Extra gate device for nanosheet
A method for forming semiconductor devices includes forming a highly doped region. A stack of alternating layers is formed on the substrate. The stack is patterned to form nanosheet structures. A dummy gate structure is formed over and between the nanosheet structures. An interlevel dielectric layer is formed. The dummy gate structures are removed. SG regions are blocked, and top sheets are removed from the nanosheet structures along the dummy gate trench. A bottommost sheet is released and forms a channel for a field effect transistor device by etching away the highly doped region under the nanosheet structure and layers in contact with the bottommost sheet. A gate structure is formed in and over the dummy gate trench wherein the bottommost sheet forms a device channel for the EG device.
1. A method for forming semiconductor devices, comprising:
forming a stack of alternating layers on a substrate over single gate (SG) regions and extra gate (EG) regions, the alternating layers including alternating semiconductor and dielectric layers;
forming a hard mask over the stack;
patterning the hard mask and the stack to form nanosheet structures;
forming a dielectric material over the hard mask and over sides of the nanosheet structures in EG regions;
recessing the dielectric material below a topmost semiconductor layer of the nanosheet structures in EG regions;
forming a spacer layer over side portions of the topmost semiconductor layer to protect the topmost semiconductor layer in EG regions;
removing the dielectric material;
etching away semiconductor layers of the nanosheet structures for EG devices other than the topmost semiconductor layer;
etching away dielectric layers formed from the stack of alternating layers of the nanosheet structures for the EG devices; and
forming a gate structure in and over a dummy gate trench wherein the topmost semiconductor layer forms a device channel for the EG device.
2. The method as recited in claim 1 , wherein forming the gate structure includes:
depositing a first dielectric layer;
blocking one of the SG regions and the EG regions; and
adjusting a thickness of the first dielectric layer of the other of the SG regions and the EG regions that is unblocked.
3. The method as recited in claim 1 , wherein the nanosheet structures are formed over N wells and P wells to form P-type and N-type devices for SG devices and EG devices.
4. The method as recited in claim 1 , wherein the nanosheet structures are formed by epitaxially growing alternating layers of the Si and SiGe.
5. The method as recited in claim 1 , wherein the SG devices includes thinner gate dielectric than EG devices.
6. The method as recited in claim 1 , wherein forming the gate structure includes forming an oxide on the topmost semiconductor layer and depositing a gate dielectric layer on the oxide.
7. The method as recited in claim 6 , further comprising forming a gate conductor on the gate dielectric layer.