High-precision film thickness determination using a laser-based ultrasonic technique

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Abstract
A noncontact and nondestructive laser-based acoustic technique called impulsive stimulated thermal scattering (ISTS) is used to measure thicknesses of metal films including Cu, Ta, W, Al, Ti, and others in single-layer and multilayer assemblies on silicon substrates. Other opaque film materials and substrates have also been examined. Thicknesses are determined with a repeatability of a few angstroms with data acquisition times of about 1 s. ISTS and conventional measurements (scanning electron microscopy, profilometry, and four-point electrical sheet resistance) are made on the same samples and the results are found to compare favorably.