Pump Probe SHG Metrology for Semiconductor Interface Analysis
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Solution Overview
Problem
Existing SHG-based metrology tools face limitations in distinguishing between interfacial properties, relying on relative measurements that cannot parse between different types of electrically active anomalies or quantify contaminants effectively.
Innovation Solution
The use of a pump and probe system where the pump is a high average power, low peak power light source that pre-excites or post-excites the sample, allowing for faster characterization and differentiation of material properties by measuring SHG signal intensity and decay curves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single laser SHG system is used, then the system is simple to operate, but it cannot effectively distinguish between different types of electrically active anomalies or quantify contaminants
Solution Approach 1:
The system segments the measurement process into distinct functional components: a pump source for charge generation, a probe laser for SHG signal generation, and separate detection paths for different signal components. This segmentation enables the system to measure multiple interfacial properties simultaneously, resolving the contradiction between measurement precision and device complexity by organizing complexity into manageable functional modules.
Solution Approach 2:
The system changes multiple parameters simultaneously - using different wavelengths (pump and probe), different power levels (high average power pump, lower peak power probe), and different timing sequences (pre-excitation or post-excitation). These parameter changes enable differentiation of various interfacial properties that cannot be distinguished by a single laser system, achieving superior measurement precision through controlled parameter variation.
2Productivity
If a pump and probe system is used with pre-excitation, then the characterization speed increases, but the system complexity and power requirements increase
Solution Approach 1:
The pump source performs preliminary action by pre-exciting the sample to generate charge carriers before the probe laser arrives. This preliminary charge generation accelerates the characterization process because the probe only needs to measure the pre-established charge distribution rather than waiting for natural charge accumulation. The system achieves faster productivity by separating the charge generation function (pump) from the measurement function (probe).
Solution Approach 2:
The system uses periodic pulsed operation where the pump and probe lasers are synchronized in a repeating cycle. The pump pulse pre-excites the sample, followed by the probe pulse measuring the SHG signal, then the cycle repeats. This periodic action enables high-speed repeated measurements while managing power delivery in controlled bursts, achieving fast characterization speed with manageable system complexity.
3Loss of time
If high average power is used to excite the sample quickly, then the characterization time is reduced, but the peak power may cause material damage
Solution Approach 1:
The system segments the power delivery function between two sources: the pump source provides high average power for safe, sustained charge generation, while the probe laser provides the necessary peak power for SHG signal generation but with lower average power. This segmentation allows the system to achieve fast characterization without concentrating all power demands in a single source, reducing material damage risk while maintaining short characterization time.
Solution Approach 2:
The pump source performs preliminary charge generation at high average power over an extended period, building up the charge carrier population safely without requiring extreme peak powers. When the probe arrives, it only needs to measure the pre-established charge distribution, requiring much lower peak power than would be needed to generate the charge from scratch. This preliminary action separates the high-power charge generation phase from the low-power measurement phase, reducing material damage risk while achieving fast characterization.
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 faster and more accurate determination of material properties, such as trap density and charge carrier lifetimes, allowing for the differentiation and quantification of defects and contaminants, thereby enhancing the throughput and precision of SHG-based metrology.
Implementation Method 1
electrons in a layered semiconductor substrate are excited, variously, by each of a pump light source and a probe light source
Implementation Method 2
Second Harmonic Generation (SHG) is a non-linear effect in which light is emitted from a material at an angle with twice the frequency of an incident source light beam. The process may be considered as the combining of two photons of energy E to produce a single photon of energy 2E
Implementation Method 3
a detector to detect the SHG signal
Data Source
Figure 1A~2B
Figure 1C
Figure 3A~4
AI summary
Second Harmonic Generation (SHG) can be used to interrogate a surface of a sample such as a layered semiconductor structure. The SHG based sample interrogation systems may simultaneously collect different polarization components of the SHG signal at a time to provide different types of information. SHG imaging systems can provide SHG images or maps of the distribution of SHG signals over a larger area of a sample. Some such SHG imaging systems employ multiple beams and multiple detectors to capture SHG signals over an area of the sample. Some SHG imaging systems employ imaging optics to image the sample onto a detector array to form SHG images.