Real impact of dynamic operation stress during burn-in on DRAM retention time

The burn-in (BI) mechanism in connection with the dynamic operation stress (DOS) has been investigated to examine the real impact on dynamic random access memory (DRAM) reliablity. In this paper, the wafer burn-in (WBI) method with equivalent screening efficiency as the package burn-in (PBI) is implemented by employing DOS. It is found that retention time degradation by BI stress in DRAM with potentially lethal defects is mainly attributed to DOS-induced hot carrier (HC) degradation of DRAM cell. Hot electrons injection in Si-SiO₂ interface brings about lots of interfacial states as well as the electrical field modification at the gate-overlapped region, causing the degradation of retention time. This is clarified by an anomalous threshold voltage (V_T) shift, and an increase of gate-induced drain leakage (GIDL) after dc HC stress having the identical stress voltage as DOS. Moreover, it is proved that a WBI procedure with the relevant DOS can screen out weak bits effectively, compared to that with only static stress.