Abstract:
A method of forming a fluid ejection device includes providing a substrate having a first side supporting an oxide layer and a conductive layer over the oxide layer; and patterning the conductive layer to define an area for an actuator of the fluid ejection device, including shaping the area with first and second ends each having a first width and at least one portion between the first and second ends having a second width less than the first width.

Description:
BACKGROUND  
       [0001]    An inkjet printing system, as one example 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 example 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]    Fabrication of the printhead may include a mixture of integrated circuit and MEMS techniques such as a combination of etching and photolithography processes. Unfortunately, the combination of such processes may result in undesired artifacts. For example, overetching may result in damaged or scarred areas which, in turn, may cause unintended light scatter during UV exposure and, therefore, may create deformities and/or residue during fabrication of the printhead. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0003]      FIG. 1  is a block diagram illustrating one example of a fluid ejection system. 
           [0004]      FIG. 2  is a schematic cross-sectional view illustrating one example of a portion of a fluid ejection device. 
           [0005]      FIGS. 3-8  schematically illustrate one example of aspects of forming a fluid ejection device. 
           [0006]      FIG. 9  schematically illustrates one example of an etch window of a resistor area mask in relation to a chamber mask for a fluid ejection chamber, and a resistor area and a resistor in association with conductive elements for the resistor. 
           [0007]      FIG. 10  is a schematic plan view of another example of a mask layer used to define an area for a resistor of a fluid ejection device. 
           [0008]      FIG. 11  schematically illustrates another example of an etch window of a resistor area mask in relation to a chamber mask for a fluid ejection chamber, and a resistor area and a resistor in association with conductive elements for the resistor. 
       
    
    
     DETAILED DESCRIPTION  
       [0009]    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 examples 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 examples 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 examples 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. 
         [0010]      FIG. 1  illustrates one example of an inkjet printing system  10 . Inkjet printing system  10  constitutes one example 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 example, inkjet printing system  10  also includes a mounting assembly  16 , a media transport assembly  18 , and an electronic controller  20 . 
         [0011]    Inkjet printhead assembly  12 , as one example 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 example, 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 example, 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. 
         [0012]    Ink supply assembly  14 , as one example of a fluid supply assembly, supplies ink to inkjet printhead assembly  12  and includes a reservoir  15  for storing ink. As such, in one example, ink flows from reservoir  15  to inkjet printhead assembly  12 . In one example, inkjet printhead assembly  12  and ink supply assembly  14  are housed together in an inkjet or fluid-jet cartridge or pen. In another example, 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. 
         [0013]    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 example, 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 example, 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 . 
         [0014]    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. 
         [0015]    In one example, 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 example, logic and drive circuitry forming a portion of electronic controller  20  is located on inkjet printhead assembly  12 . In another example, logic and drive circuitry forming a portion of electronic controller  20  is located off inkjet printhead assembly  12 . 
         [0016]      FIG. 2  illustrates one example 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. 
         [0017]    In one example, each drop ejecting element  31  includes a thin-film structure  32  with a resistor  34 , as an example of an actuator for fluid ejection device  30 , 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 an orifice or nozzle opening  38  formed in front face  37 . Orifice/barrier layer  36  also has a fluid 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 fluid chamber  39  and includes leads  35  which electrically couple resistor  34  to a drive signal and ground. 
         [0018]    Thin-film structure  32  includes one or more oxide, passivation, or insulation layers formed, for example, of silicon dioxide, silicon carbide, silicon nitride, tantalum, poly-silicon glass, tetraethylorthosilicate (TEOS), or other material. In one example, thin-film structure  32  also includes one or more conductive layers which define resistor  34  and leads  35 . The conductive layers are formed, for example, of aluminum, gold, tantalum, tantalum-aluminum, or other metal or metal alloy. 
         [0019]    Orifice/barrier layer  36  (including nozzle openings  38  and fluid chambers  39 ) 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 SU8. 
         [0020]    In one example, during operation, fluid flows from fluid feed slot  41  to fluid chamber  39  via fluid feed hole  33 . Nozzle opening  38  is operatively associated with resistor  34  such that droplets of fluid are ejected from fluid chamber  39  through nozzle opening  38  (e.g., normal to the plane of resistor  34 ) and toward a medium upon energization of resistor  34 . More specifically, in one example, fluid ejection device  30  comprises a fully integrated thermal inkjet (TIJ) printhead, and ejects drops of fluid from nozzle opening  38  by passing an electrical current through resistor  34  so as to generate heat and vaporize a portion of the fluid within fluid chamber  39  such that another portion of the fluid is ejected through nozzle opening  38 . 
