Reflective Optical Element with Localized Multilayer Period Thickness
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In ultraviolet to extreme ultraviolet lithography, reflective optical elements with conventional multilayer systems face challenges in maintaining high reflectivity and imaging quality due to varying incident angles and bandwidths, leading to reduced throughput and imaging defects.
Innovation Solution
The reflective optical element features a multilayer system with alternating materials of different refractive indices, where portions with one period thickness are arranged at locations with narrow incident angle bandwidths and portions with multiple period thicknesses are arranged at locations with broader bandwidths, adapting to the incident angle distribution across the surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional multilayer system with uniform period thickness is used, then the manufacturing process is simple, but the reflectivity decreases and imaging quality deteriorates when incident angle bandwidth varies widely
Solution Approach 1:
The patent applies local quality by dividing the reflective surface into multiple zones, each with different period thicknesses tailored to the local incident angle bandwidth characteristics. Areas with narrow incident angle bandwidths use one period thickness, while areas with broader bandwidths use different period thicknesses, optimizing reflectivity for each local region.
Solution Approach 2:
The multilayer system is segmented into multiple portions across the reflective surface, where each portion has independently optimized period thickness. This segmentation allows the system to handle varying incident angle bandwidths in different regions, improving overall reflectivity and imaging quality.
2Measurement precision
If the aperture is increased to image finer structures, then the resolution improves, but the variation in incident angle bandwidth increases leading to reduced throughput
Solution Approach 1:
By implementing local quality optimization, the patent ensures that each region of the optical element is tailored to its specific incident angle characteristics. This maintains high reflectivity across the entire aperture even when different regions experience varying bandwidths, thereby preserving both resolution and throughput.
3Measurement precision
If the aperture is increased to achieve higher resolution, then finer structures can be imaged, but imaging defects increase and throughput decreases
Solution Approach 1:
The patent addresses imaging quality by implementing local quality optimization across the reflective surface. Each local region is designed with period thickness matched to its incident angle bandwidth, preventing imaging defects that would otherwise occur in high-aperture systems with uniform multilayer structures.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design enhances reflectivity and improves imaging characteristics such as telecentricity and ellipticity, increasing throughput and reducing imaging defects in high-resolution UV and EUV lithography applications.
Implementation Method 1
Alternately arranging stacks with an absorber-spacer pair essentially simulates a crystal. Its lattice planes correspond to the absorber layers, on which Bragg reflection occurs.
Implementation Method 2
The period thickness is equal to the sum of the individual layers forming a stack. Alternately arranging stacks with an absorber-spacer pair essentially simulates a crystal.
Data Source
AI summary
For the use in illumination systems and projection exposure apparatuses for UV or EUV lithography, a reflective optical element is provided for a operating wavelength in the ultraviolet to extreme ultraviolet wavelength ranges. The reflective optical element includes a substrate and a reflective surface on the substrate. The multilayer system has layers of at least two alternating materials having different real parts of the refractive index at the operating wavelength. Radiation in the operating wavelength of a certain incident angle bandwidth distribution can impinge on the reflective optical element. The reflective surface includes one or more first portions, in which the layers have alternating materials of a first period thickness. The reflective surface includes one or more additional portions, in which the layers of alternating materials have a first period thickness and at least one additional period thickness. The arrangement of the first and additional portions across the reflective surface is adapted to the incident angle bandwidth distribution. Furthermore, a projection system and a projection exposure apparatus including such a reflective optical element are suggested.