Backside gate contact, backside gate etch stop layer, and methods of forming same

A method comprising:

• forming a multi-layer stack over a semiconductor substrate, the multi-layer stack comprising alternating semiconductor nanostructures and dummy nanostructures;
• forming lower source/drain regions, wherein lower semiconductor nanostructures of the semiconductor nanostructures extend between the lower source/drain regions;
• forming upper source/drain regions over the lower source/drain regions, wherein upper semiconductor nanostructures of the semiconductor nanostructures extend between the upper source/drain regions;
• replacing the dummy nanostructures with a lower gate stack around the lower semiconductor nanostructures and an upper gate stack around the upper semiconductor nanostructures;
• exposing a backside of the lower gate stack;
• depositing a metal-comprising backside gate etch stop layer (ESL) on the backside of the lower gate stack;
• and
• forming a backside gate contact extending through the metal-comprising backside gate ESL to electrically connect to the lower gate stack, wherein the backside gate contact overlaps the lower semiconductor nanostructures and the upper semiconductor nanostructures.

A method comprising:

• forming a device layer on a semiconductor substrate, the device layer comprising:
• a plurality of first nanostructures, the plurality of first nanostructures extending between first source/drain regions;
• a plurality of second nanostructures over the plurality of first nanostructures, the plurality of second nanostructure extending between second source/drain regions;
• a first gate stack around the plurality of first nanostructures;
• and
• a second gate stack around the plurality of second nanostructures, wherein the first gate stack is vertically stacked with the second gate stack;
• removing the semiconductor substrate to expose a backside of the first gate stack;
• depositing a backside gate etch stop layer (ESL) on the backside of the first gate stack, wherein the backside gate ESL comprises a metal;
• and
• patterning an opening through the backside gate ESL, wherein the opening exposes one of the first source/drain regions;
• and
• filling the opening with a conductive material.