Photomask Identification Marker Orientation Control
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Solution Overview
Problem
In photomask manufacturing, the orientation of identification markers on mask blanks changes when rotated, making it difficult to manage and automate the process, as sensors struggle to detect markers with varying orientations, leading to potential human errors and increased costs due to complex marker designs and increased processes.
Innovation Solution
A method where identification markers are formed on at least one end face of the mask blank substrate, allowing for orientation control using a rotating apparatus to maintain a fixed detection direction, enabling automatic placement and rotation to avoid defects during pattern transfer, and subsequent orientation restoration to ensure consistent marker detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the orientation of the mask blank is changed to avoid defective portions, then the defective portion can be avoided during pattern formation, but the orientation of the end face formed with the identification marker changes, making it difficult to manage and detect the mask blanks
Solution Approach 1:
The identification marker is moved from the end face to the main surface of the mask blank. This dimensional change allows the marker to remain in a fixed orientation on the main surface even when the mask blank is rotated in the plane parallel to its main surface, enabling continuous detection by sensors while still allowing defect avoidance through rotation.
Solution Approach 2:
The identification marker is formed on the main surface before any pattern formation or rotation operations. This preliminary positioning ensures that the marker serves as a reliable reference point for both initial orientation detection and subsequent defect avoidance maneuvers throughout the manufacturing process.
2Measurement precision
If the identification marker is provided on only one end face to serve as reference point, then the orientation of the mask blank can be identified, but when the mask blank is rotated to avoid defects, the sensor cannot detect the identification marker due to varying orientation
Solution Approach 1:
The identification marker is relocated from the end face to the main surface of the mask blank. This allows the marker to maintain a consistent position on the main surface during rotations in the plane parallel to the main surface, enabling continuous optical detection while preserving orientation identification capabilities.
3Ease of operation
If the identification marker is formed on all end faces to enable detection from fixed direction, then the marker can be detected regardless of rotation angle, but the cost of the mask blank increases due to labor for designing multiple kinds of identification markers and complexity increases
Solution Approach 1:
The identification marker is extracted from the end face and positioned on the main surface of the mask blank. This extraction eliminates the need to form markers on all end faces, reducing design complexity and manufacturing costs while maintaining the ability to detect the marker from a fixed direction during the manufacturing process.
Solution Approach 2:
The single identification marker on the main surface serves multiple functions: it provides orientation reference, enables defect avoidance through rotation, and remains detectable throughout the manufacturing process. This universal marker replaces the need for multiple end-face markers, simplifying the overall system.
Data Source
AI summary
A photomask manufacturing method includes a defect information storage step of storing defect information of a mask blank, provided with an identification marker on an end face thereof, into an information storage device in correspondence to the identification marker, a placing orientation determination step of determining a placing orientation of the mask blank with respect to an exposure/writing apparatus, and an orientation correction step of performing rotation control of a rotating apparatus so that an orientation of the mask blank coincides with the determined placing orientation.