Method of Making Ink-Jet Component

This application is related to the subject matter disclosed in the following U.S. Patents and U.S. Patent Applications, all of which are assigned to the assignee of the present invention:

U.S. patent application Ser. No. 08/336,355, now U.S. Pat. No. 5,443,713 filed on the same date as the present application by Gregory T. Hindman for a THIN-FILM STRUCTURE METHOD OF FABRICATION, incorporated herein by reference in its entirety.

The present invention generally relates to thin-film manufacturing techniques and, more specifically, to a self-aligning fabrication process used to produce thin-film mandrel structures useful for electroforming ink-jet pen components.

As is well-known to persons skilled in the art, many publications describe the details of common techniques used in thin-film fabrication processes. Reference to general texts, such as Silicon Processing for the VLSI Era by Stanley Wolf and Richard Tauber, copyright 1986, Lattice Press publishers, and VLSI Technology, S. M. Sze editor, copyright 1986, McGraw-Hill publishers (each incorporated herein by reference in applicable parts), is recommended, as those techniques can be generally used in the present invention. Moreover, the individual steps of such processes can be performed using commercially available integrated circuit fabrication machines.

The art of ink-jet technology is also relatively well developed. Commercial products such as computer printers, graphics plotters, and facsimile machines employ ink-jet technology to produce hard copy. The basics of this technology are disclosed, for example, in various articles in the Hewlett-Packard Journal, Vol. 36, No. 5 (May 1985), Vol. 39, No. 4 (August 1988), Vol. 39, No. 5 (October 1988), Vol. 43, No. 4 (August 1992), Vol. 43, No. 6 (December 1992) and Vol. 45, No. 1 (February 1994) editions, incorporated herein by reference. The state of the art is continually developing to improve the quality of the fundamental dot matrix form of printing intrinsic to ink-jet technology. Current products have achieved print densities of up to 1200 dots-per-inch ("DPI"), achieving print quality comparable to the more expensive laser printers. To that end, thin-film technology has been employed to produce precision components such as orifice plates, fine mesh ink filters, and the like, for ink-jet pens.

For example, ink-jet pens can utilize an orifice plate generally formed on a thin-film mandrel. The mandrel can consist of a glass plate coated with a conductive film. Non-conductive discs are defined on the surface of the conductive film for determining the location and size of the orifices. Generally, the discs are about three times the diameter of the target hole size. The orifice size is determined by carefully controlling the electroplating parameters (current, timing, and the like) for forming an orifice plate on the mandrel. Therefore, a variation in these parameters will directly affect the size of the orifices. Moreover, if a thicker orifice plate is needed, it is necessary to increase the disc size. Manufacturing tolerances limit such disc dimensioning, resulting in a decreased orifice diameter if the thickness of the orifice plate increases over the disc size tolerance.

A standard manufacturing process for producing mandrel structures used for electroforming ink-jet components is shown in FIG. 1 (Prior Art). The process begins with a commercially available dielectric substrate 102, such as a silicon dioxide wafer or a transparent glass (FIG. 1A). As is known in the art, such wafers have a highly polished, flat surface 104. To insure proper adhesion, the surface 104 is cleaned and then a thin-film of metal 106, such as stainless steel, is deposited across the surface 104, forming a new surface 108 (FIG. 1B). A dielectric film 110 is deposited on the surface 108 of the metal layer 106 (FIG. 1C). Next, the dielectric layer 110 is covered with a photoresist 112 (FIG. 1D). The photoresist 112 is masked and developed to a desired pattern (FIG. 1E). The dielectric layer 110 is then etched (FIG. 1F). The patterned structure, for example, disk constructs 116, can now serve as a mandrel structure for forming a workpiece (FIG. 1G). As shown in FIG. 1H, a metal workpiece 118 is electroformed on the surface 108 of the metal layer 106. During electroforming, metal is initially deposited onto the conductive areas of the structure; that is, onto the metal layer surface 108, but not onto dielectric disk constructs 116. However, as the deposited metal thickness increases, the metal flows and partially plates over the disk constructs 116. When the workpiece 118 reaches the predetermined proper thickness or proper dimensions, the plating is stopped and the electroformed workpiece 118 is removed from the mandrel structure (FIG. 1I). In actual practice, a plurality of workpieces are formed on each substrate.

