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Development of 3D silicon detectors at ITC-irst

Development of 3D silicon detectors at ITC-irst. Claudio Piemonte ITC-irst Trento piemonte@itc.it. Outline. 3D detectors: concept & status ITC-irst activity on 3D: S ingle- T ype C olumn 3D detector concept Simulation, Design, Process and First Characterization Future Activity.

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Development of 3D silicon detectors at ITC-irst

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  1. Development of 3D silicon detectors at ITC-irst Claudio Piemonte ITC-irst Trento piemonte@itc.it

  2. Outline • 3D detectors: concept & status • ITC-irst activity on 3D: • Single-TypeColumn3Ddetector concept • Simulation, Design, Process and First Characterization • Future Activity C. Piemonte IFAE 20 - 04 - 2006 Pavia

  3. Standard planar detectors (1) - ~1mm p+ Planar devices: junctions are located close to surface of the silicon bulk ~300mm n--substrate ~1mm n+ - bulk contact + - E field Normal operation: bulk is over-depleted => electric field separates the pairs and forces the carriers to drift For uniform charge deposition carriers are collected one by one 1 2 V1<V2 + C. Piemonte IFAE 20 - 04 - 2006 Pavia

  4. Standard planar detectors (2) Collection time = time needed to collect the last carrier (hole) It depends on: 1. bias voltage 2. substrate thickness Rough estimation of the collection time vs bias voltage for electrons and holes in a 300mm thick subst. We can reduce the collection time thinning the substrate but we have smaller signal!! C. Piemonte IFAE 20 - 04 - 2006 Pavia

  5. 3D detectors - concept Proposed by Parker et al. NIMA395 (1997) p-columns n-columns ionizing particle wafer surface All the carriers are collected at the same time! n-type substrate C. Piemonte IFAE 20 - 04 - 2006 Pavia

  6. 3D detectors - advantages The distance between the electrodes depends only on the detector layout. The collection time is independent from the substrate thickness! • Designing structure with small electrode pitch (i.e. 50mm): • very low full depletion voltage • short collection distance • more radiation hard • than planar detectors!! 3D detectors can find application in high energy physics experiments where radiation damage is a concern C. Piemonte IFAE 20 - 04 - 2006 Pavia

  7. 3D detectors - disadvantages 1)Electrodes are dead regions 2) Non standard fabrication process - long R&D needed - concerns on the yield no signal from this particle track The problem can be partially solved tilting the detector C. Piemonte IFAE 20 - 04 - 2006 Pavia

  8. Groups involved in 3D • SLAC (Sherwood Parker) • double columns filled with doped polysilicon, • holes all the way through the wafer thickness (150mm) • University of Glasgow • double columns: one Schottky & one diffused, deep hole • VTT (Finland) • Semi 3D: single column boron doped on n-type Si; limited depth • (150-200micron) • ITC-irst • Single-Type-Column : single column phosphorus doped on p-type Si; • limited depth (150-200micron). workshop on 3D held in february 2006 in Trento :http://tredi.itc.it/ C. Piemonte IFAE 20 - 04 - 2006 Pavia

  9. 3D detectors @ ITC-irst • Development of 3D sensors at ITC-irst started almost 2 years ago in collaboration with INFN. • Simulations of 3D-STC detectors; • Technology used in the first two fab. runs; • Electrical characterization of first prototypes; • Future Activity on 3D. C. Piemonte IFAE 20 - 04 - 2006 Pavia

  10. n+ electrodes p-type substrate Uniform p+ layer Single-Type-Column 3D detectors - concept NIM A 541 (2005) 441–448 “Development of 3D detectors ..” C. Piemonte et al ionizing particle electrons are swept away by the transversal field holes drift in the central region and diffuse towards p+ contact • Main features of proposed 3D-STC: • column etching and doping performed only once • holes not etched all through the wafer • bulk contact is provided by a backside uniform p+ implant Simplification of the fabrication process C. Piemonte IFAE 20 - 04 - 2006 Pavia

