Comparison of single event phenomena for front/back irradiations

For devices irradiated from the front and the back, where ions have the same LET in the sensitive volumes, the SEU sensitivities and charge collection spectra are different. A specific test setup has been developed to make precise measurements of both collected charge and SEU in CMOS SRAMs. We present a set of new data and discuss the possible experimental artifacts that could affect these measurements. In all the cases, the device is more sensitive when irradiated from the back than from the front. This phenomenon seems related to energy transfer mechanisms from the ion to the material target, with secondary particles from both electronic and nuclear reactions being forward emitted. This effect may influence net sensitivity of scaled down devices, with shallow sensitive layers, and heavy metal interconnects.