| Summary: | In order to continue scaling to the deep sub-micron region, device manufacturers have replaced polysilicon gates with metal gate stacks and typically use metal clad or metal silicide source/drain regions. The metals used in modern processes tend to be considerably heavier than silicon, leading to a high-Z/low-Z interface in modern devices. The secondary electron environment at a high-Z/low-Z interface has already been shown to be significantly perturbed from equilibrium under x-ray and gamma-ray irradiation. However, the secondary electron environment at a high-Z/low-Z interface under ion irradiation has not previously been explored. This is significant to radiation effects analysis, because a departure from equilibrium limits the effectiveness of conventional analysis methods based on linear energy transfer (LET). This work utilizes the MRED and PENELOPE 2008 Monte Carlo tools to explore energy deposition due to direct ionization by ions in low-Z sensitive volumes near high-Z material, and it is concluded that the high-Z material does significantly perturb the energy deposition from the equilibrium case. MRED and PENELOPE 2008 are also used to explore the impact of shrinking sensitive volume sizes on energy deposition distributions. As sensitive volumes decrease in size, the variance in the energy deposited due to direct ionization by ions increases. It is shown that due to large variance in the energy deposition distribution, direct ionization by light ions which would not be expected to contribute to error rates on an LET basis can significantly impact error rates in a 22nm SOI SRAM technology.
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