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Alvise Bagolini a , Maurizio Boscardin a ,

Production of 3D silicon pixel sensors at FBK for the ATLAS IBL. Alvise Bagolini a , Maurizio Boscardin a , Gian -Franco Dalla Betta b , Gabriele Giacomini a , Francesca Mattedi a , Marco Povoli b , Nicola Zorzi a. a Fondazione Bruno Kessler (FBK-CMM) Italy

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Alvise Bagolini a , Maurizio Boscardin a ,

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  1. Production of 3D silicon pixel sensors at FBK for the ATLAS IBL Alvise Bagolinia, Maurizio Boscardin a, Gian-Franco Dalla Bettab, Gabriele Giacominia, Francesca Mattedia, Marco Povolib, Nicola Zorzia a Fondazione Bruno Kessler (FBK-CMM) Italy • b INFN and University of Trento, Italy

  2. 3D silicon pixel sensor production • The layout has been developed in thein the framework of the ATLAS 3D Sensor Collaboration • FE-I4 (8x) • FE-I3 (9x) • CMS (3x) • test structures 3D_DDTC with passing-through columns technology was used for the first production oriented to the ATLAS insertable B-Layer

  3. Layout details of a FE_I4 sensor 50 µm FE-I4 sensor  80 x 336 pixels Ohmic Side 125 µm Junction side dead area of 200 mm

  4. 3D-DTC with passing through columns n+ col. • Column depth equal to the wafer thickness, etched from both sides • Full double side process • Surface isolation with p-spray on both sides • No support wafer • Columns (~12 µm diam.) are “empty”, doped by thermal diffusion and passivated by SiO2 • Edge protection in order to improve the mechanical yield p-sub t p-spray p+ col. edge protection

  5. Main technological aspects • Optimization of DRIE recipe for holes with higher aspect ratio in order to improve the uniformity of the etch rate throughout the process. • Optimization of edge protection in order to • increase the mechanical yield after DRIE etching • reduce the wafer bowing and consequently the leakage current

  6. Optimize DRIE recipe for holes with higher aspect ratio 208 µm ≈ 11 µm ≈ 12 µm ≈ 234 µm ≈ 5 µm ≈ 10 µm Etch stop for DRIE etching

  7. Optimize edge protection • Mechanical fragility of wafers manly due to a cracks on the wafer edge caused by D-RIE etch step: • Need a special edge protection during DRIE etching (electrostatic clamping) to prevent the creation of cracks that could cause the breakage during the processing. • Need a special care during processing Mechanical yield with the optimized edge protection:

  8. Optimize edge protection: wafer bowing Edge protection effects on the wafer bowing. A high bowing induces • High leakage current • Misalignment among columns • Bonding problem Old edge protection  wafers warp up to 120 µm Optimizededgeprotection waferswarp< 30 µm 3D_ATLAS10

  9. Wafer bowing: leakage current The wafer bowing strongly influences the leakage current. With the optimized edge protection it is reduced of one order of magnitude. Leakage current on planar test diodes (4mm2) Old edge protection Optimized edge protection

  10. Wafer bowing: Column alignment left side right side center old edge protection misalignmentof a several μm optimized edge protection layer Misalignment < 5μm

  11. Temporary metal for electrical characterization • The temporary metal shorts 336 pixels together in a strip • Allows to perform electrical tests on the FE-I4 pixel sensors before bump-bonding • The IV characteristics of 80 strips form a FE-I4 pixel sensor 336 pixels ( 2 electrodes per pixel) 80 strip

  12. Temporary Metal: IV characteristics The IV characteristics of 80 strips of two sensors The IV characteristics of FE-I4 pixel sensor as a sum of 80 IV strips curves

  13. VBDand Ileakof the FE-I4 strips Good uniformity from batch to batch related to the 80 strips of each detector

  14. Numbers of production 4 production batches Selected wafers  at least 3 FE-I4 sensors qualified • Selection criteria before bump-bonding: • Vdepl≤ 15V and • Vop≥Vdepl +10V • I (Vop) < 2mA per tile • Vbd> 25V • [I (Vop) / I(Vop – 5V)] < 2

  15. ProblemInvestigation on 3D_Atlas11 Litho n+ on junction side Problem with resist adhesion Low final yield

  16. Conclusion FBK hasdeveloped and optimized the technologyused for the production of Si-3D pixel sensors for the ATLAS IBL with a relativelygoodyield. Outlook • advantages • Production capability = double the wafers area • DRIE upgrade with a thin ceramic edge protection = increasing of the mechanical yield Upgrade to 6 inch • disadvantage • We have to learn how to process a thin wafers

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