         [0021]      FIGS. 3-8  schematically illustrate one example of aspects of forming a fluid ejection device, such as fluid ejection device  30  ( FIG. 2 ). As illustrated in  FIG. 3 , substrate  100 , as an example of substrate  40  ( FIG. 2 ), has a first side  102  and second side  104 . Second side  104  is opposite first side  102  and, in one implementation, orientated substantially parallel with first side  102 . In one example, first side  102  forms a front side of substrate  100  and second side  104  forms a backside of substrate  100 . As such, with a fluid feed slot or opening formed through substrate  100  (see, e.g., fluid feed slot  41  (FIG.  2 )), fluid flows through substrate  100  from the backside to the front side. 
         [0022]    In one example, substrate  100  is formed of silicon and, in some implementations, may comprise a crystalline substrate such as doped or non-doped monocrystalline silicon or doped or non-doped polycrystalline silicon. Other examples of suitable substrates include gallium arsenide, gallium phosphide, indium phosphide, glass, silica, ceramics, or a semiconducting material. 
         [0023]    In one example, formation of the fluid ejection device includes forming a thin-film structure, such as thin-film structure  32  ( FIG. 2 ), on first side  102  of substrate  100 . As described above, the thin-film structure includes one or more oxide, passivation, or insulation layers formed, for example, of silicon dioxide, silicon carbide, silicon nitride, tantalum, poly-silicon glass, tetraethylorthosilicate (TEOS), or other material. In addition, the thin-film structure also includes one or more conductive layers which define a resistor and corresponding conductive paths or leads, such as resistor  34  and corresponding leads  35  ( FIG. 2 ). The conductive layers are formed, for example, of aluminum, gold, tantalum, tantalum-aluminum, or other metal or metal alloy. 
         [0024]    As illustrated in the example of  FIG. 3 , an oxide layer  110 , as one layer of the thin-film structure, is formed on first side  102  of substrate  100 , and a conductive layer  112 , as another layer of the thin-film structure, is formed over oxide layer  110 . In one implementation, oxide layer  110  includes TEOS, and conductive layer  112  includes aluminum. 
         [0025]      FIG. 4  is a schematic plan view of one example of a mask layer  120  used to define an area for a thermal resistor of the fluid ejection device, such as resistor  34  of fluid ejection device  30  ( FIG. 2 ). More specifically, mask layer  120  is formed over conductive layer  112 , and is patterned to expose a portion (or portions) of conductive layer  112  to be removed before forming the thermal resistor. In one example, the exposed portion (or portions) of conductive layer  112  is removed by chemical etching. In one example, mask layer  120  is formed of photoresist and patterned using photolithography techniques, and the etch is a dry etch, such as a plasma-based fluorine (SF6) etch. As such, mask layer  120  represents an etch mask  122  that is patterned to define an etch window  124  through which material of conductive layer  112  ( FIG. 3 ) is removed. 
         [0026]    As illustrated in the schematic plan view of  FIG. 4 , etch window  124  of etch mask  122  has opposite ends  1241  and  1242 , and opposite sides  1243  and  1244 . In addition, etch window  124  of etch mask  122  has a first axis  1245  extended along a length thereof between opposite ends  1241  and  1242 , and has a second axis  1246  extended along a width thereof between opposite sides  1243  and  1244 . 
         [0027]    In one example, etch window  124  has a reduced width portion  1247  provided between opposite ends  1241  and  1242  along the length thereof. More specifically, reduced width portion  1247  constitutes a narrower width portion relative to and extending between wider width portions  1250  provided at opposite ends  1241  and  1242  of etch window  124 . As such, in the illustrated example, etch window  124  has an I-shaped profile with reduced width portion  1247  representing a “body” of the I-shaped profile, and opposite ends  1241  and  1242  representing “arms” of the I-shaped profile. In one example, etch window  124  has radiussed portions  1248  provided at each end of reduced width portion  1247 , and has radiussed portions  1249  provided at wider width portions  1250  of opposite ends  1241  and  1242 . 
         [0028]      FIG. 5  is a schematic cross-sectional view from the perspective of second axis  1246  of  FIG. 4  after etching of conductive layer  112  and removal of mask layer  120 . After etching of conductive layer  112  and removal of mask layer  120 , a resistor area  130  for a thermal resistor of the fluid ejection device, such as resistor  34  of fluid ejection device  30  ( FIG. 2 ) is formed. Resistor area  130  is formed by removed portions of conductive layer  112  and has a shape corresponding to etch window  124 . As  FIG. 5  is a schematic cross-sectional view from the perspective of second axis  1246  of  FIG. 4 , a width W 2  of resistor area  130  corresponds to a width W 1  of reduced width portion  1247  of etch window  124 . In one example, etching of conductive layer  112  may result in overetching of oxide layer  110 , as represented by  114 . 
