Determining the thickness of very thin films of TiW

In this work we show how to use ellipsometry to measure the thickness of TiW when the film thickness is ≤250 Å. Because the stoichiometry and microstructure of TiW depends strongly on the deposition parameters, the optical constants of TiW deposited in two different systems will not in general be the same. Accordingly, the optical constants of the film material are often not known. We show that the method is robust if a reasonable approximation to the optical constants is available, and we show how to obtain such an approximation. Auger electron spectroscopy is used to substantiate the conclusions.