Studies of adhesives and metal contacts on silicon strip sensors for the ATLAS Inner Tracker

260 Pages·2017·34.98 MB·English

by  Luise Poley

Studies of adhesives and metal
contacts on silicon strip sensors for
the ATLAS Inner Tracker
DISSERTATION
zur Erlangung des akademischen Grades
doctor rerum naturalium
(Dr. rer. nat.)
im Fach Physik
Spezialisierung: Experimentalphysik
eingereicht an der
Mathematisch-Naturwissenschaftlichen Fakulta¨t
der Humboldt-Universita¨t zu Berlin
von
M.Sc. Anne-Luise Poley
Pra¨sidentin/Pra¨sident der Humboldt-Universita¨t zu Berlin
Prof. Dr.-Ing. Dr. Sabine Kunst
3 Dekanin/Dekan der Mathematisch-Naturwissenschaftlichen Fakulta¨t
6
0
- Prof. Dr. Elmar Kulke
8
1
0
2
-
S
I
S
E
H8
1
T0 Gutachter/innen: 1. Priv-Doz. Dr. Klaus Mo¨nig
N-/2
2 2. Prof. Dr. Heiko Lacker
R1
E/ 3. Prof. Dr. Chris Parkes
C04
Tag der mu¨ndlichen Pru¨fung: 12.04.2018

Abstract
This thesis presents studies investigating the use of adhesives on the active area of silicon strip
sensors for the construction of silicon strip detector modules for the ATLAS Phase-II Upgrade.
60 ATLAS07 miniature sensors were tested using three UV cure glues in comparison with the
current baseline glue (a non-conductive epoxy).
The impact of irradiation on the chemical composition of all adhesives under investigation
was studied using three standard methods for chemical analysis: quadrupole time-of-flight mass
spectroscopy, gel permeability chromatography and gas chromatography combined with mass
spectrometry (GC-MS). GC-MS analyses of glue sample extracts before and after irradiation
showed molecule cross-linking and broken chemical bonds to different extents and allowed to
quantify the radiation hardness of the adhesives under investigation.
Probe station measurements were used to investigate electrical characteristics of sensors
partially covered with adhesives in comparison with sensors without adhesives. Leakage current,
bulk capacitance, inter-strip capacitance and surface resistance were measured before and after
gluing, after irradiation and after temperature cycling. The presence of glue on the active sensor
area was found to increase the sensor leakage current and inter-strip capacitance and frequently
led to early sensor breakdowns. Temperature cycling and irradiations reduced adverse effects
due to glue to a small noise difference between sensors with and without glue.
Charge collection efficiency measurements in a β-source setup were used to study the influence
of adhesives on the silicon bulk. All sensors under investigation showed equivalent charge
collection efficiencies for sensors with and without glue, as well as signal-to-noise ratios above
the required minimum of ten for the foreseen bias voltage. Before irradiation, sensors with glue
showed increased cluster sizes, which could be attributed to fluorescence effects inside the glue
using testbeam measurements.
During testbeam studies, sensor strips were found to respond inhomogeneously in bond pad
regions. Follow-up measurements confirmed that the presence of bond pads affects the electric
field within a sensor and leads to additional charge being collected around bond pads. As a
result of these findings, the sensor bond pad layout was modified in order to minimise reduced
tracking resolution caused by shifted strip responses.

Zusammenfassung
In dieser Dissertationen werden Untersuchungen zur Verwendung von Klebstoffen auf der
Oberfl¨ache von Silizium-Streifen-Sensoren fu¨r die Konstruktion von Detektormodulen fu¨r das
ATLAS Phase-II Upgrade vorgestellt. Drei UV-h¨artende Klebstoffe wurden im Vergleich zu
dem derzeitigen Standard-Klebstoff (einem nicht-leitenden Epoxid) an 60 ATLAS07 Miniatur-
Sensoren getestet.
DerEinflussvonBestrahlungaufdiechemischeZusammensetzungallerverwendetenKlebstoffe
wurde unter Verwendung von Standardmethoden zur chemischen Analyse untersucht: Flugzeit-
massenspektrometrie, Gel-Permeations-Chromatographie sowie Gaschromatographie in Kombi-
nation mit Massenspektrometrie (GC-MS). Mithilfe der GC-MS Analysen von Klebstoffproben-
Extrakten vor und nach Bestrahlung wurden verschiedene Ausmaße von Moleku¨lvernetzung
und gelo¨sten Moleku¨lbindungen festgestellt und der Grad von Strahlenha¨rte aller untersuchten
Klebstoffe quantifiziert.
