Methods for fabricating Fin field effect transistors

A method for fabricating a fin field effect transistor (FinFET), comprising:

• forming a first semiconductor fin, a second semiconductor fin and an insulator between the first semiconductor fin and the second semiconductor fin;
• forming a dummy gate strip over the insulator to cross over portions of the first semiconductor fin and the second semiconductor fin;
• cutting the dummy gate strip to form a first dummy gate, a second dummy gate and an opening, wherein an end of the first dummy gate is adjacent to an end of the second dummy gate, and the opening is an end-to-end opening between the end of the first dummy gate and the end of the second dummy gate;
• filling a dielectric layer in the opening, wherein an air gap is formed in the dielectric layer simultaneously during filling the dielectric layer in the opening;
• removing the first dummy gate and a second dummy gate;
• and
• forming a first gate and a second gate to cross over the first semiconductor fin and the second semiconductor fin respectively, wherein the first gate and the second gate are electrically insulated by the dielectric layer comprising the air gap therein.

A method for fabricating a fin field effect transistor (FinFET), comprising:

• patterning a substrate to form a first semiconductor fin, a second semiconductor fin and a trench between the first semiconductor fin and the second semiconductor fin;
• forming an insulator in the trench;
• forming a dummy gate strip over the insulator to cross over portions of the first semiconductor fin and the second semiconductor fin;
• forming an opening in the dummy gate strip, so as to separate the dummy gate strip into a first dummy gate and a second dummy gate on the first semiconductor fin and the second semiconductor fin respectively;
• forming a dielectric material to fill in the opening and cover the first dummy gate and the second dummy gate, wherein the air gap is formed simultaneously with the dielectric material;
• removing a portion of the dielectric material to form a first dielectric layer, wherein the air gap is retained in the first dielectric layer;
• and
• replacing the first dummy gate and the second dummy gate with a first gate and a second gate respectively, wherein the first gate and the second gate are electrically insulated by the first dielectric layer comprising the air gap therein, and a bottom of the air gap is higher than a bottom of at least one of the first gate and the second gate.