FT-IR Spectroscopy Baseline Correction for Silicon Impurity Detection

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Solution Overview

Problem

Conventional differential spectroscopy methods, such as those used in FT-IR for measuring impurities in silicon single crystals, face challenges in removing the influence of phonon absorbance due to baseline deviations caused by minute frequency shifts between sample and reference spectra, leading to uneven baselines and inaccurate impurity concentration measurements.

Innovation Solution

The method involves estimating and correcting for a minute frequency shift using the least squares method to remove background absorbance, thereby flattening the baseline and enhancing the detection sensitivity of impurities like substitutional carbon in silicon single crystals.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If differential spectroscopy is used to remove phonon absorbance background, then the background absorbance is reduced, but baseline deviations occur due to minute frequency shifts between sample and reference spectra

Engineering Contradiction:

Improvephonon absorbance backgroundVSAvoidbaseline flatness

Core Design Contradiction:

Object-affected harmful factorsVSMeasurement precision

Solution Approach 1:

The patent applies preliminary wave number shift correction to align the reference spectrum with the sample spectrum before performing differential spectroscopy. By anticipating and correcting the frequency misalignment in advance, the method prevents baseline deviations that would otherwise occur during the subtraction process, thus maintaining both background removal effectiveness and baseline flatness.

Inventive Principle:

Principle #10Preliminary action

2Measurement precision

If wave number shift correction is applied to align spectra, then baseline flatness is improved, but the detection sensitivity of minute absorption spectra may be reduced

Engineering Contradiction:

Improvebaseline flatnessVSAvoiddetection sensitivity

Core Design Contradiction:

Measurement precisionVSDifficulty of detecting and measuring

Solution Approach 1:

The patent optimizes the wave number shift correction by carefully controlling the shift amount to be just sufficient to align the spectra without over-correcting. This parameter optimization ensures that the baseline becomes flat while preserving the minute absorption features, thus maintaining detection sensitivity while achieving baseline flatness.

Inventive Principle:

Principle #35Parameter changes

3Difficulty of detecting and measuring

If the range of wave numbers for differential spectrum is expanded to capture more signal, then detection sensitivity is improved, but the influence of phonon absorbance background increases

Engineering Contradiction:

Improvedetection sensitivityVSAvoidphonon absorbance background

Core Design Contradiction:

Difficulty of detecting and measuringVSObject-affected harmful factors

Solution Approach 1:

The patent applies local quality by performing wave number shift correction specifically in the regions where phonon absorbance overlaps with the signal of interest, rather than uniformly across the entire spectrum. This localized correction approach maintains detection sensitivity in the target regions while minimizing the inclusion of phonon absorbance background.

Inventive Principle:

Principle #3Local quality

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 effectively removes background influence, allowing for more accurate determination of impurity concentrations with improved detection sensitivity, significantly reducing the detection limit of impurities in silicon single crystals compared to conventional methods.

Implementation Method 1

a technique is known, in which differential spectroscopy is used to obtain an infrared absorption spectrum of substitutional carbon that is an impurity included in a measurement target (sample), by means of subtraction factor correction by subtracting an infrared absorption spectrum, which has been obtained from a substantially carbon-free silicon single crystal (reference)

Methodology Applied

Scientific EffectPhonon absorbance: Absorption (EM radiation)

Implementation Method 2

an infrared absorption spectrum, which has been obtained from a substantially carbon-free silicon single crystal (reference)

Methodology Applied

Scientific EffectInfrared absorption: Absorption (EM radiation)

Data Source

PatentUS7767969B2Method and apparatus for measuring spectroscopic absorbance

Publication Date: 2010.08.03 SUMCO TECHXIV CORP

AI summary

An object of the present invention is to provide a spectroscopic method and an apparatus which can measure a trace element accurately with high sensitivity. In order to achieve this object, for example, in Fourier transformation infrared spectroscopy (FT-IR), a reference spectrum and a measurement spectrum including an impurity spectrum are measured in order to obtain a differential spectrum comprising the impurity spectrum and a flat baseline, correction including a frequency shift of the reference spectrum before calculating a differential spectrum, is performed on the reference spectrum. This makes it possible to remove baseline deformation due to phonon absorbance of silicon included in the conventional differential spectrum, and to obtain an infrared absorption spectrum of the substitutional carbon with high accuracy and high sensitivity.