| The dissertation dwells on immersion control system of immersion lithography machine. The flow mechanism of immersion liquid and its effects on lens element are systematically studied. Compared to the traditional lithography machines, an immersion liquid inserted into the space between the final lens element and wafer is the key characteristic of immersion lithography machine. By analyzing the flow mechanism of immersion liquid, some valuable results are obtained, including the optimization designs of immersion control system, the methods for stably uniform immersion flow, and the reliable connection between immersion apparatus and lens element.Firstly, a two-dimensional mathematical model for immersion flow is developed according to the characteristics of immersion liquid flow. Some quantitative results about the influence of wafer step-and-scan on immersion liquid are given, and the results are verified by the simulation with unsteady state. Secondly, during a typical period given by the two-dimensional mathematical model, the immersion liquid mechanism of three-dimensional structure is studied, especially the liquid renovation. The unsteady numerical model of three-dimensional immersion flow is developed to study the liquid renovation process and efficiency of flow, and the constructional designs and requirements for high renovation efficiency are proposed. Meanwhile, a visual detection system for immersion liquid flow is established to investigate the flow characteristics of immersion liquid, and the design requirements for high renovation efficiency are verified by experimental results based on the technology of Particle Image Velocimetry. Finally, the stress generated by immersion liquid flow and its effect on lens element are investigated. The influences of injection parameters, wafer scanning and material property on lens birefringence and distortion are studied, and the corresponding methods are proposed to reduce the negative effects.The main contents of this dissertation are briefly stated as the followings:1. Research on the flow mechanism of immersion liquid during exposure. According to the characteristics of immersion liquid flow, the two-dimensional mathematical model is constructed to study the effect of wafer motion, liquid viscosity and the height of lens-to-wafer on immersion flow. For the case of 193nm immersion lithography with water, the methods for high efficiency of liquid renovation are investigated based on the study of the relation between wafer motion and flow status, and the results are verified by the numerical simulation with unsteady state. 2. Research on the numerical simulation about the renovation efficiency of immersion liquid. Considering the influence of wafer scanning and injection structure, the mechanism of three-dimensionally unsteady model of immersion liquid flow is studied. On the basis of immersion flow analysis, some important factors of the liquid renovation efficiency are investigated, including the mean velocity and renovating cycle time of contamination in exposure area. The effect of the wafer motion on immersion liquid renovation is obtained, and the optimized designs and constructional requirements for high renovation efficiency under typical lithography process are proposed.3. Experiment research on the immersion liquid renovation. According to the characteristics of immersion flow, a flow detection scheme considering tracer particles with specified dimensions is developed. Based on this scheme, a transmission-and-control system is built to control the pressure and flow rate of immersion liquid, and a three-dimensional visual detection system is established, including an optical table, the motion platform control system, a high-speed video camera and so on. After the cross-correlation processing between two pictures of tracer particles captured by the high-speed video camera, the characteristics of immersion flow are obtained. The results show that the predictions of the simulated model are in accordance with experimental one.4. Research on the stress generated by immersion flow and its effect on lens element. The effects of injection parameters, wafer scanning and material property on lens response are analyzed, and the corresponding methods are proposed to reduce the negative effects. For the lens birefringence induced by shear stress, the mathematical model and three-dimensional computational fluid dynamics model are developed to predict it, and the results show that the height of lens-to-wafer is the key factor which influences birefringence. For the lens distortion generated by normal stress, the maximum lens distortion occurs when the directions of injection velocity and wafer scanning are opposite. In addition, the lens distortion is affected by the properties of lens and polymer used to mount the lens and the parameters of immersion liquid flow. It can be concluded that increasing lens thickness and the elastic modulus of polymer, or reducing the injection velocity are the effective ways to control lens distortion.
|
PDF Full Text Request