Electrical test structures for verifying continuity of ultra-thin insulating and conducting films

In this work, electrical characterization on insulating aluminium nitride (AlN) and conducting tungsten (W) films was performed using dedicated test structures, in order to determine the thickness at which the films reached continuity. A discontinuous-to-continuous transformation of the AlN layer (occurring around 11 nm) resulted in a transition from ohmic to non-ohmic current conduction, in addition to drastically reduced current density levels. For similar transformation of the W layer (occurring between 2–3 nm) the reverse transition was observed, which was accompanied by a rapid convergence of the film resistivity to the bulk value. The electrical analysis of film continuity was complemented optically by in-situ monitoring of the film growth and its closure, with the spectroscopic ellipsometry (SE) technique.