The Surface Shape And Profile Dimension Measurement Method And System Based On White-light Interferometric Technology

With the development of surface measurement technology, more attentions are focused on the surface measurement and evaluation in three dimensions. The point-scanning mode of the contact measurement instruments and the optical probe instruments limit their applications in three dimensional surface measurements. With the advantages of high-precision, large and unambiguous measurement range, and the line-scanning mode, vertical scanning white-light interferometric technology had been thought as a preferable method to measure super smooth surface in three dimension, and began to be applied for the surface measurements of micro-electronic component and optical component with such discontinuous characteristic as step, groove. Based on vertical scanning white-light interferometric characteristic, a new method for the absolute ordinate measurement by tracing the zero-order fringe is proposed in this dissertation. The new method broke through the limitation of the viewfield of microscope objective to measurement area, which could accomplish the large-range and large area measurement of three-dimensional surface. A surface profile measurement system for three-dimensional surface is also developed to meet the requirement of shape and profile dimension.Main outlines and innovations of this dissertation include:(1) A method for the absolute ordinate measurement by tracing the zero-order fringe based on the vertical scanning white-light interferometric technology is proposed. The model for white-light interference microscope is derived, which is helpful to analyze the influences of the bandwidth of light source, numerical aperture (NA) of microscope objective, the slope of the measured surface on the intensity contribution of white-light interference fringe.(2) A surface profile measurement system for three-dimensional surface is developed based on vertical scanning white-light interferometric measurement method and the zero-order fringe tracing method for the large-range and large area measurement of surface shape. Its measurement range is 8mm, and scanning resolution is 0.002μm in the vertical direction; while the measurement range is 40mm×40mm and the resolution is 0.2μm in the horizontal X-Y direction. The microscope objective has the magnification of 40, NA of 0.65, and the lateral resolution of 0.52μm. The repeatable measurement error for the surface profile is less than 5%, and the measurement error for the surface shape and dimension is less than 2%.(3) A three-dimensional measurement stage with a high precision and a large displacement range is developed for the surface profile measurement system. In this stage, two-grade positioning accomplished by vertical scanning displacement function mechanism with the common standard measuring system and driven by servo-motor and piezo-electronic transducer respectively, which meets the requirements to measure large range surface according to the zero-order interference fringe tracing measurement method. An invention patent for this mechanism has applied (Patent application number: 200510018618.1). The horizontal displacement mechanisms with the common baseplane are driven by servo-motor and are controlled by diffraction grating standard measuring system. The displacement performance of three-dimensional measurement stage is calibrated by double-frequency laser interferometry. Its displacement range is 8mm, and displacement resolution is 0.002μm in the vertical direction; its displacement range is 40mm×40mm and the resolution is 0.2μm in the horizontal X-Y direction; the plane error is less than 2μm.(4) The white-light interference extracting algorithms and the influences to their extracting precision are analyzed, and a linearly envelope fitting algorithm is proposed. The phenomenon of double fringe caused by the surface covered with transparent film is analyzed, and the fringe separating algorithms are developed according to its characteristic of correlogram.(5) A measurement and evaluation software system is developed for the profile and shape measurement of three-dimensional surface using vertical scanning measurement method and zero-order interference fringe tracing method. This software system also includes data pre-processing and parameter evaluation function, and the measurement and evaluation results are provided.