Examples of other processes are disclosed in U.S. Pat. Nos. 4,773,971 (Lam et al.)(assigned to the common assignee of the present invention), 4,954,225 and 4,839,001 (Bakewell) and 4,229,265 (Kenworthy).

There are several drawbacks to using the mandrel structure formed by these conventional prior art processes. Any defects in the dielectric layer, such as a stray particle, a pinhole, or any edge roughness in the pattern, will replicate as a defect in the electroformed workpiece 118. In fact, the electroforming process will inherently magnify any defect of the mandrel in the workpiece 118.

Generally, such methods of forming mandrels of a dielectric require critical alignment for the exposure process steps. A misaligned mandrel will result in an asymmetrical and offset orifice when the construct is used as a mandrel. If a second exposure process for forming the mandrels is used in a particular fabrication, the alignment between the two features so formed is absolutely critical. Thus, variations of such processes may call for more than one such critical alignment. Even small errors can negatively impact the electroforming process yield since many components are formed on one wafer.

Another problem is that if the mandrel size is fixed or otherwise constrained in size by the need to achieve a certain packing density, the electroform thickness and the dimensions of the electroformed part can not be controlled independently. The final shape of the workpiece is controlled by the physics of the electroforming steps of the process.

Therefore, there is a need for an improved thin-film process to form thin-film structures such as a mandrel structure or pattern of mandrels.

In its basic aspects, the present invention provides a process for fabricating a thin-film structure. A process for fabricating a thin-film structure in accordance with the present invention includes the steps of: forming a first predetermined construct of a conductive material on a first surface of a transparent substrate; defining a second predetermined construct of a photoresist material on said first predetermined construct by exposing a layer of photoresist material through said transparent substrate wherein said first predetermined construct functions as a mask during said exposing; masking at least a portion of said second predetermined construct for direct exposure from above said first surface; exposing said photoresist material by direct exposure from above said first surface; and forming said second construct by developing said photoresist material.

It is an advantage of the present invention that it allows fabrication of a thin-film structure to closer manufacturing tolerances.

It is another advantage of the present invention that it provides a method of manufacturing ink-jet printheads having orifice plates of a greater thickness while maintaining and improving manufacturing tolerances of the orifices.

It is another advantage of the present invention that the location of thin-film structures are self-aligning by use of predetermined patterns formed during the process.

It is yet another advantage of the present invention that it is tolerant of defects in a surface or in an edge of a dielectric thin-film mandrel structure.

It is an advantage of the present invention that the final shape of a workpiece can be controlled by the predetermined shaping of mandrel pillars formed in accordance with the disclosed process.

It is yet another advantage of the present invention that the shape of thin-film mandrel pillars can be controlled by predetermined shaping of dielectric thin-film elements.

It is an advantage of the present invention that it provides a mandrel structure which is reusable.

Other objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description and the accompanying drawings, in which like reference designations represent like features throughout the FIGURES.

FIGS. 1A through 1I, are a schematic depiction (partial and cross-sectional) of a process for forming a thin-film mandrel structure and a workpiece.

FIGS. 2A through 2L, are a schematic depiction (partial and cross-sectional) of a process for forming a thin-film mandrel structure and a workpiece in accordance with the present invention.

FIG. 3 is a flow chart of the process steps in accordance with the present invention as shown in FIG. 2.

FIGS. 4A through 4F, are a schematic depiction (FIGS. 4A and 4C through 4F are cross-sectional, partial views; FIG. 4B is a partial top view) of a process for forming a base structure for an alterative, reusable thin-film mandrel structure of the present invention as shown in FIG. 2.

The drawings referred to in this description should be understood as not being drawn to scale except if specifically noted.

