Backside source/drain contacts and methods of making same

A method comprising:

• forming a device layer over a substrate, the device layer comprising an upper transistor that is vertically stacked with a lower transistor;
• planarizing the substrate to expose a first material of the lower transistor and a second material of the lower transistor, wherein the first material and the second material have different surface energies;
• after planarizing the substrate, depositing a directed self assembly (DSA) material over the device layer, the DSA material comprising polystyrene-block-polymethyl methacrylate (PS-b-PMMA);
• performing an annealing process on the DSA material to define a polystyrene (PS) block overlapping the first material and a polymethyl methacrylate (PMMA) block overlapping the second material;
• and
• replacing the PS block with a dielectric material and the PMMA block with a conductive material.

A device comprising:

• a first nanostructure extending to a first source/drain region;
• a second nanostructure extending to a second source/drain region, wherein the second nanostructure overlaps the first nanostructure, and the second source/drain region overlaps the first source/drain region;
• a first gate electrode around the first nanostructure;
• a second gate electrode around the second nanostructure, wherein the second gate electrode overlaps the first gate electrode;
• a dielectric material contacting the first gate electrode;
• and
• a backside contact extending through the dielectric material to the first source/drain region, wherein the backside contact covers an entire lateral surface of the first source/drain region in a cross-sectional view.