Photoresist formulation

1. A planarization layer for a fluid ejection head, planarization layer having a thickness ranging from about 2 to about 3 microns, comprising from about 8.0 to about 8.5 wt. % photoacid generator based on a total weight of the layer devoid of solvent; from about 2 to about 3.6 wt. % photoinitiator based on a total weight of the layer devoid of solvent; from about 0.35 to about 0.5 wt. % green dye based on a total weight of the layer devoid of solvent; from about 35 to about 46 wt. % multifunctional epoxy compound based on a total weight of the layer devoid of solvent; from about 35 to about 50 wt. % of one or more difunctional epoxy compounds based on a total weight of the layer devoid of solvent; and from about 1 to about 2.6 wt. % silane adhesion promoter based on a total weight of the layer devoid of solvent.

2. The planarization layer of claim 1 , wherein the one or more difunctional epoxy compounds are selected from the group consisting of compounds of the formulas:

3. The planarization layer of claim 1 , wherein the multifunctional epoxy compound is selected from the group consisting of compounds of the formulas:

wherein m, n, and p are integers representing the number of repeat units in each of the polymers.

4. The planarization layer of claim 1 , wherein the one or more difunctional epoxy compounds comprises from about 3.5 to about 4.6 wt. % based on a total weight of the layer devoid of solvent of a compound of the formula:

wherein the compound of formula (III) has an epoxy equivalent weight of about 140 grams per mole, and from about 35 to about 46 wt. % based on a total weight of the layer devoid of solvent of a compound of the formula:

wherein the compound of formula (IV) has an epoxy equivalent weight of about 1700 to about 2300 grams per mole.

5. The planarization layer of claim 1 , wherein the multifunctional epoxy compound comprises from about 35 to about 46 wt. % based on a total weight of the layer devoid of solvent of a compound of the formula:

wherein the compound of formula (VI) has an epoxy equivalent weight ranging from about 195 to about 230 grams per mole.

6. The planarization layer of claim 1 , wherein the silane adhesion promoter comprises 3-glycidoxypropyltrimethoxysilane.

7. The planarization layer of claim 1 , wherein the green dye comprises a powdered green metal complex dye.

8. The planarization layer of claim 1 , wherein the photoinitiator comprises 2-isopropylthioxanthone.

9. The planarization layer of claim 1 , wherein the photoacid generator comprises a compound or mixture of compounds capable of generating a cation such as an aromatic complex salt which may be selected from the group consisting of onium salts of a Group VA element, onium salts of a Group VIA element, and aromatic halonium salts.

10. A method for planarizing a semiconductor chip for a fluid ejection head, comprising spin-coating a photoresist formulation onto a device surface of the semiconductor chip to provide a planarization layer having a thickness ranging from about 2 to about 3 microns;

drying the planarization layer to remove solvent therefrom;

exposing the planarization layer to actinic radiation through a mask;

developing the exposed planarization layer in order to define fluid ejector locations in the planarization layer;

baking the developed planarization layer to cure the planarization layer,

wherein the photoresist formulation comprises from about 3.5 to about 4.5 wt. % photoacid generator based on a total weight of the formulation; from about 0.8 to about 1.8 wt. % photoinitiator based on a total weight of the formulation; from about 0.15 to about 0.25 wt. % green dye based on a total weight of the formulation; from about 15 to about 20 wt. % multifunctional epoxy compound based on a total weight of the formulation; from about 15 to about 25 wt. % one or more difunctional epoxy compounds based on a total weight of the formulation; from about 0.5 to about 1.3 wt. % silane adhesion promoter based on a total weight of the formulation; and the balance solvent.

11. The method of claim 10 , wherein the one or more difunctional epoxy compounds are selected from the group consisting of compounds of the formulas:

12. The method of claim 10 , wherein the multifunctional epoxy compound is selected from the group consisting of compounds of the formulas:

wherein m, n, and p are integers representing the number of repeat units in each of the polymers.

13. The method of claim 10 , wherein the one or more difunctional epoxy compounds comprises a compound of the formula:

wherein the compound of formula (III) has an epoxy equivalent weight of about 140 grams per mole, and a compound of the formula:

wherein the compound of formula (IV) has an epoxy equivalent weight of about 1700 to about 2300 grams per mole.

14. The method of claim 10 , wherein the multifunctional epoxy compound comprises a compound of the formula:

wherein the compound of formula (VI) has an epoxy equivalent weight ranging from about 195 to about 230 grams per mole.

15. The method of claim 10 , wherein the silane adhesion promoter comprises 3-glycidoxypropyltrimethoxysilane.

16. The method of claim 10 , wherein the green dye comprises a powdered green metal complex dye.

17. The method of claim 10 , wherein the photoinitiator comprises 2-isopropylthioxanthone.

18. The method of claim 10 , wherein the photoacid generator comprises a compound or mixture of compounds capable of generating a cation such as an aromatic complex salt which may be selected from the group consisting of onium salts of a Group VA element, onium salts of a Group VIA element, and aromatic halonium salts.

19. The method of claim 10 , wherein the solvent is selected from the group consisting of gamma-butyrolactone, acetophenone, and mixtures thereof.

20. A semiconductor chip for a fluid ejection head comprising a planarization layer made by the method of claim 10 .