INTERMIXING AT THE TANTALUM OXIDE SILICON INTERFACE IN GATE DIELECTRIC STRUCTURES/

Metal oxides with high dielectric constants have the potential to exte nd scaling of transistor gate capacitance beyond that of ultrathin sil icon dioxide. However, during deposition of most metal oxides on silic on, an interfacial region of SiOx can form that limits the specific ca pacitance of the gate structure. We have examined the composition of t his layer using high-resolution depth profiling of medium ion energy s cattering combined with infrared spectroscopy and transmission electro n microscopy. We find that the interfacial region is not pure SiO2, bu t is a complex depth-dependent ternary oxide of Si-Ta-x-O-y with a die lectric constant at least twice that of pure SiO2 as inferred from ele ctrical measurements. High-temperature annealing crystallizes the Ta2O 5 film and converts the composite oxide to a more pure SiO2 layer with a lower capacitance density. Using low postanneal temperatures, a sta ble composite oxide structure can be obtained with good electrical pro perties and an effective SiO2 thickness of less than 2 nm with similar to 10 nm of composite oxide. (C) 1998 American Institute of Physics.