Reflective Mask Blank Coordinate Marking for Phase Defect Control
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Solution Overview
Problem
Existing methods for manufacturing reflective masks struggle to accurately detect and avoid phase defects in the multilayer reflection film, leading to reduced reflectance and difficulty in forming absorber patterns without further defects.
Innovation Solution
A method involving the formation of a coordinate reference mark on the conductive film opposite to the multilayer reflection film, allowing for precise detection and correction of phase defects by referencing the mark, enabling accurate positioning of the absorber pattern to avoid defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a phase defect detection method using dark field inspection or X-ray microscopy is employed, then phase defects in the multilayer reflection film can be accurately detected, but the position of the phase defect cannot be precisely determined after the absorber pattern is formed
Solution Approach 1:
The patent applies preliminary action by forming a coordinate reference mark on the substrate before forming the multilayer reflection film and absorber pattern. This reference mark serves as a permanent positional reference that remains accessible after subsequent layers are formed, allowing the position of phase defects to be determined relative to this pre-established coordinate system throughout the manufacturing process.
Solution Approach 2:
The patent transitions from attempting to detect phase defects only in the film layer to establishing a three-dimensional coordinate reference system that extends through the substrate. By placing the reference mark on the substrate rather than within the thin film layers, the system creates a stable reference point that can be used for positional determination across multiple processing steps and inspection stages.
2Reliability
If the absorber pattern is formed to avoid phase defects by modifying the pattern contour, then the influence of phase defects can be mitigated, but it requires accurate positioning information of phase defects which is difficult to obtain after patterning
Solution Approach 1:
The coordinate reference mark is formed in advance on the substrate before the multilayer reflection film and absorber pattern are created. This preliminary establishment of a coordinate system allows for consistent positional measurement and tracking of phase defects throughout the manufacturing process, enabling accurate pattern modification to avoid defects.
Solution Approach 2:
The coordinate reference mark acts as an intermediary element that bridges the substrate and the subsequent film layers. It provides a stable reference framework that allows inspection systems to accurately locate phase defects relative to the final absorber pattern, even after multiple processing steps have been completed.
3Measurement precision
If a coordinate reference mark is formed on the one main surface side where the multilayer reflection film is formed, then defect position can be determined, but the mark becomes buried under subsequent films making accurate positioning difficult
Solution Approach 1:
Instead of placing the coordinate reference mark on the conventional side (the side where the multilayer reflection film is formed), the patent inverts the approach by forming the reference mark on the opposite side of the substrate. This ensures the reference mark remains exposed and accessible throughout the manufacturing process, serving as a reliable coordinate reference for positioning the absorber pattern.
Solution Approach 2:
The coordinate reference mark is formed in advance on the substrate before any film deposition occurs. This preliminary action ensures the reference mark is established as a permanent feature that will not be buried or obscured by subsequent processing steps, maintaining its utility for positional measurement throughout manufacturing.
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
Enables high-accuracy detection and mitigation of phase defects, improving the formation of absorber patterns and reducing the influence of defects in the multilayer reflection film, thereby enhancing the yield and productivity of reflective masks.
Implementation Method 1
optical system used for detection of the coordinate reference mark
Implementation Method 2
a multilayer reflection film that is formed on a substrate and reflects EUV light
Implementation Method 3
an absorber film for EUV light absorption formed on one main surface of the substrate
Data Source
Figure 1A~1B
Figure 2A~2C
Figure 3A~3C
AI summary
A reflective mask blank includes a substrate (101), and a multilayer reflection film (102) for EUV light reflection, a protection film (103), and an absorber film (104) for EUV light absorption formed on one main surface of the substrate in that order from the substrate side, and a conductive film (105) formed on the other main surface of the substrate, and a coordinate reference mark (106) formed on the other main surface side. The reference mark (106) is used to define the position of defects found on the one main surface of the blank. Subsequent processing by patterning of the absorber film (104) can be adjusted to mitigate their effect.