meis mtg university of huddersfield, 8 dec 2011 meis studies in the eu anna i3 project jaap van den...
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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
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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
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MEIS mtg U of Huddersfield, 08/12/2011
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:
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MEIS mtg U of Huddersfield, 08/12/2011
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]
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MEIS mtg U of Huddersfield, 08/12/2011
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
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MEIS mtg U of Huddersfield, 08/12/2011
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
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MEIS mtg U of Huddersfield, 08/12/2011
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)
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MEIS mtg U of Huddersfield, 08/12/2011
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%
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MEIS mtg U of Huddersfield, 08/12/2011
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
STO Sr,Ti,O, N 2.8 2.8
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 !
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MEIS mtg U of Huddersfield, 08/12/2011
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
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MEIS mtg U of Huddersfield, 08/12/2011
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
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MEIS mtg U of Huddersfield, 08/12/2011
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)
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MEIS mtg U of Huddersfield, 08/12/2011
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)
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MEIS mtg U of Huddersfield, 08/12/2011
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
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MEIS mtg U of Huddersfield, 08/12/2011
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?
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MEIS mtg U of Huddersfield, 08/12/2011
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
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MEIS mtg U of Huddersfield, 08/12/2011
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MEIS mtg U of Huddersfield, 08/12/2011
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MEIS mtg U of Huddersfield, 08/12/2011
1 m
MEIS facility Daresbury Lab
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MEIS mtg U of Huddersfield, 08/12/2011
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
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MEIS mtg U of Huddersfield, 08/12/2011
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
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MEIS mtg U of Huddersfield, 08/12/2011
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
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MEIS mtg U of Huddersfield, 08/12/2011
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.)
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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
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MEIS mtg U of Huddersfield, 08/12/2011
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
)
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MEIS mtg U of Huddersfield, 08/12/2011
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)
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MEIS mtg U of Huddersfield, 08/12/2011
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
Nominal layer structure:
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
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MEIS mtg U of Huddersfield, 08/12/2011
Results D07 D08 - annealing*
Nominal layer structure:
Minor changes only due to annealingStoich. STO on TiN stable upon annealing
Thickness
layer (nm)
Based on D07 D08
STO Sr,Ti,O, N 2.8 2.6
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
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MEIS mtg U of Huddersfield, 08/12/2011
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
STO Sr,Ti,O, N 3.4 3.1
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