Methods of etching a semiconductor structure using ion milling with a variable-position endpoint detector to unlayer multiple interconnect layers, including low-k dielectric films. The ion milling process is controlled for each material type to maintain a planar surface with minimal damage to the exposed materials. In so doing, an ion beam mills a first layer and detects an endpoint thereof using an optical detector positioned within the ion beam adjacent the first layer to expose a second layer of low-k dielectric film. Once the low-k dielectric film is exposed, a portion of the low-k dielectric film may be removed to provide spaces therein, which are backfilled with a material and polished to remove the backfill material and a layer of the multiple interconnect metal layers. Still further, the exposed low-k dielectric film may then be removed, and the exposed metal vias polished.