Graphene Target Electromagnetic Sensor for Nanometer Position Measurement

The patent applies parameter changes by utilizing the frequency-dependent skin depth effect. By operating at high frequencies (typically above 1 MHz), the skin depth is reduced to a few micrometers, confining eddy currents to the target surface layer. This parameter change in operating frequency directly improves measurement precision while maintaining reliability by making the measurement less sensitive to environmental variations.

The patent segments the measurement system into distinct functional components: the electromagnetic sensor, the target structure (conductive layer on substrate), and the evaluation unit. This segmentation allows independent optimization of each component - the conductive target layer is designed with specific thickness and conductivity to control eddy current distribution, while the sensor is optimized for high-frequency operation, collectively improving both precision and reliability.

The patent applies partial action by using high frequencies only during the actual measurement phase, rather than continuously. The electromagnetic sensor operates at high frequency briefly to acquire position data, then returns to a lower power state. This partial use of high energy consumption achieves the required measurement accuracy while minimizing overall energy usage in the lithographic apparatus.

The system dynamically adjusts the operating frequency parameter based on measurement requirements. High frequencies are used when precise position measurement is needed, while lower frequencies or idle states are used otherwise. This parameter change strategy optimizes the trade-off between measurement accuracy and energy consumption in the lithographic process.