Patent Publication Number: US-6910758-B2

Title: Substrate and method of forming substrate for fluid ejection device

Description:
BACKGROUND OF THE INVENTION 
   In some fluid ejection devices, such as printheads, a drop ejecting element is formed on a front side of a substrate and fluid is routed to an ejection chamber of the drop ejecting element through an opening or slot in the substrate. Often, the substrate is a silicon wafer and the slot is formed in the wafer by chemical etching. Methods of forming the slot through the substrate include etching into the substrate from both the front side and the backside so as to form a front side opening and a backside opening in the substrate. 
   Unfortunately, since a portion of the slot is formed by etching into the substrate from the front side and a portion of the slot is formed by etching into the substrate from the backside, misalignment between the backside opening and the front side opening of the slot may occur. Such misalignment may result, for example, in undercutting of one or more layers formed on the front side of the substrate. 
   For these and other reasons, there is a need for the present invention. 
   SUMMARY OF THE INVENTION 
   One aspect of the present invention provides a method of forming an opening through a substrate having a first side and a second side opposite the first side. The method includes forming spaced stops in the first side of the substrate, partially forming a first portion of the opening in the substrate from the second side by a first process, further forming the first portion of the opening in the substrate from the second side by a second process, including forming the first portion of the opening to the spaced stops, and forming a second portion of the opening in the substrate from the first side, including forming the second portion of the opening between the spaced stops. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram illustrating one embodiment of an ink-jet printing system according to the present invention. 
       FIG. 2  is a schematic cross-sectional view illustrating one embodiment of a portion of a fluid ejection device according to the present invention. 
       FIG. 3  is a schematic cross-sectional view illustrating one embodiment of a fluid ejection device formed on one embodiment of a substrate according to the present invention. 
       FIGS. 4A-4J  illustrate one embodiment of forming an opening through a substrate according to the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In the following detailed description of the preferred embodiments, 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 invention 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 FIGURES(S) being described. Because components of the present invention 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 invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims. 
     FIG. 1  illustrates one embodiment of an inkjet printing system  10  according to the present invention. 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 . Inkjet printhead assembly  12 , as one embodiment of a fluid ejection assembly, is formed according to an embodiment of the present invention, and 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, 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. 
   Ink supply assembly  14 , as one embodiment of a fluid supply assembly, supplies ink to 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 this embodiment, ink supply assembly  14  and inkjet printhead assembly  12  can form either a one-way ink delivery system or a recirculating ink delivery system. In a one-way ink delivery system, substantially all of the ink supplied to inkjet printhead assembly  12  is consumed during printing. In a recirculating ink delivery system, however, only a portion of the ink supplied to printhead assembly  12  is consumed during printing. As such, a portion of the ink not consumed during printing is returned to ink supply assembly  14 . 
   In one embodiment, inkjet printhead assembly  12  and ink supply assembly  14  are housed together in an inkjet or fluidjet 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 (not shown). In either embodiment, reservoir  15  of ink supply assembly  14  may be removed, replaced, and/or refilled. In one embodiment, where inkjet printhead assembly  12  and ink supply assembly  14  are housed together in an inkjet cartridge, reservoir  15  includes a local reservoir located within the cartridge and/or a larger reservoir located separately from the cartridge. As such, the separate, larger reservoir serves to refill the local reservoir. Accordingly, the separate, larger reservoir and/or the local reservoir may be removed, replaced, and/or refilled. 
   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. As such, mounting assembly  16  includes a carriage for moving inkjet printhead assembly  12  relative to media transport assembly  18  to scan print medium  19 . In another embodiment, inkjet printhead assembly  12  is a non-scanning type printhead assembly. As such, mounting assembly  16  fixes inkjet printhead assembly  12  at a prescribed position relative to media transport assembly  18 . Thus, media transport assembly  18  positions print medium  19  relative to inkjet printhead assembly  12 . 
   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 includes memory for temporarily storing data  21 . Typically, data  21  is sent to ink-jet 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. 
