Trimming intermediate carbon layer to achieve nanometer scale patterning

A method comprising:

• providing a structure as a stack comprising a first metal layer, a first carbon layer, a phase change material layer, a second carbon layer, and a second metal layer, the stack extending in a first dimension;
• applying hydrogen plasma to laterally etch the second carbon layer to a width in a second dimension, the hydrogen plasma being applied with substantially no bias power and to avoid etching the first and second metal layers and the phase change material layer, the second dimension being perpendicular to the first dimension;
• and
• etching, using the second carbon layer having the width as a pattern, the phase change material layer and the first carbon layer to the width of the second carbon layer.

A method comprising:

• providing a structure as a stack comprising a first metal layer, a first carbon layer, a phase change material layer, a second carbon layer, and a second metal layer, the stack extending in a first dimension, wherein the second carbon layer is an intermediate layer in the stack and is above the phase change material layer and the first carbon layer;
• etching the first carbon layer to a first width in a second dimension, the second dimension being perpendicular to the first dimension;
• applying hydrogen plasma to laterally etch the second carbon layer to a second width in the second dimension, the hydrogen plasma being applied with substantially no bias power and to avoid etching the first and second metal layers and the phase change material layer, wherein the phase change material layer and the first carbon layer comprise a different width greater than the first width;
• and
• etching, using the second carbon layer having the second width as a pattern, the phase change material layer and the first carbon layer to the second width of the second carbon layer.