Alpha particle tracks in silicon and their effect on dynamic MOS RAM reliability

Recent investigations have found low levels of alpha radiation (< .1 counts/cm²-hour) emitted from the immediate chip environment to be responsible for soft errors in 16K MOS dynamic RAMs. We have investigated this problem in two related studies. First, we review the interaction of alpha particles with the Si lattice and present range-energy and specific ionization data. The collection dynamics of the charge track and the influence of small, built-in potentials are identified. Further, design curves are presented to allow prediction of the collected charge at shallow n⁺p functions as a incident particle energy, angle and available collection time. Second, we review the operation of current memory devices and show how soft failures in different parts of the circuitry can be identified. The experimental dependence of soft error rate on incident particle energy and angle is also shown. Finally, we propose a simple accelerated test to evaluate device susceptibility to this failure mode.