Free Form Mirror Imaging Optical System for Microlithography
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current imaging and illumination optical systems in projection exposure systems face challenges in achieving precise correction of imaging errors over the field, particularly in microlithography, where existing systems struggle to maintain optimal imaging quality with varying transverse dimensions and non-rotationally symmetrical object fields.
Innovation Solution
The design incorporates an imaging optical system with free form faces and an illumination optical system that allows for flexible field forms, including arc fields with varying transverse dimensions, enabling precise correction of imaging errors and efficient illumination without the need for absolute mirror symmetry, using field facet mirrors with non-identically formed projection faces to compensate for imaging effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional imaging optical systems are used with rotationally symmetrical reference faces, then manufacturing and measurement are simpler, but imaging error correction precision is insufficient
Solution Approach 1:
The patent applies asymmetry by replacing rotationally symmetrical reference faces with free form faces that have non-rotationally symmetrical shapes. These free form faces are specifically designed to compensate for field curvature and other imaging errors across the object field, achieving superior imaging error correction precision while maintaining manufacturability through controlled deviation from symmetrical forms.
2Adaptability or versatility
If the object field has constant transverse dimension, then the field form is simple, but it cannot adapt to varying illumination requirements and imaging quality optimization
Solution Approach 1:
The patent implements dynamics by designing the object field with varying transverse dimensions that adapt to different illumination requirements. The field form is configured to have different transverse dimensions at different locations, allowing the system to optimize imaging quality for various illumination conditions without requiring a completely complex reconfiguration system.
3Manufacturing precision
If mirror symmetry is enforced in the optical system, then the design is constrained and simpler, but it cannot compensate for imaging effects in non-symmetrical field forms
Solution Approach 1:
The patent applies asymmetry by deliberately breaking mirror symmetry in the optical design. Free form faces with non-rotationally symmetrical shapes are used to compensate for imaging effects in non-symmetrical field forms, allowing the system to achieve superior imaging quality while accepting the resulting design complexity as a necessary trade-off.
4Manufacturing precision
If free form faces with large deviations from rotationally symmetrical reference faces are used, then imaging error correction is superior, but manufacturing and measurement become more difficult
Solution Approach 1:
The patent applies local quality by designing free form faces that deviate from rotationally symmetrical reference faces only to the extent necessary to compensate for specific imaging errors at different locations. The deviations are controlled and localized rather than uniformly large throughout the entire surface, maintaining manufacturability and measurability while achieving superior imaging error correction precision where needed.
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 approach results in improved imaging quality with reduced spot sizes and efficient illumination, allowing for the production of microstructured or nanostructured components with enhanced precision and throughput in projection exposure systems.
Implementation Method 1
an imaging optical system with free form faces... the free form face may deviate from a rotationally symmetrical reference face by more than a wavelength of the illumination light
Implementation Method 2
an illumination optical system... using field facet mirrors with non-identically formed projection faces to compensate for imaging effects
Data Source
AI summary
An imaging optical system has a plurality of mirrors, which image an object field in an object plane into an image field in an image plane. A reflection face of at least one of the mirrors is configured as a free form face which cannot be described by a rotationally symmetrical function. The object field has an aspect ratio greater than 1. A ratio of a minimal and a maximal transverse dimension of the object field can be less than 0.9.