EUV Mask Absorber Edge Thickness Control for Blister Prevention
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Solution Overview
Problem
In EUV lithography, reflective masks suffer from blister-like defects at the interface between the glass substrate and films due to hydrogen internal pressure, leading to film peeling and scattering, which affects exposure quality and renders the mask unusable.
Innovation Solution
A reflective mask blank design with a multilayer reflective film, protective film, and absorber film, where the absorber film's thickness near the substrate edge is controlled to be 35 nm or less within 2.5 mm from the center, and the protective film's thickness is sufficient to reduce stress and prevent blister formation, using materials like tantalum, palladium, and ruthenium to manage hydrogen storage and stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the absorber film is formed with sufficient thickness to ensure adequate light absorption, then the light absorption performance is improved, but hydrogen internal pressure increases leading to blister formation at the substrate edge
Solution Approach 1:
The absorber film is designed with spatially varying thickness: thicker at the substrate center for adequate light absorption, and thinner (35 nm or less) at the substrate edge (within 2.5 mm from edge) to reduce hydrogen storage and prevent blister formation. This local quality variation resolves the contradiction between light absorption performance and film integrity.
Solution Approach 2:
The film thickness parameter is changed from uniform to non-uniform distribution across the substrate surface. By controlling the edge portion thickness to be 35 nm or less while maintaining sufficient center thickness, the patent optimizes both light absorption (center region) and prevents hydrogen-induced blistering (edge region).
2Reliability
If the protective film thickness is increased to prevent blister formation, then film integrity is improved, but stress management becomes more complex affecting manufacturing precision
Solution Approach 1:
The protective film thickness is optimized to a specific range (5 nm to 20 nm) that balances blister prevention with stress management. This parameter optimization ensures adequate protection without excessive stress that would compromise manufacturing precision.
Solution Approach 2:
The protective film uses composite material composition (ruthenium-based materials) that provides both protective function and stress management properties, enabling simultaneous achievement of film integrity and manufacturing precision.
3Reliability
If the absorber film thickness at the substrate edge is reduced to prevent blistering, then film integrity is improved, but the area covering with absorber film is reduced
Solution Approach 1:
The absorber film implements local quality differentiation: full coverage with sufficient thickness at the substrate center for light absorption, and reduced thickness (35 nm or less) only at the substrate edge (within 2.5 mm from edge) to prevent blistering. This minimizes the impact on total coverage area while ensuring film integrity.
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 design effectively suppresses blister occurrence at the substrate edge under EUV exposure in a hydrogen atmosphere, ensuring the reflective mask's integrity and maintaining exposure quality.
Implementation Method 1
an absorber pattern which is a patterned absorber film for absorbing exposure light, formed on the multilayer reflective film. EUV light incident on the reflective mask mounted on an exposure apparatus for performing pattern transfer onto a semiconductor substrate is absorbed in a portion having an absorber pattern
Implementation Method 2
a multilayer reflective film for reflecting exposure light, formed on a substrate
Implementation Method 3
the multilayer reflective film is formed by alternately building up a heavy element material film and a light element material film having different refractive indexes
Implementation Method 4
a protective film on the multilayer reflective film... the protective film's thickness is sufficient to reduce stress and prevent blister formation
Data Source
AI summary
Provided are a reflective mask blank, a reflective mask, a method for manufacturing a reflective mask, and a method for manufacturing a semiconductor device, capable of suppressing occurrence of a blister of a substrate edge portion under an EUV exposure environment in a hydrogen atmosphere.The reflective mask blank comprises a substrate, a multilayer reflective film on the substrate, a protective film on the multilayer reflective film, and an absorber film on the protective film. When the film thickness of the absorber film at a center of the substrate is T nm, there is at least one location where the film thickness of the absorber film in a range of 2.5 mm or less from a side surface of the substrate toward the center thereof is the smaller of 35 nm or less or (T−5) nm or less.