Mithilfe einer Sensor-Probestation wurden die elektrischen Eigenschaften von teilweise mit
Kleber bedeckten Sensoren im Vergleich mit unbeklebten Sensoren untersucht. Die Leckstro¨me,
Oberfla¨chenwidersta¨nde, Kapazita¨ten zur Sensor-Ru¨ckseite sowie Zwischen-Streifen-Kapazita¨ten
der Sensoren wurden vor und nach Bekleben, Bestrahlung und Durchfu¨hrung von Wa¨rmezyklen
gemessen. Im Vergleich zu Sensoren vor dem Bekleben zeigten mit Klebstoff bedeckte Sensoren
einen erh¨ohten Leckstrom, erh¨ohte Zwischen-Streifen-Kapazit¨aten sowie Durchbru¨che des
Leckstroms bei niedrigeren angelegten Spannungen. Durch W¨armezyklen und Bestrahlung
wurden nachteilige Effekte des Beklebens von Sensoren auf ein geringfu¨gig erh¨ohtes Rauschen
reduziert.
Messungen der Ladungssammlungseffizienz in einem β-Strahlungs-Teststand wurden verwen-
detumdenEinflussvonaufgetragenenKlebstoffenaufdasSilizium-Kristallgitterzuuntersuchen.
AllegetestetenSensoren-mitundohneaufgebrachtemKlebstoff-zeigtenvergleichbareLadungs-
sammlungseffizienzen sowie Signal-Rausch-Verha¨ltnisse oberhalb des geforderten Minimums von
zehn bei der vorhergesehenen Verarmungsspannung. Wa¨hrend der Messungen wurde festgestellt,
dass bei unbestrahlten Sensoren mit Klebung Signaleu¨ber eine durchschnittlich gro¨ßeren Anzahl
von Sensorstreifen verschmiert wurde als bei Sensoren ohne Klebung. Messungen im Teststrahl
zeigten, dass dieser Effekt durch Fluoreszenzeffekte innerhalb des Klebers verursacht wurde.
Untersuchungen von Sensoren in Teststrahlmessungen zeigten außerdem, dass Sensoren
um die zum Drahtbonden verwendeten Aluminiumfl¨achen ungleichm¨aßig Ladung sammelten.
Weiterfu¨hrende Messungen konnten best¨atigen, dass durch die Aluminiumfl¨achen und da-
runterliegende Dotierungen das elektrische Feld innerhalb des Sensors vera¨ndert und zusa¨tzliche
Ladung um die Drahtbond-Fla¨chen gesammelt wurde. In Reaktion auf die gemessene Inhomo-
genit¨at wurde die Gestaltung zuku¨nftiger Sensoren modifiziert, sodass der nachteilige Einfluss
von Drahtbond-Fl¨achen auf die Spurrekonstruktion minimiert wurde.
Contents
1 Introduction 3
2 The ATLAS Phase-II Upgrade 5
2.1 The Large Hadron Collider 5
2.1.1 The High Luminosity LHC 5
2.2 The ATLAS Detector 7
2.2.1 The ATLAS Upgrade 8
2.2.2 The ATLAS Inner Tracker 10
2.2.3 Silicon Strip Detector Modules 12
2.3 Silicon Strip Sensors for the ATLAS ITk 15
2.3.1 Electrical Specifications of Silicon Strip Sensors for the ITk 18
2.3.2 Sensor Handling during Module Construction 21
3 Sensors and Treatments 23
3.1 ATLAS07 Miniature Sensors 23
3.2 Gluing 25
3.3 Irradiations 27
3.3.1 Use of Silicon for Semiconductor Trackers 27
3.3.2 Radiation Damages in Silicon 29
3.3.3 Irradiations Approximating Radiation Levels in the Future ATLAS Strip
Tracker 32
3.4 Temperature Cycles 34
3.4.1 Temperature Changes 35
3.4.2 Ageing 38
3.4.3 Performed Cycles 39
3.5 Observations after Treatments 40
4 Material Studies of Irradiation Effects on Adhesives 43
4.1 Irradiation studies 43
4.2 Feasibility Studies 47
4.2.1 Quadrupole Time-of-Flight Mass Spectrometry 48
4.2.2 Gel Permeation Chromatography 50
4.2.3 Gas Chromatography - Mass Spectrometry 52
4.3 Results of GC-MS Analysis 56
i
Contents
4.4 Conclusions of Chemical Analyses 65
5 Studies of Electrical Sensor Characteristics 69
5.1 Sensor Characteristics under Investigation 69
5.2 Probe Station Setup 69
5.3 Measurements 71
5.3.1 Leakage Current 71
5.3.2 Bulk Capacitance 73
5.3.3 Inter-strip Capacitance 76
5.3.4 Inter-strip Resistance 83
5.3.5 Surface Resistance Measurements 86
5.4 Measurements on Blank Sensors Before Treatments 93
5.4.1 Leakage Current Measurements 94
5.4.2 Bulk Capacitance Measurements 94
5.4.3 Surface Resistance Measurements 95
