Picosecond laser microscopy for investigating localization of alpha particle induced soft error rates in deep submicron CMOS VLSI

Alpha-particle induced soft error rates (SER) due to naturally occurring radioisotopes in process metals are a serious reliability issue for deep-submicron CMOS technologies where continued scaling reduces the critical charge required to upset sensitive drains, in, for example, the off MOSET of an SRAM cell. With increased scaling the subsequent diffusion of charge from an ion strike covers a larger number of cells leading to increased multiple bit upset (MBU) rates in highly efficient designs. The amount of charge shared amongst neighboring nodes is critical in determining the overall SER. Charge sharing proceeds via two mechanisms: diffusion of carriers from the alpha strike to charge collecting nodes which depends on minority carrier diffusivity and the induction of charge on capacitive coupled nodes (V. Ferlet-Cavrois et al., 2003) as described by Ramo\´s theorem (S. Ramo, 1939). Results indicate the first mechanism to be dominant in terms of the quantity of charge collected which can lead to SER. Picosecond lasers have been widely used in simulating the energy-loss of MeV ions to better understand radiation phenomena by providing high-fidelity spatio-temporal information on charge collection processes (D. McMorrow et al., 1992), (J.S. Melinger et al., 1994). In this paper we describe the newly completed JPL picosecond laser microprobe for investigating SER and use it to investigate the temperature dependence of charge collection/sharing in a TSMC 0.18 mum CMOS "ring-like" test structure specifically designed for this task.