Semiconductor device with assisting layer and method for fabricating the same

1 . A semiconductor device, comprising:

a substrate;

a first insulating layer inwardly positioned in the substrate and comprising a U-shaped cross-sectional profile;

a first assisting layer conformally positioned on the first insulating layer and the substrate;

a first filler layer positioned on the first assisting layer; and

a capping dielectric layer positioned on the substrate and covering the first assisting layer and the first filler layer;

wherein a top surface of the first insulating layer is at a vertical level lower than a top surface of the substrate;

wherein the first assisting layer comprises a first step portion and a second step portion, the first step portion of the first assisting layer is positioned adjacent to the top surface of the first insulating layer, and the second step portion of the first assisting layer is positioned adjacent to the top surface of the substrate.

2 . The semiconductor device of claim 1 , wherein the first assisting layer comprises manganese.

3 . The semiconductor device of claim 2 , wherein a width of the first assisting layer is greater than a width of the first insulating layer.

4 . The semiconductor device of claim 3 , wherein a width of the capping dielectric layer is greater than the width of the first assisting layer.

5 . The semiconductor device of claim 4 , wherein a width of the first filler layer is less than the width of the first insulating layer.

6 . The semiconductor device of claim 5 , further comprising a second assisting layer conformally positioned between the first assisting layer and the first filler layer.

7 . The semiconductor device of claim 6 , wherein the second assisting layer comprises a first step portion and a second step portion, the first step portion of the second assisting layer covers the first step portion of the first assisting layer, and the second step portion of the second assisting layer covers the second step portion of the first assisting layer.

8 . The semiconductor device of claim 7 , wherein the second assisting layer comprises titanium silicon nitride.

9 . The semiconductor device of claim 8 , wherein a width of the second assisting layer is substantially the same as the width of the first assisting layer.

10 . The semiconductor device of claim 9 , further comprising a first dielectric layer covering the capping dielectric layer.

11 . The semiconductor device of claim 10 , further comprising a first conductive layer positioned along the first dielectric layer and the capping dielectric layer and positioned on the first filler layer.

12 . The semiconductor device of claim 11 , wherein the first filler layer comprises copper, aluminum, tungsten, or a combination thereof.

13 . A method for fabricating a semiconductor device, comprising:

providing a substrate;

forming a first trench in the substrate;

conformally forming a first insulating layer in the first trench;

conformally forming a first assisting layer on the first insulating layer and the substrate;

forming a first filler layer on the first assisting layer; and

forming a capping dielectric layer on the substrate and covering the first assisting layer and the first filler layer;

wherein a top surface of the first insulating layer is at a vertical level lower than a top surface of the substrate;

wherein the first assisting layer comprises a first step portion and a second step portion, the first step portion of the first assisting layer is adjacent to the top surface of the first insulating layer, and the second step portion of the first assisting layer is adjacent to the top surface of the substrate.

14 . The method for fabricating the semiconductor device of claim 13 , wherein the first assisting layer comprises manganese.

15 . The method for fabricating the semiconductor device of claim 14 , further comprising conformally forming a second assisting layer between the first assisting layer and the first filler layer.

16 . The method for fabricating the semiconductor device of claim 15 , wherein the second assisting layer comprises titanium silicon nitride.

17 . The method for fabricating the semiconductor device of claim 16 , wherein the first filler layer comprises copper, aluminum, tungsten, or a combination thereof.