Study On The Liquid Supply And Sealing Of Immersion Unit For Immersion Lithography

Immersion lithography seeks to extend the resolution of optical lithography by filling the gap between the final optical element and the wafer with a liquid characterized by a high index of refraction. During the scanning and exposure process, immersion liquid is injected into the space between wafer and lens with certain inlet pressure and angle. Because the liquid will act as a lens component during the lithographic process, it must maintain high uniform optical quality. One source of optical degradation may be due to liquid contamination by chemical products or impurities during exposure period. Immersion liquid renovation is probably the best solution. The semiconductor industry demands high throughput, leading to relatively large wafer scanning velocities and accelerations. For higher scanning velocities, an issue that has been identified is the deposition of the immersion liquid while confining a relatively small amount of liquid to the under-lens region. Liquid loss occurs at the receding contact line that forms when a substrate is withdrawn from a liquid, which potentially leads to defects on printed patterns.In this dissertation, the liquid dispensing structure and noncontact sealing mechanism of the immersion unit for immersion lithography is systematically investigated, focusing on the mechanism designing, processing, testing, numerical simulation and performance optimization. Also, a pipeline supplying system is designed and optimized, compatible with the immersion unit, preparing for the industrial implementation of immersion lithography manufacturing equipment. Firstly, a numerical model is built to simulate the liquid dispense-flow-collection procedure, based on which, the flow state and the renovating cycle are studied. Secondly, a noncontact sealing mechanism is designed, upon which, a new liquid injection and collection model with analytic solutions is presented and compared with experimental results. Finally, according to the principles obtained, immersion unit prototype and its revised editions are designed and manufactured. After performance testing and optimization, the dynamic sealing ability for immersion unit is proved.The main contents of this dissertation are briefly stated as the followings:Study on liquid dispensing structure and flow state within under-lens region. Three-dimensional computational fluid dynamics models are built to simulate the liquid dispense-flow-collection procedure, featuring flow field stream patterns, lens normal and shear pressure, considering fluid injecting velocity, dispense ports quantity, and direction angles. Compared with experimental results, refreshing cycle time and velocity distribution are investigated, presenting theoretical support for system optimization and compatibilityStudy on dynamic sealing for the gap flow field boundary. A noncontact sealing method is studied, aiming at avoiding the liquid leaking on wafer motion and the liquid fulfillment beneath the lens. As new liquid injection and collection model with analytic solutions is presented and compared with experimental results, in which the critical velocity for liquid loss is mainly a function of the vacuum degree, the injection flow rate, the properties of the immersion liquid. This correlation allows the critical velocity to be predicted with a given gap height between wafer and lens using only a measurement of the injection speed and knowledge of the fluid properties. This correlation represents a useful tool that can serve to approximately guide the development of fluid control for immersion systems as well as to evaluate alternative immersion fluid candidates to minimize liquid deposition while maximizing throughput.Study on immersion unit performance testing and pipeline supplying system optimization. Steady-state operating performance for immersion unit prototype is carried out to obtain the designing principles of low-pressure noncontact sealing element. A pipeline supplying system is exploratory designed and built, compatible with the input interface of immersion unit.