Abstract:
A method of forming a substrate for a fluid ejection device includes forming an opening in the substrate from a second side of the substrate toward a first side of the substrate, further forming the opening in the substrate to the first side of the substrate, anisotropically wet etching the substrate, including increasing the opening at the second side of the substrate and forming the opening with converging sidewalls from the second side to the first side, and after anisotropically wet etching the substrate, isotropically etching the substrate.

Description:
BACKGROUND 
       [0001]    An inkjet printing system, as one embodiment of a fluid ejection system, may include a printhead, an ink supply which supplies ink to the printhead, and an electronic controller which controls the printhead. The printhead, as one embodiment of a fluid ejection device, ejects drops of ink through a plurality of nozzles or orifices and toward a print medium, such as a sheet of paper, so as to print onto the print medium. Typically, the orifices are arranged in one or more columns or arrays such that properly sequenced ejection of ink from the orifices causes characters or other images to be printed upon the print medium as the printhead and the print medium are moved relative to each other. 
         [0002]    The printhead may include one or more ink feed slots which route different colors or types of ink or fluid to fluid ejection chambers communicated with the nozzles or orifices of the printhead. Due to market forces and continuing technological improvements, the spacing or width between the ink feed slots (i.e., slot pitch) has been decreasing. This decrease in slot pitch, although increasing a number of nozzles or resolution of the printhead (i.e., nozzle density), may create a challenge in forming the ink feed slots. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]      FIG. 1  is a block diagram illustrating one embodiment of a fluid ejection system. 
           [0004]      FIG. 2  is a schematic cross-sectional view illustrating one embodiment of a portion of a fluid ejection device. 
           [0005]      FIGS. 3A-3J  schematically illustrate one embodiment of forming a substrate for a fluid ejection device. 
           [0006]      FIGS. 4A and 4B  schematically illustrate one embodiment of a substrate for a fluid ejection device during forming of the substrate. 
       
    
    
     DETAILED DESCRIPTION 
       [0007]    In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the disclosure may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” “leading,” “trailing,” etc., is used with reference to the orientation of the Figure(s) being described. Because components of embodiments of the present disclosure can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims. 
         [0008]      FIG. 1  illustrates one embodiment of an inkjet printing system  10 . Inkjet printing system  10  constitutes one embodiment of a fluid ejection system which includes a fluid ejection assembly, such as an inkjet printhead assembly  12 , and a fluid supply assembly, such as an ink supply assembly  14 . In the illustrated embodiment, inkjet printing system  10  also includes a mounting assembly  16 , a media transport assembly  18 , and an electronic controller  20 . 
         [0009]    Inkjet printhead assembly  12 , as one embodiment of a fluid ejection assembly, includes one or more printheads or fluid ejection devices which eject drops of ink or fluid through a plurality of orifices or nozzles  13 . In one embodiment, the drops are directed toward a medium, such as print medium  19 , so as to print onto print medium  19 . Print medium  19  is any type of suitable sheet material, such as paper, card stock, transparencies, Mylar, fabric, and the like. Typically, nozzles  13  are arranged in one or more columns or arrays such that properly sequenced ejection of ink from nozzles  13  causes, in one embodiment, characters, symbols, and/or other graphics or images to be printed upon print medium  19  as inkjet printhead assembly  12  and print medium  19  are moved relative to each other. 
         [0010]    Ink supply assembly  14 , as one embodiment of a fluid supply assembly, supplies ink to inkjet printhead assembly  12  and includes a reservoir  15  for storing ink. As such, in one embodiment, ink flows from reservoir  15  to inkjet printhead assembly  12 . In one embodiment, inkjet printhead assembly  12  and ink supply assembly  14  are housed together in an inkjet or fluid-jet cartridge or pen. In another embodiment, ink supply assembly  14  is separate from inkjet printhead assembly  12  and supplies ink to inkjet printhead assembly  12  through an interface connection, such as a supply tube. 
         [0011]    Mounting assembly  16  positions inkjet printhead assembly  12  relative to media transport assembly  18  and media transport assembly  18  positions print medium  19  relative to inkjet printhead assembly  12 . Thus, a print zone  17  is defined adjacent to nozzles  13  in an area between inkjet printhead assembly  12  and print medium  19 . In one embodiment, inkjet printhead assembly  12  is a scanning type printhead assembly and mounting assembly  16  includes a carriage for moving inkjet printhead assembly  12  relative to media transport assembly  18 . In another embodiment, inkjet printhead assembly  12  is a non-scanning type printhead assembly and mounting assembly  16  fixes inkjet printhead assembly  12  at a prescribed position relative to media transport assembly  18 . 
