WISE 2000 - International Workshop on Spectroscopic EllipsometryUniversity of Michigan, 8-9th May 2000

Real-time, In-line and Integrated Metrology of SiGe/Si Structures

Chris PickeringDefence Evaluation and Research Agency, Malvern, UK

Tel: +44-1684-894898Fax:+44-1684-895113E-mail: cpickering@dera.gov.uk

❚ Introduction❚ Optical and epitaxy facilities❚ Ex-situ characterisation of strained SiGe structures

➜ in-line SE for SiGe process development❚ Real-time in-situ monitoring/control of SiGe

➜ data analysis methods❚ Development of integrated metrology

➜ advantages and future work

IN-SITU REAL-TIME(during process)

Processchambers

Load Locks

Cool-downchamber

INTEGRATEDIN-LINE(between

processes)

Robotwafer

handler

IN-LINE/OFF-LINE(after process)

INTEGRATED METROLOGY USING SPECTROSCOPIC ELLIPSOMETRY

Variable-AngleSPECTROSCOPIC ELLIPSOMETER

Scanning prism-grating monochromator

UV/visPM

NIRdetector

AUTOMATIC SEMulti-Layer Monitor

In-line: Si Cleanroom

Robot wafer-handlingPattern recognitionScribe line measurementsMultilayer mappingHigh throughput

REAL-TIME SE + LASER LIGHT SCATTERING

In-situ: SiGe reactor

[0.25 - 0.82 µµµµm 512 wavelengths5 spectra per sec]

FTIR interferometer

Far-IR detector

[600 - 6000 cm-1]

[0.23 - 1.7 µµµµm][0.21 - 0.85 µµµµm

Up to 1 spectrum per sec]

SPECTROSCOPIC ELLIPSOMETRY

INTEGRATED METROLOGY SE

AMAT Epi Centura Cluster ToolCombination of MLM and RTSE Cool-down chamber measurements

Applied Materials Epi Centura ®❚ single wafer cluster tool wafer sizes:

100mm, 150mm, 200mm❚ standard reduced pressure processes❚ new low pressure process❚ n- and p-type Si and SiGe multi-layers❚ selective and non-selective epitaxy❚ strain-relaxed SiGe virtual substrates❚ integrated metrology under development

Custom low-pressure cold-wall reactor❚ UHV background pressure❚ 100mm, single wafer❚ in-situ diagnostics for process control❚ n- and p-type Si and SiGe multi-layers❚ SiGe virtual substrates❚ high mobility 2D electron gases in strained-Si layers❚ SiGe/Si multi-quantum well structures

Advanced Low-Temperature Epitaxy at DERA

Representative Device Structures

HBT QWIP

HCMOS

Ge ~ 15% (strained)

Ge ~ 25% (relaxed)

Strained Si

Si collector

SiGe base

Si emitter

Prism

MultichannelDetector

Entrance Fiber

G rating

P ris m

P MT

E ntrance F iber

SOPRA Multi-Layer Monitor

Scanning

O.M.A.

Scanningchannel

O.M.A.channel

PDA

PMT

Strained Si(1-x)Ge(x)

Energy (eV)2.0 3.0 4.0 5.0

Rea

l(Die

lect

ric C

onst

ant),

ε1

Imag(D

ielectric Constant),

ε2

-40

-20

0

20

40

60

0

10

20

30

40

50

Six=0.065x=0.125x=0.17x=0.23

Strained and Relaxed Si(0.8)Ge(0.2)

Energy (eV)2.5 3.0 3.5 4.0 4.5

Rea

l(Die

lect

ric C

onst

ant),

ε 1

Imag(D

ielectric Constant),

ε2

-20

-10

0

10

20

30

40

0

10

20

30

40

50

strained, ε1relaxed, ε1strained, ε2relaxed, ε2

E1E1 + ∆∆∆∆1

Thin SiGe Layer

Energy (eV)2.5 3.0 3.5 4.0 4.5

<ε1>

<ε2 >

-20

-10

0

10

20

30

40

0

10

20

30

40

50Fit <ε1><ε2>

0 si 1 mm1 sigewv x=0.140 359.57 Å2 sio2 3.8448 Å

Thick SiGe Layer

Energy (eV)1.5 2.4 3.3 4.1 5.0

Tan

Ψ

Cos∆

0.0

0.2

0.4

0.6

0.8

-1.2

-0.9

-0.6

-0.3

-0.0

0.3

0.6Fit TanΨCos∆

0 si 1 mm1 sigewv x=0.110 6067.6 Å2 sio2 9.9339 Å

SE Characterisation of Single SiGe Epitaxial Layers

Growth Rate Vs Germanium Content (610C)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 0.05 0.1 0.15 0.2 0.25

Ge content

Gro

wth

Rat

e (A

ng/s

ec)

