EUV Lithography Mask Transmissive Layer for Contamination Protection
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Solution Overview
Problem
Current lithographic apparatuses using EUV radiation face challenges in protecting optical elements from contamination due to the absorption of EUV radiation by existing filters and pellicles, making it difficult to prevent debris from reaching the mask and other components, which can lead to defect devices.
Innovation Solution
A method is introduced to provide optical elements with a transmissive layer having a first height in cavities that is larger than the maximum height difference, and surfacing the layer to achieve a substantially flat surface, allowing for easier cleaning and protection against contamination, while being transparent to EUV radiation and opaque to other wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a pellicle or filter is used to protect the mask from contamination, then the mask is protected from debris particles, but the pellicle/filter absorbs EUV radiation and reduces transmission
Solution Approach 1:
The patent applies a thin film coating (such as silicon monoxide or silicon dioxide) directly on the mask surface. This thin film serves as a protective layer that prevents particle adhesion while being sufficiently transparent to EUV radiation, unlike traditional pellicles that are separate membranes. The film thickness is controlled to be in the nanometer range to minimize absorption while providing effective protection.
Solution Approach 2:
The invention extracts the protective function from a separate pellicle component and integrates it directly onto the mask surface as a thin film coating. This eliminates the need for a separate pellicle structure that would absorb radiation, while maintaining the contamination protection function. The protective layer is taken out from being a separate mechanical component and converted into a surface coating.
2Strength
If a pellicle with wire mesh support structure is used, then the pellicle is mechanically stable, but the wires absorb EUV radiation and create additional contamination risk
Solution Approach 1:
The patent removes the wire mesh support structure entirely from the protective system. Instead of using a pellicle with mechanical wires for support, the thin film coating is applied directly to the mask surface, which provides its own structural support through the mask's rigid substrate. This eliminates the wire absorption problem completely while maintaining mechanical stability through the integrated design.
Solution Approach 2:
The protective function and the mask structure are merged into a single integrated component. The thin film coating is applied directly on the mask surface, combining the mask's structural support with the protective function in one element, eliminating the need for separate support wires that would absorb radiation.
3Manufacturing precision
If the mask surface has submicron optical structures, then the lithographic patterning capability is achieved, but the structures are susceptible to contamination by debris particles
Solution Approach 1:
The thin film protective coating is applied in advance to the mask surface before the mask is put into service. This preliminary coating creates a protective barrier that prevents particle adhesion to the critical submicron optical structures. The coating is applied while the mask is still in a clean state, ensuring uniform coverage over the delicate patterns.
Solution Approach 2:
A thin film coating conformally covers the submicron optical structures on the mask surface. This flexible film adapts to the complex three-dimensional topography of the optical structures while providing continuous protection. The film thickness is uniform and controlled at the nanometer scale to protect the structures without affecting their optical function.
4Object-affected harmful factors
If the mask is cleaned frequently to remove contamination, then the contamination level is reduced, but the cleaning process may damage the delicate optical structures
Solution Approach 1:
The thin film protective coating is applied in advance to prevent contamination adhesion in the first place. This preliminary protective action reduces the need for frequent cleaning operations. The coating creates a non-stick surface that prevents particles from bonding strongly to the mask, allowing for easier and safer maintenance cleaning.
Solution Approach 2:
The thin film coating acts as a cushioning layer between contaminant particles and the delicate optical structures. When particles do accumulate, they adhere to the coating rather than directly to the optical structures, providing a buffer that protects the underlying structures during cleaning operations.
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 solution effectively protects optical elements by creating a cleanable and contamination-resistant surface that is transparent to EUV radiation, reducing defects in device manufacturing and enabling easier detection of contaminants.
Implementation Method 1
state of the art and commercially available filters and pellicles are typically characterized by a relative high absorption for EUV radiation
Data Source
AI summary
An optical element includes a surface including a tilted profile having height differences, thereby providing cavities and elevations having a predetermined maximum height difference, and a transmissive layer that covers the cavities and the elevations of the optical element. A first height of the transmissive layer in the cavities is substantially equal or larger than the predetermined maximum height difference and the transmissive layer has a second height on the elevations and the second height is about 10-500 nm. The transmissive layer is enabled to optically filter incident radiation, and the optical element is a grating.