Diffraction Order Enhanced Multi-Diffraction Order Utilization Overlay Error Metrology Method

Abstract Overlay error in lithography refers to the positional deviation between the patterns of two exposures and is one of the key indicators for evaluating lithography quality. Traditional overlay metrology methods are limited by the intensity of higher-order diffraction energy and mostly rely on ±1st-order diffraction light for measurements, making them susceptible to variations in the mark structure. This project proposes a diffraction-order-enhanced overlay error metrology method utilizing multiple diffraction orders. First, the scalar diffraction theory is used to derive the method for enhancing grating diffraction efficiency and explain the advantages of higher diffraction orders. Then, the Rigorous Coupled-Wave Analysis (RCWA) algorithm is used to simulate the optimized overlay (OVL) mark, demonstrating the effectiveness of the design. This method can compensate for the issue of certain wavelengths being difficult to use due to large measurement errors, achieving sub-nanometer precision while reducing sensitivity to polarization direction. By using the method of shared multiple diffraction orders, it is possible to corrected situations that are unavailable when only using ±1st order, providing more recipe options for multi-wavelength Diffraction-Based Overlay (DBO) technology. Our study presents an ingenious approach to mark optimization, enabling practitioners to make more flexible choices when dealing with different product batches, thereby enhancing the accuracy and robustness of OVL measurement.