EUV Reflective Mask Blank with Thickness Correction Layer
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Solution Overview
Problem
In EUV lithography, the in-plane distribution of peak reflectivity and center wavelength of light in the EUV wavelength region on the surface of multilayer reflective films leads to fluctuations in pattern dimensions, impairing high precision patterning, and existing solutions fail to achieve the required uniformity of peak reflectivity within ±0.18% and center wavelength within ±0.03 nm.
Innovation Solution
A substrate with a multilayer reflective film having a reflectivity distribution correction layer with a thickness distribution that satisfies the formula −0.011x^2 + 0.1x − 100 − α ≤ y ≤ −0.011x^2 + 0.1x + 100 + α, where x is the radial location and y is the thickness change, is used to correct the in-plane distribution of peak reflectivity, with the reflectivity distribution correction layer being formed by adjusting the thickness of either the low or high refractive index layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional multilayer reflective film is used without thickness correction, then the manufacturing process is simple, but the in-plane uniformity of peak reflectivity deteriorates (exceeds ±0.18% variation)
Solution Approach 1:
The patent applies local quality by introducing a reflectivity distribution correction layer with spatially varying thickness. The thickness of this correction layer is specifically designed to differ at different radial positions from the center of the substrate, creating local variations that compensate for the in-plane non-uniformity of the underlying multilayer reflective film. This localized thickness modulation enables uniform peak reflectivity across the entire surface without requiring complete redesign of the overall structure.
Solution Approach 2:
The patent utilizes parameter changes by modifying the thickness parameter of the reflectivity distribution correction layer. By carefully controlling the thickness distribution of this correction layer according to a predetermined profile, the optical parameters (peak reflectivity and center wavelength) are adjusted locally to achieve uniformity. This parameter modulation approach allows correction of reflectivity distribution while maintaining the fundamental structure of the multilayer film.
2Manufacturing precision
If a reflectivity distribution correction layer is added to correct peak reflectivity uniformity, then the in-plane uniformity of peak reflectivity is improved (within ±0.18%), but the device complexity increases
Solution Approach 1:
The reflectivity distribution correction layer implements local quality by having different thicknesses at different radial positions. This spatially varying thickness is specifically designed to compensate for local variations in the multilayer reflective film, thereby uniforming the center wavelength across the entire surface. The local thickness adjustment enables precise control of optical properties without requiring complete structural redesign.
Solution Approach 2:
The patent applies parameter changes by modulating the thickness parameter of the correction layer to achieve uniform center wavelength. By controlling the thickness distribution according to a predetermined profile, the optical parameters are adjusted locally. This approach corrects wavelength uniformity while adding only a single correction layer rather than multiple complex structures.
3Manufacturing precision
If the thickness of correction layer is increased to improve uniformity, then the in-plane uniformity of peak reflectivity is improved, but the deviation from target thickness increases
Solution Approach 1:
The correction layer implements local quality with thickness variations optimized for each radial position. By designing the thickness profile to provide greater correction where needed and minimal correction where the base film is already uniform, the patent achieves high peak reflectivity uniformity while keeping individual thickness deviations small. This position-dependent thickness design optimizes the balance between uniformity achievement and thickness control accuracy.
Solution Approach 2:
The patent applies parameter changes by precisely controlling the thickness parameter of the correction layer according to a predetermined distribution profile. This controlled parameter modulation ensures that the correction is applied optimally at each location, achieving uniform peak reflectivity while maintaining thickness within acceptable tolerances. The systematic parameter control prevents excessive thickness deviations.
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 achieves excellent in-plane uniformity of peak reflectivity and center wavelength, reducing the in-plane distribution of peak reflectivity to at most 0.18% and ensuring precise patterning in EUV lithography.
Implementation Method 1
a multilayer reflective film having a low refractive index layer with a low refractive index to EUV light and a high refractive index layer with a high refractive index to EUV light, alternately stacked to have the light reflectivity improved
Implementation Method 2
a Mo/Si multilayer reflective film having a molybdenum (Mo) layer as a low refractive index layer and a silicon (Si) layer as a high refractive index layer alternately stacked
Implementation Method 3
an absorber layer to absorb EUV light... a material having a high absorption coefficient to EUV light, specifically e.g. a material containing chromium (Cr) or tantalum (Ta) as the main component
Data Source
AI summary
A mask blank for EUV lithography (EUVL) excellent in in-plane uniformity of the peak reflectivity of light in the EUV wavelength region and in in-plane uniformity of the center wavelength of reflected light in the EUV wavelength region, at the surface of a multilayer reflective film, and a process for its production, as well as a substrate with reflective layer for EUVL to be used for the production of such a mask blank for EUVL, and a process for its production. A substrate with reflective layer for EUVL having a reflective layer for reflecting EUV light formed on a substrate, where the reflective layer is a multilayer reflective film having a low refractive index layer and a high refractive index layer alternately stacked plural times.