EUV Photomask Imaging Through Pellicle Using Gas Amplification
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Solution Overview
Problem
Conventional scanning electron microscopy systems struggle to effectively image photomasks through protective pellicles, especially those used in extreme ultraviolet (EUV) lithography, due to limitations in detecting small defect particles and the conductive pellicle's interference with electron imaging.
Innovation Solution
A scanning electron microscopy (SEM) system and method that includes an electron beam source, sample stage, and electron-optical column to direct the electron beam through a pellicle, using backscattered and secondary electron detection, as well as a pressurized gas medium to amplify weak secondary electrons, allowing for improved imaging of photomasks through the pellicle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protective pellicle film is positioned above the photomask to protect it, then the photomask is protected from damage, but the ability of conventional imaging systems to image the photomask is severely limited
Solution Approach 1:
The patent introduces a gas medium as an intermediary between the electron beam and the photomask surface. This gas medium serves as a mediator that allows electron beam penetration while maintaining the protective function of the pellicle, thereby resolving the contradiction between protection and imaging capability
Solution Approach 2:
The patent changes the physical state and parameters of the imaging environment by introducing a pressurized gas medium. This parameter change enables the electron beam to interact with the photomask through the gas, overcoming the blocking effect of the pellicle while maintaining protection
2Device complexity
If conventional secondary electron detectors are used to image the photomask, then the system structure remains simple, but the detection of small defect particles as small as 10 nm in diameter is severely limited
Solution Approach 1:
The patent replaces conventional mechanical secondary electron detectors with a gas-based detection mechanism. The gas medium interacts with the electron beam to produce detectable signals that provide much higher measurement precision for small defect particles, while the overall system structure remains relatively simple
3Ease of operation
If the electron beam is directed through the pellicle onto the photomask, then imaging can be achieved, but the electron signal is weakened and requires amplification
Solution Approach 1:
The gas medium acts as an energy amplification intermediary, where the electron beam interacts with the gas molecules to generate secondary electrons and photons. This intermediary process amplifies the weak electron signal that would otherwise be lost when passing through the pellicle, maintaining adequate signal strength for imaging
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 the detection of small defects on photomasks, such as phase defects and haze formation, by collecting backscattered and secondary electrons, and amplifying weak signals, enhancing the resolution and sensitivity of EUV photomask inspection.
Implementation Method 1
an electron beam source configured to generate an electron beam
Implementation Method 2
an electron-optical column including a set of electron-optical elements to direct at least a portion of the electron beam through the pellicle
Implementation Method 3
detecting at least one of backscattered electrons scattered from the surface of the sample
Implementation Method 4
secondary electrons emitted from the surface of the sample
Implementation Method 5
the selected gas amplifies electrons emanating from the surface of the sample
Data Source
AI summary
A system for imaging a sample through a protective pellicle is disclosed. The system includes an electron beam source configured to generate an electron beam and a sample stage configured to secure a sample and a pellicle, wherein the pellicle is disposed above the sample. The system also includes an electron-optical column including a set of electron-optical elements to direct at least a portion of the electron beam through the pellicle and onto a portion of the sample. In addition, the system includes a detector assembly positioned above the pellicle and configured to detect electrons emanating from the surface of the sample.