Panja Luukka

1
Development of Radiation Hard Sensors for Very
High Luminosity Colliders- CERN RD50
Collaboration -

• Panja Luukka
• Helsinki Institute of Physics
• on behalf of the CERN RD50 Collaboration

http//www.cern.ch/rd50
Panja Luukka, The Fifth International Forum on
Advanced Material Science and Technology (IFAMST5
2006)
2
Outline

• Background and motivation
• Introduction to the CERN RD50 Collaboration
• Radiation damage in silicon detectors
• Approaches to obtain radiation hard sensors
• Latest results of defect engineering
• Magnetic Czohralski silicon
• Epitaxial silicon
• Summary

Panja Luukka, The Fifth International Forum on
Advanced Material Science and Technology (IFAMST5
2006)
3
Background

• LHC at CERN is the first experiment to use
  silicon detectors in a large scale.
• Only few proton-proton collisions produce Higgs
  boson.
• The luminosity of the LHC beam is very high,
  causing a hostile radiation environment.
• The radiaton hardness of silicon devices is
  currently extensively studied subject.
• There are ?100 institutes within the CERN RD50
  and RD39 Collaborations

Panja Luukka, The Fifth International Forum on
Advanced Material Science and Technology (IFAMST5
2006)
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Background
The charge transportation in particle detectors
is based on drift of charge carriers, i.e.
electrons and holes.
Thus, the detectors need to be fully depleted,
i.e. the electric field extends over the entire
bulk (300µm)
Panja Luukka, The Fifth International Forum on
Advanced Material Science and Technology (IFAMST5
2006)
5
Motivation
LHC upgrade to Super-LHC Luminosity of LHC L
1034 cm-2s-1 and fluence of fast hadrons at
r4cm 31015cm-2 ? Super-LHC L 1035 cm-2s-1,
expected fast hadron fluence at r4cm
1.6?1016 cm-2.
The main constraint is the survival of the
silicon tracker in the hostile radiation
environment.
Radiation hardness studies are also beneficial
before the luminosity upgrade e.g. for other
experiments such as linear colliders.
Panja Luukka, The Fifth International Forum on
Advanced Material Science and Technology (IFAMST5
2006)
6
CERN RD50 Collaboration

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

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 (collision rate
80 MHz) - Low mass (reducing multiple
scattering) - Cost effectiveness (large area
has to be covered)

• Presently 260 members from 53 institutes

Belarus (Minsk), Belgium (Louvain), Canada
(Montreal), Czech Republic (Prague (3x)), Finland
(Helsinki, Lappeenranta), Germany (Berlin,
Dortmund, Erfurt, Freiburg, Hamburg, Karlsruhe,
Munich), Israel (Tel Aviv), Italy (Bari,
Bologna, Florence, Padova, Perugia, Pisa, Trento,
Turin), Lithuania (Vilnius), 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 (Exeter, Glasgow, Lancaster, Liverpool,
Oxford, Sheffield, Surrey), USA (Fermilab, Purdue
University, Rochester University, SCIPP Santa
Cruz, Syracuse University, BNL, University of New
Mexico)
Panja Luukka, The Fifth International Forum on
Advanced Material Science and Technology (IFAMST5
2006)
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Approaches

• Defect Engineering of Silicon
• Understanding radiation damage
• Macroscopic effects and microscopic defects
• Simulation of defect properties kinetics
• Irradiation with different particles energies
• Oxygen rich Silicon
• DOFZ, CZ, MCZ, EPI
• Oxygen dimer 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 3D detectors
• Stripixels

• Scientific strategies
• Material engineering
• Device engineering
• Change of detectoroperational conditions

