radiation tolerant sensors for solid state tracking

Radiation Tolerant Sensors for Solid State Tracking Detectors

Michael MollMichael Moll

CERN CERN -- Geneva Geneva -- SwitzerlandSwitzerland

Université de Genève, Ecole de physique, December 13, 2006

- CERN-RD50 project –http://www.cern.ch/rd50http://www.cern.ch/rd50

Michael Moll – Geneva, 13. December 2006 -2-

RD50 Outline

• Introduction: LHC and LHC experiment

• Motivation to develop radiation harder detectors

• Introduction to the RD50 collaboration

• Part I: Radiation Damage in Silicon Detectors (A very brief review)• Microscopic defects (changes in bulk material)• Macroscopic damage (changes in detector properties)

• Part II: RD50 - Approaches to obtain radiation hard sensors• Material Engineering• Device Engineering

• Summary and preliminary conclusion


RD50 LHC - Large Hadron Collider

Start : 2007

• Installation inexisting LEP tunnel

• 27 Km ring

• 1232 dipoles B=8.3T

• ≈ 4000 MCHF(machine+experiments)

• pp √s = 14 TeVLdesign = 10

34 cm-2 s-1

• Heavy ions (e.g. Pb-Pb at √s ~ 1000 TeV)

LHC experiments located at 4 interaction points

p p


RD50 LHC Experiments

CMS

+ LHCf


RD50 LHC Experiments

CMS

LHCf


RD50 LHC example: CMS inner tracker

5.4 m

2.4

m

Inner TrackerOuter Barrel

(TOB)Inner Barrel (TIB) End Cap

(TEC)Inner Disks(TID)

CMS – “Currently the Most Silicon”

• Micro Strip:• ~ 214 m2 of silicon strip sensors, 11.4 million strips

• Pixel:• Inner 3 layers: silicon pixels (~ 1m2)

• 66 million pixels (100x150µµµµm)• Precision: σ(rφ) ~ σ(z) ~ 15µµµµm• Most challenging operating environments (LHC)

CMS

Pixel

93 cm

30 cm

Pixel Detector

4 TMagnetic field

21.6mLength

15mDiameter

12500 tTotal weight


RD50 Status December 2006

• LHC Silicon Trackers close to or under commissioning

CMS Tracker Outer Barrel

• ATLAS Silicon Tracker (08/2006)August 2006 – installed in ATLAS

• CMS Tracker (12/2006)(foreseen: June 2007 into the pit)


RD50 Motivation for R&D on Radiation Tolerant Detectors: Super - LHC

• LHC upgradeLHC (2007), L = 1034cm-2s-1

φ(r=4cm) ~3·1015cm-2

Super-LHC (2015 ?), L = 1035cm-2s-1

φ(r=4cm) ~1.6·1016cm-2

• LHC ( Replacement of components)e.g. - LHCb Velo detectors (~2010)

- ATLAS Pixel B-layer (~2012)

• Linear collider experiments (generic R&D)Deep understanding of radiation damage will be fruitful for linear collider experiments where high doses of e, γ will play a significant role.

5 years

2500 fb-1

10 years

500 fb-1

×××× 5

0 10 20 30 40 50 60

r [cm]

1013

5

1014

5

1015

5

1016

Φeq

[cm

-2]

total fluence Φeqtotal fluence Φeq

neutrons Φeq

pions Φeq

other charged

SUPER - LHC (5 years, 2500 fb-1)

hadrons ΦeqATLAS SCT - barrelATLAS Pixel

Pixel (?) Ministrip (?)

Macropixel (?)

(microstrip detectors)

[M.Moll, simplified, scaled from ATLAS TDR]


RD50 The CERN RD50Collaborationhttp://www.cern.ch/rd50

• Collaboration formed in November 2001• Experiment approved as RD50 by CERN in June 2002• Main objective:

• Presently 264 members from 52 institutes

Development of ultra-radiation hard semiconductor detectors for the luminosity upgrade of the LHC to 1035 cm-2s-1 (“Super-LHC”).

Challenges: - Radiation hardness up to 1016 cm-2 required- Fast signal collection (Going from 25ns to 10 ns bunch crossing ?)- Low mass (reducing multiple scattering close to interaction point)- Cost effectiveness (big surfaces have to be covered with detectors!)

