Pump-Probe SHG Metrology for Semiconductor Interface Characterization
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Solution Overview
Problem
Existing SHG-based metrology tools face limitations in distinguishing between interfacial properties and quantifying defects or contaminants, relying on relative measurements that cannot parse between different types of electrically active anomalies.
Innovation Solution
The use of a dual-source system comprising a pump and probe light source with different power characteristics for Second Harmonic Generation (SHG) metrology, where the pump source pre-excites or post-excites the material interface to generate SHG signals, allowing for faster and more accurate characterization of material properties by varying the timing and energy of the pump and probe interactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single laser SHG system is used, then the device complexity is low, but the measurement precision and ability to distinguish interfacial properties is insufficient
Solution Approach 1:
The system segments the light source function into two distinct components: a pump source for pre-excitation and a probe source for measurement. This segmentation allows each source to be optimized for its specific function, with the pump source providing the necessary excitation energy and the probe source performing the actual SHG measurement, thereby achieving superior measurement precision while maintaining manageable system complexity through functional division
Solution Approach 2:
The pump source performs preliminary action by pre-exciting the material interface before the probe source arrives. This pre-excitation prepares the material in a specific quantum state that enhances the SHG signal from the probe, enabling the system to distinguish between different interfacial properties that would be indistinguishable with a single source
2Illumination intensity
If high power light source is used for SHG measurement, then the signal intensity is sufficient, but the risk of optical damage to the sample increases
Solution Approach 1:
The pump source performs preliminary excitation at optimized power levels that prepare the material without causing damage. By separating the excitation function (pump) from the measurement function (probe), the system can use the pump to achieve the necessary material preparation at lower intensities than would be required if a single high-power source had to perform both functions
Solution Approach 2:
The system uses periodic pulsed operation where the pump and probe sources are activated in alternating or sequential pulses. This periodic action allows the material to return to its ground state between excitations, preventing cumulative thermal damage while maintaining sufficient signal intensity through the accumulation of multiple measurement cycles
3Productivity
If conventional SHG measurement is used, then the measurement time is reasonable, but the throughput in semiconductor manufacturing is insufficient
Solution Approach 1:
The pump source performs preliminary excitation that prepares multiple measurement points simultaneously or in rapid succession. This pre-preparation of the material state allows the probe source to perform measurements without the full excitation time, effectively reducing the measurement time per wafer while maintaining measurement quality, thereby increasing overall throughput
Solution Approach 2:
The system implements continuous scanning where the pump and probe sources operate in a coordinated continuous manner across the wafer surface. Rather than completing full measurements at discrete points before moving on, the system maintains continuous useful action by overlapping pump and probe operations, ensuring that measurement is ongoing while minimizing idle time and maximizing wafer throughput
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, including charge carrier dynamics and defect identification, with reduced risk of optical damage and improved throughput in semiconductor manufacturing.
Implementation Method 1
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 2
electrons in a layered semiconductor substrate are excited, variously, by each of a pump light source and a probe light source
Data Source
AI summary
Second Harmonic Generation (SHG) can be used to interrogate a surface such as a surface of a layered semiconductor structure on a semiconductor wafer. In some instances, SHG is used to evaluate an interfacial region such as between metal and oxide. Various parameters such as input polarization, output polarization, and azimuthal angle of incident beam, may affect the SHG signal. Accordingly, such parameters are varied for different types of patterns on the wafer. SHG metrology on various test structures may also assist in characterizing a sample.