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

2. C. PiemonteIFAE20 - 04 - 2006 Pavia Outline 3D detectors: concept & status ITC-irst activity on 3D: Single-Type Column 3D detector concept Simulation, Design, Process and First Characterization Future Activity

3. C. PiemonteIFAE20 - 04 - 2006 Pavia Standard planar detectors (1) n - -substrate n + - bulk contact p+p+ 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 Planar devices: junctions are located close to surface of the silicon bulk ~1 m ~300 m ~1 m - + - + V1<V2V1<V2 1 2

4. C. PiemonteIFAE20 - 04 - 2006 Pavia 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 300 m thick subst. We can reduce the collection time thinning the substrate but we have smaller signal!!

5. C. PiemonteIFAE20 - 04 - 2006 Pavia 3D detectors - concept Proposed by Parker et al. NIMA395 (1997) n-columns p-columns wafer surface ionizing particle n-type substrate All the carriers are collected at the same time!

6. C. PiemonteIFAE20 - 04 - 2006 Pavia Designing structure with small electrode pitch (i.e. 50 m): very low full depletion voltage short collection distance more radiation hard than planar detectors!! The distance between the electrodes depends only on the detector layout. The collection time is independent from the substrate thickness! 3D detectors - advantages 3D detectors can find application in high energy physics experiments where radiation damage is a concern

7. C. PiemonteIFAE20 - 04 - 2006 Pavia 1) Electrodes are dead regions 2) Non standard fabrication process - long R&D needed - concerns on the yield 3D detectors - disadvantages The problem can be partially solved tilting the detector no signal from this particle track

8. C. PiemonteIFAE20 - 04 - 2006 Pavia Groups involved in 3D SLAC (Sherwood Parker) double columns filled with doped polysilicon, holes all the way through the wafer thickness (150 m) 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/http://tredi.itc.it/

9. C. PiemonteIFAE20 - 04 - 2006 Pavia 3D detectors @ ITC-irst Development of 3D sensors at ITC-irst started almost 2 years ago in collaboration with INFN. 1.Simulations of 3D-STC detectors; 2.Technology used in the first two fab. runs; 3.Electrical characterization of first prototypes; 4.Future Activity on 3D.

10. C. PiemonteIFAE20 - 04 - 2006 Pavia Single-Type-Column 3D detectors - concept ionizing particle electrons are swept away by the transversal field holes drift in the central region and diffuse towards p+ contact p-type substrate n + electrodes Uniform p+ layer NIM A 541 (2005) 441–448 Development of 3D detectors.. C. Piemonte et al 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

11. C. PiemonteIFAE20 - 04 - 2006 Pavia Depletion mechanism 1) V bias =0V 2) V bias =2V 3) V bias =5V 4) V bias =20V 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

12. C. PiemonteIFAE20 - 04 - 2006 Pavia 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. Signal & Charge collection 1 2 3 4 (25,25) (20,20) (10,10) Same V bias, different impact point charge collected is ¼ for interaction in the middle point First phase Transversal movement (fast) Second phase Hole vertical movement (slow) e h 250 m 50 m

13. C. PiemonteIFAE20 - 04 - 2006 Pavia Mask layout Small version of strip detectors Planar and 3D test structures 1.Low density layout to increase mechanical robustness of the wafer 2.Strip detector = easy to electrical test Large strip-like detectors

14. C. PiemonteIFAE20 - 04 - 2006 Pavia Strip detectors - layout metal p-stop hole Contact opening n+n+ Inner guard ring (bias line) Different strip-detector layouts: Number of columns from 12000 to 15000 Inter-columns pitch 80-100 m Holes Ø 6 or 10 m

15. C. PiemonteIFAE20 - 04 - 2006 Pavia n+ diffusion contact metal oxide hole 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 3D process hole Hole depth ~ 120μm hole metal strip Si: High Resistivity, p-type, Surface isolation: p-stop or p-spray Holes are empty

16. C. PiemonteIFAE20 - 04 - 2006 Pavia Current distribution @ 40V of 70 different devices Good process yield Strip detectors – IV measurements p-spray p-stop Bias line Guard ring Number of columns per detector: 12000 - 15000 0 5 10 15 20 25 30 0 5 101520 253035 404550 >50 I bias line [nA] Detectors count Average leakage Leakage current < 1pA/column

17. C. PiemonteIFAE20 - 04 - 2006 Pavia 3D diode – CCE measurements CCE @ 0V t c /t w 100% CCE @ low voltages V dep (CCE)<V dep (CV) t c t w a b Substrate thickness = 500 m Column depth = 150 m Carlo Tosi, Mara Bruzzi, Antonio De Sio INFN and University of Florence

18. C. PiemonteIFAE20 - 04 - 2006 Pavia On going activity End second run (may 2006) University of Glasgow (UK): CCE measurements with on 3D diodes and short strips SCIPP (USA): CCE measurements on large strips INFN Firenze (Italy): CCE meas with on 3D diodes; University of Freiburg (D); measurements on short strips Ljubljana: TCT and neutron irradiation

19. C. PiemonteIFAE20 - 04 - 2006 Pavia New process (within the year) Actual Process p-type Si hole depth ~ 200 m no hole filling single column single side New Process n-type Si DRIE ~ 250 m no hole filling double columns double side

20. C. PiemonteIFAE20 - 04 - 2006 Pavia New Layout Actual Layout (basically microstrip) New Layout (mainly Pixel) p-diff n-diff bump region metal

21. C. PiemonteIFAE20 - 04 - 2006 Pavia 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.