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