Reference is made now in detail to a specific embodiment of the present invention which illustrates the best mode presently contemplated by the inventor for practicing the invention. Alterative embodiments are also briefly described as applicable. The process steps described herein are performed with commercial thin-film fabrication apparatus and tools. Therefore, certain specifications will be dependent on the make and model of the equipment employed and the design of the thin-film structure to be achieved. As specifically necessary to an understanding of the present invention, exemplary technical data are set forth based upon current technology. Future developments in this art and design expedients may call for appropriate adjustments as would be obvious to one skilled in the art.

Referring to FIGS. 2 and 3, the process begins 301 with a commercially available transparent glass substrate 201 having a polished surface 203 as depicted in FIG. 2A. (For the purpose of the disclosure of this preferred embodiment, "transparent" means for wavelengths required to expose a photoresist #3, typically wavelengths longer than 350 nanometers; however, this factor will be process dependent with design variations based upon the materials employed for a particular adaptation.)

Generally, as is known in the art, the process is performed in a clean room environment.

The substrate 201 is cleaned 303. Cleaning is dependent upon the quality of the commercial substrate used. For example, for a thorough cleaning, a solution such as a sulfuric acid-hydrogen peroxide mixture is followed by a mixture of isopropyl alcohol, ammonium hydroxide, and de-ionized water. The cleaning period should be sufficient, e.g., ten minutes in each bath, to insure all imperfections, dust, and the like, have been removed from the substrate surface 203. Other solutions for cleaning the substrate and other techniques generally known in the art (such as ultrasonic scrubbing) can be employed.

As shown in FIG. 2B, a conductive layer 205 is then deposited 305 on the cleaned substrate surface 203. In the preferred embodiment, a sputtering process is used to deposit a layer of opaque, conductive material, such as chrome metal, having a thickness in the range of 800 to 1000 Angstroms.

Referring now to FIG. 2C, a layer of photoresist 207 (such as AZ 1518 by Hoechst company), approximately two microns thick, is applied 307 onto a surface 208 of the conductive layer 205. After baking 309, the photoresist layer 207 is photographically exposed 311 and developed 313 in place to provide a resist pattern in accordance with a predetermined structure on the surface 208 of the conductive layer 205 as depicted in FIG. 2D.

By using a predetermined masking pattern, the constructs can be formed into a plurality separate constructs, such as annular rings, each surrounding a central pillar. As will be shown hereinafter, the same central pillar thus can also serve as a portion of a mandrel when the process is used to provide a predetermined structure for forming thin-film ink-jet components. Essentially, in such an application as for the purpose of forming a mandrel structure for the electroforming of ink-jet pen components (such as orifice plates or mesh ink filter screens), the photoresist pattern comprises a set of raised annular rings, "donut" shaped constructs, 209 having central "island" pillars 209'.

Now referring to FIG. 2E, with the photoresist pattern constructs 209, 209' in place, using an etch chemistry (for example, ferric-oxide), the conductive layer 205 is etched 315 from surface 203 of the substrate 201. This transforms the conductive layer under the developed photoresist constructs 209, 209' into conforming conductive material "donut" constructs 205'.

The remaining unexposed photoresist 209 is then stripped 317, leaving conductive material layer constructs 205' as shown in FIG. 2F. The conductive material constructs 205' will act as a mask in the next step of the process.

As depicted in FIG. 2G, in a similar manner as the previous masking steps, a second layer of photoresist 211 is applied 319 onto the surface 203 of the substrate 201, covering the conductive material constructs 205'. This photoresist layer 211 is a thick layer, on the order of one to two mils, formed of a positive photoresist, such as AZ4230 available from Shipley company. After baking 321, as shown in FIG. 2H, the photoresist 211 is exposed 323 to ultraviolet light (represented by arrows labeled "UV") through the transparent substrate 201, such that the conductive material layer constructs 205' appropriately mask predetermined regions.

