ON THE MICROSTRUCTURE PROPERTY RELATIONSHIP OF W-TI-(N) DIFFUSION-BARRIERS

In advanced silicon technology, tungsten-rich W-Ti alloy films are frequently used as diffusion barriers and etch-stop layers in combination with aluminium-based interconnections. We have studied both microstructure and properties of magnetron sputtered W80Ti20 (atomic per cent) alloy films with and without nitrogen incorporated in the film structure. The efficiency of these films as a barrier layer has been studied by the interaction between interconnecting Al-(alloy) and W-Ti-(N) using the following samples: Al-(Cu,Si)/W-Ti-(N)/SiO2/Si. The barrier films have been characterized with the help of cross-sectional transmission electron microscopy, electron diffraction, electrical resistivity probing Rutherford backscattering spectrometry and X-ray diffraction. The W80Ti20 films exhibit a columnar microstructure. As the recrystallization temperature of these (refractory) barrier metals is far above the anneal temperature of 450-degrees-C, the columnar growth morphology is preserved on annealing. The intercolumnar material (or low density network) provides favourite sites for vacancy condensation and forms short-circuit diffusion paths in a direction perpendicular to the plane of the films. Such W80Ti20 films therefore behave as rather poor diffusion barriers. As shown in the literature by several researchers, both the incorporation of nitrogen into the structure of W-Ti films and the application of a thin oxide film at the barrier-interconnect interface may improve the barrier properties considerably. The present investigations of the film properties resulted in a better understanding of the barrier function of both binary W-Ti and ternary W-Ti-N alloy films.