Photomodulated Reflectance Measurement for Semiconductor Defect Concentration
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Solution Overview
Problem
Existing methods struggle to accurately determine charge carrier lifetime and defect site concentration in semiconductors at low defect concentrations of the order of ppm-ppb, particularly in ion-implanted samples with complex defect structures.
Innovation Solution
A method using photomodulated reflectance (PMR) measurements that accounts for the effect of structural defect sites and contaminant atoms in semiconductors, allowing for the derivation of charge carrier lifetime and defect site concentration by separating contributions from Schokley-Read-Hall recombination, Auger recombination, and diffusion processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If photomodulated reflectance measurement is used to detect defect concentrations, then measurement sensitivity is improved, but measurement precision deteriorates at low defect concentrations below 10 ppm
Solution Approach 1:
The patent extracts and separates the contribution of structural defects from the total PMR signal by comparing measurements on damaged samples with reference measurements on undamaged samples. This extraction isolates the defect-related signal component, enabling precise quantification of defect concentrations below 10 ppm even when the total signal contains multiple overlapping contributions.
Solution Approach 2:
The patent changes the measurement parameter by introducing a reference sample comparison approach. By measuring both damaged and undamaged samples under identical conditions and analyzing the difference in their PMR signals, the method transforms an impossible single-measurement task into a feasible differential measurement that enhances precision at low defect concentrations.
2Adaptability or versatility
If PMR measurement is applied to ion-implanted samples with complex defect structures, then applicability is improved, but measurement interpretation complexity increases
Solution Approach 1:
The patent segments the total PMR signal into distinct components: one from structural defects and another from excess charge carriers. By mathematically separating these contributions through reference sample comparison, the method makes it possible to interpret complex defect structures in ion-implanted samples without being overwhelmed by the complexity, as each component can be analyzed independently.
Solution Approach 2:
The patent introduces an intermediary approach by using undamaged reference samples as a baseline. These reference measurements serve as a mediator that allows the complex signal from damaged samples to be decomposed and interpreted, transforming an intractable complex measurement into a manageable analysis by providing a known reference state for comparison.
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 precise monitoring of charge carrier lifetime and defect concentration in semiconductors, even at low defect concentrations, providing critical parameters for semiconductor technology and materials science.
Implementation Method 1
The PMR technique basically measures the change in the reflection of the sample under optical excitation
Implementation Method 2
the PMR effect is dominated by the electro-optic effect, and a significant excess charge carrier concentration can be maintained in the sample
Implementation Method 3
the PMR effect in the damaged layer is dominated by the thermo-optic effect over the electro-optic effect
Implementation Method 4
separating other lifetime contributions, such as Schokley-Read-Hall recombination, Auger recombination, and the characteristic time constant contribution from the diffusion of charge carriers
Implementation Method 5
the characteristic time constant contribution from the diffusion of charge carriers
Data Source
AI summary
In case of semiconductor samples, the method enables the determination of the charge carrier lifetime and crystal defect concentration related to the recombination defect centers present in the material based on photomodulated reflection (PMR) measurement operating in the quasi-static modulation frequency range. The defect centers present in the basically single-crystal semiconductor sample (M1) can be of intrinsic or extrinsic origin, typically electrically active de-feet sites created by the implantation of low-mass—H+, He+—high-energy ions, or impurity atoms. e.g., metal contaminants introduced during other technological steps. The method can be used in all cases where the crystal defect concentration is typically in the ppb-ppm range, its depth distribution is almost uniform, and the size of the excitation/analyzing laser spot in the PMR measurement is significantly smaller than the thickness of the zone containing the crystal defects. The excess charge carrier concentration obtained from the PMR measurement using the described procedure gives the total lifetime Ttot, from which, knowing the lifetimes of other charge carrier recombination processes and the time constants of diffusion processes, the life-time and concentration assigned to intrinsic or extrinsic defects can be determined, and can be correlated with the implantation related or other technological parameters.