Development of 3D Trenched-Electrode Pixel Sensors with improved - PowerPoint PPT Presentation

Development of 3D Trenched-Electrode Pixel Sensors with improved Timing performance G. Forcolin , R. Mendicino, G.F. Dalla Betta University of Trento and TIFPA-INFN M. Boscardin, S. Ronchin TIFPA-INFN and FBK A. Lai INFN Cagliari A. Loi INFN Cagliari and University of Cagliari S. Vecchi INFN Ferrara PIXEL 2018 G. Forcolin 10 December 2018

Outline ● Introduction to 3D sensors ● Fabrication process ● 3D trench sensors – Design and TCAD simulation – Fabrication tests ● Outlook PIXEL 2018 G. Forcolin 10 December 2018

3D Sensors ● Advantages: – Low Depletion Voltage – Lateral Drift ● Fast Response ● Low Sensitivity to mag. fields – Short inter-electrode distance ● Fast Response ~100s μm ● Reduced trapping probability => more rad hard ● Disadvantages – Non-Uniform Electric Field – High Capacitance – Complicated + expensive manufacturing process ~10s μm PIXEL 2018 G. Forcolin 10 December 2018

3D sensors at HL-LHC ● Requirements: – higher hit-rate – increased granularity – higher radiation tolerance – lighter detectors ● To meet Requirements: – Produce thinner sensors (~100μm) – Reduce electrode spacing (~30μm) – Narrower electrodes (5μm) – Small/Active edges (<100μm) PIXEL 2018 G. Forcolin 10 December 2018

Single sided production method ● Use single sided process with support wafer – Can reduce active thickness without compromising mechanical properties – Active edges – Post processing required to thin support layer and deposit metal – Front side layout => processing can be complicated P- high W cm wafer P- high W cm wafer SiO 2 p++ low W cm wafer p-spray p++ low W cm wafer Metal to be deposited after thinning Metal to be deposited after thinning Handle wafer to be thinned down Handle wafer to be thinned down PIXEL 2018 G. Forcolin 10 December 2018

Fabrication Process ● Electrodes produced using Deep Reactive Ion Etching (DRIE) by the Bosch process ● Alternating etch cycles (SF 6 ) and passivation cycles (C 4 F 8 ) ● Can achieve high aspect ration (~30:1 or better) and good uniformity 5.3 m m! 3.4 m m! 117 m m! ! 155 m m G.-F. Dalla Betta et al., NIMA 824 (2016) 386 and 388 5.3 m m! 4.7 m m ! PIXEL 2018 G. Forcolin 10 December 2018

FBK Fabrication Process ● Production steps: – Etch ohmic electrodes > active thickness – Fill with Poly-Si (at least partially) – Etch junction electrodes < active thickness PIXEL 2018 G. Forcolin 10 December 2018

FBK Fabrication Process PIXEL 2018 PIXEL 2018 G. Forcolin G. Forcolin 10 December 2018 10 December 2018

Timing in 3D Trench Sensors ● 3D trench sensors being Advantages: ● High average field investigated for timing ● Uniform weighting field applications ● Initial pulse (largely) ● Some sensors produced independent of position ● Very Radiation Hard at CNM in 2013, sensors Drawbacks: worked but with high ● Possible fabrication problems leakage current ● High electrode capacitance A. Montalbano et. al. NIMA 765 (2014), 23 PIXEL 2018 G. Forcolin 10 December 2018

Trenched Sensors ● Investigating TIMEPIX compatible trench sensors ● Trenches are dead area, so minimize thickness (~4μm) ● Tests of fabrication procedure underway to optimize fabrication parameters ● Test mask produced with wide range of possible geometries and spacings for tests ● Design optimized with TCAD simulations ● New mask designed for first lot of sensors pitch-x p + trench pitch-y width gap n + dashed trenches PIXEL 2018 G. Forcolin 10 December 2018

