MICROSTRUCTURE OF TA2O5 FILMS GROWN BY THE ANODIZATION OF TANX

In this letter we show the microstructure of Ta2O5 grown by anodizatio n of TaNx. Transmission electron microscopy images show an amorphous b ilayer microstructure in the direction of growth. The bottom layer (th at closest to the Si substrate) is characterized by small (<100 Angstr om) nitrogen-rich inclusions embedded in a Ta2O5-matrix. The top layer is amorphous Ta2O5. It was found that the volume fraction of the nitr ogen-rich inclusions increased with increasing at.% N and that the ave rage sizes of the inclusions increased Linearly with increasing at.% N of the as-deposited TaN, films. The decrease in dielectric constant o f these films is explained by the increase in volume fraction of the n itrogen-rich inclusions. The interface between the TaNx and the Ta2O5 was found to be quite sharp, which may account for the high breakdown voltages of capacitors made from this growth process. (C) 1998 Elsevie r Science S.A. All rights reserved.