Phase-change memory and method of forming same

A device comprising:

• a substrate;
• a first dielectric layer over the substrate;
• a first conductive feature within the first dielectric layer;
• a second dielectric layer over the first conductive feature and the first dielectric layer;
• a bottom electrode within the second dielectric layer, wherein the bottom electrode is electrically connected to the first conductive feature, and wherein a top surface of the bottom electrode is below a top surface of the second dielectric layer;
• a phase-change layer over the bottom electrode, the phase-change layer comprising:
• a first portion extending into the bottom electrode, wherein the first portion has a convex bottom surface;
• and
• a second portion over the first portion and the second dielectric layer, wherein the second portion is wider than the first portion;
• a top electrode over the phase-change layer, wherein the top electrode and the second portion of the phase-change layer have a same width;
• a third dielectric layer over the second dielectric layer, wherein the third dielectric layer is in physical contact with sidewalls of the phase-change layer and sidewalls of the top electrode;
• a fourth dielectric layer over the third dielectric layer and the top electrode;
• and
• a second conductive feature within the fourth dielectric layer, wherein the second conductive feature is electrically connected to the top electrode.

A method comprising:

• forming a first dielectric layer over a substrate;
• forming a first conductive feature in the first dielectric layer;
• forming a second dielectric layer over the first dielectric layer and the first conductive feature;
• forming an opening in the second dielectric layer, wherein the opening exposes a portion of a top surface of the first conductive feature;
• forming spacers on sidewalls of the opening;
• filling the opening with a first conductive material to form a bottom electrode in the opening;
• recessing the bottom electrode below a top surface of the second dielectric layer to form a recess, wherein the recess extends into the bottom electrode, and wherein a width of the recess decreases as the recess extends into the bottom electrode toward the substrate;
• depositing a phase-change material in the recess and over the second dielectric layer;
• depositing a second conductive material over the phase-change material;
• and
• performing a patterning process to remove portions of the phase-change material and the second conductive material and to expose the top surface of the second dielectric layer, wherein a remaining portion of the phase-change material forms a phase-change layer, and wherein a remaining portion of the second conductive material forms a top electrode.