Trenched Sensors Trench Length: Trench Length: 41 m m 41 m m 43 m m 43 m m 45 m m 45 m m 47 m m 47 m m 49 m m 49 m m Thin metal Thin metal poly Trench Length: Trench Length: 41 m m 45 m m 43 m m 45 m m 47 m m Bump Wide metal PIXEL 2018 G. Forcolin 10 December 2018

Trenched Sensors Fabrication Test masks produced to test fabrication procedure of devices ● Try to use stepper ● Minimum feature size 350nm – Alignment accuracy 80nm – Projection => low defect level – Max exposure area ~2x2cm 2 – PIXEL 2018 G. Forcolin 10 December 2018

Trenched Sensors Fabrication Tests concluded ● Finalized fabrication process ● Ready to move on to real devices ● PIXEL 2018 G. Forcolin 10 December 2018

Weighting Field Simulations gap=16 m m gap=14 m m gap=12 m m gap=10 m m gap=8 m m gap=6 m m High dependence with Low dependence with geometry geometry 14 PIXEL 2018 G. Forcolin 10 December 2018

Capacitance Simulations Opposite electrode capacitance (half- pixel) Inter-pixel capacitance (1 neighbour) ● Strong dependance of trench dimension on inter-pixel capacitance ● Small change in capacitance between opposite electrodes due to trench dimensions 15 PIXEL 2018 G. Forcolin 10 December 2018

Capacitance Simulations ● Find relationship between interpixel capacitance and trench length ● Approximate inter-pixel capacitance using parallell plate capacitor equation ● Find effective area ~1790μm 2 16 PIXEL 2018 G. Forcolin 10 December 2018

Capacitance Simulations 17 PIXEL 2018 G. Forcolin 10 December 2018

Capacitance Simulations ● At full depletion, negligible difference in capacitance between different geometries 18 PIXEL 2018 G. Forcolin 10 December 2018

MIP Simulations ● MIP simulations carried out to understand charge collection properties of devices ● Looked at 3 hit positions and 3 trench dimensions: – Trench = 41μm (Gap = 14μm) – Trench = 45μm (Gap = 10μm) – Trench = 49μm (Gap = 6μm) 19 PIXEL 2018 G. Forcolin 10 December 2018

MIP Simulations Strong dependence of pulses on hit position ● Dependance on gap significant only in low field ● region 20 PIXEL 2018 G. Forcolin 10 December 2018

MIP Simulations 2Y θ Simulate hits at an angle going through low field ● region High angle => more charge generated outside of ● low field region 21 PIXEL 2018 G. Forcolin 10 December 2018

MIP Simulations Increased charge at higher angles due to increased length of track ● Improvement in rise time for increased angles ● 22 PIXEL 2018 G. Forcolin 10 December 2018

First Sensor Batch Technological test devices 3D Test Structures TIMEPIX sensor Temp Metal 23 PIXEL 2018 G. Forcolin 10 December 2018

Outlook + Conclusions ● 3D trench devices being investigated to provide good position+timing resolution ● Fabrication tests have been completed, verifying that such devices can be produced ● TCAD simulations have been carried out to understand and optimize properties of devices ● First batch of devices has been designed => beginning production PIXEL 2018 G. Forcolin 10 December 2018

Backup Slides PIXEL 2018 G. Forcolin 10 December 2018

ATLAS IBL Sensors ● Used double sided 3D sensors ● Advantages: ● Downsides: – Reduced process – Active edge not possible complexity – Mechanically more fragile – Backside accessible for – Wafer bowing bias – Allows slim edge ATLAS IBL, JINST 7 (2012) P11010 G. Giacomini, et al., IEEE TNS 60(3) (2013) 2357 PIXEL 2018 G. Forcolin 10 December 2018

3D Test Structures Single Pixel Test Pixel Devices Multi-Pixel Strips 27 PIXEL 2018 G. Forcolin 10 December 2018