Recess Reference Mark for EUV Reflective Mask Inspection
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Solution Overview
Problem
The existing reference marks on reflective mask blanks, with a shallow depth, fail to provide sufficient contrast for defect inspection when a multilayer reflective film is formed, leading to low positional accuracy and high defect occurrence rates, which degrades the yield in EUV lithography processes.
Innovation Solution
A recess with a depth of 10 μm or more and a width of 80 μm or more is formed on the substrate as a reference point mark, allowing for high-accuracy defect positioning even under the multilayer reflective film, and the reflective mask blank includes an absorber film and additional films like a buffer and capping film to enhance contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a shallow reference mark (depth about 3 μm) is formed on the substrate, then dust can be prevented from staying in the recess, but sufficient contrast for inspection light cannot be obtained when a multilayer reflective film is laminated, leading to low inspection accuracy
Solution Approach 1:
The patent changes the depth parameter of the reference mark from about 3 μm to 10 μm or more. This parameter change ensures that even after laminating a multilayer reflective film with total thickness of 100 nm to 1 μm, sufficient contrast (reflectivity difference of 10% or more) is maintained for inspection light, thereby achieving both dust prevention and high inspection accuracy
Solution Approach 2:
The reference mark is formed in advance before laminating the multilayer reflective film. By preparing the reference mark with sufficient depth (10 μm or more) beforehand, the patent ensures that the mark maintains adequate contrast throughout the subsequent film lamination process, enabling accurate defect positioning from the outset
2Measurement precision
If the depth of the recess is increased to maintain contrast, then inspection accuracy improves, but the complexity of the manufacturing process increases
Solution Approach 1:
The reference mark is formed as a preliminary step before multilayer film lamination. By establishing the deep recess (10 μm or more) in advance, the patent simplifies the overall process as subsequent film deposition automatically maintains the required contrast without needing additional adjustment steps or complex manufacturing interventions
3Use of energy by moving object
If a multilayer reflective film is laminated on the substrate, then EUV light reflection efficiency improves, but the depth and width of the reference mark recess decrease, reducing contrast for inspection light
Solution Approach 1:
The patent sets the reference mark depth to 10 μm or more, which is sufficiently deep to maintain contrast even after accounting for the 100 nm to 1 μm total thickness of the multilayer reflective film. This parameter ensures that the recess depth remains adequate (maintaining 10% or more reflectivity difference) while allowing the multilayer film to achieve high EUV reflection efficiency
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 accurate defect positioning with micron-level precision, improving the manufacturing accuracy of reflective masks by ensuring sufficient contrast for inspection light, thus reducing defect occurrence and enhancing yield.
Implementation Method 1
a multilayer reflective film (multilayer film) for reflecting the EUV light serving as exposure light is formed on a substrate
Implementation Method 2
high refractive index layers composed mainly of a high refractive index material and low refractive index layers composed mainly of a low refractive index material are alternately laminated
Implementation Method 3
an absorber film (metal film) for absorbing the EUV light is formed in a pattern on the multilayer reflective film
Data Source
AI summary
Provided is a reflective mask blank, wherein even if inspection light for defect inspection is irradiated onto an uppermost surface of a multilayer reflective film or of an absorber film formed over a reference point mark, sufficient contrast is obtained between a position of the reference point mark and its peripheral portion so that the position of the reference point mark can be identified with high accuracy. By forming a reference point mark (11) in the form of a recess having a depth of 10 μm or more and a width of 80 μm or more on a main surface of a substrate (12), even if a multilayer reflective film (13), an absorber film (15), and so on are formed over the reference point mark (11), sufficient contrast for the inspection light is obtained so that the position of the reference point mark (11) can be identified with high accuracy.