NIR Overlay Metrology Through Amorphous Carbon Layers

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Solution Overview

Problem

Existing overlay metrology methods using visible light face significant attenuation and performance degradation when dealing with amorphous carbon layers, leading to inaccurate alignment measurements due to attenuation and chromatic aberrations.

Innovation Solution

Employing near-infrared (NIR) radiation for overlay metrology, which increases transmission through thicker amorphous carbon layers and reduces chromatic aberrations by extending the spectral range beyond visible wavelengths, allowing for more precise measurements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If visible light is used for overlay metrology through amorphous carbon layers, then the measurement can be conducted with conventional equipment, but the light transmission is significantly attenuated leading to performance degradation

Engineering Contradiction:

Improvemetrology performanceVSAvoidlight transmission

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent changes the wavelength parameter of the illumination light from visible range to near-infrared range (700-1100 nm). This parameter change enables the light to transmit through amorphous carbon layers with significantly reduced attenuation, as a-CL materials are more transparent in the NIR spectral range compared to visible light.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If visible light metrology is used on overlay targets with amorphous carbon layers, then the existing measurement systems can be utilized, but chromatic aberrations degrade the measurement accuracy

Engineering Contradiction:

Improvealignment measurement accuracyVSAvoidchromatic aberrations

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent changes the spectral range parameter from visible light to near-infrared light. This parameter change reduces chromatic aberration effects because NIR radiation has longer wavelengths that are less susceptible to chromatic dispersion in optical systems, thereby improving measurement precision.

Inventive Principle:

Principle #35Parameter changes

3Manufacturing precision

If thicker amorphous carbon layers are used to achieve high aspect ratios and vertical sidewalls, then the hardmask performance is improved, but the attenuation of visible light increases leading to metrology performance degradation

Engineering Contradiction:

Improvesidewall verticality and aspect ratioVSAvoidlight transmission through a-CL

Core Design Contradiction:

Manufacturing precisionVSLoss of energy

Solution Approach 1:

The patent changes the wavelength parameter to near-infrared range, which allows thicker amorphous carbon layers to be used for achieving high aspect ratios and vertical sidewalls while maintaining adequate light transmission for metrology measurements. The NIR light penetrates thicker a-CL layers effectively.

Inventive Principle:

Principle #35Parameter changes

4Adaptability or versatility

If overlay metrology is conducted through opaque amorphous carbon layers using visible light, then the measurement can be performed on standard substrates, but the opaque nature of a-CL causes significant signal attenuation

Engineering Contradiction:

Improveapplicability to standard substratesVSAvoidsignal detection accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent changes the spectral range parameter to near-infrared, which transforms the interaction between light and amorphous carbon layers from highly attenuating (visible range) to more transparent (NIR range). This enables accurate signal detection while maintaining adaptability to standard substrates with a-CL layers.

Inventive Principle:

Principle #35Parameter changes

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 enhances metrology performance by increasing transmission through opaque layers, reducing chromatic aberration effects, and improving measurement precision across varying process variants and material thicknesses.

Implementation Method 1

amorphous carbon material is attractive because it can be formed into highly versatile etch stop layers... imaging through a-CL's with visible light may lead to significant attenuation... NIR radiation increases transmission through thicker amorphous carbon layers

Methodology Applied

Scientific EffectNear infrared radiation transmission: Absorption (EM radiation)

Implementation Method 2

An illumination beam is generated and filtered so that the filtered beam includes near infrared (NIR) radiation that is directed onto a sample surface to generate an optical signal

Methodology Applied

Scientific EffectOptical signal generation: Reflection

Data Source

PatentUS7684039B2Overlay metrology using the near infra-red spectral range

Publication Date: 2010.03.23 KLA TENCOR TECHNOLOGY CORP

AI summary

A method and tool for conducting NIR overlay metrology is disclosed. Such methods involve generating a filtered illumination beam including NIR radiation and directing that illumination beam onto an overlay target to produce an optical signal that is detected and used to generate overlay metrology measurements. The method is particularly suited to substrate applications having layers of opaque material that are transmissive in the NIR range (e.g., amorphous carbon) and where NIR imaging is used to obtain overlay measurements. A tool implementation includes a means for generating a filtered illumination beam extending into the NIR range and a detector for receiving NIR signal from an NIR illuminated target and a computer for processing the signal data to obtain overlay metrology measurements.