Abstract:
A method for forming an ink jet nozzle plate with ink jet nozzles, including providing a first mold formed with spaced-apart recesses; providing inlay material in the spaced-apart recesses; attaching a base to the inlay material; separating the first mold from the inlay material and the base, thereby forming a final mold having a plurality of inlay material protrusions over the base, the protrusions and base defining the shape and the size of the ink jet nozzles; providing plate forming material between the protrusions and over the base in the final mold; and releasing the plate forming material to form an ink jet nozzle plate having a plurality of ink jet nozzles.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the fabrication of ink jet nozzle plates for ink jet printing apparatus. 
     BACKGROUND OF THE INVENTION 
     Ink jet printing has become a prominent contender in the digital output arena because of its non-impact, low-noise characteristics and its compatibility with plain paper. Ink jet printings avoids the complications of toner transfers and fixing as in electrophotography and the pressure contact at the printing interface as in thermal resistive printing technologies. Ink jet printing mechanisms includes continuous ink jet and drop-on-demand ink jet. U.S. Pat. No. 3,946,398, which issued to Kyser et al. in 1970, discloses a drop-on-demand ink jet printer which applies a high voltage to a piezoelectric crystal, causing the crystal to bend, applying pressure on an ink reservoir and jetting drops on demand. Piezoelectric ink jet printers can also utilize piezoelectric crystals in push mode, shear mode, and squeeze mode. EP 827 833 A2 and WO 98/08687 disclose a piezoelectric ink jet print head apparatus with reduced crosstalk between channels, improved ink protection, and capability of ejecting variable ink drop size. 
     U.S. Pat. No. 4,723,129 issued to Endo et al discloses an electrothermal drop-on-demand ink jet printer which applies a power pulse to an electrothermal heater which is in thermal contact with water based ink in a nozzle. A small quantity of ink rapidly evaporates, forming a bubble which causes an ink drop to be ejected from small apertures along the edge of the heater substrate. This technology is known as Bubblejet™ (trademark of Canon K.K. of Japan). 
     U.S. Pat. No. 4,460,728, which issued to Vaught et al. in 1982, discloses an electrothermal drop ejection system which also operates by bubble formation to eject drops in a direction normal to the plane of the heater substrate. As used herein, the term “thermal ink jet” is used to refer to both this system and system commonly known as Bubblejet™. 
     Ink jet nozzles are an essential component in an ink jet printer. The shapes and dimensions of the ink jet nozzles strongly affect the properties of the ink drops ejected from that ink jet nozzle. For example, it is well known in the art that if the diameter of the ink jet nozzle opening deviates from the desired size, both ink drop volume and the velocity can vary from the desired values. In another example, if the opening of an ink jet nozzle is formed with an irregular shape, the trajectory of the ejected ink drop from that ink jet nozzle can also deviate from the desired direction (usually normal to the plane of the nozzle plate). 
     One method of forming ink jet nozzle plates is the electroforming process. Such a process uses a mandrel overcoated with a continuous conductive film patterned and non-conductive structures that protrude over the conductive film. A metallic nozzle plate is formed using such a mandrel by electroplating on the conductive film. Over time, the metallic layer grows in thickness. The ink jet nozzles are defined by the non-conductive structures. 
     One known problem in the above-described prior art is in the variability of the diameter of the ink jet nozzles. The growth rate of the metallic layer can vary at different areas of the mandrel in the electroforming process as well as between different batches. The growth rate variability results in variability in the size of the openings as defined by the edge of the growth front of the metallic layer. This problem is particularly severe for forming ink jet nozzles with small diameters. A slight variability in the growth rate of the metallic layer in the electroplating process will result in a large relative error in the nozzle diameter. 
     Another need for ink jet nozzles in an ink jet printing apparatus is to optimize the shape of ink jet nozzle exit and the ink funnel that feed the ink fluid to the ink jet nozzles. It is known that the ink funnel can exist in cone, cylindrical, or toroidal shapes. The ink jet nozzle can be round, square or triangular. The structural designs of the ink jet nozzles and ink funnels strongly influence the dynamics of the ink fluid during ink drop ejection, and therefore determine to a large extent the properties of the ejected ink drop. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide high quality ink jet nozzle for use in ink jet cartridges. 
