Planarization layer, planarization method and semiconductor chip

Abstract

This invention provides a planarization layer, a planarization method, and a semiconductor chip, which can effectively improve the processability of wafers containing semiconductor chips for printheads. The planarization layer has a thickness in the range of about 2 micrometers to about 3 micrometers and contains about 8.0 wt% to about 8.5 wt% of a photoacid generator; about 2 wt% to about 3.6 wt% of a photoinitiator; about 0.35 wt% to about 0.5 wt% of a green dye; about 35 wt% to about 46 wt% of a multifunctional epoxy compound; about 35 wt% to about 50 wt% of one or more bifunctional epoxy compounds; and about 1 wt% to about 2.6 wt% of a silane adhesion promoter, wherein all weight percentages are based on the total weight of the solvent-free layer.

Description

TECHNICAL FIELD

[0001] The present invention relates to an improved photoresist formulation for fluid ejection printheads and an improved method for planarizing a fluid ejection printhead, and more particularly to a planarization layer, a method of planarization, and a semiconductor chip. BACKGROUND

[0002] Fluid ejection printheads continue to evolve as the technology and use of fluid ejection printheads expand into applications other than inkjet printing applications. One important component of fluid ejection printheads is the fluid ejection printhead. Proper operation of the printhead requires that the components of the printhead be accurately manufactured and positioned relative to one another. For example, the alignment tolerance between the nozzle plate of the printhead and the semiconductor chip components is critical to the proper functioning of the printhead.

[0003] During the manufacture of the ejection printhead, the nozzle plate is aligned with the semiconductor chips on the wafer so that the fluid ejection devices on the semiconductor chips for ejecting fluid through the nozzle holes in the nozzle plate are aligned with the nozzle holes. Misalignment between the fluid ejection devices and the nozzle holes can adversely affect the accuracy of fluid droplet placement from the nozzle holes. The alignment of the fluid ejection devices and the nozzle plate can also affect the quality and speed of the fluid droplets ejected through the nozzle holes.

[0004] Producing fluid ejection printheads requires multiple manufacturing steps. First, a resistive layer, a conductive layer, and an insulating metal layer are deposited on a silicon wafer to define individual semiconductor chips. Some of the layers, such as the resistive layer, are provided at discrete locations on each chip. Thus, at a microscopic scale, the surface of the chip is substantially irregular or non-planar. The irregularities on the surface of the chip can result in poor adhesion between the nozzle plate and the chip, misalignment of the nozzle holes in the nozzle plate relative to the fluid ejection devices on the semiconductor chip, or, in the worst case, delamination between the nozzle plate and the chip.

[0005] Once the conductive, resistive, and insulating layers are deposited on the wafer and the individual dies are defined, the individual nozzle plates are attached to the dies after the nozzle plate and the dies are aligned with each other. The nozzle plate / die assembly is then cut from the wafer and the tape automated bonding (TAB) circuit or flexible circuit is then electrically connected to each of the semiconductor dies using wire bonding or tape automated bonding (TAB) process. Each of the resulting nozzle plate / die and circuit assemblies are then attached to the cartridge body in the chip pocket using die attach adhesive. Finally, the TAB circuit or flexible circuit portion of the assembly is adhesively attached to the cartridge body. Since there are multiple adhesives used in the manufacture of fluid ejection printheads, several curing steps are typically required during assembly of the printhead assembly. Misalignment of the assembly can occur during each assembly and curing step. In addition, the handling of the printhead during the assembly steps can cause delamination between the nozzle plate and the dies.

[0006] A planarization layer can be used to increase the bond between the nozzle plate and the semiconductor dies. The planarization layer can be a layer of photoresist material that is imaged and processed to expose the fluid ejection device. However, due to the reflectivity of the metal layers deposited on the dies, it is difficult to properly image and develop conventional photoresist materials, resulting in incomplete removal of the material from critical areas of the semiconductor dies. Therefore, there remains a need for an improved photoresist formulation for use as a planarization layer for attaching nozzle plates to semiconductor dies. SUMMARY