   In one embodiment, electronic controller  20  provides control of ink-jet 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 is located off inkjet printhead assembly  12 . 
     FIG. 2  illustrates one embodiment of a portion of inkjet printhead assembly  12 . Inkjet printhead assembly  12 , as one embodiment of a fluid ejection assembly, includes an array of drop ejecting elements  30 . Drop ejecting elements  30  are formed on a substrate  40  which has a fluid (or ink) feed slot  44  formed therein. As such, fluid feed slot  44  provides a supply of fluid (or ink) to drop ejecting elements  30 . 
   In one embodiment, each drop ejecting element  30  includes a thin-film structure  32 , an orifice layer  34 , and a firing resistor  38 . Thin-film structure  32  has a fluid (or ink) feed channel  33  formed therein which communicates with fluid feed slot  44  of substrate  40 . Orifice layer  34  has a front face  35  and a nozzle opening  36  formed in front face  35 . Orifice layer  34  also has a nozzle chamber  37  formed therein which communicates with nozzle opening  36  and fluid feed channel  33  of thin-film structure  32 . Firing resistor  38  is positioned within nozzle chamber  37  and includes leads  39  which electrically couple firing resistor  38  to a drive signal and ground. 
   In one embodiment, during operation, fluid flows from fluid feed slot  44  to nozzle chamber  37  via fluid feed channel  33 . Nozzle opening  36  is operatively associated with firing resistor  38  such that droplets of fluid are ejected from nozzle chamber  37  through nozzle opening  36  (e.g., normal to the plane of firing resistor  38 ) and toward a medium upon energization of firing resistor  38 . 
   Example embodiments of inkjet printhead assembly  12  include a thermal printhead, a piezoelectric printhead, a flex-tensional printhead, or any other type of fluid ejection device known in the art. In one embodiment, inkjet printhead assembly  12  is a fully integrated thermal inkjet printhead. As such, substrate  40  is formed, for example, of silicon, glass, or a stable polymer, and thin-film structure  32  is formed by one or more passivation or insulation layers of silicon dioxide, silicon carbide, silicon nitride, tantalum, poly-silicon glass, or other suitable material. Thin-film structure  32  also includes a conductive layer which defines firing resistor  38  and leads  39 . The conductive layer is formed, for example, by aluminum, gold, tantalum, tantalum-aluminum, or other metal or metal alloy. 
     FIG. 3  illustrates another embodiment of a portion of inkjet printhead assembly  12 . Inkjet printhead assembly  112 , as another embodiment of a fluid ejection assembly, includes an array of drop ejecting elements  130 . Drop ejecting elements  130  are formed on a substrate  140  which has a fluid (or ink) feed slot  144  formed therein. As such, fluid feed slot  144  provides a supply of fluid (or ink) to drop ejecting elements  130 . 
   In one embodiment, drop ejecting elements  130  include a thin-film structure  132 , an orifice layer  134 , and firing resistors  138 . Thin-film structure  132  has fluid (or ink) feed channels  133  formed therein which communicate with fluid feed slot  144  of substrate  140 . Orifice layer  134  has a front face  135  and nozzle openings  136  formed in front face  135 . Orifice layer  134  also has nozzle chambers  137  formed therein which communicate with respective nozzle openings  136  and respective fluid feed channels  133  of thin-film structure  132 . 
   In one embodiment, during operation, fluid flows from fluid feed slot  144  to nozzle chambers  137  via respective fluid feed channels  133 . Nozzle openings  136  are operatively associated with respective firing resistors  138  such that droplets of fluid are ejected from nozzle chambers  137  through nozzle openings  136  and toward a medium upon energization of firing resistors  138  positioned within respective nozzle chambers  137 . 
   As illustrated in the embodiment of  FIG. 3 , substrate  140  has a first side  141  and a second side  142 . Second side  142  is opposite of first side  141  and, in one embodiment, oriented substantially parallel with first side  141 . Fluid feed slot  144  communicates with first side  141  and second side  142  of substrate  140  so as to provide a channel or passage through substrate  140 . 
