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G.Pellegrini 1 , C.Fleta 2 , F.Campabadal 1 , M. Lozano 1 , J.M. Rafí 1 , M.Ullán 1

Technology of p-type microstrip detectors with radiation hard p-spray, p-stop and moderate p-spray insulations. G.Pellegrini 1 , C.Fleta 2 , F.Campabadal 1 , M. Lozano 1 , J.M. Rafí 1 , M.Ullán 1 1 Centro Nacional de Microelectr ó nica, Barcelona Spain 2 University of Glasgow, Glasgow, UK.

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G.Pellegrini 1 , C.Fleta 2 , F.Campabadal 1 , M. Lozano 1 , J.M. Rafí 1 , M.Ullán 1

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  1. Technology of p-type microstrip detectors with radiation hard p-spray, p-stop and moderate p-spray insulations G.Pellegrini1, C.Fleta2, F.Campabadal1, M. Lozano1, J.M. Rafí1, M.Ullán1 1Centro Nacional de Microelectrónica, Barcelona Spain 2University of Glasgow, Glasgow, UK

  2. Outline • P-type detectors • Detector isolation technologies • Simulation and measurements • Conclusions

  3. Technology: N type strips on p-type substrate N side read-out takes advantage of the presence of the high electric field on the read-out side after irradiation. Needs insulation between strips in order to compensate the electron layer formed below the oxide: P-stop P-spray Moderate p-spray More complex technology 6 or 7 photolithographic layers The most radiation hard technology P-type detectors

  4. First n-on-p detectors fabricated with p-stop isolation. Different implants were used to find the optimum value. P-stop isolation Pitch 120mm, p-stop width 7mm, strip width 20mm

  5. Radiation hardness N-on-p strip detectors with p-stop isolation (1) Pad detectors (2) • Baby microstrip detectors fabricated at CNM in collaboration with Liverpool University Efficiency of Charge Collection in 280 um thick p-type SSD After 7.5 *1015 p/cm2, charge collected is > 6,500 e- • First results on charge collection efficiency of heavily irradiated microstrip sensors fabricated on oxygenated p-type silicon. NIM-A, num 518, Feb. 2004, pp. 340-342. G. Casse, P.P. Allport, S. Martí, M. Lozano, P. R. Turner. • Comparison of radiation hardness of P-in-N, N-in-N and N-in-P silicon pad detectors IEEE Trans. on Nucl. Sci., V. 52, Issue 5, Part 2, Oct. 2005 Page(s):1468 – 1473, M. Lozano, G. Pellegrini, C. Fleta, C. Loderer, J. M. Rafí, M. Ullán, F. Campabadal, C. Martínez, M. Key, G. Casse, P. Allport

  6. Annealing p-type Annealing (@80 oC) behaviors of the collected charge after proton irradiation to 3.5. 1015 cm-2. At high voltage the collected charge appears to be stable. It is known that the full depletion voltage as determined by CV measurements appears to follow the expected evolution. Pad detectors N-on-p strip detectors with p-stop isolation G. Casse, “Overview of n-side read-out microstrip devices”, RD50/FDS meeting 2005. “Annealing Studies of Magnetic Czochralski Silicon Radiation Detectors”, G.Pellegrini et al., Nucl. Instr. and Meth. Volume 552, Issues 1-2, 21 October 2005.

  7. Electronic Noise micro-discharge noise Micro-discharges can represent the earliest mechanism of failure for micro-strip detectors when operated at high voltage. Baby microstrip detectors fabricated by Hamamatsu G. Casse, “Overview of n-side read-out microstrip devices”, RD50/FDS meeting 2005.

