Edgeless & Slim Edge Detectors Andrew Blue, on behalf of the RD50 Collaboration

Slim Edge & “Edgeless” sensors Standard silicon detectors have a relatively large insensitive region around their active area. This dead region is due to presence of multiple guard rings and the clearance for the dicing street of the sensors It can extend to more than a few mm’s, depending on the detector application To remove inactive regions around each sensor reduced edge or “edgeless” sensors are required. Such sensor designs in conjunction with through-silicon vias (TSV) would also result in a reduction in radiation length, making edgeless sensors a promising option for the particle physics community. Without the need for shingling/ overlapping of sensors Such sensors utilize one of a number of methods to reduce the number of guard rings and their pitch so to increase the active area of tiled detectors, and a (non-exhaustive) list of techniques proposed for such a reduction in dead area follows

Slim Edge Slim edges reduce the dead area by reducing the number of guard rings used in tandem with the reduction of the distance from the outer guard ring to the cut edge. Further reductions can be made in a double sided (n-on-n) process by placing the guard rings on the back surface such that they overlap the edge pixels/strips on the front side Example of slim edge devices proposed for the IBL, where edge pixels on the sensor surface overlap the guard rings structures on the back.

Active Edge Active Edge devices turn the physical cut edge of the sensor into a junction Allows the depletion of the silicon all the way to the physical edge. The sensors sidewalls are cut using dry etch techniques to eliminate the microscopic damage associated with the sawing. The sidewalls of the cut edges are then doped to compensate for the high level of defects at the sidewall, and passivated with a thermal oxide layer Active edge pixel senor under test, showing less than 50mm from the edge pixel to the sensor edge

Scribe Cleave & Passivate Diamond Stylus Laser XeF2 Etch DRIE Etch Saw cut Tweezers (manual) Loomis Industries LSD-100 Dynatex, GTS-150 Native Oxide + Radiation or N-type Native SiO2 + UV light or High T PEVCD SiO2 PEVCD Si3N4 ALD “nanostack” of SiO2 & Al203 P-type ALD of AL2O3 All treatment is post processing & low temperatures Etch scribing can be done during fabrication

RD-50 work Many studies investigating slim edge & edgeless technology being carried out via RD50 Some already covered in this conference ‘3D detectors in ATLAS’: Sebastian Grinstein ‘RD50 Overview’: Marcos Fernandez Garcia Today I will talk about Active edge devices with varying thicknesses and levels of irradiations Irradiations to study the passivation layers used for slim edge devices Micro focused X-rays for CCE measurements of SCP and Active edge devices

Active Edge – FE-I4 Assemblies Much progress is being made in to the study of Active Edge devices Latest studies include Test Beam results with thin pixel sensors at High Eta Characterization of Active edge pixels after irradiations Comparison of CCE for pixels sensors of different Active thicknesses 125mm Edge implemented in FE-I3 and FE-I4 sensors 50mm implemented in only FE-I3 devices

CCE of Active Edge pixels after irradiations 100 mm thick sensor with 125 mm slim edge bump-bonded to an FE-I3 (1500 e- threshold) 87% CCE at 300V for both inner and edge pixels after irradiations of 1x1015neq/cm2 (KIT) 5x1015neq/cm2 (Ljubljana) p-type MCZ 100 mm thick sensors with 125 mm slim edge (FEi4 & 1100e- threshold ) Compatible charge collection properties between edge and inner pixels

CCE for different thicknesses of Active Edge pixels The 100-150 mm thick sensors show higher charge collection up to a fluence of 4-5x1015neq/cm2 At higher fluence the effect of charge trapping teens to equalize the charge collection efficiency for all thicknesses 100mm thick Slim Edge Irradiated devices taking ~500V

SCP devices - Observations How does the processing involved to produce slim edge/edgeless devices affect detector efficiencies of DUT edges before and after irradiation? Emerging pattern No issues with Radiation Hardness for N-type devices However for P-type devices High currents at low ionisation doses <1x1014ncm-2 No significant excess on the edge for high ionizing dose >1x1014ncm-2 No issues for neutron-irrad. samples Has led to a series of investigations (Laser, source testbeams, irradiations) Today will talk about Irradiations to study the passivation layers used for slim edge devices Micro focused X-ray for CCE measurements of SCP & active edge devices

