A Research On White-light Interferometric Measurement System Of Surface Topography Based On The Scanning Positioning Stage

The scanning white-light interferometry (SWLI) is a relatively new measuring technology for micro-surface topography. The SWLI has features of non-contact, large measuring range, high precision and effectiveness. Based on the SWLI and developed scanning positioning stage with optical grating measuring system, by used of the innovated domestic 6JA model interferometer, an optical profiler was developed which can finish automatically such works as vertical scanning motion of the stage, positioning of CCD sampling by the optical grating measuring system, retrieving and evaluating of sample's topography etc. The technical specifications are as follows: vertical measuring range～50μm, vertical resolution 2nm, numerical aperture (NA) 0.65, transversal measuring rangeΦ0.25 mm, transversal resolution 0.52μm, repeatability is less than 5%.The core contents of the paper involve two aspects: one is the development of vertical scanning positioning stage. The other is the study of SWLI theory and algorisms of retrieving surface topography. Main innovations of the dissertation are as follows:(1) A vertical scanning positioning stage has been developed which is a set of coarse and fine two grade positioning mechanism with optical grating as displacement measuring standard. The developed stage can satisfy the requirements of both large displacement range and high resolution. The range of coarse motion mechanism is 5mm and the fine is 60μm. The positioning resolution is less than 2nm. The stage has applied the patent for invention from China Patent Office (Patent application number is 200510018618.1).(2) The model for white-light interference microscope is developed and light intensity distribution expression of interferograms under condition of monochrome light source and wide numerical aperture is derived. The influences of numerical aperture and spectrum width condition on white-light interferogram and its envelope are analyzed and their meanings to measuring sensitivity and range are explained.(3) A new white-light interference phase-shifting algorism of equal phase-shifting stepping is introduced which can retrieve the surface profile of samples efficiently. Effects of phase-shifting step length, spectrum width of light source and numerical aperture on the accuracy of algorism are simulated and conclusions of how to enhance the accuracy are obtained.(4) The developed profiler based on scanning white-light interferometry has a structure of modularization. The interference microscope and the scanning positioning stage are relative independent which makes the profiler to be very flexible. The scanning positioning stage could be coupled with different type interference microscope with different numerical aperture in order to satisfy the different measurement requirements.In conclusion, the developed SWLI profiler can satisfy the measurement and evaluation of machined surface roughness, the topography of microstructure such as integrated circuit, integrated optical element, MEMS etc. It has advantages of being non-contactive, high precision and reliability, low-cost.