Transistor contacts and methods of forming the same

1 . A method comprising:

forming a sacrificial spacer in a contact opening, the contact opening exposing a source/drain region;

depositing a spacer layer on a sidewall of the sacrificial spacer and on a top surface of the source/drain region;

forming a protective dielectric on the spacer layer and in the contact opening;

removing the sacrificial spacer to form a recess adjacent the spacer layer; and

forming a dielectric cap in an upper portion of the recess by redepositing a material of the protective dielectric and a material of the spacer layer in the upper portion of the recess, the dielectric cap sealing a lower portion of the recess to form a void, wherein redepositing the material of the protective dielectric comprises sputtering a portion of the protective dielectric.

2 . The method of claim 1 , further comprising:

patterning the contact opening through an inter-layer dielectric to expose the source/drain region, the recess formed between the spacer layer and the inter-layer dielectric.

3 . The method of claim 2 , wherein the dielectric cap is further formed by redepositing a material of the inter-layer dielectric in the upper portion of the recess.

4 . The method of claim 1 , wherein a material of the dielectric cap is a combination of the material of the protective dielectric and the material of the spacer layer.

5 . The method of claim 4 , further comprising:

removing the protective dielectric from the contact opening by selectively etching the material of the protective dielectric at a faster rate than the material of the dielectric cap.

6 . The method of claim 5 , wherein the material of the protective dielectric is silicon oxycarbide, and etching the protective dielectric comprises performing a dry etch with hydrochloric acid, nitrogen trifluoride, hydrofluoric acid, or a combination thereof.

7 . The method of claim 1 , further comprising:

forming a gate structure on a channel region, the channel region adjacent the source/drain region;

removing the protective dielectric from the contact opening;

etching the spacer layer to form a contact spacer in the contact opening; and

forming a source/drain contact in the contact opening, the contact spacer and the void disposed between the source/drain contact and the gate structure.

8 . The method of claim 1 , wherein sputtering the portion of the protective dielectric comprises bombarding the protective dielectric with ions.

9 . The method of claim 1 , wherein removing the sacrificial spacer comprises removing an entirety of the sacrificial spacer.

10 . The method of claim 1 , wherein removing the sacrificial spacer comprises removing only a portion of the sacrificial spacer.

11 . A method comprising:

patterning a contact opening through an inter-layer dielectric to expose a source/drain region;

forming a sacrificial spacer, a spacer layer, and a protective dielectric in the contact opening, the spacer layer disposed between the protective dielectric and the sacrificial spacer;

removing the sacrificial spacer to form a recess between the spacer layer and the inter-layer dielectric; and

forming a dielectric cap in an upper portion of the recess by performing a plasma treatment process, the plasma treatment process comprising sputtering portions of the protective dielectric and the spacer layer by bombarding the protective dielectric and the spacer layer with ions and with radicals.

12 . The method of claim 11 , wherein the plasma treatment process redeposits a material of the protective dielectric and a material of the spacer layer in the upper portion of the recess.

13 . The method of claim 11 , wherein the plasma treatment process densifies the dielectric cap.

14 . The method of claim 11 , wherein the plasma treatment process comprises:

generating a nitrogen plasma comprising the ions and the radicals, a quantity of the ions in the nitrogen plasma being greater than a quantity of the radicals in the nitrogen plasma.

15 . The method of claim 14 , wherein generating the nitrogen plasma comprises exciting a gas source to a plasma state with a plasma generator, the gas source comprising nitrogen gas, an inert gas, and oxygen gas or hydrogen gas.

16 . The method of claim 15 , further comprising:

determining a desired height of the dielectric cap; and

applying a bias power to the plasma generator according to the desired height of the dielectric cap.

17 . A method comprising:

forming a source/drain region adjacent to a gate spacer;

forming an inter-layer dielectric over the source/drain region;

patterning a contact opening through the inter-layer dielectric to the source/drain region;

after patterning the contact opening through the inter-layer dielectric, depositing a contact spacer layer in the contact opening, the contact spacer layer formed on a sidewall of the contact opening and on a top surface of the source/drain region;

forming a dielectric cap between the contact spacer layer and the inter-layer dielectric, a material of the dielectric cap being a combination of a material of the contact spacer layer and a material of the inter-layer dielectric, the dielectric cap defining a void between the contact spacer layer and the gate spacer;

patterning the contact spacer layer to form a contact spacer; and

forming a source/drain contact in the contact opening.

18 . The method of claim 17 , wherein the material of the contact spacer layer is silicon nitride and the material of the inter-layer dielectric is silicon oxide.

19 . The method of claim 17 , wherein a thickness of the contact spacer is larger than a thickness of the dielectric cap.

20 . The method of claim 17 , further comprising:

increasing a density of an upper region of the dielectric cap to larger than a density of a lower region of the dielectric cap.