| 摘要 |
A method and apparatus wherein the height over the complete surface of interest on a wafer/material is scanned and mapped, using either a central or non-central focus system. The type of data gathered is similar to that which is normally acquired in operation of the particular focusing system indicative of the wafer/material surface height. The difference is that according to the present invention, a much larger number of data points are sampled and then processed in a novel manner to provide improved focus information. These data are stored and used to calculate corrections in both the vertical position/height and tilt of the material/wafer for each exposure field, such as the areas (34) in FIGS. 5b and 6b. The invention sorts out selected height data indicating periodic variations in surface height. Such data are normally not indicative of true wafer surface height variations, but instead are the result of periodic variations in wafer material composition caused by underlying structure relating to the particular circuitry. These periodic variations are distinguished from non-periodic variations, and are subtracted out of the total height measurement data to yield corrected surface height data. The present invention uses the corrected surface height data to calculate an optimum focus height for a given exposure area such as 34.
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