Semiconductor device including a transistor having a metal-rich metal oxide layer

1 . A semiconductor device comprising:

a gate dielectric layer over a substrate;

a lower gate barrier layer over the gate dielectric layer; and

a lower gate electrode over the lower gate barrier layer,

wherein the lower gate electrode includes a multi-layered structure in which a plurality of metal-rich metal oxide layers has oxygen vacancy concentrations different from each other,

wherein the at least one of the plurality of metal-rich metal oxide layers has a higher metal mass ratio and a higher oxygen vacancy concentration than a metal oxide according to the Law of Definite Proportions to enhance a work function of the lower gate electrode, and

wherein the metal mass ratio is defined as a mass ratio of metal ions that are not bonded to oxygen due to an oxygen vacancy.

2 . The semiconductor device of claim 1 , wherein the multi-layered structure further includes a plurality of metal layers alternately interposed with the plurality of metal-rich metal oxide layers.

3 . The semiconductor device of claim 2 , wherein the at least one of the plurality of metal-rich metal oxide layers and the metal layers include a same metal.

4 . The semiconductor device of claim 3 , wherein the metal layers include molybdenum.

5 . The semiconductor device of claim 1 , wherein the at least one of the plurality of metal-rich metal oxide layers includes molybdenum oxide.

6 . The semiconductor device of claim 1 , further comprising:

an upper gate barrier layer formed over the lower gate electrode.

7 . The semiconductor device of claim 6 , further comprising:

an upper gate electrode formed over the upper gate barrier layer.

8 . The semiconductor device of claim 7 , wherein the upper gate electrode includes tungsten.

9 . The semiconductor device of claim 1 , further comprising:

an interface insulating layer formed between the substrate and the gate dielectric layer.

10 . The semiconductor device of claim 1 , wherein the lower gate barrier layer includes at least one of Ti, TiN, Ti/TIN, Ta, TaN, Ta/TaN, WN, and conductive barrier materials.

11 . The semiconductor device of claim 1 , wherein the at least one of the plurality of metal-rich metal oxide layers has a metal concentration gradient and an oxygen concentration gradient.

12 . A semiconductor device comprising:

an interface insulating layer formed over a substrate;

a gate dielectric layer formed over the interface insulating layer;

a lower gate barrier layer formed over the gate dielectric layer;

a lower gate electrode formed over the lower gate barrier layer;

an upper gate barrier layer formed over the lower gate electrode; and

an upper gate electrode formed over the upper gate barrier layer,

wherein the lower gate electrode includes a plurality of metal-rich metal oxide layers having oxygen vacancy concentrations different from each other,

wherein the plurality of metal-rich metal oxide layers has a higher metal mass ratio and a higher oxygen vacancy concentration than a metal oxide according to the Law of Definite Proportions to enhance a work function of the lower gate electrode, and

wherein the metal mass ratio is defined as a mass ratio of metal ions that are not bonded to oxygen due to an oxygen vacancy.

13 . The semiconductor device of claim 12 , wherein:

the upper gate barrier layer surrounds side surfaces and a bottom surface of the upper gate electrode,

the lower gate electrode surrounds side surfaces and a bottom surface of the upper gate barrier layer,

the lower gate barrier layer surrounds side surfaces and a bottom surface of the lower gate electrode, and

the gate dielectric layer surrounds side surfaces and a bottom surface of the lower gate barrier layer.

14 . The semiconductor device of claim 12 , wherein the plurality of metal-rich metal oxide layers includes molybdenum oxide.

15 . The semiconductor device of claim 12 , wherein the lower gate electrode includes the plurality of metal-rich metal oxide layers and a plurality of metal layers alternately stacked.

16 . The semiconductor device of claim 15 , wherein the plurality of metal layers includes molybdenum.

17 . The semiconductor device of claim 12 , wherein the plurality of metal-rich metal oxide layers has a metal concentration gradient and an oxygen concentration gradient.

18 . A semiconductor device comprising:

a fin region protruding from a substrate;

a field insulating layer formed over the substrate and surrounding a lower portion of the fin region;

an interface insulating layer formed over a surface of the fin region;

a gate dielectric layer formed over an upper surface of the field insulating layer and an upper surface of the interface insulating layer;

a lower gate barrier layer formed over the gate dielectric layer; and

a lower gate electrode formed over the lower gate barrier layer,

wherein the lower gate electrode includes a multi-layered structure in which a plurality of metal-rich metal oxide layers have oxygen vacancy concentrations different from each other,

wherein the plurality of metal-rich metal oxide layers has a higher metal mass ratio and a higher oxygen vacancy concentration than a metal oxide according to the Law of Definite Proportions to enhance a work function of the lower gate electrode, and

wherein the metal mass ratio is defined as a mass ratio of metal ions that are not bonded to oxygen due to an oxygen vacancy.

19 . The semiconductor device of claim 18 , wherein the plurality of metal-rich metal oxide layers includes a plurality of molybdenum oxide layers.

20 . The semiconductor device of claim 18 , wherein the multi-layered structure further includes a plurality of metal layers alternately interposed with the plurality of metal-rich metal oxide layers.