         [0012]    Electronic controller  20  communicates with inkjet printhead assembly  12 , mounting assembly  16 , and media transport assembly  18 . Electronic controller  20  receives data  21  from a host system, such as a computer, and may include memory for temporarily storing data  21 . Data  21  may be sent to inkjet printing system  10  along an electronic, infrared, optical or other information transfer path. Data  21  represents, for example, a document and/or file to be printed. As such, data  21  forms a print job for inkjet printing system  10  and includes one or more print job commands and/or command parameters. 
         [0013]    In one embodiment, electronic controller  20  provides control of inkjet printhead assembly  12  including timing control for ejection of ink drops from nozzles  13 . As such, electronic controller  20  defines a pattern of ejected ink drops which form characters, symbols, and/or other graphics or images on print medium  19 . Timing control and, therefore, the pattern of ejected ink drops, is determined by the print job commands and/or command parameters. In one embodiment, logic and drive circuitry forming a portion of electronic controller  20  is located on inkjet printhead assembly  12 . In another embodiment, logic and drive circuitry forming a portion of electronic controller  20  is located off inkjet printhead assembly  12 . 
         [0014]      FIG. 2  illustrates one embodiment of a portion of a fluid ejection device  30 . Fluid ejection device  30  includes an array of drop ejecting elements  31 . Drop ejecting elements  31  are formed on a substrate  40  which has a fluid (or ink) feed slot  41  formed therein. As such, fluid feed slot  41  provides a supply of fluid (or ink) to drop ejecting elements  31 . Substrate  40  is formed, for example, of silicon, glass, or ceramic. 
         [0015]    In one embodiment, each drop ejecting element  31  includes a thin-film structure  32  with a resistor  34 , and an orifice/barrier layer  36 . Thin-film structure  32  has a fluid (or ink) feed hole  33  formed therein which communicates with fluid feed slot  41  of substrate  40 . Orifice/barrier layer  36  has a front face  37  and a nozzle opening  38  formed in front face  37 . Orifice/barrier layer  36  also has a nozzle chamber  39  formed therein which communicates with nozzle opening  38  and fluid feed hole  33  of thin-film structure  32 . Resistor  34  is positioned within nozzle chamber  39  and includes leads  35  which electrically couple resistor  34  to a drive signal and ground. 
         [0016]    Thin-film structure  32  is formed, for example, by one or more passivation or insulation layers of silicon dioxide, silicon carbide, silicon nitride, tantalum, poly-silicon glass, or other material. In one embodiment, thin-film structure  32  also includes a conductive layer which defines resistor  34  and leads  35 . The conductive layer is formed, for example, by aluminum, gold, tantalum, tantalum-aluminum, or other metal or metal alloy. 
         [0017]    In one embodiment, during operation, fluid flows from fluid feed slot  41  to nozzle chamber  39  via fluid feed hole  33 . Nozzle opening  38  is operatively associated with resistor  34  such that droplets of fluid are ejected from nozzle chamber  39  through nozzle opening  38  (e.g., normal to the plane of resistor  34 ) and toward a medium upon energization of resistor  34 . 
         [0018]    Example embodiments of fluid ejection device  30  include a thermal printhead, as previously described, a piezoelectric printhead, a flex-tensional printhead, or any other type of fluid-jet ejection device known in the art. In one embodiment, fluid ejection device  30  is a fully integrated thermal inkjet printhead. 
         [0019]      FIGS. 3A-3J  illustrate one embodiment of forming an opening  150  through a substrate  160 , with opening  150  and substrate  160  representing one embodiment of fluid feed slot  41  and substrate  40 , respectively, of fluid ejection device  30  ( FIG. 2 ). In one embodiment, substrate  160  is a silicon substrate and opening  150  is formed in substrate  160  as described below. Substrate  160  has a first side  162  and a second side  164 . Second side  164  is opposite of first side  162  and, in one embodiment, oriented substantially parallel with first side  162 . Opening  150  communicates with first side  162  and second side  164  of substrate  160  so as to provide a channel or passage through substrate  160 . While only one opening  150  is illustrated as being formed in substrate  160 , it is understood that any number of openings  150  may be formed in substrate  160 . 
         [0020]    In one embodiment, first side  162  forms a front side of substrate  160  and second side  164  forms a back side of substrate  160  such that fluid flows through opening  150  and, therefore, substrate  160  from the back side to the front side. Accordingly, opening  150  provides a fluidic channel or fluid (or ink) feed slot for the communication of fluid (or ink) with drop ejecting elements  31  ( FIG. 2 ) through substrate  160 . 
