In scanning systems for surface profile measurement, e.g., stylus systems, the profile of a surface is generally determined by measuring the distance of the surface relative to a reference plane. This can be either a plane defined by a moving stage under a rigid stylus or a plane defined by a moving stylus if a fixed stage is used. In both cases, the measurement precision is limited by the straightness of a linear motion. This paper presents a new interferometric profile measurement technique based on using a rigid differential interferometer probing the test object which is moved by a stage. Information on the surface profile is obtained by scanning the surface with two laser spots simultaneously and measuring the optical path difference between the reflected light beams. This makes the profile measurement largely insensitive to flatness errors of the mechanical stage and enables extremely precise measurements. Data processing is done digitally using a storage scope and a microprocessor. The suitability of this method for measuring the profiles of magnetic sliders and SIMS sputter craters has been investigated. The experimental work includes long- and short-term repeatability tests and an extensive investigation of the temperature dependent behavior of the measuring instrument.
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