Transistor having strain-inducing anchors and a strain-enhancing suspended channel

1. A method of fabricating a field effect transistor (FET), the method comprising fabrication operations that include:

forming a first-region channel structure over a first region of a substrate, wherein a central region of the first-region channel structure functions as a channel of the FET;

wherein the first-region channel structure further comprises lateral sidewalls having a length (L), a first end sidewall having a first width (W 1 ), and a second end sidewall having a second width (W 2 );

wherein L is greater than W 1 ;

wherein L is greater than W 2 ;

forming a first stress anchor on the first end sidewall of the first-region channel structure;

forming a second stress anchor on the second end sidewall of the first-region channel structure;

wherein the first stress anchor is configured to impart strain through the first end sidewall to the first-region channel structure;

wherein the second stress anchor is configured to impart strain through the second end sidewall to the first-region channel structure;

wherein the first stress anchor and the second stress anchor result in a first level of the strain imparted through the first end sidewall and the second end sidewall to the first-region channel structure;

configuring the first-region channel structure such that, for a predetermined duration of time, the first-region channel structure is supported only by the first stress anchor and the second stress anchor; and

selecting the predetermined duration of time such that the first stress anchor and the second stress anchor increase the first level of the strain to a second level of the strain.

2. The method of claim 1 , wherein the strain imparted by the first stress anchor and the second stress anchor comprises a tensile strain.

3. The method of claim 1 , wherein the strain imparted by the first stress anchor and the second stress anchor comprises a compressive strain.

4. The method of claim 1 , wherein forming the first stress anchor and the second stress anchor comprises applying a patterned mask over a sacrificial fill material, removing selected portions of the sacrificial fill material defined by the patterned mask to form anchor trenches, filling a first one of the anchor trenches with a first stress anchor material, and filling a second one of the anchor trenches with a second stress anchor material.

5. The method of claim 4 , wherein:

the first-region channel structure is one of a plurality of first-region channel structures;

the plurality of first-region channel structures comprises a first-region stack of nanosheet layers; and

forming the first-region stack of nanosheet layers comprises forming an elongated fin-shaped nanosheet stack, applying the patterned mask such that the patterned mask is over the elongated fin-shaped nanosheet stack and the sacrificial fill material, and removing selected portions of the elongated fin-shaped nanosheet stack define by the patterned mask to form the first-region stack of nano sheet layers.

6. The method of claim 4 , wherein configuring the first-region channel structure comprises:

subsequent to forming the first stress anchor and the second stress anchor, exposing a bottom surface of the first-region channel structure, wherein exposing the bottom surface of the first-region channel structure increases the strain imparted by the first stress anchor and the second stress anchor; and

forming the first-region channel structure such that the bottom surface of the first-region channel structure is on a sacrificial layer;

wherein exposing the bottom surface of the first-region channel structure comprises removing the sacrificial layer from the bottom surface of the first-region channel structure.

7. The method of claim 1 , wherein the first-region channel structure is one of a plurality of first-region channel structures.

8. The method of claim 7 , wherein the plurality of first-region channel structures comprise a first-region stack of nanosheet layers.

9. A method of fabricating a plurality of field effect transistors (FETs), the method comprising fabrication operations that include:

forming a first-region channel structure over a first region of a substrate, wherein a central region of the first-region channel structure functions as a channel of a first one of the plurality of FETs;

wherein the first-region channel structure comprises lateral sidewalls having a first length (L 1 ), a first end sidewall having a first width (W 1 ), and a second end sidewall having a second width (W 2 );

wherein L 1 is greater than W 1 ;

wherein L 1 is greater than W 2 ;

forming a first stress anchor on the first end sidewall of the first-region channel structure;

forming a second stress anchor on the second end sidewall of the first-region channel structure;

wherein the first stress anchor is configured to impart strain through the first end sidewall to the first-region channel structure;

wherein the second stress anchor is configured to impart strain through the second end sidewall to the first-region channel structure;

forming a second-region channel structure over a second region of the substrate, wherein a central region of the second-region channel structure functions as a channel of a second one of the plurality of FETs;

wherein the second-region channel structure further comprises lateral sidewalls having a second length (L 2 ), a third end sidewall having a third width (W 3 ), and a fourth end sidewall having a fourth width (W 4 );

wherein L 2 is greater than W 3 ;

wherein L 2 is greater than W 4 ;

forming a third stress anchor on the third end sidewall of the second-region channel structure;

forming a fourth stress anchor on the fourth end sidewall of the second-region channel structure;

wherein the third stress anchor is configured to impart strain through the third end sidewall to the second-region channel structure;

wherein the fourth stress anchor is configured to impart strain through the fourth end sidewall to the second-region channel structure;

wherein the first stress anchor and the second stress anchor result in a first level of the strain imparted through the first end sidewall and the second end sidewall to the first-region channel structure;

configuring the first-region channel structure such that, for a predetermined duration of time, the first-region channel structure is supported only by the first stress anchor and the second stress anchor;

wherein the third stress anchor and the fourth stress anchor result in a second level of the strain imparted through the third end sidewall and the fourth end sidewall to the second-region channel structure;

configuring the second-region channel structure such that, for the predetermined duration of time, the second-region channel structure is supported only by the third stress anchor and the fourth stress anchor; and

selecting the predetermined duration of time such that:

the first stress anchor and the second stress anchor increase the first level of the strain to a third level of the strain; and

the third stress anchor and the fourth stress anchor increase the second level of the strain to a fourth level of the strain.

10. The method of claim 9 , wherein:

the strain imparted by the first stress anchor and the second stress anchor comprises a tensile strain; and

the strain imparted by the third stress anchor and the fourth stress anchor comprises a compressive strain.

11. The method of claim 9 , wherein configuring the first-region channel structure further comprises, subsequent to forming the first stress anchor and the second stress anchor, exposing a bottom surface of the first-region channel structure.

12. The method of claim 11 , wherein exposing the bottom surface of the first-region channel structure increases the strain imparted by the first stress anchor and the second stress anchor.

13. The method of claim 12 , wherein exposing the bottom surface of the first-region channel structure comprises:

forming the first-region channel structure such that the bottom surface of the first-region channel structure is on a first-region sacrificial layer; and

removing the first-region sacrificial layer from the bottom surface of the first-region channel structure.

14. The method of claim 8 , wherein configuring the second-region channel structure comprises, subsequent to forming the third stress anchor and the fourth stress anchor, exposing a bottom surface of the second-region channel structure.

15. The method of claim 14 , wherein:

exposing the bottom surface of the second-region channel structure increases the strain imparted by the third stress anchor and the fourth stress anchor; and

exposing the bottom surface of the first-region channel structure comprises:

forming the second-region channel structure such that the bottom surface of the second-region channel structure is on a second-region sacrificial nanosheet layer; and

removing the second-region sacrificial nanosheet layer from the bottom surface of the second-region channel structure.

16. The method of claim 9 , wherein the first-region channel comprises a first-region stack of nanosheet layers.

17. The method of claim 16 , wherein the second-region stack comprises a second-region stack of nanosheet layers.