1. M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005 The issue of doping disuniformity in p-type MCz Si sensors M. Bruzzi, M. Scaringella, D. Menichelli, A. Macchiolo INFN Firenze M. Boscardin, C. Piemonte, N. Zorzi ITC – IRST, Trento D. Creanza, N. Manna, V. Radicci INFN Bari A.Messineo, L. Borrello, G. Segneri B.INFN Pisa I. W. Henderson, H. Sadrozinski SCIPP, UCSC, Santa Cruz

2. M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005 n-on-p microstrip detectors by SMART INFN processed in 2004 at IRST- Trento processed in 2004 at IRST- Trento FZ p-spray 3E12 - 5E12 p-type >5000  cm 525  m p-type >5000  cm 200  m MCzno OG; p-spray 3E12 - 5E12 p-type >1800  cm 300  m Layout 10 mini-strip 0.6x4.7cm 2 50 and 100  m pitch, AC coupled 37 pad diodes and various text structures SIMS analysis on Okmetic MCz Si wafers [Oi] ~ 4.6x10 17 cm -3 [G. Pellegrini et al. NIM A 2005] MCz Si wafers from Okmetic, Finland, RD50 procurement

3. M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005 Microstrip minisensors 3 51248 10679 AC coupled poly resistor biased die ~6x47mm 2 pitch 50 µm 64 strips pitch 100 µm 32 strips

4. M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005 n-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)

5. M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005 Previous works on TD activation by Thermal Treatment Thermal treatment after process MCz-Si starting V fd = 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 n TD = 2 - 4·10 12 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) Si 3 N 4 @300 0 C, which contains H 2 10-30%. See talk by Esa Tuovinen at 3 rd RD50 Workshop http://rd50.web.cern.ch/RD50/3rd-workshop/

6. M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005 380°C 430°C TD +/++ TD 0/+ P Study of Thermal Donors in n-MCZ Si processed by IRST in p-on-n diodes non irradiated Standard No 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  > 500  cm n-MCz Si

7. M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005 We have studied shallow defects (TDs) on two single pad diodes with different V fd (wafer 9 samples n.14, 5). V fd =10 V,110 V. Area A=13.6 mm 2 w = 300  m.  >1.8 k  cm corresponding to N A <7.7x10 12 cm -3.

8. M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005 From B peak integration in TSC: N’ A = (7.0  1.5)x10 12 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]

9. M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005 Observation by TSC of Thermal Donors in p-type MCz Si Sample 14; V fd = 10V; [TD]  3.3x10 12 cm -3

10. M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005 Sample 5; V fd = 110V; [TD]  1.4- 2.0x10 12 cm -3 Observation by TSC of Thermal Donors in p-type MCz Si

11. M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005 V fd =110 V corresponding to N eff =1.6x10 12 cm -3. Expected thermal donor concentration: [TD]=0.5x(N A -N eff )<3x10 12 cm -3, from manufactory data about  [TD]=0.5x(N A ’-N eff )≈2.7x10 12 cm -3, from our estimate of [B] From direct TSC integration of TD peaks: [TD]=1.4-2.0x10 12 cm -3 V fd =10 V corresponding to N eff =1.5x10 11 cm -3 Expected thermal donor concentration: [TD]=0.5x(N A -N eff )<3.8x10 12 cm -3, from manufactory data about  [TD]=0.5x(N A ’-N eff )>3.6x10 12 cm -3, from our estimate of [B] From direct TSC integration of TD peaks: [TD]=3.3x10 12 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.

12. M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005 THERMAL DONORS FORMATION RATE At 430°C x ~ 3 - 4 Range 350-400°C x ~ 2 D i = D  ·e -Ea/KT, with D  =0.13cm 2 /s and E a =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 N TD ~ 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 process T = 420°C annealing

13. M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005 Effects of N eff disuniformity on microstrip sensors Simulation of the backplane capacitance in a 50mm pitch microstrip detector Taking into consideration the doping disuniformity measured on diodes along the diameter. Full depletion voltage spread: 90 - 140 V   V = 50V

14. M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005 Full depletion voltage spread: 4 - 90 V   V = 85V Full depletion voltage spread: 70 - 120 V   V = 50V

15. M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005 C-V measured with SMART p-type MCz Si microstrip sensors and comparison with the simulated CV taking into account of the V fd disuniformity. INFN Bari Wafer 9 Sensor s5 Proton irradiated 24GeV/c 4x10 13 n/cm 2 SCIPP UCSC Wafers 14 & 37 Sensor s5 Non irradiated

16. M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005 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 V fd 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 10 12 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.