Abstract:
The invention provides an improved method for grit blasting slots in a silicon wafer. The method includes, providing a silicon wafer having a first surface and a second surface, the first surface containing resistive, conductive and insulative layers defining individual semiconductor components, applying a first substantially permanent non-water soluble layer selected from silane, photoresist materials and a combination of a silane layer and a photoresist layer to the first surface of the wafer to provide a first substantially permanent layer thereon, applying a water-soluble protective material to the first layer to provide a second layer, grit blasting slots in the wafer corresponding to the individual semiconductor components, and subsequently, removing the water-soluble protective layer from the wafer. The protective layer provides enhanced protection for the electrical components on a silicon wafer during a grit blasting process so that a higher yield of useable semiconductor chips may be made.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to the field of ink jet printers. More particularly, this invention relates to improved manufacturing methods for making printheads and printhead components.  
         BACKGROUND OF THE INVENTION  
         [0002]    Ink jet printers contain semiconductor chips which are electrically activated to eject ink droplets on demand through nozzle holes in a nozzle plate attached to the chips. In a “roof shooter” type printhead, ink is provided to the active surface of the chips for ink droplet ejection through ink vias or ink feed slots which are formed through the thickness dimension of the chips. In order to produce printhead chips in large quantities with minimum production costs, grit blasting is conventionally used to blast slots in a silicon wafer prior to dicing the wafer to form individual semiconductor chips. The silicon wafers are typically processed prior to grit blasting to contain insulative, conductive, resistive, passivation and/or cavitation layers which provide the active surface for ink ejection. During the grit blasting process, which is typically conducted from the side of the wafer opposite the active surface, some of the grit passing through the wafer may ricochet and impinge on the active surface side of the wafer thereby causing electrical shorts and open circuits. The shorts or open circuits must be repaired or the chips containing the damaged circuits discarded, these steps resulting in lower product yields and/or lower production rates. There is a need, therefore, for improved methods for grit blasting ink feed vias or slots in silicon wafers used to make ink jet printhead chips.  
         SUMMARY OF THE INVENTION  
         [0003]    The foregoing and other needs are provided by an improved method for grit blasting slots in a silicon wafer. The method includes providing a silicon wafer having a first surface and a second surface, the first surface containing resistive, conductive and insulative layers defining individual semiconductor components, applying a first substantially permanent non-water soluble layer selected from silane, photoresist materials and a combination of a silane layer and a photoresist layer to the first surface of the wafer to provide a first substantially permanent layer thereon, applying a water-soluble protective material to the first layer to provide a second layer, grit blasting slots in the wafer corresponding to the individual semiconductor components. Each of the slots extend from the second surface of the wafer through the wafer and through the first and second layers. Subsequently, removing the water-soluble protective layer from the wafer.  
           [0004]    In another aspect the invention provides a method for making ink jet printheads containing a silicon substrate with an ink feed via grit blasted therein. The method includes spin coating a substantially water-insoluble first material selected from the group consisting of a silane material, a photoresist material and a combination of silane and photoresist materials on a first surface of the silicon substrate wafer to provide a first layer. The first surface of the wafer preferably contains resistive, conductive and insulative layers defining individual semiconductor components. A substantially water-soluble protective material is spin-coated onto the first layer to provide a second layer. Ink vias are grit blasted in the wafer from a second surface side thereof opposite the first surface. Substantially all of the second layer is removed from the wafer. Nozzle plates are attached to the chips to provide nozzle plate/chip assemblies and the wafer is diced to provide individual nozzle plate/chip assemblies. TAB circuits or flexible circuits are electrically connected to the nozzle plate/chip assemblies and the nozzle plate/chip assemblies and connected circuits are adhesively attached to printhead bodies to provide ink jet printheads.  
           [0005]    The first and/or second layers applied to the wafer provide enhanced protection to delicate electrical components on the wafer surface during wafer processing procedures such as grit blasting. The layers are selected so that the layers may be applied to the entire surface of the wafer with coating techniques such as spin coating so that the entire surface of the wafer is protected. Since the protective layer is preferably selected to be substantially completely removable from the first layer, any grit passing through the wafer from the second surface side to the device surface side of the wafer may be removed with the second layer.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    Further advantages of the invention will become apparent by reference to the detailed description of preferred embodiments when considered in conjunction with the drawings, which are not to scale, wherein like reference characters designate like or similar elements throughout the several drawings as follows:  
         [0007]    FIGS.  1 A- 1 D are cross-sectional views not to scale illustrating a wafer processing step according to a first embodiment of the invention;  
         [0008]    FIGS.  2 A- 2 D are cross-sectional views not to scale illustrating a wafer processing step according to a second embodiment of the invention;  
         [0009]    FIGS.  3 A- 3 D are cross-sectional views not to scale illustrating a wafer processing step according to a third embodiment of the invention; and  
         [0010]    [0010]FIG. 4 is a cross-sectional view not to scale of an ink jet printhead made according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0011]    With reference to FIG. 1A, a silicon wafer  10  containing a first protective layer  12  is shown. The wafer  10  has a device surface  14  containing a plurality of layers including insulating, conductive, resistive, passivation and/or cavitation layers which together provide an active layer for ink ejection for individual chips made from the wafer  10 . The silicon wafer  10  preferably has a thickness ranging from about 200 to about 800 microns and the active layer on the device surface  12  preferably has an overall thickness ranging from about 1 micron to about 5 microns, most preferably from about 2 to about 3 microns. The first layer  12  is deposited over the device surface  14  to provide a substantially planar surface  16  and/or to provide adhesion enhancement for attaching a nozzle plate thereto as described in more detail below.  
