Fabian Hügging – University of Bonn – February WP3: Post processing and 3D Interconnection M. Barbero, L. Gonella, F. Hügging, H. Krüger and N. Wermes AIDA Kick-Off Meeting CERN, –

Fabian Hügging – University of Bonn – February Introduction Post processing and 3D Interconnection –many possibilities e.g. material reduction of futures trackers. Vendors offer new processes: –Through silicon Vias –Thinning of IC, sensors –3D connection within CMOS –mirco bump bonding –etc. Bonn - IZM Berlin: long term relationship –main bump bonding vendor for ATLAS Pixel –development of new pixel module concepts –started 3 years with TSV and thin chips bump bonding

Fabian Hügging – University of Bonn – February Current ATLAS Pixel Modules Material is an issue in trackers for HEP experiments for both radiation length and space issues: –In the present ATLAS pixel detector modules the FE (190µm thick) accounts for 0.26% of X 0 –Material introduced by services: wings, module flex, connectors: Using the IBL as an example (note: TSV will not be used for the IBL!): Al flex + wire bonds + pass. comp.: ~0.13%of X 0 IBL module FE-I4

Fabian Hügging – University of Bonn – February Advanced Pixel Module Concepts Power Flex Data Flex EoS FE-Chip Sensor pass. componentsTSVs tapered backside metal lines on ICs HV?  Thin chip bump bonding and Through Silicon Vias required!

Fabian Hügging – University of Bonn – February Thin chip bump bonding 1x1 FE-I3, 190µm ok 2x3 FE-I3 (FE-I4 size), 190µm not ok 2x3 FE-I3 (FE- I4 size), 300µm not sufficient Current flip chip technique: IZM solder SnAg Chip bow during flip chip –Due to CTE mismatch between Si bulk and metals –~ 1/d 3, d = chip diagonal New techniques using handle-wafers during flip chip and lift-off after flip chipping are needed –3 methods studied so far with IZM Berlin 7.4mm 11.1 mm FE-I3 20.2mm 16.8 mm FE-I4 FE-I3 ~ peak temp. of reflow process 190µm thick  0.26% X 0 Bow profile along a diagonal µm thick  ~0.5% X 0 15µm

Fabian Hügging – University of Bonn – February First investigations and problems First two methods used resp. a wax and a Brewer glue for carrier bonding Not successful –thinning ok, but chips bent up at the corners, opposite to the End Of Column region –Bump bonds do not connect in this area ATLAS pixel module with 90 µm thick FE-I2 1st method: wax open bumps at the corner of the FE 2x2 FE-I3 array = 66% FE-I4, 90 µm, on dummy sensor 2nd method: Brewer glue w/ carrier chip w/o carrier chip

Fabian Hügging – University of Bonn – February Polyimide method 90 µm Glass carrier on Si testchip before laser exposure_25x Glass carrier on Si testchip after laser exposure_25x thinning of FE wafer Mounting on glass carrier wafer using polyimide glue Bumping process on FE frontside Dicing of FE wafer and carrier wafer package FE flip chip bonding to sensor tile Laser exposure of chip backside Carrier chip detach Process steps: 2x2 FE-I2 array, 90um, on dummy sensor Cross section cut of first column  all bumps are connected!

Fabian Hügging – University of Bonn – February Results of electrical tests All bumps connected in “critical” area…..and across the chip Some disconnected bumps close to the End of Column region  Handling problems during wire bonding Normal threshold behavior = unconnected bumps Polyimide method works. Chosen thinning method for the FE- I4 thin chip modules prototyping program  FE-I4 will be 16.8 x 20.2mm 2, ~100 – 200 µm thick

Fabian Hügging – University of Bonn – February Module concepts with TSV TSV allows routing of signals on the FE backside  direct connection of service flex on FE backside (e.g. via wire bonding) –Less material: no need for wings, module flex, connectors Using the IBL as an example : ~0.13%X0 –Easy interconnection scheme 2 IZM Berlin: Straight Side Walls and Tapered Side Walls TSVs –Both working, tapered side walls TSVs faster process  ATLAS pixel module with 90 µ m thick FE-I2 and tapered TSVs with simple backside metallization FE-Chip Sensor pass. comp. TSVs backside metal lines on FE flex FE backside View from top Stave top view Single chip modules (cont…) (… from End of Stave …) bonding area actually connected flex bonding area pads

