Applications of laser-generated surface acoustic waves for copper film process monitoring in integrated circuit industry (abstract)

Abstract

We describe applications of a compact commercial instrument for laser generation and detection of surface acoustic waves (SAWs) to problems in metal film process control for the integrated circuit (IC) industry. [M. Gostein, M. Banet, M. Joffe, A. A. Maznev, R. Sacco, J. A. Rogers, and K. A. Nelson, in Handbook of Silicon Semiconductor Metrology, edited by A. C. Diebold (Marcel Dekker, New York, 2001)] The IC industry is undergoing dramatic changes with the continued drive to reduce feature size and increase circuit speed. One of the most important of these changes is the industry-wide move to replace circuit interconnect processes based on aluminum metallization with copper-based processes. The unique process challenges of copper metallization, coupled with the increasing cost of IC manufacturing in general, have resulted in an increased need for metal film thickness measurement for process control. Laser-generated and detected surface acoustic waves provide an ideal method for nondestructively measuring film thickness on product wafers as they move through an IC factory. A patented version of the technique has been incorporated into a commercial high-throughput measurement station. The measurement station analyzes specialized test structures in the scribe lines in between IC chips on a product wafer. Here, we describe application of the technique to all stages of the copper metallization process, including measurement of seed-layer copper and its associated underlying barrier metals, measurement of electroplated copper deposited atop the seed layer, and measurement of remaining copper film thickness following a chemical–mechanical polishing step. We highlight special capabilities to measure test arrays of submicron metal lines that closely resemble actual circuit elements. In addition, we discuss characterization of the elastic properties of typical and emerging thin film materials used in the semiconductor industry, which is a necessary step in setting up the SAW instrument for measurements on IC film stacks.