SEM Brightness Matching by Pattern Density for Wafer Imaging
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Solution Overview
Problem
Conventional brightness adjustment mechanisms in electron microscopes are inefficient, especially for samples with varying electron emission efficiency and pattern densities, leading to unstable inspection and measurement results and reduced throughput during large-area scanning.
Innovation Solution
A method that determines a reference area with specific pattern density, calculates adjustment areas with similar densities, and adjusts brightness parameters to match the reference area, allowing for continuous image generation with stable brightness without decreasing throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If beam irradiation is performed on a narrow area for brightness adjustment, then brightness can be adjusted based on histogram, but brightness changes with each beam irradiation and correct brightness adjustment may not be achieved
Solution Approach 1:
The patent creates a virtual reference area by copying the imaging position coordinates to the reference area coordinates, allowing brightness adjustment based on the reference area's pattern density rather than performing physical beam irradiation on a narrow adjustment area. This eliminates the brightness change caused by repeated beam irradiation while maintaining accurate brightness adjustment.
2Ease of manufacture
If brightness is adjusted at a location distant from the imaging position, then brightness adjustment can be performed, but the adjustment may not be correct due to beam irradiation history effects
Solution Approach 1:
The patent introduces a reference area as an intermediary between the imaging position and the brightness adjustment mechanism. The reference area serves as a mediator that captures the local pattern density characteristics without being affected by beam irradiation history, enabling accurate brightness adjustment without direct beam irradiation on the imaging position.
3Adaptability or versatility
If brightness adjustment is performed in areas with different pattern densities, then brightness can be adjusted for various targets, but stable brightness adjustment cannot be achieved
Solution Approach 1:
The patent applies local quality by matching the reference area's pattern density to the imaging position's pattern density. By selecting reference areas with similar pattern densities (within a predetermined range), the system ensures that brightness adjustment parameters are appropriate for the local characteristics of each imaging position, achieving both adaptability and stability.
4Measurement precision
If beam irradiation is performed for brightness adjustment, then brightness can be adjusted, but additional time is consumed and throughput is reduced
Solution Approach 1:
The patent replaces the mechanical beam irradiation process with a computational approach. Instead of using the electron beam to irradiate adjustment areas for brightness adjustment, the system uses coordinate copying and pattern density calculation to determine appropriate brightness parameters, eliminating the time-consuming beam irradiation step while maintaining brightness adjustment capability.
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 enables stable brightness adjustment across multiple target areas with minimal additional time, maintaining high throughput by using reference and adjustment areas with similar pattern densities, reducing the need for frequent brightness recalibration.
Implementation Method 1
a sample whose electron emission efficiency is likely to change due to beam irradiation
Data Source
AI summary
The method includes: determining a reference area in a surface of the workpiece; calculating a pattern density of the reference area from design data for patterns in the reference area; determining adjustment areas having pattern densities that approximate the calculated pattern density within a predetermined range; generating an image of the reference area with a scanning electron microscope; generating an image of one of the adjustment areas with the scanning electron microscope; adjusting set values of parameters for adjusting the brightness of the image of the one adjustment area so as to reduce a difference between a brightness histogram of the image of the one adjustment area and a brightness histogram of the image of the reference area; and generating images of intermediate areas in the surface of the workpiece with the scanning electron microscope.