SEM Overlay Measurement Using SUMLINE Profiles at Low SNR
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Solution Overview
Problem
Existing overlay measurement techniques struggle to achieve accurate pattern shift measurement between layers in highly miniaturized semiconductor devices, particularly when using charged particle radiation, due to low signal-to-noise ratios and reduced throughput caused by high electron beam energy and increased frame numbers.
Innovation Solution
An overlay measurement system utilizing a scanning electron microscope with secondary and backscattered electron detectors, forming secondary and backscattered electron images, and creating a SUMLINE profile to calculate overlay error using positional information from these images, reducing the need for high electron beam energy and frame numbers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If larger energy is applied to the sample to detect the unexposed pattern, then measurement accuracy is improved, but resist shrinkage increases and throughput decreases
Solution Approach 1:
The patent changes the detection parameter from direct high-energy electron beam imaging to optical imaging of fluorescent signals. By converting the detection method to optical wavelengths and using fluorescent markers, the system achieves pattern detection without applying harmful high-energy electron beams that cause resist shrinkage, thus maintaining measurement accuracy while eliminating the harmful effect.
Solution Approach 2:
The patent introduces fluorescent markers as intermediaries between the electron beam and the detection system. These markers are attached to the unexposed pattern and emit fluorescent signals when excited, allowing indirect detection of the pattern position without directly imaging the sensitive resist material with high-energy electrons, thereby preventing resist shrinkage while maintaining measurement capability.
2Measurement precision
If cumulative frame number is increased to achieve clear image, then measurement accuracy is improved, but throughput decreases
Solution Approach 1:
The patent uses fluorescent markers as intermediaries that emit strong optical signals when excited by the electron beam. These fluorescent signals provide high-contrast, easily detectable markers for pattern position determination, achieving clear image quality with minimal frame numbers and thus maintaining high measurement throughput.
Solution Approach 2:
The patent changes the imaging modality from direct electron microscopy to optical fluorescence detection. This parameter change enables pattern detection with much lower signal integration requirements, as fluorescent signals provide high contrast and are easily distinguishable from background noise, allowing accurate measurement with reduced cumulative frame numbers and improved throughput.
3Productivity
If optical measurement techniques are used, then throughput is maintained, but measurement accuracy is insufficient for highly miniaturized devices
Solution Approach 1:
The patent introduces fluorescent markers as intermediaries that bridge the gap between optical detection capabilities and nanoscale pattern dimensions. The fluorescent markers provide optically detectable signals at the location of miniaturized patterns, enabling optical measurement systems to achieve the precision required for highly miniaturized semiconductor devices while maintaining high throughput.
Solution Approach 2:
The patent changes the detection parameter from direct optical imaging of physical patterns to optical detection of fluorescent signals. This parameter transformation enables the measurement system to overcome the diffraction limit and achieve high measurement precision for miniaturized patterns using optical techniques, thereby maintaining both accuracy and throughput.
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 accurate overlay error measurement with low signal-to-noise ratios and improved throughput by optimizing image acquisition with reduced electron beam exposure, enhancing measurement precision and efficiency.
Implementation Method 1
an electron optical system that applies a primary electron beam to the sample
Implementation Method 2
a secondary electron detector that detects secondary electrons among signal electrons emitted by scanning a surface of the sample with the primary electron beam
Implementation Method 3
a backscattered electron detector that detects backscattered electrons among the signal electrons
Data Source
AI summary
The present invention enables an overlay error between processors to be measured from a pattern image, the SN ratio of which is low. To this end, the present invention forms a secondary electron image 200 from a detection signal of a secondary electron detector 107, forms a reflected electron image 210 from a detection signal of a reflected electron detector 109, creates a SUMLINE profile 701 that is obtained by adding luminance information in the reflected electron image along the longitudinal direction of a line pattern, and calculates an overlay error of a sample by using position information about an upper layer pattern detected from the secondary electron image and position information about a lower layer pattern that is detected by using an estimation line pattern 801 estimated on the basis of the SUMLINE profile from the reflected electron image.