Studies on X-ray reflectivity technique and application in thickness measurements in wafer fabrication

In advanced ULSI technologies, 90nm and beyond, ultra-thin materials play a key role in device performance and its reliability. Conventional optical techniques, which rely on measuring the complex refractive index, do not provide accurate estimate of film thickness for stacks of two or more layers. X-ray reflectivity (XRR) is a reliable method of measuring thickness of composite film stack of total thickness up to 1 μm, irrespective of whether it is crystalline or amorphous and, conducting or nonconducting films. In this paper, the results of correlation studies between XRR and TEM are presented. The emphasis is on thickness measurements of different types of films, which are 100 -15k thick. It is shown that a good agreement is obtained between the two techniques for film thickness less than l000.