Inkjet printhead nozzle plate

Methods of forming a nozzle plate include forming a first reverse imageable positive photoresist layer on the substrate and protecting an area thereof adjacent an ink ejection element from ultraviolet energy while exposing other than the protected area to such energy. Thereafter, the non-protected area is rendered insoluble by heating. Thereafter, the protected area is exposed to ultraviolet energy to weaken its structure for later removal. A second reverse imageable positive resist layer gets formed on the first layer and exposed to ultraviolet energy in a region directly above the ink ejection element. In a single step, both the protected area of the first layer and the non-protected region of the second layer are removed to form an ink flow feature, a bubble chamber or an orifice of the nozzle plate. The remainders of the first and second layers become blanket exposed to ultraviolet energy and cured in place.

FIELD OF THE INVENTION

The present invention relates to inkjet printheads. In particular, it relates to a nozzle plate thereof formed with at least two positive photoresist layers that undergo a single removal of unwanted photoresist materials.

BACKGROUND OF THE INVENTION

The art of inkjet printing is relatively well known. In general, an image is produced by emitting ink drops from a printhead at precise moments such that they impact a print medium at a desired location. The printhead is supported by a movable print carriage within a device, such as an inkjet printer, and is caused to reciprocate relative to an advancing print medium and emit ink drops at times pursuant to commands of a microprocessor or other controller. The timing of the ink drop emissions corresponds to a pattern of pixels of the image being printed. Other than printers, familiar devices incorporating inkjet technology include fax machines, all-in-ones, photo printers, and graphics plotters, to name a few.

A conventional thermal inkjet printhead includes access to a local or remote supply of color or mono ink, a heater chip, a nozzle or orifice plate attached or formed with the heater chip, and an input/output connector, such as a tape automated bond (TAB) circuit, for electrically connecting the heater chip to the printer during use. The heater chip, in turn, typically includes a plurality of thin film resistors or heater elements fabricated by deposition, masking and etching techniques on a substrate such as silicon.

To print or emit a single drop of ink, an individual heater is uniquely addressed with a predetermined amount of current to rapidly heat a small volume of ink. This causes the ink to vaporize in a local bubble chamber (between the heater and nozzle plate) and be ejected through the nozzle plate towards the print medium.

Typically, nozzle plates that attach to the heater chip, post-chip-formation, have certain economic and mechanical drawbacks relating to the alignment between the nozzle plate orifices and the heater elements. As is known, poor alignment causes product defects or ineffectiveness. On the other hand, nozzle plates concurrently formed with the heater chip often suffer deformations in ink flow features or nozzle orifice shapes upon subsequent chip processing steps. Again, product defects or ineffectiveness can result. In addition, concurrently formed nozzle plates often require multiple solvent dissolving/removal steps which add cost and complexity to the fabrication sequence.

Accordingly, a need exists in the nozzle plate art for economic and simple designs that overcome misalignment and malformation and require minimal processing steps.

SUMMARY OF THE INVENTION

The above-mentioned and other problems become solved by applying the principles and teachings associated with the hereinafter described inkjet printhead having a nozzle plate formed with at least two positive acting photoresist layers.

In one embodiment, the invention teaches a nozzle plate for a substrate made by initially forming a first reverse imageable positive photoresist layer on the substrate. In an area thereof adjacent an ink ejection element, the first layer is protected from energy rays while areas other than the protected area are subjected to such energy. The non-protected area is heated to cross-link it and make it substantially insoluble. Thereafter, energy rays expose the protected area to weaken its composition for later removal. A second reverse imageable positive resist layer gets formed on the first layer and, in a region directly above the ink ejection element, is exposed to energy rays. Subsequently, both the protected area of the first layer and the non-protected region of the second layer are removed in a single processing step by an alkaline solvent. This forms an ink flow feature, a bubble chamber and/or a nozzle orifice of the nozzle plate. Finally, the remaining portions of the first and second layers are blanket exposed to energy rays and heated to cure them in place.

