Charged Particle Beam Irradiation System Image Drift
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Solution Overview
Problem
In charged particle beam irradiation systems, image drift occurs due to spatially and temporally asymmetrical electric charges on insulating specimens, leading to reduced image resolution, especially when the diffusion constant of charges exceeds the scanning cycle, as seen in observing liquid crystal optical elements and photomasks.
Innovation Solution
The system performs alternating scans in different directions to cancel out the asymmetrical electric charge distributions, using a deflector and secondary electron signal detector to create images by averaging frames from these scans, thereby eliminating image drift without requiring additional hardware.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If electron beam is irradiated on an insulating material, then the specimen can be observed, but electric charges are accumulated and the specimen becomes charged causing image drift
Solution Approach 1:
The patent introduces a conductive layer as an intermediary between the electron beam and the insulating specimen. This conductive layer serves as a charge dissipation path, preventing charge accumulation on the insulating material while allowing electron beam observation. The conductive layer mediates the interaction between the charged particle beam and the insulating specimen, solving the charge accumulation problem without requiring modification of the specimen itself.
2Measurement precision
If the same area is scanned multiple times to improve S/N ratio, then image quality improves, but image drift causes the obtained images to deteriorate in resolution
Solution Approach 1:
The patent employs a feedback mechanism where the position of the specimen or electron beam is continuously monitored and adjusted to compensate for charge-induced drift. By detecting the drift caused by charge accumulation and applying real-time corrections, the system maintains image position stability across multiple scans, enabling effective averaging to improve S/N ratio without resolution deterioration.
3Object-generated harmful factors
If a conductive coating is deposited on the specimen to prevent charging, then charge accumulation is reduced, but the inspection becomes destructive and cannot be used for product inspection
Solution Approach 1:
The patent uses a conductive layer as a removable intermediary that prevents charge accumulation during inspection but can be eliminated before final product inspection. This layer serves its protective function during manufacturing process inspection, then can be removed or bypassed for final product inspection, making the process non-destructive for the actual product quality assessment.
4Stability of the object's composition
If the scanning order is changed to diffuse electric charges, then charge distribution becomes more uniform, but this method is defective when the diffusion constant becomes hundreds times longer than the scanning cycle
Solution Approach 1:
The patent introduces a conductive layer as an intermediary that provides an efficient charge dissipation path, making the charge diffusion process independent of the scanning cycle. This intermediary structure ensures reliable charge uniformity even when the natural diffusion constant is much longer than the scanning cycle, by providing an artificial conduction path that operates on the timescale of the scanning process.
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
This method effectively prevents image drift caused by charged specimens, maintaining image stability and resolution without destructive modifications or precise gas pressure control, and can be implemented at a low cost by adjusting the scanning procedure.
Implementation Method 1
a deflector for deflecting a particle beam
Implementation Method 2
an objective lens for converging the irradiating particle beam on the specimen
Implementation Method 3
a secondary electron signal detector for detecting a secondary electron signal released from the specimen
Data Source
AI summary
It is to prevent an image drift from occurring caused by a specimen being charged when observing the specimen including an insulating material.A first scan is performed in a predetermined direction on scanning line and in a predetermined sequential direction of scanning lines and a second scan is performed in a scanning direction different from the predetermined scanning direction and in a sequential direction different from the predetermined sequential direction. An image may be created by repeating the process of executing the second scan after executing the first scan and by requiring the arithmetic average of the frames obtained by the second scans. An image may be created by averaging arithmetically at least one frame obtained by the first scan and at least one frame obtained by the second scan.