Tungsten Alloy Absorber Film for EUV Lithography
Solution Overview
Problem
Current reflective mask blanks for EUV lithography face challenges in achieving high pattern resolution and accuracy due to low etching rates of absorber films, surface roughness, and heat resistance issues, particularly when using tungsten as the sole material for the absorber film.
Innovation Solution
A reflective mask blank comprising a substrate with a multilayer reflection film and an absorber film containing tungsten, along with at least one element from metalloids or metals excluding tungsten, and at least one light element from nitrogen, oxygen, carbon, or hydrogen, which enhances etching rates, reduces surface irregularity, and provides improved heat resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a thick absorber film is used to achieve high etching rate, then etching speed improves, but pattern resolution deteriorates due to shadowing effect
Solution Approach 1:
The invention changes the material composition parameters of the absorber film by incorporating tungsten (W) as the primary material with specific atomic percentages (W: 50-100 at%, Mo: 0-50 at%, Ru: 0-50 at%). This compositional parameter change enables achieving both high etching rate and fine pattern formation capability simultaneously, resolving the contradiction between etching speed and pattern resolution.
Solution Approach 2:
The invention uses a composite absorber film material system consisting of tungsten-based alloy compositions (W-Mo, W-Ru, or W-Mo-Ru). This composite material approach combines the advantages of different metals: tungsten provides high etching rate, while molybdenum and ruthenium contribute to low refractive index and surface flatness, enabling both high productivity and manufacturing precision.
2Manufacturing precision
If a thin absorber film is used to improve pattern resolution, then shadowing effect reduces, but etching rate decreases
Solution Approach 1:
By changing the material composition parameters to tungsten-based alloys with specific ratios (W: 50-100 at%, Mo: 0-50 at%, Ru: 0-50 at%), the invention achieves high etching rate in thinner film configurations, thereby improving pattern resolution without sacrificing etching productivity.
3Productivity
If simple substance tungsten is used for absorber film to achieve high etching rate, then etching speed improves, but surface roughness increases
Solution Approach 1:
The invention employs composite tungsten-based alloy materials (W-Mo, W-Ru, or W-Mo-Ru) where tungsten provides high etching rate and molybdenum/ruthenium contribute to surface flatness and low refractive index. This composite material system simultaneously achieves high etching productivity and smooth surface finish, resolving the contradiction between etching rate and surface roughness.
Solution Approach 2:
The invention changes the material composition from pure tungsten to tungsten-based alloys with controlled atomic percentages (Mo: 0-50 at%, Ru: 0-50 at%). This parameter change modifies the surface morphology characteristics, reducing surface roughness while maintaining high etching rate through the synergistic effects of the alloy components.
4Manufacturing precision
If absorber film is used as phase shift function to thin the film, then pattern resolution improves, but material with smaller refractive index is required
Solution Approach 1:
The invention uses tungsten-based composite materials (W-Mo, W-Ru, or W-Mo-Ru alloys) where molybdenum and ruthenium components contribute to lower refractive index compared to pure tungsten. This enables the absorber film to function as a phase shift film with reduced thickness while maintaining or improving pattern resolution, despite the increased material composition complexity.
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 proposed solution results in a reflective mask with improved pattern resolution, surface conditions, and stability at high temperatures, enabling accurate transfer of fine patterns to semiconductor substrates using EUV light.
Implementation Method 1
a multilayer reflection film that is formed on a substrate and reflects exposure light
Implementation Method 2
The multilayer reflection film is formed by laminating alternately layers having different refraction indexes
Implementation Method 3
an absorber film that is formed on the multilayer reflection film and absorbs EUV light, and such a mask is used as a common reflective mask. A pattern is formed on an object to transfer the pattern such as a silicon wafer by utilizing a difference of reflectance of EUV light as an exposure light, caused by presence and absence of the absorber film on the multilayer reflection film
Data Source
AI summary
A reflective mask blank that is a material for a reflective mask used in EUV lithography using EUV light as exposure light, including a substrate, a multilayer reflection film that is formed on one main surface of the substrate and reflects the exposure light, and an absorber film containing tungsten, and another metal, a metalloid or a light element that is formed on the multilayer reflection film and absorbs the exposure light.