         [0012]    With regard to the device surface  14  of the wafer  10 , active devices such as heater resistors are attached to an insulating layer which is preferably a metal oxide layer, most preferably silicon dioxide having a thickness ranging from about 1.0 to about 2.0 microns. A phosphorous silicon glass (PSG) layer having a thickness ranging from about 1000 to about 1200 Ångstroms is preferably deposited over the insulating layer. A resistive material of tantalum/aluminum, or alpha phase tantalum is next deposited on at least a portion of the PSG layer. The resistive material provides heater resistors which upon activation urge ink to be ejected through the nozzle holes in the nozzle plate attached to the chip. The resistive material preferably has a thickness ranging from about 900 to about 1100 Ångstroms.  
         [0013]    Conductive layers made of an aluminum/copper alloy, gold, beta phase tantalum, aluminum and the like are deposited on one or more portions of the resistive layer. The conductive layers provide electrical connection between the resistors and a printer controller. The conductive layers each preferably have a thickness ranging from about 5000 to about 6000 Ångstroms.  
         [0014]    In order to protect the conductive and resistive layers from ink corrosion, passivation layers are preferably deposited over the resistive layer and conductive layers. The passivation layers may be a composite layer of silicon nitride and silicon carbide, or may be individual layers of silicon nitride and silicon carbide, respectively. The passivation layers are preferably deposited directly on the conductive layers and the resistive layer. It is preferred that the silicon carbide layer has a thickness ranging from about 2000 to about 3000 Ångstroms, most preferably from about 2600 Ångstroms. The silicon nitride layer preferably has a thickness ranging from about 4000 to about 5000 Ångstroms, most preferably about 4400 Ångstroms.  
         [0015]    A cavitation or additional passivation layer of tantalum or diamond like carbon (DLC) is preferably deposited over at least a portion of the passivation layers, most preferably adjacent the heater resistor. The cavitation layer provides protection to the heater resistor during ink ejection operations which could cause mechanical damage to the heater resistor in the absence of the cavitation layer. The cavitation layer is believed to absorb energy from a collapsing ink bubble after ejection of ink from the nozzle holes. The cavitation layer thickness may range from about 2500 to about 7000 Ångstroms or more.  
         [0016]    In order to adhesively attach a nozzle plate to the device surface  14  of a chip made from the wafer  10 , the first layer  12  is preferably spin coated onto the device surface  14  of the wafer  10  (FIG. 1A). The first layer  12  is preferably derived from a group consisting of a silane material; a radiation and/or heat curable polymeric film material preferably containing a difunctional epoxy material, a polyfunctional epoxy material and suitable cure initiators and catalyst; and a silane material and radiation and/or heat curable polymeric film material. Particularly preferred materials for providing the first layer  12  include a silane adhesion promoter available from Dow Corning of Midland, Mich. under the trade name Z6032 and the polymeric photoresist material described in U.S. Pat. No. 5,907,333 to Patil et al., the disclosure of which is incorporated herein by reference as if fully set forth.  
         [0017]    In the case of a silane material providing the first layer  12 , the first layer  12  is relatively thin compared to silicon wafer  10  and may have a thickness ranging from about 1 Ångstroms to about 10 Ångstroms, preferably about 4 to about 8 Ångstroms and most preferably about 6 Ångstroms. If a photoresist material is selected to provide the first layer (described with respect to FIGS.  3 A- 3 D below) or if a silane material and photoresist material are selected to provide the first layer (described with respect to FIGS.  2 A- 2 D below), the thickness of the first layer  12  may range from about 1 to about 10 microns, most preferably about 2.5 microns.  
         [0018]    It is preferred to deposit the first layer  12  over the entire device surface  14  of the wafer  10 . Prior to grit blasting the ink vias or ink feed slots in the wafer  10 , the photoresist material of the first layer  12  is selectively removed, i.e., “patterned”, to provide ink chambers and windows for electrical connections to the conductive layers on the device surface  14 . Patterning the photoresist material of the first layer  12  may be conducted by conventional photolithographic techniques.  
