Pattern forming method

1. A pattern forming method comprising:

(a) forming a porous layer above an etching target layer;

(b) forming an organic material with a transferred pattern on the porous layer;

(c) forming, by use of the transferred pattern, a processed pattern in a transfer oxide film that is more resistant to etching than the porous layer, wherein the (c) forming includes:

(c1) forming the transferred pattern in the porous layer, and

(c2) forming, in the transfer oxide film, the processed pattern that is the same as the transferred pattern; and

(d) transferring the processed pattern to the etching target layer by use of the transfer oxide film as a mask, wherein the (a) forming includes:

(a1) forming the transfer oxide film on the etching target layer, and

(a2) forming the porous layer on the transfer oxide film.

2. The pattern forming method according to claim 1 , wherein the (c) forming includes:

(c3) forming the transfer oxide film on the porous layer;

(c4) etching back the transfer oxide film until a top surface of the porous layer is exposed; and

(c5) removing the porous layer,

wherein the forming the transferred pattern in the porous layer is by use of the organic material as a mask.

3. The pattern forming method according to claim 1 , wherein, at the (c1) forming, the transferred pattern is formed in the porous layer using, as a mask, the organic material reduced down by etching sidewall portions of the organic material laterally inward.

4. The pattern forming method according to claim 3 , wherein the sidewall portions of the organic material are etched laterally inward by an isotropic etching technique.

5. The pattern forming method according to claim 4 , wherein, at the (c1) forming, the transferred pattern is formed in the porous layer by dry-etching the porous layer with a CF-based gas.

6. The pattern forming method according to claim 2 , wherein the porous layer is made of an oxide film having a lower density than an oxide film formed by an LPCVD method.

7. The pattern forming method according to claim 3 , wherein the porous layer is made of an oxide film having a lower density than an oxide film formed by an LPCVD method.

8. The pattern forming method according to claim 5 , wherein the porous layer is made of an oxide film having a lower density than an oxide film formed by an LPCVD method.

9. The pattern forming method according to claim 1 , wherein the porous layer has a density of 1.8 g/cm 3 or lower.

10. The pattern forming method according to claim 2 , wherein the porous layer has a density of 1.8 g/cm 3 or lower.

11. The pattern forming method according to claim 3 , wherein the porous layer has a density of 1.8 g/cm 3 or lower.

12. The pattern forming method according to claim 5 , wherein the porous layer has a density of 1.8 g/cm 3 or lower.