microstrip detectors with radiation hard p-spray, p insulations

Transcription

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

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

3 P-type detectors 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 3

4 P-stop isolation First n-on-p detectors fabricated with p-stop isolation. Different implants were used to find the optimum value. Concentration (cm-3) 1,E+21 1,E+20 1,E+19 1,E+18 1,E+17 1,E+16 1,E+15 1,E+14 1,E+13 N+/P/P+ Strip back inplant P-stop 1E13 cm-2 P-stop 1E14 cm-2 1,E+12 1,E+11 1,E+10 1,E d (nm) Pitch 120μm, p-stop width 7μm, strip width 20μm 4

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 *10 15 p/cm 2, charge collected is > 6,500 e - (1) First results on charge collection efficiency of heavily irradiated microstrip sensors fabricated on oxygenated p-type silicon. NIM-A, num 518, Feb. 2004, pp G. Casse, P.P. Allport, S. Martí, M. Lozano, P. R. Turner. (2) 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 Page(s): , M. Lozano, G. Pellegrini, C. Fleta, C. Loderer, J. M. Rafí, M. Ullán, F. Campabadal, C. Martínez, M. Key, G. Casse, P. Allport 5

6 Annealing p-typep Annealing o C) behaviors of the collected charge after proton irradiation to 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 Annealing Studies of Magnetic Czochralski Silicon Radiation Detectors, G.Pellegrini et al., Nucl. Instr. and Meth. Volume 552, Issues 1-2, 21 October

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

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

9 Simulation of p-sprayp p-spray V BD (V) Diodes Energy (kev) Dose (cm -2 ) Simulated Measured V 700 V V 650 V V 250 V Electric field at the breakdown point Without p-spray 9

10 P-spray: calibration runs Energy (kev) p-spray Dose (cm -2 ) Current at V FD +20 V Strips Ring ± 30 na 2 ± 1 ma ± 40 na 150 ± 40 µa ± 1.1 µa 300 ± 30 na Characteristics of n-in-p pad detectors with p-spray isolation 10

11 Effect of oxide charge Fast build-up of damage in the oxide layer Reach a saturation value for the oxide charge of about cm -2 at about 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: cm -2 After: cm -2 Strip detector 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

12 Neutron irradiation [Source - No Irrad.] - Charge.vs. Vbias Q (nvs) Vbias (V) P-type irradiated with neutrons (10 15 n/cm 2 ) Q (pvs) [Laser - Irrad] Charge.vs. Vbias Vbias (V) Signal induced by 1060 nm pulsed laser illumination, n-in-p detector after p cm -2. (G.Casse,RD50 Status Report 2004) p-type read a 3cm p-type detector using the ATLAS SCTDAC readout. SCTDAC is optimised for n-type sensor. SCT readout: binary ABCD3T chip n-type Please look at C. Lacasta poster in this conference 12

13 Final process Rd50 mask 1.E NP-DOFZ 300um, SILHRP(9/05) OXG 1.E-06 (A) 1.E-07 1.E-08 Guard rings Wafer 5 Wafer 5 Wafer 6 1.E-09 Wafer Wafer 8400 Vrev (V) Wafer 9 CCE and noise measurements on strip detector undergoing by RD50 collaboration 13

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 14

15 Moderated p-sprayp 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. 15

16 Simulation of moderated p-p spray 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: cm -2 (non-irradiated device) P-implant parameters: Fixed energy, dose: 50 kev, 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 16

17 Technology 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 cm -2 ) Finish with the usual fabrication process 17

18 Simulated Devices profiles I-V curves 18

19 Doping profile comparison -5 N strip P-stop A c c e p t o r C o n c e n t r a t io n 2. 2 E E E E E P-stop only E X -2 P-spray AcceptorConcentrati 2.2E+19 Moderated p-spray E E E E E X 19

20 Electric field comparison - 5 N strip microdischarches? P-stop E le c t r ic F ie ld 3. 2 E E E E E P-stop only E Moderated p-spray X P-spray X ElectricField 3.2E E E E E E+00 20

21 Experimental Results 21

22 Experimental Results x10 5 Gamma irradiation total dose 50 Mrad Resistance (ohm) Resistance (ohm) 6x10 5 5x10 5 4x10 5 3x10 5 2x x moderate 228moderate 260moderate 290 p-spray p-stop 0 moderate 228moderate 260moderate 290 p-spray p-stop Test structure to measure interstrip resistance 22

23 Conclusions 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 23