In other aspects of the invention, the layers become formed by spin casting a solution or laminating a dry film of positive photoresist material directly on the substrate containing ink ejection elements. Exposure of the layers to energy rays, such as ultraviolet radiation, followed by heat, leads to cross-linking of the layers in specific patterns consistent with a pattern of a photomask.

Inkjet printers and inkjet printheads are also disclosed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference toFIG. 3, and appreciating that an individual ink ejection element is one of many ink ejection elements on a heater chip, skilled artisans know the economy of scale achieved by fabricating ink ejection elements as thin film layers on a wafer or a substrate through a series of growth layers, deposition layers, masking, patterning, photolithography, and/or etching or other processing steps. In general, the thin film layers of a heater chip15include, but are not limited to: a base substrate102(including any base semiconductor structure such as silicon-on-sapphire (SOS) technology, silicon-on-insulator (SOI) technology, thin film transistor (TFT) technology, doped and undoped semiconductors, epitaxial layers of silicon supported by a base semiconductor structure, as well as other semiconductor structures known or hereinafter developed); a thermal barrier layer104on the substrate; a heater or resistor layer106on the thermal barrier layer; a conductor layer (bifurcated into positive112and negative114electrode sections, i.e., anodes and cathodes) on the resistor layer to heat the resistor layer through thermal conductivity during use; passivation layer(s)124, such as SiC and/or SiN; and an overlying cavitation layer (not shown) on the passivation layer(s). By incorporation by reference, co-pending application Ser. No. 10/146,578, entitled “Heater Chip Configuration for an Inkjet Printhead and Printer,” filed May 14, 2002 and having common assignee, teaches suitable layers, thicknesses, compositions and stable ink jetting energy ranges relevant to the instant invention. For simplicity,FIG. 1shows the heater chip15of the invention as a wafer or substrate10containing at least one ink ejection element12for ejecting ink from an attendant inkjet printhead during use.

As is known, various methods for processing the thin film layers include, but are not limited to, any variety of chemical vapor depositions (CVD), physical vapor depositions (PVD), epitaxy, ion beam deposition, evaporation, sputtering or other similarly known techniques. Preferred CVD techniques include low pressure (LP), atmospheric pressure (AP), plasma enhanced (PE), high density plasma (HDP) or other. Preferred etching techniques include, but are not limited to, any variety of wet or dry etches, reactive ion etches, deep reactive ion etches, etc. Preferred photolithography steps include, but are not limited to, exposure to ultraviolet or x-ray light sources, or other known or hereinafter developed technologies.

In still other embodiments, the substrate itself comprises a silicon wafer of p-type, 100 orientation, having a resistivity of 5-20 ohm/cm. Its beginning thickness is preferably, but not necessarily required, any one of 525+/−20 microns, 625+/−20 microns, or 625+/−15 microns with respective wafer diameters of 100+/−0.50 mm, 125+/−0.50 mm, and 150+/−0.50 mm.

The thermal barrier layer overlying the substrate includes a silicon oxide layer mixed with a glass such as BPSG, PSG or PSOG with an exemplary thickness of about 0.5 to about 3 microns, especially 1.82+/−0.15 microns. This layer can be deposited or grown according to manufacturing preference.

The heater element layer on the thermal barrier layer is about a 50-50% tantalum-aluminum composition layer of about 900 or 1000 angstroms thick. In other embodiments, the resistor layer includes essentially pure or composition layers of any of the following: hafnium, Hf, tantalum, Ta, titanium, Ti, tungsten, W, hafnium-diboride, HfB2, Tantalum-nitride, Ta2N, TaAl(N,O), TaAlSi, TaSiC, Ta/TaAl layered resistor, Ti(N,O), WSi(O) and the like.

The conductor layer overlying portions of the heater layer includes an anode and a cathode with about a 99.5-0.5% aluminum-copper composition of about 5000+/−10% angstroms thick. In other embodiments, the conductor layer includes pure aluminum or diluted compositions of aluminum with 2% copper or aluminum with 4% copper.

