1. Study of radiation damage induced by 24/c GeV and 26MeV protons on heavily irradiated MCz and FZ silicon detectors
N. Manna
Dipartimento Interateneo di Fisica & INFN di Bari on behalf of the SMART Collaboration*
(*) INFN sections of Bari, Firenze, Perugia, Pisa;
External collaborators INFN Padova, Trieste & ITC-IRST Trento
Layout and materials of SMART detectors
Pre-irradiation measurements
Post-irradiation measurements
Conclusions
7th RD50 - Workshop on Radiation hard semiconductor devices for very high luminosity colliders CERN, November, 2005

2. Wafer Layout Test2: GCD, Van der Paw Test1: Diode+Mos Square MG-diodes
Microstrip detectors
Inter-strip Capacitance test
Test2: GCD, Van der Paw
Test1: Diode+Mos
Square MG-diodes
Round MG-diodes
50 mm pitch 64 strips
100 mmpitch 32 strips
S1 S2 S3 S4 S5
S6 S7 S8 S9 S10
RD50 common wafer procurement (produced by Okmetic - Vantaa, Finland)
Wafer Layout designed by the SMART Collaboration
Masks and process by ITC-IRST
10 different strip geometries
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3. PRODUCTION MCz Samples RUN I p-on-n 22 wafers RUN II n-on-p 24 wafers
Fz Samples
<100> ρ>500 W*cm thick=300μm
Standard: LTO, 420C
no LTO (pass. layer), 380C
no LTO, 350C
no LTO, 380C + TDK
<111> ρ>6KΩ*cm thick=300μm
Standard Process
380C
RUN I p-on-n
22 wafers
<100> ρ>1.8 KW*cm thick=300μm
No over-glass passivation
Low dose p-spray (3.0E12 cm-2)
High dose p-spray (5.0E12 cm-2)
<100> ρ>5KΩ*cm thick=200 mm
Low dose p-spray (3.0E12 cm-2)
High dose p-spray (5.0E12 cm-2)
RUN II n-on-p
24 wafers
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4. Pre Irradiation Characterization - Diodes -
Measurements
Leakage currents  Vbreakdown
Depletion Voltage  Initial resistivity and Uniformity of a wafer
(1) OK Fz
(2) non uniformity of the Depletion Voltage in the MCz, especially for p-type production
Map of the diodes Vdepl in a p-type MCz wafer
Probably due to fluctuations of the oxygen concentration in MCz material
(see talk Piemonte 5th RD50 workshop Firenze, oct 2004)
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5. Pre Irradiation Characterization - Minisensors (Leakage Current)-
Good performances of the n-type detectors in terms of breakdown voltages and current uniformity
Problems for the p-type detectors:
low breakdown voltages for the 100 mm pitch detectors, due to the adopted isolation technique (p-spray), enhanced for the highest dose
Disuniformity of the wafer resistivity, explained with a different oxygen concentration leading to a spread in the thermal donor activation (as seen on diodes)
MCz p-type High p Spray
MCz p-type Low p Spray
Ileak/V (nA/cm-2)
Ileak/V (nA/cm-2)
-Vbias (Volt)
-Vbias (Volt)
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6. Pre Irradiation Characterization - Minisensors (Interstrip Capacitance)-
MCz n-type
Good performances of the n-type detectors (interstrip capacitance depends, as expected, on the minisensors geometry: strip width, pitch, metal overhang…)
Cint /l (pF/cm)
Different behaviour for the p-type detectors:
Interstrip capacitance decreases with Vbias reaching saturation at voltages much higher than depletion due to the existence of an electron layer behind the oxide. The saturation is faster in low p spray and for high pitches. No differences between Fz and MCz.
Vbias (Volt)
MCz p-type High p Spray
FZ p-type High p Spray
MCz p-type Low p Spray
Cint /l (pF/cm)
Cint /l (pF/cm)
Cint /l (pF/cm)
-Vbias (Volt)
-Vbias (Volt)
-Vbias (Volt)
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7. Irradiation October 2004 Irradiation with 24 Gev/c protons at CERN SPS
Set up for the CERN(Geneva)
Irradiation with 24 Gev/c protons at CERN SPS
3 fluences: 6.0x x x MeV n/cm2
27 mini-sensors, 90 diodes
75 % n-type, 25 % p-type
Thanks to M. Glaser
Set up for the FZK(Karlsruhe)
May 2005
Irradiation with 26 MeV protons at the
Cyclotron of the Forschungszentrum Karlsruhe
11 fluences: 1.4x x MeV n/cm2
62 mini-sensors, 100 diodes
38 % n-type, 62 % p-type
Thanks to A. Furgeri
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8. Post Irradiation Characterization
On Diodes:
IV and CV measurements 0 °C or 20 °C)
- immediately after irradiation before annealing
- repeated after annealing steps 20, 60 or 80 °C)
in order to:
(1) follow the radiation damage evolution on bulk current
and effective doping concentration;
(2) determine the effective irradiation fluences
(3) estimate the inversion fluence
(4) compare different sintering procedures in terms of Vdep
On Minisensors:
IbiasV, IstripV, CV and Interstrip Capacitance measurements 0 0C)
- repeated after annealing 60 or 80 0C,to be
in order to study:
(1) the performance of ptype sensors
(2) low and high dose p spray on p-type substrates;
(3) geometry influence on noise and current level
(4) MCz vs Fz sensors behaviour
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9. After Irr. Ileak on diodes Estimation of irradiation fluences
The neutron equivalent fluences of irradiation were estimated with the fit of the annealing current curve on Fzn materials using the standard parameterisations for α(t,T) (Rose Collaboration – M.Moll PhD theses)
Universality of α 
(in order to check the nominal
fluences)
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MCz: improved reverse annealing
MCz: improved reverse annealing