[0007] With regard to the foregoing, embodiments of the present disclosure provide a planarization layer and method thereof. The planarization layer has a thickness in the range of about 2 microns to about 3 microns and includes about 8.0 wt% to about 8.5 wt% of a photoacid generator based on the total weight of the layer exclusive of solvent; about 2 wt% to about 3.6 wt% of a photoinitiator based on the total weight of the layer exclusive of solvent; about 0.35 wt% to about 0.5 wt% of a green dye based on the total weight of the layer exclusive of solvent; about 35 wt% to about 46 wt% of a multifunctional epoxy compound based on the total weight of the layer exclusive of solvent; about 35 wt% to about 50 wt% of one or more difunctional epoxy compounds based on the total weight of the layer exclusive of solvent; and about 1 wt% to about 2.6 wt% of a silane adhesion promoter based on the total weight of the layer exclusive of solvent.

[0008] In another embodiment, a method for planarizing a semiconductor chip for a fluid ejection head is provided. The method includes spin coating a photoresist formulation onto a device surface of a semiconductor chip to provide a planarization layer having a thickness in a range of about 2 microns to about 3 microns. The planarization layer is dried to remove solvent therefrom and then the planarization layer is exposed to actinic radiation through a mask. The exposed planarization layer is developed to define fluid ejection site locations in the planarization layer and finally the developed planarization layer is baked to cure the planarization layer. The photoresist formulation includes about 3.5 wt% to about 4.5 wt% photoacid generator; about 0.8 wt% to about 1.8 wt% photoinitiator; about 0.15 wt% to about 0.25 wt% green dye; about 15 wt% to about 20 wt% multifunctional epoxy compound; about 15 wt% to about 25 wt% one or more difunctional epoxy compounds; about 0.5 wt% to about 1.3 wt% silane adhesion promoter; and a balance of solvent, based on the total weight of the formulation.

[0009] In some embodiments, the one or more difunctional epoxy compounds are selected from compounds of the following formula:

[0010]

[0011] and

[0012]

[0013] In some embodiments, the multifunctional epoxy compound is selected from compounds of the following formula:

[0014]

[0015]

[0016] and

[0017]

[0018] where m, n, and p are integers representing the number of repeat units in each of the compounds.

[0019] In some embodiments, the one or more difunctional epoxy compounds comprise about 3.5 wt% to about 4.6 wt% of a compound of the following formula, based on the total weight of the layer exclusive of solvent:

[0020]

[0021] wherein the compound of Formula (III) has an epoxide equivalent weight of about 140 grams per mole, and about 35 weight percent to about 46 weight percent of the following compound based on the total weight of the layer free of solvent:

[0022]

[0023] wherein the epoxide equivalent weight of the compound of Formula (IV) is about 1700 grams to about 2300 grams per mole.

[0024] In some embodiments, the multifunctional epoxy compound comprises about 35 weight percent to about 46 weight percent of the following compound based on the total weight of the layer free of solvent:

[0025]

[0026] wherein the epoxide equivalent weight of the compound of Formula (VI) is about 195 grams to about 230 grams per mole.

[0027] In some embodiments, the silane adhesion promoter is 3-glycidyloxypropyltrimethoxysilane.

[0028] In some embodiments, the green dye is a powdered green metal complex dye.

[0029] In some embodiments, the photoinitiator is 2-isopropylthioxanthone.

[0030] In some embodiments, the photoacid generator is a compound or mixture of compounds capable of generating cations, such as aromatic onium salts, which can be selected from onium salts of Group VA elements, onium salts of Group VIA elements, and aromatic halonium salts.

[0031] In some embodiments, the solvent is selected from gamma-butyrolactone, phenylacetone, and mixtures thereof.

[0032] In some embodiments, a semiconductor chip is provided for a fluid nozzle, the fluid nozzle including a planarization layer formed by spin-coating a photoresist formulation onto a device surface of the semiconductor chip to provide a planarization layer with a thickness ranging from about 2 micrometers to about 3 micrometers. The planarization layer is dried to remove solvent therefrom, and then exposed to photochemical radiation through a mask. The exposed planarization layer is developed to define fluid ejector locations within the planarization layer, and finally the developed planarization layer is baked to cure the planarization layer. The photoresist formulation comprises, by weight of about 3% to about 5% of a photoacid generator; by weight of about 0.8% to about 1.8% of a photoinitiator; by weight of about 0.15% to about 0.25% of a green dye; by weight of about 15% to about 20% of a multifunctional epoxy compound; by weight of about 15% to about 25% of one or more bifunctional epoxy compounds; by weight of about 0.5% to about 1.3% of a silane adhesion promoter; and the balance being a solvent.

