1. G. Steinbrück, University of Hamburg, SLHC Workshop, Perugia, 3-4 April 20061 Epitaxial Silicon Detectors for Particle Tracking Overview on Radiation Tolerance at Extreme Hadron Fluence Joint Project: Bucharest-Hamburg-Ljubljana with ITME (EPI), CiS (diodes), CERN (PS-p) work done in the RD 50 collaboration presented by: Georg Steinbrück Hamburg University  Motivation  Material parameters  Results for proton and neutron irradiated devices  S-LHC scenario: simulation and experimental data  Outlook

2. G. Steinbrück, University of Hamburg, SLHC Workshop, Perugia, 3-4 April 20062Motivation  LHC upgrade to Super-LHC Luminostity LHC: L ~ 10 34 cm -2 s -1  S-LHC: L ~ 10 35 cm -2 s -1 Expected radiation at inner pixel layer (4 cm) under S-LHC conditions: Fluence for fast hadrons: 1.6  10 16 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 10 16 cm-2 by e  20  m, h  10  m small pixel size needed, allows thin devices with acceptable capacitance for S/N  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

3. G. Steinbrück, University of Hamburg, SLHC Workshop, Perugia, 3-4 April 20063 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)  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) epi Cz-substrate O concentration dep. on thickness

4. G. Steinbrück, University of Hamburg, SLHC Workshop, Perugia, 3-4 April 20064 Quasi-Stable Damage Component N eff (t 0 ): Value taken at annealing time t 0 at which V fd maximal  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

5. G. Steinbrück, University of Hamburg, SLHC Workshop, Perugia, 3-4 April 20065 Shallow Donors, the real issue for EPI -Comparison of 25, 50 and 75 µm Diodes- 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 Strong correlation between [O]-[BD]-g C generation of O (dimer?)-related BD reason for superior radiation tolerance of EPI Si detectors

6. G. Steinbrück, University of Hamburg, SLHC Workshop, Perugia, 3-4 April 20066 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  10 -2 cm -1  Introduction rate for neutrons: Value for 25 µm slightly lower compared to 50 µm, average value: g Y1 = 1.7  10 -2 cm -1 Amplitude in N eff

7. G. Steinbrück, University of Hamburg, SLHC Workshop, Perugia, 3-4 April 20067 Temperature Dependence of Temperature Dependence of  Y1 23 GeV protons  Arrhenius relation: 1/  Y = k 0  exp(-E a /k B T) Y1 component: E a = 1.3 eV, k 0 = 1.5  10 15 s -1 High resistivity FZ Si: M. Moll, PhD thesis Rises linearly  reliable extrapolation to operating temperature/room temperature! LT annealing No difference between FZ and EPI wrt. LT annealing!

8. G. Steinbrück, University of Hamburg, SLHC Workshop, Perugia, 3-4 April 20068 Reliability check: Annealing at 20°C parameter20°C data fit80°C data fit Stable dam. N C -8.9·10 13 cm -3 -8.6 ·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 -3 1.8 ·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  Analyzed parameters agree reasonably well  Projection from our 60°C, 80°C-results to RT annealing reliable

9. G. Steinbrück, University of Hamburg, SLHC Workshop, Perugia, 3-4 April 20069 Charge Collection Efficiency  Charge collection efficiency measured with 90 Sr electrons(mip’s), shaping time 25 ns  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 !  No degradation of CCE at low temperatures !

10. G. Steinbrück, University of Hamburg, SLHC Workshop, Perugia, 3-4 April 200610 S-LHC CERN scenario experiment  Simulation: reproducing the experimental scenario with damage parameters from analysis  Experimental parameter:  Irradiation: fluence steps  2.2  10 15 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!

11. G. Steinbrück, University of Hamburg, SLHC Workshop, Perugia, 3-4 April 200611 S-LHC operational scenario simulation results  RT storage during beam off periods extremely beneficial  Damage during operation at -7°C compensated by 265 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)

12. G. Steinbrück, University of Hamburg, SLHC Workshop, Perugia, 3-4 April 200612 Summary Thin low resistivity EPI diodes (grown on Cz) are extremely radiation tolerant No type inversion observed up to Φ eq = 10 16 cm -2 for protons and neutrons Radiation induced stable donor generation related most likely to O-dimers Elevated temperature annealing results verified at 20°C Dedicated CERN scenario experiment shows benefits of RT storage Simulation of real SLHC operational scenario with RT storage demonstrated 50 µm EPI Detectors withstand 5y SLHC with V op ≤ 300V (full depl.) Future plans: p-type epi, thicker n-type epi, thin Cz …..

13. G. Steinbrück, University of Hamburg, SLHC Workshop, Perugia, 3-4 April 200613 BACKUP

14. G. Steinbrück, University of Hamburg, SLHC Workshop, Perugia, 3-4 April 200614 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 min @ 80C ≈ 500 days @ RT)  EPI never inverted at RT, even for 10 16

15. G. Steinbrück, University of Hamburg, SLHC Workshop, Perugia, 3-4 April 200615 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))

16. G. Steinbrück, University of Hamburg, SLHC Workshop, Perugia, 3-4 April 200616 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)

17. G. Steinbrück, University of Hamburg, SLHC Workshop, Perugia, 3-4 April 200617 Reverse Annealing Time Constants  Protons: above 10 15 cm -2  Y1 and  Y2  constant Ratio  Y1 (60°C)/  Y1 (80°C) = 11 Ratio  Y2 (60°C)/  Y2 (80°C) = 10 below 10 15 cm -2  Y2  1/  eq  Neutrons: above 2  10 15 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

18. G. Steinbrück, University of Hamburg, SLHC Workshop, Perugia, 3-4 April 200618 Current Generation Result almost identical to FZ silicon: Current related damage rate α = 4.1·10 -17 Acm -1 (Small deviations in short term annealing)