RD50: Development of Radiation Hard Semiconductor Devices for High Luminosity Colliders

Belarus (Minsk), Belgium (Louvain), Canada (Montreal), Czech Republic(Prague (3x)), Finland (Helsinki, Lappeenranta), Germany (Berlin, Dortmund, Erfurt, Freiburg, Hamburg, Karls ruhe),

Israel (Tel Aviv), Italy (Bari, Bologna, Florence, Padova, Perugia, Pisa, Trento, Turin), Lithuania (Vilnius), The Netherlands(Amsterdam), Norway (Oslo (2x)), Poland(Warsaw (2x)), Romania (Bucharest (2x)),Russia

(Moscow), St.Petersburg), Slovenia(Ljubljana), Spain (Barcelona, Valencia), Switzerland (CERN, PSI), Ukraine (Kiev), United Kingdom (Diamond, Exeter, Glasgow, Lancaster, Liverpool, Sheffield),

USA (Fermilab, Purdue University, Rochester University, SCIPP Santa Cruz, Syracuse University, BNL, University of New Mexico)


RD50 Outline



•Part I: Radiation Damage in Silicon Detectors (A very brief review)

• Microscopic defects (changes in bulk material)• Macroscopic damage (changes in detector properties)

• Part II: RD50 - Approaches to obtain radiation hard sensors• Material Engineering• Device Engineering



RD50 Radiation Damage – Microscopic Effects

particleparticleparticleparticle SiSVacancy

+ Interstitial

point defects (V-O, C-O, .. )

point defects and clusters of defects

EK>25 eV

EK > 5 keV

V

I

I

I

V

V

♦ Spatial distribution of vacancies created by a 50 keV Si-ion in silicon.(typical recoil energy for 1 MeV neutrons)

van Lint 1980

M.Huhtinen 2001


RD50 Radiation Damage – Microscopic Effects

particleparticleparticleparticle SiSVacancy

+ Interstitial

point defects (V-O, C-O, .. )

point defects and clusters of defects

EK>25 eV

EK > 5 keV

V

I

•Neutrons (elastic scattering)• En > 185 eV for displacement• En > 35 keV for cluster

•60Co-gammas•Compton Electronswith max. Eγ ≈1 MeV(no cluster production)

•Electrons•Ee > 255 keV for displacement•Ee > 8 MeV for cluster

Only point defects point defects & clusters Mainly clusters

10 MeV protons 24 GeV/c protons 1 MeV neutronsSimulation:

Initial distribution of vacancies in (1µµµµm)3

after 1014 particles/cm2

[Mika Huhtinen NIMA 491(2002) 194]


RD50 Primary Damage and secondary defect formation

• Two basic defects

I - Silicon Interstitial V - Vacancy

• Primary defect generationI , I 2 higher order I (?)

⇒⇒⇒⇒ I -CLUSTER (?)V, V2, higher order V (?)

⇒⇒⇒⇒ V -CLUSTER (?)

• Secondary defect generation

Main impurities in silicon: Carbon (Cs)Oxygen (Oi)

I+C s →→→→ Ci ⇒ Ci+Cs →→→→ CiCSCi+Oi →→→→ CiOiCi+Ps →→→→ CiPS

V+V →→→→ V2 V+V2 →→→→ V3 V+Oi →→→→ VO i ⇒ V+VO i →→→→ V2OiV+Ps →→→→ VPs

I+V2 →→→→ V I+VOi →→→→ Oi .......................

I

I

V

V

Damage?! (“V2O-model”)

Damage?!


RD50 Example of defect spectroscopyExample of defect spectroscopy-- neutron irradiated neutron irradiated --

50 100 150 200 250Temperature [ K ]

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

DLT

S-s

igna

l (b 1)

[pF

]

60 min 60 min170 days170 days

CiCs(-/0)CiCs(-/0)

VOi(-/0)VOi(-/0)

VV (--/-)VV (--/-)

Ci(-/0)Ci(-/0)

CiOi(+/0)CiOi(+/0)

H(220K)H(220K)

Ci(+/0)Ci(+/0)

E(40K)E(40K)E(45K)E(45K)

E(35K)E(35K)

? + VV(-/0) + ?? + VV(-/0) + ? Introduction RatesNt/ΦΦΦΦeq:

Ci :1.55 cm-1

CiCs : CiOi :0.40 cm-1 1.10 cm-1

Introduction rates of main defects ≈≈≈≈ 1 cm-1

Introduction rate of negative space charge ≈≈≈≈ 0.05 cm-1

example : ΦΦΦΦeq = 1××××1014 cm-2

defects≈≈≈≈ 1××××1014 cm-3

space charge ≈≈≈≈ 5××××1012cm-3

Deep Level Transient Spectroscopy


RD50 Impact of Defects on Detector properties

ShockleyShockley--ReadRead--Hall statistics Hall statistics (standard theory)(standard theory)

Impact on detector properties can be calculated if all defect paImpact on detector properties can be calculated if all defect pa rameters are known:rameters are known:σσσσσσσσn,pn,p : cross sections : cross sections ∆∆∆∆∆∆∆∆E : ionization energy E : ionization energy NNtt : concentration: concentration

Trapping (e and h)⇒⇒⇒⇒ CCE

shallow defects do not contribute at room

temperature due to fast detrapping

charged defects ⇒⇒⇒⇒ Neff , Vdep

e.g. donors in upper and acceptors in

lower half of band gap

generation⇒⇒⇒⇒ leakage current

Levels close to midgap

most effective

enhanced generation⇒⇒⇒⇒ leakage current⇒⇒⇒⇒ space charge

InterInter--center chargecenter chargetransfer model transfer model

(inside clusters only)(inside clusters only)


RD50

depleted zone

neutral bulk(no electric field)

Poisson’s equation

Reverse biased abrupt pReverse biased abrupt p ++--n junctionn junction

Electrical Electrical charge densitycharge density

Electrical Electrical field strengthfield strength

Electron Electron potential energypotential energy

( ) effNq

xdx

d ⋅=−0

02

2

εεφ

2

0

0 dNq

V effdep ⋅⋅=εε

effective space charge density

depletion voltage

Full charge collection only for VB>Vdep !