[0033] The advantages of the compositions and methods according to the disclosed embodiments are that the metal reflectivity is reduced and the process window is increased during imaging and development of the planarization layer for the printhead. The increased process window allows for improved alignment of the mask with the semiconductor chip, thereby defining printhead features in the planarization layer for multiple semiconductor chips on the wafer. Therefore, the formulations and methods described herein effectively improve the processability of wafers containing semiconductor chips for the printhead.

[0034] For the purposes of this disclosure, "bifunctional epoxy material" refers to a material having only two epoxy functional groups in the compound. "Multifunctional epoxy material" refers to an epoxy material having more than two epoxy functional groups in the compound. Attached Figure Description

[0035] Other advantages of the invention will become apparent from the detailed description taken in conjunction with the accompanying drawings, which are not drawn to scale, wherein the same reference numerals denote the same elements in several views, and in the drawings:

[0036] Figure 1 This is a non-scale cross-sectional view of a portion of the fluid nozzle according to this disclosure.

[0037] Figure 2 This is done before the planarization layer is applied to the cavitation layer on the semiconductor substrate. Figure 1 A non-scale cross-sectional view of a portion of a fluid nozzle.

[0038] Figure 3 is a plan view, not to scale, of a wafer containing a plurality of semiconductor substrates.

[0039] Figures 4 to 6 A process for fabricating a fluid ejection head containing a planarization layer is shown in accordance with the present disclosure.

[0040] Figure 7 is a perspective view, not to scale, of a fluid ejection head. Figure 1

[0041] Figure 8 is a perspective view, not to scale, of a fluidic cartridge of a fluid ejection head containing Figure 1

[0042] Figure 9 is a photomicrograph image in plan view of a portion of a prior art fluid ejection head.

[0043] Figures 10 to 11 is a photomicrograph image in plan view of portions of a prior art fluid ejection head.

[0044] Figures 12 to 13 is a photomicrograph image in plan view of portions of a fluid ejection head in accordance with the present disclosure.DETAILED DESCRIPTION

[0045] With respect to embodiments of the present disclosure, fluid ejection heads have been fabricated in which a plurality of photoresist layers are bonded to a silicon substrate. To improve the assembly and operation of the fluid ejection head, the imaging of the flow features within the photoresist layers is a critical step in aligning the fluid ejection devices with the fluid chambers and fluid ejection nozzles. In accordance with the present embodiments, a nozzle plate containing flow features such as fluid chambers, fluid supply channels, and nozzle holes is laminated to a semiconductor substrate containing fluid ejection devices. Figure 1 A perspective view, not to scale, of a portion of a fluid ejection head 10 in accordance with the present disclosure is shown. The fluid ejection head 10 includes a silicon substrate 12 containing a silicon dioxide passivation layer 14, a resistive layer 16 preferably made of aluminum and copper or other resistive metal (e.g., beta phase tantalum), a conductive layer 18 (e.g., alpha phase tantalum, gold or similar element), a passivation layer 20 (e.g., silicon carbide and / or silicon nitride), and a void layer 22 made of tantalum. In the embodiment shown, the fluid ejection device is a heating resistor 24 which heats fluid supplied from a fluid supply channel 28 to an ejection chamber 26. The supply channel 28 and supply chamber 26 as well as the ejection nozzle 30 are formed in a nozzle plate 32 which is thermally laminated to a semiconductor substrate 34 by an adhesive 36. A suitable nozzle plate 32 is made of a polyimide film containing a phenolic adhesive 36 on one surface thereof. The nozzle plate 32 and adhesive 36 are laser ablated to form the fluid chamber 26, fluid supply channel 28, and nozzle hole 30 therein. Figure 1 In the embodiment shown, the fluid ejection device is a heating resistor 24 which heats fluid supplied from a fluid supply channel 28 to an ejection chamber 26. The supply channel 28 and supply chamber 26 as well as the ejection nozzle 30 are formed in a nozzle plate 32 which is thermally laminated to a semiconductor substrate 34 by an adhesive 36. A suitable nozzle plate 32 is made of a polyimide film containing a phenolic adhesive 36 on one surface thereof. The nozzle plate 32 and adhesive 36 are laser ablated to form the fluid chamber 26, fluid supply channel 28, and nozzle hole 30 therein. ​​

