Reflective EUV Mask Contamination Inspection Pattern
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Solution Overview
Problem
The use of extreme ultraviolet (EUV) light in semiconductor lithography requires reflective masks, but C-based contamination accumulates on these masks, leading to decreased reflectance and pattern dimension variations, making it difficult to distinguish contamination on the mask from contamination in the optical system, resulting in reduced process margins and yield.
Innovation Solution
A reflective exposure mask structure with a support substrate, a reflective multilayer film, and an absorption layer, including a contamination inspection pattern, allows for the differentiation of contamination on the mask by measuring variations in wafer transfer patterns, enabling efficient contamination monitoring and cleaning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a reflective exposure mask is used for EUV lithography, then pattern width reduction and manufacturing precision are improved, but contamination accumulates on the mask leading to decreased reflectance and pattern dimension variations
Solution Approach 1:
The patent segments the mask surface into two distinct regions: a reflective region with high reflectance for normal exposure, and a low-reflective region with reduced reflectance for contamination inspection. This segmentation allows simultaneous monitoring of contamination accumulation while maintaining exposure functionality, resolving the contradiction between maintaining high reflectance and detecting contamination that degrades reflectance.
Solution Approach 2:
The low-reflective region acts as an intermediary indicator region that mediates between the exposure function and contamination monitoring function. By comparing the reflected light intensity from this intermediary region against reference values, the system can detect contamination accumulation without interfering with the primary exposure function of the reflective region.
2Measurement precision
If direct measurement of contamination on the reflective mask is performed, then measurement precision is improved, but device downtime and productivity are reduced due to mask movement
Solution Approach 1:
The mask structure provides self-inspection capability through the integrated low-reflective region. The mask itself serves as the measurement target, eliminating the need to move the mask to a separate measuring device. The contamination inspection pattern on the mask enables in-situ monitoring, allowing the mask to inspect itself during the exposure process without causing downtime.
3Productivity
If monitoring is based on wafer transfer pattern dimensions, then productivity is maintained, but measurement precision is reduced due to inability to distinguish mask contamination from optical system contamination
Solution Approach 1:
The patent applies local quality by creating a specific low-reflective region with distinct optical properties different from the surrounding reflective regions. This localized region with different reflectance characteristics serves as a dedicated contamination sensor, enabling precise identification of mask contamination versus optical system contamination by comparing light reflection patterns from this specific local area against reference values.
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 solution allows for accurate determination and removal of contamination on the reflective mask, improving pattern precision and process yield by distinguishing mask contamination from contamination in the optical system, thus maintaining optimal exposure conditions.
Implementation Method 1
a reflective multilayer film formed on the support substrate and having a light reflecting part which reflects the exposure light
Implementation Method 2
an absorption layer formed on the light reflecting part and having a light absorbing part which absorbs the exposure light
Data Source
AI summary
According to one embodiment, a reflective exposure mask comprises a first layer formed on a substrate and including a first light absorbing part which absorbs exposure light and a light reflecting part which reflects the exposure light, and a second layer formed on the light reflecting part and including a second light absorbing part which absorbs the exposure light.