With reference toFIG. 4, an inkjet printhead of the present invention for housing the heater chip is shown generally as101. The printhead101has a housing121formed of a body161and a lid160. Although shown generally as a rectangular solid, the housing shape varies and depends upon the external device that carries or contains the printhead. The housing has at least one compartment, internal thereto, for holding an initial or refillable supply of ink and a structure, such as a foam insert, lung or other, maintains an appropriate backpressure therein during use. In another embodiment, the internal compartment includes three chambers for containing three supplies of ink, especially cyan, magenta and yellow ink. In other embodiments, the compartment may contain black ink, photo-ink and/or plurals of cyan, magenta or yellow ink. It will be appreciated that fluid connections (not shown) may exist to connect the compartment(s) to a remote source of ink.

A portion191of a tape automated bond (TAB) circuit201adheres to one surface181of the housing while another portion211adheres to another surface221. As shown, the two surfaces181,221exist substantially perpendicularly to one another about an edge231.

The TAB circuit201has a plurality of input/output (I/O) connectors241fabricated thereon for electrically connecting a heater chip251to an external device, such as a printer, fax machine, copier, photo-printer, plotter, all-in-one, etc., during use. Pluralities of electrical conductors261exist on the TAB circuit201to electrically connect and short the I/O connectors241to the bond pads281of the heater chip251and various manufacturing techniques are known for facilitating such connections. Skilled artisans should appreciate that while eight I/O connectors241, eight electrical conductors261and eight bond pads281are shown, any number are possible and the invention embraces all variations. The invention also embraces embodiments where the number of connectors, conductors and bond pads do not equal one another.

The heater chip251contains at least one ink via321that fluidly connects the heater chip to a supply of ink internal to the housing. During printhead manufacture, the heater chip251preferably attaches to the housing with any of a variety of adhesives, epoxies, etc. well known in the art. As shown, the heater chip contains two columns of ink ejection elements on either side of via321. For simplicity in this crowded figure, dots or small circles depict the ink ejection elements in the columns. In an actual printhead, hundreds or thousands of ink ejection elements may be found on the printhead and may have various vertical and horizontal alignments, offsets or other. A nozzle plate, to be described below, is formed over and concurrently with the heater chip such that the nozzle orifices align with the ink ejection elements.

With reference toFIG. 5, an external device in the form of an inkjet printer contains the printhead101and is shown generally as401. The printer401includes a carriage421having a plurality of slots441for containing one or more printheads. The carriage421is caused to reciprocate (via an output591of a controller571) along a shaft481above a print zone461by a motive force supplied to a drive belt501as is well known in the art. The reciprocation of the carriage421is performed relative to a print medium, such as a sheet of paper521, that is advanced in the printer401along a paper path from an input tray541, through the print zone461, to an output tray561.

In the print zone, the carriage421reciprocates in the Reciprocating Direction generally perpendicularly to the paper Advance Direction as shown by the arrows. Ink drops from the printheads (FIG. 4) are caused to be ejected from the heater chip at such times pursuant to commands of a printer microprocessor or other controller571. The timing of the ink drop emissions corresponds to a pattern of pixels of the image being printed. Often times, such patterns are generated in devices electrically connected to the controller (via Ext. input) that are external to the printer such as a computer, a scanner, a camera, a visual display unit, a personal data assistant, or other.

To print or emit a single drop of ink, an ink ejection element is uniquely addressed with a short pulse of current to rapidly heat a small volume of ink. This vaporizes a thin layer of the ink on the ink ejection element surface; the resulting vapor bubble expels a column of ink out of the orifice and towards the print medium. Alternatively, the ink ejection elements may include piezoelectric features, such as a flexing diaphragm, that emit ink drops by converting an electrical firing signal into a mechanical deflection of the diaphragm.

A control panel581having user selection interface601may also provide input621to the controller571to enable additional printer capabilities and robustness.

