SMART Study of radiation damage induced by 24GeV/c and 26MeV protons on heavily irradiated MCz and FZ silicon detectors V. Radicci Dipartimento Interateneo di Fisica & INFN di Bari on behalf of the SMART Collaboration* 7th International Conference on Large Scale Applications and Radiation Hardness of Semiconductor Detector October 5-7, Florence, Italy (*) INFN sections of Bari, Firenze, Perugia, Pisa; External collaborators INFN Padova, Trieste & ITC-IRST Trento  Motivation  Layout and materials used in the production of the SMART sample  Pre-irradiation measurements and irradiation campaigns  Results of the post-irradiation measurements  Conclusions and outlook

SMART Valeria Radicci 2/22 RD05 October 5-7, Florence, Italy Motivations LHC SLHC Beam energy 7 Tev 12.5 TeV Luminosity cm -2 s cm -2 s -1 Radial distances of the Fluences foreseen Fluences foreseen CMS S-LHC Pixel: 4 cm => 1  cm  cm cm => 4  cm  cm -2 Microstrip: 22 cm => 1  cm -2 8  cm cm => 8  cm -2 1  cm -2 A Luminosity upgrade of the CERN Large Hadron Collider (LHC) is already envisaged

SMART Valeria Radicci 3/22 RD05 October 5-7, Florence, Italy Our Strategies  New data are needed for prediction of S-LHC operational scenario:  Full set of damage parameters for |ΔN eff | vs. annealing time  Full annealing cycles at elevated temperatures (at least 2 temperatures)  Charge collection efficiency at very high fluences (CCE is limited by carrier trapping)  New radiation hard materials and devices are needed for Future High Energy Physics experiments: the CERN RD50 Collaboration and the INFN SMART project within RD50 are aimed at developing new :  Oxygen enriched Silicon: Radiation induced V 2 O depressed in favor of less damaging VO or oxygen aggregates: - Diffused Oxygen Float Zone (DOFZ) (Improved radiation hardness already shown by RD48) - Magnetic Czochralski (MCz) (DOFZ: ~ 2x1017[O]/cm 3 – MCz: ~ 5x1017[O]/cm 3 )  n-on-p devices: - improved charge collection (collection of electrons with higher mobility and lower trapping time ) - always p-type substrate: after irradiation the junction is still of the strips side, and detectors can work in partial depletion

SMART Valeria Radicci 4/22 RD05 October 5-7, Florence, Italy Wafer Layout 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 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

SMART Valeria Radicci 5/22 RD05 October 5-7, Florence, Italy Materials and Processing RUN II n-on-p 24 wafers ρ>500  *cm thickn.=300μm Standard: LTO, 420C no LTO (pass. layer), 380C no LTO, 350C no LTO, 380C + TDK ρ>6 k  *cm thickn.=300μm Standard Process 380C  ρ>1.8 k  *cm thickn.=300μm No over-glass passivation Low dose p-spray (3.0E12 cm -2 ) High dose p-spray (5.0E12 cm -2 ) ρ>5 k  *cm thickn.=200 μ m Low dose p-spray (3.0E12 cm -2 ) High dose p-spray (5.0E12 cm -2 ) MCz Samples Fz Samples RUN I p-on-n 22 wafers

SMART Valeria Radicci 6/22 RD05 October 5-7, Florence, Italy Pre Irradiation Characterization - Diodes - Map of the diodes V depl in a p-type MCz wafer Measured in IRST 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 Probably due to fluctuations of the oxygen concentration in MCz material (see talk Piemonte 5th RD50 workshop Firenze, oct 2004) SMART2 - n + /p - MCz 300  m

SMART Valeria Radicci 7/22 RD05 October 5-7, Florence, Italy 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:  Disuniformity of the wafer resistivity, explained with a different oxygen concentration leading to a spread in the thermal donor activation (as seen on diodes)  low breakdown voltages for the 100  m pitch detectors (big dots) enhanced for the highest p-spray dose, due to the adopted isolation technique (p-spray). MCz n-type I leak /V (nA/cm -2 ) V bias (Volt) -V bias (Volt) MCz p-type Low p-Spray I leak /V (nA/cm -2 ) 250 MCz p-type High p-Spray -V bias (Volt) I leak /V (nA/cm -2 ) 70

SMART Valeria Radicci 8/22 RD05 October 5-7, Florence, Italy Good performances of the n-type detectors (interstrip capacitance depends, as expected, on the minisensors geometry: strip width, pitch, metal overhang…) MCz p-type Low p Spray -V bias (Volt) C int /l (pF/cm) MCz p-type High p Spray C int /l (pF/cm) -V bias (Volt) FZ p-type High p Spray C int /l (pF/cm) -V bias (Volt) 50µm 100µm C int /l (pF/cm) V bias (Volt) MCz n-type 50µm 100µm Pre Irradiation Characterization - Minisensors (Interstrip Capacitance)- Different behaviour for the p-type detectors:  Interstrip capacitance decreases with V bias reaching saturation at voltages much higher (!!) than depletion (~100V), due to the existence of an electron layer under the oxide. The saturation is faster in low p spray and for high pitches. No differences between Fz and MCz.