     Another object is to provide ink jet nozzles with high precision and tolerances using conventional semiconductor fabrication techniques. 
     These objects are achieved by a method for forming an ink jet nozzle plate with ink jet nozzles, comprising the steps of: 
     a) providing a first mold formed with spaced-apart recesses; 
     b) providing inlay material in the spaced-apart recesses; 
     c) attaching a base to the inlay material; 
     d) separating the first mold from the inlay material and the base, thereby forming a final mold having a plurality of inlay material protrusions over the base, the protrusions and base defining the shape and the size of the ink jet nozzles; 
     e) providing plate forming material between the protrusions and over the base in the final mold; and 
     f) releasing the plate forming material to form an ink jet nozzle plate having a plurality of ink jet nozzles. 
     ADVANTAGES 
     An advantage of the present invention is that ink jet nozzles for ink jet cartridges are effectively provided and with precise tolerance such that the ink drop ejection properties can be optimized. 
     A further advantage of the present invention is that the fabrication methods in the present invention can produce different shapes in the ink jet nozzle for improved ink drop injection. 
     Yet a further advantage of the present invention is that the size of the ink jet nozzle is insensitive to variations in the conditions of manufacture. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 a - 1   l  illustrate a series of steps that are used in practicing the method of the present invention to produce an ink jet nozzle plate in accordance with a first embodiment of the present invention; 
     FIGS. 2 a - 2   e  illustrate a series of steps that are used in a second embodiment of the present invention: and 
     FIGS. 3 a -3 c  illustrate a series of steps that are used in practicing the method of the present invention to produce an ink jet nozzle plate in accordance with a third embodiment of the present invention: 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is described with relation to the formation of ink jet nozzle plates. Specifically, the present invention relates to providing a mold for forming an ink jet nozzle plate. 
     The first embodiment of the present invention is depicted in FIGS. 1 a  to  11 . In FIG. 1 a , there is provided a substrate  10 , preferably a silicon wafer substrate of crystallographic orientation, commonly used for semiconductor Integrated Circuitry (IC) manufacture. In FIG. 1 b , a mask  20  is next provided on the substrate  10 . The mask is preferably silicon dioxide that can be thermally grown on the substrate  10 . The mask  20  can also be silicon nitride that can be deposited by low pressure Chemical Vapor Deposition (CVD). 
     The substrate  10  is next modified, as shown in FIG. 1 b , to form a modified substrate  10   a . The mask  20  is first uniformly coated by a photoresist such as KTI  820 . Selective areas on the mask  20  are patterned photo-lithographically on the photoresist layer. The selected areas of the mask  20  are removed by chemical etching. The silicon wafer substrate  10  under the selected areas is subsequently etched to form a plurality of first etched regions  12  in the modified substrate  10   a . The etching can be made by a wet etchant having an aqueous solution of potassium hydroxide (KOH). This etchant forms first inclined walls  25 , as is well known in the art of semiconductor processing, that are defined by the [ 111 ] crystalline planes of silicon. 
     Next, referring to FIG. 1 c , the modified substrate  10   a  is further subjected to an anisotropic dry etch, preferably by a high density plasma etch, which etches the modified substrate  10   a  vertically at the bottom surfaces of the first etched regions  12 . The dry etching step thereby creates recesses  34  with vertical recess sides  34   a , FIG. 1 e , typically extending 1 to 50 microns into the modified substrate  10   a , while leaving the first inclined walls  25  in the first etched region  12  substantially unchanged. A first mold  30  is thereby formed from themodified substrate  10   a . A top view of the first mold is shown in FIG. 1 d.    
     In the field of ink jet printing, it is usually desirable to optimize the shapes of the internal walls in an ink jet nozzle. These optimized shapes may include curved surfaces rather than flat faces as defined by a crystalline plane such as the silicon planes. In addition, the internal walls and the ink jet nozzles are often preferably to be round or cylindrically symmetric around the ink jet nozzle axis. In accordance to the present invention, as it will be understood in the description below, these above requirements can be achieved by a shaped etch region  36  defined by a curved and round shaped side wall  32 , as shown in FIG. 1 e . The shaped etch regions  36  can be formed in the modified substrate  10   a  by a plasma etch that is capable of both isotropic and anisotropic etching. The plasma etch forms the shaped side walls  32  to an optimized shape and symmetry. The shaped side walls  32  can be made to be either isotropic or anisotropic around the axis of the shaped etch region  36 . As in the previous case, an anisotropic dry etch can then be used to form recesses  34  with vertical recess sides  34   a , as shown in FIG. 1 e . A top view of a first mold  30   a  achieved by forming round shaped side walls  32  is shown in FIG. 1 f . 