  11. 1) Vbias=0V 4) Vbias=20V 2) Vbias=2V 3) Vbias=5V Depletion mechanism Do not consider the hot spot in the pictures, it is the charge released by a particle. DRAWBACK of 3D-stc: once full depletion is reached it is not possible to increase the electric field between the columns C. Piemonte IFAE 20 - 04 - 2006 Pavia

  12. 1 2 (10,10) (20,20) (25,25) e h 3 4 250mm 50mm 50mm Signal & Charge collection First phase Transversal movement (fast) Same Vbias, different impact point Second phase Hole vertical movement (slow) In the worst case of a track centered the central region, 50% of the charge is collected at t ~ 300ns Outside this region, 50% of the charge is collected within 1ns. charge collected is ¼ for interaction in the middle point C. Piemonte IFAE 20 - 04 - 2006 Pavia

  13. Mask layout “Large” strip-like detectors Small version of strip detectors Planar and 3D test structures • “Low density layout” to increase mechanical robustness of the wafer • Strip detector = “easy” to electrical test C. Piemonte IFAE 20 - 04 - 2006 Pavia

  14. Strip detectors - layout Inner guard ring (bias line) metal p-stop hole • Different strip-detector layouts: • Number of columns from 12000 to 15000 • Inter-columns pitch 80-100 m • Holes Ø 6 or 10 m n+ Contact opening C. Piemonte IFAE 20 - 04 - 2006 Pavia

  15. metal oxide hole metal strip hole contact n+ diffusion hole Hole depth ~ 120μm 3D process • Deep RIE performed at CNM, Barcelona (it will be available at IRST within this year) • Wide superficial n+ diffusion around the hole to assure good contact • Passivation of holes with oxide • Si: High Resistivity, p-type, <100> • Surface isolation: p-stop or p-spray • Holes are “empty” C. Piemonte IFAE 20 - 04 - 2006 Pavia

  16. p-stop p-spray 30 25 20 Detectors count 15 10 Bias line Guard ring 5 0 >50 0 5 25 30 35 10 15 20 40 45 50 I bias line [nA] Strip detectors – IV measurements Current distribution @ 40V of 70 different devices Number of columns per detector: 12000 - 15000 Good process yield Average leakage Leakage current < 1pA/column C. Piemonte IFAE 20 - 04 - 2006 Pavia

  17. tc tw b a 3D diode – CCE measurements Carlo Tosi, Mara Bruzzi, Antonio De Sio INFN and University of Florence • CCE @ 0V ≈ tc/tw • 100% CCE @ low voltages • Vdep(CCE)<Vdep(CV) • Substrate thickness = 500mm • Column depth = 150mm C. Piemonte IFAE 20 - 04 - 2006 Pavia

  18. On going activity • End second run (may 2006) • University of Glasgow (UK): CCE measurements with a, b, g on 3D diodes and short strips • SCIPP (USA): CCE measurements on large strips • INFN Firenze (Italy): CCE meas with b,on 3D diodes; • University of Freiburg (D); measurements on short strips • Ljubljana: TCT and neutron irradiation C. Piemonte IFAE 20 - 04 - 2006 Pavia

  19. New Process • n-type Si • DRIE ~ 250mm • no hole filling • double columns • double side New process (within the year) • Actual Process • p-type Si • hole depth ~ 200mm • no hole filling • single column • single side C. Piemonte IFAE 20 - 04 - 2006 Pavia

  20. New Layout (mainly Pixel) p-diff n-diff bump region metal New Layout Actual Layout (basically microstrip) C. Piemonte IFAE 20 - 04 - 2006 Pavia

  21. Conclusion • 3D detectors are extremely interesting devices for high luminosity • colliders (inner tracking layers). • R&D is ongoing at ITC-irst: • - fabricated first prototypes of 3D-stc detectors with excellent • results • - within the year double column detectors will be ready. C. Piemonte IFAE 20 - 04 - 2006 Pavia

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