Inner spacer formation and contact resistance reduction in nanosheet transistors
A nanosheet field effect transistor device includes a semiconductor substrate including a stack of semiconductor nanosheets and a gate structure. The gate structure has an electrically conductive gate contact on the nanosheets and defines a channel region interposed between opposing source or drain (S/D) regions. The nanosheet field effect transistor further includes an electrically conductive cladding layer that encapsulates an outer surface of the S/D regions, and inner spacers on the sidewalls of the gate structure. The inner spacers are interposed between the cladding layer and the gate contact.
1. A method of fabricating a semiconductor device, the method comprising:
forming a stack of alternating layers of sacrificial nanosheets and semiconductor nanosheets on a semiconductor substrate;
forming a gate structure on the stack to define a channel region of the semiconductor nanosheets, the channel region interpose between opposing source or drain (S/D) regions;
depositing a sacrificial layer comprising a first dielectric material on the S/D regions of the semiconductor nanosheets and sidewalls of the sacrificial nanosheets; and
converting a portion of the sacrificial layer into a second dielectric material different form the first dielectric material to form inner spacers of the semiconductor device.
2. The method of claim 1 , further comprising partially etching the sacrificial nanosheets while preserving the semiconductor nanosheets to form the S/D regions of the semiconductor nanosheets and the sidewalls of the sacrificial nanosheets.
3. The method of claim 2 further comprising:
forming at least one cladding layer on the S/D regions; and
forming electrically conductive S/D contacts on the cladding layer.
4. The method of claim 3 , wherein the S/D contacts wrap around an entire circumference of the S/D regions of each semiconductor nanosheet.
5. The method of claim 4 , wherein forming the S/D contacts comprises:
forming a first cladding layer comprising a first semiconductor material on an outer surface of the S/D regions;
forming a second cladding layer comprising a second semiconductor material on the first cladding layer to define a S/D contact profile;
removing the second cladding layer while preserving the first cladding layer to form S/D contact trenches; and
filling the S/D contact trenches with an electrically conductive contact material to form the S/D contacts having the S/D contact profile.
6. The method of claim 5 , wherein the first semiconductor material has a first amount of selected dopants and the second semiconductor material has a different amount of the selected dopants.
7. The method of claim 6 , wherein the first semiconductor material is silicon germanium (SiGe) comprising a first amount of germanium (Ge), and the second semiconductor material is SiGe comprising a second amount of Ge greater than the first amount of Ge.