Total dose induced hole trapping in trench oxides

Ionization effects in polysilicon-filled trenches used for component isolation in an advanced commercial bipolar technology are examined. Contact to the trench polysilicon was used to sweep the subthreshold characteristics of a parasitic trench field-effect transistor formed by the trench and two buried layers. The subthreshold-charge-separation technique was used to analyze the buildup of trapped holes and interface states. For typical microcircuit layouts, the irradiation data at a total dose of greater than 1 Mrad(SIO₂ ) showed identical saturation of the threshold voltage shift and minimal interface-stage buildup regardless of the source and drain irradiation bias conditions. However, the radiation responses for the various irradiation bias conditions prior to saturation were significantly different. The complex irradiation response and implications for the use of trenched bipolar microcircuits in radiation environments are discussed