A method of making a through wafer via. The method includes: forming a trench in a semiconductor substrate, the trench open to a top surface of the substrate; forming a polysilicon layer on sidewalls and a bottom of the trench; oxidizing the polysilicon layer to convert the polysilicon layer to a silicon oxide layer on the sidewalls and bottom of the trench, the silicon oxide layer not filling the trench; filling remaining space in the trench with an electrical conductor; and thinning the substrate from a bottom surface of the substrate and removing the silicon oxide layer from the bottom of the trench. The method may further include forming a metal layer on the silicon oxide layer before filling the trench.