5.4.4 Inter-strip Capacitance Measurements 96
5.4.5 Results 98
5.5 Impact of Gluing on Sensor Characteristics 99
5.6 Impact of Irradiation with 23MeV Protons 109
5.7 Impact of Temperature Cycling on Sensor Characteristics 114
5.8 Impact of Temperature Cycling after Irradiation 119
5.9 Impact of Irradiation with 800MeV Protons 123
5.10 Impact of Irradiation with Reactor Neutrons 125
5.11 Conclusion of Probe Station Measurements 128
6 Sensor Studies in a Beta-Source Setup 131
6.1 Signal Generation of Charged Particles in Silicon Strip Sensors 131
6.1.1 Energy Deposition in Silicon Sensors 131
6.1.2 Signal Collection in Silicon Strip Sensors 133
6.2 Beta-Source Setup 134
6.3 Sensor Test Setup 135
6.4 Data Taking with an ALiBaVa System 137
6.4.1 Latency 138
6.4.2 Triggering 138
6.4.3 Calibration with Internal Calibration Function 138
6.4.4 Calibration with Reference Sensors 142
6.4.5 Pedestals 143
6.5 Testing Procedure 144
6.6 Data Analysis 146
6.6.1 Selection of a Time Cut 151
6.7 Results 154
6.7.1 Results for Blank Sensors 155
6.7.2 Results for Sensors with Glue 155
6.7.3 Results for Sensors Irradiated with 23MeV Protons or Neutrons 158
ii
Contents
6.7.4 Results for Sensors after Temperature Cycling 165
6.7.5 Results for Sensors after Irradiation with 23MeV Protons and Temperat-
ure Cycling 166
6.7.6 Results for Sensors Irradiated with 800MeV Protons 168
6.8 Discussion of Results 168
6.9 Conclusion of β-Source Setup Measurements 169
7 Sensor Performance Study in an Electron Beam 171
7.1 Testbeam 171
7.1.1 Beam Telescope 172
7.1.2 Setup for Sensor Tests in Electron Beam 173
7.1.3 Adjustment of Beam Position and Energy 174
7.1.4 Data Taking 176
7.2 Data Reconstruction 177
7.2.1 ALiBaVa Data Analysis 177
7.2.2 Data Merging 179
7.2.3 Telescope Data Processing 179
7.2.4 Event Reconstruction 185
7.3 Results 185
7.4 Conclusion 189
8 Investigation of Charge Cluster Widening by Glue 191
8.1 Measurement Setup for Glue Fluorescence Studies 193
8.2 Performed Scans for Glue Fluorescence Studies 196
8.3 Results of Glue Fluorescence Scans 199
8.4 Conclusions 206
9 Studying the Impact of Local Sensor Geometries in Testbeams 209
9.1 Geometrical Inhomogeneity of Silicon Sensors Strips 209
9.2 Initial X-ray Beam Measurements 211
9.2.1 Signal Readout in X-ray Beam Measurements 211
9.3 Sensor Scans Performed Using an X-ray Beam 212
9.3.1 Results from 1-dimensional Sensor Scan with an X-ray Beam 213
9.4 Studies of Sensor Geometry Using Electrons 214
9.5 Sensor Layout Considerations 216
9.6 Detailed 2D-mapping in an X-ray Beam 219
9.6.1 Setup for 2D Sensor Scans Using an X-ray Beam 219
9.6.2 Results of 2D Sensor Scans Using an X-ray Beam 223
9.7 Comparison of Sensor Maps with Simulations 227
9.7.1 Conclusion of Sensor Geometry Studies 229
10 Conclusion 231
iii
List of Figures
2.1 The ATLAS detector and its major sub-systems from [3] 7
2.2 The layout of the future ATLAS ITk (from [12]) 11
2.3 Layout of a silicon strip detector module from the Inner Detector (from [34]) 12
2.4 Layout of a silicon strip detector module for the Inner Tracker (from [12]) 13
2.5 Total fluence and dose expected in the ITk 14
2.6 FEA temperature simulation of a petal in the strip tracker after 3000fb−1 15
2.7 Corner of an ATLAS07 miniature sensor with marks on the inactive area 16
2.8 Protective rings around the active area of ATLAS strip sensors 17
2.9 Architecture of a silicon sensor strip 19
2.10 Connection of sensor strips to the bias ring 20
3.1 Wafer layout for ATLAS07 silicon strip sensors 24
3.2 Overview of architectures of ATLAS07 miniature sensors 25
3.3 Examples of ATLAS07 miniature sensors with glue samples on the surface of the
active area 27
3.4 Energy levels in semiconductors with and without doping 28
