Design and First Tests of a Radiation-Hard Pixel Sensor for the European X-Ray Free-Electron Laser

The high intensity and high repetition rate of the European X-ray Free-Electron Laser, presently under construction in Hamburg, requires silicon sensors which can stand X-ray doses of up to 1 GGy for 3 years of operation at high bias voltage. Within the AGIPD Collaboration the X-ray-radiation damage in MOS Capacitors and Gate-Controlled Diodes fabricated by four vendors on high-ohmic n-type silicon with two crystal orientations and dif- ferent technological parameters, has been studied for doses between 1 kGy and 1 GGy. The extracted values of oxide-charge and surface-current densi- ties have been used in TCAD simulations, and the layout and technological parameters of the AGIPD pixel sensor optimized. It is found that the op- timized layout for high X-ray doses is significantly different from the one for non-irradiated sensors. First sensors and test structures have been de-livered in early 2013. Measurement results for X-ray doses of 0 to 10 MGy and their comparison to simulations are presented. They demonstrate that the optimization has been successful and that the sensors fulfill the required specifications

Surface Effects in Segmented Silicon Sensors

Silicon detectors in Photon Science and Particle Physics require silicon sensors with very demanding specifications. New accelerators like the European X-ray Free Electron Laser (EuXFEL) and the High Luminosity upgrade of the Large Hadron Collider (HL-LHC), pose new challenges for silicon sensors, especially with respect to radiation hardness. High radiation doses and fluences damage the silicon crystal and the SiO2 layers at the surface, thus changing the sensor properties and limiting their life time. Non-Ionizing Energy Loss (NIEL) of incident particles causes silicon crystal damage. Ionizing Energy Loss (IEL) of incident particles increases the densities of oxide charge and interface traps in the SiO2 and at the Si-SiO2 interface. In this thesis the surface radiation damage of the Si-SiO2 system on high-ohmic Si has been investigated using circular MOSFETs biased in accumulation and inversion at an electric field in the SiO2 of about 500 kV/cm. The MOSFETs have been irradiated by X-rays from an X-ray tube to a dose of about 17 kGy(SiO2) in different irradiation steps. Before and after each irradiation step, the gate voltage has been cycled from inversion to accumulation conditions and back. From the dependence of the drain-source current on gate voltage the threshold voltage of the MOSFET and the hole and electron mobility at the Si-SiO2 interface were determined. In addition, from the measured drain-source current the change of the oxide charge density during irradiation has been determined. The interface trap density and the oxide charge has been determined separately using the subthreshold current technique based on the Brews charge sheet model which has been applied for first time on MOSFETs built on high-ohmic Si. The results show a significant field-direction dependence of the surface radiation parameters. The extracted parameters and the acquired knowledge can be used to improve simulations of the surface radiation damage of silicon sensors

Micro-Raman Spectroscopy Study of Crystal Silicon Induced by High Energy Ion Implantation

