Research On White Light Interference Based Measurement Methods And System For Ultra-precision Surface Topography

With the development of ultra-precision processing technology, the semiconductor industry, MEMS and NEMS technology, the need for ultra-precision surface topography measurement at the nanoscale is urgent. Instruments for measuring ultra-precision surface topography should have high lateral resolution, high vertical resolution and large measurement range. The innovative design and key technologies of the ultra-precision surface topography measurement system are discussed. Both lateral resolution and vertical resolution of the measurement system can achieve nano-scale with measuring range of millimeters. The main research contents, results and new ideas are as follows:Using the characteristics of white light interference fringes, a novel atomic force probe scanning measurement method based on white light interference is proposed, in which the deflection of atomic force probe cantilever is obtained by measuring the movement of white light interference central fringe. The extraction algorithms of the centerline of zero-order fringe and the calculation method of the centerline movement amount are analyzed. The relationship between the deflection of the atomic force probe cantilever and the movement amount of the central fringe is analyzed, and nonlinearity error correction of probe cantilever deflection measurement is proposed.The basic theory of atomic force probe scanning measurement is investigated. To overcome the shortcomings of the contact mode of atomic force microscopy, a new contact operation mode which combines the displacement of vertical scanning system and the deformation of the cantilever is proposed according to the characteristics of the measurement system. Traceable tracking measurement of atomic force probe scanning was realized.A measurement method for measuring ultra-precision surface topography, based on one interference microscope substrate, which combined non-contact optical measurement with atomic force scanning probe measurement, is proposed. According to different measurement requirements of ultra-precision surface, different measurement methods can be used. In addition, complementary quantitative measurement can be implemented for same surface.An ultra-precision surface topography measuring system, which combined atomic force probe scanning measurement with non-contact optical measurement, based on the measurement methods and measurement principles for ultra-precision surface topography measuring is developed successfully. Nano driving system, which including metrological vertical scanning system and coplanar 2D precision stage with large-stroke and nanopositioning resolution, is developed. A laser interference displacement measuring system is developed and four-quadrant optoelectronic detectors are used to detect laser interference fringes. The conditions to get a couple of quadrature signals, the non-orthogonal error caused by changes of the width of fringe period and/or the offset angle in the measurement process and the causes of measurement errors in detecting laser interference fringes are analyzed. A method combining hardware circuits and software is used to compensate measurement errors caused by the signal errors. The software for ultra-precision surface measurement is developed and atomic force probe scanning measurement, white light interference vertical scanning measurement, phase shifting interferometry measurement were realized.The measurement method proposed and measurement system developed in this paper can be used to measure ultra-precision machining engineering surface, optical surface, geometry of micro-nano, is developed successfully. The results of accuracy testing and measurement examples are given.