Wavefront Aberration Measurement Technique Based on Principal Component Analysis of Aerial Image for Lithographic Projection Lens

Objective Lithography is a key technique in the manufacture of very large scale integrated circuits. The imaging quality of the lithographic projection lens directly affects the critical dimensions of integrated circuits. The wavefront aberration of the projection lens reduces lithographic imaging quality and affects the lithographic resolution. Therefore, measuring the wavefront aberration of the lithographic projection lens is crucial for improving lithographic imaging quality. The wavefront aberration measurement technique based on principal component analysis of aerial images for the lithographic projection lens is characterized by fast process and in- situ measurement. However, this technique is affected by the illumination condition, scanning range, sensor, and other factors in practical engineering applications. It also faces a number of problems, such as image shift and noise. This study investigates the above engineering issues, proposes engineering application suggestions, and verifies the effectiveness of the proposed method by simulation and experiments. Methods The commercial lithographic simulation software Santaurus lithography of Synopsys is employed for simulation research. The influences of different factors on the performance of wavefront aberration measurement are studied. An actual sensor structure is adopted to examine the influences of sensor parameters on the accuracy of wavefront aberration measurement, and the validity of the sensor model is verified by aerial image reconstruction experiments. The influence of the centering error on the accuracy of wavefront aberration measurement is analyzed. Two centering methods are compared to determine their respective applicability. The effectiveness of the centering method is verified by aerial image reconstruction experiments and two sensor experiments. The effects of different denoising methods on aerial images are studied, and an average denoising method tailored to the unique noise type of aerial images is proposed. Results and discussions The simulation and experimental results show that illumination and the scanning range have a great influence on the accuracy of wavefront aberration measurement. The measurement accuracy is high when the partial coherence parameter of illumination is in the range of 0. 5-0. 8 and the sampling length of the aerial image along the focus (F) direction is above 5000 nm. In terms of centering, the centering accuracy of the six-term model is higher in the X direction. In the F direction, the three-term model is suitable for centering the 0 degrees aerial image while the six-term model is applicable for centering the 90 degrees aerial image. Regarding denoising, the average denoising method proposed in this study can significantly improve the accuracy of wavefront aberration measurement and can be applied in engineering. The simulation results prove that the proposed technique can be used to correct the short- term aberration drift of the scanner. Conclusions This study systematically investigates the wavefront aberration measurement technique based on principal component analysis of aerial images for the lithographic projection lens. Specifically, it analyzes the engineering problems of this technique and further presents some application suggestions. The simulation and experimental results show that the measurement accuracy of this technique can be effectively improved by selecting appropriate illumination conditions, scanning range, sensor model, and centering method. The proposed denoising method can effectively remove the noise in the aerial image and improve the accuracy of wavefront aberration measurement. The simulation results prove that the proposed technique can be used to correct the short- term aberration drift of the scanner.