Soft errors induced by alpha particles

Abstract

Soft errors induced by alpha particles can be a reliability concern for microelectronics, especially semiconductor memory devices packaged in ceramic. In dynamic random-access memory devices (DRAM), the data are stored as the presence or absence of minority carrier charges on storage capacitors. For example, in n-channel MOS memory devices, the charge carriers are electrons and the capacitors are potential wells in the p-type silicon. Alpha particles emitted from trace levels of uranium and thorium in the packaging materials can penetrate the surface of the semiconductor die. As the alpha particle passes through the semiconductor device, electrons an dislodged from the crystal lattice sites along the track of the alpha particle. If the total number of generated electrons collected by an empty storage well exceeds the number of electrons that differentiates between a 1 and a 0, the collected electron charge can flip a 1 to a 0 generating a soft error in the memory device. The trend toward increased chip density, smaller device dimensions, and lower voltages further increases the susceptibility of DRAM to soft errors. The susceptibility of DRAM to soft errors is typically measured by accelerated tests or real-time SER tests, each of which have strengths and weaknesses. Knowledge of the factors which lead to soft errors can be used to improve reliability in DRAM by using a physics-of-failure approach to monitor variables in the manufacturing process resulting in building reliability into the manufacturing process.