Dielectric layer for nanosheet protection and method of forming the same

A device comprising:

• a gate stack comprising a top portion;
• a stacked structure underlying the top portion of the gate stack, the stacked structure comprising:
• a plurality of semiconductor nanostructures, with upper nanostructures in the plurality of semiconductor nanostructures overlapping lower nanostructures in the plurality of semiconductor nanostructures;
• and
• a plurality of gate structures, each comprising a lower portion of the gate stack, wherein each of the plurality of gate structures is between two of the plurality of semiconductor nanostructures;
• a dielectric layer extending on a top surface and a sidewall of the stacked structure, wherein the dielectric layer comprises:
• a lower sub layer comprising a first dielectric material;
• and
• an upper sub layer over the lower sub layer, wherein the upper sub layer comprises a second dielectric material different from the first dielectric material;
• a gate spacer on the dielectric layer;
• and
• a source/drain region aside of the gate stack.

A device comprising:

• a semiconductor substrate;
• a first dielectric isolation region and a second dielectric isolation region comprising at least some parts in the semiconductor substrate;
• a protruding structure protruding higher than top surfaces of the first dielectric isolation region and the second dielectric isolation region, wherein the protruding structure is laterally between the first dielectric isolation region and the second dielectric isolation region, and wherein the protruding structure comprises:
• a plurality of semiconductor layers;
• and
• a plurality of gate stack portions, wherein the plurality of semiconductor layers and the plurality of gate stack portions are located alternatingly;
• a plurality of inner spacers comprising a plurality of pairs, with each pair being on opposite sides of one of the plurality of gate stack portions;
• and
• a dielectric layer comprising:
• a top portion over the protruding structure, wherein the top portion has a first thickness;
• and
• a sidewall portion contacting one of the plurality of inner spacers, wherein the sidewall portion has a second thickness different from the first thickness.