Thin Film Thickness Measurement via Polarized Light Diffraction

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Solution Overview

Problem

Current methods for measuring semiconductor thin film thickness, such as TEMs, Spectroscopic Ellipsometry, and reflectometry, are either expensive, require prior knowledge, or lose accuracy for thicker films exceeding 10 μm, making them inadequate for nanoscale device fabrication and thin film characterization.

Innovation Solution

The method employs diffraction of a polarized light beam through a thin film sandwiched between optically opaque walls, forming a diffraction pattern that is measured to indirectly determine the film's thickness using equations for normalized intensity, allowing for thickness determination without the need for expensive instruments or prior spectral modeling.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If Spectroscopic Ellipsometry is used to measure thin film thickness, then measurement accuracy is improved for ultra-thin films, but the technique loses accuracy for thicknesses exceeding 10 μm

Engineering Contradiction:

Improvethin film thickness measurement accuracyVSAvoidapplicability range for different film thicknesses

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The patent changes the measurement parameter from spectroscopic ellipsometry (which uses polarization changes upon reflection) to single-slit diffraction pattern analysis. By using a polarized light beam diffracted through the thin film to create an interference pattern, and measuring the intensity distribution across the diffraction pattern at different angles or positions, the method achieves accurate thickness measurement for both ultra-thin and thick films (up to 100 μm), thus expanding the applicable thickness range while maintaining measurement accuracy.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If cross-sectional Transmission Electron Microscopes are used to measure thin film thickness, then measurement accuracy is improved, but the cost of the instrument increases

Engineering Contradiction:

Improvethin film thickness measurement accuracyVSAvoidcost of measurement instrument

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The patent replaces expensive specialized instruments (cross-sectional TEMs costing hundreds of thousands of dollars) with a simple, inexpensive optical setup consisting of a polarized light source, the thin film sample, and a detector to measure the diffraction pattern. This low-cost apparatus achieves comparable measurement accuracy, making thickness measurement accessible without requiring expensive equipment.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Ease of operation

If Spectroscopic Ellipsometry or reflectometry is used to measure thin film thickness, then measurement capability is provided, but prior knowledge or spectral modeling of optical functions is required

Engineering Contradiction:

Improvemeasurement capabilityVSAvoidrequirement for prior spectral modeling knowledge

Core Design Contradiction:

Ease of operationVSDevice complexity

Solution Approach 1:

The patent extracts the essential measurement information from the diffraction pattern by analyzing the intensity distribution of light at different diffraction angles or positions. By using the relationship between the diffraction pattern characteristics and film thickness through appropriate equations, the method directly determines thickness without requiring prior knowledge of the film's optical functions or complex spectral modeling, thus simplifying the measurement process and reducing operational complexity.

Inventive Principle:

Principle #2Taking out (Extraction)

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 provides an accurate and cost-effective method for measuring thin film thickness, applicable to both ultra-thin and relatively thick films, overcoming the limitations of existing techniques by using a simple and inexpensive setup.

Implementation Method 1

A polarized light beam with a wavelength λ is diffracted through the thin film such that a diffraction pattern is formed on a surface

Methodology Applied

Scientific EffectDiffraction: Diffraction

Implementation Method 2

A polarized light beam with a wavelength λ is diffracted through the thin film such that a diffraction pattern is formed on a surface

Methodology Applied

Scientific EffectInterference: Interference

Data Source

PatentUS12259226B1Method of measuring thickness of thin films using diffraction of polarized light through a thin film

Publication Date: 2025.03.25 KING SAUD UNIVERSITY

AI summary

The method for measuring the thickness of thin films uses diffraction of a polarized light beam through a thin film to indirectly measure its thickness. The thin film is prepared on an optically opaque substrate and the thin film and the optically opaque substrate are sandwiched between a pair of optically opaque walls, in a manner similar to a conventional single-slit diffract setup where the thin film serves as the slit. A polarized light beam with a wavelength λ is diffracted through the thin film such that a diffraction pattern is formed on a surface. A set of light intensities of the diffraction pattern formed on the surface is measured for multiple values of a diffraction angle θ. A thickness, d, of the thin film is then determined by fitting the measured set of light intensities to an equation for normalized intensity, Inor(θ, d, λ), given byIn⁢o⁢r(θ,d,λ)=[sin⁡(π⁢dλ⁢θ)π⁢dλ⁢θ]2.