   In one embodiment, fluid feed slot  144  includes a first portion  145  and a second portion  146 . First portion  145  is formed in and communicates with second side  142  of substrate  140  and second portion  146  is formed in and communicates with first side  141  of substrate  140 . First portion  145  and second portion  146  communicate with each other so as to form fluid feed slot  144  through substrate  140 . Fluid feed slot  144 , including first portion  145  and second portion  146 , is formed in substrate  140  according to an embodiment of the present invention. In one embodiment, fluid feed slot  144 , including first portion  145  and second portion  146 , is formed in substrate  140  by chemical etching, as described below. 
   In one embodiment, substrate  140  includes spaced stops  148 . Stops  148  extend into substrate  140  from first side  141  and, in one embodiment, are oriented substantially perpendicular to first side  141 . Stops  148  control etching of substrate  140  and, therefore, formation of first portion  145  and second portion  146  of fluid feed slot  144 . As such, stops  148  are formed of a material which is resistant to etchant used for etching substrate  140 , as described below. Thus, stops  148  constitute etch stops of substrate  140 . 
   Stops  148  define and control formation of fluid feed slot  144  in substrate  140 . More specifically, stops  148  limit fluid feed slot  144  and define a maximum dimension of second portion  146  and a minimum dimension of first portion  145  of fluid feed slot  144 . In addition, stops  148  establish a location of second portion  146  at first side  141  and accommodate misalignment between first portion  145  and second portion  146 , as described below. Furthermore, stops  148  provide for self-alignment between first portion  145  and second portion  146  of fluid feed slot  144 . 
     FIGS. 4A-4J  illustrate one embodiment of forming an opening  150  through a substrate  160 . In one embodiment, substrate  160  is a silicon substrate and opening  150  is formed in substrate  160  by chemical etching, 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 . 
   In one embodiment, substrate  160  represents substrate  140  of ink-jet printhead assembly  112  and opening  150  represents fluid feed slot  144  formed in substrate  140 . As such, drop ejecting elements  130  of inkjet printhead assembly  112  are formed on first side  162  of substrate  160 . Thus, first side  162  forms a front side of substrate  160  and second side  164  forms a backside of substrate  160  such that fluid flows through opening  150  and, therefore, substrate  160  from the backside to the front side. Accordingly, opening  150  provides a fluidic channel for the communication of ink with drop ejecting elements  130  through substrate  160 . 
   In one embodiment, opening  150  is formed in substrate  160  after drop ejecting elements  130  are formed on substrate  160 . More specifically, opening  150  is formed in substrate  160  after thin-film structure  132 , firing resistors  138 , and orifice layer  134  are formed on first side  162  of substrate  160 . In one embodiment, processing of substrate  160  for forming opening  150  is started after thin-film structure  132  and firing resistors  138  of drop ejecting elements  130  are formed on first side  162  of substrate  160 . 
   As illustrated in the embodiments of  FIGS. 4A-4D , before opening  150  is formed, etch stops  170  are formed in substrate  160 . In one embodiment, etch stops  170  are formed in substrate  160  by chemical etching into substrate  160  and disposing an etch resistant material in substrate  160 , as described below. 
   In one embodiment, as illustrated in the embodiment of  FIG. 4A , to form etch stops  170  in substrate  160 , a masking layer  180  is formed on substrate  160 . More specifically, masking layer  180  is formed on first side  162  of substrate  160 . Masking layer  180  is used to selectively control or block etching of first side  162 . As such, masking layer  180  is formed along first side  162  of substrate  160  and patterned to expose areas of first side  162  and define where etch stops  170  are to be formed in substrate  160 . In one embodiment, masking layer  180  is formed over thin-film structure  132  and firing resistors  138 . 