  8. To avoid the problem of microdischarges p-spray isolation was used to fabricate microstrip and pad detectors. P-spray isolation • P-spray has to: • Insulate strips • Keep VBD > VFD • Variables: • Oxide thickness • Implant dose • Implant energy • Thermal budget fixed • Optimization through: • Simulation (ISE-TCAD) • Engineering runs (3) Conflicting conditions

  9. Simulation of p-spray Electric field at the breakdown point

  10. P-spray: calibration runs Characteristics of n-in-p pad detectors with p-spray isolation

  11. Effect of oxidecharge • Fast build-up of damage in the oxide layer • Reach a saturation value for the oxide charge of about 2-31012 cm-2 at about 100-200 krad (few LHC weeks) • The oxide charge will be saturated well before the bulk damage will start to affect the operation of the detectors • This oxide charge increases inversion layer, canceling the p-spray insulation • It is very important to ensure that insulation is maintained after first irradiation, not only in fresh or bulk damaged detectors. • Irradiation: • 50 Mrad, • Co60 gamma source • MOS Capacitor CV measurements • Oxide charge • Before: 11011 cm-2 • After: 31012 cm-2 “Technology development of p-type microstrip detectors with radiation hard p-spray isolation” , G. Pellegrini et al., Nucl. Instr. and Meth A 2006 In Press, Corrected Proof, Available online 28 July 2006 Strip detector

  12. Neutron irradiation Signal induced by 1060 nm pulsed laser illumination, n-in-p detector after 7.5 1015 p cm-2. (G.Casse,RD50 Status Report 2004) P-type irradiated with neutrons (1015 n/cm2) • read a 3cm p-type detector using the ATLAS SCTDAC readout. • SCTDAC is optimised for n-type sensor. • SCT readout: binary ABCD3T chip Please look at C. Lacasta poster in this conference

  13. Final process Rd50 mask Guard rings CCE and noise measurements on strip detector undergoing by RD50 collaboration

  14. P-spray vs p-stop • P-spray • Is a critical technology • Low repeatability of the p-spray process. • Detectors performance are very sensitive to the p-spray isolation dose implanted. • Isolation dependent on charge oxide before and after irradiation • The surface damage usually leads to higher leakage currents before irradiation • P-stop • Requires a minimum strip pitch depending on the design rules of the manufacturer • ‘Leaky channels’ can severely reduce the yield, hence the necessity of a minimum width of the p-stop implant • High electrical field in P-stop corner • This high electric files may cause micro-discharge noise

  15. Moderated p-spray • We can take the best from the two options: Moderated P-spray • An old (1997) patent from MPI presented the basics • Technology has to be optimized • We have developed through simulation a technology for p-type detectors with moderated p-spray insulation • Boron implant parameters are selected from our previous experience with microstrip with p-stops • With less p-spray implanted charge, we obtain: • Higher breakdown voltages • Good insulation before and after irradiation • Eliminate the high field corner in the p-stop causing microdischarges • No necessity of redundancy in the p-stop implants.

  16. Simulated device RD50 mask set (pitch 80 μm, strip width 32 μm) Single p-stop between the strips: width 10 μm Substrate: P-type, <100>, 30 kΩ·cm Oxide charge density: 1011 cm-2 (non-irradiated device) P-implant parameters: Fixed energy, dose: 50 keV, 1013 cm-2 Fixed oxide implant thickness for the p-stop area We have fabricated devices with these p-stop implant parameters and they show a satisfactory electrical behavior The objective of the simulations is to determine the optimum profile in the p-spray area Simulation of moderated p-spray

  17. First: oxidation, photolithography p-stop regions, wet oxide etching, oxidation, photoresist striping At this point there are two different oxide thicknesses thin oxide in the p-stop area and a thicker oxide on the rest of the silicon surface (“p-spray area”) P-implant (Energy 50 keV, dose 1013 cm-2) Finish with the usual fabrication process Technology

  18. Simulated Devices profiles I-V curves

  19. Doping profile comparison N strip P-stop P-stop only P-spray Moderated p-spray

  20. Electric field comparison N strip microdischarches? P-stop P-stop only P-spray Moderated p-spray

  21. Experimental Results

  22. Experimental Results Test structure to measure interstrip resistance

  23. P-type detectors seems the best detector option for the future sLHC experiments as they gather beneficial properties: electron collection junction always at the strip side partial depletion operation possible very high radiation hardness stable annealing We have developed three technologies for p-type detectors with the different isolation techniques: p-spray, p-stops and moderated p-spray Detectors have been fabricated, irradiated with protons, neutrons, and gammas, and they work properly Conclusions

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