103 σ.Στη παρούσα εργασία μελετήθηκαν οι αλλαγές στη κρυσταλλικότητα του πυριτίου ως συνάρτηση του βάθους σε περιοχές κρυσταλλικού πυριτίου που έχουν εμφυτευθεί ιόντα 16O2+ , 12C2+ και 28Si2+, με ενέργειες εμφύτευσης 5 MeV,4 MeV και 8 MeV αντίστοιχα. Η εμφύτευση ιόντων υψηλής ενέργειας πραγματοποιήθηκε με τυχαίο (random) και καναλικό (channeling) τρόπο. Ο χαρακτηρισμός του πυριτίου έγινε με φασματοσκοπική μελέτη micro-Raman κατά μήκος της εγκάρσιας διατομής της περιοχής που έχουν εμφυτευθεί τα ιόντα. Τα δεδομένα των πειραματικών μετρήσεων συγκρίνονται με τα αποτελέσματα της φασματοσκοπίας οπισθοσκέδασης Rutherford πρωτονίων ενέργειας 1.2-MeV.Η σκέδαση Rutherford έλαβε μέρος κατά τη διάρκεια της εμφύτευσης για να προσδιορισθεί το βάθος διείσδυσης των ιόντων. Επιπρόσθετα οι εικόνες ηλεκτρονικής μικροσκοπίας σάρωσης (SEM) της εγκάρσιας διατομής των εμφυτευμένων περιοχών, επιβεβαιώνουν το βάθος των εμφυτευμένων ιόντων και την αλλαγή φάσης του κρυσταλλικού πυριτίου. Η τροποποίηση του πλέγματος λόγω της εμφύτευσης αιτιολογείται από το μοντέλο εντοπισμού του φωνονίου-Phonon Confinement Model PCM.Η φασματοσκοπία micro-Raman επιλέχθηκε για το χαρακτηρισμό της κρυσταλλικότητας του πυριτίου, καθώς παρέχει υψηλή ευαισθησία και εντοπισμένη πληροφορία της δυναμικής του πλέγματος.Ion implantation is one of the most important techniques used in the siliconbased semiconductor industry.Using the ion axial channeling effect, which occurs when an ion beam is oriented along a crystallographic axis, it is theoretically possible to implant ions deeper in the crystal, in comparison with the random ion beam solid orientation, while at the same time minimizing the induced crystal lattice damage.In the present work, 4 MeV 12C2+, 5 MeV 16O2+ and 8 MeV 28Si2+ ions were implanted in highpurity [110] Si crystal wafers at dose of the order of 1017 particles/cm2, in both the channeling and random orientations.The resulting profiles were measured using dNRA (Nuclear Reaction Analysis), i.e implementing the 12C(d; p0) and 16O(d; p0; 0) reactions respectively, at Ed;lab = 1:21:4 MeV.The results were validated using SEM (Scanning Electron Microscope), while the extent of crystalline damage was monitored during the implantation via RBS (Rutherford Backscattering Spectroscopy) spectra.The resulting profiles clearly demonstrate the capabilities of highenergy channeling implantations, as well as, the accuracy of dNRA profiling measurements[1].MeV implantation provides device designers with increased possibilities for the development of novel structures, but a characterization of the lattice disorder accompanying the MeV radiation is required for the full exploitation of MeV implantation technology.Raman spectroscopy, which allows nondestructive, rapid, micronscale assessment of damage is well suited to this thesis.In this work the question of just how sensitive Raman spectroscopy is to lattice in MeV implanted silicon is explored.The analysis is aided by the fact that the profile of damage created by an MeV beam is such that there is a nearly uniform distribution of defects.Especially by using the microRaman scanning technique along the crystal transversal cross section of the ion implanted region, it is possible to investigated the dependence of the ion implantation induced amorphization on the crystal depth. Raman line intensities, shapes and shifts have been used to investigate the defects in the ion implanted region.Above doses of 1017 particles/cm2, Raman provides evidence for the presence of amorphous silicon islands within the crystalline structure.The phonon confinement model (PCM) which is based on the breakdown in wavevector selection rules due to scattering from finite domain sizes has been used to explain the effective average crystal damage[14].The obtained silicon amorphization maxima are in excellent agreement with the corresponding estimated maxima of the implanted ions concentration in silicon[2].Concerning the depth profile of the ion induced damage, the results of microRaman, from SEM and RBS are in full agreement, which prove the ability of the microRaman technique to probe accurately the lattice modifications from ion implantation.Ιωάννης Χ. Κοψαλή

