The issue of doping disuniformity in p-type MCz Si sensors

M. Bruzzi, M. Scaringella, D. Menichelli, A. MacchioloINFN Firenze

M. Boscardin, C. Piemonte, N. ZorziITC – IRST, Trento

D. Creanza, N. Manna, V. RadicciINFN Bari

A. Messineo, L. Borrello, G. SegneriB. INFN Pisa

I. W. Henderson, H. SadrozinskiSCIPP, UCSC, Santa Cruz

n-on-p microstrip detectors by SMART INFNn-on-p microstrip detectors by SMART INFN processed in 2004 at IRST- Trento processed in 2004 at IRST- Trento

FZ p-spray 3E12 - 5E12<100> p-type >5000cm 525m<100> p-type >5000cm 200m

MCz no OG; p-spray 3E12 - 5E12<100> p-type >1800cm 300m

Layout10 mini-strip 0.6x4.7cm2

50 and 100m pitch, AC coupled37 pad diodes and various text structures

SIMS analysis on Okmetic MCz Si wafers [Oi] ~ 4.6x1017cm-3 [G. Pellegrini et al. NIM A 2005]

MCz Si wafers from Okmetic, Finland, RD50 procurement

Microstrip minisensors

3 51 2 4 8 106 7 9 det# pitchp+ implant

widthpolysilicon

width metal width[um] [um] [um] [um]

1 50 15 10 232 50 20 15 283 50 25 20 334 50 15 10 195 50 15 10 276 100 15 10 237 100 25 20 338 100 35 30 439 100 25 20 37

10 100 25 20 41

• AC coupled •poly resistor biased

die ~6x47mm2

pitch 50 µm 64 strips pitch 100 µm 32 strips

n-on-p – CV on diodesn-on-p – CV on diodes

Probably due to fluctuations in the Thermal Donors activation.

Quite high doping variations!!

( N. Zorzi, Trento RD50 Meeting, Feb. 2005)( N. Zorzi, Trento RD50 Meeting, Feb. 2005)

Previous works on TD activation by Thermal Treatment

Thermal treatment after process•MCz-Si starting Vfd = 230V (Okmetic) •p+/p/n+ diodes Helsinki University •in collaboration with J. Harkonen and Z. Li.

J. Harkonen et al. 4th RD50 Workshop, May, CERN; M. Bruzzi et al. 5th RD50 Workshop, October, Florence .

430°C up to 120min

nTD = 2 - 4·1012 cm-3

Evaluated by TSC after 430°C - 120min

Helsinki Group have not observed enhanced TD generation when the passivation was made by PECVD (Plasma Enhanced CVD) Si3N4 @3000C, which contains H2 10-30%.See talk by Esa Tuovinen at 3rd RD50 Workshop http://rd50.web.cern.ch/RD50/3rd-workshop/

380°C430°C

TD+/++

TD0/+

P

Study of Thermal Donors in n-MCZ Si processed by IRST in p-on-n diodes non irradiated

StandardNo LTO and sintering at 380°C

In standard process the TDs are activated, if T < 380°C the TDs are almost absent.Presented by D. Menichelli, 6° RD50 Workshop, Helsinki, June 2005

> 500cm n-MCz Si

We have studied shallow defects (TDs) on two single pad diodes with different Vfd

(wafer 9 samples n.14, 5). Vfd=10 V,110 V. Area A=13.6 mm2 w = 300 m. >1.8 kcm corresponding to NA<7.7x1012 cm-3.

8 10 12 14 16 18 200

0.5

1

1.5

2

2.5

3

3.5x 10

-11

10V20V50V100V

From B peak integration in TSC: N’A = (7.01.5)x1012 cm-3 . Uncertainty due to:- Peak not saturated at 100 V - Including any signal below 20 K - the initial current decay superimposed to the signal has been subtracted

Evaluation of Boron Concentration in p-type MCz Si

T [K]

TSC [A]

