Conduction mechanisms in Ta2O5/SiO2 and Ta2O5/Si3N4 stacked structures on Si

In this paper, the conduction mechanisms in Ta2O5/SiO2 and Ta2O5/Si3N4 stacked structures on Si are investigated both experimentally and theoretically. Amorphous Ta2O5 films (20-60 nm thick) were deposited by low pressure chemical vapor deposition or electron cyclotron resonance plasma enhanced chemical vapor deposition and some layers were annealed for crystallization at 800 degrees C in O-2. The Si3N4 layers were formed by plasma nitruration or low pressure chemical vapor deposition. The SiO2 films studied were intentionally obtained by dry oxidation of the Si substrates, or as a result of the Ta2O5 deposition process (due to the oxidizing atmosphere), or of the Ta2O5 postdeposition annealing treatment under O-2. The conduction mechanisms were identified by comparing the experimental current-voltage traces to the theoretical curves calculated in steady-state regime by using the Kirchhoff voltage law and the current continuity equation. In amorphous Ta2O5, the conduction mechanisms identified are the electronic hopping process and the Poole-Frenkel effect. For the corresponding interfacial SiO2 or Si3N4 films, the current transport is governed by tunneling processes or trap-modulated mechanisms, depending on the nature and deposition method of these interfacial layers. In crystalline Ta2O5 on SiO2 capacitors, no combination of basic conduction mechanisms can correctly fit the experimental curves, certainly due to the complex structure of crystalline Ta2O5 (high inhomogeneity and cracks). (C) 1999 American Institute of Physics. [S0021-8979(99)03713-5].