         [0029]      FIG. 6  is a schematic plan view of one example of a mask layer  140  used to define a width of a thermal resistor of the fluid ejection device, such as resistor  34  of fluid ejection device  30  ( FIG. 2 ), after material (e.g., WSiN) of the thermal resistor has been deposited over conductive layer  112 , and define conductive lines for a thermal resistor of the fluid ejection device, such as leads  35  for resistor  34  of fluid ejection device  30  ( FIG. 2 ), in conductive layer  112 . More specifically, mask layer  140  is formed over conductive layer  112  and the material of the thermal resistor, and is patterned to expose material to be removed. As such, mask layer  140  extends over and beyond resistor area  130  as formed from etch window  124 . In one example, the exposed portions are removed by chemical etching. In one example, mask layer  140  is formed of photoresist and patterned using photolithography techniques, and the etch is a dry etch, such as a plasma-based fluorine (SF6) etch. 
         [0030]      FIG. 7  is a schematic cross-sectional view from the perspective of line  7 - 7  of  FIG. 6  after etching of the material of the thermal resistor and conductive layer  112 , and removal of mask layer  140 . After etching of the material of the thermal resistor and conductive layer  112 , and removal of mask layer  112 , thermal resistor  150  is defined. As  FIG. 7  is a schematic cross-sectional view from the perspective of line  7 - 7  of  FIG. 6 , thermal resistor  150  has a width W 4  corresponding to a width W 3  of mask layer  140 . As illustrated in  FIG. 7 , width W 4  of thermal resistor  150  is less than width W 2  of resistor area  130  as defined by reduced width portion  1247  of etch window  124  ( FIG. 4 ). In one example, etching of the material of thermal resistor  150  and conductive layer  112  may, again, result in overetching of oxide layer  110 , as represented by  115 . In one example, such overetching results in thermal resistor  150  being formed on a “mesa” of oxide layer  110 . 
         [0031]    As illustrated in  FIG. 8 , a barrier layer  160 , as an example of barrier layer  36  ( FIG. 2 ), is formed on first side  102  of substrate  100 . More specifically, barrier layer  160  is formed on first side  102  of substrate  100  over the thin-film structure (including oxide layer  100 ). Similar to fluid chamber  39  of barrier layer  36  ( FIG. 2 ), barrier layer  160  forms a fluid chamber  162  encompassing thermal resistor  150 . 
         [0032]    In one example, barrier layer  160  is formed of a photo-imageable polymer such as SU8. As such, the photo-imageable polymer is polymerized by UV light, represented by arrows  164 , to form barrier layer  160 . In one example, fluid chamber  162  is formed by blocking UV light with a chamber mask  170 , and preventing polymerization of the photo-imageable polymer in the area of fluid chamber  162 . 
         [0033]    In one example, and as illustrated in  FIG. 8 , width W 2  of resistor area  130 , as corresponding to width W 1  of reduced width portion  1247  of etch window  124  ( FIG. 4 ), is less than a width W 5  of chamber mask  170 . As such, stray reflections of UV light from surfaces of resistor area  150  are minimized during formation of barrier layer  160  and fluid chamber  162 . More specifically, reflection of UV light from, for example, overetched areas of oxide layer  110  (e.g., overetching  115 ), are minimized since such areas are covered or “masked” by chamber mask  170 . Thus, deformities and/or residue that may result from unintended polymerization of the photo-imageable material by stray reflections during formation of barrier layer  160  and fluid chamber  162  are minimized. 
         [0034]      FIG. 9  is a schematic plan view illustrating one example of etch window  124  (of etch mask  122  for resistor area  130 ) in relation to chamber mask  170  (for chamber layer  160  and fluid chamber  162 ). As illustrated in the example of  FIG. 9 , etch window  124  of etch mask  122 , including reduced width portion  1247 , is encompassed by chamber mask  170  such that chamber mask  170  surrounds or “encloses” etch window  124 , including reduced width portion  1247 . Thus, as described above, stray reflections of UV light during formation of chamber layer  160  and fluid chamber  162  ( FIG. 8 ) are minimized since areas within etch window  124  of etch mask  122  (i.e., areas of resistor area  130 ) are covered or “masked” by chamber mask  170 . 