P-type SCP Devices After Irradiation To investigate, 12 SCP p-type strip devices (CIS) were irradiated at LANL in 2011 Results were inconclusive High fluence devices (3/3 at 1x1016neq & 3/3 at 1x1015neq) show expected post-rad leakage current Low fluence devices (1/3 at 1x1013neq & 1/3 at 1x1014neq) showed early breakdown! Post-Irrad 8mA 0.8mA 0.1mA Pre-Irrad Leakage currents do not scale with fluence low fluence (< 1x1014): reduced edge performance high fluence (>1x1014): resistive edge

Irradiated P-type SCP devices Possible issues with the Si-Alumina interface One theory is that a thin layer of AlxSiOy forming between Si and Al2O3 Forms as part of the ALD process This oxide layer gains more of its (positive) interface charges with first few Mrad, counteracting the necessary negative oxide from alumina To check this hypothesis MOS capacitors were fabricated at the CNM microfabrication facility with Al2O3 as the dielectric. The capacitors allow assessment of the effective charge density via C-V curves We irradiated the devices to figure out how the charge density changes with dose The capacitors were irradiated at LANL with 800 MeV protons in January 2014. The fluence was up to 6.8x1014 p/cm2 (34 Mrad) (equivalence: 1015 p/cm2 = 0.71x1015 neq/cm2 = 50 Mrad) Irradiations with gammas took place at BNL in December 2013, up to 30 Mrad

Test Devices 4 Wafers: 100 mm-diameter (100) Cz Si P-type 5 Squared shaped MOS 4 Wafers: 100 mm-diameter (100) Cz Si P-type 400nm SiO2 field isolation & patterning Al2O3 Process 1 Wafer 1: 40nm CNM Wafer 2: 20nm CNM Cleaning ALS (ToC, precursors) Post-deposition anneal Atomic Layer Deposition Al2O3 Al2O3 Process 2 Wafer 3: 20nm NRL Wafer 4: 40nm NRL 500 nm Al (99.5%)/Cu (0.5%) & patterning Wafer backside metallization ½ wafer post metallization anneal (PMA) 20 min @350oC in N2/H2

Capacitance-Voltage Wafer Mapping 25 chips ½ wafer A2 = 2.3·10-3 cm2 Good yield Good uniformity

positive charge trapping gamma-radiation-hardness C-V Results from Gamma Irradiations 0.1, 0.3, 1, 3, 10 & 30 Mrad Positive Charge Rad-hard positive charge trapping in process 1 Al2O3 gamma-radiation-hardness in process 2 Al2O3 with PMA

gamma-radiation-hardness positive charge trapping C-V Results from Proton Irradiations 0.07, 0.35, 0.96, 3.97, 7.35 & 34.2 Mrad Positive Charge Rad-hard gamma-radiation-hardness in process 2 Al2O3 with PMA positive charge trapping in process 1 Al2O3

Summary of Al203 Irradiations MOS capacitors designed to assess the radiation hardness of Al2O3 layer used in Scribing Cleaving Passivation (SCP) process for p-type bulk Si devices have been successfully fabricated. The capacitors allow us to measure the effective dielectric charge density, critical for the SCP performance Al2O3 was deposited with 2 different processes at 2 facilities Additionally, we intentionally varied the deposition thickness (20 nm and 40 nm) and post- metallization annealing step The devices were irradiated at LANL with protons and at BNL with gammas with TID up to 34 Mrad The initial assessment of post-rad performance indicates an interesting dichotomy between the 2 deposition processes: In one case the radiation-induced changes in effective charge density are negligible In another case it scales nearly linearly with dose We may need to vary the processing with a future fabrication to figure out which of the processing differences influenced the different radiation performance

Further CCE studies of SCP devices Many studies in various technologies (n-type & p-type) have taken place Would like to use technique for studying Edge Pixels/Strips Inter-strip/pixel charge collection profile (<5mm beam spot) Use Focussed X-rays Sensor Type Origin Edge-Active area Distance (mm) Signal Readout Beam Ref P-type strips PPS (CIS) ~200 Binary (PTSM) 90Sr V. Fadeyev et al ‘Pixel 2012, NIM A 731 (260-262) 2013 N-type Strips GLAST (HPK) Analog (ALiBaVa) R. Mori et al JINST 7 P05002 2012 P-type 3D pixels IBL (CNM) 50 FEi3 & FEi4 CERN Testbeam S Grinstein et al ‘RESMDD12, NIM A 730 (28-32) 2013 G. Pellegrini et al Pixel 2012, NIM A 731 (198-200) 2013 P-type Strips A. Macchiolo P-type Strips n-irradiated 110-220 Single-channel Laser-TCT I Mandić et al., NIMA 751 (2014) 41-47. 150 A. Macchiolo