Positive space charge, Neff =[P](ionized Phosphorus atoms)

particle (mip)

+V <VB dep +V >VB dep


RD50 Macroscopic Effects – I. Depletion Voltage

Change of Depletion Voltage Vdep (Neff)

…. with particle fluence:

before inversion

after inversion

n+ p+ n+

• “Type inversion”: Neff changes from positive to negative (Space Charge Sign Inversion)

10-1 100 101 102 103

Φeq [ 1012 cm-2 ]

1

510

50100

5001000

5000

Ud

ep [

V]

(d

= 30

0µm

)

10-1

100

101

102

103

| Ne

ff |

[ 10

11

cm-3

]

≈ 600 V

1014cm-2

type inversion

n-type "p-type"

[M.Moll: Data: R. Wunstorf, PhD thesis 1992, Uni Hamburg]

• Short term:“ Beneficial annealing”• Long term:“ Reverse annealing”- time constant depends on temperature:

~ 500 years (-10°C)~ 500 days ( 20°C)~ 21 hours ( 60°C)

- Consequence:Detectors must be cooledeven when the experiment is not running!

…. with time (annealing):

NC

NC0

gC Φeq

NYNA

1 10 100 1000 10000annealing time at 60oC [min]

0

2

4

6

8

10

∆ N

eff [1

011 c

m-3

]

[M.Moll, PhD thesis 1999, Uni Hamburg]

p+


RD50 Radiation Damage – II. Leakage Current

1011 1012 1013 1014 1015

Φeq [cm-2]

10-6

10-5

10-4

10-3

10-2

10-1

∆I /

V

[A/c

m3 ]

n-type FZ - 7 to 25 KΩcmn-type FZ - 7 KΩcmn-type FZ - 4 KΩcmn-type FZ - 3 KΩcm

n-type FZ - 780 Ωcmn-type FZ - 410 Ωcmn-type FZ - 130 Ωcmn-type FZ - 110 Ωcmn-type CZ - 140 Ωcm

p-type EPI - 2 and 4 KΩcm

p-type EPI - 380 Ωcm

[M.Moll PhD Thesis][M.Moll PhD Thesis]

• Damage parameter αααα (slope in figure)

Leakage currentper unit volume

and particle fluence

• αααα is constant over several orders of fluenceand independent of impurity concentration in Si

can be used for fluence measurement

eqV

I

Φ⋅∆=α

80 min 60°°°°C

Change of Leakage Current (after hadron irradiation)

…. with particle fluence:

• Leakage current decreasing in time (depending on temperature)

• Strong temperature dependence

Consequence:Cool detectors during operation!Example: I (-10°C) ~1/16 I (20°C)

1 10 100 1000 10000annealing time at 60oC [minutes]

0

1

2

3

4

5

6

α(t)

[10-1

7 A

/cm

]

1

2

3

4

5

6

oxygen enriched silicon [O] = 2.1017 cm-3

parameterisation for standard silicon [M.Moll PhD Thesis]

80 min 60°°°°C

…. with time (annealing):

−∝ TkE

IB

g

2exp


RD50

Deterioration of Charge Collection Efficiency (CCE) by trapping

⋅−= tQtQ

heeffhehe

,,0,

1exp)(

τ

0 2.1014 4.1014 6.1014 8.1014 1015

particle fluence - Φeq [cm-2]

0

0.1

0.2

0.3

0.4

0.5

Inve

rse

trap

ping

tim

e 1

/τ

[ns-1

]

data for electronsdata for electronsdata for holesdata for holes

24 GeV/c proton irradiation24 GeV/c proton irradiation

[M.Moll; Data: O.Krasel, PhD thesis 2004, Uni Dortmund][M.Moll; Data: O.Krasel, PhD thesis 2004, Uni Dortmund]

Increase of inverse trapping time (1/τ) with fluence

Trapping is characterized by an effective trapping time τeff for electrons and holes:

….. and change with time (annealing):

5 101 5 102 5 103

annealing time at 60oC [min]

0.1

0.15

0.2

0.25

Inve

rse

trap

ping

tim

e 1

/τ

[ns-1

]data for holesdata for holesdata for electronsdata for electrons

24 GeV/c proton irradiation24 GeV/c proton irradiationΦeq = 4.5.1014 cm-2 Φeq = 4.5.1014 cm-2

[M.Moll; Data: O.Krasel, PhD thesis 2004, Uni Dortmund][M.Moll; Data: O.Krasel, PhD thesis 2004, Uni Dortmund]

where defectsheeff

N∝,

1

τ

Radiation Damage – III. CCE (Trapping)


