Wavefront Correction Element Using Refractive Index Variation
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Solution Overview
Problem
Existing wavefront correction methods in microlithographic projection exposure and mask inspection systems face challenges such as mechanical destabilization due to thickness variations in film elements and accuracy limitations from protective layers, which affect the precision of optical wavefront correction.
Innovation Solution
A wavefront correction element utilizing a carrier film with a varying real part of the complex refractive index, achieved through doping with foreign atoms, allows for precise wavefront correction without thickness variations and can be applied after protective layers, enabling accurate adaptation to desired wavefront aberration correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the thickness profile of a wavefront correction layer is adjusted to correct wavefront aberration, then wavefront correction accuracy is improved, but mechanical stability of the optical element deteriorates
Solution Approach 1:
The patent changes the physical parameter from thickness variation to refractive index variation. Instead of adjusting the thickness profile of the wavefront correction layer, the invention varies the refractive index within a uniform thickness layer, thereby achieving wavefront correction without mechanical instability.
Solution Approach 2:
The patent replaces the mechanical approach (thickness adjustment) with a physical/optical approach (refractive index modulation). By using doping to change the refractive index rather than physically removing or adding material, the system achieves wavefront correction without mechanical destabilization.
2Reliability
If a protective layer is applied to the wavefront correction element, then mechanical protection and oxidation resistance are improved, but wavefront correction accuracy deteriorates
Solution Approach 1:
The patent performs the wavefront correction function before applying the protective layer. By doping the carrier layer with foreign atoms to create the required refractive index distribution prior to protective coating, the system ensures that the protective layer does not interfere with the precision of the wavefront correction.
Solution Approach 2:
The invention changes the approach from post-correction protection to pre-correction doping. The refractive index profile is established through doping before the protective layer is applied, ensuring that the protective layer serves its mechanical function without compromising optical precision.
3Adaptability or versatility
If carrier material is removed or added to create varying layer thickness, then wavefront correction capability is improved, but mechanical stability and structural integrity worsen
Solution Approach 1:
The patent changes the physical parameter controlled in the carrier layer from thickness to refractive index. By doping the carrier layer with foreign atoms, the refractive index varies spatially to provide wavefront correction while the layer thickness remains uniform, preserving structural integrity.
Solution Approach 2:
The patent uses a composite structure consisting of a carrier layer doped with foreign atoms. This composite material approach allows the carrier layer to maintain its mechanical strength while the doping creates the necessary refractive index variation for wavefront correction.
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 enables precise wavefront correction with reduced mechanical destabilization and improved accuracy, allowing for effective compensation of wavefront aberrations in optical systems, particularly in EUV ranges, while maintaining the desired correction effect and minimizing intensity fluctuations.
Implementation Method 1
the real part of the complex refractive index varies over a useful area of the surface of the carrier film
Implementation Method 2
the phase of a wave front passing through the wave front correction element or the carrier film can be influenced - alternatively or in addition to any thickness variation - also via a variation of the refractive index
Implementation Method 3
producing the above-described variation of the real part of the refractive index in a carrier film by doping with foreign atoms
Data Source
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Figure 5a
AI summary
The invention relates to a wavefront correction element for use in an optical system, in particular in an optical system of a microlithographic projection exposure apparatus or a mask inspection apparatus, comprising a carrier film (110, 210, 410) which transmits at least partially electromagnetic radiation that is incident on the carrier film during operation of the optical system and has a working wavelength of the optical system, the carrier film (110, 210, 410) being designed such that the real component of the complex refractive index varies over a useful area of the surface of the carrier film (110, 210, 410).