© Alexander Bol,shakov1.

Ames Research CenterNASA, MNASA, MNASA, Moooffffffett ett ett FFFiiieeeldldld,,, CACACA 940359403594035

Alexander A.Alexander A. BoBoľľshakov shakov Brett A.Brett A. Cruden Cruden

SurendraSurendra P. Sharma P. Sharma

Plasma Diagnostics for Nanoscale Fabrication

Plasma Diagnostics for Plasma Diagnostics for NanoscaleNanoscale FabricationFabrication

October 9October 920032003

© Alexander Bol,shakov2.

Presentation outlinePresentation outlineIntroduction:

micro/nano-electronics roadmapdiode lasers

Experimental setupTemperature determinationSimulation of plasma mechanismsEstimation of densities of speciesConclusions

© Alexander Bol,shakov3.

ITRS functional dimensionsITRS functional dimensions

1000

100

10

1990 1995 2000 2005 2010 2015 2020

10

100

1000

Elec

trons

per

dev

ice

Crit

ical

size

,nm

Years

16M 64M 256M 1G 4G 16GElementary devices (transistors) per chip

* International Technology Roadmap for Semiconductors

CCММOSOS

© Alexander Bol,shakov4.

NanotubeNanotube--based transistorbased transistor

Carbon nanotube

SiSiO2

Electrodes(Au)

* S.J. Wind, J. Appenzeller, R. Martel, V. Derycke, P. Avouris, J. Vac. Sci. Technol. B

© Alexander Bol,shakov5.

Carbon nanotubesCarbon nanotubes

GraphenGraphen layerlayer NanotubesNanotubes

~20 atoms in circumference, ~2 nm in diam.

Semiconducting or metallic

Useful as transistors or interconnect

© Alexander Bol,shakov6.

NanorodsNanorods/wires/wires –– nanolasersnanolasersLasing output Lasing output

ExcitationExcitationZnO

λ = 380 nm* M.H. Huang, S. Mao, H. Feick, H. Yan, Y. Wu, H. Kind, E. Weber, R. Russo, P. Yang, Science.

© Alexander Bol,shakov7.

Current and future needsCurrent and future needsAdvanced process control required Must be non-intrusive, compact, and simpleMonitoring of chemical species:

end-point detection process optimization and control contamination “management”

Local temperature monitoring:plasma uniformityintentionally non-uniform (!?)

© Alexander Bol,shakov8.

Semiconductor process gasesSemiconductor process gases

Inert (e.g., Ar, He, N2)

Corrosive (e.g., HCl, HBr, SF6, NF3, CF4)

Highly Toxic (e.g., AsH3, PH3)

Pyrophoric (e.g., SiH4)

Reactive (e.g., NH3, N2O, WF6, CO2, O2)

© Alexander Bol,shakov9.

Impurity transferImpurity transfer

Plasma treatment

nn--step nn+1+1--stepstep step

More than 300 technology steps for one chip

High variety of materials in use

© Alexander Bol,shakov10.

How to monitor processesHow to monitor processes??

Emission:

Absorption:

Fluorescence:

Mass spectrometry:

Electrical:

low resolution only emitting species

limited if FTIR or UV diode lasers - ideal

requires powerful lasers

intrusive, cumbersome

non-selective

© Alexander Bol,shakov11.

Commercial diode lasersCommercial diode lasers

Wavelength, µm0.3 0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1 2.3

AlGaAs/GaAs

InGaAs/GaAs

InGaAsP/InP

InGaAsP/InGaAs or InAsP

AlGaAsSb/InGaAsSb

AlGalnP/GaAs

Doubled frequency

GaNZnSe

Room temperature operation

© Alexander Bol,shakov12.

Accessible elementsAccessible elements

Probed already Possible Excited only

Al, Ba, Ca, Cr, Ag, Co, Eu, Ar, As, B, Cs, Cu, Hg, I, Fe, Ga, Gd, Br, Cl, F, H, In, K, La, Li, Mn, Hf, Ho, Lu, Kr, N, Ne,Pb, Rb, Sm, Sr, Mo, Nb, Nd, O, P, S, Si, U, Y, Zr Ni, Os, Re, Xe, Zn & etc.

Rh, Ru, Sc, Tb, Th, Ti, Tl, Tm, V, W

H2O, OH, O2,CH, CO, CO2, CH4,NH3, HCl, HBr

N2, Cl2, F2, CF, CN, SiF, AlCl and etc.

© Alexander Bol,shakov13.

Diode laser characteristicsDiode laser characteristics

Tunable over absorption features

Provide spectrally narrow linewidths

Compact and simple to use

Can be multiplexed

Commercially available

Relatively inexpensive

© Alexander Bol,shakov14.

