Semiconductor device and manufacturing method thereof

1. A semiconductor device, comprising:

a semiconductor substrate;

an interface layer formed on the semiconductor substrate;

a high-k gate dielectric film formed on the interface layer; and

a gate electrode formed on the high-k gate dielectric film, wherein

the high-k gate dielectric film contains La,

the high-k gate dielectric film has a higher La concentration in an interface with the gate electrode than in an interface with the interface layer, and

the high-k gate dielectric film has the La concentration (atomic %) of 3% or less in the interface with the interface layer.

2. The semiconductor device of claim 1 , wherein the high-k gate dielectric film has the La concentration (atomic %) of 2% or less in the interface with the interface layer.

3. The semiconductor device of claim 1 , wherein the high-k gate dielectric film has the La concentration (atomic %) of 7% or less in the interface with the gate electrode.

4. The semiconductor device of claim 1 , wherein the interface layer has the La concentration (atomic %) of 2% or less in an interface with the semiconductor substrate.

5. The semiconductor device of claim 4 , wherein the interface layer has the La concentration (atomic %) of 1% or less in the interface with the semiconductor substrate.

6. The semiconductor device of claim 1 , wherein the La concentration distribution in the high-k gate dielectric film is such that the La concentration decreases monotonically from the gate electrode side toward the semiconductor substrate.

7. The semiconductor device of claim 6 , wherein the La concentration distribution in the high-k gate dielectric film is such that the La concentration decreases sharply from the gate electrode side toward a central portion in a height direction of the high-k dielectric film, and then decreases gradually toward the interface layer.

8. The semiconductor device of claim 1 , wherein the high-k gate dielectric film is made of an oxide film containing hafnium or zirconium.

9. The semiconductor device of claim 1 , wherein the gate electrode is made of titanium nitride (TiN), tantalum nitride (TaN), carbon-containing tantalum (TaC), or aluminum-containing titanium nitride (TiAlN).

10. A method for manufacturing a semiconductor device, comprising the steps of:

(a) forming an interface layer on a semiconductor substrate having a P-type transistor formation region and an N-type transistor formation region;

(b) forming a high-k gate dielectric film on the interface layer;

(c) forming on the high-k gate dielectric film a hard mask that covers the P-type transistor formation region;

(d) after the step (c), forming the La layer over the semiconductor substrate;

(e) performing an annealing process to diffuse La from the La layer into the high-k gate dielectric film in the N-type transistor formation region;

(f) removing the La layer remaining after the step (e); and

(g) after the step (f), forming in the P-type transistor formation region a P-type gate electrode on the high-k gate dielectric film via the hard mask, and forming in the N-type transistor formation region an N-type gate electrode on the high-k gate dielectric film, wherein

the high-k gate dielectric film has a higher La concentration in an interface with the gate electrode than in an interface with the interface layer.

11. The method of claim 10 , wherein

the formation of the La layer in the step (d) is a step that is performed by using a PVD method, a CVD method, or an atomic layer deposition method by using the La or La 2 O 3 target, and

the annealing process in the step (e) is a step that is performed at a temperature between 400° C. and 800° C., both inclusive.