Semiconductor device with air gap and method for fabricating the same

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

forming a plurality of bit line structures over a semiconductor substrate;

forming a line-type opening between the bit line structures;

forming a sacrificial spacer on both sidewalls of the line-type opening;

forming a line-type plug by filling the line-type opening over the sacrificial spacer;

forming a plurality of plug isolation openings that expose the sacrificial spacer by etching a portion of the line-type plug in a direction crossing the bit line structures;

forming a plurality of air gaps by removing the exposed sacrificial spacer;

removing a remaining line-type plug below the plug isolation openings to form a plurality of island-type plugs; and

forming a plug isolation layer inside the plug isolation openings to isolate neighboring island-type plugs from each other.

2. The method of claim 1 , wherein in the forming of the plurality of the air gaps by removing the exposed sacrificial spacer,

each of the air gaps is formed to have a linear shape that is extended in parallel with both sidewalls of each of the bit line structures.

3. The method of claim 1 , wherein the forming of the plug isolation layer inside the plug isolation openings to isolate the neighboring island-type plugs from each other includes:

transforming the air gaps into isolated-type air gaps that are disposed between the bit line structures and the island-type plugs, wherein the isolated-type air gaps are isolated from each other by the plug isolation layer.

4. The method of claim 1 , further comprising, after the forming of the plug isolation layer inside the plug isolation openings to isolate the neighboring island-type plugs from each other:

recessing an upper portion of each of the island-type plugs to form a plug recess portion;

forming a surrounding spacer on a sidewall of the plug recess portion;

forming an ohmic contact layer on a surface of the recessed island-type plug; and

forming a metal plug filling the plug recess portion over the ohmic contact layer.

5. The method of claim 1 , wherein the forming of the plurality of the plug isolation openings that expose the sacrificial spacer by etching the portion of the line-type plug in the direction crossing the bit line structures includes:

forming a plurality of mask layers that are extended in a direction crossing the bit line structures and the line-type plug over the bit line structures and the line-type plug; and

etching the line-type plug by using the mask layer and the bit line structures as etch barriers in a depth that the sacrificial spacer is exposed.

6. The method of claim 1 , wherein the sacrificial spacer includes a material having an etch selectivity with respect to the line-type plug.

7. The method of claim 1 , wherein the sacrificial spacer includes a titanium nitride.

8. The method of claim 1 , wherein the forming of the line-type plug by filling the line-type opening over the sacrificial spacer includes:

forming a polysilicon layer over the bit line structures to fill the line-type opening; and

isolating the polysilicon layer to be exposed at the same level as upper surfaces of the bit line structures.

9. The method of claim 1 , wherein the forming of the plurality of the bit line structures over the semiconductor substrate includes:

forming an inter-layer dielectric layer over the semiconductor substrate;

forming a bit line contact hole by etching the inter-layer dielectric layer;

forming a preliminary plug that fills the bit line contact hole;

sequentially forming a conductive layer and a hard mask layer over the preliminary plug and the inter-layer dielectric layer;

sequentially etching the hard mask layer, the conductive layer, and the preliminary plug to form the bit line structures where a bit line contact plug, a bit line, and a bit line hard mask layer are sequentially stacked; and

forming a bit line spacer on both sidewalls of the bit line, the bit line contact plug, and the bit line hard mask layer.

10. The method of claim 9 , wherein the air gaps are formed between the bit line and the island-type plugs and are extended vertically to be positioned between the island-type plug and the bit line contact plug.

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

forming a plurality of bit line structures over a semiconductor substrate;

forming a line-type opening between the bit line structures;

forming a sacrificial spacer on both sidewalls of the line-type opening;

forming a line-type plug by filling the line-type opening between the bit line structures over the sacrificial spacer;

forming a plurality of island-type plugs and a plurality of plug isolation openings by etching the line-type plug in a direction crossing the bit line structures; and

forming a plurality of air gaps by removing the sacrificial spacer exposed by the plug isolation openings, and

forming a plug isolation layer inside the plug isolation openings to isolate neighboring island type plugs from each other.

12. The method of claim 11 , wherein in the forming of the plurality of the air gaps by removing the sacrificial spacer exposed by the plug isolation openings,

each of the air gaps is formed to have a linear shape that is extended in parallel with both sidewalls of each of the bit line structures.

13. The method of claim 11 , wherein the forming of the plug isolation layer inside the plug isolation openings to isolate the neighboring island-type plugs from each other include:

transforming the air gaps into isolated-type air gaps that are disposed between the bit line structures and the island-type plugs, wherein the isolated-type air gaps are isolated from each other by the plug isolation layer.

14. The method of claim 11 , further comprising, after the forming of the plug isolation layer inside the plug isolation openings to isolate the neighboring island-type plugs from each other:

recessing an upper portion of each of the island-type plugs to form a plug recess portion;

forming a surrounding spacer on a sidewall of the plug recess portion;

forming an ohmic contact layer on a surface of the recessed island-type plug; and

forming a metal plug filling the plug recess portion over the ohmic contact layer.

15. The method of claim 11 , wherein the forming of the plurality of the island-type plugs and the plurality of the plug isolation openings by etching the line-type plug in the direction crossing the bit line structures includes:

forming a plurality of mask layers that are extended in a direction crossing the bit line structures and the line-type plug over the bit line structures and the line-type plug; and

etching the line-type plug by using the mask layer and the bit line structures as etch barriers.

16. The method of claim 11 , wherein the sacrificial spacer includes a material having an etch selectivity with respect to the line-type plug.

17. The method of claim 11 , wherein the sacrificial spacer includes a titanium nitride.

18. The method of claim 11 , wherein the forming of the line-type plug by filling the line-type opening over the sacrificial spacer includes:

forming a polysilicon layer over the bit line structures to fill the line-type opening; and

isolating the polysilicon layer to be exposed at the same level as upper surfaces of the bit line structures.

19. The method of claim 11 , wherein the forming of the plurality of the bit line structures over the semiconductor substrate includes:

forming an inter-layer dielectric layer over the semiconductor substrate;

forming a bit line contact hole by etching the inter-layer dielectric layer;

forming a preliminary plug that fills the bit line contact hole;

sequentially forming a conductive layer and a hard mask layer over the preliminary plug and the inter-layer dielectric layer;

sequentially etching the hard mask layer, the conductive layer, and the preliminary plug to form the bit line structures where a bit line contact plug, a bit line, and a bit line hard mask layer are sequentially stacked; and

forming a bit line spacer on both sidewalls of the bit line, the bit line contact plug, and the bit line hard mask layer

wherein the bit line contact plug is disposed between the semiconductor substrate and the bit line.

20. The method of claim 19 , wherein the air gaps are formed between the bit line and the island-type plugs and are extended vertically to be positioned between the island-type plug and the bit line contact plug.

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

forming a plurality of bit line structures over a semiconductor substrate each bit line structure including a bit line contact plug, and a bit line;

forming a line-type opening between the bit line structures;

forming a sacrificial spacer on both sidewalls of the line-type opening;

forming a line-type plug by filling the line-type opening between the bit line structures over the sacrificial spacer;

forming a plurality of island-type plugs and a plurality of plug isolation openings by etching the line-type plug in a direction crossing the bit line structures; and

forming a plurality of air gaps by removing the sacrificial spacer exposed by the plug isolation openings,

wherein each of the air gaps extends vertically from a first position located above a top surface of a corresponding bit line and below a top surface of a corresponding island-type plug to a second position substantially coplanar with a bottom surface of the bit line contact plug.