Replacement sidewall spacers

1 . A method, comprising:

forming an initial spacer structure around a sacrificial gate structure by depositing an initial spacer material over the sacrificial gate structure and etching the initial spacer material so that the initial spacer material remains on a sidewall of the sacrificial gate structure, wherein the sacrificial gate structure has a height extending from a lower surface to an upper surface;

forming a replacement spacer structure;

etching the sacrificial gate structure to form the sacrificial gate structure with a recessed upper surface and a reduced height and to uncover an inner sidewall surface of an upper portion of the initial spacer structure; and

etching the inner sidewall surface of the upper portion of the initial spacer structure laterally to widen a cavity, wherein a remaining portion of the initial spacer structure is not removed, wherein the remaining portion of the initial spacer structure is laterally adjacent to the sacrificial gate structure and below the cavity, wherein the replacement spacer structure is adjacent to the remaining portion of the initial spacer structure, and wherein the remaining portion of the initial spacer structure and the replacement spacer structure form a combined spacer structure.

2 . The method of claim 1 , wherein the initial spacer structure has a faster etch rate than the replacement spacer structure for a selected etchant.

3 . The method of claim 1 , wherein etching the inner sidewall surface of the initial spacer structure laterally to widen the cavity comprises removing the upper portion of the initial spacer structure located above the reduced height of the sacrificial gate structure.

4 . The method of claim 1 , wherein etching the inner sidewall surface of the upper portion of the initial spacer structure laterally to widen the cavity comprises uncovering an inner surface of the replacement spacer structure facing the cavity and etching the inner surface of the replacement spacer structure.

5 . The method of claim 1 , wherein:

the initial spacer structure has a first outer sidewall surface and an opposite second outer sidewall surface;

the replacement spacer structure is formed on the first outer sidewall surface and the second outer sidewall surface of the initial spacer structure;

the initial spacer structure has a spacer width defined from the first outer sidewall surface to the second outer sidewall surface; and

after etching the inner sidewall surface of the initial spacer structure laterally to widen the cavity, the cavity has a cavity width greater than the spacer width.

6 . The method of claim 1 , wherein the initial spacer structure is formed from SiOCN and the replacement spacer structure is formed from SiCN.

7 . The method of claim 2 , wherein the method further comprises etching the combined spacer structure with the selected etchant to form a final spacer structure; and wherein the method comprises removing the initial spacer structure when etching the combined spacer structure with the selected etchant to form the final spacer structure.

8 . A method, comprising:

forming a sidewall spacer around a sacrificial gate structure, wherein the sidewall spacer has an inner surface adjacent the sacrificial gate structure and has an outer surface distanced from the inner surface by an initial spacer width;

forming an epitaxial structure adjacent to the outer surface of the sidewall spacer, wherein the epitaxial structure has a height extending from a lower surface to an upper surface;

etching the sidewall spacer to form the sidewall spacer with a recessed outer surface wherein the recessed outer surface is distanced from the inner surface by a reduced spacer width, wherein etching the sidewall spacer to form the sidewall spacer with the recessed outer surface comprises etching the epitaxial structure to form the epitaxial structure with a recessed upper surface and a reduced height;

forming an etch stop layer over the sidewall spacer, wherein the etch stop layer has an inner side adjacent the recessed outer surface of the sidewall spacer and has an outer side distanced from the inner side by an etch stop layer width;

depositing an interlayer dielectric material;

removing a portion of the interlayer dielectric material over the sacrificial gate structure; and

removing the sacrificial gate structure to form a gate cavity, wherein the gate cavity is separated from the interlayer dielectric material by the etch stop layer.

9 . The method of claim 8 , wherein removing the sacrificial gate structure to form the gate cavity comprises etching with an etchant, wherein the etchant etches the sidewall spacer at a first etch rate and etches the etch stop layer at a second etch rate, and wherein the first etch rate is greater than the second etch rate.

