Nanosheet transistor having wrap-around bottom isolation
Embodiments of the invention are directed to a method of performing fabrication operations to form a nanosheet field effect transistor (FET) device. The fabrication operations include forming a sacrificial structure over a substrate, wherein the sacrificial structure includes a central region, a first leg at a first end of the central region, and a second leg at a second end of the central region. A nanosheet stack is formed over the central region. An isolation material is deposited within a space that was occupied by the sacrificial structure to form a wrap-around bottom dielectric isolation (BDI) structure having a BDI central region, a first BDI leg at a first end of the BDI central region, and a second BDI leg at a second end of the BDI central region.
1. A method of performing fabrication operations to form a nanosheet field effect transistor (FET) device, wherein the fabrication operations include:
forming a sacrificial structure over a substrate, wherein the sacrificial structure comprises a central region, a first leg at a first end of the central region, and a second leg at a second end of the central region;
forming a nanosheet stack over the central region;
forming shallow trench isolation (STI) regions over portions of the substrate;
wherein the substrate comprises a sub-fin region;
removing the sacrificial structure; and
depositing an isolation material within a space that was occupied by the sacrificial structure to form a wrap-around bottom dielectric isolation (BDI) structure having a BDI central region, a first BDI leg at a first end of the BDI central region, and a second BDI leg at a second end of the BDI central region;
wherein the sub-fin region is positioned under the BDI central region; and
wherein a top surface of a first one of the STI regions is below a top surface of the sub-fin.
2. The method of claim 1 , wherein the first BDI leg is positioned between the sub-fin and the first one of the STI regions.
3. The method of claim 2 , wherein the second BDI leg is positioned between the sub-fin and a second one of the STI regions.
4. The method of claim 3 , wherein a top surface of the second one of the STI regions is below the top surface of the sub-fin.
5. The method of claim 4 , wherein:
the top surface of the first one of the STI regions is at a first level when the first one of the STI regions is formed; and
the fabrication operations unintentionally recess the top surface of the first one of the STI regions to a second level;
wherein the second level is below the top surface of the sub-fin.
6. The method of claim 5 , wherein:
the top surface of the second one of the STI regions is at a third level when the second one of the STI regions is formed; and
the fabrication operations unintentionally recess the top surface of the second one of the STI regions to a fourth level;
wherein the fourth level is below the top surface of the sub-fin.
7. A method of performing fabrication operations to form a nanosheet field effect transistor (FET) device, wherein the fabrication operations include:
forming a sub-fin of a substrate;
forming a sacrificial structure over the sub-fin of a substrate, wherein the sacrificial structure comprises a central region, a first leg at a first end of the central region, and a second leg at a second end of the central region;
forming a nanosheet stack over the central region;
wherein a first portion of the first leg is on a first sidewall of the nanosheet stack;
wherein a second portion of the first leg is on a first sidewall of the sub-fin;
wherein a first portion of the second leg is on a second sidewall of the nanosheet stack;
wherein a second portion of the second leg is on a second sidewall of the sub-fin;
depositing a dielectric layer over the substrate and adjacent the first leg and the second leg;
recessing the dielectric layer to form STI regions and expose the first portion of the first leg and the second portion of the second leg;
removing the first portion of the first leg and the second portion of the second leg;
removing the sacrificial structure; and
depositing an isolation material within a space that was occupied by the sacrificial structure to form a wrap-around bottom dielectric isolation (BDI) structure having a BDI central region, a first BDI leg at a first end of the BDI central region, and a second BDI leg at a second end of the BDI central region.
8. The method of claim 7 , wherein the first BDI leg is positioned between the sub-fin and a first one of the STI regions.
9. The method of claim 8 , wherein the second BDI leg is positioned between the sub-fin and a second one of the STI regions.
10. The method of claim 9 , wherein a top surface of the first one of the STI regions is below a top surface of the sub-fin.
11. The method of claim 10 , wherein a top surface of the second one of the STI regions is below the top surface of the sub-fin.
12. The method of claim 11 , wherein:
the top surface of the first one of the STI regions is at a first level when the first one of the STI regions is formed; and
the fabrication operations unintentionally recess the top surface of the first one of the STI regions to a second level;
wherein the second level is below the top surface of the sub-fin.
13. The method of claim 11 , wherein: the top surface of the second one of the STI regions is at a third level when the second one of the STI regions is formed; and the fabrication operations unintentionally recess the top surface of the second one of the STI regions to a fourth level; wherein the fourth level is below the top surface of the sub-fin.