P. Riedler- GGT Meeting 3/4/20061 Status of Sensor Irradiation and Bump Bonding P. Riedler, G. Stefanini P. Dalpiaz, M. Fiorini, F. Petrucci

P. Riedler- GGT Meeting 3/4/20062 Outlook Status of sensor irradiation Next steps Status of processed IRST wafers Short overview of process steps in bump bonding Thinning options to reduce material budget - possible problems

P. Riedler- GGT Meeting 3/4/20063 First Irradiated Samples 6 Diodes from 2 IRST sensor wafers (200µm) Diced at IRST PCBs provided by M. Glaser Transport boxes built by A. Gonidec Diodes mounted and bonded by I. Macgill

P. Riedler- GGT Meeting 3/4/20064 T B Slide by C. Piemonte, A. Pozza, M. Boscardin/IRST

P. Riedler- GGT Meeting 3/4/20065 Diodes Diodes A (7 mm x 7 mm, multi-guard) Diodes B (3 mm x 3 mm, multi-guard) A1: wafer 570-T A2: wafer 566-B B1: wafer 570-T, 4 multi B2: wafer 570-T, 12 multi B3: wafer 566-B, 4 multi B4: wafer 566-B, 12 multi

P. Riedler- GGT Meeting 3/4/20066 Pre-Irradiation Tests I-V and C-V measured in RD50 lab at CERN Total leakage current at 23.7°C C-V indicate V fd ~15V One diode (B1) with higher current (~4µA)

P. Riedler- GGT Meeting 3/4/20067 Irradiaton in Ljubljana TRIGA reactor, 250kW, irradiation with fast neutrons Samples are irradiated in a tube placed in the reactor core occupying the position of one rod Samples transported by M. Glaser, irradiation done by I. Mandic/JSI Ljubljana - end December 2005

P. Riedler- GGT Meeting 3/4/20068 Irradiation in Ljubljana All diodes biased at 30V during irradiation Guard and pad contact connected together Immediately after irradiation stored in freezer (-20°C) Irraditiation to different fluences: 2E14 1MeV n/cm 2 : A1, B1 3E13 1MeV n/cm 2 : A2 1E13 1MeV n/cm 2 : B4 2E12 1MeV n/cm 2 : B3 1E12 1MeV n/cm 2 : B2

P. Riedler- GGT Meeting 3/4/20069 Fluences in the GGT Fluences: 1 MeV n equivalent cm 2 Added safety factor of 2 A1,B1 A2 B4 B3 B2

P. Riedler- GGT Meeting 3/4/ Annealing Diodes were returned to CERN beginning of February Measurements to be carried out using CERN setup Apart from 8 hour car transport, diodes were stored at -20°C at all time after irradiation to slow down annealing Annealing study according to ROSE standards with I- V and C-V measurements planned in the next weeks Operating temperature assumed to be approx. 5°C (to be discussed)

P. Riedler- GGT Meeting 3/4/ Further Irradiations More irradiations can be carried out using the T7 facility at CERN Alternatives: Ljubljana, Helsinki Few diodes still available from two diced wafers More diodes will become available from processed wafers in short time

P. Riedler- GGT Meeting 3/4/ Bump Bonding and Thinning

P. Riedler- GGT Meeting 3/4/ Status of IRST Wafers at VTT Wafers 565 and 571 sent to VTT for processing (autumn 2005) Both wafers showed strong bow (~60-70µm) - potential problem for bb processing (max. 30 µm) Visual inspection showed excellent quality Both IRST wafers were broken in the photo-resist track at VTT Probably the bow of the wafers and tight limits in the centering stage caused the breaking of the wafers. The limit settings have been changed and tested with blank 4” wafers New reworked wafers with smaller bow already arrived at VTT and will be processed this week

P. Riedler- GGT Meeting 3/4/ Status of IRST Wafers at VTT In week 8 a fire occurred in the VTT cleanroom which affected some processing steps For sensor wafers i.e. the electroplating step (Ni and Pb-Sn deposition) and the reflow oven were affected Equipment needed to be moved to second cleanroom, cleaned and inspected No wafer processing possible until this week

Process Steps for Flip Chip in M1 M1 Sputtering of Ti-W/Cu Field Metal Photolithography Electroplating (Ni/Pb-Sn) Field Metal Etching Post-plating Reflow (Optional) Back Grinding (Optional) CMP Polishing Dicing Flip Chip (Tack) Bonding Assembly Reflow M1 M1 = 'Old' Side of Clean Room J. Salonen/VTT Only r.o. wafers

P. Riedler- GGT Meeting 3/4/ Thinning Goal: thin readout chips to 100µm or less to reduce material budget (no margin for sensor wafers due to signal!) First thinning tests carried out before VTT fire One blank 200µm wafer thinned successfully to 100µm Next tests (as soon as CMP is back up): thin bumped 200µm wafer to 100µm and dice Discussion with VTT end of March concerning thinning - several points of concern were discussed and tests planned

P. Riedler- GGT Meeting 3/4/ Considerations Concerning Thinning Two options: bump deposition before thinning (ALICE) or after thinning Problem: wafers after thinning are very fragile - might not survive bumping process unless a support wafer is attached to it (wafer bonding) If bumping is done before thinning one critical step remains: removal of the protection tape used during grinding

P. Riedler- GGT Meeting 3/4/ Tests are necessary to test which process order is best Wafer bonding experience exists at VTT New lamination tape being investigated Further consideration: stress on thin wafers Considerations Concerning Thinning

P. Riedler- GGT Meeting 3/4/ Considerations Concerning Thinning Back side grinding induces damage layer in the crystal -> stress CMP helps to remove part of this damage layer Trials necessary to optimize thinning with respect to stress on wafer (depends also on front side process) Additional suggestion: deposition of compensation layer on thinned wafer back side

P. Riedler- GGT Meeting 3/4/ Stress is also induced due to dicing of the thinned wafer (cutting of individual chips) First observations already with ALICE chips Considerations Concerning Thinning 150µm chip

P. Riedler- GGT Meeting 3/4/ Considerations Concerning Thinning Possible steps to reduce stress on chip edges: Investigate dicing parameters Backside layer deposition could present improvement Laser cutting instead of diamond blade dicing Tests required

P. Riedler- GGT Meeting 3/4/ Conclusion First diodes irradiated in Lubljana Annealing studies to be carried out in next weeks First 200 mm blank wafer thinned to 100µm Detailed studies required to optimize processing steps for thin wafers and to reduce stress Processing of the reworked sensor wafers and thinning tests will continue as soon as possible