10 . The method of claim 8 , wherein removing the sacrificial gate structure to form the gate cavity comprises etching with an etchant, wherein the etchant etches the sidewall spacer at a first etch rate and etches the etch stop layer at a second etch rate, and wherein the first etch rate is at least three times greater than the second etch rate.

11 . The method of claim 8 , wherein removing the sacrificial gate structure to form the gate cavity comprises etching with an etchant, wherein the etchant etches the sidewall spacer at a first etch rate and etches the etch stop layer at a second etch rate, and wherein the first etch rate is at least five times greater than the second etch rate.

12 . The method of claim 8 , wherein the outer side of the etch stop layer is distanced from the inner surface of the sidewall spacer by a total width, and wherein a ratio of the etch stop layer width to the total width is at least 1:3.

13 . The method of claim 8 , wherein the outer side of the etch stop layer is distanced from the inner surface of the sidewall spacer by a total width, and wherein the total width is at least 90% of the initial spacer width.

14 . The method of claim 8 , wherein the outer side of the etch stop layer is distanced from the inner surface of the sidewall spacer by a total width, and wherein the total width is substantially equal to the initial spacer width.

15 . The method of claim 8 , wherein removing the sacrificial gate structure to form the gate cavity comprises forming an upper portion of the gate cavity that directly contacts the etch stop layer and forming a lower portion of the gate cavity that directly contacts a remaining portion of the sidewall spacer.

16 . The method of claim 8 , wherein the sacrificial gate structure has a height extending from a lower surface to an upper surface, and wherein etching the sidewall spacer to form the sidewall spacer with the recessed outer surface comprises etching the sacrificial gate structure to form the sacrificial gate structure with a recessed upper surface and a reduced height.

17 . The method of claim 8 , wherein:

removing the sacrificial gate structure to form the gate cavity comprises etching with an etchant;

the etchant etches the sidewall spacer at a first etch rate and etches the etch stop layer at a second etch rate;

the first etch rate is greater than the second etch rate;

the outer side of the etch stop layer is distanced from the inner surface of the sidewall spacer by a total width; and

a ratio of the etch stop layer width to the total width is at least 1:3.

18 . The method of claim 8 , wherein:

the outer side of the etch stop layer is distanced from the inner surface of the sidewall spacer by a total width;

a ratio of the etch stop layer width to the total width is at least 1:3;

the total width is at least 90% of the initial spacer width.

19 . The method of claim 8 , wherein:

removing the sacrificial gate structure to form the gate cavity comprises etching with an etchant;

removing the sacrificial gate structure to form the gate cavity comprises forming an upper portion of the gate cavity that directly contacts the etch stop layer and forming a lower portion of the gate cavity that directly contacts a remaining portion of the sidewall spacer;

the etchant etches the sidewall spacer at a first etch rate and etches the etch stop layer at a second etch rate;

the first etch rate is greater than the second etch rate;

the outer side of the etch stop layer is distanced from the inner surface of the sidewall spacer by a total width;

a ratio of the etch stop layer width to the total width is at least 1:3;

the total width is at least 90% of the initial spacer width;

the epitaxial structure has a height extending from a lower surface to an upper surface;

etching the sidewall spacer to form the sidewall spacer with the recessed outer surface comprises etching the epitaxial structure to form the epitaxial structure with a recessed upper surface and a reduced height.

20 . A method, comprising:

forming an initial spacer structure;

forming an epitaxial structure adjacent to the initial spacer structure, wherein the epitaxial structure has a height extending from a lower surface to an upper surface;

removing a portion of the initial spacer structure, wherein a remaining portion of the initial spacer structure is not removed, and wherein removing the portion of the initial spacer structure comprises etching the epitaxial structure to form the epitaxial structure with a recessed upper surface and a reduced height;

forming a replacement spacer structure adjacent to the remaining portion of the initial spacer structure to form a combined spacer structure, wherein the initial spacer structures etches faster than the replacement spacer structure for a selected etchant; and

etching the combined spacer structure with the selected etchant to form a final spacer structure.