Reflective Photomask with Capping Layer for EUV Lithography
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Solution Overview
Problem
Conventional photomasks for EUV lithography are prone to damage during fabrication and cleaning processes, leading to non-uniform pattern transfer due to the sensitivity of reflective layers, and require new equipment and materials that are difficult to integrate into existing processes.
Innovation Solution
A reflective photomask with a projecting pattern and a multilayer reflective structure, including integral pairs of silicon and molybdenum layers, is developed, featuring a capping layer for protection and a conductive film for stability, which allows for improved adhesion and resistance to chemical damage, enabling stable pattern formation and reduced pattern shift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional reflective photomask with multiple layers (reflective layer, capping layer, buffer layer, absorbing layer) is used, then the pattern transfer capability is achieved, but the mask is prone to damage during fabrication and cleaning processes
Solution Approach 1:
The patent removes the buffer layer and absorbing layer from the conventional multi-layer reflective photomask structure, retaining only the reflective layer and capping layer. This extraction of unnecessary layers simplifies the overall structure while maintaining the essential function of reflecting EUV light for pattern transfer, thereby reducing fabrication complexity and damage risk during manufacturing processes.
Solution Approach 2:
The patent employs a composite material structure consisting of a silicon-based reflective layer and a silicon oxide-based capping layer. This composite structure provides both the necessary optical reflection properties for EUV lithography and enhanced mechanical/chemical stability during fabrication and cleaning processes, improving overall mask reliability without adding structural complexity.
2Measurement precision
If the reflective layer is made sensitive to achieve high reflection efficiency, then the resolution is improved, but the mask becomes vulnerable to damage during cleaning and fabrication
Solution Approach 1:
The patent applies a capping layer made of silicon oxide over the silicon-based reflective layer before the mask undergoes cleaning or fabrication processes. This capping layer acts as a protective cushion that shields the sensitive reflective layer from chemical damage during cleaning and fabrication, while allowing the reflective layer to maintain its high reflection efficiency for achieving fine pattern resolution.
3Ease of manufacture
If a simple two-layer structure (reflective layer and capping layer) is used, then the fabrication process is simplified, but the adhesion and resistance to chemical damage may be insufficient
Solution Approach 1:
The patent uses a composite material system where the silicon-based reflective layer provides excellent adhesion to the substrate and the silicon oxide-based capping layer provides superior chemical resistance. This combination of materials in a simple two-layer structure achieves both ease of manufacture and sufficient strength for adhesion and chemical damage resistance during cleaning processes.
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 enhances the stability and uniformity of pattern transfer in EUV lithography, improving the resolution and productivity of semiconductor device fabrication while minimizing equipment and material costs.
Implementation Method 1
The reflective layer 120 may function to reflect incident EUV light
Implementation Method 2
the absorbing layer 150 may function to absorb incident EUV light so as not to reflect the EUV light
Implementation Method 3
a multilayer reflective structure, including integral pairs of silicon and molybdenum layers
Data Source
AI summary
A reflective photomask for EUV light is disclosed. The reflective photomask may include a projecting pattern selectively formed on a substrate and a reflective layer on the substrate and the projecting pattern.