RD50 Summary: Radiation Damage in Silicon Sensors

Two general types of radiation damage to the detector materials:

• Bulk (Crystal) damagedue to Non Ionizing Energy Loss (NIEL)- displacement damage, built up of crystal defects –

I. Change of effective doping concentration (higher depletion voltage, under- depletion)

II. Increase of leakage current(increase of shot noise, thermal runaway)

III. Increase of charge carrier trapping (loss of charge)

• Surface damagedue to Ionizing Energy Loss (IEL)- accumulation of positive in the oxide (SiO2) and the Si/SiO2 interface –

affects: interstrip capacitance (noise factor), breakdown behavior, …

Impact on detector performance and Charge Collection Efficiency(depending on detector type and geometryand readout electronics!)

Signal/noise ratio is the quantity to watch ⇒⇒⇒⇒ Sensors can fail from radiation damage !

Same for all tested Silicon

materials!

Influenced by impuritiesin Si – Defect Engineeringis possible!

Can be optimized!


RD50 Outline



• Part I: Radiation Damage in Silicon Detectors (A very brief review)• Microscopic defects (changes in bulk material)

• Macroscopic damage (changes in detector properties)

• Part II: RD50 - Approaches to obtain radiation hard sensors• Material Engineering

• Device Engineering



RD50 Approaches of RD50 to develop radiation harder tracking detectors

• Defect Engineering of Silicon• Understanding radiation damage

• Macroscopic effects and Microscopic defects• Simulation of defect properties and defect kinetics• Irradiation with different particles at different energies

• Oxygen rich silicon• DOFZ, Cz, MCZ, EPI

• Oxygen dimer enriched silicon• Hydrogen enriched silicon• Pre-irradiated silicon• Influence of processing technology

• New Materials• Silicon Carbide (SiC), Gallium Nitride (GaN)• Diamond: CERN RD42 Collaboration

• Device Engineering (New Detector Designs)• p-type silicon detectors (n-in-p)• Thin detectors• 3D and Semi 3Ddetectors• Cost effective detectors• Simulation of highly irradiated detectors

Scientific strategies:

I. Material engineering

II. Device engineering

III. Variation of detectoroperational conditions

CERN-RD39“Cryogenic Tracking Detectors”


RD50

• Influence the defect kinetics by incorporation of impurities or defects

• Best example: Oxygen

Initial idea: Incorporate Oxygen to getter radiation-induced vacancies⇒⇒⇒⇒ prevent formation of Di-vacancy (V2) related deep acceptor levels

Observation: Higher oxygen content ⇒⇒⇒⇒ less negative space charge(less charged acceptors)

• One possible mechanism: V2O is a deep acceptor

O VO (not harmful at room temperature)V

VO V2O (negative space charge)

Defect Engineering of Silicon

V2O(?)

Ec

EV

VO

V2 in clusters


RD50 Spectacular Improvement of γγγγ-irradiation tolerance

• No type inversion for oxygen enriched silicon!• Slight increase of positive space charge

(due to Thermal Donor generation?)

[E.Fretwurst et al. 1st RD50 Workshop] See also:- Z.Li et al. [NIMA461(2001)126]- Z.Li et al. [1st RD50 Workshop]

0 200 400 600 800 1000dose [Mrad]

0

50

100

150

200

250

Vde

p [V

]

0

10

20

30

40

Nef

f [10

11 c

m-3

]

CA: <111> STFZ CA: <111> STFZ CB: <111> DOFZ 24 hCB: <111> DOFZ 24 hCC: <111>DOFZ 48 hCC: <111>DOFZ 48 hCD: <111> DOFZ 72 hCD: <111> DOFZ 72 hCE: <100> STFZCE: <100> STFZCF: <100> DOFZ 24hCF: <100> DOFZ 24hCG: <100> DOFZ 48hCG: <100> DOFZ 48hCH: <100> DOFZ 72hCH: <100> DOFZ 72h

(a)(a)

Depletion Voltage

0 200 400 600 800 1000dose [Mrad]

0

500

1000

1500

I rev [

nA]

CA: <111> STFZCA: <111> STFZCB: <111> DOFZ 24hCB: <111> DOFZ 24hCC: <111> DOFZ 48hCC: <111> DOFZ 48hCD: <111> DOFZ 78hCD: <111> DOFZ 78h

(b)(b)

CE: <100> STFZ CE: <100> STFZ CF: <100> DOFZ 24hCF: <100> DOFZ 24hCG: <100> DOFZ 48hCG: <100> DOFZ 48hCH: <100> DOFZ 72hCH: <100> DOFZ 72h

(b)

• Leakage increase not linear and depending on oxygen concentration

Leakage Current


RD50 Characterization of microscopic defects- γ γ γ γ and proton irradiated silicon detectors -

• 2003: Major breakthrough on γγγγ-irradiated samples• For the first timemacroscopic changes of the depletion voltage and leakage current

can be explained by electrical properties of measured defects !

