Semiconductor Wafer Lifetime Evaluation Under Surface Recombination
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Solution Overview
Problem
Existing methods for determining recombination lifetime in semiconductor samples, such as silicon wafers, fail to accurately account for surface recombination, leading to distorted decay curves and inaccurate measurements, particularly in high-cleanliness samples.
Innovation Solution
A method involving multiple measurements with varying surface charge densities, followed by signal data processing using a model expression with exponential and constant terms, allows for the determination of both recombination and surface recombination lifetimes, using equations to derive SRH and surface recombination lifetimes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the PCD measurement is performed under the assumption that decay is exponential caused by SRH recombination only, then the measurement process is simple, but the measurement precision deteriorates due to surface recombination effects distorting the decay curve
Solution Approach 1:
The patent segments the recombination lifetime measurement into two distinct components: SRH recombination lifetime (bulk lifetime) and surface recombination lifetime. By applying different analysis methods to different segments of the decay curve and using different physical models for bulk and surface effects, the patent achieves accurate measurement of both components separately, resolving the contradiction between measurement simplicity and precision.
Solution Approach 2:
The patent changes the analysis parameters by introducing surface recombination velocity as an additional parameter to be determined. By modifying the decay curve analysis to include surface recombination effects and using numerical integration methods instead of simple exponential fitting, the patent maintains measurement simplicity while significantly improving precision for high-cleanliness samples.
2Ease of operation
If conventional PCD methods are used for high-cleanliness silicon wafers, then the measurement process is straightforward, but the reliability deteriorates due to non-exponential decay caused by surface recombination
Solution Approach 1:
The patent introduces an intermediary approach by using numerical integration of the decay curve combined with a physical model that accounts for both bulk and surface recombination. This intermediary method bridges the gap between simple exponential fitting and complex multi-parameter analysis, providing reliable results for high-cleanliness samples while maintaining ease of operation through automated calculation procedures.
3Device complexity
If surface recombination is neglected in the measurement model, then the analysis is simple, but the measurement precision worsens for samples with high cleanliness levels
Solution Approach 1:
The patent applies a dynamic analysis model that adapts to different sample conditions. By using numerical integration that can accommodate varying surface recombination velocities and by allowing the model to dynamically adjust between bulk-dominated and surface-dominated recombination regimes, the patent achieves high measurement precision across different cleanliness levels without excessively increasing model 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
Accurately determines recombination lifetime and surface recombination lifetime, improving measurement precision and reducing errors in semiconductor sample evaluation.
Implementation Method 1
a method of measuring a recombination lifetime through the PCD method is standardized... Noncontact Measurement of Photoconductivity Decay by Microwave Reflectance
Implementation Method 2
which employs a Shockley-Read-Hall (SRH) recombination lifetime (that is, bulk lifetime) τb
Implementation Method 3
Noncontact Measurement of Photoconductivity Decay by Microwave Reflectance
Data Source
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AI summary
Provided is a semiconductor sample evaluation method including acquiring, a plurality of times, a decay curve by performing measurement on a semiconductor sample which is an evaluation target in accordance with a photoconductive decay method while changing a surface charge density; performing signal data processing using a model expression including an exponential decay term and a constant term on at least one decay curve among decay curves obtained through the plurality of measurements; obtaining a recombination lifetime τeff of the semiconductor sample from an exponential decay expression obtained through the signal data processing; obtaining a quadratic function, in which a surface charge density related value is represented by a variable x and a value related to the constant term is represented by a variable y, from measurement results obtained through the plurality of measurements; and obtaining a surface recombination lifetime τs of the semiconductor sample from the quadratic function.