Thermal stability of Ta2O5 in metal-oxide-metal capacitor structures

Using x-ray photoelectron spectroscopy and Rutherford backscattering spectr ometry, we have studied structures used in metal-oxide-metal capacitors inc luding Ta2O5/TiN/Ti, Ta2O5/Ti, Ta2O5/TaN/Ti, Ta2O5/WN/Ti, and Ta2O5/M, wher e M=Ta, Pt, W, Al, and Si. We find that Ti and Al are able to reduce the Ta 2O5 to Ta, forming oxides of Ti and Al, respectively. The diffusion barrier s TiN, TaN, and WN hamper the diffusion of oxygen and therefore postpone th e reduction of Ta2O5 to higher temperatures. As judged by the temperatures at which the reduction of Ta2O5 occurs, TaN and WN are more effective oxyge n-diffusion barriers than TiN. We observe no oxygen remaining in the diffus ion barrier when a Ti layer is present underneath. We observe no reduction of Ta2O5 when M=Pt, W, or Si. (c) 1999 American Institute of Physics. [S000 3-6951(99)01324-8].