A method for forming a through silicon via (TSV) in a substrate may include forming a dielectric layer on the substrate; forming an opening through the dielectric layer and into the substrate using a single mask over the dielectric layer; expanding the opening in the dielectric layer, undercutting the single mask, to form an expanded upper portion; removing the single mask; and filling the opening, including the expanded upper portion, with a conductor. A resulting structure may include a substrate; a dielectric layer over the substrate; and a self-aligned through silicon via (TSV) extending through the dielectric layer and the substrate.