     In accordance to the present invention, the following descriptions in relation to FIGS. 1 g - 11  can be similarly applied using either the first mold  30  or the first mold  30   a , as respectively illustrated in FIGS. 1 c  and  1   e . Referring now to FIG. 1 g , the mask  20  is next removed by oxygen plasma stripping from the first mold  30  (or  30   a ). A first inlay  40  is provided inside first etched regions  12  and the recess  34  and over the top surface  35  of first mold  30 . The first inlay  40  can be spin-coated by polymeric materials such as silicon rubber, polyimides, polymethyl methacrylate, or hydrofluorocarbons such as Teflon, made by the duPont Company. The first inlay  40  can also be deposited by planarizable materials well known in the art of semiconductor manufacturing: boron containing silicon oxides or mixtures of silicon oxide and silicon nitride. Preferably, the top surface  41  of first inlay  40  is planar. Planarization techniques such as chemical mechanical polishing can be used to render the top surface  41  to be substantially planar. 
     Next, in FIG. 1 h , a base  50 , made of an electrically conductive material such as aluminum, is attached to top surface  41  by, for example, thermal bonding or epoxy bonding between base  50  and top surface  41 . After the bonding is complete, the modified substrate ( 30  (or  30   a  ) is removed to form a released portion  60 , shown in FIG. 1 i , comprising the base  50  and the first inlay  40  that is bounded by the vertical walls  40   a , second inclined walls  40   b , and horizontal portion  40   c . The vertical wall  40   a , originally created by vertical recess side  34   a  of recess  34 , is essential for providing ink jet nozzle diameters with low manufacturing variability. The removal of the modified substrate  10   a  is preferably conducted by first grinding away a large portion of the material and then by etching away the remainder by a fluorine based plasma etch. Alternatively, it is known in the art that a thin release layer such as an oxide can be deposited in the first mold before providing first inlay  40 . The released portion  60  can then be separated from the first mold  30  by chemically dissolving the thin release layer. 
     Referring to FIG. 1 j , the horizontal portion  40   c  of the material of first inlay  40  is etched away using an anisotropic etch, such as an oxygen reactive ion plasma etch, to expose a conductive surface  50   a  on the base  50 , thereby forming final mold  62 . The shape of the vertical walls  40   a  and second inclined walls  40   b  are substantially unchanged by this etch. In particular, the vertical walls  40   a  remain vertical, due to the anisotropic nature of the etch. The final mold  62  includes the continuous conductive surface  50   a  and non-conductive protrusions that are defined by the vertical walls  40   a  and second inclined walls  40   b . Each protrusion includes a top portion  40   d  with vertical walls  40   a  and a lower portion  40   e  with second inclined walls  40   b . The vertical walls  40   a  define the ink jet nozzle diameter when the plate forming material is provided between the protrusions. 
     Now referring to FIGS. 1 k  and  11 , a second inlay  70  which forms ink jet nozzle plate  80  is made of a hardenable plate forming material. The plate forming material is preferably electroplated into the final mold  62  in an electroforming bath. A metallic layer is grown from the continuous conductive surfaces  50   a , that is used as an electrode, onto the non-conducting surfaces on the second inclined walls  40   b  and the vertical walls  40   a  on the final mold  62 . The metal for electroplating can include nickel, gold, metallic alloys, or metal-organic mixtures as is well known in the art of electroplating. The electrolyte is preferably an aqueous solution comprising salt of the corresponding metallic ions. The second inlay  70  is then removed, for example, by mechanically peeling, from the base  50 , to provide the ink jet nozzle plate  80 , as shown in FIG.  11 . The ink jet nozzle plate  80  comprises bore region  84  with vertical walls  84   a  and cavity regions  82 . 
