Microlithographic Projection Lens Pupil Transmission Correction
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Solution Overview
Problem
High-aperture optical imaging systems, such as microlithographic projection lenses, face challenges in maintaining uniform intensity distribution in the exit pupil due to varying angles of incidence and material properties, leading to imaging quality issues and critical dimension variations in produced structures.
Innovation Solution
Incorporating diffraction structures on a correction surface within the optical imaging system, designed to steer excess light into uncritical regions via diffraction, thereby modifying the intensity distribution in the exit pupil without absorption or heating, thus compensating for unwanted transmission variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high-aperture optical imaging systems are used to achieve good imaging performance, then imaging quality is improved, but intensity distribution uniformity in the exit pupil deteriorates due to varying angles of incidence and material properties
Solution Approach 1:
The patent applies local quality by introducing a correction surface with spatially varying transmission properties at a specific location in the optical path. This correction surface has locally tailored optical characteristics that compensate for the non-uniform intensity distribution caused by high-aperture rays, thereby maintaining both high imaging quality and uniform intensity distribution across the exit pupil.
2Illumination intensity
If optical filtering is used to modify the pupil transmission function, then intensity distribution is improved, but device complexity increases due to additional optical elements
Solution Approach 1:
The patent merges the correction surface into an existing optical element (such as a lens element or mirror) already present in the high-aperture optical imaging system. By integrating the intensity correction function into a component that is already necessary for the optical path, the patent avoids adding separate filtering elements, thus modifying the pupil transmission function without significantly increasing device complexity.
3Illumination intensity
If diffraction structures are produced on the correction surface to steer excess light, then intensity distribution uniformity is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent replaces complex mechanical or physical diffraction structures with a more manufacturable correction surface that achieves similar intensity redistribution through controlled optical properties. The correction surface can be fabricated using standard optical manufacturing techniques such as coating deposition or surface figuring, which have well-established precision capabilities, thereby reducing the manufacturing precision requirements compared to creating precise diffraction patterns.
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 effectively reduces intensity distribution variations in the exit pupil, enhancing imaging quality by ensuring a more uniform exposure dose across the substrate, thereby improving the precision of microstructured components.
Implementation Method 1
producing diffraction structures (DS) in an optically used region (UA) of the correction surface according to a predeterminable local distribution in such a way that, during operation, the diffraction structures guide a component of the intensity of the rays incident on the diffraction structures into uncritical regions outside of the imaging beam path via diffraction
Data Source
AI summary
A projection exposure method for exposing a radiation-sensitive substrate with at least one image of a pattern of a mask is provided in which an illumination field of the mask is illuminated by illumination radiation with an operating wavelength λ that was provided by an illumination system.