Kinetic Analysis of X-Ray Irradiation Induced Static Refresh Failure Mechanism in DRAM

DRAM products are susceptible to low-dose X-ray irradiation with levels as low as 120 Rad(Si), much lower than previously reported values related to total ionizing dose (TID). A large variance in this susceptibility was observed among DRAM vendors. The key parameter affected by X-ray irradiation was static refresh, where the damage manifested as an increase in junction leakage of the storage node cell. Both junction leakage and gate-induced drain leakage currents (GIDL) were characterized, and results indicated that junction leakage was the dominant mechanism in static refresh (tref) degradation. The static refresh of both the extrinsic and intrinsic bit populations were affected by the low-dose ionizing radiation. However, in typical manufacturing X-ray inspection procedures, the tail bits can fall out of spec conditions and render the device a failure. Thermal annealing did lead to some recovery in tref; however, a complete recovery was not observed, even at high temperatures that may not be practical for components.