Thin Substrate Attenuation Filter for Microlithography
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Solution Overview
Problem
Microlithographic projection lenses face challenges with optical proximity effects and thermally induced wavefront variation errors due to the small size of structures being imaged, which affect imaging performance and require complex corrections that are difficult to implement without causing secondary issues.
Innovation Solution
An attenuation filter with a substrate and absorption layer is designed to attenuate ultraviolet radiation in a specific wavelength range, featuring a thin, transparent substrate and a locally varying absorption layer that minimizes thermally induced wavefront errors by controlling the absorption and transmission of ultraviolet radiation, and can be configured with anti-reflection layers and a wavefront correction layer for improved imaging performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If an attenuation filter with a thick substrate is used to provide sufficient mechanical strength and stability, then the structural integrity is improved, but thermally induced wavefront variation errors increase due to greater absorption of ultraviolet radiation
Solution Approach 1:
The patent employs a thin substrate (thickness less than 100 μm) instead of a thick substrate, transforming the traditional robust structure into a thin-film structure that minimizes thermal absorption while maintaining functional integrity. This thin substrate reduces the path length for ultraviolet radiation, thereby minimizing thermally induced wavefront variation errors while still providing sufficient mechanical support when combined with the absorption layer and anti-reflection coatings.
2Object-affected harmful factors
If the substrate is made thinner to reduce thermally induced wavefront errors, then imaging performance is improved, but mechanical strength and stability deteriorate
Solution Approach 1:
The patent creates a composite structure consisting of a thin substrate combined with an absorption layer and anti-reflection coatings. This composite design allows the thin substrate to minimize thermal effects while the absorption layer provides the necessary optical function and the anti-reflection coatings enhance overall performance. The composite structure achieves both mechanical adequacy and thermal performance that neither component could achieve alone.
3Manufacturing precision
If an absorption layer is added to the substrate to provide the required attenuation function, then the attenuation performance is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent achieves the required attenuation function by precisely controlling the thickness parameter of the absorption layer rather than using complex multi-layer structures or specialized materials. By optimizing the absorption layer thickness to work in conjunction with the thin substrate, the design achieves the desired attenuation performance with a relatively simple two-layer structure, reducing manufacturing complexity while maintaining high precision.
4Use of energy by moving object
If anti-reflection layers are added to reduce reflection losses, then optical transmission is improved, but device complexity and manufacturing steps increase
Solution Approach 1:
The patent implements anti-reflection layers on the substrate to reduce reflection losses and improve optical transmission. While this adds manufacturing steps, the anti-reflection layers are applied as thin-film coatings that integrate well with the existing thin-substrate design. The improvement in optical transmission efficiency justifies the additional manufacturing complexity, as the enhanced energy utilization directly impacts imaging performance and wafer throughput.
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 attenuation filter enhances imaging performance by reducing thermally induced wavefront variation errors and allows for correction of manufacturing inaccuracies and drift effects, maintaining high wafer throughput and cost-effectiveness in semiconductor chip manufacturing.
Implementation Method 1
The absorption layer absorbs incident ultraviolet radiation of a specified working wavelength according to the specifiable local distribution at different locations of a used area to varying degrees
Implementation Method 2
a thickness of the substrate is less than 100 μm... configured such that thermally induced wavefront variation errors in the ultraviolet radiation which has passed through the attenuation filter are avoided or at least reduced as compared to prior art
Data Source
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AI summary
An attenuation filter (AF, AF', AF1, AF2, AF3) is configured for the defined attenuation of the intensity of ultraviolet radiation (LR1I, LR2I) with a specified working wavelength from a wave-length range of 150 nm to 370 nm according to a specifiable local distribution in a projection lens (PO, PO') of a microlithographic projection exposure apparatus (WSC). The attenuation filter has a substrate (SU, SU') and an absorption layer (AL). The substrate is sufficiently transparent at the working wavelength. The absorption layer is arranged on the substrate and absorbs incident ultraviolet radiation of the working wavelength according to the specifiable local distribution at different locations (Z1, Z2) of a used area (UA) to varying degrees. The attenuation filter is designed for reducing or avoiding a thermally induced wavefront variation error in the ultraviolet radiation (LR1O, LR2O) which has passed through the attenuation filter owing to locally varying heating of the substrate, which is caused by the absorption of the ultraviolet radiation that varies locally over the substrate. A thickness (TS) of the substrate (SU) is less than 100 µm.