Workshop on 3D and p-type Sensors Phil Allport (University of Liverpool) 26/02/10 5th Trento Workshop on Advanced Silicon Radiation Detectors University of Manchester Introduction Status of 3D Sensor Technology and Recent Results Latest results with Planar Detectors after Extreme Irradiation New Theoretical Understanding of Signals at the Highest Doses Conclusions

Possible Post-Chamonix Schedule for with 2 Major Shutdowns

CMS Tracker Upgrade with Trigger Layers Both Experiments need new trackers to survive 3000fb-1 at the sLHC CMS needs to exploit PT information from tracker to keep trigger rate at 100 kHz major new feature for CMS tracker - ideas how to do it are still developing Current assumption is that there will probably be dedicated PT layers, providing prompt trigger information i.e. different from more conventional, triggered pipeline chip, layers Several ideas for triggering layers summarised here Longer barrel layers to match PT layers, at present locations one possible “strawman” layout X section through one quarter of tracker Remaining end caps with present locations Stereo layers Stereo rings h = 2.5 PT layers to cover full h range Paired Trigger layers Pixel System Pixels: 4 barrel layers + increased size Endcap could be 3 disks/endcap?

ATLAS Tracker Upgrade Layout Barrel Pixel Tracker Layers: Short Strip (2.4 cm) -strips (stereo layers): Long Strip (9.6 cm) -strips (stereo layers): r = 3.7cm, 7.5cm, 15cm, 21cm r = 38cm, 50cm, 62cm r = 74cm, 100cm 400 Pile-up 100 GeV Electrons

Radiation Background Simulations for sLHC Completed design of neutron moderator to reduce silicon damage fluences (cyan coloured regions in layout on right). More detailed geometry and material description implemented in FLUKA SLHC simulations for ID. In particular, investigate impact of latest service and support material information. Providing feedback to community on maximum fluence and dose values at critical positions, for calculation of damage and signal to noise. ×2 → 1.3 × 1015 neq/cm2

Technology in Current Highest Dose Regions LHC vertex detectors all used n+ implants in n- bulk: Because of advantages after heavy irradiation from collecting electrons on n+ implants, the detectors at the LHC (ATLAS and CMS Pixels and LHCb Vertex Locator) have all adopted the n+ in n- configuration for doses of 5 – 10 × 1014 neqcm-2 Requires 2-sided lithography ATLAS 100 million Pixels LHCb Vertex Locator Z(mm)=0-990

Motivations for P-type Silicon Wafers Starting with a p--type substrate offers the advantages of single-sided processing while keeping n+-side read-out: Processing Costs (~50% cheaper). Greater potential choice of suppliers. High fields always on the same side. Easy of handling during testing. No delicate back-side implanted structures to be considered in module design or mechanical assembly. So far, capacitively coupled, polysilicon biased p-type devices fabricated to ATLAS provided mask designs by: Micron Semiconductor (UK) Ltd (existing ATLAS barrel: 6cm×6cm and RD50 miniatures: 1cm ×1cm), CNM Barcelona (RD50 miniatures: 1cm×1cm), ITC Trento (RD50 miniatures: 1cm×1cm) CiS and HLL MPI Munich (miniatures) Hamamatsu Photonics HPK (1cm×1cm and 10cm×10cm Full ATLAS prototypes)

n-in-p (p-type substrate) FZ Irradiations 900V 500V GRad ie ~10MGy Micro-strip Tracker Pixel Tracker 8

ATLAS Pixel Module Upgrade Current pixel module → Single chip pixel modules on stave

Stanford Nano-fabrication Facility Stanford Nanofabrication Facility (SNF) is a Stanford Nano Science and Technology Lab. All the fabrication work is performed at SNF in the CIS building, which was completed in 1985. The Stanford Nanofabrication Facility is a 10,000 sq. foot, Class 100 cleanroom housing a complete suite of tools for the micro- and nano- fabrication of devices

3D process consists of > 100 steps WAFER BONDING (mechanical stability). After complete processing this support wafer will be removed. 2. PHOTOLITHOGRAPHY 3. MAKING THE HOLES 4. FILLING THE HOLES 5. DOPING THE HOLES AND ANNEALING 6. METAL DEPOSITION Due to modest topography on the wafer surface (e.g. poly-filled holes), it makes it difficult to spin on a uniform layer of photoresist, which is a critical step repeated many times. When plasma etching either holes, edges etc., the use of thick resist is required, however, high-viscosity resists seem to have more particulates and clumps of resist associated with them. Mechanical fractures can occur during the plasma dicing or fusion bonding steps. When patterning the metal, some aluminum contact strips would etch away.

