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Abstract

A device for measuring changes in the relative height or depth of microscopic surface features of a sample that allows crater depth measurements to be made while depth profile analyses are proceeding is provided. The depth monitor comprises a dual beam optical interferometer, that is preferably adapted for use with analytical instruments, such as SIMS, XPS, ESCA, and AES instruments. The monitor provides substantially accurate depth measurements and a continuous readout for monitoring the sputter rate of an ion beam etch in real time, for correcting for any variations in the sputter rate as craters are formed in the sample. The invention also allows integration of real time depth measurements into data collecting software to eliminate the assumption that the material comprising the sample has the same sputter rate as a reference material. The in situ depth measurements provided by the invention are more accurate than prior art crater depth analysis and reduce processing times. The dual beam design of the monitor assures that fluctuations in the total path length of the beams, do not affect depth measurement of craters in the sample. Vibrations do not affect depth measurements, since the monitor uses common mode rejection, with the beams sharing a common optical path and any increase or decrease in total path length is common to both beams. Thus, changes in path length due to vibrations does not affect any length differentiation between the two beams and depth measurements are not affected.

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First Claim