         [0019]    Since the first layer  12  does not protect all of the delicate circuitry on the device surface  14 , a second layer  18  is preferably applied to the first layer  12  to cover substantially the entire wafer surface including the patterned areas which expose the device surface  14  to mechanical damage. The second layer  18  is preferably derived from a material selected from the group consisting of substantially water soluble polymers, including but not limited to, polyacrylamide materials.  
         [0020]    The second layer  18  is preferably a water-soluble polymeric material which is applied to the first layer  12  by a spin coating technique (FIG. 1B). Water-soluble polymeric materials for use as the second layer  18  include, but are not limited to, polyacrylamide, polyvinyl alcohol and polyethylene oxide. A preferred water-soluble polymeric material is polyacrylamide. When a polyacrylamide material is used to provide protective layer  18 , the polyacrylamide layer  18  is preferably derived from a 50 wt. % polyacrylamide solution in water wherein the preferred polyacrylamide has a weight average molecular weight of about 10,000. Such a polyacrylamide is available from Aldrich Chemical Company of Milwaukee, Wis. under catalog no. 43,494-9. The foregoing aqueous solution of polyacrylamide is preferably applied to the first layer  12  to provide a second layer  18  having a thickness ranging from about 20 to about 25 microns or more as shown in FIG. 1B.  
         [0021]    After applying the first and second layers  12  and  18  to the wafer  10 , the wafer is grit blasted to abrasively form ink feed slots or ink vias  20  in the wafer (FIG. 1C). Grit blasting the wafer  10  is preferably conducted from a back side  22  opposite the device surface  14  containing the first and second layers  12  and  18 . The slots or vias  20  typically have dimensions of about 9.7 millimeters long and about 0.4 millimeters wide. Individual ink jet chips made from the wafers  10  typically have dimensions ranging from about 2 to about 8 millimeters wide by about 10 to about 20 millimeters long. Each of the chips contains at least one ink feed slot or via  20 . Abrasive materials used in the grit blasting process is preferably selected from alumina and silicon carbide. The average particle size of the abrasive material preferably ranges from about 15 to about 25 microns.  
         [0022]    Subsequent to grit blasting the slots or vias  20  in the wafer  10 , substantially all of the second layer  18  is removed from the wafer  10  as shown in FIG. 1D to provide a wafer containing the first layer  12  and ink slot or via  20 . It will be recognized that abrasive material from the grit blasting step may impinge on and/or imbed in the second layer  18 . Accordingly, removal of substantially all of the second layer  18  also effectively removes any abrasive material which may be attached to the second layer  18 . It will also be recognized that since the protective material  18  covers the entire surface of the first layer and device surface  14  of the wafer  10 , damage to the delicate device surface  14  is minimized during the slot or via forming process.  
         [0023]    With regard to the process illustrated in FIGS.  1 A- 1 D, the first layer  12  is preferably derived from a silane adhesion promoter material and the second layer  18  is derived from a water soluble polymeric material. Accordingly, the second layer  18  may be removed by washing the wafer  10  after conducting the grit blasting step.  
         [0024]    With reference to FIGS.  2 A- 2 D, a second embodiment of the invention will now be described. As shown in FIG. 2A, a first layer  26 , preferably includes a material derived from a silane adhesion promoter material as described above applied to the device surface  14  of the wafer  10 . The first layer  26  also includes a substantially water-insoluble polymeric material  24  applied to the silane material  12 . The silane material  12  preferably has a thickness ranging from about 1 to about 10 Ångstroms and the polymeric material  24  preferably has a thickness ranging from about 1 to about 10 microns. Next a substantially water-soluble polymeric protective material is applied to the first layer  26  to provide layer  18 . The protective layer  18  preferably has a thickness ranging from about 20 to about 25 microns and is preferably derived from a polyacrylamide material as set forth above.  
         [0025]    The photoresist material provides a layer  24  with a thickness ranging from about 1 to about 10 microns and is derived from materials including acrylic and epoxy-based photoresists such as the photoresist materials available from Clariant Corporation of Somerville, N.J. under the trade names AZ4620 and AZ1512. Other photoresist materials are available from Shell Chemical Company of Houston, Tex. under the trade name EPON SU8 and photoresist materials available from Olin Hunt Specialty Products, Inc., a subsidiary of the Olin Corporation of West Paterson, N.J. under the trade name WAYCOAT. A particularly preferred photoresist material includes from about 10 to about 20 percent by weight difanctional epoxy compound, less than about 4.5 percent by weight multifunctional crosslinking epoxy compound, and from about 1 to about 10 percent by weight of a photoinitiator capable of generating a cation, and from about 20 to about 90 percent by weight non-photoreactive solvent as described in U.S. Pat. No. 5,907,333 to Patil et al., the disclosure of which is incorporated by reference herein as if fully set forth.  
