EUV Spectral Purity Filter with Anti-Reflective Coating
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Solution Overview
Problem
Lithographic apparatuses using extreme ultraviolet (EUV) radiation sources face issues with unwanted secondary radiation, such as infrared and deep ultraviolet radiation, which cause substrate heating and reduce spectral purity, leading to unwanted heating and contrast loss in the patterning process.
Innovation Solution
A spectral purity filter is designed to include an anti-reflective coating and a multi-layer stack that reflects EUV radiation while transmitting infrared radiation, effectively suppressing secondary radiation and improving spectral purity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a spectral purity filter is designed to transmit infrared radiation while reflecting EUV radiation, then spectral purity is improved, but device complexity increases due to the multi-layer coating structure
Solution Approach 1:
The filter is divided into multiple functional layers: a substrate, an anti-reflective coating layer, and a multi-layer stack with alternating high and low refractive index materials. Each layer serves a specific function in the spectral filtering process, allowing independent optimization of each layer's properties to achieve the desired spectral purity while managing overall device complexity.
Solution Approach 2:
The filter employs composite material structures, specifically a multi-layer stack comprising alternating layers of materials with different refractive indices (such as Mo/Si or W/B4C). This composite structure enables selective reflection of EUV radiation while maintaining transmission of infrared radiation, resolving the contradiction between spectral purity and structural simplicity through material composition rather than complex geometry.
2Reliability
If secondary radiation is suppressed using traditional filtering methods, then spectral purity improves, but EUV transmission efficiency decreases due to absorption losses
Solution Approach 1:
The filter design converts potentially harmful EUV radiation into reflected energy rather than absorbed energy. The multi-layer stack is engineered to reflect EUV wavelengths selectively while allowing infrared transmission, thereby suppressing secondary radiation effects without significant EUV loss. The anti-reflective coating further minimizes unwanted reflections that would otherwise represent energy loss.
Solution Approach 2:
The filter optimizes transmission by carefully controlling layer thicknesses and refractive indices. By adjusting these parameters, the multi-layer stack achieves constructive interference for transmitted EUV waves while creating destructive interference for reflected secondary radiation, maximizing EUV transmission efficiency while maintaining spectral purity.
3Ease of manufacture
If the filter uses a simple single-layer coating, then ease of manufacture improves, but spectral purity is insufficient to adequately suppress secondary radiation
Solution Approach 1:
The filtering function is segmented across multiple layers with distinct purposes: the anti-reflective coating handles infrared transmission and minimizes reflections, while the multi-layer stack provides selective EUV reflection. This segmentation allows each layer to be optimized independently for its specific function, achieving high spectral purity through a systematic approach that remains manufacturable using standard thin-film deposition techniques.
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 filter significantly reduces the reflection of unwanted infrared and deep ultraviolet radiation, enhancing the proportion of desired EUV radiation and minimizing substrate heating, thereby improving the accuracy and efficiency of the lithographic process.
Implementation Method 1
a multi-layer stack configured to reflect extreme ultraviolet radiation and to substantially transmit infrared radiation
Implementation Method 2
an anti-reflective coating on a top surface of the substrate configured to transmit infrared radiation
Implementation Method 3
configured to transmit or absorb non-EUV secondary radiation and to reflect extreme ultraviolet radiation
Data Source
AI summary
A spectral purity filter is configured to reflect extreme ultraviolet radiation. The spectral purity filter includes a substrate, and an anti-reflective coating on a top surface of the substrate. The anti-reflective coating is configured to transmit infrared radiation. The filter also includes a multi-layer stack configured to reflect extreme ultraviolet radiation and to substantially transmit infrared radiation.