• since 2004:Big steps in understanding the improved radiation tolerance ofoxygen enriched and epitaxial silicon after proton irradiation

[APL, 82, 2169, March 2003]

Almost independent of oxygencontent:• Donor removal•“Cluster damage” ⇒⇒⇒⇒ negative charge

Influenced by initial oxygencontent:• I–defect: deep acceptor level at EC-0.54eV

(good candidate for the V2O defect)⇒⇒⇒⇒ negative charge

Influenced by initial oxygen dimercontent (?):• BD-defect: bistable shallow thermal donor

(formed via oxygen dimers O2i)⇒⇒⇒⇒ positive charge

Levels responsible for depletion voltage changes after proton irradiation:

ΒΒΒΒD-defectI-defect

[I.Pintilie, RESMDD, Oct.2004]


RD50 Oxygen enriched silicon – DOFZ- proton irradiation -

• DOFZ (Diffusion Oxygenated Float Zone Silicon) 1982 First oxygen diffusion tests on FZ [Brotherton et al. J.Appl.Phys.,Vol.53, No.8.,5720]

1995 First tests on detector grade silicon[Z.Li et al. IEEE TNS Vol.42,No.4,219]

1999 Introduced to the HEP community by RD48 (ROSE)

0 1 2 3 4 5Φ24 GeV/c proton [1014 cm-2]

0

2

4

6

8

10

|Nef

f| [1

012 c

m-3

]

100

200

300

400

500

600

Vde

p [V

] (30

0 µm

)

Carbon-enriched (P503)Standard (P51)O-diffusion 24 hours (P52)O-diffusion 48 hours (P54)O-diffusion 72 hours (P56)

Carbonated

Standard

Oxygenated

[RD48-NIMA 465(2001) 60]

http://cern.ch/rd48

ROSERD48

First tests in 1999 show clear advantage of oxygenation

Later systematic tests reveal strong variations with no clear dependence

on oxygen content

0 2 4 6 8 10Φ 24G eV /c pro ton [1014 cm-2]

0123456789

10

|Nef

f| [1

012cm

-3]

100

200

300

400

500

600

700

Vde

p [V

] (30

0 µm

)15 KΩ cm <111> - oxygenated

15 KΩ cm <111> - standard

[M .M oll - N IM A 511 (2003) 97]

However, only non-oxygenated diodes show a “bad” behavior.


RD50 Silicon Growth Processes

Single crystal silicon

Poly silicon

RF Heating coil

Float Zone Growth

• Floating Zone Silicon (FZ) • Czochralski Silicon (CZ)

Czochralski Growth

• Basically all silicon detectors made out of high resistivety FZ silicon

• Epitaxial Silicon (EPI)

• The growth method used by the IC industry.

• Difficult to producevery high resistivity

• Chemical-Vapor Deposition (CVD) of Si

• up to 150 µµµµm thick layers produced

• growth rate about 1µµµµm/min


RD50

0 10 20 30 40 50 60 70 80 90 100Depth [µm]

51016

51017

51018

5

O-c

once

ntra

tion

[1/c

m3 ]

SIMS 25 µm SIMS 25 µm

25 m

u25

mu

SIMS 50 µmSIMS 50 µm

50 m

u50

mu

SIMS 75 µmSIMS 75 µm

75 m

u75

mu

simulation 25 µmsimulation 25 µmsimulation 50 µmsimulation 50 µmsimulation 75µmsimulation 75µm

Oxygen concentration in FZ, CZ and EPI

DOFZ and CZ silicon Epitaxial silicon

• EPI: O i and O2i (?) diffusion from substrateinto epi-layer during production

• EPI: in-homogeneous oxygen distribution

[G.Lindström et al.,10th European Symposium on Semiconductor Detectors, 12-16 June 2005]

• DOFZ: inhomogeneous oxygen distribution

• DOFZ: oxygen content increasing with time at high temperature

EPIlayer CZ substrate

0 50 100 150 200 250depth [µm]

5

1016

5

1017

5

1018

O-c

once

ntra

tion

[cm-3

]

51016

51017

51018

5

DOFZ 72h/1150oCDOFZ 48h/1150oCDOFZ 24h/1150oC

Data: G.Lindstroem et al.

[M.Moll]

• CZ: high Oi (oxygen) and O2i (oxygen dimer)concentration (homogeneous)

• CZ: formation of Thermal Donors possible !

0 50 100 150 200 250depth [µm]

5

1016

5

1017

5

1018

O-c

once

ntra

tion

[cm-3

]

51016

51017

51018

5

Cz as grown

DOFZ 72h/1150oCDOFZ 48h/1150oCDOFZ 24h/1150oC

Data: G.Lindstroem et al.