[0046] As seen in Figure 2 Once all of the passivation layers, insulating layers, and conductor layers have been applied to the silicon substrate, the exposed surface 38 of the semiconductor substrate 34 is no longer smooth. If the nozzle plate 32 is applied directly to the rough surface of the semiconductor substrate 34, delamination of the nozzle plate from the semiconductor substrate 34 can occur. Therefore, a planarization layer 40 is preferably used to provide a smooth surface for the lamination of the nozzle plate 32 to the semiconductor substrate 34. The planarization layer 40 is applied to the exposed surface 38 of the semiconductor substrate 34. A silicon wafer 42 Figure 3 is typically used to provide a plurality of semiconductor substrates 34 thereon.

[0047] According to an exemplary procedure for applying the planarization layer 40 to the exposed surface 38 of the semiconductor substrate 34, the non-photoreactive solvent is mixed together with the one or more difunctional epoxide compounds in a suitable container, such as an amber bottle or flask, and the mixture is placed in a roll mill overnight at about 60°C to ensure proper mixing of the components. After mixing the solvent with the difunctional epoxide compounds, the multifunctional epoxide compound is added to the container, and the resulting mixture is rolled on the roll mill for 2 hours at about 60°C. The other components are also added to the container one at a time, and the container is rolled at about 60°C for about 2 hours after each component is added to the container to provide a wafer coating mixture. The resulting photoresist mixture can also contain various additives, such as conventional fillers (e.g., barium sulfate, talc, glass bubbles), viscosity modifiers (e.g., fumed silica), pigments, and the like. These fillers can be used to control the viscosity of the mixture for spin coating onto the wafer 42.

[0048] To apply the photoresist formulation to the surface 38 to planarize the surface 38, the silicon wafer 42 is placed in the center of a chuck of a resist spinner or conventional wafer resist deposition track having a chuck of the appropriate size. The photoresist formulation is dispensed into the center of the wafer 42 by hand or mechanically. The chuck holding the wafer 42 is then rotated at a predetermined number of revolutions per minute to evenly spread the photoresist formulation from the center of the wafer to the edge of the wafer 42. The speed of rotation of the wafer can be adjusted, or the viscosity of the photoresist formulation can be varied, to vary the thickness of the resulting resin film. A speed of rotation of 2500 rpm or greater can be used. The amount of photoresist formulation applied to the surface 38 should be sufficient to substantially planarize the surface 38. Thus, the thickness of the planarization layer 40 can vary depending on the actual surface irregularities to be planarized. For most surfaces 38, a layer 40 having a thickness in the range of about 1 micron to about 5 microns is generally sufficient. A typical layer 40 has a thickness in the range of about 2 microns to about 3 microns.

[0049] The resulting coated silicon wafer 42 is then removed from the chuck manually or mechanically and placed on a temperature-controlled heating plate or in a temperature-controlled oven at approximately 90°C for approximately 30 seconds to approximately 1 minute, until the material is “soft-baked.” This baking step removes at least a portion of the solvent from the planarization layer 40, thereby forming a partially dried film on surface 38. The silicon wafer 42 is then removed from the heat source and allowed to cool to room temperature.

[0050] To define patterns in the planarization layer 40, such as the jetting device location 24 and the bonding pad location 50, the planarization layer 40 is masked and exposed to a radiation source. A suitable mask 44 containing opaque regions 46 and transparent regions 48 is used to expose portions of the planarization layer 40 to the radiation source for image formation of the planarization layer 40 to define the location of the fluid jetting device 24 and the bonding pad 50 for electrical connection to the semiconductor substrate 34. Figure 7 The planarization layer 40 is cured when the photoresist formulation is exposed to photochemical radiation with wavelengths in the ultraviolet and visible spectral regions. Depending on the specific epoxy material and the amount of aromatic complex salt used, and depending on the radiation source, the distance from the radiation source, and the thickness of the layer 40 to be cured, the exposure time can range from less than about 1 second to 10 minutes or greater than 10 minutes, preferably from about 5 seconds to about 1 minute. The planarization layer 40 can also be cured by exposure to electron beam radiation. This process is similar to a standard semiconductor photolithography process. After exposure, the planarization layer 40 is baked at a temperature of about 90°C for about 30 seconds to about 10 minutes, preferably about 1 minute to about 5 minutes, to complete the curing of the planarization layer 40.

