Charged Particle Beam Signal Synthesis for Noise Reduction
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Solution Overview
Problem
Scanning electron microscopes face challenges in achieving a balance between noise reduction and dosage reduction, particularly when imaging miniaturized semiconductor devices, as increasing the number of frames improves image quality but increases electron dosage and risks sample damage, and existing noise reduction methods are inefficient and difficult to adjust for varying sample types and apparatus conditions.
Innovation Solution
A method and apparatus that synthesizes signals from multiple scans by multiplying and calculating the inverse of the number of scans, effectively reducing noise while maintaining signal stability and reducing electron dosage, using a calculating unit and pixel-multiplying unit to process image signals across frames.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of frames is increased to reduce noise and improve image quality, then image quality and length measurement repeatability are improved, but electron dosage increases and sample damage occurs
Solution Approach 1:
The patent changes the signal synthesis parameter from arithmetic mean to geometric mean (multiplication followed by exponentiation with 1/N). This mathematical transformation allows achieving the same noise reduction effect with fewer frames, thereby reducing electron dosage and sample damage while maintaining image quality.
2Measurement precision
If the number of frames is increased to reduce noise, then noise reduction effect is improved, but image capture time increases
Solution Approach 1:
By changing the signal synthesis method from arithmetic mean to geometric mean, the patent achieves equivalent or superior noise reduction with fewer frames. This reduces the total scanning time required while maintaining the noise reduction effect, thus resolving the time-consuming issue of conventional multi-frame averaging.
3Measurement precision
If the number of frames is increased to improve image quality, then signal-to-noise ratio is improved, but charge amount on sample surface increases causing field of view drifting and image distortion
Solution Approach 1:
The patent applies geometric mean synthesis instead of arithmetic mean, which achieves the same signal-to-noise ratio improvement with fewer frames. This reduces the total charge accumulated on the sample surface, thereby minimizing field of view drifting and image distortion while maintaining high signal-to-noise ratio.
4Measurement precision
If conventional averaging method is used to reduce noise, then noise suppression is achieved, but adjustment for varying sample types and apparatus conditions is difficult
Solution Approach 1:
The geometric mean synthesis method is inherently adaptive to different sample types and apparatus conditions without requiring manual parameter adjustment. The mathematical operation automatically optimizes the synthesis result based on the input signal characteristics, providing self-adaptive noise suppression that works effectively across various conditions.
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 approach allows for stable synthesized signals with reduced noise, enabling high SN ratio images even with a small number of frames, such as 16 frames or less, while minimizing sample damage from electron beam irradiation.
Implementation Method 1
When an electron beam is accelerated and irradiated on a sample in a vacuum, depending on the surface condition of the sample, secondary electrons (SE) or backscattered electrons (BSE) are emitted from the sample surface
Data Source
AI summary
An object of the present invention is to provide a synthesized signal forming method and an apparatus thereof for realizing both noise reduction and dosage reduction when synthesizing signals detected based on scans performed on a charged particle beam. In order to achieve the above object, with a method that synthesizes signals detected based on a plurality of scans performed on a charged particle beam to form a synthesized signal, a multiplication is performed among a plurality of signals obtained by the plurality of scans and, at the same time, for a multiplied signal, a calculation is performed in which an inverse of the number of previous scans is used as an exponent.