   In one embodiment, masking layer  180  is formed by deposition and patterned by photolithography and etching to define exposed portions of first side  162  of substrate  160 . More specifically, masking layer  180  is patterned to outline where slots  166  ( FIG. 4B ) are to be formed in substrate  160  from first side  162 . In one embodiment, slots  166  are formed in substrate  160  by chemical etching, as described below. Thus, masking layer  180  is formed of a material which is resistant to etchant used for etching slots  166  into substrate  160 . Examples of a material suitable for masking layer  180  include silicon dioxide, silicon nitride, or photoresist. 
   Also, as illustrated in the embodiment of  FIG. 4A , a masking layer  182  is formed on second side  164  of substrate  160 . In one embodiment, masking layer  182  is formed by growing an oxide on second side  164 . The oxide is resistant to the etchant selected for use in etching opening  150  through substrate  160 , as described below. The oxide may include, for example, silicon dioxide. Masking layer  182  is patterned to expose an area of second side  164  and define where substrate  160  is to be etched to form a portion of opening  150  (FIGS.  4 I- 4 J). 
   Next, as illustrated in the embodiment of  FIG. 4B , slots  166  are formed in substrate  160 . More specifically, slots  166  are formed in substrate  160  by etching into first side  162 . Slots  166  include at least one pair of slots spaced along first side  162  so as to define where opening  150  is to communicate with first side  162 . In one embodiment, slots  166  are oriented substantially perpendicular to first side  162  and are formed in substrate  160  using an anisotropic etch process which forms slots  166  with substantially parallel sides. In one embodiment, the etch process is a dry etch such as a plasma based fluorine (SF 6 ) etch. In a particular embodiment, the dry etch is a reactive ion etch (RIE) and, more specifically, a deep RIE (DRIE). 
   During the deep RIE, an exposed section is alternatively etched with a reactive etching gas and coated until a slot is formed. In one exemplary embodiment, the reactive etching gas creates a fluorine radical that chemically and/or physically etches the substrate. In this exemplary embodiment, a polymer coating that is selective to the etchant used is deposited on inside surfaces of the forming slot, including the sidewalls and bottom. The coating is created by using carbon-fluorine gas that deposits (CF 2 ) n , a low surface energy fluorinated hydrocarbon, on these surfaces. In this embodiment, the polymer substantially prevents etching of the sidewalls during the subsequent etch(es). The gases for the etchant alternate with the gases for forming the coating on the inside of the slots. 
   As illustrated in the embodiment of  FIG. 4C , after slots  166  are formed in substrate  160 , masking layer  180  is stripped or removed from substrate  160 . As such, first side  162  of substrate  160  is revealed or exposed. In one embodiment, when masking layer  180  is formed of an oxide, masking layer  180  is removed, for example, by a chemical etch. In another embodiment, when masking layer  180  is formed of photoresist, masking layer  180  is removed, for example, by a resist stripper. 
   Next, as illustrated in the embodiment of  FIG. 4D , etch stops  170  are formed in substrate  160 . In one embodiment, etch stops  170  are formed by disposing an etch resistant material in slots  166  of substrate  160 . In one embodiment, forming of etch stops  170  includes filling slots  166  and forming a layer  172  on first side  162  of substrate  160 . In one embodiment, layer  172  is formed over thin-film structure  132  and firing resistors  138 . 
   In one embodiment, etch stops  170  and layer  172  are formed by disposing a material in slots  166  and on first side  162 . The material is resistant to the etchant selected for use in etching opening  150  through substrate  160 , as described below. In one embodiment, etch stops  170  and layer  172  are formed of a conformal material which is spun-deposited on first side  162 . In one embodiment, the material includes an epoxy and, more specifically, a photoimageable epoxy. An example of such a material includes SU 8 . 
   As illustrated in the embodiment of  FIG. 4E , after etch stops  170  are formed in first side  162  and layer  172  is formed on first side  162 , layer  172  is patterned to expose areas of first side  162  and define where substrate  160  is to be etched to form a portion of opening  150  (FIGS.  4 I- 4 J). In one embodiment, layer  172  is patterned by photolithography to define exposed portions of first side  162  and define openings  173  in layer  172 . 