With reference toFIGS. 2A-2H, a substrate10with a plurality of ink ejection elements has formed thereon a first positive resist layer14, especially a reverse imageable positive resist layer such as AZ 5214 available from Clariant Corporation. Preferably, but not required, the layer14becomes formed by either spin casting a solution or laminating a dry film of the positive resist material on a surface13(FIG. 1) of the substrate to a uniform thickness or depth of about 14 to about 16 microns. The process conditions under which this layer becomes formed includes spin casting between 2000 and 4000 r.p.m. followed by baking at a temperature of about below 100° C. Skilled artisans should appreciate that the foregoing materials, process conditions and thicknesses are merely a function of user preference and should not be used to limit the claim unless such limitations are found in the claim.

Once the first layer is formed, a photomask16having light passing regions18and non-light passing regions20is introduced between an energy source22and the substrate to expose desired areas27of the first positive resist layer to energy rays (arrows24) while protecting an area26adjacent the ink ejection elements12from exposure. In a preferred embodiment, the energy source is an ultraviolet (UV) source operating at I-line frequencies for a period of about 3-20 seconds. In other embodiments, the energy source comprises deep UV radiation, electron rays, X-rays or the like.

Once exposed, the wafer is heated to a temperature sufficient to cross-link or otherwise render areas27insoluble. In a preferred embodiment, the heating occurs at a substantially constant temperature of about 175 degrees Celsius for a period of about 15 minutes. In other embodiments, the heating of the first positive resist layer occurs throughout a range of temperatures between 100 and 225 degrees Celsius or at a selected plurality of discrete temperatures in such range and all embodiments are embraced herein.

InFIG. 2C, with the photomask16removed, an entirety of the first positive resist layer14(i.e., both areas24and27) are exposed to energy rays24via a blanket energy exposure. In this manner, area26becomes structurally weakened (as indicated by the scattered marks) to facilitate later removal. Alternatively, a photomask that only exposes area26to energy rays may be used to protect areas27previously exposed to the energy.

InFIG. 2D, a second positive resist layer30becomes formed on an upper surface29of the first positive resist layer. Preferably, but not required, the second positive resist layer30is formed to a substantially uniform thickness or depth by spin casting a solution or laminating a dry film of the second positive resist material to a thickness approximately the same thickness as the first positive resist layer. Preferred second positive resist materials include, but are not limited to, AZ 5214 available from Clariant Corporation. Similar to the first positive resist layer, the composition, process conditions and thickness are dictated by user preference or application.

InFIG. 2E, a second photomask40having light passing42and non-light passing regions44becomes inserted between the energy source22and the substrate to expose the second positive resist layer in accordance with the pattern of the second photomask. In a preferred embodiment, the photomask is configured such that a region46above the ink ejection element12is exposed to energy rays24from the energy source. In this manner, similar to the first positive resist layer, the second positive resist layer becomes weakened for subsequent removal.

InFIG. 2F, application of a suitable solvent develops the substrate by removing or stripping the region46of the second positive resist layer30and the area26of the first positive resist layer adjacent the ink ejection elements. What remains is a nozzle orifice50and a bubble chamber or other ink flow feature52above or around the ink ejection elements. Preferred solvents for this removal or stripping step include, but are not limited to, alkaline aqueous developers.

Skilled artisans will appreciate that the photomasks taught herein will have fiducials corresponding exactly to the fiducials of the photomasks used to fabricate the ink ejection elements12during previous processing steps such that the nozzle orifice50will have desirable and accurate alignment therewith.

Further, skilled artisans will appreciate that the structure now remaining does not have a cross-linked second positive resist layer capable of use. Accordingly, inFIG. 2G, the remaining portions54of the first and second layers undergo a second blanket exposure or energy rays24from energy source22. Thereafter, the substrate and layers are heated which completes the formation of the nozzle plate60on the substrate10as seen inFIG. 2H. The exposure and heating steps can be performed under conditions comparable to those already described. It should be appreciated that the finished nozzle plate may have any variety of shapes and cross-sections and should not be limited to that shown. Even further, the invention may include more than two positive resist layers and/or layers other than positive resists.

The foregoing description is presented for purposes of illustration and description of the various aspects of the invention. The descriptions are not intended to be exhaustive or to limit the invention to the precise form disclosed. The embodiments described above were chosen to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally and equitably entitled.