Electron Beam Inspection Test Structure Using Lock-In Amplifier
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Solution Overview
Problem
Electron beam inspection tools have poor capability in detecting high-resistance defects due to weak signals from poor signal-to-noise ratio (S/N ratio) and small gray level value differences, making it difficult to determine the degree of failure in semiconductor wafer manufacturing.
Innovation Solution
A test structure with a cap dielectric layer on a connection structure between conductive regions is used, along with a lock-in amplifier to amplify signals received by an instant detector, enhancing the signal-to-noise ratio and accuracy of electron beam inspection by forming a capacitance and utilizing the relaxation time of signals as an additional index for defect determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional electron beam inspection is used to detect high-resistance defects, then the inspection process is simple, but the signal-to-noise ratio is poor and detection accuracy is low
Solution Approach 1:
A lock-in amplifier is introduced as an intermediary device between the electron beam inspection system and the detector. This intermediary amplifies the weak signals from high-resistance defects by comparing them against a reference frequency, effectively separating the defect signals from background noise and significantly improving the signal-to-noise ratio for accurate defect detection.
Solution Approach 2:
The inspection method employs periodic modulation of the electron beam or excitation signal at a specific reference frequency. By using periodic action, the lock-in amplifier can selectively amplify signals at this reference frequency while rejecting non-periodic noise, thereby enhancing the detectability of periodic defect signals in high-resistance structures.
2Measurement precision
If signal amplification is applied to improve defect detection, then the signal-to-noise ratio improves, but the inspection time increases
Solution Approach 1:
By using periodic modulation and lock-in amplification, the system can achieve signal amplification with relatively fast response times. The lock-in amplifier processes signals synchronously with the reference frequency, allowing for rapid accumulation of signal information without requiring excessively long measurement periods, thus balancing improved signal-to-noise ratio with acceptable inspection time.
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
The proposed solution significantly improves the signal-to-noise ratio and accuracy of electron beam inspection, enabling effective detection of defects by amplifying signals and using relaxation time as an index, thereby enhancing the precision of defect determination in semiconductor wafers.
Implementation Method 1
a capacitance may be formed by the cap dielectric layer and used in the electron beam inspection for improving the signal-to-noise ratio (S/N ratio)
Implementation Method 2
signals received by the detector within a period of time are amplified by the lock-in amplifier, and the signal-to-noise ratio and the accuracy of the electron beam inspection may be enhanced accordingly
Data Source
AI summary
A test structure for electron beam inspection and a method for defect determination using electron beam inspection are provided. The test structure for electron beam inspection includes a semiconductor substrate, at least two conductive regions disposed on the semiconductor substrate, a connection structure disposed on the two conductive regions, and a cap dielectric layer disposed on the connection structure. The method for defect determination using the electron beam inspection includes the following steps. An electron beam inspection is preformed to a test structure with an instant detector and a lock-in amplifier. Signals received by the detector within a period of time are amplified by the lock-in amplifier. A defect in the test structure is determined by monitoring the signals received by the detector and amplified by the lock-in amplifier. The inspection accuracy is improved by the test structure and the method for defect determination in the present invention.