3D Detector – Fabrication Steps SiO2 1μm Si Support Wafer 1μm SiO2 Al Si Substrate SiO2 1μm Si Support Wafer Si Substrate N+ poly N+ N+ poly 1μm SiO2 Si Support Wafer 1μm SiO2 Si Substrate N+ Support Wafer SiO2 1μm SINTEF attempted to reproduce the Stanford process in a more industrial/ production enviroment in 2007 Wafer Bonding DRIE 250µm deep, 14µm diameter Fill Holes with n-doped poly Etching of polysilicon Oxide cap SiO2 SiO2 1μm Si Support Wafer Si Substrate N+ Trench 7μm 600Å oxide Al p-hole 14μm Oxide cap SiO2 SiO2 1μm Si Support Wafer N+ Trench 7μm p-spray P+ Trench 7μm SiO2 p+ N+ p+ P+ SiO2 1μm Si Support Wafer P+ poly Etching of polysilicon and oxide etch DRIE, holes and trenches Filling holes and trenches with p-doped poly

1. 3D lateral cell size can be smaller than wafer thickness, so 2. in 3D, field lines end on electrodes of larger area, so 3. most of the signal is induced when the charge is close to the electrode, where the electrode solid angle is large, so planar signals are spread out in time as the charge arrives, and 4. Landau fluctuations along track arrive sequentially and may cause secondary peaks 5. if readout has inputs from both n+ and p+ electrodes, shorter collection distance 2. higher average fields for any given maximum field (price: larger electrode capacitance) 3. 3D signals are concentrated in time as the track arrives 4. Landau fluctuations (delta ray ionization) arrive nearly simultaneously 5. drift time corrections can be made Speed: planar 3D 4.

Medipix

CNM: Leakage current after irradiation CV Extracted Vdepletion Irradiated p-type, no annealing, -10ºC Annealing time Charge multiplication? Leakage current, -10ºC, 1016 neq/cm2 Leakage current increases with irradiation dose Two competing effects in annealing curves: Annealing of leakage current at low V Charge multiplication? More pronunced and earlier for longer annealing times CV Extracted Vdepletion

New Hamamatsu R&D Wafer Strips (30-89) 10 mm x 10 mm Pixel (1-29) 10.5 mm x 10 mm PTP study Strips mini 58-71 Slim edge study Diodes 1-20 Guard ring study 21-32 Diodes (1-32) 4mm x 4mm HPK 6 inch (150 mm) wafers, p-type and n-type Y. Unno, 5th "Trento" Workshop, Manchester, UK, 24-26 Feb., 2010 26

Slim Edge - Measurement Square root of V_bias is linearly dependent on the edge distance Reflecting the depletion along the surface Distance can be ≤500 µm for the bias voltage up to 1 kV (Almost) No safety margin for a thickness of 320 µm More than a factor of 2 safety margin for a thickness of 150-200 µm One of FE-I3 pixel sensor Thinned Pixel Sensors Wafer thickness P-type: 320 µm N-type: thinned to 200 µm 150 µm possible Excellent I-V performance ≤1,000 V Both in the p-type and n-type

Studies With Micron Semiconductor Miniature Strip Detectors on Enhanced Signal After Extreme Fluences Expected Signal No Multiplication 28

Manufacturer Comparisons At the lowest fluence, there may be some differences between Micron and Hamamatsu Most likely systematic error At higher fluence, no trend seen 900 V 500 V Appears once multiplication dominates, no strong differences between manufacturer, isolation and pitch’s tested. Weird!! 29 A. Affolder – 5th Trento Workshop, 24-26 Feb 2010, Manchester, UK

A. Affolder – 5th Trento Workshop, 24-26 Feb 2010, Manchester, UK Thickness Overview Below 5×1014 neqcm-2, charge advantage to being thicker Above 3×1015 neqcm-2, charge advantage to being thinner 30 A. Affolder – 5th Trento Workshop, 24-26 Feb 2010, Manchester, UK

Annealing of S/N, 1E15 n cm-2 0oC -25oC Noise is the sum in quadrature of shot noise and parallel noise (taken from the Beetle chip specs, and estimated as 600ENC) 0oC -25oC 31

CCE Measurements Thinned Detectors (MPI HLL) Expected before irradiation Measurements performed at T=-30 oC (for sensors irradiated at F=1x1015 neq/cm2 ) and at T=-40oC (for the sensor irradiated at F=3x1015 neq/cm2), before any intentional annealing The error bands correspond to 500 e- uncertainty estimated on each measured point. At F=(1-3)x1015 neq/cm2 signal sizes close to the ones measured before irradiations are obtained Further measurements at F=(3-10)x1015 neq/cm2 are presently ongoing

Conclusions The schedule for upgrades at LHC already start to put significant pressure on the sensor community to provide more radiation hard pixel and strip designs Studies with both 3D and planar p-type (and n-in-n as current pixels) now all show results which promise adequate signal/noise even at the most extreme doses Planar p-type being processes with 3 mainstream sensor companies with excellent pre-irradiation results and very consistent post-irradiation performance Commercialisation of 3D is progressing with SINTEF, but results mainly with research laboratory production: Stanford, CNM Barcelona ICT Trento It seems the understanding of charge multiplication is needed to understand recent results with both sensor types At first, avalanche multiplication seemed not to fit all effects observed but huge progress has been made is terms of modelling including trapping and device studies with the post-irradiation sensors can explain the data with modest 3-4 multiplication

Our understanding is getting better and better but there is still a challenge to predict the avalanches