Transistor with airgap spacer

1. A method for forming a semiconductor device, the method comprising:

forming a gate structure on a substrate;

forming a sacrificial region between the gate structure and a contact spacer;

recessing the gate structure and the contact spacer to enlarge the sacrificial region; and

depositing a dielectric material in the enlarged sacrificial region to form an airgap between a remaining portion of the contact spacer and the gate structure,

wherein forming the sacrificial region comprises:

forming a sacrificial layer against a gate spacer of the gate structure;

forming the contact spacer against a sidewall of the sacrificial layer; and

removing the sacrificial layer to define a void in the sacrificial region between the contact spacer and the gate spacer, and

wherein removing the sacrificial layer comprises:

forming a sacrificial base portion of the sacrificial layer on a base portion of the gate spacer;

forming the contact spacer on the sacrificial base portion;

removing the sacrificial base portion while preserving the contact spacer and the base portion of the gate spacer to form a divot between the contact spacer, the base portion and a remaining portion of the sacrificial layer;

filling the divot with a hardmask material to form a divot plug; and

etching away the sacrificial layer while preserving the contact spacer, the base portion and the divot plug to define the void.

2. The method of claim 1 , wherein the dielectric material is deposited so that an upper portion of the sacrificial region is completely filled without completely filling a middle portion of the sacrificial region to form the airgap.

3. The method of claim 2 , wherein the airgap is located between an upper portion of the dielectric material and a lower portion of the dielectric material.

4. The method of claim 1 , wherein enlarging the sacrificial region includes recessing a sidewall of the contact spacer and a sidewall of the gate spacer to increase a size of the void.

5. The method of claim 1 , wherein the airgap is located between an upper portion of the dielectric material and the divot plug without etching the dielectric material.

6. A method for forming a semiconductor device including an airgap spacer, the method comprising:

forming a gate on a substrate;

forming a multi-layer spacer on sidewalls of the gate;

forming opposing lower and upper divots in a sacrificial layer of the multi-layer spacer;

filling the opposing divots with a hardmask material to form lower and upper divot plugs such that a remaining portion of the sacrificial layer is completely encased;

removing the upper divot plug and etching away the remaining portion of the sacrificial layer to form a void in the multi-layer spacer;

etching the multi-layer spacer to increase the size of the void; and

depositing a dielectric material in the void so that an upper portion and lower portion of the void are completely filled without completely filling a middle portion of the sacrificial region to form the airgap in the multi-layer spacer.

7. The method of claim 6 further comprising:

forming a source or drain (S/D) on the substrate and depositing an intermediate layer dielectric against the S/D;

depositing a dielectric cap to cover the intermediate layer dielectric; and

after depositing the dielectric cap, etching away the remaining portion of the sacrificial layer to form the void.

8. The method of claim 7 , wherein forming the S/D comprises performing an epitaxy process to grow the S/D from an upper surface of the substrate while the upper and lower divot plugs and contact spacer isolate the sacrificial layer from the epitaxy process.

9. The method of claim 7 , wherein forming the multi-layer spacer comprises:

forming a gate spacer layer on an upper surface of the gate and on the sidewalls of the gate;

forming a sacrificial layer on an upper surface of the gate spacer layer;

forming a contact spacer layer on an upper surface of the sacrificial layer such that the sacrificial layer is directly interposed between the gate spacer layer and the contact spacer layer; and

etching portions of the gate spacer layer, the sacrificial layer and the contact spacer layer to form the multi-layer spacer.

10. The method of claim 9 , wherein the gate spacer layer comprises silicon boron carbon nitride (SiBCN), the sacrificial layer comprises silicon oxide (SiO 2 ), and the contact spacer layer comprises (SiN).

11. The method of claim 9 , wherein etching the multi-layer spacer includes performing an etching process that recesses the gate spacer layer, the lower divot plug, and the contact spacer layer.

12. The method of claim 11 , wherein the airgap is located between an upper portion of the dielectric material and the lower divot plug without etching the dielectric material.

13. A semiconductor device comprising:

a gate including a gate spacer formed on a semiconductor substrate and a source or drain (S/D) formed on the substrate a distance away from the gate;

a S/D contact including a contact spacer formed on an upper surface of the S/D;

a dielectric layer interposed between the gate spacer and the contact spacer; and

an airgap in the dielectric layer,

wherein the dielectric layer includes an upper dielectric portion and a lower dielectric portion, and wherein the airgap is interposed between the upper dielectric portion and the lower dielectric portion, and

wherein the gate spacer includes a base portion, and wherein the semiconductor device further comprises a divot plug on an upper surface of the base portion.

14. The semiconductor device of claim 13 , wherein the divot plug is interposed between the base portion of the gate spacer and the lower portion of the dielectric layer.

15. The semiconductor device of claim 14 , wherein the contact spacer is formed on the divot plug.

16. The semiconductor device of claim 15 , wherein the gate spacer comprises silicon boron carbon nitride (SiBCN), the dielectric layer comprises silicon nitride (SiN), and the contact spacer comprises (SiN).