Study of radiation damage induced by 24/c GeV and 26MeV protons on heavily irradiated MCz and FZ silicon detectors N. Manna Dipartimento Interateneo di Fisica & INFN di Bari on behalf of the SMART Collaboration* (*) INFN sections of Bari, Firenze, Perugia, Pisa; External collaborators INFN Padova, Trieste & ITC-IRST Trento Layout and materials of SMART detectors Pre-irradiation measurements Post-irradiation measurements Conclusions 7th RD50 - Workshop on Radiation hard semiconductor devices for very high luminosity colliders CERN, 14-16 November, 2005

Wafer Layout Test2: GCD, Van der Paw Test1: Diode+Mos Square MG-diodes Microstrip detectors Inter-strip Capacitance test Test2: GCD, Van der Paw Test1: Diode+Mos Square MG-diodes Round MG-diodes 50 mm pitch 64 strips 100 mmpitch 32 strips S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 RD50 common wafer procurement (produced by Okmetic - Vantaa, Finland) Wafer Layout designed by the SMART Collaboration Masks and process by ITC-IRST 10 different strip geometries NORMAN MANNA

PRODUCTION MCz Samples RUN I p-on-n 22 wafers RUN II n-on-p 24 wafers Fz Samples <100> ρ>500 W*cm thick=300μm Standard: LTO, sintering @ 420C no LTO (pass. layer), sint. @ 380C no LTO, sintering @ 350C no LTO, sintering @ 380C + TDK <111> ρ>6KΩ*cm thick=300μm Standard Process sintering @ 380C RUN I p-on-n 22 wafers <100> ρ>1.8 KW*cm thick=300μm No over-glass passivation Low dose p-spray (3.0E12 cm-2) High dose p-spray (5.0E12 cm-2) <100> ρ>5KΩ*cm thick=200 mm Low dose p-spray (3.0E12 cm-2) High dose p-spray (5.0E12 cm-2) RUN II n-on-p 24 wafers NORMAN MANNA

Pre Irradiation Characterization - Diodes - Measurements Leakage currents  Vbreakdown Depletion Voltage  Initial resistivity and Uniformity of a wafer (1) OK Fz (2) non uniformity of the Depletion Voltage in the MCz, especially for p-type production Map of the diodes Vdepl in a p-type MCz wafer Probably due to fluctuations of the oxygen concentration in MCz material (see talk Piemonte 5th RD50 workshop Firenze, 14-16 oct 2004) NORMAN MANNA

Pre Irradiation Characterization - Minisensors (Leakage Current)- Good performances of the n-type detectors in terms of breakdown voltages and current uniformity Problems for the p-type detectors: low breakdown voltages for the 100 mm pitch detectors, due to the adopted isolation technique (p-spray), enhanced for the highest dose Disuniformity of the wafer resistivity, explained with a different oxygen concentration leading to a spread in the thermal donor activation (as seen on diodes) MCz p-type High p Spray MCz p-type Low p Spray Ileak/V (nA/cm-2) Ileak/V (nA/cm-2) -Vbias (Volt) -Vbias (Volt) NORMAN MANNA

Pre Irradiation Characterization - Minisensors (Interstrip Capacitance)- MCz n-type Good performances of the n-type detectors (interstrip capacitance depends, as expected, on the minisensors geometry: strip width, pitch, metal overhang…) Cint /l (pF/cm) Different behaviour for the p-type detectors: Interstrip capacitance decreases with Vbias reaching saturation at voltages much higher than depletion due to the existence of an electron layer behind the oxide. The saturation is faster in low p spray and for high pitches. No differences between Fz and MCz. Vbias (Volt) MCz p-type High p Spray FZ p-type High p Spray MCz p-type Low p Spray Cint /l (pF/cm) Cint /l (pF/cm) Cint /l (pF/cm) -Vbias (Volt) -Vbias (Volt) -Vbias (Volt) NORMAN MANNA

Irradiation October 2004 Irradiation with 24 Gev/c protons at CERN SPS Set up for the irradiation @ CERN(Geneva) Irradiation with 24 Gev/c protons at CERN SPS 3 fluences: 6.0x1013 3.0x1014 3.4x1015 1-MeV n/cm2 27 mini-sensors, 90 diodes 75 % n-type, 25 % p-type Thanks to M. Glaser Set up for the irradiation @ FZK(Karlsruhe) May 2005 Irradiation with 26 MeV protons at the Cyclotron of the Forschungszentrum Karlsruhe 11 fluences: 1.4x1013 - 2.0x1015 1-MeV n/cm2 62 mini-sensors, 100 diodes 38 % n-type, 62 % p-type Thanks to A. Furgeri NORMAN MANNA

