1. Field of the Invention The present invention relates generally to thin-film manufacturing techniques and, more specifically, to a fabricating process used to produce thin-film mandrel structures useful for electroforming ink-jet pen components.
2. Description of the Related Art
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 pertinent 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 an 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.
A standard manufacturing process for producing mandrel structures used for electroforming such components is shown in FIG. 1 (Prior Art). The process begins with a commercially available dielectric substrate 102 such as a silicon dioxide wafer (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 thinfilm of metal 106 is deposited across the surface 104, forming a new surface 108 (FIG. 1B). A dielectric film, such as silicon nitride 110, is deposited on the surface 108 of the metal layer 106 (FIG. 1C). Next, the silicon nitride layer 108 is masked to a desired pattern and etched (FIG. 1D). The patterned structure, for example, ring-shaped pillars 116, can now serve as a mandrel structure 112 for forming a workpiece. As shown in FIG. 1E, a metal workpiece 114 is electroformed on the surface of the metal layer 106. During electroforming, metal is deposited onto the conductive areas of the structure; that is, onto the metal layer surface 108, but not onto dielectric ring pillars 116. However, as the deposited metal thickness increases, the metal flows and partially plates over the dielectric pillars 116. When the workpiece 114 reaches the predetermined proper thickness or proper dimensions, the plating is stopped and the electroformed workpiece 114 is removed from the mandrel structure 112 (FIG. 1F). In actual practice, a plurality of workpieces are formed on each substrate.
There are several drawbacks to using the mandrel structure 112 formed by this conventional process. 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 114. In fact, the electroforming process will inherently magnify any defect of the mandrel in the workpiece 114.
Another problem is that if the pillar 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.
Generally, such methods of forming pillars of a dielectric as shown in FIG. 1D require critical alignment for the exposure process. If a second exposure process for forming the pillars is used, the alignment between these two features is 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.
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).
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.