[0051] like Figure 6 As shown, in the development process, the area of ​​planarization layer 40 that is not exposed to photochemical radiation below the opaque region 46 of mask 44 is removed from planarization layer 40. Developer is brought into contact with silicon wafer 42 by immersion and agitation in a tank configuration or by spraying. Spraying or immersion of wafer 42 will sufficiently remove excess material defined by photomasking and exposure. Illustrative developers include, for example, butylated cellulose acetate, a mixture of xylene and butylated cellulose acetate, and C... 1-6 Acetic acid esters, such as butyl acetate. After developing the planarization layer 40, and before laminating the nozzle plate 32 onto the semiconductor substrate 34, the wafer 42 is baked for about 1 minute to about 60 minutes, preferably about 15 minutes to about 30 minutes, at a temperature ranging from about 150°C to about 200°C, preferably from about 170°C to about 190°C, to remove any residual solvent. The laser-ablated nozzle plate 32 is then bonded to each of the semiconductor substrates 34 on the wafer using a thermal lamination process to form a plurality of nozzles 10. The nozzles 10 are then cut off from the wafer 42.

[0052] In Figure 7 a non-scale perspective view of a showerhead 10 cut from wafer 42 is shown. Each showerhead 10 can be attached to a fluidic cartridge 60 as shown in Figure 8 Flexible circuit 62 containing electrical traces 64 and electrical contact pads 66 are attached to bond pads 50 on showerhead 10 for electrical control and activation of fluid ejection devices on showerhead 10.

[0053] One important feature of the disclosed embodiments is the use of planarization layer 40 which effectively reduces the metal reflectivity of the metal layers on silicon substrate 12 and increases the process window during imaging and development of planarization layer 40. The process window increase can increase the alignment of mask 44 to semiconductor substrate 34 for defining showerhead features in planarization layer 40 for multiple showerheads 10 on wafer 42.

[0054] Planarization layer 40 is made from an improved photoresist formulation that is spin coated onto wafer 42 containing semiconductor substrate 34. The improved photoresist formulation described herein includes one or more difunctional epoxy components, multifunctional epoxy components, silane adhesion enhancer, photoacid generator, photoinitiator, dye, and one or more solvents. The resin formulation is applied to surface 26 of chip 10 using a non-photoreactive solvent.

[0055] The one or more difunctional epoxy components can be selected from difunctional epoxy compounds including diglycidyl ether of bisphenol-A, 3,4-epoxy cyclohexylmethyl-3,4-epoxy cyclohexene carboxylate, 3,4-epoxy-6-methylcyclohexyl-methyl-3,4-epoxy-6-methylcyclohexene carboxylate, bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate, and bis(2,3-epoxycyclopentyl) ether. Representative difunctional epoxy compounds can be selected from, but not limited to, the following compounds:

[0056]

[0057] and

[0058]

[0059] A particularly preferred difunctional compound is a mixture of compound (III) and compound (IV) in a weight ratio of compound (III) to compound (IV) ranging from about 0.05:1 to about 0.15:1. Compound (III) has an epoxy equivalent weight of about 140 grams per mole, and compound (IV) has an epoxy equivalent weight ranging from about 1700 grams per mole to about 2300 grams per mole.

[0060] The total amount of difunctional compound in solventless layer 40 can range from about 35 weight percent to about 55 weight percent. In some embodiments, the amount of compound (III) can range from about 3.5 weight percent to about 4.6 weight percent, based on the total weight of solventless layer 40, and the amount of compound (V) can range from about 35 weight percent to about 46 weight percent, based on the total weight of solventless layer 40.

