Impurity Concentration Measurement via Modulated Light Phase Delay
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Solution Overview
Problem
Existing devices struggle to accurately measure the concentration of impurities in a measurement target object, particularly when the concentration is unknown.
Innovation Solution
A concentration measurement device that uses a combination of measurement light and stimulus light, where the stimulus light is intensity-modulated and has a wavelength higher than the band-gap energy of the semiconductor substrate, allowing for the estimation of impurity concentration based on phase delays in the detection signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a pumping light source and probe light source are used to measure carrier quantity changes, then the change in carrier quantity over time can be measured, but the exact concentration of impurities cannot be measured when the concentration is unknown
Solution Approach 1:
The invention changes the parameter of light frequency from a single frequency to multiple frequencies. By irradiating the measurement target with pump light at a first frequency and probe light at a second frequency, the system can detect phase delays that are sensitive to impurity concentration. This multi-frequency approach transforms the measurement capability from merely observing carrier quantity changes to accurately determining impurity concentration through frequency-dependent phase delay analysis
Solution Approach 2:
The invention introduces phase delay as an intermediary parameter that connects the optical measurement to impurity concentration. The phase delay of the probe light, caused by carrier generation from pump light absorption, serves as a mediator that encodes information about impurity concentration. By measuring this intermediate phase delay parameter and comparing it against stored reference data, the system can accurately determine impurity concentration without directly measuring the concentration itself
2Reliability
If stimulus light with wavelength higher than band-gap energy is used, then carrier generation and extinction can be measured, but accurate impurity concentration measurement remains difficult without prior concentration knowledge
Solution Approach 1:
The invention performs preliminary action by storing phase delay information for multiple frequencies in advance before the actual measurement. A database or storage unit contains reference phase delay values corresponding to known impurity concentrations at different frequencies. During measurement, the system compares the measured phase delay against this pre-stored reference data to determine the unknown concentration, eliminating the need to have prior knowledge of the sample's concentration
Solution Approach 2:
The invention employs periodic action by using alternating pump light and probe light irradiation cycles. The pump light is irradiated periodically to generate carriers, and the probe light is periodically measured to detect phase delays. This periodic measurement approach allows the system to capture dynamic carrier generation and extinction processes while maintaining reliable measurements of impurity concentration through repeated observations at different frequencies
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 accurate measurement of impurity concentration by identifying the frequency of the detection signal causing a predetermined phase delay, even when the concentration is uncertain, and efficiently sets the frequency of stimulus light for precise measurement.
Implementation Method 1
stimulus light subjected to intensity modulation due to a modulation signal including a default frequency and having a wavelength higher than a band-gap energy of a semiconductor configuring a measurement target object
Implementation Method 2
a frequency at which the phase delay has a predetermined value is estimated on the basis of the phase delay of the detection signal with respect to the modulation signal
Data Source
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AI summary
A concentration measurement method for measuring a concentration of impurities includes a step of irradiating a DUT 10 serving as a measurement target object with measurement light and stimulus light subjected to intensity modulation using a modulation signal including a default frequency, a step of outputting a detection signal by detecting an intensity of reflected light from the DUT 10 or transmitted light through the DUT 10, and a step of detecting a phase delay of the detection signal with respect to the modulation signal, obtaining a frequency at which the phase delay has a predetermined value, and estimating a concentration of impurities in the measurement target object on the basis of the frequency.