Thin-film thickness measurements with thermal waves

We have developed a method for measuring the thickness of thin films that is nondestructive, noncontact and that can make measurements with 2-μm spatial resolution (i.e., 2-μm spot size) on both optically opaque as well as optically transparent films. With this method, which is based on the use of high-frequency thermal waves, thicknesses of Al and SiO2 films on Si substrates have been measured in the 500–25 000-Å range.