[M.Moll]


RD50 Silicon Materials under Investigation by RD50

~ 7××××101750 – 100EPI–DODiffusion oxygenated Epitaxial layers on CZ

~ 5××××1017~ 1××××10 3MCzMagnetic Czochralski Si, Okmetic, Finland(n- and p-type)

< 1××××101750 – 400EPIEpitaxial layers on Cz-substrates, ITME, Poland(n- and p-type, 25, 50, 75, 150 µm thick)

~ 8-9××××1017~ 1××××10 3CzCzochralski Si, Sumitomo, Japan (n-type)

~ 1–2××××10171–7××××10 3DOFZDiffusion oxygenated FZ (n- and p-type)

< 5××××10161–7××××10 3FZStandard FZ (n- and p-type)

[O i] (cm-3)ρρρρ (ΩΩΩΩcm)SymbolMaterial

• DOFZ silicon - Enriched with oxygen on wafer level, inhomogeneousdistribution of oxygen

• CZ/MCZ silicon - high Oi (oxygen) and O2i (oxygen dimer) concentration (homogeneous)- formation of shallow Thermal Donors possible

• Epi silicon - high Oi , O2i content due to out-diffusion from the CZ substrate (inhomogeneous)- thin layers: high doping possible (low starting resistivity)

• Epi-Do silicon - as EPI, however additional Oi diffused reaching homogeneousOi content

standardfor

particledetectors

used for LHC Pixel

detectors

“new”material


RD50 Standard FZ, DOFZ, Cz and MCz Silicon

24 GeV/c proton irradiation

• Standard FZ silicon• type inversion at ~ 2××××1013 p/cm2

• strong Neff increase at high fluence

• Oxygenated FZ (DOFZ)• type inversion at ~ 2××××1013 p/cm2

• reduced Neff increase at high fluence

• CZ silicon and MCZ silicon no type inversionin the overall fluence range (verified by TCT measurements)

(verified for CZ silicon by TCT measurements, preliminary result for MCZ silicon)⇒⇒⇒⇒ donor generation overcompensates acceptor generation in high fluence range

• Common to all materials (after hadron irradiation): reverse current increase

increase of trapping (electrons and holes) within ~ 20%

0 2 4 6 8 10proton fluence [1014 cm-2]

0

200

400

600

800

Vd

ep (

300µ

m)

[V]

0

2

4

6

8

10

12

|Ne

ff| [

101

2 cm

-3]

FZ <111>FZ <111>DOFZ <111> (72 h 11500C)DOFZ <111> (72 h 11500C)MCZ <100>MCZ <100> CZ <100> (TD killed) CZ <100> (TD killed)


RD50• Epitaxial silicon

• Layer thickness: 25, 50, 75 µµµµm (resistivity: ~ 50 Ωcm); 150 µµµµm (resistivity: ~ 400 Ωcm)

• Oxygen: [O] ≈≈≈≈ 9××××1016cm-3; Oxygen dimers (detected via IO2-defect formation)

EPI Devices – Irradiation experiments

• Only little change in depletion voltage

• No type inversionup to ~ 1016 p/cm2 and ~ 1016 n/cm2

high electric field will stay at front electrode!reverse annealing will decreases depletion voltage!

• Explanation: introduction of shallow donors is biggerthan generation of deep acceptors

G.Lindström et al.,10th European Symposium on Semiconductor Detectors, 12-16 June 2005G.Kramberger et al., Hamburg RD50 Workshop, August 2006

0 2.1015 4.1015 6.1015 8.1015 1016

Φeq [cm-2]

0

1014

2.1014

Nef

f(t0)

[cm

-3]

25 µm, 80 oC25 µm, 80 oC

50 µm, 80 oC50 µm, 80 oC

75 µm, 80 oC75 µm, 80 oC

23 GeV protons23 GeV protons

≈≈≈≈320V (75µµµµm)

≈≈≈≈105V (25µµµµm)

≈≈≈≈230V (50µµµµm)

• CCE (Sr90 source, 25ns shaping): 6400 e (150 µµµµm; 2x1015 n/cm-2)

3300 e (75µµµµm; 8x1015 n/cm-2)

2300 e (50µµµµm; 8x1015 n/cm-2)

0 20 40 60 80 100Φeq [1014 cm-2]

0

2000

4000

6000

8000

10000

12000

Sign

al [

e]

150 µm - neutron irradiated 75 µm - proton irradiated 75 µm - neutron irradiated 50 µm - neutron irradiated 50 µm - proton irradiated

[M.Moll]

[Data: G.Kramberger et al., Hamburg RD50 Workshop, August 2006]


RD50 Advantage of non-inverting materialp-in-n detectors (schematic figures!)

Fully depleted detector(non – irradiated):


RD50

inverted to “p-type”, under-depleted:

• Charge spread – degraded resolution

• Charge loss – reduced CCE

Advantage of non-inverting materialp-in-n detectors (schematic figures!)

Fully depleted detector(non – irradiated):

heavy irradiation

inverted

non-inverted , under-depleted:

•Limited loss in CCE

•Less degradation with under-depletion

non inverted

Be careful, this is a very schematic explanation, reality is more complex !


