FIG. 6A is a vertical cross-sectional view of the interconnect structure after the processing steps illustrated in FIGS. 3A-3E, (i.e., after metal layer 10 z and sacrificial layer 18 z have been deposited on substrate 14 z and patterned, and look material 26 z has been deposited to cover substrate 14 z and gap fill metal layer 10 z and sacrificial layer 18 z).