A study of high-accuracy stand-alone wafer metrology tool for high-productivity of exposure apparatus

As wafer process complexity increases, demand for precise overlay accuracy including measurement of wafer deformation in advanced photolithography processes has increased. In general, wafer deformation can be measured with high accuracy by obtaining wafer alignment position information at multiple sites on a wafer. However, when a photolithography exposure system is used to perform the necessary wafer alignment measurements to improve overlay accuracy, the productivity of the exposure system will be drastically reduced due to the increase in total alignment measurement time. Canon developed the stand-alone wafer metrology tool (MS-001) as a solution to improve the overlay accuracy and the productivity of semiconductor manufacturing. MS-001 is used to perform Feed Forward Alignment (FFA) correction in which the wafer deformation is measured before the wafer is transferred to the exposure system and the data is sent to the exposure system. This reduces the number of alignment measurements required in the exposure system, making it possible to combine high productivity with high overlay accuracy. MS-001 also features improved selectivity of measurement marks by image detection and enhanced selectivity of measurement wavelengths by a new alignment light source unit (Hi-ALS). These allow MS-001 to select the optimal measurement mark and wavelength according to the wafer process. In addition, it has become possible to monitor process changes as well as alignment. In this paper, we demonstrated the performance of MS-001 and overlay accuracy improvement by FFA correction using DRAM product wafers. And we also verified the feasibility of a wafer monitor function using MS-001 to detect wafer deformation occurring in the manufacturing process. These results show that MS-001 can solve the challenges posed by complex processes. These results indicate that MS-001 has the potential to solve challenges caused by complex processes.