Capacitive Sensor Silicon Thin Film Defect Detection

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Solution Overview

Problem

Current methods for measuring free carrier lifetime in silicon thin films, especially thin films, are limited by their non-contact and non-destructive capabilities, and struggle to accurately assess crystallinity and defect detection due to measurement errors from air-gap deviations and low carrier generation rates.

Innovation Solution

A capacitive sensor system with a detection electrode, charge pumping electrode, and reference electrode is used to measure conductivity changes and photoconductivity in silicon thin films, employing ultraviolet light to generate free carriers and normalize measurements for air-gap errors, allowing for non-contact and non-destructive assessment of free carrier lifetime and crystallinity, and defect detection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If a capacitive sensor is used to measure conductivity changes in silicon thin films, then free carrier lifetime and crystallinity can be measured in a non-contact manner, but measurement errors occur due to air-gap deviations between the sensor and the thin film sample

Engineering Contradiction:

Improvenon-contact measurement capabilityVSAvoidmeasurement accuracy

Core Design Contradiction:

Ease of operationVSMeasurement precision

Solution Approach 1:

The patent replaces mechanical contact-based measurement systems with a capacitive sensing system that uses electrical field interaction through the air-gap. The capacitive sensor detects conductivity changes in the silicon thin film without physical contact, substituting mechanical coupling with electrical field coupling, thereby enabling non-contact measurement while maintaining measurement capability through the air-gap.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent measures and compensates for air-gap deviations by monitoring capacitance changes and using this information to correct conductivity measurements. By changing the measurement parameter from direct conductivity to capacitance-based indirect measurement, the system can account for and compensate air-gap variations, resolving the precision issue while maintaining non-contact operation.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If ultraviolet light is used to generate free carriers in silicon thin films, then photoconductivity can be measured, but carrier generation rates are low in thin films with low carrier concentrations

Engineering Contradiction:

Improvephotoconductivity measurement capabilityVSAvoidfree carrier concentration

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The patent employs periodic modulation of the ultraviolet excitation light at specific frequencies (1-100 kHz) to generate free carriers in a controlled, oscillating manner. This periodic action allows the capacitive sensor to detect conductivity changes at the same modulation frequency, improving signal-to-noise ratio and enabling reliable photoconductivity measurement even when the total carrier concentration is low, as the periodic stimulation creates detectable AC signals from the small carrier populations.

Inventive Principle:

Principle #19Periodic action

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 method effectively measures free carrier lifetime and crystallinity in silicon thin films with high accuracy, reducing measurement errors and improving defect detection resolution, even in thin films with low carrier concentrations.

Implementation Method 1

measuring a conductivity change of the silicon thin film sample using the capacitive sensor

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

measuring a photoconductivity of the silicon thin film sample by measuring a quantity of transferred charges

Methodology Applied

Scientific EffectPhotoconductivity: Photoconductivity

Implementation Method 3

illuminating an excitation light on the silicon thin film sample by turning-on the excitation light source module, the excitation light including an ultraviolet light

Methodology Applied

Scientific EffectPhotoelectric Effect: Photoelectric Effect

Data Source

PatentUS9140742B2Method of measuring a silicon thin film, method of detecting defects in a silicon thin film, and silicon thin film defect detection device

Publication Date: 2015.09.22 SAMSUNG DISPLAY CO LTD

AI summary

A method of measuring conductivity of a silicon thin film is provided. By the method, a capacitive sensor is positioned over a silicon thin film sample with an air-gap between the sensor and the sample, a size of the air-gap is measured using the capacitive sensor while an excitation light source module is turned off, an excitation light is illuminated on the silicon thin film sample by turning on the excitation light source module, where the excitation light is an ultraviolet light, a conductivity change of the silicon thin film sample is measured using the capacitive sensor, and a measurement error due to a deviation of the air-gap is eliminated by normalizing the conductivity change based on a measurement result of the size of the air-gap.