         [0026]    As shown in FIG. 2C and described in detail above, an ink feed slot or ink via  20  is abrasively formed in the silicon wafer  10 , first layer  26 , and second layer  18 . After forming the ink feed slot or via  20 , the substantially water-soluble protective layer  18  containing imbedded abrasive material is removed from the first layer  26  preferably by dissolving the protective layer  18  in a water washing procedure. The resulting wafer as shown in FIG. 2D preferably includes a first layer containing a silane material  12  and a photoresist material  24 .  
         [0027]    According to FIGS.  3 A- 3 D, a third embodiment of the invention will now be described. According to this embodiment, the first layer  24  is derived from a photoresist material as set forth above. The first layer  24  preferably has a thickness ranging from about 1 to about 10 microns and is patterned as set forth above with reference to FIGS.  1 A- 1 D. Next, the second layer  18 , preferably derived from a substantially water-soluble polymeric material, preferably a polyacrylamide material as described above, is applied to the first layer  24 . The second layer preferably has a thickness ranging from about 20 to about 25 microns.  
         [0028]    After forming the ink feed slots or vias  20  through the wafer  10 , the first layer  24  and the second layer  18 , the second layer  18  is preferably removed from the first layer  24  by washing as described above to provide the wafer illustrated in FIG. 3D containing only first layer  24  thereon. Accordingly, abrasive material adhered to or imbedded in the second layer  18  is also removed with the second layer  18 .  
         [0029]    A nozzle plate  30  is then preferably adhesively attached to the first layer  12 ,  26  or  24  (FIGS. 1D, 2D and  3 D) remaining on the chip to provide a nozzle plate/chip assembly  28 / 30  (FIG. 4). The nozzle plate  30  may be made of metals or plastics and is preferably made of a polyimide polymer which is laser ablated to provide ink chambers, nozzle holes, and ink supply channels herein. The adhesive used to attach the nozzle plate  30  to the chip  28  is preferably any B-stageable material, including some thermoplastics. Examples of B-stageable thermal cure resins include phenolic resins, resorcinol resins, urea resins, epoxy resins, ethylene-urea resins, furane resins, polyurethanes, and silicone resins. Suitable thermoplastic, or hot melt, materials include ethylene-vinyl acetate, ethylene ethylacrylate, polypropylene, polystyrene, polyamides, polyesters and polyurethanes. The adhesive is preferably applied with a thickness ranging from about 1 to about 25 microns. In the most preferred embodiment, the adhesive is a phenolic butyral adhesive such as that used in RFLEX R1100 or RFLEX R1000 films, commercially available from Rogers of Chandler, Ariz. Once the nozzle plates  30  are attached to the wafers  10 , and the adhesive used to attach the nozzle plates  30  is cured, the wafers  10  are diced to provide individual nozzle plate/chip assemblies  30 / 28  such as the nozzle plate/chip assembly  30 / 28  shown in FIG. 4.  
         [0030]    A flexible circuit or tape automated bonding (TAB) circuit  32  is attached to the nozzle plate/chip assembly  30 / 28  to provide a nozzle plate/chip/circuit assembly  30 / 28 / 32 . The nozzle plate/chip/circuit assembly  30 / 28 / 32  is preferably adhesively attached to a printhead body portion  34  to provide a printhead  36  for an ink jet printer. The nozzle plate/chip assembly  30 / 28  may be attached as by means of a die bond adhesive, preferably a conventional die bond adhesive such as a substantially transparent phenolic polymer adhesive which is commercially available from Georgia Pacific under the product designation “BKS 2600”, in a chip pocket  38  of a printhead body portion  34 . The flexible circuit or TAB circuit  32  is adhesively attached to surface  40  of the printhead body portion  34  after attaching the nozzle plate/chip assembly  30 / 28  in the chip pocket  38 . A portion  42  of the flexible circuit or TAB circuit  32  is preferably folded around edge  44  of the body portion  34  to provide locations for electrical contact to a printer controller in the ink jet printer.  
         [0031]    Ink supplied from an ink reservoir adjacent an ink surface  46  of the printhead body portion  34  flows through an ink path in the body portion  34  and through the ink via or slot  20  described above to the device surface  14  of the chip. Activation of the devices on the device surface  14  of the chip causes ink to be ejected through nozzle holes in the nozzle plate  30 .  
         [0032]    It is contemplated, and will be apparent to those skilled in the art from the preceding description and the accompanying drawings, that modifications and changes may be made in the embodiments of the invention. Accordingly, it is expressly intended that the foregoing description and the accompanying drawings are illustrative of preferred embodiments only, not limiting thereto, and that the true spirit and scope of the present invention be determined by reference to the appended claims.