   In one embodiment, as illustrated in the embodiment of  FIG. 4F , orifice layer  134  including nozzle openings  136  and nozzle chambers  137  is formed on first side  162  of substrate  160 . In one embodiment, orifice layer  134  is formed over layer  172 . As such, openings  173  in layer  172  define fluid feed holes or channels  133  which communicate with corresponding nozzle chambers  137  formed in orifice layer  134 . 
   Also, as illustrated in the embodiment of  FIG. 4F , a masking layer  184  is formed on second side  164  of substrate  160 . In one embodiment, masking layer  184  is formed on second side  164  over masking layer  182 . Masking layer  184  is formed of a material which is resistant to the etchant used for forming opening  150  in substrate  160 , as described below. The material may include, for example, photoresist. Masking layer  184  is patterned to expose an area of second side  164  and define an opening  185  where substrate  160  is to be etched to partially form a first portion  152  of opening  150  (FIGS.  4 G- 4 H). 
   In one embodiment, etch stops  170  are spaced at a first dimension D 1  in a first direction (i.e., a horizontal direction with reference to the FIGURES) and masking layer  184  is patterned to define opening  185  with a second dimension D 2  in the first direction. In some embodiments, second dimension D 2  is equal to or less than first dimension D 1 . In addition, second dimension D 2  is typically positioned within first dimension D 1 . 
   As illustrated in the embodiment of  FIG. 4G , first portion  152  of opening  150  is partially formed in substrate  160 . In one embodiment, first portion  152  is partially formed by etching into substrate  160  from second side  164 . As such, first portion  152  of opening  150  is partially formed by etching an exposed portion or area of substrate  160  within opening  185  of masking layer  184  from second side  164  toward first side  162 . 
   In some embodiments, first portion  152  of opening  150  is partially formed using an anisotropic etch process which initially forms first portion  152  with substantially parallel sides. In one embodiment, the etch process is a dry etch, such as a plasma based fluorine (SF 6 ) etch. In a particular embodiment, the dry etch is a reactive ion etch (RIE) and, more specifically, a deep RIE (DRIE), as described above. It is, however, within the scope of the present invention for first portion  152  of opening  150  to be partially formed using other fabrication techniques such as laser machining. 
   When initially etching first portion  152  of opening  150  into substrate  160  from second side  164 , masking layer  184  defines where substrate  160  is etched. As such, first portion  152  of opening  150  is initially formed with second dimension D 2  in the first direction. In one embodiment, initial etching of first portion  152  is stopped before reaching first side  162  of substrate  160  and, more specifically, before reaching etch stops  170  in substrate  160 . In another embodiment, initial etching of first portion  152  is continued between etch stops  170  to the side of layer  172  at first side  162  of substrate  160 . 
   As illustrated in the embodiment of  FIG. 4H , after first portion  152  of opening  150  is partially formed in substrate  160 , masking layer  184  is stripped or removed from substrate  160 . As such, masking layer  182  is revealed or exposed. In one embodiment, where masking layer  184  is formed of photoresist, masking layer  184  is removed, for example, by a resist stripper. 
   As illustrated in the embodiment of  FIG. 4I , first portion  152  of opening  150  is further etched into substrate  160  from second side  164  and second portion  154  of opening  150  is etched into substrate  160  from first side  162 . As such, first portion  152  of opening  150  is further formed by etching an exposed portion or area of substrate  160  from second side  164  toward first side  162  and second portion  154  of opening  150  is formed by etching exposed portions or areas of substrate  160  from first side  162  toward second side  164 . Thus, first portion  152  of opening  150  and second portion  154  of opening  150  are simultaneously etched into substrate  160 . 
   Typically, first portion  152  is further formed and second portion  154  is formed 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 tetra-methyl ammonium hydroxide (TMAH), potassium hydroxide (KOH), or other alkaline etchant. As such, a geometry of opening  150  through substrate  160  is defined by crystalline planes of the silicon substrate. For example, first portion  152  of opening  150  follows crystalline planes  168  of substrate  160  and second portion  154  of opening  150  follows crystalline planes  169  of substrate  160 . 
