Reflective Photomask Blank With RuTaN Phase Shift Film for EUV Shadowing
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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, particularly when used in miniaturized semiconductor manufacturing.
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 protective film and multilayer reflection film on a substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a phase shift film is used to improve pattern resolution, then the resolution and depth of focus are improved, but the light intensity at the boundary of the opening and adjacent portion increases due to interference
Solution Approach 1:
The patent changes the optical parameters of the phase shift film by controlling the thickness to achieve a phase shift of 175-185 degrees and transmittance of 6-30%, which optimizes the interference effect to improve resolution while controlling boundary light intensity
Solution Approach 2:
The patent uses composite materials in the phase shift film, particularly materials containing silicon (Si) and molybdenum (Mo), to achieve the desired optical properties of phase shift and transmittance that resolve the contradiction between resolution improvement and boundary light intensity control
2Object-affected harmful factors
If a light-shielding film composed of chromium is used to prevent exposure light leakage, then the optical density is increased, but the film thickness must be precisely controlled to achieve desired optical density
Solution Approach 1:
The patent controls the thickness parameter of the chromium-based light-shielding film to achieve the desired optical density, precisely balancing the prevention of light leakage with manufacturing feasibility
Solution Approach 2:
The light-shielding film serves multiple functions: it prevents exposure light leakage, acts as an etching mask for patterning the phase shift film, and provides optical density control, reducing the need for separate components
3Manufacturing precision
If the phase shift film thickness is increased to achieve desired phase shift, then the phase shift value improves, but the shadowing effect increases reducing wafer transfer characteristics
Solution Approach 1:
The patent optimizes the thickness parameter of the phase shift film to achieve the desired phase shift of 175-185 degrees while controlling the shadowing effect, finding the optimal balance point that satisfies both requirements
Solution Approach 2:
The use of composite materials with specific optical properties allows achieving the required phase shift with optimized thickness, reducing the shadowing effect while maintaining wafer transfer characteristics
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 results in a reflective photomask with improved wafer transfer characteristics (high NILS value) and reduced susceptibility to shadowing effects, enabling precise pattern formation on wafers.
Implementation Method 1
a light absorbing film that is formed on the protection film, absorbs the exposure light
Implementation Method 2
a phase shift of not less than 205 degrees and not more than 225 degrees with respect to the exposure light
Implementation Method 3
a multilayer reflection film that is formed on the substrate and reflects exposure light being light in extreme ultraviolet range
Data Source
Figure 1~2
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.