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Summary of Sensor Quality Tests List of Problems

Summary of Sensor Quality Tests List of Problems. F. Hartmann, CMS Tracker Collaboration. Total Number of Sensor Delivered. *Passing CMS QTC tests February 14, 2003. Summary of Quality Tests. Restrict summary and discussion to sensors delivered after

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Summary of Sensor Quality Tests List of Problems

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  1. Summary of Sensor Quality Tests List of Problems F. Hartmann, CMS Tracker Collaboration

  2. Total Number of Sensor Delivered *Passing CMS QTC tests February 14, 2003

  3. Summary of Quality Tests Restrict summary and discussion to sensors delivered after December 1, 2002 (introduction of new QA steps): 187 OB2 32 W7A W5B 12 W7B W6B Sensors in total

  4. Sensors to be rejected Sensors measured in Pisa not included.

  5. Checklist for Pre-Series Qualification Goal of qualification not yet reached.

  6. 20383204 Back view 1342 m 549 m 1464 m Optical Inspection I Quality of cut edges has significantly improved. Still some sensors outside specifications (last delivery). Further improvement needed. Still 4 rejects out of 261

  7. 23412505 bad Cac short 23412517 23412513 Optical Inspection II Many scratches on the surface of almost all sensors: In many cases no electrical failure. In other cases broken or shorted aluminium lines ! Where and how are these scratches introduced ? Can these scratches be avoided with new scheme skipping IV after cutting? Agreed to try on 1000 OB2 sensors. But then we are even more concerned about cutting defects effecting the IV performance. (On single strip basis & and on overall performance!)

  8. Bad Cac values • Two cases: • Bad Cac values correlated with scratches. (shorts & opens) • One batch (4 sensors): All sensors having hundreds of too low Cac values. • AUTOMATIC Cac CAPACITORS MEASUREMENT Is this or will this be introduced ????

  9. IV problem - breakdown I Example of W7A, W7B & W6A, W6B sensors: Limit Correlation observed: Sensors with higher leakage current have strips with high leakage current AND strips with high leakage current are often in areas with scratches!

  10. IV problem - breakdown II Time dependence observed for some sensors. Important to agree on test procedure.

  11. Same IV up to “soft strip breakdown” First strip Second strip

  12. Leaky strips -- scratches

  13. Hints • Almost each high IV sensor has a few „high leaky“ strips! • Σ leaky strips ~ IV ( few strips drive IV) • EACH leaky strip is scratched ! –not all scratched strips are leaky • Clear correlation between IV and leaky strips and scratches on sensors observed! • No IV-breaks on Minisensors!  different handling !  Scratch test: • Scratchtest on minisensors to reproduce effect • Needle • Pencil (2B) • screwdriver

  14. Scratches on minisensor „Soft“ scratches with probe needle Carbon residues of pencil

  15. Deep scratches on minisensor „Not-so-SOFT“ scratches with screwdriver

  16. Global IV and Individual strip IV Total current Single strip current x3 x70

  17. Strip scan (Current) Undamaged minisensor @ 400V: Ileak ~ 0,2nA x 192 strips ~ 35nA IV ~ 38nA Damaged minisensor @ 400V:  Ileak damaged strips ~ 55nA  Ileak all ~ 100nA IV ~ 120nA A few single strips show high leakage current!

  18. Idiel on scratched Minisensor No pinholes created! • Effect is located in the Al layer, above the oxide! • CMS sensors have metal strip overhang!!! Scratches remove the overhang and introduce pointlike defects

  19. Scratch on bias & guard (minisensor)

  20. Preliminary field simulations (with ISE TCAD)

  21. Solution!?! Scratches -obviously happening very late in the measuring procedure at ST- are critical! Avoiding scratches will certainly improve the yield with respect to CaC (strip failure) , leaky strips (strip failure) and to global IV! BUT There is no guarantee, that avoiding scratches solves ALL problems! Is it enough to skip the IV after cutting?????

  22. Update Contact Persons CMS ST General M. Krammer G. Fallica Technical M. Krammer G. Valvo Mask Design E. Focardi G. Valvo Contract and Payment M. Mannelli G. Di Stefano Schedule A. Cattai G. Mendola Shipments M. Krammer G. Kauerauf Data Files

  23. CMS Module Production CMS Tracker collaboration has to produce ~15000 silicon detector modules until end of 2004. We need to procure 19000 ST sensors in 2 years production time. During full production only samples of sensors can be tested by CMS. We have to relay on Quality Control by ST ! Acceptance limit on sensor failure is max 1% ! Due to delays in pre-series production the time schedule is very tight and we have to compress the module production.

  24. Example of a CMS Module A module consists of 2 sensors, electronic hybrid, 4-6 APV chips, pitch adapter, carbon frame, etc. For many sensors: The first test of silicon sensor after ST quality control is on an assembled module. Replacement of single sensors is basically impossible! The present failure rate of 10% is not acceptable 20% of all modules would fail!

  25. Summary • Strip failure: Add. measurements by CMS • CaC AUTOMATIC Cac CAPACITORS MEASUREMENT!?! • Leaky Strips (scratches only??) • IV (scratches only??) • Optical inspection has to be improved! • Some improvements in the shipping logistic needed! • Acceptance rate must be increased to 99% • Otherwise sensor failure will be detected about 1 year later (2 sensors assembled together with electronics and mechan. parts)

  26. Strip leakage current

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