This paper describes an instrument and method for high-resolution characterization of lens components and assemblies for DUV retardance performance at various stages of manufacture. The instrument is a bespoke rotating analyzer Stokes polarimeter designed for DUV wavelengths (e.g. 193 nm, 213 nm, 266 nm, etc.). Using a laser source, the polarimeter delivers a small diameter beam with a characterized polarization state to the optical lens element or objective assembly at the “as-used” design angles of incidence (AOI) to characterize the retardance through the lens or objective at an arbitrary location. The polarization characteristics are usually described by the retardance at specific locations on a component or sub-assembly that can be used to characterize components during development and manufacturing or optimize performance of an assembly.
This paper highlights two examples of the use of full surface metrology to allow for functional tolerancing of components in the areas of EUV lithography (reticle characterization) and DUV precision lens manufacturing (lens holder metrology). For both examples, the measurement of the full surface is a key enabler to understanding the critical characteristics to control and tolerance for functionality or performance. Interferometric techniques are used to provide high resolution and accurate measurements for both examples. Subsequently, this data can be used to identify the surface characteristics that contribute to the end functionality and provide a means for deterministic correction or compensation.
Adhesive mounting of lenses can allow flexible position control of each optical element, low stress, low part count, and precise alignment of lens assemblies in addition to high durability with respect to thermal expansion, shock, and vibration. Historic implementations of this method carried risk of UV degradation, photo contamination, long term stability, and long assembly cycle times. Others have developed non-adhesive friction/contact approaches to mount lenses but with significant compromises in durability and product cost. These two methods are compared and an optimal approach to achieve high lens mounting durability, low cycle time and negligible photo-contamination is demonstrated. Durability of this adhesive mounting solution will be established with examples including shock and vibration, mechanical stress decoupling factors, and optical stability over a wide range of shipping temperatures.
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