Transient Contrast Defect Detection in Semiconductor Circuitry
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Solution Overview
Problem
Voltage contrast defect detection in scanning electron microscopes is complicated by the dependency on secondary electron escape probability and collection efficiency, which is affected by non-uniform surface potentials, and often results in background noise overwhelming the defect of interest, making it difficult to isolate and detect subsurface defects effectively.
Innovation Solution
The method involves manipulating transient contrast by adjusting scan rates and directions, specifically using parallel and perpendicular scans, and varying time delays to isolate the defect of interest by exploiting the RC time constant of the structure, allowing for effective suppression of background noise and identification of defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage contrast detection is used to detect subsurface defects, then detection capability is improved, but background noise from other defects overwhelms the defect of interest
Solution Approach 1:
The inspection process is segmented into multiple scans with different scan rates. By dividing the inspection into sequential scans (first scan at first scan rate, second scan at second scan rate), the method isolates defects with specific RC time constants, thereby separating the defect of interest from background noise and enabling selective detection.
2Measurement precision
If scan rate is reduced to enhance transient contrast, then defect visibility is improved, but inspection productivity decreases
Solution Approach 1:
The scan rate is dynamically adjusted between different scans based on the RC time constant characteristics of the defects being inspected. The system transitions between different scan rates (first scan rate for initial inspection, second scan rate for enhanced transient contrast), optimizing both productivity and defect visibility for different inspection phases.
3Measurement precision
If multiple scans with different scan rates are performed, then defect isolation is improved, but inspection time increases
Solution Approach 1:
The inspection method changes the scan rate parameter between scans to exploit the RC time constant characteristics of different defects. By performing a first scan at a first scan rate and a second scan at a second scan rate, the method identifies defects with specific time constant characteristics, enabling selective defect isolation while minimizing unnecessary inspections.
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 the reliable detection and isolation of defects by enhancing the visibility of transient contrast without compromising scan rates, thereby improving the accuracy and efficiency of defect detection in multi-layer structures like semiconductor wafers.
Implementation Method 1
contrast formation is directly related to the emission of secondary and/or backscattering electrons from the defect in question
Implementation Method 2
the probability that secondary electrons escape from a specimen may be modulated substantially by the surface potential
Data Source
AI summary
One embodiment relates to a method for detecting defects in circuitry formed on a semiconductor substrate. A first scan of said circuitry is performed by scanning a primary electron beam in a first scan direction relative to said circuitry, and secondary electrons emitted during the first scan are detected so as to form a first voltage-contrast image. A second scan of said circuitry is performed by scanning the primary electron beam in a second scan direction relative to said circuitry, and secondary electrons emitted during the second scan are detected so as to form a second voltage-contrast image. The second scan direction is non-parallel to the first scan direction. The first and second voltage-contrast images are then compared to detect electrically-active defects. Other embodiments, aspects and features are also disclosed.