Patent ID: 8163593

Claim:
A method for forming a switchable semiconductor element, the method comprising: forming a pillar having a width and comprising a conductive or semiconductor material, wherein a first dielectric fill material surrounds the pillar and has a fill top surface, wherein the pillar has a pillar top surface, wherein the pillar top surface is recessed relative to the fill top surface, and wherein a recess volume has sidewalls, a width substantially equal to the width of the pillar and occupies space between the fill top surface and the pillar top surface; forming a layer of a conformal dielectric material on the fill top surface, the recess volume sidewalls, and the pillar top surface; removing portions of the conformal dielectric layer from the fill top surface and the pillar top surface by anisotropic etch wherein a spacer formed of the conformal dielectric material remains on the pillar top surface and against a sidewall of the recess volume, defining a reduced recess volume having a width less than the width of the pillar; depositing a phase-change material, wherein a bottom portion of the phase-change material fills the reduced recess volume and has a width less than the width of the pillar, and such that remaining portions of the spacer not on the pillar top surface or against a sidewall of the recess volume are surrounded by and in direct physical contact with the phase-change material; surrounding a top portion of the phase-change material with a second dielectric fill material, the top portion of the phase-change material over and in direct physical contact with the bottom portion of the phase-change material and having a width substantially equal to the width of the pillar, but misaligned with the pillar such that a first amount of the top portion of the phase-change material would be to one side of a vertical line bisecting the pillar and a second amount of the to portion of the phase-change material, different than the first amount, would be to the other side of the line, where the vertical line extends from a bottom of the pillar up to and through the pillar to surface, a top surface of the second dielectric fill material substantially flush with a top surface of the top portion of the phase-change material or a top surface of a CMP stop layer if the CMP stop layer is formed over the phase-change material, but the second dielectric fill material not covering the top surface of the top portion of the phase-change material, or the top surface of the CMP stop layer if the CMP stop layer is included, and forming a top conductor over the top surface of the top portion of the phase-change material, or the top surface of the CMP stop layer if the CMP stop layer is included, such that a width of the top conductor is substantially equal to the width of the pillar and a bottom surface of the top conductor is substantially flush with the top surface of the second dielectric fill material.