Technical NoteThin Film Analysis Device

• Filmthickness

• Sheetresistance

• Color

• Reflection/transmission

• n/k-determination

• In-line,real-timemonitoring

• Suitableforvacuum

Fig. 1: ThinFilmAnalysisdevice

Applications

Thickness of thin films or layer stacks

• Analysisoflayersbetween10nmand50µm

Moisture content

• H2OcontentdeterminationintheNIR

Reflection / transmission characteristics

Sheet resistance

• Non-contactopticalmeasurement

• Canbecorrelatedtoconventional4-point-

probemeasurements

Reflection / transmission characteristics

Color

• EvaluationofL*a*b*orLUVparameter

Industries using a TFA

Printed Electronics

Roll-to-roll coater (R2R)

Semiconductors

Glass

Photovoltaic

Automotive

Paper

• ITO,OPV,PEDOT:PSSonPET

• Reflection/transmissioncharacteristics

• Barriermaterials

• Coatedmetals

• ITO,OPV,PEDOT:PSSonPET

• SiO2/Si3N4layerthicknessonSi

• Bandgapofdopedlayers

• ITOonfloatglass

• Low-Ecoatings

• Structuredglasses

• ConductinglayersonCIGS

• OPVonPET

• MoistureofPVBinterlayersinwindscreens

• Colorofvarnish

• Moisturecontent

OuromtsYs-seriesThinFilmAnalysis (TFA)device isavailable forbothscientificand industrialapplica-

tions.The TFAdevice leverages reflectometry (ameasurementof reflectionand/or transmissionover

alargespectralrange)todetermineawidevarietyofsampleparameterssuchasfilmthickness(ranging

from10nm–50µm),sheetresistance,absolutecolor,moisturecontent,orindexofrefraction.

TheTFAincludesanintegrated,broadbandlightsourcethatdeliversmaximumbrightnesswithlongterm

stabilitytothesampleandadetectionunitbasedonstate-of-the-artspectrometersandelectronics.Custom

softwaredevelopedbyouropticalengineersallowsforexpertsandnovicestodeterminetheparameters

ofinterestwiththeTFA.

Forlaboratory use,thestandardTFAconfiguration

canbeexpandedtoincludemotorizedstagesand

video monitoring.These devices are identical in

constructiontoourprocesscontrolTFAsolutions,

easingamovefromthelaboratorytothefield.

For in-line, process control application, various

TFA solutions for vacuum operation and harsh

environmentsareavailable.OurTFAdeviceshave

beensuccessfullyincorporatedinavarietyoffacto-

riesworldwideforthinfilmanalysis.

Optical Determination ofSheet resistance

KEY WORDS

Thin Film Analysis

Sheet Resistance

Doped ZnO

Industrial Monitoring

APPLICATION NOTE

By measuring and analyzing optical transmittance spectra in the visible and infrared range of the electromagnetic spectrum with ’s in-line TFA metrology tool, it is possible to calculate the doped ZnO film thickness as well as the sheet resistance of this layer. The sheet resistance can be related to measurements taken by a conventional 4-point probe. To analyze the optical transmission measurements, it is necessary to have models for the index of refraction for the glass substrate as well as the doped ZnO layer. In general a Drude model can be used determine the sheet resistance of conducting layers.

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Example: doped ZnO

ZnO is an ideal material for display technology and photovoltaics. First, it is transparent in the visible range of the optical spectrum. Second, when doped with aluminum and deposited on a glass substrate, the resulting layer is conductive and can be used as an electrode.

Physics behind the Drude Model

The classical Drude model relies on a damping constant, which does not depend on frequency. This is a good approximation in most cases. However, there are situations where the damping of the free carriers exhibits a characteristic dependence on frequency, such as in the case of scattering by charged impurities. A rather simple, but successful choice of the frequency dependence of the damping term is the following:

Thin Film Analysis (TFA) device

At the leading edge of design, custom builds optical tools and scanner systems for stand-alone laboratory and in-line industrial applications. Here we introduce

’s robust TFA system (see Fig. 1) for measurement of sheet resistance. Our TFA measurement heads, designed for industrial use and supporting operations in vacuum as well as harsh environments, have been successfully installed in factories worldwide. The system is equipped with a built-in halogen light source with an option for xenon flash lamps and the customized software system for data acquisition and analysis system can be individually programmed to measure reflection and transmission over a range from 190-2500 nm. Besides measuring sheet resistance, the system is able to measure film thickness, optical density, moisture as well as color.

