Katharina Kaska 1
RD50
Trento Workshop :Materials and basic measurement problems
Katharina Kaska
Katharina Kaska 2
RD50 Overview
• Epitaxial Silicon• MCz • “High fluence puzzle”• Depletion voltage comparison
Katharina Kaska 3
RD50 EPI I
• Why Epi?Thinner device =>
• Smaller current and Vfd (but larger capacitance)
• Less chance for trapping (but less e-h pairs)
• Material• From 25 to 150 μm EPI layers on low resisitvity Cz substrate (O2 out-
diffusion)
Overview talk on Epi given by Gregor Kramberger
Katharina Kaska 4
RD50
The irradiation with 24 GeV p (200 MeV p, 26 MeV p) introduces positive space charge.SIMS profiling:
[O](25µm) > [O](50µm) ;
[O](75µm)>[O](100µm)> [O](150µm)
Stable Damage:
Neff(25µm) > Neff(50µm); geff=-0.038 cm-1 > geff=-0.017 cm-1
Neff(75µm) > Neff(100µm) > Neff (150µm)
geff=-0.015 cm-1 > geff=-0.008 cm-1 > geff=-0.007 cm-1
TSC Defect Spectroscopy:
[BD](25µm) > [BD](50µm) >[BD](75µm)
G. Lindström et al., NIM A556 (2006) 451.
Generation of shallow donors BD (Ec-0.23 eV) strongly related to [O] Possibly caused by O2i
dimers, outdiffused from Cz with larger diffusion constant dimers monitored by IO2 complex
t0~8 min@80oC
Influence of thicknessInfluence of thickness
Additional oxydation Additional oxydation
geff [epi-DO]>geff [epi-ST]
The oxygenation increases introduction rate of positive space charge by some 30% at all thicknesses
CiS - process
J. Lange et al., 13th RD50 Workshop, CERN, 2008.
Space charger vs. fluence
Gregor Kramberger
Katharina Kaska 5
RD50 Protons vs. neutrons
0.0 8.0x1014 1.6x1015 2.4x1015 3.2x10150
5
10
15
20
25
30
0
100
200
300
400
500
|Nef
f| [1
012
cm
-3]
eq
[cm-2]
neutron irradiatedn-type
HIP-004-C CNM-11-E
p-type CNM-22-E
proton irradiatedn-type
HIP-004-C CNM-11-E
p-type CNM-22-E
Vd [
V]
V. Khomenkov et al., presented at IEEE-NSS, 2008
Lower damage rates from neutron than proton irradiation
type / radiation
10-3 cm-1
10-3 cm-1
n-Epi / protons -15.6 -7.5
p-Epi / protons -10.5 -7.4
n-Epi / neutrons 5.8 4.2
p-Epi / neutrons 3.7 3.1
But quite different results for the rates:
Gregor Kramberger
Katharina Kaska 6
RD50 CCE for different EPI samples
• The thickness becomes less important as the fluence grows – as expected.
• The CCE at high fluences is significantly larger than predicted!
• p-type epi shows better performance after neutron irradiation than the rest
0.00E+00
2.00E+03
4.00E+03
6.00E+03
8.00E+03
1.00E+04
1.20E+04
0 2E+15 4E+15 6E+15 8E+15 1E+16 1.2E+16
n-type, neutron (50,50)n-type, neutron (75,50)n-type, neutron (150,500)n-type, neutron (75,150 DOFZ)n-type, neutron (75,150)p type, neutron (150,1500)p-type, protons (150,1500)n-type, protons (150,1500)n-type, protons (75,50)n-type, protons (50,50)n-type, neutron (150), CERNp-type, neutron (150), CERN
G. Kramberger et al., NIM 552 (2005).K. Kaska et al., presented at 11th RD50 Workshop,2007.V. Khomenkov et al., presented at IEEE-NSS, 2008
Gregor Kramberger
Katharina Kaska 7
RD50 MCz I
Why Cz now and not before?
• No demand for high resistivity Cz-Si -> No availability
• Price for custom specified ingot 25,000 € - 40,000 € (too much for university lab)
• Now RF-IC industry shows interest on high resistivity Cz-Si (=lower substrate losses of RF-signal)
Katharina Kaska 8
RD50 MCz II
“p-like” annealing behaviour
The most irradiated diode shows an n-like annealing behaviour
p-type MCz
Nicola Pacifico
Katharina Kaska 9
RD50 Charge correction method
))(
exp()( 00
eff
tttQQ
The corrected charge is constant with voltage if V>Vfd
Katharina Kaska 10
RD50 MCz III
Undepleted (340 V)
Peak Ratio: 1.48
Peak ratio: 1
Trapping time fromCharge Correction Method: 3-3.5 ns Trapping time for equal peak ratio (front/back) constraint: 7.5-9 ns Nicola Pacifico
Katharina Kaska 11
RD50 High fluence puzzle I
Phenomenon:
CCE signal is too high and show inexplicable behavior at high fluences.
Reasons?– active region (electric field) is different than expected – trapping probability decreases– mobility increases (not likely)
Katharina Kaska 12
RD50 Puzzle II: strips detectors
βe = 3.2·10-16 cm2/ns βh = 3.5·10-16 cm2/ns
No trapping, only Neff:
Black: measured, Red: simulation Black: measured, Red: simulation
SIMULATION FAILS COMPLETELY! Even if trapping is off - the active region assumed by depletion is not enough to reproduce the signal!
