Reference Point Mark with Upright Walls for EUV Reflective Mask
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Solution Overview
Problem
The existing reference marks on reflective mask blanks, formed with a shallow concave shape, struggle to provide sufficient contrast for defect inspection due to the stacking of multilayer reflective films, capping films, and absorber films, leading to low detection accuracy and high defect occurrence rates.
Innovation Solution
A multilayer reflective film coated substrate with a reference point mark having a concave or convex shape and upright side walls is developed, allowing for sufficient contrast detection with inspection light or an electron beam, even with a depth or height of 30 nm or more, and enabling accurate defect position specification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a shallow concave reference mark is formed on the substrate, then dust can be prevented from staying in the recess, but the depth and width of the recess decrease upon laminating multilayer reflective films, resulting in insufficient contrast for inspection light
Solution Approach 1:
The invention changes the geometric parameters of the reference mark by forming it with upright side walls instead of a shallow concave shape. This structural modification maintains the mark's visibility through multilayer films while preventing dust accumulation, resolving the contradiction between dust prevention and detection accuracy
Solution Approach 2:
The invention transitions from a two-dimensional shallow concave mark to a three-dimensional structure with upright side walls and significant depth. This dimensional change allows the reference mark to maintain sufficient contrast through multiple film layers while preserving its dust-free characteristics
2Measurement precision
If the depth of the reference mark recess is increased to improve contrast detection, then detection accuracy improves, but dust is more likely to stay in the deeper recess
Solution Approach 1:
Instead of creating a concave recess that traps dust, the invention inverts the approach by forming a convex structure or a concave structure with upright walls that prevent dust entrapment. This inversion allows deep structures to be created without the harmful dust accumulation effect
Solution Approach 2:
The invention employs asymmetric wall angles in the reference mark structure, with upright or converging side walls that create a geometry unfavorable for dust retention. This asymmetric design enables deep structures that maintain detection accuracy while preventing dust contamination
3Productivity
If YAG laser irradiation is used to form the reference mark, then the reference mark can be formed efficiently, but the edge roughness of the formed portion becomes large, reducing detection accuracy
Solution Approach 1:
The invention replaces the thermal field method (YAG laser irradiation) with a mechanical field method (ion beam irradiation). This substitution eliminates the edge roughness problem caused by thermal effects while maintaining efficient mark formation capability
Solution Approach 2:
The invention changes the formation method parameters from laser-based thermal processing to ion beam-based physical sputtering. This parameter change produces smoother edges with lower roughness while maintaining productive mark formation
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 enables high-accuracy detection of reference point marks, allowing for precise defect avoidance during pattern transfer and reducing defect occurrence rates in reflective mask manufacturing.
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
the multilayer reflective film having a structure in which 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
Implementation Method 4
enabling sufficient contrast detection with inspection light or an electron beam
Implementation Method 5
enabling sufficient contrast detection with inspection light or an electron beam
Data Source
AI summary
By forming on a substrate a reference point mark having a concave or convex shape with its side walls being generally upright, even if a multilayer reflective film, an absorber film, and so on are formed over the reference point mark, sufficient contrast for inspection light is obtained so that the position of the reference point mark can be identified with high accuracy.