Metrology tool fleet management: Applying FMP tool matching and monitoring concepts to an overlay fleet

Overlay tool matching and accuracy issues are quickly reaching a comparable complexity to that of critical dimensional metrology. While both issues warrant serious investigation, this paper deals with the matching issues associated with overlay tools. Overlay tools need to run and measure as if they are a single tool they need to act as one. In this paper a matching methodology is used to assess a set of overlay tools in a multiple of overlay applications. The methodology proposed in a prior(2) SPIE paper is applied here to a fleet of two generations of overlay tools to detect measurement problems not seen with convention Statistical Process Control techniques. Four studies were used to examine the benefits of this matching methodology for this fleet of overlay tools. The first study was a matching assessment study. The second study was a hardware comparison between generations of tools. The third study was a measurement strategy comparison. The final study was a long term matching exercise where one example of a traditional long term monitoring strategy was compared to a new long term monitoring strategy. It is shown that this new tool matching method can be effectively applied to overlay metrology.