Method of forming a semiconductor device including a pitch multiplication

1. A method comprising:

forming a hard-mask layer over a semiconductor substrate;

patterning the hard-mask layer to form a patterned hard-mask; and

selectively removing the semiconductor substrate by using the patterned hard-mask as an etching mask;

wherein the patterning the hard-mask layer comprises:

forming a first layer over the hard-mask layer;

forming a second layer over the first layer;

forming a third layer over the second layer;

forming a plurality of patterns over the third layer apart from each other;

transferring the plurality of patterns to the third and second layers so that the third layer is converted into a patterned third layer and the second layer is converted into a patterned second layer;

further converting the patterned second layer into a further patterned second layer so that the further patterned second layer is different in pattern from the patterned second layer; and

transferring the further patterned second layer to the first layer and the hard-mask layer to form the patterned hard-mask.

2. The method of claim 1 , wherein the hard-mask layer comprises carbon.

3. The method of claim 1 , further comprising, before forming the hard-mask layer, forming a pad dielectric film over the substrate.

4. The method of claim 3 , further comprising, before forming the hard-mask layer, forming a field dielectric film over the pad dielectric material.

5. The method of claim 1 , wherein the further converting the patterned second layer into the further patterned second layer comprises:

covering the patterned second layer with a fourth layer;

patterning the fourth layer to from a patterned fourth layer; and

transferring the patterned fourth layer to the patterned second layer to form the further patterned second layer.

6. The method of claim 5 , wherein the patterned second layer is covered with the fourth layer while the patterned third layer is intervening between the patterned second layer and the fourth layer so that the patterned fourth layer is further transferred to the patterned third layer.

7. The method of claim 1 , wherein the forming the plurality of patterns comprises:

forming first and second core portions; and

forming a gap portion between the first and second core portions.

8. The method of claim 7 , wherein the forming the gap portion comprises:

forming a sacrificial layer over the first and second core portions to form a concave portion between the first and second core portions;

filling the concave portion with dielectric material; and

removing respective portions of the sacrificial layer between the first core portion and the dielectric material and between the second core portion and the dielectric material to expose corresponding portions of the third layer.

9. The method of claim 1 , wherein the selectively removing the semiconductor substrate causes to form a plurality of trenches into the semiconductor substrate.

10. The method of claim 9 , further comprising filling the plurality of tranches with dielectric material to form a plurality of active regions defined by the plurality of tranches.

11. The method of claim 10 , further comprising:

forming a plurality of buried word lines into the semiconductor substrate, each of the plurality of buried word lines crossing associated one or ones of the plurality of active regions; and

forming a plurality of access transistors into the plurality of active regions, respectively, each of the access transistors comprising a first diffusion region, a second diffusion region and a channel region along an associated one of the buried word lines between the first and second diffusion regions.

12. The method of claim 11 , further comprising forming a plurality of capacitors each in electrical contact with the first diffusion region of an associated one of the plurality of access transistors.

13. A structure made by the method of claim 1 .