ABSTRACT
This is the most common requirement in semiconductor fabrication lines. X-ray reflectivity (XRR) is the most versatile x-ray method for thickness measurement, since it does not depend upon the crystal structure or state of aggregation of the material, only upon the electron density variation with depth. As we have seen, we may use XRR to measure thicknesses of almost any films below 500 to 1000 nm in thickness. But there are always limits, either from the nature of the material or from the requirements of factory metrology, e.g., requiring a very small spot. In this (and the remaining chapters in Part 1) we address the questions:
• Can we use x-rays to measure this parameter in our wafers? • What are the limits of measurement?