CERN RD39 CollaborationCryogenic Tracking
Detectors
Panja Luukka, The Fifth International Forum on
Advanced Material Science and Technology (IFAMST5
2006)
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Radiation induced microscopic damage
Frenkel pair
V
Si
particle
Vacancy Interstitial
I
EK gt 25 eV
EK gt 5 keV
point defects (V-V, V-O .. )
clusters
Influence of defects on the material and device
properties
trapping (e and h)? CCEshallow defects do not
contribute at room temperature due to fast
detrapping
charged defects ? Neff , Vdepe.g. donors in
upper and acceptors in lower half of the band gap
generation ? leakage currentlevels close to
middle of the bandgap most effective
Panja Luukka, The Fifth International Forum on
Advanced Material Science and Technology (IFAMST5
2006)
9
Vacancy amount and distribution
Ratio of point/cluster defects depends on the
particle type and energy
M. Huhtinen NIMA 491(2002) 194
Only point defects point defects
clusters Mainly clusters
60Co-g, Eg 1MeV Displacement no clusters
Electrons Ee gt 255 keV displacement Ee gt 8 MeV
clusters
Neutrons En gt 185 keV displacement En gt 35 keV
clusters
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Radiation damage macroscopic effects
Change of leakage current - can be helped with
coolingChange of the full depletion voltage
Vdep (effective doping concentration Neff). -
every p-n-junction has a finite breakdown
voltageDecrease of the charge collection
efficiency - limited by partial depletion,
trapping, type inversion
Evolution of the Neff for n-type initial doping
Change of the leakage current
Panja Luukka, The Fifth International Forum on
Advanced Material Science and Technology (IFAMST5
2006)
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Defect engineering of silicon

• Influence the defect kinetics by incorporation of
  impurities or defects
• - good example oxygen
• Initial idea Incorporate oxygen to getter
  radiation-induced vacancies
• ? prevent formation of di-vacancy (V2) related
  deep acceptor levels
• Higher oxygen content ? less negative
  space charge
• One possible mechanism V2O is a deep
  acceptor O VO (not harmful at RT) V
  VO V2O (negative space charge)

DOFZ (Diffusion Oxygenated Float Zone Silicon)
RD48 NIMA 465 (2001) 60
Panja Luukka, The Fifth International Forum on
Advanced Material Science and Technology (IFAMST5
2006)
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Magnetic Czohralski silicon

• High resistivity magnetic Czochralski silicon
  (MCZ-Si)
• Oxygen has experimentally been found to improve
  the radiation hardness of silicon detectors (CERN
  RD48 ROSE Collaboration).
• contains intrinsically high level of oxygen
  (typically 1017-1018 cm-3).
• formation of thermal donors ? p-type MCZ-Si can
  be compensated by intentionally introducing
  thermal donors (TDs).
• Depletion voltage of detectors can be tailored by
  adjusting
• a) oxygen concentration in the bulk.
• b) thermal history of wafers (Thermal
  Donor killing).
• Possibility for internal gettering.
• Higher mechanical strength.
• Less prone to slip defect formation.
• Cost effectiveness compared to e.g. Float Zone
  silicon (FZ).

SNIC - Int Symp Development of Detectors for
Particle, Astro-Particle and Synchrotron
Radiation Experiments Mara Bruzzi on behlaf of
the CERN RD50 Collaboration Radiation Tolerant
Tracking Detectors - SLAC, April 5, 2006
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Shallow donors in oxygen rich detector materials

• Shallow donors have twofold influence on
  detector propeties
• - shallow oxygen thermal donors (TD) can be
  utilized to manipulate the Neff during
  processing.
• - shallow donors interact with radiation defects
  and influence the radiation hardness.
• The TDs are shallow donor levels within 0.01-0.2
  eV energy range below the conduction band.
• - their formation stronly depends on the
  temperature and the oxygen concentration of the
  silicon material.
• - heat threatment between 400-600ºC can yield to
  a TD concentration comparable with the initial
  doping concentration of the high resistivity
  material

Panja Luukka, The Fifth International Forum on
Advanced Material Science and Technology (IFAMST5
2006)
14
Thermal activation of TDs in MCZ-Si

• The TD activation was performed through an
  isochronal annealing treatment at 430ºC up to
  total time of 120 min.
• the shallow levels related to TDs were studied
  by thermally stimulated currents (TSC) in 10-70
  K.

