Ru-Ta-N EUV Photomask Blank for Shadowing and NILS Balance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing reflective photomasks for EUV lithography face challenges in achieving high wafer transfer characteristics (high NILS value) and are susceptible to shadowing effects due to phase shift films with inappropriate reflectance and phase shift values, especially in miniaturized patterns.
Innovation Solution
A reflective photomask blank comprising a light absorbing film made of ruthenium (Ru), tantalum (Ta), and nitrogen (N) with specific at% compositions, free of oxygen (O), and having a thickness of 38-50 nm, providing a reflectance of 10-14% and phase shift of 205-225 degrees, along with a multilayer reflection film and protection film.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a phase shift film is used to improve pattern resolution through phase inversion, then resolution and depth of focus are improved, but shadowing effects occur in miniaturized patterns
Solution Approach 1:
The patent changes the optical parameters of the phase shift film by controlling its thickness to be 38-50 nm and its composition (Ru: 80-90 at%, Ta: 5-15 at%, N: ≤10 at%). These parameter changes optimize the reflectance (10-14%) and phase shift (205-225 degrees) to reduce shadowing effects while maintaining high pattern resolution in miniaturized semiconductor devices
Solution Approach 2:
The patent uses a composite material consisting of ruthenium (Ru), tantalum (Ta), and nitrogen (N) for the phase shift film. This composite material provides optimized optical properties including controlled reflectance and phase shift values that reduce shadowing effects while maintaining high resolution, overcoming the limitations of single-material phase shift films
2Measurement precision
If the phase shift film thickness is increased to achieve desired phase shift, then phase shift value improves, but shadowing effect increases
Solution Approach 1:
The patent optimizes the thickness parameter of the phase shift film to be 38-50 nm, which is a specific range that achieves the desired phase shift value (205-225 degrees) while minimizing shadowing effects. This precise parameter control allows simultaneous achievement of both goals
Solution Approach 2:
The composite material (Ru-Ta-N) enables achieving the required phase shift value with a thinner film compared to conventional materials, thereby reducing shadowing effects. The specific composition ratios (Ru: 80-90 at%, Ta: 5-15 at%, N: ≤10 at%) are optimized to provide the right balance between phase shift capability and shadowing reduction
3Object-affected harmful factors
If reflectance is increased to reduce shadowing effects, then shadowing effect decreases, but wafer transfer characteristics (NILS value) deteriorate
Solution Approach 1:
The patent precisely controls the reflectance parameter to be within 10-14%, which is an optimized range that simultaneously reduces shadowing effects and maintains high wafer transfer characteristics (high NILS value). This specific parameter range represents the optimal balance between the two competing requirements
Solution Approach 2:
The Ru-Ta-N composite material with specific composition ratios enables achieving the optimized reflectance range (10-14%) while maintaining appropriate phase shift characteristics. The material composition is specifically designed to provide the right balance between reflectance and phase shift to achieve both reduced shadowing and high NILS values
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 achieves high wafer transfer characteristics (high NILS value) with reduced shadowing effects, enabling precise pattern formation on wafers with improved resolution and contrast.
Implementation Method 1
a phase shift of not less than 205 degrees and not more than 225 degrees with respect to light in extreme ultraviolet range
Implementation Method 2
a reflectance of not less than 10% and not more than 14% with respect to light in extreme ultraviolet range
Data Source
AI summary
A reflective mask blank including a substrate, a multilayer reflection film, a protection film and a light absorbing film that has a phase shift function is provided. The light absorbing film contains ruthenium, tantalum and nitrogen and is free of oxygen, and has a ruthenium content of 80 to 90 at %, a tantalum content of 5 to 15 at %, and a nitrogen content of not more than 10 at %, a thickness of 38 to 50 nm, and a reflectance of 10 to 14% and a phase shift of 205 to 225 degrees, with respect to exposure light being light in extreme ultraviolet range.