         [0035]      FIG. 9  also schematically illustrates one example of resistor area  130 , as formed from etch window  124 , and resistor  150 , as patterned by mask layer  140  ( FIG. 6 ), in association with conductive lines  1121  and  1122  for resistor  150 , as formed from conductive layer  112  and patterned by mask layer  140  ( FIG. 6 ). As illustrated in the example of  FIG. 9 , conductive lines  1121  and  1122  extend from opposite ends of resistor area  130 . In addition, resistor  150  is positioned within resistor area  130  such that the reduced portion of resistor area  130 , as defined by reduced width portion  1247  of etch window  124 , extends along the edges or opposite sides of resistor  150 . 
         [0036]      FIG. 10  is a schematic plan view of another example of a mask layer  220  used to define an area for a thermal resistor of the fluid ejection device, such as resistor  34  of fluid ejection device  30  ( FIG. 2 ). Similar to etch mask  122 , etch mask  222  is patterned to define an etch window  224  through which material of conductive layer  112  ( FIG. 3 ) is removed. In one example, similar to etch mask  122 , etch mask  222  is formed off photoresist and patterned using photolithography techniques, and exposed areas or portions of conductive layer  112  are removed by chemical etching. In one example, the chemical etching is a dry etch, such as a plasma-based fluorine (SF6) etch. 
         [0037]    As illustrated in the schematic plan view of  FIG. 10 , similar to etch window  124  of etch mask  122 , etch window  224  of etch mask  222  has opposite ends  2241  and  2242 , and opposite sides  2243  and  2244 . In addition, etch window  224  of etch mask  222  has a first axis  2245  extending along a length thereof between opposite ends  2241  and  2242 , and has a second axis  2246  extended along a width thereof between opposite sides  2243  and  2244 . 
         [0038]    In the example illustrated in  FIG. 10 , etch window  224  has a plurality reduced width portions  2247  provided between opposite ends  2241  and  2242  along the length thereof. More specifically, reduced width portions  2247  represent individual or discrete reduced width portions provided at spaced intervals along the length of etch window  224 . Thus, reduced width portions  2247  constitute narrower width portions relative to and extending between wider width portions  2250  provided along the length of etch window  224 . Accordingly, reduced width portions  2247  of etch window  224  are provided between wider width portions  2250  which represent “fingers” projecting along opposite sides  2243  and  2244  of etch window  224 . As such, in the illustrated example, etch window  224  has a serpentine profile along opposite sides  2243  and  2244  over the length thereof. As illustrated in  FIG. 10 , reduced width portions  2247  each have a width W 6 . In one example, also as illustrated in  FIG. 10 , etch window  224  has radiussed portions  2248  provided at each end of reduced width portions  2247 , and has radiussed portions  2249  provided at opposite ends  2241  and  2242  and radiussed portions  2251  provided at the ends of wider width portions  2250 . 
         [0039]      FIG. 11  is a schematic plan view illustrating one example of etch window  224  (of etch mask  222  for resistor area  230 ) in relation to chamber mask  170  (for chamber layer  160  and fluid chamber  162 ). As illustrated in the example of  FIG. 11 , reduced width portions  2247  of etch mask  222  are encompassed by chamber mask  170  such that chamber mask  170  surrounds or “encloses” reduced width portions  2247 . Thus, similar to that described above, stray reflections of UV light during formation of chamber layer  160  and fluid chamber  162  ( FIG. 8 ) are minimized since areas within etch window  224  of etch mask  222  (i.e., areas of resistor area  230 ) are covered or “masked” by chamber mask  170 . Accordingly, deformities and/or residue that may result from unintended polymerization of the photo-imageable material by stray reflections during formation of barrier layer  160  and fluid chamber  162  are minimized. 
         [0040]    In addition, by providing etch mask  222  with the plurality of reduced width portions  2247 , the etch rate along the sides of etch window  224  is slowed down such that surface angles of overetched areas (e.g., overetching  114  ( FIG. 5 )) are reduced. Accordingly, stray reflections of UV light which may develop during formation of chamber layer  160  and fluid chamber  162  will have a small reflected angle thereby minimizing possible reflection of the UV light back out of the photo-imageable material and, therefore, minimizing polymerization of unintended material. 
         [0041]      FIG. 11  also schematically illustrates one example of resistor area  230 , as formed from etch window  224 , and resistor  150 , as patterned by mask layer  140  ( FIG. 6 ), in association with conductive lines  1121  and  1122  for resistor  150 , as formed from conductive layer  112  and patterned by mask layer  140  ( FIG. 6 ). As illustrated in the example of  FIG. 11 , conductive lines  1121  and  1122  extend from opposite ends of resistor area  230 . In addition, resistor  150  is positioned within resistor area  230  such that the reduced width portions of resistor area  230 , as defined by reduced width portions  2247  of etch window  224 , extend along the edges or opposite sides of resistor  150 . 
         [0042]    Although specific examples 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 examples 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 examples discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.