meis mtg university of huddersfield, 8 dec 2011 meis studies in the eu anna i3 project jaap van den...

MEIS Mtg University of Huddersfield, 8 Dec 2011

MEIS studies in the EU ANNA I3 project

Jaap van den BergInternational Institute for Accelerator Applications, University of Huddersfield

Michael ReadingCentre for Materials and Physics, University of Salford

Acknowledgement: EU FP6 I3 project “ANNA” (contract no. 026134 RII3) Paul Bailey, Tim Noakes, Daresbury MEIS facility

MEIS mtg U of Huddersfield, 08/12/2011

Outline

• ANNA I3 project

• MEIS experimental aspects

• MEIS quantification

• MEIS analysis of:

– Ultra thin STO/TiN high-k MIM cap nanolayer structures:

• layer thickness & composition

• the effect of processing steps, e.g. segregation, layer interdiffusion

– Post annealing of shallow Sb implants into Si following SPER

• Sb precipitation and pile-up under the oxide


ANNA I3 project

Analytical Network for Nanotechnology

FP 6 project completed in February 2011 Details: www.i3-anna.net

• Networking - formation of a Joint (distributed) Analytical Laboratory with individual ISO 9000 certification • Joint Research Activities – 6 themes, e.g. nanolayer characterisation

• Transnational Access EU funded user access (Uni’s, Research institutes, SME’s) to analytical facilities not available in home country, e.g. MEIS

Integrated Infrastructure Initiative - 3 strands:


MEIS Experimental aspects• 100 – 200 keV He+ ions incident along the [-1-11] channel

• scattered ions detected along the [111] & [211] blocking directions. ( i.e. 70.5º and 90º scattering angle)

• Double alignment conditions to minimize the dechanneling background • Sub-nm depth resolution (near-surface)

Energy spectra to depth profile conversion:

Elastic E loss yields the mass of scattering atom Inelastic E loss yields the depth of scattering event

Quantification of yield & depth (energy spectrum simulation)

He+ ions: - higher dE/dz, better depth resolution

- higher scattering cross section (move target vertically during analysis)

- any assymmetry in inel. energy loss function reduced compared to H+

[211]

Si (001) surface

[001]

Detector

[111]

[332]


MEIS - quantitative?

Stopping powers: from SRIM 2003 onwards - consistent results for 50 - 200 keV ions on SiO2 layers of different thicknesses - checked against other techniques

Ion Yields affected by Scattering X-section and Neutralisation

Scattering X-section: Not Rutherford (electron screening), less repulsion- effectively higher energy & reduced cross section. Use Andersen correction for dσ/dΩ using the BZ potential

Neutralisation: FOM 50 -100 measurements on a variety of targets: neutralisation state depends on energy (PB) or velocity (M&Y)

Charge fractions:

CF (H) = 1-exp(-0.019*E)

CF (He) = 1-exp(-0.0061*E)

(P Bailey, Daresbury Lab. UK)

Depth1.0

0.8

0.6

0.4

0.2

0.0

charg

e fra

ctio

n

20016012080400ion energy [keV]

M+Y hydrogen H data M+Y helium He data


DRAM MIMcapsOngoing scale reduction in microelectronics: 40 nm node for DRAM (2011)

SiO2 oxide thickness < 1 nm - serious tunneling leakage current

Need for high k & small d in DRAM but leakage current < 10 -7 cm-2 @ 1V

• Accurate materials characterisation of these nanolayer structures is vital for understanding their properties

TEVB1 VB2 VT

TESTO

BESiO2

Si

VG

TiN

Si

Dielectric: STO, TiO2 ...

Bottom electrode:TiN

Top electrode:TiN

• Materials solution search – range of high-k oxides

SrTiO3 the most promising candidate:

high dielectric constant (bulk) ≥ 200 , band gap ~ 3.3eV

ITRS roadmap for DRAM: Equivalent Oxide Thickness in SiO2 (EOT) for C=25 fF/cell

TiN electrodes, low cost, manufacturing - friendly

2010-11 EOT 0.6 nm

2012-13 EOT 0.5 nm

Collaboration with IMEC, Leuven: Christoph Adelmann, Michaela Popovici

Planar and high aspect ratio structures


Results D02

IGOR spectrum simulation:

• excellent fit: TiN layer 2.6 nm

• Ti & N profiles coincide

• No evidence of SiO2 layer underneath

• Near surface reoxidation of TiN

• disordering of Si lattice to 5 nm depth (consistent with XRR results)

