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Background Material

Background Material. Top Metal Layer (Metal 3 in RT54SX32S, Metal 4 in RT54SX72S). Barrier Metal Layer. Amorphous Silicon. Barrier Metal Layer. Second Metal Layer (Metal 2 in RT54SX32S, Metal 3 in RT54SX72S). What is an Antifuse?. Antifuses start life as capacitors

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Background Material

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  1. Background Material

  2. Top Metal Layer (Metal 3 in RT54SX32S, Metal 4 in RT54SX72S) Barrier Metal Layer Amorphous Silicon Barrier Metal Layer Second Metal Layer (Metal 2 in RT54SX32S, Metal 3 in RT54SX72S) What is an Antifuse? • Antifuses start life as capacitors • Layer of amorphous silicon between layers of titanium nitride barrier metal

  3. Conducting Filament Programming an Antifuse • Programming • High voltage causes the amorphous silicon to break down • As conduction begins to occur, localized heating causes the amorphous silicon and barrier metal to fuse, forming a conducting filament • Careful control of voltage and current during programming pulses ensures tight distribution of programmed antifuse resistance

  4. About Programmed Antifuse Failures • 11 Confirmed failures. Other cases are suspected. • "Cluster of failures" - small number of users reporting a small percentage of failures on 0.25µm MEC SX-A/RTSX-S devices • Failures are occurring in a “dirty” or "out-of-spec" environment • Data strongly suggests early failures under "dirty" electrical environment • Experiments ongoing: • Determine reliability under “in-spec” conditions with respect to I/O and VCCA noise • Determine sensitivity to “out-of-spec” conditions, with respect to I/O and VCCA noise.

  5. Usage History • More than 1.2 Million commercial 0.25 µm MEC SX-A units shipped • Four aerospace customers with confirmed failures report an approximate failure rate of 2%-7% • These are from a small sample of shipped units • Actel does not see an overall 2% functional failure return rate • Actel Failure Analysis group reports 58 units of SX-A products submitted for analysis in the last 2 years • One of these 58 units were traced to antifuse damage • Breakdown of other failure causes • Design Timing Fault • EOS of the non-antifuse nature (e.g., clock pin EOS damage, ref IAT) • ESD

  6. Actel Published MEC 0.25µm Reliability Data • High Temperature Operating Life(HTOL): • 1 antifuse failure out of 805 devices • Equivalent 601,440 device hours • Failure occurred after 184 hrs (1st pull point) • The burnin system induced out of specification spikes of 9V on VCCA. This sequence has been since corrected. • Low Temperature Operating Life(LTOL): • 0 failures out of 334 devices • Equivalent 309,000 device hours

  7. EOS Model Reliability Data • Clean Burn-in (no VCCA spikes observed >3V) • 0/77 failures for 168 hrs HTOL at 150°C • No I/Os switching • Special burn-in stress: antifuses are stressed with operating current levels using VPP • 0/100 failures at 168 hrs HTOL. Subsequent additional 168 hours in LTOL had zero failures. • Contractor X application • Contractor X found zero failures in their applications. Typical designs were 33MHz, one at 120MHz. • Contractor X measured I/O undershoot of –1.8V. But only 1 or 2 pins switching. • On the PCI bus with 33 Simultaneously Switching Outputs, care was taken to limit the undershoot to less than 500 mV. • The above results support the Simultaneously Switching Undershoot model

  8. Early failure under out of specification conditions • Actel data and userdata indicates an early failure problem under out of specification conditions: • Actel experiments: • 10/246 units failed at 168 hours HTOL, LTOL “dirty” burn-in (out of spec -1.1V undershoots on I/Os) • First pull point for both HTOL and LTOL (first observation point) was at 168 hours • 0/207 fail at 500 hours cumulative HTOL, LTOL (same “dirty” burn-in) • 29 units held back due to burnin board capacity issues. • Single failure reported in Actel published reliability data was at first observation (184 hrs) • Extended burn-in • 0/8 RT54SX32S failures with 5000 hrs burn-in at 125°C • 0/8 RT54SX32S failures with 2000 hrs burn-in at 150°C • 0/22 RT54SX32S failures with 2000 hrs burn-in at 125°C

  9. Early failure under out of specification conditions • Sanitized Actel Customer data • Contractor A • 3/101 failed at first observation on ATE (unconfirmed failures) • Contractor A has no flight box failures. More than 3500 device hours on system. Some units >400hrs. (reported on 2/13/04) • Contractor B • Measured I/O undershoots exceed Actel maximum operating conditions. • 8 failures reported out of 100+ devices. Four parts confirmed antifuse failures. One failure could not be duplicated at Actel. One part was not returned to Actel. FA ongoing on other two units. • 1 failure was immediate. 6 failures less than 168 hrs. 1 failures at 0-400hrs (first observation) • No more failures seen. Contractor B has approx. 63,000 failure free hours (reported Dec 16, 2003). 18 parts >2000 hrs. 18 parts >1000 hrs. 18 parts >500 hrs. • Contractor C • Programmer with expired calibration, intermittent fan found. 1/5 device failure rate, of every 5 units programmed one failed • 10 failures reported out of 100+ devices. All in one design. All at first observation (< 1hr). Antifuse failure confirmed on 1 device. • No more failures seen after new programmer (replace bad fan). More than 100,000 device hrs (reported 2/13/04). Some parts more than 1year testing.

  10. Early Failure under out of specification conditions • Sanitized Actel Customer data (cont'd) • Contractor D • Awaiting information relating to device operating conditions • 2/6 failed at device level testing at time zero. Remaining 4 units pass on board level. • Contractor E • Industry review of post-programming burn-in setup identified critical design deficiencies • no bypass capacitors • clock signal termination not employed • 1/59 failed from 96 hours in post-programming burn-in test. No failures seen since.

  11. Field failures Hundreds of units zero failures

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