         [0021]    In one embodiment, as illustrated in  FIG. 3A , before opening  150  is formed through substrate  160 , thin-film structure  32  including resistors  34  ( FIG. 2 ) is formed on first side  162  of substrate  160 . As described above, thin-film structure  32  includes one or more passivation or insulation layers formed, for example, of silicon dioxide, silicon carbide, silicon nitride, tantalum, poly-silicon glass, or other material. In addition, thin-film structure  32  also includes a conductive layer which defines resistors  34  and corresponding conductive paths and leads  35  ( FIG. 2 ). The conductive layer is formed, for example, of aluminum, gold, tantalum, tantalum-aluminum, or other metal or metal alloy. 
         [0022]    Also, as illustrated in  FIG. 3A , orifice/barrier layer  36  is formed on first side  162  of substrate  160  over thin-film structure  32 . Orifice/barrier layer  36  (including nozzle openings  38  and nozzle chambers  39 ) ( FIG. 2 ) includes one or more layers of material compatible with the fluid (or ink) to be routed through and ejected from fluid ejection device  30 . Material suitable for orifice/barrier layer  36  includes, for example, a photo-imageable polymer such as SUB. Other materials, however, may be used for orifice/barrier layer  36 . 
         [0023]    In one embodiment, as illustrated in  FIG. 3A , a backside layer or stack  170  including one or more mask or protective layers is formed on second side  164  of substrate  160 . One example of backside layer or stack  170  includes a multi-layer structure of poly-silicon, silicon nitride, and silicon dioxide, which acts as a stress relief oxide (SRO) between the silicon substrate and silicon nitride. 
         [0024]    In one embodiment, as illustrated in  FIG. 3B , a protective layer  172  is formed over thin-film structure  32  and orifice/barrier layer  36 . One example of material suitable for protective layer  172  includes a low temperature dielectric material such as silicon nitride. Other materials or manners of protecting thin-film structure  32  and/or orifice/barrier layer  36  for subsequent processing of substrate  160  and forming of opening  150 , however, may also be used. 
         [0025]    As illustrated in  FIG. 3C , backside layer or stack  170  is patterned such that select portions of backside layer or stack  170  are removed to expose areas of second side  164  of substrate  160 . As such, backside layer or stack  170  defines where opening  150  is to be formed in substrate  160  at second side  164 . A dimension of the exposed area of second side  164  of substrate  160  is represented by width WW. In one embodiment, backside layer or stack  170  is patterned and portions thereof removed by laser processing. Other manners of patterning backside layer or stack  170 , however, maybe also be used. 
         [0026]    In one embodiment, as illustrated in  FIG. 3D , after backside layer  170  is patterned, a cleaning process is performed. The cleaning process removes debris, such as silicon debris, and in one embodiment, removes the poly-silicon material from backside layer or stack  170 . In one embodiment, the cleaning process is a chemical cleaning process and uses a combination of tetra-methyl-ammonium hydroxide (TMAH) and standard cleaning solution #1 (SC1). 
         [0027]    As illustrated in  FIG. 3E , a sacrificial mask layer  174  is formed on second side  164  of substrate  160 . More specifically, sacrificial mask layer  174  is formed over backside layer or stack  170  and over exposed portions or areas of second side  164  of substrate  160 . In one embodiment, sacrificial mask layer  170  is a metal layer formed by deposition. One example of material suitable for sacrificial mask layer  170  includes a layer of titanium and aluminum. 
         [0028]    In one embodiment, as illustrated in  FIG. 3F , an initial or first portion  152  of opening  150  is formed in substrate  160 . First portion  152  of opening  150  is formed in substrate  160  from second side  164  toward first side  162  such that a depth d of first portion  152  is less than a full thickness T of substrate  160 . As such, first portion  152  of opening  150  does not extend completely through substrate  160 . In addition, in one embodiment, a width w of first portion  152  of opening  150  at second side  164  of substrate  160  is less than width WW of the previously exposed area of second side  164  of substrate  160  through patterned backside layer or stack  170  ( FIG. 3C ). As such, first portion  152  forms a subset of opening  150  of width w. In one embodiment, first portion  152  of opening  150  is formed in substrate  160  by laser processing through sacrificial mask layer  174 . In one embodiment, first portion  152  of opening  150  includes substantially parallel sidewalls from second side  164  to depth d. In another embodiment, first portion  152  of opening  150  includes sidewalls at angles greater than ninety degrees to the extent that width w of first portion  152  does not exceed width WW whereby a width of first portion  152  at depth d is less than a width of first portion  152  at second side  164 . 
