EUV Camera Pellicle Positioning for Photomask Inspection
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Solution Overview
Problem
Existing photomask inspection methods risk contamination during the inspection process, which can impair measurement results and potentially transfer contaminants to the photomask, affecting the quality of integrated circuits produced.
Innovation Solution
A method and device using an EUV camera with a pellicle arranged between the projection lens and image sensor, allowing EUV radiation to pass through while blocking particles, reducing contamination risk by ensuring EUV radiation passes through the pellicle only once and using materials like carbon nanotubes or silicon for high transmissivity and particle blocking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a pellicle is arranged in the EUV beam path to prevent contamination, then contamination protection is improved, but EUV radiation power loss increases due to multiple passages through the pellicle
Solution Approach 1:
Instead of placing the pellicle in the conventional position where EUV radiation passes through it twice (before and after reflection at the photomask), the patent inverts the approach by positioning the pellicle between the projection lens and image sensor. This ensures the EUV radiation passes through the pellicle only once, reducing energy loss while maintaining contamination protection.
Solution Approach 2:
The pellicle acts as an intermediary element that selectively blocks particles and contaminants while allowing EUV radiation to pass through. By optimizing its position and using appropriate materials (such as silicon-based materials or carbon nanotubes), it mediates between the need for contamination protection and the requirement to minimize radiation power loss.
2Object-affected harmful factors
If a glass pane is used to protect against contamination in visible light, then contamination protection is improved, but EUV radiation absorption increases preventing sufficient intensity from reaching the image sensor
Solution Approach 1:
The patent changes the material parameter from conventional glass (which absorbs EUV radiation) to specialized materials such as silicon-based materials or carbon nanotubes. These materials have different optical properties that allow high transmissivity for EUV radiation while maintaining particle blocking capability, thus resolving the contradiction between contamination protection and radiation intensity.
Solution Approach 2:
The pellicle may be constructed using composite material structures, such as silicon nitride membranes or carbon nanotube arrays, which combine the properties of particle filtration with high EUV radiation transmissivity. These composite structures achieve both contamination protection and sufficient radiation intensity transmission.
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
The solution effectively reduces contamination risk during photomask inspection, maintaining measurement accuracy and preventing contamination from the inspection process, while ensuring sufficient EUV radiation intensity reaches the image sensor, thus ensuring high-quality image recording.
Implementation Method 1
A pellicle refers to a membrane that is designed to allow EUV radiation to pass through but suppresses a passage of particles
Implementation Method 2
The pellicle is a CNT (carbon nanotubes) pellicle, i.e. a membrane made of carbon nanotubes. The density and the bundle structure of the carbon nanotubes can be chosen such that the membrane is transmissive to EUV radiation on the one hand, while, on the other hand, particles are stopped at the membrane
Implementation Method 3
a photomask is illuminated by very short-wave extreme ultraviolet radiation (EUV radiation)
Implementation Method 4
EUV radiation reflected at the photomask is guided via a projection lens to an image sensor of an EUV camera such that the photomask is imaged on the image sensor
Data Source
AI summary
A method for inspecting photomasks, in which a photomask is illuminated by EUV radiation emitted by an EUV radiation source). EUV radiation reflected at the photomask is guided via a projection lens to an image sensor of an EUV camera such that the photomask is imaged on the image sensor. The EUV radiation passes through a pellicle which is arranged between the projection lens and the image sensor. The invention also relates to an EUV camera and to a measuring device for inspecting photomasks.