10. Depletion voltage after irr. (Fz n Type inversion)
T=200C
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11. Depletion voltage after irr. (MCz n Type inversion?)
The annealing behaviour is typical of type inverted (p-type) material after Φ4 , but no SCSI observed
(see Menichelli’s talk)
T=200C
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12. Annealing @ high temperature
Type non-inverted: depletion voltage has a maximum
? No SCSI observed
MCz: improved reverse annealing
Type inverted: depletion voltage has a minimum
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Type non-inverted: depletion voltage has a maximum
Type inverted: depletion voltage has a minimum

13. Depletion voltage after irr.
n type
Wafer
 (10-2 cm-1)
W1253 Fz
0.63  0.04
W1254 Fz
0.46  0.05
W91 MCz
0.61  0.03
W115 MCz
0.42  0.03
W127 MCz
0.65  0.02
W179 MCz
0.58  0.04
p type
Wafer
 (10-2 cm-1)
W84 Fz high
0.90  0.05
W64 Fz high
1.01  0.05
W248 MCz high
0.20  0.02
W130 MCz high
0.7  0.2
W127 MCz high
0.65  0.02
W179 MCz low
0.63  0.03
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14. After Irr. Ileak minisens
n type MCz & Fz
IV curves of n- and p-type detectors for the full fluence range before annealing (measured at 0oC):
Current levels in MCz detectors are comparable with Fz at a given fluence
Leakage currents measured at Vdepl scale as the received fluences.
The performances of Fz and MCz p-type detectors, comprising sensors with 100 mm pitch, are much improved after irradiation.
Sensors with low p-spray have breakdown voltages comparable with n-type detectors in all the fluence range.
Detectors with a high p-spray dose still have breakdown problems at lower fluences (< 4.0 * MeV n/cm2) whereas they have very good performances at the highest fluences.
Bias Voltage (V)
SENSOR GEOMETRY # 1
Leakage Current (A)
MCz Low p spray
MCz High p spray
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15. Interstrip Capacitance
No particular problem with irradiation for n-type MCz (and Fz)
For irradiated p-type MCz:
As before irradiation, interstrip capacitance decreases with Vbias, reaching saturation at voltages much higher than VFD.
The saturation is faster with respect to un-irradiated sensors
The saturation is still faster in low p spray and for large pitches. No differences between Fz and MCz.
MCz n <100>
In order to better see this, it is useful to compare the behaviour of different materials and technological production splittings for a given sensor geometry
 next slide
MCz Low p spray
Fz p High p spray
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16. Interstrip Capacitance
Vdep
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17. Conclusions
The MCz detectors of the SMART production are fully comparable with Fz regarding leakage currents values and breakdown voltages.
Depletion voltages as a function of bias voltage and annealing time follow a different behaviour in the two materials  the “type inversion” on MCz material is under investigation: no SCSI observed.
Better behaviour of Vdep on MCz detectors after irradiation and in particular during the reverse annealing
The study of the detectors properties during the annealing procedure must be completed in order to fix the parameters of the simulation of MCz behaviour after irradiation
Measurements on interstrip capacitance and leakage current on p-type detectors show that an improved strip isolation technique is needed  a new production run is foreseen.
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