Reflective Photomask Blank Multilayer Hard Mask for 30 nm Assist Patterns
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Solution Overview
Problem
Conventional reflective photomasks struggle to form fine assist patterns with line widths of about 30 nm or less, particularly when using a resist film thickness of not more than 80 nm, due to issues like pinhole defects and pattern collapse during the dry etching process.
Innovation Solution
The proposed solution involves a reflective photomask blank with a multilayer hard mask film comprising a first layer resistant to chlorine-based dry etching but removable by fluorine-based dry etching, and a second layer resistant to fluorine-based dry etching but removable by chlorine-based dry etching. This configuration allows for the formation of a thin resist film and reduces the aspect ratio of the resist pattern, minimizing the impact of developing solution and water during rinsing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a thin resist film (not more than 80 nm) is used to enable fine assist pattern formation, then the line width of assist patterns can be reduced to about 30 nm, but the aspect ratio of the resist pattern increases causing pattern collapse and pinhole defects during dry etching
Solution Approach 1:
The hard mask film is divided into a multilayer structure with different materials having different etching rates for chlorine-based and fluorine-based dry etching. This segmentation allows the resist pattern to be protected during the etching process by having the hard mask film removed in stages, preventing pattern collapse and pinhole defects while enabling fine assist pattern formation with line widths of about 30 nm
Solution Approach 2:
The hard mask film uses composite materials with different etching characteristics - at least one layer resistant to chlorine-based dry etching and removable by fluorine-based dry etching, and another layer resistant to fluorine-based dry etching and removable by chlorine-based dry etching. This composite structure provides differential etching protection that maintains pattern integrity during the manufacturing process
2Reliability
If a multilayer hard mask film with differential etching resistance is used, then resist pattern reliability is improved by preventing collapse and pinhole defects, but the device complexity increases
Solution Approach 1:
The invention changes the etching resistance parameters of the hard mask film layers by selecting materials with specific etching characteristics. At least one layer is made resistant to chlorine-based dry etching and removable by fluorine-based dry etching, while another layer is made resistant to fluorine-based dry etching and removable by chlorine-based dry etching. This parameter change approach simplifies the overall process by enabling selective removal and protection of film layers during patterning
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
This approach enables the satisfactory formation of assist patterns with line widths of about 30 nm, even with a thin resist film, by reducing the aspect ratio of the resist pattern and preventing pinhole defects and pattern collapse, thereby achieving high-resolution transfer patterns.
Implementation Method 1
the first layer is composed of a material that is resistant to chlorine-based dry etching, and removable by fluorine-based dry etching, the second layer is composed of a material that is resistant to fluorine-based dry etching, and removable by chlorine-based dry etching
Data Source
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AI summary
A reflective photomask blank includes a substrate, a multilayer reflection film that reflects exposure light being light in extreme ultraviolet range, a protection film, a light-absorbing film that absorbs the exposure light, and a hard mask film that is formed in contact with the light-absorbing film. The hard mask film is constituted by a multilayer including a first layer disposed at the side remotest from the substrate, and is composed of a material that is resistant to chlorine-based dry etching, and removable by fluorine-based dry etching, and a second layer composed of a material that is resistant to fluorine-based dry etching, and removable by chlorine-based dry etching. An etching clear time of the light-absorbing film on fluorine-based dry etching under one condition is longer than an etching clear time of the first layer on the fluorine-based dry etching under the same condition.