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

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 Messineo, L. Borrello, G. Segneri INFN Pisa

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

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  1. 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 • Messineo, L. Borrello, G. Segneri • INFN Pisa • I. W. Henderson, H. Sadrozinski • SCIPP, UCSC, Santa Cruz M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005

  2. n-on-p microstrip detectors by SMART INFN processed in 2004 at IRST- Trento FZ p-spray 3E12 - 5E12 <100> p-type >5000Wcm 525mm <100> p-type >5000Wcm 200mm MCz no OG; p-spray 3E12 - 5E12 <100> p-type >1800Wcm 300mm Layout 10 mini-strip 0.6x4.7cm2 50 and 100mm pitch, AC coupled 37 pad diodes and various text structures MCz Si wafers from Okmetic, Finland, RD50 procurement SIMS analysis on Okmetic MCz Si wafers [Oi] ~ 4.6x1017cm-3 [G. Pellegrini et al. NIM A 2005] M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005

  3. 6 7 9 10 1 2 4 5 8 3 Microstrip minisensors pitch 50 µm 64 strips pitch 100 µm 32 strips • AC coupled • poly resistor biased die ~6x47mm2 M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005

  4. n-on-p – CV on diodes ( N. Zorzi, Trento RD50 Meeting, Feb. 2005) Quite high doping variations!! Probably due to fluctuations in the Thermal Donors activation. M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005

  5. 430°C up to 120min 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 . Evaluated by TSC after 430°C - 120min nTD = 2 - 4·1012 cm-3 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/ M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005

  6. Study of Thermal Donors in n-MCZ Si processed by IRST in p-on-n diodes non irradiated TD0/+ Standard No LTO and sintering at 380°C TD+/++ P • > 500Wcm n-MCz Si 430°C 380°C Presented by D. Menichelli, 6° RD50 Workshop, Helsinki, June 2005 In standard process the TDs are activated, if T < 380°C the TDs are almost absent. M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005

  7. 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 mm. r >1.8 kWcm corresponding to NA<7.7x1012 cm-3. M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005

  8. Evaluation of Boron Concentration in p-type MCz Si From B peak integration in TSC: N’A = (7.01.5)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 TSC [A] T [K] M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005

  9. Observation by TSC of Thermal Donors in p-type MCz Si Sample 14; Vfd = 10V; [TD]  3.3x1012 cm-3 M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005

  10. Observation by TSC of Thermal Donors in p-type MCz Si Sample 5; Vfd = 110V; [TD]  1.4- 2.0x1012 cm-3 M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005

  11. Sample 5 • 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 r • [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 Sample 14 • 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 r • [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 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 . M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005

  12. THERMAL DONORS FORMATION RATE 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). Good agreement with p- type diodes processed at Helsinki At 430°C x ~ 3 - 4 Range 350-400°C x ~ 2 M. Bruzzi et al.,5° RD50 Workshop, submitted to J. App. Phys. J. Harkonen et al., Wildbad Kreuth conference, in press on NIM A T = 370°C process T = 420°C annealing Open Problem 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. M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005

  13. Effects of Neff 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  DV = 50V M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005

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

  15. C-V measured with SMART p-type MCz Si microstrip sensors and comparison with the simulated CV taking into account of the Vfd disuniformity. Non irradiated Proton irradiated 24GeV/c 4x1013n/cm2 SCIPP UCSC Wafers 14 & 37 Sensor s5 INFN Bari Wafer 9 Sensor s5 M. Bruzzi, the issue of p-type disuniformity, 7° RD50 Workshop, CERN, November 14-16, 2005

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

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