Nominal layer structure

Ti, Si, O and N peaks well separated (90º)

Narrow O peak due to surface reoxidation

D02: TiN SiO2 Si bulk

3 nm ~1nm

SiO2 IMEC cleanTiN deposited by PVD (Anelva)


Results D05, D06 - annealing

• Sr/(Sr +Ti) = 0.65; cf. RBS 0.62 (20 nm)

• D06 (annealed): more uniform Sr / Ti ratio

• Sr loss ~20% (where?); Ti 20% gain in STO

• Ti outdiffusion - TiN layer thickness reduced

Nominal layer structure:

D05: near surface Sr enrichment (ARXPS)

Thickness

layer (nm)

Based on D05 D06

STO Sr,Ti,O, N 3.3 3.2

TiN Sr,Ti,O, N 2.9 2.6

D05: STO Sr rich TiN SiO2 Si bulk

3 nm 3 nm ~1nmD06: D05 + RTA 650 ºC, 15 s in N2

(after crystallisation of STO)

D06: Sr reduction, Ti increase in STO:10-15%


Results D11 D12 - annealing

D11: TiN STO stoich TiN SiO2 Si

2 nm 3 nm 3 nmD12: D11 + RTA 650 ºC, 15 s in N2

Nominal layer structure (full MIMcap):

Thickness

layer (nm)

Based on D09 D10

TiN top Sr,Ti,O, N 2.0 ±.1 2.0 ±.1


TiN bottom 2.9 2.8

Clear interdiffusion of TiN/ STO at i/f

Increased Ti fraction in STO

Surface segregated Sr reduced post annealing

Thin layer surface reoxidation

Surface segregation of Sr on top of TiN !


Sb shallow implants in Si

Current generation CMOS transistors require ultra shallow S/D extension junctions; N dopant typically As

Collaboration with Fraunhofer IIS-b, Erlangen Stephane Koffel, Peter Pichler

S/D Extension junction depths < 15 nm High doping levels to obtain the required sheet resistance (Rs)

Sb potential replacement for As as n- type implant for S / D extensions

• Larger stopping, less straggle • leading to shallower implant and steeper profile• Higher activation? Lower sheet resistance observed• Active Sb concentration up to 1021 cm-3 measured • Diffusion only via V’s, less “ transient” diffusion

BUT problems: Sb pile up at SiO2/Si interface on annealing

Cause? Snowploughing during SPER ?

Combined SIMS, MEIS and XTEM study


20 keV Sb in Si - SIMS

20 keV Sb @ 1x1015 cm-2 implant Rp~18 nm

(to separate bulk and surface effects)

RTP @ 650 ºC 20 s in N2 SPER & activation

Post annealing

SIMS depth profiling

@ 800ºC 120 s to 1 hr• No visible broadening• Reduction of peak concentration• Sb pile-up at SiO2/Si interface@ 900ºC 120 s to 1200 s• broadening at 1200 s• increased Sb pile-up at SiO2/Si i/f

SIMS problems: sputter profiling, ion beam mixing, sputter rate changes


Sb implants in Si - MEIS MEIS energy spectrum200 keV He+ (Probe sample depth up to ~30 nm)

Peaks due to scattering off O, Si and Sb

Depth scales added (approx)

After RTP (crystal regrown by SPER):

Little Sb visible (non-substitutional)No pile-up under oxide after SPER!Si disorder at projected Sb range

After RTP + 20 mins anneal:

Sb becomes non-substitutional in implant range clear Sb pile-up peak under oxide; (hint @ +10 mins)


Sb depth profiles

Concentration depth profiles (of non-substitutional Sb)

After RTP (SPER): > 80% Sb substitutional No pile-up under

oxide

MEIS can quantify amounts, location and movement of Sb

After RTP + 20 mins post activation anneal: • 50 - 60% of Sb becomes visible (= non-

substitutional) around projected range

• Beginning of movement to and pile-up under oxide (hint @ +10 mins)


Sb implants in Si - TEM

> RTP (SPER)Band of EoR defectsSi was amorphisedX-tal regrown by SPERNo Sb precipitates !

TEM Micrographs

Sb precipitation !

