Epitaxial Silicon Detectors for Particle Tracking Overview on Radiation Tolerance at Extreme Hadron Fluence G. Lindström (a), E. Fretwurst (a), F. Hönniger (a), G. Kramberger (b), M. Moll (c), E. Nossarzewska (d), I. Pintilie (e), R. Röder (e) (a) Institute for Experimental Physics, University of Hamburg (b) Jozef Stefan Institute, University of Ljubljana (c) CERN (d) ITME Institute of Electronic Materials Technology, Warsaw (e) National Institute for Materials Physics, Bucharest (f) CiS Institut für Mikrosensorik gGmbH, Erfurt Joint Project: Bucharest-Hamburg-Ljubljana with ITME (EPI), CiS (diodes), CERN (PS-p)  Motivation  Material parameters  Results for proton and neutron irradiated devices  S-LHC scenario: simulation and experimental data  Summary 1G. Lindström, University of Hamburg, 10th European Symposium on Semiconductor Detectors, Wildbad Kreuth,12-16 June 2005

Motivation  LHC upgrade to Super-LHC Luminostity LHC: L ~ cm -2 s -1  S-LHC: L ~ cm -2 s -1 Expected radiation at inner pixel layer (4 cm) under S-LHC conditions: Fluence for fast hadrons: 1.6  cm -2 Dose: 420 Mrad  Proposed Solution: thin EPI-SI for small size pixels Si best candidate: low cost, large availability, proven technology thickness doesn’t matter! CCE limited at cm -2 by e  20  m, h  10  m small pixel size needed, allows thin devices with acceptable capacitance for S/N high N eff,0 (low ρ) provides large donor reservoir, delays type inversion  Needed data for prediction of S-LHC operational scenario:  Reliable projection of damage data to S-LHC operation  Full annealing cycles at elevated temperatures  Charge collection efficiency at very high fluences 2G. Lindström, University of Hamburg, 10th European Symposium on Semiconductor Detectors, Wildbad Kreuth,12-16 June 2005

Material Parameters  Oxygen depth profiles SIMS-measurements after diode processing O diffusion from substrate into epi-layer interstial O i + dimers O 2i [O] 25 µm > [O] 50 µm process simulation yields reliable [O] (SIMS-measurements: A. Barcz/ITME, Simulations: L. Long/CiS) 3G. Lindström, University of Hamburg, 10th European Symposium on Semiconductor Detectors, Wildbad Kreuth,12-16 June 2005  Resistivity profiles SR  before diode process, C-V on diodes SR coincides well with C-V method Excellent homogeneity in epi-layers (SR-measurements: E. Nossarzewska, ITME)

Typical Annealing Curves Comparison EPI- with FZ-device: V fd development: short term: EPI increasing, FZ decreasing long term: EPI decreasing, FZ increasing  EPI not inverted, FZ inverted, already immediately after irradiation Typical annealing behavior of EPI-devices: V fd development: Inversion only(!) during annealing (  ) (100 80C ≈ 500 RT)  EPI never inverted at RT (t < 500d), even for G. Lindström, University of Hamburg, 10th European Symposium on Semiconductor Detectors, Wildbad Kreuth,12-16 June 2005

Parameterization of Annealing Results Annealing components:  Short term annealing  N A ( ,t(T))  Stable damage  N C (  ) N C = N C0 (1-exp(-cΦ eq ) + g C Φ eq g C negative for EPI (effective positive space charge generation!)  Long term (reverse) annealing: Two components:  N Y,1 ( ,t(T)), first order process  N Y,2 ( ,t(T)), second order process N Y1, N Y2 ~ Φ eq, N Y1 +N Y2 similar to FZ Change of effective “doping“ concentration:  N eff = N eff,0 – N eff ( ,t(T)) Standard parameterization:  N eff = N A ( ,t(T)) + N C (  ) + N Y ( ,t(T)) 5G. Lindström, University of Hamburg, 10th European Symposium on Semiconductor Detectors, Wildbad Kreuth,12-16 June 2005

