Superposition Measurement Using Layer-Specific Contrast Optimization
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Solution Overview
Problem
Conventional superposition measurement techniques using scanning electron microscopes face challenges in achieving high accuracy due to low signal-to-noise ratios for lower-layer patterns, requiring multiple frame additions and suboptimal contrast for both upper and lower-layer patterns.
Innovation Solution
A superposition measuring apparatus and method that optimize image contrast for upper and lower-layer patterns by generating separate added images using charged particle ray irradiation, allowing for precise position measurement between layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional simple frame adding processing is used to measure superposition error, then the signal-to-noise ratio of the lower-layer pattern can be increased, but the contrast is not optimal for both upper-layer and lower-layer patterns and multiple additions are required
Solution Approach 1:
The patent segments the image processing into two distinct contrast optimization paths: one for upper-layer patterns and one for lower-layer patterns. By dividing the processing into separate contrast optimization stages rather than using a single simple frame addition approach, the system achieves optimal contrast for both layers simultaneously, reducing the number of frame additions needed while maintaining high measurement precision.
Solution Approach 2:
The patent applies different contrast optimization settings to different regions/layers of the semiconductor structure. Upper-layer patterns receive one type of contrast optimization while lower-layer patterns receive another type, allowing each layer to be measured with optimal contrast specific to its characteristics, thereby improving measurement accuracy without requiring excessive frame additions.
2Measurement precision
If the scanning electron microscope is used to measure superposition error between upper-layer and lower-layer patterns, then position measurement can be performed, but the signal-to-noise ratio of the lower-layer pattern is often lower
Solution Approach 1:
The patent changes the contrast parameters differently for upper-layer and lower-layer pattern images. By adjusting contrast parameters specifically optimized for each layer's signal characteristics, the system enhances the signal-to-noise ratio for the lower-layer pattern while maintaining measurement capability for both layers, thereby improving reliability without sacrificing position measurement precision.
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 high-accuracy superposition measurement between different semiconductor layers by optimizing image contrast for each layer, enhancing measurement precision and reducing the need for multiple frame additions.
Implementation Method 1
measure a difference between a position of an upper-layer pattern of a sample and a position of a lower-layer pattern thereof by using an image obtained by irradiation of a charged particle ray
Data Source
AI summary
When a scanning electron microscope is used to measure a superposition error between upper-layer and lower-layer patterns, an SN of the lower-layer pattern may often be lower, so that when simple frame adding processing is used, the adding processing needs to be performed many times. Further, in an image obtained through such simple adding processing, contrast may not be optimal for both the upper-layer and lower-layer patterns. In a superposition measuring apparatus and superposition measuring method that measure a difference between a position of an upper-layer pattern and a position of a lower-layer pattern by using an image obtained by irradiation of a charged particle ray, portions of images having contrasts optimized for the respective upper-layer and lower-layer patterns are added to generate a first added image optimized for the upper-layer pattern and a second added image optimized for the lower-layer pattern, and the difference between the position of the upper-layer pattern identified by using the first added image and position of the lower-layer pattern identified by using the second added image is calculated.