Collection of charge from alpha-particle tracks in silicon devices

Experimentally and by computer simulation, we have investigated the collection process of alpha-particle-generated charge in silicon devices. We studied the total charge collected and the transient characteristics of collection for various structures. Analytic results indicate that a strong drift field extends far beyond the original depletion layer, and funnels a large number of carriers into the struck node. This field-funneling component of charge collection is a strong function of substrate resistivity and bias voltage. It is relatively independent of the area of the struck device. The collection is less efficient for a small capacitance node. The funneling also occurred with a time delay when an alpha particle missed the field region by a short distance. Devices on an n-type substrate were also studied. They exhibit a similar funneling effect as the p-type substrate. The agreement between measurement and simulation is excellent. The impact on future VLSI design is discussed.