Stable Damage Component N eff (t 0 ): Value taken at annealing time t 0 at which V fd maximum  No space charge sign inversion after proton and neutron irradiation Introduction of shallow donors overcompensates creation of acceptors  Protons: Stronger increase for 25 µm compared to 50 µm  higher [O] and possibly [O 2 ] in 25 µm (see SIMS profiles)  Neutrons: Similar effect but not nearly as pronounced most probably due to less generation of shallow donors and as strong influence of acceptors 6G. Lindström, University of Hamburg, 10th European Symposium on Semiconductor Detectors, Wildbad Kreuth,12-16 June 2005

Shallow Donors, the real issue for EPI -Comparison of 25, 50 and 75 µm Diodes- 7G. Lindström, University of Hamburg, 10th European Symposium on Semiconductor Detectors, Wildbad Kreuth,12-16 June 2005 SIMS profiling: [O](25µm) > [O](50µm) > [O](75µm) Stable Damage: N eff (25µm) > N eff (50µm) > N eff (75µm) TSC Defect Spectroscopy: [BD](25µm) > [BD](50µm) > [BD](75µm) SIMS profiling of [O] Stable Damage after PS p-irradiation Generation of positive space charge most pronounced in 25 µm diodes Defect spectroscopy after PS p-irradiation Generation of recently found shallow donors BD (Ec-0.23 eV) strongly related to [O] Possibly caused by O-dimers, outdiffused from Cz with larger diffusion constant dimers monitored by IO 2 complex Strong correlation between [O]-[BD]-g C generation of O (dimer?)-related BD reason for superior radiation tolerance of EPI Si detectors

Annealing Curves for 25 µm and 50 µm  Nearly identical time dependence, constant difference between both curves  Shift due to higher introduction of shallow donors in 25 µm epi-Si  Concentration of donors not affected by long term annealing  Radiation induced donors are stable at 80°C (verified by TSC) 8G. Lindström, University of Hamburg, 10th European Symposium on Semiconductor Detectors, Wildbad Kreuth,12-16 June 2005

Examples of parameter evaluation from annealing: Fluence Dependence of N Y1  Introduction rate for protons: Independent of epi-layer thickness and annealing temperature g Y1 = 3.1  cm -1  Introduction rate for neutrons: Value for 25 µm slightly lower compared to 50 µm, average value: g Y1 = 1.7  cm -1 9G. Lindström, University of Hamburg, 10th European Symposium on Semiconductor Detectors, Wildbad Kreuth,12-16 June 2005

Reverse Annealing Time Constants  Protons: above cm -2  Y1 and  Y2  constant Ratio  Y1 (60°C)/  Y1 (80°C) = 11 Ratio  Y2 (60°C)/  Y2 (80°C) = 10 below cm -2  Y2  1/  eq  Neutrons: above 2  cm -2  Y1 and  Y2  constant  Y1 (50 µm) = 1.3  10 2 min,  Y1 (25 µm) = 3.3  10 2 min  Y2 (50 µm) = 2.9  10 3 min,  Y2 (25 µm) = 5.3  10 3 min 10G. Lindström, University of Hamburg, 10th European Symposium on Semiconductor Detectors, Wildbad Kreuth,12-16 June 2005

Temperature Dependence of Temperature Dependence of  Y1 and  Y2 23 GeV protons  Arrhenius relation: 1/  Y = k 0  exp(-E a /k B T) Y 1 component: E a = 1.3 eV, k 0 = 1.5  s -1 Y 2 component: E a = 1.3 eV, k 0 = 5.4  s -1 High resistivity FZ Si: M. Moll, PhD thesis 11G. Lindström, University of Hamburg, 10th European Symposium on Semiconductor Detectors, Wildbad Kreuth,12-16 June 2005

