Experimental Research On Separation Of Immersion Flow In Immersion Lithography

A thin liquid film will formed between two micro-interval body, if there is liquid in the gap, and the thin liquid film shows great adhesive attraction. Especially, when the size of the component or system is less than 1mm, the force about surface will be greater than the volume force, which is called scale effect. Similarly, the scale effect stands out in immersion flow of immersion lithography because of its sub-millimeter size. The immersion liquid forms liquid bridge between the last objective lens and silicon wafer, called immersion flow. The immersion flow is about 0.1mm when work, so it will generate extreme adhesive force when separating the liquid bridge because of scale effect. The objective lens and wafer deform and even the etching structure ruins with the exceptional adhesive force. This paper is focused on the effect on silicon wafer blow when quick separating the liquid bridge, including four parts blow:1) Theoretical model of the capillary force of liquid bridge was built with theoretical analysis in immersion flow. The simplified model was got by analyzing the immersion flow. Then the capillary forces were conducted based on capillary effect and Laplace-Young function, including the meniscus force Fm about surface tension and the viscous force Fv related to liquid curvature. At last, numerical simulation was done to shows the change of capillary force when separating.2) Design and build the flow observation experiment system to simulate separation of immersion flow in immersion lithography. The design requirement was got by analyzing the immersion flow. Then a detailed explanation about the system was shown, including the motion control system、 the measurement scheme for force and displacement and the integrated control software.3) The separation experiments were conducted on the flow observation experiment system. Separate the liquid bridge with various velocities and get the data from the force and displacement sensors. All the data were processed and the final conclusion about the tendency of capillary force with separate velocity was get.4) A reference analysis in separation of immersion flow was made to give advice on separation velocity in immersion lithography, based on the pressure tendency with separate velocity which is transformed from the experimental conclusion. Analysis in separation of immersion flow has been made from the results of experiment, which provided consulting opinions and testing data on safety separation velocity, with the mechanics information of the single crystal silicon wafer and technical index in design of immersion lithography. Besides, some possible superior separate strategies were preliminarily proposed and stated.