reflection principle and the step height is detected by the astigmatic principle. Both methods can realize the resolution of 1 nm. Experimental results show that for the edge detection of micro cavities and the measurement of micro linewidth, the standard deviation is less than 40 nm. For the step height measurement, the standard deviation is less than 22 nm. This novel super resolution technique is a breakthrough of the conventional diffraction limit. Keywords: Focus probe, nanopositioning stage, super resolution, edge detection, step height 1. Introduction As the miniaturized microstructures are fabricated by advanced processes, such as MEMS, micro machining, lithography, nano-imprinting etc., conventional methods are no more capable to measure the physical dimension. Diffraction limits around half the wavelength in the far-field physically inhibits imaging of nanostructures with visible light [1]. Many superresolution methods to extend the limit are all of the image-based optical metrology, such as the through-focus technique [2, 3], scatterfield microscopy [4], stimulated emission depletion (STED) microscopy [5], fluorescence photoactivated localization microscopy (PALM) [6], absorbance modulation imaging (AMI) [7], phase modulation microscopy [8], etc. These are either based on the statistical approach or required complicate optical system. Although electron and X-ray microscopy could provide nano-scale imaging, vacuum requirement is a necessary condition. In this paper, a new technique by using the focus probe in association with a nanopositioning stage is presented for the edge detection of micro cavities and the step-height measurement of a thin film. The edge is detected by the total energy reflection principle and the step height is detected by the astigmatic principle. Both methods can realize the resolution of 1 nm. Experimental results show that for the edge detection of micro cavities and the measurement of micro linewidth, the standard deviation is less than 40 nm. For the step height measurement, the standard deviation is less than 11 nm. This novel super resolution technique is a breakthrough of the conventional diffraction limit. 2. Measurement principle 2-1 Microcavity measurement The principle of edge detection of a cavity is simply based on the light reflection theory. When a beam spot is focused on the surface, the total light will be reflected back to the receiver. While the spot is moved across the edge of the surface, only partial light will be reflected back. Fig. 1 shows the situation when the spot has passed a distance (x) from the edge (CD) of the surface W. The amount of reflected light is proportional to the remaining spot area on the surface. Let the radius of the spot be r (x < 2r), the sector area of OAF is r 2 θ