Study of FSG/SiO2 double interlayer conditions to prevent Al wiring delamination for sub-0.18-μm device integration

A double interlayer of high-density plasma fluorinated silica glass (FSG) and SiO₂ has been developed to control fluorine instability for sub-0.18-μm devices. However, the interlayer conditions need further study for robust integration. The authors investigate the optimum conditions to prevent Al wiring delamination. The correlation between the incidence of delamination and F concentration at Ti-SiO₂ was demonstrated by the three-dimensional mapping of interfacial F concentrations with various thicknesses of SiO₂ and F contents in FSG. Detailed analysis of the Ti-SiO₂ interface reveals that the anomalous growth of the interface layer by absorbing F atoms into the Ti layer causes delamination. The properties of SiO₂, such as the compressive stress and the density of oxygen deficiency, were adjusted to reduce F diffusion. In addition, the thickness was controlled to above 4500 Å to suppress F accumulation at Ti-SiO₂ to within the permissible level. These conditions resulted in preventing delamination and obtaining integration reliability without increasing the capacitance between adjacent metal lines.