Quality Assurance methodology for the ATLAS ITk Strip Sensor Production

The production of the strip sensors for the ATLAS Inner Tracker (ITk) will start in 2020. Nearly 22000 large area sensors will be produced over a period of roughly 4 years. A Quality Assurance (QA) strategy has been prepared to be carried out during the whole production period. Once the process has been characterized as providing the required pre-irradiation specifications and the proper radiation hardness, the onus is on the manufacturer to rigidly stick to that qualified process. Still, sample testing with specific device-element structures and irradiation of devices should be implemented by the ITk collaboration. The main devices that will be used by the collaboration for QA purposes are miniature strip sensors (1x1 cm2), monitor diodes (8x8 mm2), and the ATLAS test chip. The ATLAS test chip contains several test structures to monitor specific technological and device-element parameters, such as conductive layers sheet resistance, critical parameters of the device oxides such as capacitance, thickness, breakdown voltage, flat-band voltage, etc; Si/SiO2 interfaces charges, and strip and inter-strip electrical characteristics

Evaluation of MOS and Gated Diode Devices of the ATLAS ITk Test Chip

The new ATLAS Inner Tracker (ITk) sub-detector is necessitated by the impending High Luminosity Large Hadron Collider (HL-LHC) upgrade. This replacement is part of the phase-II upgrade programme for the HL-LHC which will see a sevenfold increase in peak instantaneous luminosity with a total ionizing dose of 53 MRad. The fully solid state ITk will employ silicon n^{+}-in-p microstrip sensors in the outer layers of the tracking detector. The main sensors are manufactured on 6” diameter silicon wafers. Periphery wafer area (halfmoons) to which the main sensor does not extend serves as convenient venues for the implementation of test devices. The primary utility of the test devices is Quality Assurance (QA), that is, the monitoring of the consistency and reliability of the manufacturing process. A Metal-Oxide-Semiconductor (MOS) and Gate-Controlled Diode (GCD) are two such test devices aimed at characterizing the surface oxide and silicon-oxide interface. Measurement procedures and parameters for QA are established for these devices and the viability of these tests for gamma irradiated samples is evaluated. The suitability of these devices to further monitor the strip sensor fabrication process is also investigated

Effect of irradiation and annealing performed with bias voltage applied across the coupling capacitors on the interstrip resistance of ATLAS ITk silicon strip sensors

The powering configuration of the silicon strip modules developed for the new Inner Tracker of the ATLAS experiment includes a voltage of up to 0.5 V across the coupling capacitor of each individual strip. However, this voltage is usually not applied in the sensor irradiation studies due to the significant technical and logistical complications. To study the effect of an irradiation and a subsequent beneficial annealing on the strip sensors in real experimental conditions, four prototype ATLAS17LS miniature sensors were irradiated by $^{60}$Co source and annealed, both with and without the bias voltage of 0.5 V applied across the coupling capacitors. The values of interstrip resistance measured on irradiated samples before and after annealing indicate that increase of radiation damage caused by the applied voltage can be compensated by the presence of this voltage during annealing

Effect of irradiation and annealing performed with bias voltage applied across the coupling capacitors on the interstrip resistance of ATLAS ITk strip silicon sensors

In order to cope with the occupancy and radiation doses expected at the High-Luminosity LHC, the ATLAS experiment will replace its Inner Detector with an all-silicon Inner Tracker (ITk), containing pixel and strip subsystems. The strip detector will be built from modules, consisting of one or two n+-in-p silicon sensors, PCB hybrids accommodating the front-end electronics, and powerboard providing high voltage, low voltage, and monitoring electronics. The aluminium strips of the silicon sensors developed for the ITk project are AC-coupled with n-type implants in a p-type float-zone silicon bulk. The module powering configuration includes a voltage of up to 0.5 V across the sensor coupling capacitor. However, this voltage is usually not applied in the sensor irradiation studies due to the significant technical and logistical complications. To study the effect of an irradiation and a subsequent beneficial annealing on the ITk strip sensors in real experimental conditions, four prototype ATLAS17LS miniature sensors were irradiated by Co60 source and annealed for 80 minutes at 60°C, both with and without the bias voltage of 0.5 V applied across the coupling capacitors. The values of interstrip resistance measured on irradiated samples before and after annealing indicate that increase of radiation damage caused by the applied voltage can be compensated by the presence of this voltage during annealing