Reliability check: Annealing at 20°C 12G. Lindström, University of Hamburg, 10th European Symposium on Semiconductor Detectors, Wildbad Kreuth,12-16 June 2005 parameter20°C data fit80°C data fit Stable dam. N C -8.9·10 13 cm ·10 13 cm -3 Benef. Ann. N a 3 ·10 13 cm -3 5 ·10 13 cm -3 Rev. Ann. N Y1 2.2 ·10 14 cm ·10 14 cm -3 Example: EPI 50 µm, Φp = 1.01·10 16 cm -2  20°C annealing results can be fitted with Hamburg model  RT Analysis agrees reasonably well with results from 60°, 80°C  Projection from high T annealing to behavior at RT reliable

Charge Collection Efficiency  CCE degradation linear with fluence if the devices are fully depleted CCE = 1 –    ,   = 2.7  cm2  CCE(10 16 cm -2 ) = 70 %  Charge collection efficiency measured with 244 Cm  -particles (5.8 MeV, R  30 µm) Integration time window 20 ns  Charge collection efficiency measured with 90 Sr electrons(mip’s), shaping time 25 ns  CCE no degradation at low temperatures ! degradation linear with fluence if the devices CCE measured after n- and p-irradiation  CCE(Φ p =10 16 cm -2 ) = 2400 e (mp-value) Extracted trapping parameters coincide with those measured in FZ diodes for small Φ, for large Φ less trapping than expected ! 13G. Lindström, University of Hamburg, 10th European Symposium on Semiconductor Detectors, Wildbad Kreuth,12-16 June 2005

Current Generation 14G. Lindström, University of Hamburg, 10th European Symposium on Semiconductor Detectors, Wildbad Kreuth,12-16 June 2005 Result almost identical to FZ silicon: Current related damage rate α = 4.1· Acm -1 (Small deviations in short term annealing)

S-LHC CERN scenario experiment  Simulation: reproducing the experimental scenario with damage parameters from analysis  Experimental parameter:  Irradiation: fluence steps  2.2  cm -2 irradiation temperature  25°C  After each irradiation step annealing at 80°C for 50 min, corresponding 265 days at 20°C Excellent agreement between experimental data and simulated results  Simulation + parameters reliable! 15G. Lindström, University of Hamburg, 10th European Symposium on Semiconductor Detectors, Wildbad Kreuth,12-16 June 2005 Stable donor generation at high Φ would lead to larger Vfd, but acceptor generation during RT anneal could compensate this. Proposal: Storage of EPI- detectors during beam off periods at RT (in contrast to required cold storage for FZ) Check by dedicated experiment:

S-LHC operational scenario simulation results 16G. Lindström, University of Hamburg, 10th European Symposium on Semiconductor Detectors, Wildbad Kreuth,12-16 June 2005  RT storage during beam off periods extremely beneficial  Damage during operation at -7°C compensated by 100 d RT annealing  Effect more pronounced for 50 µm: less donor creation, same acceptor component  Depletion voltage for full SLHC period less than 300 V S-LHC: L=10 35 cm -2 s -1 Most inner pixel layer operational period per year: 100 d, -7°C, Φ = 3.48·10 15 cm -2 beam off period per year 265 d, +20°C (lower curves) -7°C (upper curves)

Summary 17G. Lindström, University of Hamburg, 10th European Symposium on Semiconductor Detectors, Wildbad Kreuth,12-16 June 2005 Thin low resistivity EPI diodes (grown on Cz) are extremely radiation tolerant No type inversion observed up to Φ eq = cm-2 for protons and neutrons, space charge sign remains positive even during long time annealing Annealing experiments at elevated temperatures reveal stable donor generation (in contrast to FZ), overcompensating the damage induced acceptor concentration Elevated temperature annealing results verified at 20°C Dedicated CERN scenario experiment shows benefits of RT storage in contrast to required cooling for FZ silicon, experimental results in excellent agreement with simulations using the Hamburg model parameters Simulation of real SLHC operational scenario with RT annealing during beam off periods show that V fd kept at <300V (50μm), <150V (25μm) for full 5 y SLHC Donors identified: BD point defects (E C eV) most likely related to O-dimers strong correlation found between [O](SIMS)-[BD](TSC)-N C (annealing exp.) Trapping almost as expected from FZ, 2400 e measured for mips after cm -2 Current related damage rate 4· Acm -1 (as known for FZ)