Experimental SetupExperimental Setup

PC

DiodeLaser

FastAmplifier

Digitizer12 bit

MatchingNetwork

RF PowerSupply

ThresholdDetector

DC bias& Reset

High LimitDetector

FunctionGenerator

PulldownCircuit

Slow Ramp

Temp.Controller

Cavity modulation, 1 kHzData acquisition, 20 MHzDiode laser scan, 5 min

Start

ICP

Isolator

PD

Piezo

© Alexander Bol,shakov15.

Simplified SetupSimplified Setup

Data acquisition, 0.1 kHz

PC

DiodeLaser PD

Etalon

Low Noisepreamplifier

Digitizer8 bit

MatchingNetwork

RF PowerSupply

LabViewsoftware

Slow Ramp

Temp.Controller ICP reactor

PD

Wafer

© Alexander Bol,shakov16.

Rate of energy loss from cavityRate of energy loss from cavityLaser АОМ DetectorCavityLaserLaser АОМАОМ DetectorDetectorCavityCavity

L

Reflectance L=50 сm L=100 сmτ (µs) τ (µs)

Number of passes

9699

99.999.99

99.999

0.040.171.67

16.67166.67

0.080.333.33

33.33333.33

25100

100010000

100000

© Alexander Bol,shakov17.

Etching ICP ReactorEtching ICP ReactorMatching NetworkRF Power Supply

Gate Valve

Turbo Pump &Backing Pump

Plasma

Gas Inlet

Throttle Valve & Roughing Pump

Coil

PoweredLowerElectrode

RF Head

Matching Network

RFPowerSupply

Turbo Pump

Backing Pump

Penning Gauge

Aperture (100 m)µ

MHV CoaxialRF FeedIon OpticsIon Source

Energy Analyzer

Quadrupole

ChanneltronIon Detector

13.56 MHz

100 kHz

© Alexander Bol,shakov18.

Diagnostics objectivesDiagnostics objectives

Determination of plasma parameters: gas temperature electron temperature degree of ionization

Identification of species in etching plasmasMeasurement of concentrations of speciesSimulation of plasma etching mechanismsbased on acquired experimental data

© Alexander Bol,shakov19.

0

200000

400000

600000

762.3 762.8 763.3 763.8 764.3

Wavelength, nm

Inte

nsity

90 mTorr50 W20 µm

25 C

35 C30 C

Laser Scan over Argon LineLaser Scan over Argon LinePlasma:

Laser:VCSELIop=4.9 mA∆ν=5 MHzPop=0.5 mW

Argon line:763.51 nm

© Alexander Bol,shakov20.

Absorption by Argon PlasmaAbsorption by Argon Plasma

0

100000

200000

300000

700 750 800 850 900 950

Time (frame number)

763.3

763.4

763.5

763.6

763.7

763.8

763.6 nm

763.4 nm

Plasma: Laser:Iop=4.9 mAT=32-20 C

Ar line:763.51 nm

200 mTorr, 100 W40 mTorr, 100 W

Wav

elen

gth,

nm450 K

550 K

Abso

rptio

n

© Alexander Bol,shakov21.

Laser wavelength calibrationLaser wavelength calibration

0

2000

4000

6000

8000

10000

762.7 762.8 762.9 763.0 763.1 763.2 763.3 763.4 763.5 763.6 763.7Wavelength, nm

Etalon fringe

Laser scan

ArPQ9 PP9

PP7PQ7PP5

PQ5

Argon and ambient airabsorption

© Alexander Bol,shakov22.

Ambient oxygen absorptionAmbient oxygen absorption

759 760 761 762 763 764 765 766Wavelength, nm

Ar 763.51

PQ9PP9

PP7PQ7

PP5

PQ5

O2 (b1Σg – X3Σg)

© Alexander Bol,shakov23.

Temperature in Ar/NTemperature in Ar/N22 plasmaplasma

0

100

200

300

400

500

600

700

800

900

0 50 100 150 200 250 300 350 400 450 500Pressure, mTorr

Tem

pera

ture

, K

300 W

100 W

100 W

0-D model

3% N2 in Ar

100% Ar

3% N2 in Ar

Doppler temperatureRotational temperature0-D simulation in Ar

45% N2 in Ar

© Alexander Bol,shakov24.

Temperature in Ar/NTemperature in Ar/N22 plasmaplasmaTe

mpe

ratu

re, K

Pressure, mTorr

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

0 50 100 150 200 250 300 350 400 450 500

300 W45% N2 in Ar

3% N2 in Ar

45% N2 in Ar

90% N2 in Ar

90% N2 in Ar

Doppler temperatureRotational temperature

© Alexander Bol,shakov25.

Argon plasma simulationArgon plasma simulation

300

400

500

600

700

800

-130 -110 -90 -70 -50 -30 -10 10 30 50 70 90 110 1300

1

2

3

4

5

6

7

Tem

pera

ture

, K

Reactor radial dimension, mm

Tgas

Ar m

etas

tabl

e de

nsity

, 101

0cm

- 3Arms

100 W100 mTorr

© Alexander Bol,shakov26.