         [0029]    Next, as illustrated in the embodiment of  FIG. 3G , another or second portion  154  of opening  150  is formed in substrate  160 . Second portion  154  of opening  150  is formed in substrate  160  from first portion  152  of opening  150  to first side  162  of substrate  160 . As such, second portion  154  extends from first portion  152  to first side  162  of substrate  160  such that first portion  152  and second portion  154  together extend completely through substrate  160 , so as to communicate with first side  162  and second side  164  of substrate  160 . In one embodiment, second portion  154  of opening  150  is formed in substrate  160  by a dry etch process, and is performed through first portion  152  of opening  150  to first side  162  of substrate  160 . In one embodiment, the dry etch process is a reactive ion etch (RIE) using a fluorine-based plasma etch such as, for example, sulfur hexafluoride. 
         [0030]    As illustrated in the embodiment of  FIG. 3H , after first portion  152  and second portion  154  of opening  150  are formed in substrate  160 , another or third portion  156  of opening  150  is formed in substrate  160 . In one embodiment, a maximum dimension of third portion  156  of opening  150  at second side  164  of substrate  60  is defined by width WW of the exposed area or portion of second side  164  of substrate  160  of patterned backside layer or stack  170  ( FIG. 3C ). In addition, sidewalls of third portion  156  converge from second side  164  of substrate  160  to first side  162  of substrate  160  such that a dimension (e.g., width) of opening  150  decreases from second side  164  to first side  162 . 
         [0031]    In one embodiment, third portion  156  of opening  150  is formed in substrate  160  using an anisotropic chemical etch process. More specifically, the chemical etch process is a wet etch process and uses a wet anisotropic etchant such as TMAH, potassium hydroxide (KOH), or other alkaline etchant. In addition to forming third portion  156  of opening  150 , the anisotropic wet etch process also removes sacrificial mask layer  174  ( FIG. 3E ). With the anisotropic wet etch process, as further illustrated and described below in association with  FIG. 4A , third portion  156  of opening  150  follows and is defined by crystalline planes of substrate  160  as a silicon substrate. 
         [0032]    In one embodiment, as illustrated in  FIG. 3I , after third portion  156  of opening  150  is formed in substrate  160 , substrate  160  is further processed to further form opening  150  in substrate  160 . In one embodiment, substrate  160  is further processed using an isotropic chemical etch process. The isotropic chemical etch process uses, for example, xenon difluoride. Performing the isotropic etch process after the anisotropic wet etch process provides stress relief at intersecting orthogonal crystalline planes of a silicon substrate of &lt;110&gt; orientation developed during the anisotropic wet etch process. In one embodiment, as further illustrated and described below in association with  FIG. 4B , the isotropic etch process provides stress relief by smoothing or rounding (i.e., eliminating orthogonal corners of) intersecting crystalline planes of substrate  160  as a silicon substrate. 
         [0033]    In one embodiment, as illustrated in  FIG. 3J , after the isotropic etch process is completed and opening  150  is formed in substrate  160 , protective layer  172  is removed from first side  162  of substrate  160 . In one embodiment, protective layer  172  is removed by a buffered oxide etch (BOE). 
         [0034]      FIGS. 4A and 4B  schematically illustrate one embodiment of substrate  160  during forming of opening  150 . More specifically,  FIG. 4A  illustrates a schematic plan view of opening  150  in substrate  160  after the anisotropic wet etch process illustrated and described in association with  FIG. 3H  and before the isotropic etch process illustrated and described in association with  FIG. 3I .  FIG. 4B , however, illustrates a schematic plan view of opening  150  in substrate  160  after the isotropic etch process illustrated and described in association with  FIG. 3I . 
         [0035]    As illustrated in  FIG. 4A , after the described anisotropic wet etch process, opening  150  includes intersecting crystalline planes forming substantially ninety degree angles or corners. These corners, however, may produce areas of increased stress thereby possibly leading to cracks in substrate  160  propagating from the corners. After the described isotropic etch process, however, the angles or corners of the intersecting orthogonal crystalline planes are smoothed or rounded, as illustrated in  FIG. 4B , such that the potential areas of increased stress are reduced or minimized, and strength of substrate  160  is increased. 
         [0036]    While the above description refers to the inclusion of substrate  160  having opening  150  formed therein in an inkjet printhead assembly, it is understood that substrate  160  having opening  150  formed therein may be incorporated into other fluid ejection systems including non-printing applications or systems as well as other applications having fluidic channels through a substrate, such as medical devices or other micro electro-mechanical systems (MEMS devices). Accordingly, the methods, structures, and systems described herein are not limited to printheads, and are applicable to any slotted substrates. In addition, while the above description refers to routing fluid or ink through opening  150  of substrate  160 , it is understood that any flowable material, including a liquid such as water, ink, blood, or photoresist, or flowable particles of a solid such as talcum powder or a powdered drug, or air may be fed or routed through opening  150  of substrate  160 . 
         [0037]    Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.