Method of forming a contact plug using an hourglass-shaped opening to prevent a bowing profile

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

forming an opening in a dielectric layer to expose a conductive feature underlying the opening;

lining sidewalls and a bottom of the opening with a first protection layer;

forming a second protection layer in the opening over the first protection layer;

performing an anisotropic etching process to remove a first portion of the second protection layer from the bottom of the opening, wherein after the anisotropic etching process, a second portion of the second protection layer remains along the sidewalls of the opening;

after the anisotropic etching process, performing an isotropic etching process to remove, from the sidewalls of the opening, an upper portion of the first protection layer distal from the conductive feature and a lower portion of the first protection layer proximate to the conductive feature, wherein after the isotropic etching process, a middle portion of the first protection layer between the upper portion and the lower portion remains along the sidewalls of the opening;

after the isotropic etching process, performing an anneal process to at least partially convert the second portion of the second protection layer into an oxide; and

after the anneal process, filling the opening with an electrically conductive material to form a contact.

2 . The method of claim 1 , wherein after the isotropic etching process and before the anneal process, the second portion of the second protection layer is spaced apart from the dielectric layer, wherein after the anneal process, the second portion of the second protection layer contacts and extends along the dielectric layer.

3 . The method of claim 1 , wherein the anneal process converts the second portion of the second protection layer into a third protection layer, wherein the third protection layer comprises a first segment distal from the conductive feature, a second segment proximate to the conductive feature, and a third segment between the first segment and the second segment, wherein the first segment and the second segment contact and extend along the dielectric layer, and the third segment contacts and extends along the middle portion of the first protection layer.

4 . The method of claim 1 , wherein the contact has a top portion distal from the conductive feature, a bottom portion proximate to the conductive feature, and a middle portion between the top portion and the bottom portion, wherein the top portion and the bottom portion of the contact are wider than the middle portion of the contact.

5 . The method of claim 1 , wherein the anisotropic etching process is performed using a first etchant selective to the second protection layer, and the isotropic etching process is performed using a second etchant selective to the first protection layer.

6 . The method of claim 1 , wherein the first protection layer is formed of a metallic compound, wherein the second protection layer is formed of a semiconductor material.

7 . The method of claim 6 , wherein the anisotropic etching process is a plasma etching process, and the isotropic etching process is a wet etching process.

8 . The method of claim 7 , wherein the plasma etching process is performed using a hydrofluorocarbon gas.

9 . The method of claim 8 , wherein the wet etching process is performed using an alkaline solution or an acid solution.

10 . The method of claim 6 , wherein the second portion of the second protection layer is completely converted into the oxide of the semiconductor material by the anneal process.

11 . The method of claim 6 , wherein the anneal process converts exterior portions of the semiconductor material into the oxide of the semiconductor material, wherein after the anneal process, an inner portion of the semiconductor material remains unchanged and is interposed between the converted oxide of the semiconductor material.

12 . A method of forming a semiconductor device, the method comprising:

forming a dielectric layer over a gate structure, wherein the gate structure is over a fin and between source/drain regions;

forming an opening in the dielectric layer, wherein the opening exposes an upper surface of the gate structure and sidewalls of the dielectric layer;

conformally forming a first protection layer over an upper surface of the dielectric layer and in the opening;

conformally forming a second protection layer over the first protection layer;

selectively removing the second protection layer from the upper surface of the dielectric layer and from a bottom of the opening by performing a first etching process, wherein after the first etching process, the second protection layer extends along the sidewalls of the dielectric layer;

after the first etching process, selectively removing the first protection layer from the upper surface of the dielectric layer, from the bottom of the opening, and from portions of the sidewalls of the dielectric layer by performing a second etching process, wherein after the second etching process, a remaining portion of the first protection layer extends along the sidewalls of the dielectric layer;

after the second etching process, performing an anneal process, wherein the anneal process converts the second protection layer into a third protection layer; and

after the anneal process, forming a gate contact by filling the opening with an electrically conductive material.

13 . The method of claim 12 , wherein after the second etching process and before the anneal process, there is a gap between the sidewalls of the dielectric layer and the second protection layer, wherein after the anneal process, the third protection layer contacts and extends along the sidewalls of the dielectric layer.

14 . The method of claim 13 , wherein after the anneal process, the third protection layer further contacts and extends along the remaining portion of the first protection layer.

15 . The method of claim 12 , wherein the second protection layer is formed of a semiconductor material, wherein the anneal process converts the semiconductor material into an oxide of the semiconductor material.

16 . The method of claim 12 , wherein the second protection layer is formed of a semiconductor material, wherein the anneal process converts exterior portions of the second protection layer into an oxide of the semiconductor material, wherein an inner portion of the second protection layer remains as the semiconductor material after the anneal process.

17 . A method of forming a semiconductor device, the method comprising:

surrounding a gate structure with a first dielectric layer;

forming a second dielectric layer over the gate structure and the first dielectric layer;

forming an opening in the second dielectric layer over the gate structure, wherein the opening exposes an upper surface of the gate structure and sidewalls of the second dielectric layer;

lining sidewalls and a bottom of the opening with a first protection layer;

forming a second protection layer in the opening over the first protection layer, wherein the second protection layer is formed of a different material from the first protection layer;

removing a first portion of the second protection layer from the bottom of the opening, wherein after removing the first portion of the second protection layer, a second portion of the second protection layer remains along the sidewalls of the opening;

after removing the first portion of the second protection layer, removing an upper portion of the first protection layer and a lower portion of the first protection layer from the sidewalls of the opening, wherein the upper portion of the first protection layer is distal from the gate structure, and the lower portion of the first protection layer is proximate to the gate structure, wherein after removing the upper portion and the lower portion of the first protection layer, a middle portion of the first protection layer between the upper portion and the lower portion remains along the sidewalls of the opening;

after removing the upper portion and the lower portion of the first protection layer, performing an anneal process to convert the second portion of the second protection layer into a third protection layer; and

after performing the anneal process, filling the opening with an electrically conductive material to form a gate contact.

18 . The method of claim 17 , wherein removing the first portion of the second protection layer comprises performing an anisotropic etching process to remove the first portion of the second protection layer from the bottom of the opening, wherein removing the upper portion of the first protection layer and the lower portion of the first protection layer comprises performing an isotropic etching process to remove the upper portion of the first protection layer and the lower portion of the first protection layer from the sidewalls of the opening.

19 . The method of claim 18 , wherein the first protection layer is formed of a metallic compound material, and the second protection layer is formed of a semiconductor material, wherein the third protection layer comprises an oxide of the semiconductor material.

20 . The method of claim 19 , wherein the anneal process converts exterior portions of the second protection layer into the oxide of the semiconductor material, wherein inner portions of the second protection layer remain as the semiconductor material after the anneal process.