Emission from Ar plasmaEmission from Ar plasma

0

0.2

0.4

0.6

0.8

1

Rel

ativ

e in

tens

ity

Pressure, mTorr

763.5 nm

602.5 nm

603.2 nm667.7 nm

© Alexander Bol,shakov27.

Passive Optical Cavity Passive Optical Cavity

CF4

ArMFC

MFC

DiodeLaser

Plasma

Top View

λ = 2.12 µmIsolator

PD

Back Mirroron Piezomount

FrontMirror Planar ICP Reactor

© Alexander Bol,shakov28.

Composite Spectrum of CFComposite Spectrum of CFXX

2.0 2.5 3.0 4.0 5.0 7.0 10 15

5000 4000 3000 2000 1000

Wavenumber, cm-1

Wavelength, µm

100

102

104

106

108

CFCFCFCF22CFCF33CFCF44

Fundamental, overtone and combination bands

Band

inte

nsity

, m-2

atm

-1

© Alexander Bol,shakov29.

Cavity Modes and Laser LineCavity Modes and Laser LineLaser is slowly scanned throughout ~400 GHzCavity length is fast modulated within ±100 MHz

Frequency, MHz

<100 MHz

laser scan

200 MHz

50 kHz

Doppler-broadened line~1GHz

© Alexander Bol,shakov30.

Detection of plasma speciesDetection of plasma speciesHigh anisotropy & selectivity in etching of Siover SiO2 or SiN3 is necessary; research in CFx radicals plasmachemistry is neededAbsolute densities of CxHy, CFx radicals and kinetics in plasma can be measured by cavity absorption spectroscopy at ~1 km of the equivalent optical pathlengthUseful for diagnostics, analysis, monitoring and control of both nano- and microelectronic fabrication processes and development of micro- and nanodevice-based sensors

© Alexander Bol,shakov31.

Spot Size at MirrorsSpot Size at Mirrors

1

0

2

3

1 10 1000.1Radius of curvative, m

Spot

siz

e, m

m

Cavity length:0.5 m0.7 m1.0 m

λ = 2 µm; λ = 3 µm

Con

cent

ric

Confocal configuration

© Alexander Bol,shakov32.

νν33 Fundamental Band of CFFundamental Band of CF44

OnOnOffOff

Plasma:

0.05 Torr100 W

Q0

Q1

Q2

R branch

0.8

0.6

Abso

rban

ce

0.4

0.2

0.01270 1275 1280 1285 1290

Wavenumber, cm-1

* B.A.Cruden, M.V.V.S.Rao, S.P.Sharma, M.Meyyappan, Plasma Sci. Source Technol.

© Alexander Bol,shakov33.

Emission from CFEmission from CF44 PlasmaPlasma

185 195 205 215 225

CCF

Si

Species detected include C, C2, F, CF, Si, O, COWavelength, nm

Inte

nsity

0.03 Torr, 0.3 kW

* B.A.Cruden, M.V.V.S.Rao, S.P.Sharma, M.Meyyappan, J. Vac. Sci. Technol. B

© Alexander Bol,shakov34.

Impurity AbsorptionImpurity Absorption

Wavelength, µm1.0 1.5 2.0 2.5 3.0

H2O

CO2

CO

10-210-1

10-3

10-2

10-4

10-2

10-5

10-3

10-4Line

stre

ngth

, cm

-2at

m-1

Interference-free window between 2.1– 2.2 µm* M.E.Webber, J.Wang, S.T.Sanders, D.S.Baer, R.K.Hanson, Proc. 28 Int. Symp.Combustion

© Alexander Bol,shakov35.

Sensitivity EstimatesSensitivity Estimates

Minimum absorption coeff. ~10-10 cm-1Hz-½

CFx radicals detection limit ~1011 cm-3

(λ = 2.12 µm; Cavity leakout time =100 µs)

Single molecule absorption can in principlebe detected at strong fundamental bands

(α ~10-15 cm-1Hz-½; λ = 8 µm)

© Alexander Bol,shakov36.

ConclusionsConclusions

Diode lasers operating in the 0.3 - 2.3 µm region are convenient, compact, inexpensive, tunable, of spectrally narrow bandwidth, and require no cryogenic coolingLocal and averaged temperature can be determined with different thermometric speciesAbsolute densities of atoms, radicals and molecules can be monitoredMulti-parametric measurements possible

© Alexander Bol,shakov37.

ConclusionsConclusionsChecking overall chamber health in real timeChamber clean-up/ fast start-up optimizationEnd-point for small features, cost-effectively Dopant species detection for end-pointingMonitoring atomic metal species in ALDReplacing the slow techniques (TXRF, SIMS) B and P implants detection in gate etch Aerosol detection in photoresist processing

© Alexander Bol,shakov38.

AcknowledgementsAcknowledgements

Alexander Boľshakov held NRC senior re-search associateship award at NASA AmesResearch Center while performing this work

Brett Cruden’s work was contracted throughEloret Corporation