EUV Mask Pellicle Swapping for Interference-Free Inspection
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Solution Overview
Problem
The use of pellicles in EUV lithographic apparatuses is challenging due to the need for maintaining a vacuum environment and the reflective nature of the masks, which complicates the inspection and attachment of pellicles without interfering with the inspection beam.
Innovation Solution
A method involving the removable attachment of an alternative pellicle transparent to the inspection beam, allowing inspection without interference from the EUV transparent pellicle, followed by reattachment of the EUV transparent pellicle after inspection, while maintaining a clean environment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an EUV transparent pellicle is attached to the mask, then the mask is protected from particle contamination, but the pellicle interferes with inspection beam transmission
Solution Approach 1:
The pellicle attachment system is segmented into a mask, a pellicle frame, and an attachable/detachable pellicle. This allows the pellicle to be removed during inspection and reattached for operation, resolving the contradiction between protection and inspection accessibility
Solution Approach 2:
The pellicle attachment mechanism is made dynamic rather than permanent. The pellicle can be attached when protection is needed and detached when inspection is required, allowing the system to adapt its state based on operational requirements
2Use of energy by moving object
If the pellicle is made transparent to EUV radiation, then EUV lithography can proceed, but the pellicle becomes opaque to inspection beams
Solution Approach 1:
The system dynamically switches between having the pellicle attached (for EUV operation) and detached (for inspection). This temporal separation allows the pellicle to be EUV-transparent when needed while not blocking inspection beams when removed
Solution Approach 2:
The inspection process is segmented into phases where the pellicle is removed before inspection and reattached after, allowing separate optimization for both EUV transmission and inspection beam transmission at different times
3Reliability
If the pellicle frame is permanently attached to the mask, then the pellicle remains securely in place, but the mask cannot be easily inspected or maintained
Solution Approach 1:
The attachment mechanism is designed to be dynamically reversible. The pellicle frame can be securely attached during operation and easily detached for inspection, providing both security and accessibility as needed
Solution Approach 2:
The attachment system is segmented into separate components (mask, pellicle frame, pellicle) with standardized interfaces. This modular design allows the pellicle to be securely mounted yet easily removed and reattached, facilitating maintenance and inspection
Data Source
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AI summary
A method comprising the steps of receiving a mask assembly comprising a mask and a removable EUV transparent pellicle held by a pellicle frame, removing the pellicle frame and EUV transparent pellicle from the mask, using an inspection tool to inspect the mask pattern on the mask, and subsequently attaching to the mask an EUV transparent pellicle held by a pellicle frame. The method may also comprise the following steps: after removing the pellicle frame and EUV transparent pellicle from the mask, attaching to the mask an alternative pellicle frame holding an alternative pellicle formed from a material which is substantially transparent to an inspection beam of the inspection tool; and after using an inspection tool to inspect the mask pattern on the mask, removing the alternative pellicle held by the alternative pellicle frame from the mask in order to attach to the mask the EUV transparent pellicle held by the pellicle frame.