Composition and method for lithography patterning

1. A method for lithography patterning, comprising:

receiving a substrate;

applying an anti-reflective coating (ARC) composition over the substrate;

forming an ARC layer by radiating the ARC composition with an ultraviolet (UV) radiation to crosslink the ARC composition;

reducing a film density of the ARC layer by cleaving an acid labile group (ALG) in the ARC layer; and

after the reducing the film density of the ARC layer, forming a resist layer over the ARC layer.

2. The method of claim 1 , wherein the cleaving of the ALG includes baking the ARC layer at a first temperature so as to thermally generate an acid in the ARC layer.

3. The method of claim 1 , wherein the applying of the ARC composition includes a spin coating process.

4. The method of claim 1 , further comprising:

patterning the resist layer, resulting in a patterned resist layer; and

etching the ARC layer using the patterned resist layer as an etch mask.

5. The method of claim 4 , wherein the etching of the ARC layer is by dry etching.

6. The method of claim 4 , wherein the patterning of the resist layer includes:

exposing the resist layer; and

developing the resist layer in a developer that does not substantially dissolve the ARC layer.

7. The method of claim 1 , wherein the substrate includes silicon.

8. The method of claim 1 , wherein prior to the reducing the film density of the ARC layer, the ARC layer has a first etching rate associated with an etching chemical, and

wherein after the reducing the film density of the ARC layer, the ARC layer has a second etching rate associated with the etching chemical, wherein the second etching rate is higher than the first etching rate.

9. A method for lithography patterning, comprising:

receiving a substrate;

applying an anti-reflective coating (ARC) composition over the substrate wherein the ARC composition comprises a polymer, an acid labile group (ALG) connecting a chromophore to a polymer backbone of the polymer; and a thermal acid generator;

forming an ARC layer by baking the ARC composition at a first temperature to crosslink the polymer;

reducing a film density of the ARC layer by baking the ARC layer at a second temperature higher than the first temperature, wherein the reducing the film density of the ARC layer includes:

removing the ALG and the chromophore connected to the ALG in the ARC layer; and

forming a resist layer over the ARC layer.

10. The method of claim 9 , wherein the ARC composition further comprises a crosslinker.

11. The method of claim 9 , wherein the baking the ARC layer at the second temperature causes the thermal acid generator to generate a first acid.

12. The method of claim 11 , wherein the crosslinking of the polymer is in the presence of a second acid that is different from the first acid.

13. The method of claim 12 , wherein the baking the ARC composition at the first temperature causes a second thermal acid generator of the ARC composition to generate the second acid.

14. The method of claim 11 , wherein the reducing the film density of the ARC layer includes:

cleaving the ALG of the ARC layer using the first acid.

15. The method of claim 14 , wherein after the reducing the film density, the ARC layer has a lower etching resistance.

16. The method of claim 9 , further comprising:

patterning the resist layer, resulting in a patterned resist layer; and

applying a dry etching process to the ARC layer using the patterned resist layer as an etch mask, resulting in a patterned ARC layer underneath the patterned resist layer.

17. The method of claim 16 , further comprising:

processing the substrate using the patterned resist layer and the patterned ARC layer as a mask.

18. An anti-reflective coating (ARC) composition for use in lithography patterning, comprising:

a polymer, about 35% to about 95% by weight, wherein the polymer includes a chromophore;

an acid labile group (ALG), more than 5% by weight,

wherein the ALG connects the chromophore to a polymer backbone of the polymer;

a first thermal acid generator for generating a first acid for crosslinking the polymer at a first temperature; and

a second thermal acid generator for generating a second acid for cleaving the ALG and removing the chromophore connected to the ALG at a second temperature higher than the first temperature, wherein the second acid is different from the first acid.

19. The ARC composition of claim 18 , wherein the second thermal acid generator is more than 0.05% by weight.

20. The ARC composition of claim 18 , further comprising:

a crosslinker, less than about 60% by weight.