Layout Dependence of Total Ionizing Dose Effects on 12-nm Bulk FinFET Core Digital Structures

An apparent layout dependence for total ionizing dose (TID) susceptibility in a commercial 12-nm fin-based field-effect transistor (FinFET) technology is identified. While drain current scales with the width-to-length ratio prior to irradiation, after exposure, layout location becomes the dominant factor in TID response. To examine this effect, devices across multiple chip locations were biased and irradiated. All structures exhibited the same layout dependence regardless of the position on the test chip. In addition, TID responses were examined using both X-rays and γ-ray sources, and it was found that this effect did not depend on the type of radiation source. As a method of examining possible reasons of this effect, TCAD simulations were performed to evaluate the impact of sub-fin doping on the TID response of these structures. It was determined that small deviations of the sub-fin doping concentration could result in large changes in the drain current after the TID exposure. Hence, the overall TID response of these structures may be heavily dependent on the doping level in the sub-fin region.