EUV Mask Blank Stray Light Suppression via Segmented Absorber
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Solution Overview
Problem
Conventional EUV lithography masks face issues with unnecessary exposure of resist due to reflected light from regions outside the mask pattern, particularly during overlay exposure, due to insufficient phase shift effect in the peripheral areas, leading to reduced pattern accuracy and dimension accuracy.
Innovation Solution
The development of an EUV mask with a substrate having a mask pattern region and an EUV light-absorbing region outside the pattern, where the absorber layer's reflectivity is minimized to less than 1% and the absorber layer's thickness is optimized between 10 to 60 nm, combined with a second absorber layer to reduce reflected light, and specific materials like tantalum and nitrogen are used to enhance absorption and etching selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the absorber layer thickness is reduced to improve pattern accuracy, then shadow formation is reduced and pattern accuracy improves, but reflected light from outside the mask pattern region increases causing unnecessary exposure
Solution Approach 1:
The mask structure is segmented into multiple functional regions: the mask pattern region with optimized absorber layer thickness for phase shift effect, and the EUV light-absorbing region outside the pattern with sufficient thickness to absorb stray light. This segmentation allows each region to be optimized for its specific function without compromise.
Solution Approach 2:
Different regions of the mask are assigned different absorber layer thicknesses according to their specific requirements. The mask pattern region has thin absorber layer (10-60 nm) for phase shift effect, while the peripheral EUV light-absorbing region has thicker absorber layer to achieve reflectivity of at most 1%, ensuring local optimization of both pattern accuracy and stray light suppression.
2Manufacturing precision
If the absorber layer thickness is made thin to reduce shadow formation, then dimension accuracy of transferred pattern improves, but the phase shift effect in peripheral areas becomes insufficient leading to reduced contrast
Solution Approach 1:
The mask is divided into mask pattern region where thin absorber layer provides phase shift effect for high contrast, and EUV light-absorbing region where sufficient thickness ensures stray light absorption. This segmentation resolves the contradiction by allowing each region to have appropriate thickness for its function.
Solution Approach 2:
The absorber layer thickness is locally optimized: thin (10-60 nm) in the mask pattern region to maintain phase shift effect and contrast, and thicker in the peripheral EUV light-absorbing region to suppress reflected light while maintaining sufficient contrast through material selection and thickness optimization.
3Ease of manufacture
If a single-layer absorber structure is used to simplify manufacturing, then manufacturing complexity is reduced, but the ability to independently optimize mask pattern region and peripheral region is limited
Solution Approach 1:
The absorber structure is segmented into functionally distinct regions with different thickness requirements. This can be implemented through selective deposition or deposition with selective removal, allowing independent optimization of each region while maintaining manufacturing feasibility through established semiconductor fabrication techniques.
Solution Approach 2:
The mask structure implements local quality by providing different absorber layer characteristics in different regions. This is achieved through controlled deposition processes that can vary thickness locally, or through selective removal of absorber material in the mask pattern region while maintaining sufficient thickness in the peripheral region.
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 configuration effectively suppresses reflected light from outside the mask pattern region, minimizing unnecessary exposure and enabling improved pattern accuracy and dimension accuracy in EUV lithography, allowing for more precise semiconductor manufacturing.
Implementation Method 1
an EUV light-absorbing region located outside the mask pattern region of the substrate... the reflectivity of a surface of the EUV light-absorbing region for EUV light being at most 1%
Implementation Method 2
a reflective layer for reflecting EUV light provided on the mask pattern region of the substrate
Implementation Method 3
the reflectivity of a surface of the absorber layer for EUV light being from 5 to 15%... having a portion in which an absorber layer is present on the reflective layer and a portion in which no absorber layer is present on the reflective layer
Data Source
AI summary
Provision of an EUV mask whereby an influence of reflected light from a region outside a mask pattern region is suppressed, and an EUV mask blank to be employed for production of such an EUV mask.A reflective mask for EUV lithography (EUVL), comprising a substrate having a mask pattern region and an EUV light-absorbing region located outside the mask pattern region; a reflective layer provided on the mask pattern region of the substrate for reflecting EUV light and having a portion on which an absorber layer is present and a portion on which no absorber layer is present; the portion on which an absorber layer is present and the portion on which no absorber layer is present being arranged so as to constitute a mask pattern;wherein the reflectivity of a surface of the absorber layer for EUV light is from 5 to 15% and the reflectivity of a surface of the EUV light-absorbing region for EUV light is at most 1%.