26 June 2003 Preliminary microfluidic simulations for immersion lithography
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The premise behind immersion lithography is to improve the resolution for optical lithography technology by increasing the index of refraction in the space between the final projection lens of an exposure system and the device wafer. This is accomplished through the insertion of a high index liquid in place of the low index air that currently fills the gap. The fluid management system must reliably fill the lens-wafer gap with liquid, maintain the fill under the lens throughout the entire wafer exposure process, and ensure that no bubbles are entrained during filling or scanning. This paper presents a preliminary analysis of the fluid flow characteristics of a liquid between the lens and the wafer in immersion lithography. The objective of this feasibility study was to identify liquid candidates that meet both optical and specific fluid mechanical requirements. The mechanics of the filling process was analyzed to simplify the problem and identify those fluid properties and system parameters that affect the process. Two-dimensional computational fluid dynamics (CFD) models of the fluid between the lens and the wafer were developed for simulating the process. The CFD simulations were used to investigate two methods of liquid deposition. In the first, a liquid is dispensed onto the wafer as a “puddle” and then the wafer and liquid move under the lens. This is referred to as passive filling. The second method involves the use of liquid jets in close proximity to the edge of the lens and is referred to as active filling. Numerical simulations of passive filling included a parametric study of the key dimensionless group influencing the filling process and an investigation of the effects of the fluid/wafer and fluid/lens contact angles and wafer direction. The model results are compared with experimental measurements. For active filling, preliminary simulation results characterized the influence of the jets on fluid flow.
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Alexander C. Wei, Alexander C. Wei, Greg F. Nellis, Greg F. Nellis, Amr Y. Abdo, Amr Y. Abdo, Roxann L. Engelstad, Roxann L. Engelstad, Cheng-Fu Chen, Cheng-Fu Chen, Michael Switkes, Michael Switkes, Mordechai Rothschild, Mordechai Rothschild, } "Preliminary microfluidic simulations for immersion lithography", Proc. SPIE 5040, Optical Microlithography XVI, (26 June 2003); doi: 10.1117/12.497495; https://doi.org/10.1117/12.497495

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