Photomask Hardmask Film for High-Resolution Pattern Transfer
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Solution Overview
Problem
Conventional phase-shift masks face challenges in forming fine resist film patterns and light-shielding film patterns due to the thick resist film required, which hinders the creation of high-resolution, precise critical dimension (CD) features necessary for advanced semiconductor lithography, especially for patterns of 45 nm or less.
Innovation Solution
A blankmask design incorporating a transparent substrate with a phase-shift layer and a hardmask film, along with a light-shielding film, allowing for a thinner resist film and improved CD characteristics, including high resolution, precision, CD mean-to-target (MTT), CD uniformity, and CD linearity, by using materials like silicon and various metals, and forming the films in single or multi-layer configurations with varying compositions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick light-shielding film is used to achieve high optical density, then light blocking capability is improved, but resist film thickness must be increased which deteriorates fine pattern formation capability
Solution Approach 1:
The patent introduces a hardmask film as an intermediary layer between the light-shielding film and the resist film. This hardmask film has high etch selectivity against the phase-shift layer, allowing the use of a thinner resist film (reducing loading effect) while maintaining the necessary optical density through the light-shielding film. The hardmask film acts as a mediator that decouples the relationship between light-shielding thickness and resist thickness.
Solution Approach 2:
The patent changes the etch selectivity parameter by introducing materials with significantly different etch rates. The hardmask film is specifically selected to have high etch selectivity against the phase-shift layer, enabling precise pattern transfer with thinner resist films. This parameter change allows the system to achieve both high optical density and fine pattern formation capability.
2Manufacturing precision
If a thick resist film is used to etch the light-shielding film, then sufficient etching depth is achieved, but loading effect increases which deteriorates critical dimension characteristics
Solution Approach 1:
The hardmask film serves as an intermediary that reduces the required resist film thickness. By providing a layer with high etch selectivity, the hardmask film allows the resist film to be thinner while still achieving sufficient pattern definition. This intermediary layer reduces the loading effect during exposure and development, improving critical dimension characteristics.
Solution Approach 2:
The patent segments the masking function into multiple layers: the light-shielding film provides optical density, while the hardmask film provides etch selectivity. This segmentation allows each layer to be optimized independently - the light-shielding film can be thick for high optical density without requiring a proportionally thick resist film, since the hardmask film provides the necessary etching contrast.
3Ease of manufacture
If conventional phase-shift mask structure is used, then manufacturing process is simple, but fine resist film pattern formation is difficult which prevents high-resolution pattern transfer
Solution Approach 1:
The patent segments the mask structure into functionally distinct layers: the light-shielding film handles optical blocking, while the hardmask film handles pattern transfer with high etch selectivity. This segmentation enables fine pattern formation by providing a dedicated layer (hardmask) that offers strong contrast for resist patterning, while maintaining a relatively simple overall manufacturing process that builds upon conventional phase-shift mask fabrication.
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 proposed blankmask enables the transfer of high-resolution patterns down to 32 nm or less, enhancing CD features and reducing the loading effect during photomask manufacturing, thus applicable for 193 nm ArF lithography and immersion lithography.
Implementation Method 1
a phase-shift mask has been developed to improve both the resolution and DoF of a semiconductor circuit pattern using a phase-shift layer that shifts the phase of exposure light by 180 degrees
Implementation Method 2
The light-shielding film should have a predetermined optical density so as to effectively block light
Data Source
AI summary
Provided are a method of manufacturing a photomask, in which a hardmask film pattern is used as an etch mask for etching a phase-shift layer under the hardmask film pattern, a blankmask, and a photomask using the blankmask. In the method, a resist film for patterning a hardmask film may be formed to a thin thickness, and the phase-shift layer may be etched using the hardmask film pattern having a high etch selectivity with respect to the phase-shift layer. Accordingly, an optical density may be maintained to be 3.0 due to use of a light-shielding film pattern, thereby increasing the resolution and precision of a pattern, reducing a loading effect, and improving critical dimension (CD) features, such as CD uniformity and CD linearity.