Sensor Test Status

1. Sensor Test Status E. Fiandrini, N. Dinu INFN Perugia • Apparent Problems with Colibrys sensors • Available Sensors for Assembly • IRST Sensors Aachen, 18-19 Mar 2002

2. Problems with Colibrys Sensors: • The overall yield of the last 215 sensors received is VERY LOW: 0.45 vs 0.9 normal • The reason is a very high nbr of Hot Strips (HS) on P side • HS show up sistematically in between strips #300-#500 • Yield degrades in time

3. Summary of Batches from August 2001 First Bad Batch

4. Hot Strip Occupancy Accumulation of HS Problem starts form Lot051101, Batch C111 (01011)

5. Oct 01 Nov 01 Aug+Sep 01 Dic 01 Feb 02 a Feb 02 b Yield degrades in time: a contamination source present?

6. Set Up Checks • Every cable was checked with grounding connections • An old known silicon sensor was retested obtaining nice • agreement with previous meas. • Open Circuit I @ 80 V was 10-13-10-14 A • Some bad sensors were mounted inverted on probe chuck • and scanned from strip 642 to 1: the HS region appears • inverted too • 23 IRST sensors did not show HS regions at all • Blind tests done at IRST confirm the presence of the HS • region

7. Very accurate optical inspections done on ALL the HS to • look for optical counterpart of electrical defects. • Defined 4 classes of optical defects: • Scratched Strips • Strips with Metallic Defects • Stained Strips • Etched Strips Visual Inspections

8. Visual Inspections: scratched Strips Very few sensors found scratched, no one in the HS region

9. Visual Inspections: metallic defects Two examples of huge metallic spots under passivation on HS.

10. Visual Inspections: metallic defects Single strip defect Double strip defect Found on a about 20% of HS, spread over all surface. In 9 cases, nbr of defective strips exceeds the max allowed This type of HS are shorted and apparently are not seen in Colibrys test because sensors would have been marked as bad

11. Visual Inspections: Stained Strips Dark areas under passivation on some HS

12. Visual Inspections: Stained Strips Dark filaments on HS Huge dark stain on 4 strips Found on few percent of HS with no relevant correlation with HS region

13. Visual Inspections: Etched Strips No metal On few sensors HS strip Al was etched too much: strip width is much narrower. In some case Al is completely missing resulting in an infinite metal resistance

14. Different Optically abnormal strips appear to be HS • Uniformly distribuited over all the surface • No relevant correlation found with HS region • No relevant chipping observed • Most of the strips in the HS region have normal • optical aspect and dont show any visible damage Visual Inspections: Summary

15. Dicing and Cleaning Checks • Dicing at Selmic: • good and bad sensors were cut with the same blade, • same parameters, in the same day by same operator • sensors not touched on active area at Selmic • N side and not P side is glued on blue tape • Cleaning: • good and bad sensors have been cleaned • together

16. Detailed Electrical Tests Because of lack of any relevant damage on the HS region, single strip current vs. Vbias, strip voltage drop to guard, interstrip and guard-to-strip resistance at working point on normal and HS strips were measured

17. Detailed Electrical Tests: Single Strip Current Scan HS region Zoom on HS

18. Detailed Electrical Tests: Single Strip Current Scan HS Region Zoom on HS

19. Detailed Electrical Tests: Single Strip Current vs. Vbias Normal Strips Transition Strips HS Full HS

20. Detailed Electrical Tests: Single Strip Current vs. Vbias Normal Strips Transition Strips HS Full HS

21. Detailed Electrical Tests: Resistances and V drop @ V=80 V

22. Detailed Electrical Tests: Resistances and V drop @ V=80 V

23. Detailed Electrical Tests: Isolated HS Current vs. Vbias HS Normal Strips HS Normal Strips

24. Summary on Colibrys Sensors • Yield is dramatically decreasing in time • Batch C111 has been identified as the first bad batch • Badness due to very high nbr of HS on P side • HS found sistematically in between strips #300-#500 • No visible sistematic damage found in HS region • No correlation with dicing and cleaning • HS are shorted each other with few kOhm of Rint and with • low Rgs

25. Comments • The results seem to indicate two possible problems at • producer premises: • the negative slope of yield as a function of time could • indicate the presence of a contamination source which is • propagating in the production chain • electrical measurement for the shorts has clearly problems • because it fails to spot macroscopic metallic spots

26. Sensors Available for Assembly Due to the mentioned problems we have now: 9 good sensors 817 tested Assembly is STOPPED

27. IRST Sensors: production Batch I110 tested at IRST on wafer and retested at PG after cut at IRST and before cleaning on both sides

28. IRST Sensors: test P, cut Selmic

29. IRST Sensors: test N, cut Selmic

30. IRST Sensors: test P, cut IRST IRST Sensors: test N, cut IRST

31. IRST Sensors: Optical Aspect The first 13 sensors had very different optical colors due to different oxide thickness. However they had different process steps and have not to be considered as production sensors. This made very difficult to align sensors in a automatic way. Uniform optical aspect is a crucial issue for test and assembly automatic alignment. The first 10 production sensors appear to have much better aspect. : only 2 alignments failed because of very different colors.

32. IRST Sensors: Comments First sensors look promising for electrical and optical quality. We could start to use IRST sensors for assembly

33. Set Up Checks: Inverted Scan