In described examples of an integrated circuit (IC) there is a substrate of semiconductor material having a first region with a first transistor formed therein and a second region with a second transistor formed therein. An isolation trench extends through the substrate and separates the first region of the substrate from the second region of the substrate. An interconnect region having layers of dielectric is disposed on a top surface of the substrate. A dielectric polymer is disposed in the isolation trench and in a layer over the backside surface of the substrate. An edge of the polymer layer is separated from the perimeter edge of the substrate by a space.