Pump-Probe SHG Wafer Metrology for Trap Density Measurement
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Solution Overview
Problem
Current Second Harmonic Generation (SHG) techniques face challenges in semiconductor manufacturing and metrology due to limitations in sensitivity, speed, and accuracy, particularly in characterizing surface and interface properties of layered semiconductor substrates, which hinder their adoption as a standard method.
Innovation Solution
An SHG metrology tool utilizing a combination of a pump light source with different power characteristics and a probe light source, such as a UV flash lamp and a femtosecond laser, is employed to excite electrons in semiconductor substrates, allowing for faster characterization and reduced risk of optical damage by controlling the average and peak power levels, enabling time-dependent and time-independent signal measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single laser source is used for SHG measurement, then the measurement can be performed with a simple setup, but the characterization time is too long and throughput is low
Solution Approach 1:
The patent employs periodic pulsed laser action with a pump-probe scheme where a pump laser prepares the sample state and a probe laser measures the SHG signal at different time delays. This periodic pulsed operation enables fast time-resolved measurements that dramatically reduce characterization time while maintaining high throughput, directly resolving the contradiction between measurement speed and characterization time.
2Measurement precision
If high power light source is used to improve signal strength, then measurement sensitivity improves, but optical damage to the sample increases
Solution Approach 1:
The pump laser performs preliminary action by preparing the sample in a specific excited state before the probe measurement. This pre-excitation allows the probe laser to use lower peak power for detection, reducing optical damage risk while maintaining sufficient signal strength through the accumulated effect of the pump preparation, thus resolving the sensitivity versus damage contradiction.
Solution Approach 2:
The patent dynamically controls the temporal profile of light interaction by using time-resolved pump-probe measurements with variable delay times. This dynamic approach allows optimization of signal strength at each time point while keeping instantaneous power levels below damage thresholds, enabling sensitive measurements without causing optical damage.
3Measurement precision
If conventional SHG techniques are used, then the setup is relatively simple, but sensitivity to surface and interface properties is insufficient
Solution Approach 1:
The time-resolved periodic pump-probe measurement scheme captures dynamic surface and interface phenomena that static measurements miss. By measuring SHG signals at multiple time delays after pump excitation, the system achieves enhanced sensitivity to surface and interface properties through time-dependent signal variations, justifying the increased system complexity.
Solution Approach 2:
The pump laser acts as an intermediary that prepares specific surface and interface states before probe measurement. This intermediary action enhances the probe's sensitivity to surface and interface properties by creating distinct excited states that produce stronger or more distinctive SHG signals, thereby improving measurement precision despite added system complexity.
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 significantly reduces the time required for wafer characterization, enhances throughput, and allows for more accurate determination of material properties like trap density, facilitating high-speed, high-accuracy testing in semiconductor manufacturing.
Implementation Method 1
a pump light source with different power characteristics... to excite electrons in a layered semiconductor substrate
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
Implementation Method 3
for the purpose of Sum Frequency Generation (SFG) (e.g., typically SHG)
Data Source
AI summary
Various approaches to can be used to interrogate a surface such as a surface of a layered semiconductor structure on a semiconductor wafer. Certain approaches employ Second Harmonic Generation and in some cases may utilize pump and probe radiation. Other approaches involve determining current flow from a sample illuminated with radiation.