Lithography process with enhanced etch selectivity

1. A method for lithography patterning, comprising:

coating a bottom layer on a substrate, wherein the bottom layer includes a carbon-rich material;

forming a middle layer on the bottom layer, wherein the middle layer has a composition such that its silicon concentration is enhanced to be greater than 42% in weight;

coating a photosensitive layer on the middle layer;

performing an exposing process to the photosensitive layer; and

developing the photosensitive layer to form a patterned photosensitive layer.

2. The method of claim 1 , wherein the forming of the middle layer includes:

spin-on coating a middle material solution on the bottom layer; and

after the spin-on coating, performing a baking process to the middle material solution to form the middle layer with enhanced silicon concentration.

3. The method of claim 2 , wherein the middle material solution includes linear polymer chains and a cross-linking additive mixed in a solvent.

4. The method of claim 3 , wherein the linear polymer chains include silicon hydroxides with a molecular weight ranging between 2000 Dalton and 3000 Dalton.

5. The method of claim 3 , wherein the linear polymer chains have a chemical structure formulated as

wherein n is an integer and R is a chemical group bonded to each hydroxyl end of silicon hydroxide, wherein the chemical group is chosen from hydrogen (H), hydroxyl group (OH), methyl group (CH 3 ), and ethyl group (C 2 H 5 ).

6. The method of claim 5 , wherein:

the linear polymer chains have a molecular weight ranging between 2000 Dalton and 3000 Dalton; and

the cross-linking additive includes a chemical structure with a molecular weight less than 130 and pKa less than 7.

7. The method of claim 3 , further comprising preparing the middle material solution before the spin-on coating of the middle material solution, wherein the preparing the middle material solution further includes a preheating process to form the linear polymer chains with a desired polymer chain length.

8. The method of claim 7 , wherein the preheating process includes a preheating temperature ranging from 40° C. to 120° C. and a preheating duration ranging from 30 minutes to 720 minutes.

9. The method of claim 3 , wherein the performing of the baking process to the middle material solution includes:

performing a curing baking process to the middle material solution with a first baking temperature, thereby cross-linking the linear polymer chains; and

thereafter performing an outgassing baking process to the middle material solution with a second baking temperature, thereby outgassing the cross-linking additive, wherein the second baking temperature is greater than the first baking temperature.

10. The method of claim 9 , wherein

the first baking temperature ranges from 150° C. to 200° C.; and

the second baking temperature ranges from 200° C. to 300° C.

11. The method of claim 1 , wherein the bottom layer is a carbon-rich material having a plurality of phenol bonded together.

12. The method of claim 1 , further comprising

performing a first etching process to selectively etch the middle layer through openings of the patterned photosensitive layer using a first etchant containing fluorine, thereby forming a patterned middle layer; and

performing a second etching process to selectively etch the bottom layer through openings of the middle layer using a second etchant containing oxygen, thereby forming a patterned bottom layer.

13. A method for lithography patterning, comprising:

coating a bottom layer on a substrate, wherein the bottom layer includes a carbon-rich material;

coating a middle material solution on the bottom layer, wherein the middle material solution includes linear polymer chains and a cross-linking additive mixed in a solvent;

performing a curing baking process to the middle material solution with a first baking temperature;

thereafter performing an outgassing baking process to the middle material solution with a second baking temperature greater than the first baking temperature, thereby forming a middle layer with enhanced silicon concentration;

coating a photosensitive layer on the middle layer;

performing an exposing process to the photosensitive layer; and

developing the photosensitive layer to form a patterned photosensitive layer.

14. The method of claim 13 , wherein

the linear polymer chains includes silicon hydroxide with each hydroxyl end bonded with a chemical group, wherein the chemical group is chosen from hydrogen (H), hydroxyl group (OH), methyl group (CH 3 ), and ethyl group (C 2 H 5 ), wherein a molecular weight of the linear polymer chains is greater than 800 Dalton; and

the cross-linking additive includes a chemical structure with a molecular weight less than 130 and pKa less than 7.

15. The method of claim 13 , wherein the middle material solution is free of a phenyl group.

16. The method of claim 13 , wherein the cross-linking additive is a chemical chosen from Oxalic acid, Formic acid, Acetic acid, Propionic acid, Butyric acid, Valeric acid, Caproic acid, and Succinic acid.

17. The method of claim 13 , further comprising preparing the middle material solution before the coating of the middle material solution, wherein the preparing the middle material solution further includes a preheating process to form the linear polymer chains.

18. The method of claim 17 , wherein the preheating process includes a preheating temperature ranging from 40° C. to 120° C. and a preheating duration ranging from 30 minutes to 720 minutes.

19. The method of claim 13 , wherein

the first baking temperature ranges from 150° C. to 200° C.; and

the second baking temperature ranges from 200° C. to 300° C.

20. A method for lithography patterning, comprising:

coating a bottom layer on a substrate, wherein the bottom layer is made of a carbon-rich material having a phenol group;

preparing a middle material solution on the bottom layer, wherein the middle material solution includes linear polymer chains, a cross-linker and a cross-linking additive mixed in a solvent, wherein the cross-linker includes a silicon hydroxide, wherein the preparing of the middle material solution includes preheating;

coating the middle material solution to the bottom layer;

performing a curing baking process to the middle material solution with a first baking temperature;

thereafter performing an outgassing baking process to the middle material solution with a second baking temperature greater than the first baking temperature, thereby forming a middle layer with enhanced silicon concentration;

coating a photosensitive layer on the middle layer; and

performing an exposing process to the photosensitive layer.