<title>Elimination of monitor wafers in metal film process control</title>

Abstract

Typically metal film processes have been controlled by using monitor wafers. A representative film is deposited on the monitor wafer (witness sample) then the sheet resistance uniformity is measured with a four- point probe. It is assumed that the films on subsequently processed product wafers will have the same characteristics as the film on the monitor. Monitor wafer costs are becoming prohibitive as the industry transitions to 200 millimeter wafers and beyond. Also monitor wafer preparation takes valuable time which could be used for production. Finally monitor wafers also take up valuable space in processing equipment, which could be occupied by product wafers, reducing the overall fab capacity. A mutual inductance technique is described which can be used to measure the sheet resistance of blanket metal films directly on product wafers. This not only reduces the need for sheet resistance monitor wafers and adds system capacity but also gives valuable insight into film properties on the actual product wafer. Data will be presented showing the incorporation of this technique into a 150 millimeter production facility.