RD50 Epitaxial silicon - Annealing

• 50 µµµµm thick silicon detectors:- Epitaxial silicon (50ΩΩΩΩcm on CZ substrate, ITME & CiS) - Thin FZ silicon (4KΩΩΩΩcm, MPI Munich, wafer bonding technique)

• Thin FZ silicon: Type inverted, increase of depletion voltage with time

• Epitaxial silicon: No type inversion, decrease of depletion voltage with time⇒⇒⇒⇒ No need for low temperature during maintenance of SLHC detectors!

[E.Fretwurst et al.,RESMDD - October 2004]

100 101 102 103 104 105

annealing time [min]

0

50

100

150

Vfd

[V]

EPI (ITME), 9.6.1014 p/cm2EPI (ITME), 9.6.1014 p/cm2

FZ (MPI), 1.7.1015 p/cm2FZ (MPI), 1.7.1015 p/cm2

Ta=80oCTa=80oC

[E.Fretwurst et al., Hamburg][E.Fretwurst et al., Hamburg]

0 20 40 60 80 100proton fluence [1014 cm-2]

0

50

100

150

200

250

Vd

ep [

V]

0.20.40.60.81.01.21.4

|Ne

ff| [

101

4 cm

-3]

EPI (ITME), 50µmEPI (ITME), 50µm

FZ (MPI), 50µmFZ (MPI), 50µm

Ta=80oCTa=80oC

ta=8 minta=8 min


RD50

Property Diamond GaN 4H SiC Si Eg [eV] 5.5 3.39 3.3 1.12 Ebreakdown [V/cm] 107 4·106 2.2·106 3·105 µe [cm2/Vs] 1800 1000 800 1450 µh [cm2/Vs] 1200 30 115 450 vsat [cm/s] 2.2·107 - 2·107 0.8·107 Z 6 31/7 14/6 14 εr 5.7 9.6 9.7 11.9 e-h energy [eV] 13 8.9 7.6-8.4 3.6 Density [g/cm3] 3.515 6.15 3.22 2.33 Displacem. [eV] 43 ≥≥≥≥15 25 13-20

New Materials: Epitaxial SiC“A material between Silicon and Diamond”

• Wide bandgap (3.3eV) ⇒ lower leakage current

than silicon

• Signal:Diamond 36 e/µµµµmSiC 51 e/µµµµmSi 89 e/µµµµm

⇒ more charge than diamond

• Higher displacement threshold than silicon

⇒ radiation harder than silicon (?)

R&D on diamond detectors:RD42 – Collaborationhttp://cern.ch/rd42/


RD50 SiC: CCE after neutron irradiation

• CCE before irradiation• 100 % with αααα particles and MIPS

• CCE after irradiation (example)• material produced by CREE• 55 µµµµm thick layer• neutron irradiated samples• tested with ββββ particles

• Conclusion:• SiC is less radiation tolerant than

expected

• Consequence:• RD50 will stop working on this topic

[F.Moscatelli, Bologna, December 2006]

0.1 1E14 1E15 1E160

1000

2000

3000

Before irradiation

Col

lect

ed C

harg

e (

e- )Fluence ((1MeV) n/cm2)

@ 950 V


RD50 Outline



• Part I: Radiation Damage in Silicon Detectors (A very brief review)• Microscopic defects (changes in bulk material)

• Macroscopic damage (changes in detector properties)

• Part II: RD50 - Approaches to obtain radiation hard sensors• Material Engineering

• Device Engineering



RD50

p-on-n silicon, under-depleted:

• Charge spread – degraded resolution

• Charge loss – reduced CCE

p+on-n

Device engineeringp-in-n versus n-in-p detectors

n-on-p silicon, under-depleted:

•Limited loss in CCE

•Less degradation with under-depletion

•Collect electrons (fast)

n+on-p

n-type silicon after high fluences: p-type silicon after high fluences:

Be careful, this is a very schematic explanation,reality is more complex !


RD50

0 2 4 6 8 10fluence [1015cm-2]

0

5

10

15

20

25

CC

E (

103

elec

tron

s)

24 GeV/c p irradiation24 GeV/c p irradiation

[M.Moll][M.Moll]

[Data: G.Casse et al., NIMA535(2004) 362][Data: G.Casse et al., NIMA535(2004) 362]

n-in-p microstrip detectors

• n-in-p microstrip detectors (280µm) on p-type FZ silicon

• Detectors read-out with 40MHz

CCE ~ 6500 e (30%)after 7.5 1015 p cm-2

at 900V

n-in-p: - no type inversion, high electric field stays on structured side- collection of electrons

• no reverse annealingvisible in the CCE measurement !e.g. for 7.5 ×××× 1015 p/cm2 increase of Vdep from Vdep~ 2800V to Vdep > 12000V is expected !