Fabian Hügging – University of Bonn – February Through Silicon Vias at IZM Thin chips are mandatory for Through Silicon Vias (TSV)! The process is a Via Last process done in two steps: –Via etching on the backside Bonding to carrier wafer (1) Thinning of the backside (2) Via etching (3) → stops at oxide layer Oxide deposition on via walls (4) Deposition of metal seed on via walls (5) Via filling (6) Structuring of the back side (7) Carrier wafer is detached using moderate heating (7-8) Via etching from the frontside (8) –In our case we just use the FE-chip as FEOL (no BEOL) and flip chip to the sensor afterwards. IZM offers two Via Last TSV processes –Straight Side Wall Vias –Tapered Side Wall Vias SiO 2 pads Si (FEOL) Si (BEOL) FE wafer cross-section (not to scale) (1) (2) (3) (4) (5)(6) (7) (8)

Fabian Hügging – University of Bonn – February Straight Side Wall TSV on Monitor Wafer Backside Redistribution with Probe pads Via Filling Si Etching Via etching though silicon wafer works well The process is rather time consuming –The via is etched and passivated in steps → Bosch process

Fabian Hügging – University of Bonn – February Si Etch on Monitor Wafer until Oxide Layer Via bottom shape optimization –Clearly defined via edges, konvex via bottom shape –Still etch diameter inhomgenities on via bottom across the wafer Left – 40µm Front side view through temporary glass carrier wafer Back side view into Si via Center – 71µmRight – 58µm

Fabian Hügging – University of Bonn – February TSV etching with Tapered Side Walls Faster process –Vias are etched in one step and after oxide is depositied Walls are not straight –Side wall angle 72° –Si thickness 77µm Max 100µm given the aspect ratio of the process Higher Si thickness possible with straight side wall TSV –Via diameter on bottom 41µm –Via diameter on top 95µm The bigger via diameter on the top is not a problem if the FE-chip is thin enough. –It normally fits in the pad dimension on the back side

Fabian Hügging – University of Bonn – February Signals Routing on Backside and Flex FEI4 Backside bonding area pads d<1500 μ m (cont…) (… from End of Stave …) bonding area actually connected Example: Single chip option

Fabian Hügging – University of Bonn – February Ongoing Tapered TSVs processing on ATLAS FE-I2 batch Tapered side walls TSV Backside redistribution Bump deposition and dicing Al pad opening by wet etching Cu electroplating – interconnection plug to Al pad BEOL SiO 2 stack etching Front side processing Back side processing Thin chip! 90µm Done Final step Process demonstrated on Monitor- and ATLAS FE-I Wafer  Prototyping of an ATLAS pixel module with 90µm thin FE-I2, Tapered TSVs, and simple backside metallization is ongoing with IZM Berlin. First samples expected in 04/2011

Fabian Hügging – University of Bonn – February D Tezzaron-Chartered Milestones of 3D electronics: –2D Chartered based on FE-I4 prototype (analog tier) in 2009 –3D Chartered-Tezzaron submitted in D back in D still to come – plan for full FE-I4 in 3D in 2012 collaboration with CPPM M5 M4 M3 M2 M1 M6 SuperContact M1 M2 M3 M4 M5 M6 SuperContact Bond Interface Tier 2- Digital Tier 1 - Analog (thinned wafer) Back Side Metal sensor Sensor layout : Anna Macchiolo, MPI Munich

Fabian Hügging – University of Bonn – February Summary Bonn contributions to WP3: –demonstrate a pixel module with FE-I3/4 in 2-3 years: Through Silicon Vias Thin FE chips backside re-routing of signals –Bonn contribution to 3D electronics: further participation in 3D Tezzaron-Chartered Consortium design of digital tier based on FE-I4 go to full 3D FE-I4 14 by 61 pixels layout of digital tier