MICRON RD50 n+-p FZ detectors
Gregor Kramberger
Katharina Kaska 13
RD50 Puzzle III: pad detectors
• Trapping probabilities should be the same• Electric field in most of the detector also, except close to strips
Alpha TCT (25 ns integration) - 100% CCE also observed
Vertical bars denote full depletion voltage. The onset of charge saturation is matches the Vfd up to 4∙1015 cm-2.
At high fluences and high voltages there are indications rapid increase of charge – indication of charge multiplication?
Gregor Kramberger
Katharina Kaska 14
RD50 Mixed irradiation
MCz-nFirst proton than neutron irradiation
=> Vd goes down
MCz-pFirst proton than neutron irradiation
=> Vd goes up
||~|| ,,,, neqncpeqpceff ggN
All as expected Gregor Kramberger
Katharina Kaska 15
RD50 Annealing
Always annealing at elevated temperature to increase speed, but how does it compare to RT annealing?
The minimum in Vfd:• after ~300 days at 20oC• after ~80 min at 80oC
Compatible with acceleration of ~6500 for Ea=1.3eV
Similar long term annealing for neutron and proton irradiated samples irradiated to the similar fluences!
Gregor Kramberger
Katharina Kaska 16
RD50 Difference in depletion voltage
0 1x1014 2x1014 3x1014 4x1014 5x1014 6x10140
50
100
150
200
250
300
350
400
dep
leti
on
vo
ltag
e [V
]
proton fluence [cm2]
CV IV CCE
CNM-03 (Fz n-type)
IV < CV < CCE (β)
100 200 300 400 500 600 70020
30
40
50
60
70
80
arb
itra
ry u
nit
s
bias voltage [V]
1/C CCE
CNM-03-F-56 4.43 x 1014 p/cm224 GeV/c proton irradiated
50 100 150 200 250 300 35040010
20
30
40
50
60
70
arb
itra
ry u
nit
s
bias voltage [V]
CV CCE
p069-44 5.42 x 1014 p/cm2
0.0 2.0x1014 4.0x1014 6.0x1014 8.0x1014 1.0x10150
50
100
150
200
dep
leti
on
vo
ltag
e [V
]
proton fluence [cm-2]
CV IV CCE
p-069 (MCz p-type)
IV < CCE (beta) = CV
Katharina Kaska 17
RD50
Correlation of Vfd (CCE, CV)
0
200
400
600
800
1000
1200
0 200 400 600 800 1000 1200
Vfd (measured from CV)
Vfd
(mea
sure
d fro
m k
ink
in C
CE)
Pad detectors
strips, binary
strips, analogas irradiated (5e14)
5∙1014 cm-2
1∙1015 cm-2
1∙1014 cm-2
Vfd from C-V is determined for pad detectors ( 80min @ 60oC – end of beneficial annealing )
•Vfd from CV underestimates the onset of saturation in CCE by max. 100-150 V!•after Vfd the collected charge continues to increase due to shorter drift•due to growth of depletion depth from electrode side the offset is smaller than with p-on-n!
•The correlation holds for all investigated fluences in range of full depletion voltages up to 1000V!
Difference in depletion voltage
Gregor Kramberger
Katharina Kaska 18
RD50 Admittance Spectroscopy I
CV measurements strongly dependent on frequency used
C(V ) 1
d 1
C d
CCE(V ) d
d = depleted depth
Admittance Spectroscopy can reveal important properties of deep levels introduced during irradiation, which are responsible for the frequency dependence of the capacitance
Hartmut Sadrozinski
Katharina Kaska 19
RD50 Admittance Spectroscopy II
Frequency dependent filling and emptying of trapsContributes to C
Frequency correlated to emission rate
I(T) dependent on emission rateFrequency to be used for CVdepends on temperature
T ( C) 22 -10 -20
f (Hz) 10k ~400 ~250
T ( C) 22 -10 -20
f (Hz) 10k ~400 ~250
N.B.: At low temperature, low frequency must be used for CV:
M.K. Petterson, etal., Nucl. Instr. andMeth. A (2007)
Try to scale f with T doesn’t really workbecause 10 kHz at RT already doesn’t give
the right value (difference CCE and CV curves)
Hartmut Sadrozinski
Katharina Kaska 20
RD50 Admittance Spectroscopy III
How to figure out true capacitance? • => Admittance measurements
In order to contribute to the admittance, the AC signal has to correspond to the emission time for a particular trap.
Equivalent circuit with G(f) and C(f)
Take into account deep level traps, free carriers and transition region between space charge and neutral bulk
Use C of deep traps as free parameter to fit data
Extract concentration, energy, and majority capture cross section for deep levels
simulate d(V) and compare to CCEHartmut Sadrozinski
Katharina Kaska 21
RD50 Admittance Spectroscopy IV
Comparison of d(V) for CCE and from admitance measurements
0
0.5
1
1.5
2
2.5
3
3.5
0
0.00005
0.0001
0.00015
0.0002
0.00025
0.0003
0 100 200 300 400 500 600 700
Voltage (V)
Neutron
2552-7-1-24-25 P MCz 5e14
2552-7-9 N-on-P MCz (Micron) 5e14 neutron
0
0.5
1
1.5
2
2.5
3
3.5
0.00E+00
5.00E-05
1.00E-04
1.50E-04
2.00E-04
2.50E-04
3.00E-04
0 200 400 600 800 1000 1200
Voltage (V)
Pion
2535-8-1-2 N Fz 4.2e14
2535-9-3-3 N FZ 3.23e14
Only two samples evaluated…
Hartmut Sadrozinski