We have developed a novel technique for performing simple phase-sensitive optical measurements in a sub-micrometer area. We presently use this technique to measure film stacks commonly found in the semiconductor industry. This article explains the theory behind this technique and presents several examples demonstrating the capabilities of the system.
The semiconductor industry is moving towards thinner dielectric films (less than 100 angstroms), more complex film structures (oxide on polysilicon on oxide on silicon) and smaller lateral geometries (less than 1 micron). The attendant measurement requirements demand more than incremental improvement of existing methods. In this paper, a novel laser-based dielectric film measurement system is described that meets these requirements by bridging the gap between spectrophotometer speed and ellipsometer precision while measuring with a 0.9 micron focused laser spot. The operating principles of a new technique which we call Beam Profile Reflectometry are discussed and data are presented for a number of different single- and multi-layer film structures relevant to microelectronics processing.
Measurements of ultra-thin films (<100A) and small geometries (< 1/mm) of IC product wafers require more than simply a smaller measurement spot size. An optical artifact has been discovered when using spectrophotometers to measure ultra-thin films near feature edges. A model of this effect will be presented. This artifact is a subtle effect that produces measurable reflectivity errors tens of microns from a feature edge. While this error is small, it is not negligible for film thickness measurements below 400A. Experiments have been performed on typical spectrophotometers and data from these experiments will be presented. These data will be compared to a newly developed laser-based dielectric film thickness measurement system that significantly reduces this edge effect.