SMART Valeria Radicci 9/22 RD05 October 5-7, Florence, Italy CCE mesurements with a β source A few mini-sensors have been assembled in a detector unit and tested with a LHC-like DAQ system Measurement with a  source: DAQ system configured in peak mode Measurement performed at over-depletion for not-irradiated sensors Fz n-type MCz n-type MCz S=17.8 ± 0.2, N=1.02 S/N 500 V Fz S=18.8 ± 0.3, N=0.98 S/N 200 V Measured in Pisa (see talk of 6 th RD50 Workshop-Helsinki 2-4 June 2005)

SMART Valeria Radicci 10/22 RD05 October 5-7, Florence, Italy Irradiation Irradiation with 24 Gev/c protons at CERN SPS 3 fluences: 6.0x x x MeV n/cm 2 27 mini-sensors, 90 diodes 75 % n-type, 25 % p-type Thanks to M. Glaser Irradiation with 26 MeV protons at the Cyclotron of the Forschungszentrum Karlsruhe 11 fluences: 1.4x x MeV n/cm 2 62 mini-sensors, 100 diodes 38 % n-type, 62 % p-type Thanks to A. Furgeri October 2004 May 2005 Set up for the CERN(Geneva) Set up for the FZK(Karlsruhe)

SMART Valeria Radicci 11/22 RD05 October 5-7, Florence, Italy 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 V dep  On Minisensors:  I bias V, I strip V, CV, Interstrip Resistances and Capacitance measurements 0 ° C) - immediately after irradiation before annealing - repeated after annealing 60 or 80 ° C, to be 20 ° C)  Charge Collection Efficiency (to be done) 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

SMART Valeria Radicci 12/22 RD05 October 5-7, Florence, Italy After Irr. I leak on diodes Estimation of irradiation fluences The irradiation neutron equivalent fluences were estimated by a fit of the annealing current curve on Fz-n 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)

SMART Valeria Radicci 13/22 RD05 October 5-7, Florence, Italy In STFZ n-type irradiated devices: Type inversion at fluences of the order of due to: Donor removal Creation of deep acceptors Neff variation with annealing time: Short term annealing: annealing of acceptors (or formation of donors) Long term annealing: creation of acceptors (or annealing of donors) RADIATION EFFECTS ON EFFECTIVE DOPING CONCENTRATION N eff IN STFZ

SMART Valeria Radicci 14/22 RD05 October 5-7, Florence, Italy Depletion voltage measurements after irr. (Fz type-n) The starting Fz n-type material is inverted at the lowest fluence: 0.2*10 14 n cm -2

SMART Valeria Radicci 15/22 RD05 October 5-7, Florence, Italy Depletion voltage after irr. (MCz-n type inversion?) The annealing behaviour for the first 4 fluence points (up to 1.4*10 14 n cm -2 ) is typical of n type material; for all higher fluence points the behaviour is “p-type”- like, BUT... see Monica talk! In this case the interpretation is not straightforward

SMART Valeria Radicci 16/22 RD05 October 5-7, Florence, Italy |Neff| vs Fluences (n-type vs p-type) No sensible difference between Fz and MCz substrate values after irradiation. β ~ 7*10 -3 cm -3 (literature values (*) : β [O] ~ 4*10 -3 cm -3 and β St ~ 15*10 -3 cm -3 ) good Fz!!! (*) RD48 Status Reports Lower depletion voltage values measured on MCz vs Fz

SMART Valeria Radicci 17/22 RD05 October 5-7, Florence, Italy high temperature (reverse annealing) Type non-inverted: depletion voltage has a maximum Type inverted: depletion voltage has a minimum Type non-inverted: depletion voltage has a maximum Type inverted: depletion voltage has a minimum MCz: improved reverse annealing

SMART Valeria Radicci 18/22 RD05 October 5-7, Florence, Italy Bias Voltage (V) SENSOR GEOMETRY # 1 Leakage Current (A) After Irr. I leak minisens IV curves of n- and p-type detectors for the full fluence range before annealing (measured at 0 o C): (1)Current levels in MCz detectors are comparable with Fz at a given fluence (2)Leakage currents measured at V depl scale as the received fluences. (3)The performances of Fz and MCz p- type detectors, comprising sensors with 100 mm pitch, are much improved after irradiation. (4)Sensors with low p-spray have breakdown voltages comparable with n-type detectors in all the fluence range. (5)Detectors with a high p-spray dose still have breakdown problems at lower fluences (< MeV n/cm2) whereas they have very good performances at the highest fluences. MCz High p spray MCz Low p spray

SMART Valeria Radicci 19/22 RD05 October 5-7, Florence, Italy Interstrip Capacitance MCz n Fz n Fz p High p spray MCz Low p spray OK Typical of Si Same problem (slow saturation) found for not irradiated sensors.Slightly improved after irradiation.

SMART Valeria Radicci 20/22 RD05 October 5-7, Florence, Italy 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 V bias, reaching saturation at voltages much higher than V FD.  The saturation is still faster in low p spray and for large pitches. No differences between Fz and MCz.  The saturation is faster with respect to un-irradiated sensors 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

SMART Valeria Radicci 21/22 RD05 October 5-7, Florence, Italy Interstrip Capacitance

SMART Valeria Radicci 22/22 RD05 October 5-7, Florence, Italy 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  under investigation the “type inversion” on MCz material!(*) 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. Measurements of the Charge Collection Efficiency of irradiated minisensors are planned in order to study:  p-type irradiated substrates (noise– interstrip capacitance measurements, S/N)  n-type MCz irradiated substrates (noise– interstrip cap, S/N, type inversion studies) (*) previous talk

SMART Valeria Radicci 23/22 RD05 October 5-7, Florence, Italy |ΔNeff| vs Fluences (n-type vs p-type)

SMART Valeria Radicci 24/22 RD05 October 5-7, Florence, Italy