Multilayer work function metal in nanosheet stacks using a sacrificial oxide material
A semiconductor structure is formed using a nanosheet stack that is over a semiconductor substrate. The semiconductor structure includes multiple layers of work function that surround each channel of a plurality of channels in the nanosheet stack and are on the semiconductor substrate under the nanosheet stack. Adjacent layers of the work function metal in the semiconductor structure are separated by an oxide material. The oxide material is a very thin layer of an oxide with a thickness of several angstroms or less. The semiconductor structure includes an n-type work function metal that is over an outer layer of the multiple layers of the work function metal. The n-type work function metal can be an aluminum containing metal that is covered by a capping material under a gate electrode material.
1 . A semiconductor structure, comprising:
a plurality of channels in a nanosheet stack over a semiconductor substrate;
for each channel of the plurality of channels in the nanosheet stack:
a first work function metal layer surrounding a respective channel in the nanosheet stack;
a first oxide material layer fully surrounding the first work function metal layer;
a second work function metal layer surrounding the first oxide material layer;
a second oxide material layer fully surrounding the second work function metal layer;
a third work function metal layer surrounding the second oxide material layer; and
a third oxide material layer over the third work function metal layer;
a fourth work function metal layer over the third oxide material layer;
a fifth work function metal layer over the fourth work function metal layer;
a cap layer over the fifth work function metal layer;
a gate electrode material over the cap layer; and
wherein the first work function metal layer, the first oxide material layer, the second work function metal layer, and the second oxide material layer are further stacked on the semiconductor substrate and present between the semiconductor substrate and the third work function metal layer of the respective channel of the plurality of channels in the nanosheet stack that is closest to the semiconductor substrate.
2 . The semiconductor structure of claim 1 , wherein the first oxide material layer and the second oxide material layer are each yttrium oxide.
3 . The semiconductor structure of claim 2 , wherein the third oxide material layer has a composition of Y 2 O 3 .
4 . The semiconductor structure of claim 2 , wherein the third oxide material layer has a composition of La 2 O 3 .
5 . The semiconductor structure of claim 1 , wherein the first work function metal layer is a metal nitride material.
6 . The semiconductor structure of claim 1 , wherein the second oxide material layer has a lanthanum-titanium mixed interface layer.
7 . The semiconductor structure of claim 1 , wherein the fifth work function metal layer is an aluminum containing work function material.
8 . The semiconductor structure of claim 1 , wherein the first work function metal layer, the second work function metal layer, the third work function metal layer, and the fourth work function metal layer are each composed of a same material.
9 . The semiconductor structure of claim 1 , wherein the first oxide material layer and the second oxide material layer are each lanthanum oxide.
10 . The semiconductor structure of claim 9 , wherein the third oxide material layer has a composition of Y 2 O 3 .
11 . The semiconductor structure of claim 9 , wherein the third oxide material layer has a composition of La 2 O 3 .
12 . A semiconductor structure, comprising:
a first plurality of channels in a first nanosheet stack over a semiconductor substrate;
a first plurality of work function metal layers:
surrounding each channel of the first plurality of channels in the first nanosheet stack, wherein adjacent layers of the work function metal of the first plurality of work function metal layers are each separated and fully surrounded by an oxide material; and
on the semiconductor substrate, between the semiconductor substrate and a channel of the plurality of channels in the first nanosheet stack that is closest to the semiconductor substrate, wherein the adjacent layers of the work function metal of the first plurality of work function metal layers are each separated by the oxide material; and
a second plurality of channels in a second nanosheet stack, wherein:
a second plurality of work function metal layers surrounds each channel of the second plurality of channels; and
the second plurality of work function metal layers comprises a different number of layers than are present in the first plurality of work function metal layers.
13 . The semiconductor structure of claim 12 , further comprising:
an n-type work function metal over an outside layer of the first plurality of layers;
a cap layer over the n-type work function metal; and
a gate electrode material over the cap layer.
14 . The semiconductor structure of claim 12 , wherein the first plurality of work function metal layers comprises at least four layers.