3.5 Displacement energies of different particle types 30
3.6 Examples of bulk damages in a silicon lattice 30
3.7 Climate diagram for temperature cycles of sensor samples 39
3.8 Cracks inside glue layers on a sensor 40
4.1 Polyethylene plate with glue samples for irradiation 44
4.2 Glue samples after irradiation in Los Alamos and at KIT 45
4.3 Stopping powers for different plastics 46
4.4 Mass/charge spectra obtained from quadrupole time-of-flight mass spectrometry
analysis 49
4.5 Results of Size Exclusion Chromatography for an irradiated and an unirradiated
sample of DYMAX 6-621 51
4.6 Isobornyl acrylate molecule and possible breaking points 53
4.7 Gas chromatograph/mass spectrometer spectra for cured and irradiated DYMAX
6-621 glue 55
4.8 Observedmassspectrometerassociatedtoagaschromatographypeakandspectra
of possible matches 58
4.9 Patterns observed in the comparison of GC-MS spectra for cured and irradiated
glue samples 59
iv
List of Figures
4.10 GC-MS spectra of DYMAX 3013 before and after irradiation 60
4.11 GC-MS spectra of DYMAX 6-621 before and after irradiation 61
4.12 GC-MS spectra of Loctite 3525 before and after irradiation 62
4.13 GC-MS spectra of Epolite FH-5313 before and after irradiation 63
4.14 Summed up radiation induced changes in GC-MS spectra for different glues 64
5.1 Probe station setup for silicon strip sensor measurements 70
5.2 Schematic of a leakage current measurement setup 72
5.3 Measurement of the leakage current dependency on the sensor temperature 74
5.4 Schematic of a bulk capacitance measurement setup 75
5.5 Bulk Capacitance measurements for different temperatures and measurement
frequencies 76
5.6 Calculation of the depletion voltage from linear fits of 1/C2 77
bulk
5.7 Schematic of an inter-strip capacitance measurement setup 78
5.8 ATLAS miniature sensor in the probe station during inter-strip capacitance
measurement 79
5.9 ATLAS miniature sensor with glue used for test measurements 80
5.10 Inter-strip capacitances measured at different frequencies 81
5.11 AC pads after multiple probe needle contacts 81
5.12 Inter-strip capacitance measurements with one and two neighbour contacts 82
5.13 Inter-strip capacitances measured for different sensor temperatures 82
5.14 Schematic of an inter-strip resistance measurement setup 84
5.15 Example for inter-strip resistance measurements on a sensor 84
5.16 Currents in R and R measurement 85
bias int
5.17 Inter-strip resistance measurements at different sensor temperatures 85
5.18 Contributions to surface resistance on an ATLAS07 miniature sensor 87
5.19 Resistances involved in surface resistance measurement 89
5.20 Schematic measurement setup for surface resistivity 90
5.21 Surface current measurements for 25 strips on an ATLAS07 miniature sensor 90
5.22 Repeated surface current measurements on 25 strips of a sensor 91
5.23 Surface resistivities calculated for 25 sensor strips 92
5.24 Calculated surface resistances for different surface resistances and sensor currents 93
5.25 Leakage current measurements for ATLAS07 miniature sensors 94
5.26 Bulk capacitance measurements for ATLAS07 miniature sensors 95
5.27 Surface resistances measured on ATLAS07 sensors 96
5.28 Inter-strip capacitance measurements for ATLAS07 sensors 97
5.29 Ratios of sensor leakage currents before and after gluing 99
5.30 Leakage currents of sensors before and after gluing 100
5.31 Sensor bulk capacitances before and after gluing 101
5.32 Bulk capacitance increase after gluing 102
5.33 Surface resistances of sensors before and after gluing 103
5.34 Average surface currents on FZ2 ATLAS07 sensors 104
5.35 Inter-strip capacitances of ATLAS07 miniature sensors before and after gluing 106
v