Semiconductor device and methods of formation

Some implementations described herein provide a semiconductor device and methods of formation. The semiconductor device includes a transistor structure that is electrically connected to a metal layer. Described techniques include forming an interconnect structure that electrically connects the metal layer to a backside power rail structure. The techniques include forming a first portion of the interconnect structure using a layer of silicon germanium as an etch stop and, after removal of the layer of the silicon germanium, forming a second portion of the interconnect structure.