MEIS Sb depth profiles

SPER+10 min anneal: Precipitates at ~15 nmNo Sb defects (precipitates) under Si oxide i/f

SPER+1 hr anneal:Precipitates at Rp still visible + Sb precipitatesat Si oxide i/f

Excellent correspondencebetween MEISdepth profiles and TEM


Analysis - Sb movement

Sheet concentrations (0-8 nm) & (10-25 nm) as function of anneal time (after RTP)

• Most Sb is substitutional after RTP; following post anneal rapid depopulation of substitutional Sb sites up to 20 mins then slow decay

• Pile-up peak increases linearly with anneal time

Pile-up is not due to snowploughing during SPER

Growth of near-surface precipitates is “diffusion limited”

Calculated diffusion coefficients unrealistic for Fermi-level dependent diffusivity (Pichler)

Percolation process?


Conclusions• MEIS (with energy spectrum simulation) provides high depth resolution, quantitative compositional and structural information on nano-layers:

• Layer thickness (precision of ± 0.1- 0.2 nm) (accuracy depends on e.g. density)

• Layer stoichiometry close to the nominal parameters / HR RBS data

• Dopant concentration and location (Sb implants)

• MEIS shows effect of processing steps on materials

in MIMcap nano layers:

• TiN PVD (sputtering) process removes SiO2 and causes deeper Si disorder:

• Clear layer interdiffusion at the STO/ TiN interfaces upon annealing

• Small but distinct Sr segregation on top of the TiN top electrode

in shallow Sb implants into Si:

• the depopulation of Sb in substitutional sites and Sb movement quantitatively

• indicates the operation of an unusual Sb diffusion process


1 m

MEIS facility Daresbury Lab


MEIS - Yield corrections

AuO

± 5%

Mass 20 - 160 product of X-section * neutralisation correction factor ± 5%

MEIS is “quantitative” Included in spectrum simulation

Combined effect of X-section correction & neutralisation factor

Ti

Hf

N

Conditions:

[-1-11] in [111 out]

Θ= 70.5o

SrSi

An

der

sen

* n

eutr

alis

atio

n

corr

ecti

on

fac

tor

Atomic number

Sb


DRAM MIMcapsOngoing microelectronic scale reduction: 40 nm node for DRAM (2011)

SiO2 oxide thickness < 1 nm - serious tunneling leakage current

In DRAM, the scale reduction forces high k & small d but leakage current < 10 -7 cm-2 @ 1V

• Accurate materials characterisation of such nanolayer structures is vital to understand their properties

TEVB1 VB2 VT

TESTO

BESiO2

Si

VG

TiN

Si

Dielectric: STO, TiO2 ...

Bottom electrode:TiN

Top electrode:TiN

• Materials solution search

SrTiO3 the most promising candidate: dielectric constant (bulk) ≥ 200 , band gap ~ 3.3eV

ITRS roadmap for DRAM: Equivalent Oxide Thickness in SiO2 (EOT) for C=25 fF/cell

TiN electrodes, low cost, manufacturing- friendly

EOT 0.65 nm EOT 0.5 nm

Collaboration with IMEC, Leuven: Christoph Adelmann, Michaela Popovici


MIM cap layers analysedSTO / TiN layers grown by ALD / PVD @ IMEC (STO = SrTiO3)Systematic change of variable

D02: TiN SiO2 Si bulk

3 nm

D03: STO Sr rich SiO2 Si bulk

3 nm

D05: STO Sr rich TiN SiO2 Si bulk

3 nm 3 nm

D06: + RTA 650 ºC, 15 s in N2

(crystallisation of STO)

D04: STO stoich SiO2 Si bulk

3 nm ~1nm

D07: STO stoich TiN SiO2 Si bulk

3 nm 3nm

D08: + RTA 650 ºC, 15 s in N2

D09: TiN STO Sr rich TiN SiO2 Si

2 nm 3 nm 3 nm

D10: + RTA 650 ºC, 15 s in N2

D11: TiN STO stoich TiN SiO2

Si

2 nm 3 nm 3 nm

TiN PVD (Anelva)

SiO2 ~1nm IMEC clean

STO Stoichiom. (4:3 recipe) ALD

STO Sr rich (3:1 recipe) ALD

D12: + RTA 650 ºC, 15 s in N2


Spectrum simulation• Dechannelling background subtracted from the spectrum

• A trial sample layer structure based on available information is sliced up in layers of 0.1 nm thick

• These layers are transformed into Gaussians, to account for energy resolution and depth dependent straggling

• The Z22 dependence of X-section

determines the backscattering yield. All Gaussians are summed.

