The Flow Field Detection And Structure Optimization For Immersion Lithography

Immersion lithography machine is the key equipment for VLSI manufacturing, and it is the only technology that has been used for the IC production line about 45-nm and below. From the traditional lithography to the immersion lithography, the immersion fluid transmission and control system is the key technology and the immersion unit is one of the most important components of the system, which is used between the last project lens and the wafer. The high refractive index liquid which is filled between the final project lens and wafer has been used to improve the optical resolution of the immersion lithography. As part of the optical system, its main function is to provide and recover the immersion liquid. But the resist leaching and liquid heating can occur during immersion exposure process, so the immersion liquid will be polluted and the uniformity of flow field will be undermined. At the same time, it may cause the image quality defect. So, the liquid renovation must be considered in the immersion lithography because of its ability of pollution elimination and heat dispersion. At present, the method of rapid updating immersion liquid is used to bring the pollutants and the heat during the exposure process. If the flow rate of the immersion liquid is faster, the update velocity and the efficiency, will be improved, and the uniformity of fluid will be better. However, to improve the update rate of the liquid immersion by increasing the pressure of the immersion liquid method, it may increase the deformation of the project lens. In addition, the velocity fluctuation of the exposure area will also affect the efficiency of the immersion liquid update, because local lower flow may lead to pollution and heat retention. Therefore, the optimization for the immersion unit structure and improve the liquid update velocity and efficiency, are one of the key issues must be considered during the design of immersion lithography machine.In this paper, the immersion unit and immersion flow field was studied, and the main contents are briefly stated as the followings:Firstly, the CFD models of the immersion flow field with different injection shapes and the height of the gap flow have been established to study the influences on the flow state.Secondly, the method of the immersion fluid flow field velocity detection was studied. The light sheet of the Particle Image Velocity (PIV) has been designed to detect the velocity distribution, and the tracer particle method based on the high speed camera was designed. At the same time, the formula was educed for calculating the following behaviors of the tracer in the flow and the particle image processing algorithms based on fast Fourier transform were studied.Finally, the visualization system was integrated with high-speed camera and the data acquisition instrument, and the gap flow field velocity field distributions were obtained from the digital image processing software (MatPIV). The numerical simulation results were verified by the experimental results, and the optimized parameters of injection and recovery ports and the structure of the immersion unit have been proposed. Finally, the theoretical mathematical model of the exposure area was established to verify the accuracy of the experimental results.