10 20 30 40 50 60 70 80-0.5

0

0.5

1

1.5

2

2.5x 10

-11

temperature [K]

curr

ent

[A]

w914, TSC

Vrev=100 VVrev=10 VVrev=20 VVrev=50 V

Observation by TSC of Thermal Donors in p-type MCz Si

Sample 14; Vfd = 10V; [TD] 3.3x1012 cm-3

20 25 30 35 40 45 50 55 60 650

0.5

1

1.5x 10

-11

temperature [K]

curr

ent

[A]

w95, TSC

Vrev=10 VVrev=20 VVrev=100VVrev=200V

Sample 5; Vfd = 110V; [TD] 1.4- 2.0x1012 cm-3

Observation by TSC of Thermal Donors in p-type MCz Si

Vfd=110 V corresponding to Neff=1.6x1012 cm-3.Expected thermal donor concentration:[TD]=0.5x(NA-Neff)<3x1012 cm-3, from manufactory data about [TD]=0.5x(NA’-Neff)≈2.7x1012 cm-3, from our estimate of [B]From direct TSC integration of TD peaks: [TD]=1.4-2.0x1012 cm-3

Vfd=10 V corresponding to Neff=1.5x1011 cm-3

Expected thermal donor concentration:[TD]=0.5x(NA-Neff)<3.8x1012 cm-3, from manufactory data about [TD]=0.5x(NA’-Neff)>3.6x1012 cm-3, from our estimate of [B]From direct TSC integration of TD peaks: [TD]=3.3x1012 cm-3

Sample 5

Sample 14

Our measurements put into evidence that TDs can be an important source of doping disuniformity also after a process at 380°C, in case of high resistivity p-type Si .

THERMAL DONORS FORMATION RATE

At 430°C x ~ 3 - 4 Range 350-400°C x ~ 2

Di = D·e-Ea/KT, with D=0.13cm2/s and Ea=2.53eV, k = 4.61x10-52 C. A. Londos et al. Appl.Phys.Lett. 62, 1525 (1993).

According to this model there should be no thermal donor activation at 380°C NTD ~ 0 !!! Does not explain the results with p-type processed at IRST-Trento.

Good agreement with p- type diodes processed at Helsinki

M. Bruzzi et al.,5° RD50 Workshop, submitted to J. App. Phys. J. Harkonen et al., Wildbad Kreuth

conference, in press on NIM A

Open Problem

T = 370°C processT = 420°C annealing

Effects of Neff disuniformity on microstrip sensors

Simulation of the backplane capacitance in a 50mm pitch microstrip detectorTaking into consideration the doping disuniformity measured on diodes along the diameter.

Full depletion voltage spread: 90 - 140 V V = 50V

non-irradiated p-type sensor

0,00E+00

1,00E+20

2,00E+20

3,00E+20

4,00E+20

0 50 100 150Vrev [Volt]

1/C

^2

[1/F

^2]

non uniform Vfd

uniform Vfd

Full depletion voltage spread: 4 - 90 V V = 85V

Full depletion voltage spread: 70 - 120 V V = 50V

non irradiated p-type sensor

0,00E+00

5,00E+19

1,00E+20

1,50E+20

2,00E+20

2,50E+20

3,00E+20

3,50E+20

4,00E+20

0 50 100 150 Vrev [Volt]

1/C

^2 [1

/F^2

]

non uniform Vfd

uniform Vfd

non irradiated p-type sensor

0,00E+00

5,00E+19

1,00E+20

1,50E+20

2,00E+20

2,50E+20

3,00E+20

3,50E+20

0 50 100 150Vrev [Volt]

1/C

^2

[1

/F^

2]

non uniform Vfd

uniform Vfd

C-V measured with SMART p-type MCz Si microstrip sensors and comparison with the simulated CV taking into account of the Vfd disuniformity.

INFN Bari Wafer 9 Sensor s5

Proton irradiated 24GeV/c 4x1013n/cm2

SCIPP UCSC Wafers 14 & 37Sensor s5

Non irradiated

Conclusions

Samples studied: P-type detectors processed at IRST-Trento with up to 380°C for the Italian SMART INFN network on Okmetic MCz Si high resistivity wafers.

Maps of full depletion voltage along the wafers show a spread along the wafer diameter with variations of 30 to 100V.

Two samples with Vfd 110V and 10V respectively have been studied by TSC to analyse the presence of thermal donors. Peaks related to Thermal Donors (TD) have been detected by TSC. TD concentrations accounts for the different full depletion. [TD] range: 1-3 1012 cm-3.

Open problem: Based on the model of C.A. Londos et al., which well describe TD activations in p-type detectors t 430°C, there should not be any TD activation at 380°C !

The behaviour of the CV characteristics ( backplane capacitance ) of the microstrip detectors made in the same process has been explained in terms of doping disuniformity. A significant distortion of CV is observed only when the voltage spread is of the order of 100V.