Mask Blank Layer Structure for 20 Nm Assist Pattern Formation
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Solution Overview
Problem
Conventional mask blanks face difficulties in manufacturing transfer masks with assist patterns as small as 20 nm, due to challenges in forming precise, fine patterns and maintaining electric conductivity during electron beam exposure.
Innovation Solution
A mask blank structure is developed with a thin film for pattern formation, a first hard mask film containing oxygen and silicon or tantalum, and a second hard mask film with reduced transition metal content, allowing for precise formation of assist patterns through controlled etching and improved electric conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional mask blank structure with a single hard mask film is used, then the manufacturing process is simple, but it is difficult to form precise assist patterns as small as 20 nm
Solution Approach 1:
The hard mask film is divided into two distinct layers: a first hard mask film (5-20 nm thick) and a second hard mask film (10-30 nm thick). This segmentation allows each layer to serve specific functions - the first layer enables precise pattern formation down to 20 nm, while the second layer provides structural support and etching protection, resolving the contradiction between precision and complexity.
Solution Approach 2:
Different regions of the mask blank are optimized with different material properties. The first hard mask film contains oxygen (40-70 at%) to reduce charge-up and improve conductivity for electron beam exposure, while the second hard mask film has lower oxygen content (20-50 at%) to provide mechanical strength. This local quality differentiation enables both precise patterning and structural integrity.
2Reliability
If the hard mask film has high transition metal content for durability, then etching resistance is improved, but electric conductivity decreases causing charge-up during electron beam exposure
Solution Approach 1:
The oxygen content parameter is optimized differently in each hard mask film layer. The first hard mask film has high oxygen content (40-70 at%) to reduce charge-up and improve electron beam exposure accuracy, while the second hard mask film has moderate oxygen content (20-50 at%) to maintain etching resistance. This parameter optimization resolves the contradiction between conductivity and etching durability.
3Ease of manufacture
If a single-layer hard mask film is used, then the manufacturing process is straightforward, but charge-up occurs during electron beam exposure
Solution Approach 1:
The mask blank uses a composite structure with two hard mask films having different material compositions. The first hard mask film is designed with high oxygen content to provide good electric conductivity and prevent charge-up during electron beam exposure, while the second hard mask film provides structural support. This composite approach maintains manufacturing feasibility while solving the conductivity issue.
Data Source
AI summary
Provided is a mask blank.The mask blank has a structure where a thin film for pattern formation, a first hard mask film, and a second hard mask film are stacked in this order on a main surface of a substrate, the thin film for pattern formation contains a transition metal, the first hard mask film contains oxygen and one or more elements selected from silicon and tantalum, the second hard mask film contains a transition metal, a content of transition metal of the second hard mask film is less than the content of transition metal of the thin film for pattern formation, a region where the first hard mask film is formed on the main surface is smaller than a region where the thin film for pattern formation is formed, and the second hard mask film and the thin film for pattern formation are in contact with each other at least in part.