   In one embodiment, substrate  160  has a &lt;100&gt; Si crystal orientation and the wet anisotropic etches of first portion  152  and second portion  154  follow &lt;111&gt; Si planes of substrate  160 . As such, crystalline planes  168  and  169  include &lt;111&gt; Si planes of substrate  160 . Thus, sides of first portion  152  of opening  150  and sides of second portion  154  of opening  150  are oriented at angles of approximately 54 degrees to second side  164  and first side  162 , respectively. 
   As illustrated in the embodiment of  FIG. 4J , etching into substrate  160  from second side  164  toward first side  162  and/or from first side  162  toward second side  164  continues such that first portion  152  and second portion  154  of opening  150  connect or communicate. As such, opening  150  is formed through substrate  160 . 
   As described above, etch stops  170  are formed of a material resistant to the wet anisotropic etchant used to further form first portion  152  and form second portion  154  of opening  150 . As such, etch stops  170  define a maximum dimension of second portion  154  and a minimum dimension of first portion  152 , as described below. In addition, etch stops  170  establish a location of second portion  154  at first side  162  and accommodate misalignment between first portion  152  formed from second side  164  and second portion  154  formed from first side  162 . 
   More specifically, when etching into substrate  160  from first side  162 , etch stops  170  limit etching of substrate  160  to areas between etch stops  170  and prevent etching laterally of etch stops  170 . As such, undercutting or etching into substrate  160  under the edges of layer  172  and, more specifically, thin-film structure  132  is avoided when etching into substrate  160  from first side  162 . Thus, etch stops  170  define substantially vertical sidewalls of second portion  154  of opening  150  and control a width of opening  150  at first side  162 . Etch stops  170 , therefore, control where opening  150  communicates with first side  162 . 
   Furthermore, when etching into substrate  160  from second side  164 , etch stops  170  cause further etching of first portion  152  to self-terminate. More specifically, when further etching of first portion  152  reaches etch stops  170 , etching of first portion  152  continues to follow the crystalline orientation or crystalline planes of substrate  160 . For example, in one embodiment, as described above, etching of first portion  152  follows &lt;111&gt; Si planes of substrate  160 . As such, when etching of first portion  152  reaches one or more etch stops  170 , etching continues along &lt;111&gt; Si planes of substrate  160 . 
   A depth at which etch stops  170  extend into substrate  160  from first side  162 , however, is selected such that etching of first portion  152  toward first side  162  and beyond etch stops  170  self-terminates before reaching first side  162 . As such, etch stops  170  provide for self-alignment between first portion  152  as formed from second side  164  and second portion  154  as formed from first side  162 . More specifically, etch stops  170  accommodate misalignment between first portion  152  and second portion  154  by confining second portion  154  between spaced etch stops  170  and causing first portion  152  to self-terminate at etch stops  170 . In addition, a dimension of second portion  154  of opening  150  is self-limiting and self-aligned by etch stops  170 . 
   While the above description refers to the inclusion of substrate  160  having opening  150  formed therein in an inkjet printhead assembly, as one embodiment of a fluid ejection assembly of a fluid ejection system, 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. Accordingly, the present invention is not limited to printheads, but is 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, photoresist, or organic light-emitting materials or flowable particles of a solid such as talcum powder or a powdered drug, may be fed or routed through opening  150  of substrate  160 . 
   Although specific embodiments have been illustrated and described herein for purposes of description of the preferred embodiment, it will be appreciated by those of ordinary skill in the art that a wide variety of alternate and/or equivalent implementations calculated to achieve the same purposes may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. Those with skill in the chemical, mechanical, electromechanical, electrical, and computer arts will readily appreciate that the present invention may be implemented in a very wide variety of embodiments. This application is intended to cover any adaptations or variations of the preferred embodiments discussed herein. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.