Reflow of AlCu into Vias during CVD TiN barrier deposition

A novel Via failure mechanism for a 0.35 /spl mu/m technology is analyzed in this work. Failure analysis of the failed Vias reveal an anomalous layer at the bottom of the Via hole. Electron diffraction spectra (EDS) of this layer confirms that the main component is AlCu with clusters of titanium aluminide; fluorine is also detected. The root cause of this failure was AlCu extrusion into the Via during the preheat step prior to CVD TiN deposition. It was also found that an improved Ti barrier step coverage can reduce the occurrence of Al extrusions.