Force-Modulated SSRM for Accurate Carrier Concentration
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Solution Overview
Problem
State-of-the-art scanning spreading resistance microscopy (SSRM) struggles to accurately measure the spatial distribution of free charge carriers in highly doped semiconductor devices, particularly as device dimensions are scaled down, due to dominance of bulk or back-contact resistances in total resistance measurements.
Innovation Solution
The implementation of a force-modulated SSRM method, where the contact force is modulated at a specific frequency, allowing the decoupling of spreading resistance from total resistance through Fast Fourier Transform (FFT) analysis, enabling the derivation of carrier concentration by filtering the amplitude of modulated resistance at the modulation frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional SSRM is used to measure free charge carrier distribution, then spatial resolution and sensitivity are improved, but measurement accuracy deteriorates for highly doped devices due to dominance of bulk or back-contact resistances
Solution Approach 1:
The patent applies dynamic modulation of the contact force between the AFM probe and sample at a specific frequency. By dynamically varying the contact force rather than keeping it constant, the spreading resistance becomes modulated at the same frequency, allowing it to be distinguished from static bulk or back-contact resistances through frequency-selective measurement
Solution Approach 2:
The patent utilizes mechanical vibration by oscillating the contact force at a defined modulation frequency. This mechanical oscillation of the probe-sample contact generates a corresponding oscillation in the spreading resistance signal, which can then be extracted using synchronous detection or FFT methods to separate it from non-oscillating series resistances
2Reliability
If contact force is increased to maintain physical contact, then measurement reliability is improved, but spreading resistance measurement accuracy deteriorates due to dominance of series resistances
Solution Approach 1:
The patent employs dynamic modulation of contact force that maintains physical contact while creating a time-varying signal. The oscillating contact force produces a modulated spreading resistance signal that can be extracted through frequency analysis, allowing accurate measurement even when static series resistances are present in the measurement path
Solution Approach 2:
The patent uses frequency modulation as an intermediary mechanism to separate the spreading resistance signal from series resistance interference. By encoding the spreading resistance information in the frequency domain through contact force modulation, the measurement system can selectively retrieve this information while rejecting DC or low-frequency series resistance components
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 effectively decouples spreading resistance from other series resistances, providing accurate carrier concentration measurements even in devices with high dopant concentrations and increased series resistance, enhancing the characterization of semiconductor devices by maintaining physical contact and improving signal-to-noise ratio.
Implementation Method 1
measuring the spreading resistance of the sample... modulating the force applied between the AFM probe and the sample, while preserving the physical contact, thereby modulating at the modulation frequency the spreading resistance of the sample
Implementation Method 2
the modulated spreading resistance is derived by measuring the spreading current using a current-to-voltage amplifier thereby converting the voltage signal into a resistance signal
Data Source
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AI summary
The disclosure is related to a SSRM method for measuring the local resistivity and carrier concentration of a conductive sample, whereby the method comprises contacting the conductive sample at one side with an AFM probe and at another side with a contact electrode, modulating, at a modulation frequency, the force applied to maintain physical contact between the AFM probe and the sample while preserving the physical contact between the AFM probe and the sample thereby modulating at the modulation frequency the spreading resistance of the sample, measuring the current flowing through the sample between the AFM probe and the contact electrode, and deriving from the measured current the modulated spreading resistance, wherein deriving the modulated spreading resistance comprises measuring the spreading current using a current-to-voltage amplifier, converting the voltage signal into a resistance signal, and, filtering out from the resistance signal the resistance amplitude at the modulation frequency.