Micro focused X-rays for CCE measurements Used the Diamond Light Source base in Oxford, UK Beam station B16 Comprises of a water-cooled fixed-exit double crystal monochromator that is capable of providing monochromatic beams over a 2-20 Kev photon energy range. An unfocused monochromatic beam is provided to the experimental hutch. A compound refractive lens (CRL) was used to produce a 15 Kev micro-focused X-ray beam. The size of the micro-focussed beam was determined by measuring transmissions scans with a 200 mm gold wire. The derivative of these scans gave a beam shape which had a FWHM of 2.5mm

SCP devices SCP strip sensors N-type & P-type 80mm Strip pitch Irradiated Bulk Thickness (mm) Strip Pitch (mm) Edge strip to edge (mm) 1 - N 200 80 28 2 4.8x1014 ncm-2 P 100 170 SCP strip sensors N-type & P-type 80mm Strip pitch Wire bonded to ALiBaVa readout system Irradiated samples cooled to -15oC With peltier + chiller

Micro-focussed X-Ray beam: CCE of SCP Scan of the edge of the strip detector with full guard ring structures a) shows the mean signal size with an ADC cut of 10, (b) has an ADC cut of 40. (b) (a) Scan of the cleaved edge of the strip detector. (a) Shows the mean signal size with an ADC cut of 10, (b) has an ADC cut of 40.

Irradiated SCP devices Edge Strip: 305mm to SCP edge Preliminary results from latest testbeam. After 4.8x1014 ncm-2, charge is collected on edge strips 12KeV beam, 2.5mm FWHM 10mm Step size,. T= -8oC Analysis to follow (CCE v bias)

Calculated Full depletion voltage (V) Active Edge devices Device Implant Bulk Thickness (mm) Pixel to Edge (mm) Calculated Full depletion voltage (V) NN-200-50 N 200 50 28 NP-100-100 P 100 10 NP-100-50 VTT/Advacam Active Edge sensors Sensors flip-chip bonded to Timepix2 55mm x 55mm pixels Measurements taken in pixel counting mode

Over Edge Scans - Active Edge/Timepix

Side & Corner Scans – Active Edge/Timepix

Future Work & Conclusions A lot of work continues in RD50 investigating slim edge & Edgeless devices Shown today Studies of Active Edge Devices Effect of sensor thickness, geometries, radiation hardness etc. Investigations into the effect of interface irradiations AlxSiOy layers effecting p-type SCP devices Use of micro focus X ray beam for charge collection measurements Technique developed to study inter-strip/pixel behaviour Future work (includes) 2nd Production of Active Edge devices at Advacam 50, 100 & 150 mm thicknesses Pixels & diodes with different edges to investigate post-irradiation breakdown properties More irradiations and tests planned for SCP devices

Backup Slides

5 Selected Wafers 6 proton fluences 6 gamma doses 0.1, 0.3, 1, 3, 10, 30 Mrad 6 proton fluences 20 nm & 40 nm Al2O3 from processes 1 & 2 with PMA + 40 nm Al2O3 from process 2 without PMA 6 gamma doses 1.39x1012, 6.94x1012, 1.92x1013, 7.93x1013, 1.47x1014, 6.84x1014 p/cm2 0.070, 0.347, 0.960, 3.965, 7.350, 34.200 Mrad

proton-radiation-hardness I-V Results from Proton Irradiations process 1 Al2O3 Fowler-Nordheim conduction regime (f≈2.8 eV) proton-radiation-hardness in process 2 Al2O3 with PMA

gamma-radiation-hardness Fowler-Nordheim conduction regime I-V Results from Gamma Irradiations gamma-radiation-hardness in process 2 Al2O3 with PMA Fowler-Nordheim conduction regime (f≈2.8 eV) process 1 Al2O3

Capacitance-Voltage Wafer Mapping