Air spacers around contact plugs and method forming same

A device comprising:

• a gate stack;
• a source/drain region on a side of the gate stack;
• a silicide region over the source/drain region;
• a contact plug over the silicide region;
• a dielectric isolation layer forming a ring encircling the contact plug;
• and
• an air spacer, wherein in a top view of the device, the air spacer comprises a first portion forming a full ring encircling the contact plug, and wherein a top surface of the source/drain region is exposed to the air spacer.

A device comprising:

• a bulk semiconductor substrate;
• isolation regions over the bulk semiconductor substrate;
• a semiconductor fin laterally between opposing portions of the isolation regions, wherein the semiconductor fin is higher than a top surface of the isolation regions;
• a gate stack on the semiconductor fin;
• a gate spacer on a first sidewall of the gate stack;
• a dielectric region on a second sidewall of the gate spacer, wherein the dielectric region and the gate stack are on opposing sides of the gate spacer;
• an air spacer, wherein the dielectric region is exposed to the air spacer;
• a source/drain region comprising a sidewall, wherein an upper portion of the sidewall of the source/drain region contacts the gate spacer;
• and
• a silicon layer overlying and contacting the source/drain region, wherein the silicon layer comprises an amorphous structure or a polysilicon structure.