0 100 200 300 400 500time at 80oC[min]

0 500 1000 1500 2000 2500time [days at 20oC]

02468

101214161820

CC

E (

103

elec

tron

s)

800 V800 V

1.1 x 1015cm-2 1.1 x 1015cm-2 500 V500 V

3.5 x 1015cm-2 (500 V)3.5 x 1015cm-2 (500 V)

7.5 x 1015cm-2 (700 V)7.5 x 1015cm-2 (700 V)

M.MollM.Moll

[Data: G.Casse et al., to be published in NIMA][Data: G.Casse et al., to be published in NIMA]


RD50• “3D” electrodes: - narrow columns along detector thickness,

- diameter: 10µm, distance: 50 - 100µm

• Lateral depletion: - lower depletion voltage needed- thicker detectors possible- fast signal- radiation hard

3D detector - concepts

n-columns p-columnswafer surface

n-type substrate

Introduced by: S.I. Parker et al., NIMA 395 (1997) 328

p+

------

++

++

++

++

--

--

++

300

µµ µµm

n+

p+

50 µµµµm

----

--

++++

++++

----

++

3D PLANARp+


RD50• “3D” electrodes: - narrow columns along detector thickness,

- diameter: 10µm, distance: 50 - 100µm

• Lateral depletion: - lower depletion voltage needed- thicker detectors possible- fast signal- radiation hard

3D detector - concepts

n-columns p-columns wafer surface

n-type substrate

• Simplified 3D architecture • n+ columns in p-type substrate, p+ backplane

• operation similar to standard 3D detector

• Simplified process

• hole etching and doping only done once

• no wafer bonding technology needed

• Simulations performed• Fabrication:

• IRST(Italy), CNM Barcelona

[C. Piemonte et al., NIM A541 (2005) 441]

hole

hole metal strip

C.Piemonte et al., STD06, September 2006

Hole depth 120-150µmHole diameter ~10µm

• First CCE tests under way


RD50

1014 1015 10160

5000

10000

15000

20000

25000

#

elec

tron

s

1 MeV n fluence [cm-2]

strips

pixels

p FZ Si 280µm; 25ns; -30°C [1] p-MCz Si 300µm;0.2-2.5µs; -30°C [2] n EPI Si 75µm; 25ns; -30°C [3] n EPI Si 150µm; 25ns; -30°C [3] sCVD Diam 770µm; 25ns; +20°C [4] pCVD Diam 300µm; 25ns; +20°C [4] n EPI SiC 55µm; 2.5µs; +20°C [5] 3D FZ Si 235µm [6]

[1] G. Casse et al. NIM A (2004)[2] M. Bruzzi et al. STD06, September 2006[3] G. Kramberger, RD50 Work. Prague 06[4] W: Adams et al. NIM A (2006)[5] F. Moscatelli RD50 Work.CERN 2005[6] C. Da Vià, "Hiroshima" STD06

(charge induced by laser)

Comparison of measured collected charge on differen t radiation-hard materials and devices

Line to guide the eye for planar devices

160V

M. Bruzzi, Presented at STD6 Hiroshima Conference,Carmel, CA, September 2006

• Thick (300µµµµm) p-type planar detectorscan operate in partial depletion, collected charge higher than 12000e up to 2x1015cm-2.

• Most charge at highest fluences collected with3D detectors• Silicon comparable or even better than diamondin terms of collected charge

(BUT: higher leakage current – cooling needed!)


RD50 Summary – Radiation Damage

• Radiation Damage in Silicon Detectors• Change ofDepletion Voltage(type inversion, reverse annealing, …)

(can be influenced by defect engineering!)• Increase ofLeakage Current (same for all silicon materials)• Increase ofCharge Trapping (same for all silicon materials)

Signal to Noise ratiois quantity to watch (material + geometry + electronics)

• Microscopic defects• Good understanding of damage after γ-irradiation (point defects)• Damage after hadron damage still to be better understood (cluster defects)

• CERN-RD50 collaboration working on:• Material Engineering (Silicon: DOFZ, CZ, EPI, other impurities,. ) (Diamond)• Device Engineering (3D and thin detectors, n-in-p, n-in-n, …)

⇒To obtain ultra radiation hard sensors a combination of material and device engineering approaches depending on radiation environment, application and available readout electronics will be best solution


RD50 Summary – Detectors for SLHC• At fluences up to 1015cm-2 (Outer layers of SLHC detector) the change of the depletion

voltage and the large area to be covered by detectors are major problems.

• CZ silicon detectors could be a cost-effective radiation hard solution no type inversion (to be confirmed), use cost effective p-in-n technology

• oxygenated p-type siliconmicrostrip detectors show very encouraging results:CCE ≈ 6500 e; Φeq

= 4×1015 cm-2, 300µm

• At the fluence of 1016cm-2 (Innermost layers of SLHC detector) the active thickness of any silicon material is significantly reduced due to trapping.

The two most promising options besides regular replacement of sensors are: Thin/EPI detectors : drawback: radiation hard electronics for low signals needed

(e.g. 2300e at Φeq 8x1015cm-2, 50µm EPI)

3D detectors : drawback: technology has to be optimized

• SiC and GaN have been characterized and abandoned by RD50.

Further information: http://cern.ch/rd50/

radiation tolerant sensors for solid state tracking

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