a key hole structure and method for forming a key hole structure to form a pore in a memory cell . the method includes forming a first dielectric layer on a semiconductor substrate having an electrode formed therein , forming an isolation layer on the first dielectric layer , forming a second dielectric layer on the isolation layer , and forming a planarization stop layer on the second dielectric layer . the method further includes forming a via to extend to the first dielectric layer and recessing the isolation layer and the stop layer with respect to the second dielectric layer , depositing a conformal film within via and over the stop layer , forming a key hole within the conformal film at a center region of the via such that a tip of the key hole is disposed at an upper surface of the second dielectric layer , and planarizing the conformal film to the stop layer .