High-field/current stress and breakdown properties of Ag(gate)-Hf:Ta2O5/SiOxNy-Si(substrate) structures

In this work high-field/current stress and breakdown properties of Ag gated MIS structures containing thin films of Hf:Ta₂O₅/SiO_xN_y insulating stacks on Si with total thickness of 8 nm were studied. Two dominant effects are observed during the constant current stress of Ag-Hf:Ta₂O₅/SiO_xN_y-Si structures. The first one is reversible trapping of negative charges on preexisting traps. The second one is the irreversible wearout of the interfacial SiO_xN_y layer, leading to a substantial increase of leakage currents. Breakdown distributions of TDDB events at CVS for Ag-Hf:Ta₂O₅/SiO_xN_y-Si structures exhibit important similarities with the distribution obtained in the case of Al-Hf:Ta₂O₅/SiO₂-Si structures. t_bd values at 63.2% failure are substantially higher in the case of Ag-Hf:Ta₂O₅/SiO_xN_y-Si structures then in the case of Al-Hf:Ta₂O₅/SiO₂-Si structures. Therefore, the nitridation of the Si substrate in addition to the use of Ag gate improves breakdown properties of Hf:Ta₂O₅ based MIS structures.