Hot-Carrier Damage in N-Channel EDMOS Used in Single Photon Avalanche Diode Cell through Quasi-Static Modeling

A single photon avalanche diode (SPAD) cell using N-channel extended-drain metal oxide semiconductor (N-EDMOS) is tested for its hot-carrier damage (HCD) resistance. The stressing gate-voltage (V_GS) dependence is compared to hot-hole (HH) injection, positive bias temperature (PBT) instability and off-mode (V_GS = 0). The goal was to check an accurate device lifetime extraction using accelerated DC to AC stressing by applying the quasi-static (QS) lifetime technique. N-EDMOS device is devoted to 3D bonding with CMOS imagers obtained by an optimized process with an effective gate-length L_eff = 0.25 µm and a SiO₂ gate-oxide thickness T_ox = 5 nm. The operating frequency is 10 MHz at maximum supply voltage V_DDmax = 5.5 V. TCAD simulations are used to determine the real voltage and timing configurations for the device in a mixed structure of the SPAD cell. AC device lifetime is obtained using worst-case DC accelerating degradation, which is transferred by QS technique to the AC waveforms applied to N-EDMOS device. This allows us to accurately obtain the AC device lifetime as a function of the delay and load for a fixed pulse shape. It shows the predominance of the high energy hot-carriers involved in the first substrate current peak during transients.