In the next step, as shown in FIG. 21, a crudely aligned mask construct 215 is formed 325 on the surface 213 of photoresist layer 211. This mask is formed by a standard photolithography technique using chrome mask blanks. The purpose of the crude mask construct 215 is to protect the central pillar of the "donut" construct during the next phase of the process in which the photoresist layer 211 is then exposed 327 to ultraviolet radiation from the top (rather than through substrate 201).

The resist is thereafter developed 329, leaving a pillar construct 211' on the center conductive layer construct 205' of the donut as shown in FIG. 2J.

In this manner the pillar 211' so formed can define a mandrel 211' for electroforming 331 a workpiece having an orifice with the dimensions of the pillar 211'.

Formation of such a workpiece 217 is depicted in FIG. 2K. When the electroforming process is finished, the workpiece 217 is peeled 335 from the mandrel. As will be recognized by a person skilled in the art, the depiction of the process as shown in FIG. 2 is for one of a series of mandrels on the substrate.

In the exemplary embodiment of fabricating an ink-jet pen nozzle plate, the mandrel construct is plated with a nickel compound. The final shape of the electroformed workpiece 217, that is, the cross-sectional shape of the orifices of the nozzle plate, will be controlled by the shape of the mandrel pillars 211'. Moreover, the final dimensions of the electroformed workpiece 217, that is, the dimensions of the orifices of the nozzle plate, are also controlled independently of shape over a range established by the height of the pillars 211'.

Defects in the dielectric or in the edge of the dielectric pattern are no longer replicated in the workpiece 217.

A mandrel construct fabricated in accordance with the present invention can be made reusable and should exhibit longevity substantially exceeding that fabricated in accordance with the prior art by the addition of another set of base layers to the construct shown in FIG. 2J. A relatively permanent mandrel construct could be fabricated with a metal film provided the metal has relatively strong adhesion to the substrate frontside surface and is etched with smooth edges.

As shown in FIGS. 4A and 4B, in accordance with standard fabrication techniques such as discussed above, metal donut structures 401 are formed on a glass substrate 102 using any metal which exhibits a good adhesion to the substrate surface 104, where the clear substrate areas 403 form a "donut" shape. Edges of the donuts 401 are tapered 405 so that subsequent electroplating steps do not lift the donuts structures 401.

Starting with these defined metal donut structures 401 on the substrate 102, a layer of a dielectric material 407 applied, such as by a CVD process (FIG. 4C).

Next, a layer of negative photoresist 409 is applied, then exposed through the transparent substrate 102 ("backside" exposure; represented by arrows labelled "UV") (FIG. 4D). The donuts 401 act as a mask such that when the photoresist is then developed, pillars of photoresist 409' remain on the structure (FIG. 4E).

Both the remaining photoresist pillars 409' and the uncovered regions of dielectric material 407 are etched from the structure (FIG. 4F). What remains is a metal layer structure having the donuts' clear areas 403 "filled" with a dielectric. This protects the edges of the metal donuts during subsequent process steps.

From this structure, the process as shown in FIGS. 2G through 2L are performed, leaving the structure as shown in FIG. 4F as a reusable mandrel structure.

The interdependency and limitations on the electroform thickness and the dimensions of the workpiece 217 as prevalent in the prior art is eliminated. With such problems eliminated, a relatively large increase of the packing density can be achieved. That is, in the exemplary embodiment disclosed, the spacing of orifices in an ink-jet pen nozzle plate, can be greatly reduced and the bore diameter held to tighter tolerances. Similar advantages are realized in the formation of ink filter screens. This results in the ability to increase the DPI density on a print medium, thus increasing print quality.

While in the preferred embodiment described above, a metal layer has been used as a first construct of a thin-film mandrel, it will be recognized by those skilled in the art that in the alterative any material capable of acting as a photoresist mask for the step of exposing a photoresist through the substrate can be substituted.

The foregoing description of the preferred embodiment of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in this art. Similarly, any process steps described might be interchangeable with other steps in order to achieve the same result. The embodiment was chosen and described in order to best explain the principles of the invention and its best mode practical application to thereby enable others skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.