Semiconductor Inspection Device Electron Beam Absorption Current Sensitivity
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Solution Overview
Problem
Current electron beam absorbed current (EBAC) observation methods face challenges in detecting small resistance defects due to blunt contrast in images, loss of information during digital processing, and interference from capacitive time constants and mixed semiconductor and metal layers, which hinders precise failure analysis in fine-structured devices.
Innovation Solution
A semiconductor inspection device that utilizes a sample stage, electron optical system, measurement probe, and information processing device to acquire and process measurement values by distinguishing between electron beam radiation and non-radiation periods, creating detailed electrical characteristic map images and voltage or current maps to enhance sensitivity and accuracy in defect detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a larger probe current is used to increase the voltage signal for small resistance defects, then the detection sensitivity is improved, but the quality of the defective portion changes due to excessive radiation
Solution Approach 1:
The patent applies periodic action by using alternating current (AC) excitation signals instead of direct current (DC) to drive the electron beam. This periodic excitation allows the measurement system to operate at specific frequencies where the signal-to-noise ratio is optimized, enabling detection of small resistance defects without requiring excessive electron beam current that would damage the sample. The AC modulation technique separates the measurement signal from background noise and DC offsets.
Solution Approach 2:
The patent implements feedback through lock-in amplification techniques where the detected signal is continuously compared with the reference excitation signal. The system uses phase-sensitive detection to provide feedback that enhances the desired signal while rejecting noise and interference. This feedback mechanism allows for high-sensitivity measurement at low electron beam currents by amplifying only the signal component that is coherent with the excitation frequency.
2Ease of operation
If digital processing is applied to enhance the EBAC image, then the visualization is improved, but information is lost due to blackening of contrast
Solution Approach 1:
The patent applies preliminary action by performing analog signal processing and noise filtering before the signal is digitized and displayed. The lock-in amplifier and bandpass filters are applied in the analog domain to preserve the full dynamic range of the measurement signal before it undergoes digital processing. This ensures that contrast information is preserved throughout the measurement and processing chain.
Solution Approach 2:
The patent uses partial action by selectively processing only the relevant signal components through digital filtering and enhancement techniques. Instead of applying aggressive digital processing to the entire signal range, the system focuses enhancement on the specific frequency bands and signal components that contain the measurement information, thereby avoiding information loss in other parts of the signal spectrum.
3Measurement precision
If a lock-in amplifier is introduced to increase sensitivity, then the measurement sensitivity is improved, but the measurement signal is attenuated when capacitive time constant is present
Solution Approach 1:
The patent applies dynamics by making the measurement system adaptable to different sample characteristics through variable frequency excitation and adjustable time constants. The system can dynamically adjust the excitation frequency and lock-in amplifier time constant based on the capacitive properties of the sample, ensuring optimal signal detection without excessive attenuation. This dynamic adjustment allows the system to maintain high sensitivity across a range of capacitive time constants.
Solution Approach 2:
The patent uses parameter changes by varying the excitation frequency, amplitude, and lock-in amplifier time constant to optimize the measurement for different sample conditions. When capacitive time constants are present, the system adjusts these parameters to compensate for signal attenuation, maintaining measurement sensitivity. The ability to change measurement parameters allows the system to adapt to different electrical characteristics of the sample under test.
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 high-sensitivity detection of abnormalities in fine-structured devices by removing noise and preserving information, particularly for small resistance defects and mixed layer samples, improving the precision of failure analysis.
Implementation Method 1
In normal SEM observation, a structure of a sample surface is observed by detecting secondary electrons generated when an electron beam (primary electrons) is incident on a sample, and a part of the primary electrons incident at this time does not contribute to generation of the secondary electrons but loses energy and becomes a weak current (an absorption current) flowing in the sample.
Data Source
AI summary
A semiconductor inspection device capable of detecting an abnormality with high sensitivity in a failure analysis of a fine-structured device is provided. An electron optical system radiates an electron beam to a sample on a sample stage. A measurement device measures an output from a measurement probe that is in contact with the sample. An information processing device starts and stops the radiation of the electron beam to the sample, sets a first measurement period in which the measurement device measures the output from the measurement probe during the radiation and a second measurement period in which the measurement device measures the output from the measurement probe after the radiation, and obtains the measurement value of the output from the measurement probe based on a difference between a first measurement value measured in the first measurement period and a second measurement value measured in the second measurement period.