• Energy loss rates obtained from SRIM (for up to two regions of different stopping powers)

•The model is optimized until a best fit (min

2) with the spectrum is obtained.

Energy spectra are simulated using a program developed at Daresbury Laboratory that runs as a macro within the IGOR© graphics software.(Paul Bailey, Daresbury Lab.)

MEIS Mtg University of Huddersfield, 8 Dec 2011

Fra

ctio

nal

com

p.C

oun

ts

Any dechannelling background subtracted from the spectrum

Energy spectra are simulated using a program developed at Daresbury Lab that runs as a macro within the IGOR© graphics software. (Paul Bailey, Daresbury Lab.)

Example: Energy spectrum from SiO2 on Si

SiO2

Si (disordered)Si (100) crystal

The Z22 dependence of X-section determines

the backscattering yield. All Gaussians are summed

Energy loss rates obtained from SRIM for up to two regions of different stopping powers

The model is optimized until a best fit (min2)

with the spectrum is obtained.

These layers are transformed into Gaussians, to account for energy resolution and depth dependent straggling

A trial sample layer structure based on available information is sliced up in layers of 0.1 nm thick

OSi

O

Si

Spectrum simulation


MEIS - Analysis

• Energy spectra converted into damage/dopant depth profiles (conc. of Si / dopant atoms vs. depth)

• Ion yields are referenced to the random level• Depth scales obtained from inelastic energy loss data (SRIM)

Mass & Depth profile analysis

Elastic energy loss gives the mass of scattering atom.

Inelastic energy loss within sample enables depth analysis

Quantification issues

• Only scattering from near-surface Si atoms and displaced Si or dopant atoms (due to shadow cones).

For 100-200 keV H or He ions sub-nm near surface depth resolution due to:• Beam energy near max in inelastic energy loss curve;

• Large Θ1 and Θ2: long pathways in target;

• Hi res electrostatic energy analyser. (0.4% En. Res.)

Inel

. En

. lo

ss (

eV/Å

)


2-D spectra

2 -D Yield vs. E - spectra

• Scattered ions detected using a toroidal electrostatic analyzer and 2-d detector. • Thus a 2D spectrum of yield vs scattering angle and energy is obtained. • A cut taken along the [111] blocking direction provides the energy spectrum.

Si (surface)

N (surface)

Hf (buried)

Si (buried)

O (surface)

<11

1>

100

90

80

70

60

55 65 75

Ene

rgy

(keV

)

Scattering angle (deg)


Results D03 & D04

• thickness taken as half height Ti & Si

20 & 40 % under nominal values:

• Sr diffusion into SiO2 during growth?

• D03 Sr/(Sr +Ti) = 0.65 cf. RBS = 0.62

• D04 Sr/(Sr +Ti) = 0.42 cf. RBS 0.5


Thickness

layer (nm)

Based on

D03 D04

STO Sr, O 2.8 2.0

Ti, Si 2.4 1.7

Clear difference in Sr/Ti ratios & peak widths

D03: STO Sr rich SiO2 Si bulk

3 nm ~1nm

D04: STO stoich SiO2 Si bulk

3 nm ~1nm


Results D07 D08 - annealing*


Minor changes only due to annealingStoich. STO on TiN stable upon annealing

Thickness

layer (nm)

Based on D07 D08


TiN Sr,Ti,O, N 2.8 2.8

• Sr/(Sr +Ti) ratio

D07 = 0.53 D08 = 0.5 cf. RBS 0.5

• D07 & D08: N peak >1 nm deeper into SiO2

• Some interdiffusion at STO/TiN i/f

D07: STO Stoich TiN SiO2 Si bulk

3 nm 3nm ~1nmD08: D07 + RTA 650 ºC, 15 s in N2

N O S i

Ti

Sr


Results D09 D10 annealingNominal layer structure:

D09: TiN STO Sr rich TiN SiO2 Si

2 nm 3 nm 3 nmD10: D09 + RTA 650 ºC, 15 s in N2

Thickness

layer (nm)

Based on D09 D10

TiN top Sr,Ti,O, N 1.9 ±.1 1.9±.1


TiN bottom 2.9 2.8

D09 single scan, high noise level

Interdiffusion at TiN/STO i/f post annealing

Some Sr segregation at surface (≤0.4 nm)

Surface reoxidation

meis mtg university of huddersfield, 8 dec 2011 meis studies in the eu anna i3 project jaap van den...

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