[0061] The multifunctional epoxy component of the photoresist formulation used for planarization layer 40 can be selected from aromatic epoxides, such as glycidyl ethers of polyphenols. Exemplary multifunctional epoxy compounds can be selected from, but are not limited to, the following compounds:

[0062]

[0063]

[0064] and

[0065]

[0066] In some embodiments, the multifunctional compound is compound (VI) having an epoxy equivalent weight ranging from about 195 grams per mole to about 230 grams per mole. The amount of compound (VI) in layer 40 can range from about 35 weight percent to about 46 weight percent, based on the total weight of solventless layer 40.

[0067] The photoresist formulation can include an effective amount of an adhesion enhancing agent, such as a silane compound. Silane compounds that are compatible with the components of the photoresist formulation generally have a functional group capable of reacting with at least one selected from the group consisting of multifunctional epoxy compounds, difunctional epoxy compounds, and photoacid generators. Such adhesion enhancing agents can be silanes having epoxide functional groups (e.g., 3-(guanidino)propyltrimethoxysilane) and glycidyloxyalkyltrialkoxysilanes (e.g., gamma-glycidoxypropyltrimethoxysilane). The amount of silane compound present in the photoresist formulation can range from about 1.0 weight percent to about 2.5 weight percent, such as from about 1.5 weight percent to about 2.1 weight percent, based on the total weight of solventless layer 40, including all ranges subsumed therein.

[0068] To image and develop the photoresist formulation used as the planarization layer, a photoacid generator can be used, and optionally an initiator. The photoacid generator is a compound or mixture of compounds capable of generating a cation, such as an aromatic complex salt, that can be selected from onium salts of Group VA elements, onium salts of Group VIA elements, and aromatic halonium salts. The aromatic complex salt is capable of generating an acid moiety that initiates reaction with the epoxide when exposed to ultraviolet radiation or electron beam radiation. The photoacid generator can be present in the solvent-free layer 40 in an amount ranging from about 7 wt% to about 10 wt%, and suitably from about 8.0 wt% to about 8.5 wt%, based on the weight of the layer 40.

[0069] Compounds that can be used as photoacid generators and that generate a protic acid when irradiated with active rays include, but are not limited to, aromatic iodonium complex salts and aromatic sulfonium complex salts. Examples include bis-(tert-butylphenyl)iodonium triflate, diphenyliodonium tetrakis(pentafluorophenyl)borate, diphenyliodonium hexafluorophosphate, diphenyliodonium hexafluoroantimonate, di(4-nonylphenyl)iodonium hexafluorophosphate, [4-(octyloxy)phenyl]phenyl iodonium hexafluoroantimonate, triphenylsulfonium triflate, triphenylsulfonium hexafluorophosphate, triphenylsulfonium hexafluoroantimonate, triphenylsulfonium tetrakis(pentafluorophenyl)borate, 4,4'-bis[diphenylsulfonium]diphenyl sulfide, bis-hexafluorophosphate, 4,4'-bis[di((beta)-hydroxyethoxy)phenylsulfonium]diphenyl sulfide bis-hexafluoroantimonate, 4,4'-bis[di((beta)-hydroxyethoxy)phenylsulfonium]diphenyl sulfide-bis-hexafluorophosphate, 7-[di(p-tolyl)sulfonium]-2-isopropylthioxanthone hexafluorophosphate, 7-[di(p-tolyl)sulfonium]-2-isopropylthioxanthone hexafluoroantimonate, 7-[di(p-tolyl)sulfonium]-2-isopropyltetrakis(pentafluorophenyl)borate, phenylcarbonyl-4'-diphenylsulfonium diphenyl sulfide hexafluorophosphate, phenylcarbonyl-4'-diphenylsulfonium diphenyl sulfide hexafluoroantimonate, 4-tert-butylphenylcarbonyl-4'-diphenylsulfonium diphenyl sulfide hexafluorophosphate, 4-tert-butylphenylcarbonyl-4'-diphenylsulfonium diphenyl sulfide hexafluoroantimonate, 4-tert-butylphenylcarbonyl-4'-diphenylsulfonium diphenyl sulfide tetrakis(pentafluorophenyl)borate, diphenyl[4-(phenylthio)phenyl]sulfonium hexafluoroantimonate, and the like.

