Reliability in VHSIC-level 1.25 μm radiation-hard CMOS IC devices

An experiment was performed on 1.25 μm radiation-hard, very high-speed integrated circuit (VHSIC)-level 2 K×8 static random access memory (SRAM) devices with the objective of investigating the relationship between the SRAM reliability and the die yield at wafer probe. The SRAMs were product-level devices that were included as part of a test chip, the yield/circuit/reliability analysis tool (YCRAT). There were 54 YCRAT sites on each four-inch wafer. After all wafer-level tests, 423 SRAMs were packaged in 24-pin flatpacks and subjected to a 1000 h, 125°C life test. 183 of the parts were from wafers judged to be bad, i.e. for some reason the SRAM dice or test structures did not pass wafer-level screening, and 240 parts were from wafers judged to be good, i.e. they passed wafer-level screening. The results of the test showed that wafers exhibiting metal/dielectric problems had poor yields through screening and somewhat worse reliability