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Fig. 1: Thin Film Analysis Device, table top system, the measuring head can be used in in-line production applications

m-u-tGmbH

Marlene-Dietrich-Str.5

89231Neu-Ulm,Germany

tel:+49731-98588-623

fax:+49731-98588-511

info@mut-group.com

Copyrightm-u-tGmbH.Them-u-tlogoisaregisteredtrademarkofm-u-tGmbH.Allrightsreserved.Allcompanyandproductnamesaretrademarksand/orregisteredtrademarksoftheirrespectiveowners.Features,pricing,availabilitiesandspecificationsareallsubjecttochangewithoutnotice.

TN_TFA

_eng_2.0

Standard configuration

Reflection measurement head

Size:185x135x135mm3

Reflectionunit

• 8°angleofincidence

• Beam path folded by mirror for easy fiber

handling

• SMAfiberconnector

• Spotsize~4mm

Lightsourcemonitor

• Measurementofactualsampleillumination

• Sameopticsasreflectionunit

Integratingsphere

Built-inhalogenlightsource

• Extremelybrightatcomparablylowpower

Software

• Controlofspectrometersandmultiplexers

• DeterminationofR/T

Transmission measurement head

Size:85x75x30mm3

Transmissionunit

• 8°angleofincidence

• Beampathfoldedbymirrorforeasy

fiberhandling

• SMAfiberconnector

• Spotsize~4mm

Control box

19”Box(3HE)includinglightsource

controllerandspectrometer

• Spectralrange400–1000nm

• DetectorNMOS,256pixels

• SMAfiberconnector

• Opticalmultiplexer

Extensions

Measurement head

Spotsize

• Microspotoption(approx.10µm)

• Built-invideosystemformeasurements

onstructuredsamplesincombinationwith

microspot

Factory intergration packages

SoftwareGUI(customerconfigurable)

I/Ocontrol

Statisticalinformation

Supportofprocessautomationprotocols

• TCP-IP,SECS/GEM,Profibus

andindustrialcontrolsystemprotocol

• OPC

Optical models

forthinfilmanalysis

Spectrometer

Spectralrange(detector)

• 200–400nm(NMOS/CCD)

• 400–1000nm(CCD)

• 950–1700nm(InGaAs,cooled)

• 950–2200nm(InGaAs,cooled)

Stage

Slidingtable(manual)sampleholder

• Samplesize:min.30x30mm2

Motorizedstages(x-ytables)

• Movingsampleormovingprobedesigns

available

Traversingaxis

(withmountformeasurementheads)

• Ontoporunderneathawebdriveor

productionline

• Driverangeupto3300mm

Fig. 2: Measuringhead

reflectionandtransmission

Fig. 3: Slidingtable

Fig. 4: Lightoutput

Fig. 5: Controller

andspectrometer

Light�source

Spectrometer

Measuring�head

Stage

Transmission�unit

Additional�light�source�port

Specular�excluded�option

Spot�size

8°�angle�of�incidenceBeam�path�folded�by�mirror�for�easy�fiber�handlingSMA�fiber�adaptorSpot�size�4�-�10�mm

Coupling�via�fiber�(xenon�permanent)Directly�attached�(xenon-flash)

(additional�port�opening�in�integration�sphere)Plug-in�module�for�inclusionPlug-in�module�for�exclusion

Microspot�option�(approx.�200�µm)Built-in�video�system�for�measurements�on�structured�samples�incombination�with�microspot

Manual�stage

Motorized�stages

Custom�made�in-line�stages

With�opening�for�transmission�/�reflection�measurements�simultaneously

(x-y�or�x-y-z�tables)150�x�150�mm200�x�200�mm300�x�300�mmmoving�sample�or�moving�probe�designs�available

(mounting�of�measuring�heads�in-line)Attached�to�a�flangeInside�a�vacuum�chamberOn�top�or�underneath�a�web�drive�or�production�line

Integrated�light�sources

Fiber�coupled�light�source

Xenon�flash�lampHalogen�/�xenon�flash�lamp�combined

Xenon�lampMercury�/�xenon�lamp

Spectral�range�/�Detector

Optics

150�-�500�nm�(CCD�or�CMOS)900�-�1700�nm�(InGaAs�cooled�or�uncooled)1100�-�2200�nm�(InGaAs�cooled)1300�-�2500�nm�(InGaAs�cooled)

Grating�and�slit�according�to�customer�requirementsCylinder�lense�add-on�for�improved�sensitivity�with�round-to-linear�fiberbundles

EXTENSIONS

Fig.�2: Measuring�headreflection�and�transmission

Fig.�3: Sliding�table

Fig.�4: Light�output

Fig.�4: Controller�andspectrometer