[0070] The optional photoinitiator can be selected from a thioxanthone or an alkyl or aryl substituted thioxanthone compound. Suitable alkyl substituted thioxanthone compounds include, but are not limited to, butyl thioxanthone, 2-phenyl thioxanthone, 2-benzyl thioxanthone, 2-cyclohexyl thioxanthone, 4-isopropyl thioxanthone, 2-acetyl thioxanthone, thioxanthone, 2-methyl thioxanthone, 2-ethyl thioxanthone, and the like. The amount of thioxanthone compound in the solvent-free layer 40 can range from about 2.5 wt% to about 3.5 wt%.

[0071] Various dyes and pigments can be added to the photoresist formulation used for planarization layer 40 to reduce metal reflectivity during the imaging process of planarization layer 40. The dyes that can be included in the photoresist formulation are not particularly limited. Specific examples of dyes include, for example, the following dyes: azo dyes, metal complex azo dyes, pyrazolone azo dyes, naphthoquinone dyes, anthraquinone dyes, phthalocyanine dyes, carbonium dyes, quinonimine dyes, methine dyes, cyanine dyes, squarylium dyes, pyrilium salts, and metal mercapto salt complexes. A particularly suitable dye is a green metal complex dye in powder form. The amount of green metal complex dye in solvent-free layer 40 can range from about 0.35 wt% to about 0.5 wt%.

[0072] To form planarization layer 40, the photoresist formulation typically includes a solvent to provide a formulation that can be used to spin coat substrate 34 on wafer 42. Suitable solvents are preferably non-photoreactive solvents. Non-photoreactive solvents include, but are not limited to, γ-butyrolactone, C 1-6 acetate, tetrahydrofuran, low molecular weight ketones, mixtures thereof, and the like. A particularly preferred non-photoreactive solvent is a mixture of γ-butyrolactone and phenylacetone. The non-photoreactive solvent is included in the formulation mixture used to make planarization layer 40 in an amount ranging from about 40 wt% to about 70 wt%, preferably ranging from about 45 wt% to about 65 wt%, based on the total weight of the photoresist formulation. The non-photoreactive solvent is preferably not retained in the cured planarization layer 40 and is therefore removed prior to or during the curing step of planarization layer 40.

[0073] To demonstrate the unexpected improvement provided by the planarization layer according to the present disclosure, the following non-limiting examples are provided. As provided in Table 1, semiconductor substrates 34 were coated with a prior art planarization material according to a prior art photoresist formulation and an improved planarization material according to an improved photoresist formulation.

[0074] Table 1

[0075]

[0076] The prior art planarization material and the improved planarization material were imaged and developed to provide fluid ejection site locations and bond pad locations in the respective planarization layers. The prior art planarization material and the improved planarization material were imaged and developed using the same exposure and development conditions. Figure 9 and Figure 11 Plan views of the imaged and developed planarization layers for prior art formulations 1 and 2 are shown in FIGS. Figure 9 As shown in FIG. 1 (prior art formulation 1), as the amount of green dye in the formulation increased, wrinkles 70 were present in planarization layer 40 due to underexposure. For prior art formulation 2, FIG. 2, wrinkles 70 were not present in planarization layer 40. As shown in FIG. 3 (improved formulation), wrinkles 70 were not present in planarization layer 40. Figure 10Excessive exposure of the planarization layer 40 is shown to result in incomplete imaging and development of the planarization layer over the fluid ejection devices, as shown by the material 72 remaining over the fluid ejection devices 24. Also, for the prior art formulation 2, the excessive exposure of the planarization layer 40 over the bond pads 50 results in excess planarization material 74 remaining on the bond pads 50. However, as shown by the improved formulation, the removal of the planarization material over the fluid ejection devices 24 and the bond pads 50 is significantly improved. For the improved formulation, the increase in photoacid generator and the decrease in green dye surprisingly and unexpectedly reduces the reflectivity of the metal during the imaging process. Figure 12 and Figure 13 As shown, the improved formulation significantly improves the removal of the planarization material over the fluid ejection devices 24 and the bond pads 50. For the improved formulation, the increase in photoacid generator and the decrease in green dye surprisingly and unexpectedly reduces the reflectivity of the metal during the imaging process.

[0077] Having described various aspects and embodiments of the present application and several of its advantages, those skilled in the art will recognize that the application is amenable to various modifications, substitutions and alterations of form and details without departing from the spirit and scope of the appended claims.

