Transmissive Photomask for eUV Lithography
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Solution Overview
Problem
Conventional eUV photomasks experience significant optical losses due to reflection and refraction in reflective types and light absorption in transmissive types, especially at low wavelengths, and are prone to peeling or distortion under high power environments during eUV lithography operations.
Innovation Solution
A transmissive type photomask with a simplified structure, featuring a patterned photomask plate and a supporting member, optimized for high optical efficiency, fabricated using materials with low thermal expansion coefficients and high melting points, eliminating the need for extra reflective layers and enhancing durability under high power conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional reflective type eUV photomask is used, then the desired pattern can be transferred onto the semiconductor wafer, but significant optical loss occurs due to reflection and refraction losses at respective layers
Solution Approach 1:
The patent extracts and removes the complex multi-layer reflective structure from the photomask design. By eliminating the reflective layers and associated anti-reflective coatings, the invention achieves a simplified transmissive structure that allows eUV light to pass through with minimal reflection and refraction losses, directly addressing the optical loss problem while reducing structural complexity
Solution Approach 2:
The invention changes the fundamental optical parameter of the photomask from reflective to transmissive operation. This parameter change allows the photomask to transmit eUV light directly through the substrate and pattern regions, avoiding the multiple reflection and refraction events that occur in conventional reflective designs, thereby significantly reducing optical losses
2Loss of energy
If a conventional transmissive type eUV photomask is used, then the structure is simpler, but the substrate absorbs a percentage of light (especially components of low wavelengths, such as 13.5 nm, 22 nm, etc.)
Solution Approach 1:
The patent employs composite material construction for the photomask substrate, combining materials with complementary properties. The substrate is made from materials that exhibit high transmittance at eUV wavelengths (13.5 nm, 22 nm) while maintaining structural integrity and resistance to absorption losses. This composite approach allows the photomask to achieve both low light absorption and high durability simultaneously
Solution Approach 2:
The invention optimizes the optical and thermal parameters of the substrate material to achieve high transmittance at specific eUV wavelengths while maintaining structural stability. By carefully selecting and tuning material parameters such as bandgap energy, thermal conductivity, and melting point, the photomask achieves minimal light absorption at operational wavelengths while maintaining durability under high power conditions
3Productivity
If a conventional eUV photomask is utilized under a high power environment, then lithography operation can proceed, but some components (e.g. eUV reflective layers) are likely to be peeled or distorted
Solution Approach 1:
The patent removes the vulnerable eUV reflective layers from the photomask structure, eliminating the components that are prone to peeling and distortion under high power conditions. By adopting a transmissive design without reflective coatings, the invention eliminates the structural weaknesses while maintaining full lithography operational capability
Solution Approach 2:
The invention changes the thermal and structural parameters of the photomask by selecting substrate materials with high melting points, low thermal expansion coefficients, and high thermal conductivity. These parameter changes enable the photomask to withstand high power eUV irradiation environments without experiencing peeling, distortion, or other forms of structural degradation, ensuring both productivity and compositional stability
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 solution significantly reduces optical transmission losses, lowers fabrication costs, minimizes particle issues, and facilitates easier inspection, while maintaining photomask integrity under high power environments, thereby improving overall lithography performance.
Implementation Method 1
A transmissive type photomask with a simplified structure, featuring a patterned photomask plate and a supporting member, optimized for high optical efficiency
Implementation Method 2
fabricated using materials with low thermal expansion coefficients and high melting points, eliminating the need for extra reflective layers and enhancing durability under high power conditions
Data Source
AI summary
A photomask includes a patterned photomask plate and a supporting member. The patterned photomask plate has a pattern region and a peripheral region surrounding the pattern region. The patterned photomask plate includes a plurality of openings in the pattern region. The supporting member directly abuts the patterned photomask plate and is in a peripheral region of the patterned photomask plate. The supporting member is formed from a different material than the patterned photomask plate.