New directions in process control

摘要

Abstract: The Orbot wafer inspection system is designed to implement an automatic defect detection strategy. It employs the unique Perspective Darkfield Imaging (PDI$+TM$/) technology to produce simultaneously four different high resolution images of the scanned wafer area. In PDI images defects appear in multiple perspectives as isolated, bright `stars' on a mostly dark background. This allows high detection sensitivity of 0.1 $mu@m defects on advanced complex, dense wafers (0.35 $mu@m design rule) with topography. In this paper we demonstrate the advantages of PDI as implemented in the Orbot WF-710. The tool used to emphasize and exploit the very high signal to noise ratio for small defects is the PDI histogram. It is shown that on these histograms submicron defects as small as 0.15 $mu@m are significantly separated from the normal wafer pixel population and so can be easily detected. Furthermore PDI histograms can be considered as being the `finger print' of a particular product and layer. The natural extension of this is that PDI histograms can be used to monitor process anomalies not reflected by defects, and so trace process instabilities. A brief description of PDI technology is provided. PDI histograms and the experimental results are set out. !1