     In accordance with the present invention, the second inlay  70 , shown in FIG. 1 k , is grown to a height within the height range of the vertical wall  40   a . In other words, the second inlay  70  does not grow higher than the vertical wall  40   a  of the first inlay  40  nor below the intersection between the vertical wall  40   a  and the second inclined wall  40   b . In this manner, the bore region  84  of ink jet nozzle plate  80  has an exit diameter that is independent of the exact height of thesecond inlay  70 , which reduces the variability in the nozzle diameter in the fabrication process. Moreover, vertical walls  84   a  at the exit end of the bore region  84  are known to be desirable for ink jet nozzle plates. 
     A second embodiment of the present invention is now described in relation to FIGS. 2 a  to  2   e . This embodiment teaches a different approach for the formation of a final mold for the electroforming process. A first mold  130  of FIG. 2 a  is provided with a conformal insulator  140  in FIG. 2 b . For example, the first mold  130  can be silicon and the conformal insulator  140  can be silicon oxide. The conformal insulator  140  can also be a deposited film of polymer such as Teflon. The conformal insulator  140  is removed from top surface  130   a  of first mold  130  forming a modified conformal insulator  140   a , shown in FIG. 2 c . Next, as shown in FIG. 2 d , a conductive material  142  is provided over the top surface  130   a  and the modified conformal insulator  140   a . The bottom surface  142   a  of the conductive material  142  is in contact with top surface  130   a . Final mold  162  is then made by bonding top surface  142   b  of the conductive material  142  to a base  150  and removing the first mold  130  as shown in FIG. 2 e . The first mold  130  can be removed, for example, by mechanical grinding, or chemical or plasma etching. The structure is shown inverted in FIG. 2 e  with bottom surface  142   a  upwards to provide a continuous conductive surface to be used as an electrode in the electroplating process for forming the metallic ink jet nozzle plate, similar to the description in relation to FIGS. 1 k  and  11  . 
     A third embodiment of the present invention, shown in FIGS. 3 a - 3   c  is particularly useful in making the top portion  40   d  of FIG. 1 e  described in the first embodiment. The substrate  10  is replace by a composite substrate  210 , comprising a top substrate layer  214 , a buried layer  216 , and a bottom substrate layer  218 . Preferably composite substrate  210  is an SOI (silicon on insulator) substrate, commercially available for the manufacture of semiconductor devices, for example high voltage silicon devices. In this preferred case, the top and bottom substrates  214  and  218  are made of silicon material and the buried layer  216  is silicon dioxide. As shown in FIG. 3 a  and  3   b , a mask  220  is used to define openings for a shaped etch region  212 , made similarly to first etched region  12  of the first embodiment. Next, as shown in FIG. 3 c , buried layer  216  is etched, preferably by a reactive ion plasma etch, to form the first mold  230  that includes a plurality of projections  234  with vertical sides  234   a . The vertical sides  234   a  are analogous to the vertical sides  34   a  in FIG. 1 d . The length of the vertical wall  234   a  is precisely defined by the thickness of buried layer  216 , since the bottom substrate layer  218  can act as an etch stop for etching buried layer  216 . A final mold can be formed from the first mold  230  using procedures similar to the descriptions in FIGS. 1 g  to  1   j . 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
     PARTS LIST 
       10  substrate 
       10   a  modified substrate 
       12  first etched region 
       20  mask 
       25  first inclined wall 
       30  first mold 
       30   a  first mold 
       32  shaped side wall 
       34  recess 
       34   a  vertical recess side 
       35  top surface 
       36  shaped etch region 
       40  first inlay 
       40   a  vertical wall 
       40   b  second inclined wall 
       40   c  horizontal portion 
       40   d  top portion 
       40   e  lower portion 
       41  top surface 
       50  base 
       50   a  conductive surface 
       60  first released portion 
       62  final mold 
       70  second inlay 
       80  ink jet nozzle plate 
       82  cavity region 
       84  bore region 
       84   a  vertical walls PARTS LIST (con&#39;t) 
       130  first mold 
       130   a  top surface 
       140  conformal insulator 
       140   a  modified conformal insulator 
       142  conductive material 
       142   a  bottom surface 
       142   b  top surface 
       150  base 
       162  final mold 
       210  composite substrate 
       212  shaped etch region 
       214  top substrate layer 
       216  buried layer 
       218  bottom substrate 
       220  mask 
       230  first mold 
       234  projection 
       234   a  vertical side