• TSC spectra of MCZ-Si diodes before and after
  annealing treatment of 120 min. at 430ºC.
• reverese bias 10 V
• heating rate 0.1 K/s
• deep levels filled at lower temp. by 1 min.
  forward current injection

• The evolution of the space charge density caused
  by the annealing was related to the activation of
  TDs by the means of current deep level transient
  spectroscopy and TSC.

Panja Luukka, The Fifth International Forum on
Advanced Material Science and Technology (IFAMST5
2006)
15
TSC spectra of proton irradiated MCZ-Si

• TSC spectra of proton irradiated MCZ detector.
• fluence 4 x 1014 p/cm2 (24 GeV protons)
• annealing 1260 min at 60C.

• The TSC speak visible in 30 K has been related to
  a shallow charged defect
• the occurence of the Poole Frenkel defect
  (evidenced by the characteristic shift of the
  peak temperature as the applied reverse voltage
  is changed) indicates that the radiation induced
  defect should be charged, possibly donor-like.
• the peaks related to the TD emissions (TD0/)
  and (TD/) are not present
• when compared to reference FZ-Si samples the
  MCZ-Si samples have higher concentrations of VO
  complex and shallow donor at 30 K.

Panja Luukka, The Fifth International Forum on
Advanced Material Science and Technology (IFAMST5
2006)
16
Bistable donors
In addition to the oxygen rich silicon materials
(DOFZ, MCZ-Si), detectors made on epitaxial
silicon (EPI-Si) have been proved to be very
radiation hard in terms of the effective doping
concentration evolution.

• The effective doping concentration measured after
  the end of the beneficial annealing as a function
  of fluence (24 GeV proton irradiation).
• for larger fluences the possible creation of
  acceptors is over-compensated by the donors
  causing an almost linear increase of Neff.
• the effect of stable donor generation is largely
  depending on the thickness of the device
• the differences in the Neff are also correlated
  with the oxygen concentration profiles measured
  from the samples.

Panja Luukka, The Fifth International Forum on
Advanced Material Science and Technology (IFAMST5
2006)
17
Bistable donors
The well known point defects like CiOi, double
vacancy and the peak at 115 K are measured with
concentrations independent of the diode type and
hence of the oxygen concentration. The TSC
signal due to the shallow donor (BD) have very
similar dependence on the material as the average
oxygen concentration and the stable damage
generation. The strong similarity of the BD
complex to the thermal double donors, especially
with respect to their bistability and the well
known fact that the oxygen dimers (O2i) are one
of the precursors for the formation of the
thermal donors leads to the assumption Dimers
are involved in the damage produced BD defects.
The TSC spectra for n-type EPI-Si diodes after 24
GeV proton irradiation, with Feq1.8 x 1014 cm-2.

Panja Luukka, The Fifth International Forum on
Advanced Material Science and Technology (IFAMST5
2006)
18
Conclusions

• The formation of thermal donors can be utilized
  to tailor the full depletion voltage of the
  detectors.
• detectors with high oxygen concentration and low
  Vfd can be fabricated with relatively easy
  process.
• it is suggested that the shallow defect as a
  donor, is partially compensating the radiation
  induced deep acceptors ? yields to the improved
  radiation hardness of the MCZ-Si devices compared
  to standard FZ-Si devices
• EPI-Si devices exhibit a very high radiation
  tolerance.
• this is mainly due to the high concentration of
  oxygen as interstitial atoms (Oi) and so-called
  oxygen dimers (O2).
• the high Oi concentration leads to a suppression
  of deep acceptors and high concentration of O2
  promotes the formation of shallow donors
  resulting in the compensation of the radiation
  induced negative space charge

Panja Luukka, The Fifth International Forum on
Advanced Material Science and Technology (IFAMST5
2006)