SEXRD

Germanium Content Vs Gas Ratio

0

0.05

0.1

0.15

0.2

0.25

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08

Gas Ratio (GeH4 / SiH4)

Ge

Co

nten

t

XRDSE

Calibration of DERA SiGe Epi Process

substrate

high-low15%

7%

992 Å

low-high

substrate

10%18%

917 Å

SE Characterisation of Graded SiGe Layers

Energy (eV)2.0 2.5 3.0 3.5 4.0 4.5

<ε1>

<ε2 >

-20

-10

0

10

20

30

40

0

10

20

30

40

50

Fit high-lowlow-high

-4 -3 -2 -1 0 1 2 3 4-4-3-2-101234

0.135-0.13750.1325-0.1350.13-0.1325

1 2 3 4 5S1

S2

S3

S4

S5725-750700-725675-700650-675625-650600-625575-600550-575

-4 -3 -2 -1 0 1 2 3 4-4

-3

-2

-1

0

1

2

3

4

370-375365-370360-365

1 2 3 4 5S1

S2

S3

S4

S50.139-0.14

0.138-0.139

0.137-0.138

0.136-0.137

0.135-0.136

VG Reactor AMAT Reactor

Ge fraction Ge

fraction

SiGe thickness (Å)

SiGe thickness (Å)

LLS PC

Xe lamp

700

Windows

Analyzer

Collimating Optics

Optical Fibre

PRISM SPECTROMETERWITH INTENSIFIED

PHOTODIODE ARRAY(250 - 825 nm)

Diaphragm

Heater and Wafer

Rotating Polarizer

Shutter

Collimating Optics

Diaphragm

ELLIPSOMETER CONTROL

ELECTRONICS

REACTOR CONTROL

PC

To Reactor Mass Flow Controllers

and Heater

Xe Lamp Power Supply

Zoom Lens

Filter

PM Tube

Amp-Disc

Ar Laser(488 nm)

Shutter

Real-time Spectroscopic Ellipsometry and Laser

Light Scattering

ELLIPSOMETRY PC

DSP

ANALYSIS OF REAL-TIME MULTI-WAVELENGTH DATA

� Normal Spectral Regression�average x and total thickness

� Virtual Interface Spectral Regression�surface x and growth rate as f(time) - demonstrated�accumulated thickness - endpointing demonstrated

� Artificial Neural Networks (with Principal Components)�surface x as f(time) independent of growth rate - achieved�extensive training required for specific structures�very fast

� Bayesian Statistical Tracking�surface x and growth rate as f(time) - achieved�predictive tracking based on trends and system models�provides statistical confidence limits

-20

-10

0

10

20

30

40

2 2.5 3 3.5 4 4.5 5

Energy (eV)

εε εε 11 11

0

5

10

15

20

25

30

35

40

εε εε 22 22

Si

20% Ge

610ºC

SiGe High Temperature Reference Spectra(0, 4, 6, 9, 11, 14, 17, 20% Ge)

0

0.05

0.1

0.15

0.2

0.25

0 200 400 600 800Time (sec)

x

0

100

200

300

400

500

600

700

800

Thick

ness

(Ang

)

Ge fraction, x

Thickness

GeH4 valve

closed at 550 Å

Controlled Growth of 550 Å SiGe Layer

Sequential Bayesian estimation of composition

Bayesian approach to composition estimation using state of the art tracking methods:

PriorPrior

PosteriorPosterior

ObservationsObservations

Prior knowledge is updated to

Posterior knowledge in the

light of observations.

Incorporation of system model to track specified trajectory

Real-time SE and Off-line SIMS Data for Stepped Ge Layer Profile

0

0 .02

0 .04

0 .06

0 .08

0 .1

0 .12

0 .14

0 .16

0 .18

0 .2

0 500 1 000 1 500 200 0 250 0

D e p th (A n g stro m s)

Ge

frac

tion

RTSE

SIMS

Spectrometer

Xenon Lamp

Cool-down chamber

Electronics and Power supplies

Optical

ibreEllipsometer

head

Transfer chamber

X-Y-Z stage with Autofocus & Pattern Recognition

MEDEA T618 Metrology Platform WP3.2

Advantages of Integrated Metrology

❚ Rapid process development❚ Evaluation of in-situ cleaning❚ Run-to-run and chamber-to-

chamber repeatability❚ Cross-wafer uniformity❚ Go/no go after each process

step❚ Accurate measurement of

layers obscured by later processing, eg buried thin

Si or SiGe, gradients❚ Run-to-run control and early

fault detection

❚ Implementation of SE in cool-down chamber of AMAT Epi Centura

- Adapt and test SE instrument- Reference spectra measurement- Methodology and system integration

❚ Evaluation of applicability- Measurements between processes

and off-line verification- Tests on patterned wafers

❚ Recommendation for improved cost-effectiveness

- Throughput, minimum requirements

Future Work