A gradual change in thermal oxide surface state from hydrophilic to
hydrophobic was observed with time -delay in a clean room environment.
Surface quality and reflectivity for the Al/Ti metal layers showed a strong
dependency on the oxide surface state. From the hydrophilic oxide substrate,
a lower (002) Ti preferred orientation was obtained than from hydrophobic
ones. This resulted in a degraded (111) Al preferred orientation and rough
metal surface. The RF-etch process increased the smoothness and hydrophobic
surface property for the inter -metal dielectric (IMD) oxides, and therefore
greatly improved Al/Ti surface quality. When conventional CMOS double layer
metal interconnection process is performed, metal inter-line bridge yield
was strongly affected by the surface state of substrate oxides.