Patent ID: 7682868

Claim:
A method for creating a keyhole opening during the manufacture of a memory cell, comprising: forming a base layer comprising a bottom electrode; selecting a material for a first layer that increases its volume when subjected to a chosen process; selecting a material for a second layer that does not increase its volume when subjected to the chosen process; forming an upper layer on the base layer, the upper layer forming step comprising forming the second layer over the base layer and the first layer over the second layer; forming an opening through the upper layer to expose a surface of the base layer and to create a first memory cell subassembly, the opening comprising a first, upper opening segment formed within the first layer and a second opening segment formed within the second layer, the first and second opening segments having first and second widths; and subjecting the first memory cell subassembly to the chosen process thereby increasing the volume of the first layer and creating an overhanging portion extending into the opening, the overhanging portion decreasing the size of the first opening segment to create a decreased size, keyhole opening, the first opening segment having a decreased first width, the decreased first width being shorter than the second width by an overhang dimension, the overhang dimension being no more than 10% of the second width.