Claims

1. A planarization layer for a fluid ejection head, wherein the planarization layer has a thickness in a range of about 2 microns to about 3 microns and comprises about 8.0 wt% to about 8.5 wt% of a photoacid generator based on the total weight of the planarization layer exclusive of solvent; about 2 wt% to about 3.6 wt% of a photoinitiator based on the total weight of the planarization layer exclusive of solvent; about 0.35 wt% to about 0.5 wt% of a green dye based on the total weight of the planarization layer exclusive of solvent; about 35 wt% to about 46 wt% of a multifunctional epoxy compound based on the total weight of the planarization layer exclusive of solvent; about 35 wt% to about 50 wt% of one or more difunctional epoxy compounds based on the total weight of the planarization layer exclusive of solvent; and about 1 wt% to about 2.6 wt% of a silane adhesion promoter based on the total weight of the planarization layer exclusive 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 following formulae:

3. The planarization layer of claim 1, wherein the multifunctional epoxy compound is selected from the group consisting of compounds of the following formulae: wherein m, n, and p are integers representing the number of repeat units in each of the compounds.

4. The planarization layer of claim 1, wherein the one or more difunctional epoxy compounds comprise about 3.5 wt% to about 4.6 wt% of a compound of the following formula based on the total weight of the planarization layer exclusive of solvent: wherein the compound of formula (III) has an epoxy equivalent weight of about 140 grams per mole, and about 35 wt% to about 46 wt% of a compound of the following formula based on the total weight of the planarization layer exclusive of solvent: wherein the compound of formula (IV) has an epoxy equivalent weight of about 1700 grams to about 2300 grams per mole.

5. The planarization layer of claim 1, wherein the multifunctional epoxy compound comprises about 35 wt% to about 46 wt% of a compound of the following formula based on the total weight of the planarization layer exclusive of solvent: wherein the compound of formula (VI) has an epoxy equivalent weight in a range of about 195 grams to about 230 grams per mole.

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

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 an aromatic onium salt selected from the group consisting of onium salts of Group VA elements, onium salts of Group VIA elements, and aromatic halonium salts.

10. A method for planarizing a semiconductor die for a fluid ejection head, comprising spin coating a photoresist formulation onto a device surface of the semiconductor die to provide a planarization layer having a thickness in a range of about 2 microns 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 to define fluid ejection site locations in the planarization layer; baking the developed planarization layer to cure the planarization layer, wherein the photoresist formulation includes about 3.5 wt% to about 4.5 wt% photoacid generator based on the total weight of the photoresist formulation; about 0.8 wt% to about 1.8 wt% photoinitiator based on the total weight of the photoresist formulation; about 0.15 wt% to about 0.25 wt% green dye based on the total weight of the photoresist formulation; about 15 wt% to about 20 wt% multifunctional epoxy compound based on the total weight of the photoresist formulation; about 15 wt% to about 25 wt% one or more difunctional epoxy compounds based on the total weight of the photoresist formulation; about 0.5 wt% to about 1.3 wt% silane adhesion promoter based on the total weight of the photoresist formulation; and a balance of the 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 following formula: and 12. The method of claim 10, wherein the multifunctional epoxy compound is selected from the group consisting of compounds of the following formula: and wherein m, n, and p are integers representing the number of repeat units in each of the compounds.

13. The method of claim 10, wherein the one or more difunctional epoxy compounds include a compound of the following formula: wherein the compound of formula (III) has an epoxy equivalent weight of about 140 grams per mole, and a compound of the following formula: wherein the compound of formula (IV) has an epoxy equivalent weight of about 1700 grams to about 2300 grams per mole.

14. The method of claim 10, wherein the multifunctional epoxy compound includes a compound of the following formula: wherein the compound of formula (VI) has an epoxy equivalent weight of about 195 grams to about 230 grams per mole.

15. The method of claim 10, wherein the silane adhesion promoter includes 3- glycidyloxypropyltrimethoxysilane.

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

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

18. The method of claim 10, wherein the photoacid generator includes a compound or mixture of compounds capable of generating an aromatic onium salt selected from the group consisting of onium salts of Group VA elements, onium salts of Group VIA elements, and aromatic halonium salts.

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

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

Images