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A unique interferometer which can automatically measure the thickness of a film with a simultaneous reference level control is described. This is achieved by using a grating to split a laser beam into various orders. The interference between the diffracted components of the 0 and -1 orders is used to control the reference level and the interference between the diffracted components of there two orders gives a measurement of the film thickness. Theoretical calculations show a very good linearity and high precision. Aluminium films with thicknesses ranging from 700 to 3000 Å were measured with a precision of ±200 Å. Remedies for an improvement of the precision are discussed.
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Chitnis et al. (1986) studied this question.
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