Post Irradiation Characterization On Diodes: IV and CV measurements (@ 0 °C or 20 °C) - immediately after irradiation before annealing - repeated after annealing steps (@ 20, 60 or 80 °C) in order to: (1) follow the radiation damage evolution on bulk current and effective doping concentration; (2) determine the effective irradiation fluences (3) estimate the inversion fluence (4) compare different sintering procedures in terms of Vdep On Minisensors: IbiasV, IstripV, CV and Interstrip Capacitance measurements (@ 0 0C) - repeated after annealing steps(@ 60 or 80 0C,to be done @200C) in order to study: (1) the performance of ptype sensors (2) low and high dose p spray on p-type substrates; (3) geometry influence on noise and current level (4) MCz vs Fz sensors behaviour NORMAN MANNA

After Irr. Ileak on diodes Estimation of irradiation fluences The neutron equivalent fluences of irradiation were estimated with the fit of the annealing current curve on Fzn materials using the standard parameterisations for α(t,T) (Rose Collaboration – M.Moll PhD theses) Universality of α  (in order to check the nominal fluences) NORMAN MANNA MCz: improved reverse annealing MCz: improved reverse annealing

Depletion voltage after irr. (Fz n Type inversion) T=200C NORMAN MANNA

Depletion voltage after irr. (MCz n Type inversion?) The annealing behaviour is typical of type inverted (p-type) material after Φ4 , but no SCSI observed (see Menichelli’s talk) T=200C NORMAN MANNA

Annealing @ high temperature Type non-inverted: depletion voltage has a maximum ? No SCSI observed MCz: improved reverse annealing Type inverted: depletion voltage has a minimum NORMAN MANNA Type non-inverted: depletion voltage has a maximum Type inverted: depletion voltage has a minimum

Depletion voltage after irr. n type Wafer  (10-2 cm-1) W1253 Fz 0.63  0.04 W1254 Fz 0.46  0.05 W91 MCz 0.61  0.03 W115 MCz 0.42  0.03 W127 MCz 0.65  0.02 W179 MCz 0.58  0.04 p type Wafer  (10-2 cm-1) W84 Fz high 0.90  0.05 W64 Fz high 1.01  0.05 W248 MCz high 0.20  0.02 W130 MCz high 0.7  0.2 W127 MCz high 0.65  0.02 W179 MCz low 0.63  0.03 NORMAN MANNA

After Irr. Ileak minisens n type MCz & Fz IV curves of n- and p-type detectors for the full fluence range before annealing (measured at 0oC): Current levels in MCz detectors are comparable with Fz at a given fluence Leakage currents measured at Vdepl scale as the received fluences. The performances of Fz and MCz p-type detectors, comprising sensors with 100 mm pitch, are much improved after irradiation. Sensors with low p-spray have breakdown voltages comparable with n-type detectors in all the fluence range. Detectors with a high p-spray dose still have breakdown problems at lower fluences (< 4.0 *1014 1-MeV n/cm2) whereas they have very good performances at the highest fluences. Bias Voltage (V) SENSOR GEOMETRY # 1 Leakage Current (A) MCz Low p spray MCz High p spray NORMAN MANNA

Interstrip Capacitance No particular problem with irradiation for n-type MCz (and Fz) For irradiated p-type MCz: As before irradiation, interstrip capacitance decreases with Vbias, reaching saturation at voltages much higher than VFD. The saturation is faster with respect to un-irradiated sensors The saturation is still faster in low p spray and for large pitches. No differences between Fz and MCz. MCz n <100> In order to better see this, it is useful to compare the behaviour of different materials and technological production splittings for a given sensor geometry  next slide MCz Low p spray Fz p High p spray NORMAN MANNA

Interstrip Capacitance Vdep NORMAN MANNA

Conclusions The MCz detectors of the SMART production are fully comparable with Fz regarding leakage currents values and breakdown voltages. Depletion voltages as a function of bias voltage and annealing time follow a different behaviour in the two materials  the “type inversion” on MCz material is under investigation: no SCSI observed. Better behaviour of Vdep on MCz detectors after irradiation and in particular during the reverse annealing The study of the detectors properties during the annealing procedure must be completed in order to fix the parameters of the simulation of MCz behaviour after irradiation Measurements on interstrip capacitance and leakage current on p-type detectors show that an improved strip isolation technique is needed  a new production run is foreseen. NORMAN MANNA