Verification metrology system by using inline reference metrology

For robustness improvement of inline metrology tools, we propose an inline reference metrology system, named verification metrology system (VMS). This system combines inline metrology and nondestructive reference metrology tools. VMS can detect the false alarm error and the nondetectable error caused by measurement robustness decay of inline metrology tools. Grazing-incidence small-angle x-ray scattering (GI-SAXS) was selected as the inline reference metrology tool. GI-SAXS has high robustness capability for under-layer structural changes. VMS with scatterometry and GI-SAXS was evaluated for measurement robustness. The potential to detect metrology system errors was confirmed using VMS. Cost reduction effect of VMS was estimated for the false alarm case. Total cost is obtained as a sum of the false alarm losses and the metrology costs. VMS is effective for total cost reduction with low sampling. Also, it is important that the sampling frequency of reference metrology is optimized based on process qualities.