OPC model space approach to in-line process monitoring structures

摘要

With shrinking technology nodes and increasing geometries criticity, it has become more and more difficult to conceive fast and accurate in-line check to insure process quality for each lithography level. Time and costs limit metrology options.A commonly accepted solution consists in some CD measurement on high contrast structure for each critical level. However, the RET complexity of current layouts makes this solution no longer fully reliable and allows non-conform materials to pass through the check. The idea behind this article (patent pending) is to add a second verification by creating a set of small structures layouted to cover specific coordinates in the model parameters space. Extrapolated model parameters allow to layout geometries encircling the OPC space region occupied by the production device. Those structures shall bridge or pinch for litho or process deviations before any detectable impact on the most sensitive shapes present in the product. Total size of few square microns is required to stay within a single SEM picture. The use of image processing based on pattern recognition on SEM pictures to assess their sensitivity to process variations permits a fast analysis. As a matter of fact, this approach will allow getting reliability by watching the whole model space and economic compatibility as the procedure is fast and cost-effective.