EUV Mirror Surface Correction via Composite Multilayer Coating
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Solution Overview
Problem
Microlithography projection exposure apparatuses face challenges in achieving precise surface form correction of mirrors used for extreme ultraviolet (EUV) radiation, leading to imaging aberrations that affect the minimum feature size that can be imaged.
Innovation Solution
A method involving a correction layer with alternating layers of different refractive indices is applied to the mirror, where correction radiation with location-dependent energy density is used to grow a layer with optimal surface form, improving reflectivity and reducing surface roughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional mirror surface correction methods are used, then manufacturing complexity is reduced, but surface form precision deteriorates leading to imaging aberrations
Solution Approach 1:
The patent applies a composite multilayer coating structure consisting of alternating high-refractive-index and low-refractive-index layers on the mirror substrate. This composite structure enables precise control of the mirror surface form and optical properties, resolving the contradiction between manufacturing simplicity and surface precision by using material composition rather than complex mechanical correction processes.
Solution Approach 2:
The patent changes the optical parameters of the mirror by controlling the thickness and refractive index of each layer in the multilayer coating. By precisely adjusting these parameters during the coating process, the mirror surface form is corrected to achieve diffraction-limited imaging performance, thereby improving surface form precision without requiring complex post-manufacturing correction devices.
2Manufacturing precision
If mirror surface form is corrected using conventional methods, then device complexity remains low, but imaging quality deteriorates due to surface aberrations
Solution Approach 1:
The multilayer composite coating structure with alternating high and low refractive index layers is designed to correct surface aberrations and achieve diffraction-limited imaging. The composite structure enables precise control of wavefront errors, thereby improving imaging quality and reliability while maintaining a relatively simple mirror substrate structure.
Solution Approach 2:
The patent applies local quality control by varying the thickness of individual layers in the multilayer coating at different locations on the mirror surface. This localized adjustment of layer thickness compensates for local surface form deviations, thereby correcting imaging aberrations and improving overall imaging quality without requiring complete redesign of the entire mirror system.
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
The method achieves higher surface quality and reflectivity for EUV radiation, allowing for more precise imaging and correction of surface aberrations, enhancing the capability to produce smaller microstructured components.
Implementation Method 1
applying a correction radiation having a location-dependent radiation energy density to the mirror such that a correction layer having a location-dependent layer thickness variation grows on the irradiated surface of the mirror
Implementation Method 2
introducing the mirror into an atmosphere comprising a reaction gas
Data Source
AI summary
A method for correcting a surface form of a mirror (1) for reflecting radiation in the wavelength range of 5-30 nm, which includes:applying a correction layer (13) having a layer thickness variation (21) for correcting the mirror's surface form, andapplying a first group (19) of layers to the correction layer.The first group (19) of layers includes first (9) and second (11) layers arranged alternately one above another, wherein the first layers have a refractive index at the operating wavelength which is greater than the refractive index of the second layers for that radiation.The correction layer (13) is applied by:introducing the mirror into an atmosphere including a reaction gas (15),applying a correction radiation (17) having a location-dependent radiation energy density, such that a correction layer having a location-dependent layer thickness variation (21) grows on the mirror's irradiated surface.