Integrated chips and methods of forming the same include forming a stack of layers, including a device stack above a first sacrificial layer, above a substrate. The first sacrificial layer is replaced with a first etch stop layer. The substrate is removed, exposing a substrate-side of the stack of layers. The substrate-side of the stack of layers is etched to form a trench, stopping on the first etch stop layer. A conductive line is formed in the trench.