Feature: Sensors
Figure 9: Four capacitive sensors measure the tilt of the lens carrier
Figure 8: Four confocal sensors detect the tilt of the lens
the position of the wafer stage or wafer platform; see Figure 10. Here, they measure the XYZ movements of the stage, where extremely high accelerations occur. T e high-precision optical interferometers achieve sub-nanometer resolution and ensure that the wafer is optimally positioned for exposure. Vacuum-compatible measuring heads and insensitivity to strong magnetic fi elds enable the high-precision sensors to be used in demanding environments. Capacitive displacement sensors are
used for fi ne positioning on the wafer stage. T ey measure its position at various points, which is necessary for fi ne alignment. Due to their triaxial design, the sensors are insensitive to electromagnetic fi elds and achieve resolution in the nanometer range. In addition, they achieve extremely high long-term stability. T ese non-contact sensors are suitable for both vacuum and UHV.
Quality control For quality control, sensors are used in various areas, for example, for testing coating thickness and for monitoring defl ection, as well as separation; see Figure 11. In addition to high precision,
Figure 10: High-resolution measurements under extreme conditions – UHV, magnetic fi elds and high accelerations are among the requirements for displacement sensors
Figure 11: Confocal sensors are used for numerous measurement tasks in quality control
www.electronicsworld.co.uk February 2023 37
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