Abstract:
A method for forming a self-aligned hole through a substrate to form a fluid feed passage is provided by initially forming an insulating layer on a first side of a substrate having two opposing sides; and forming a feature on the insulating layer. Next, etch an opening through the insulating layer, such that the opening is physically aligned with the feature on the insulating layer; and coat the feature with a layer of protective material. Patterning the layer of protective material will expose the opening through the insulating layer. Dry etching from the first side of the substrate forms a blind feed hole in the substrate corresponding to the location of the opening in the insulating layer, the blind feed hole including a bottom. Subsequently, grind a second side of the substrate and blanket etch it to form a hole through the entire substrate.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of prior U.S. patent application Ser. No. 12/241,747, filed Sep. 30, 2008, now U.S. Pat. No. 8,173,030 which is hereby incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to the formation of a fluid feed and, more particularly, to ink feeds used in ink jet devices and other liquid drop ejectors. 
     BACKGROUND OF THE INVENTION 
     Drop-On-Demand (DOD) liquid emission devices have been known as ink printing devices in ink jet printing systems for many years. Early devices were based on piezoelectric actuators such as are disclosed by Kyser et al., in U.S. Pat. No. 3,946,398 and by Stemme in U.S. Pat. No. 3,747,120. A currently popular form of ink jet printing, thermal ink jet (or “thermal bubble jet”), uses electrically resistive heaters to generate vapor bubbles which cause drop emission, as is discussed by Hara et al., in U.S. Pat. No. 4,296,421. Although the majority of the market for drop ejection devices is for the printing of inks, other markets are emerging such as ejection of polymers, conductive inks, or drug delivery. 
     The printhead used for drop ejection in a thermal inkjet system includes a nozzle plate having an array of ink jet nozzles above ink chambers. At the bottom of an ink chamber, opposite the corresponding nozzle, is an electrically resistive heater. The ink chamber, nozzle plate, and heater are formed on a substrate, typically made of silicon, which also contains circuitry to drive the electrically resistive heaters. In response to an electrical pulse of sufficient energy, the heater causes vaporization of the ink, generating a bubble that rapidly expands and ejects an ink drop from the ink chamber. Ink is replenished to the ink chamber through ink feed channels, located adjacent the ink chamber, typically formed through the silicon substrate on which the ink chambers are formed. 
     The ink feed channels of the prior art have been formed in various ways using laser drilling, wet etching, or dry etching of the silicon. Printheads are typically fabricated using silicon wafers. The ink feed channels of the prior art has a long slot formed by patterning and etching through the silicon wafer from the back or non-device side. Most printheads of the prior art, use a single long slot for each color of ink. Multiple long slots are therefore formed in a thick silicon substrate, one for each color. 
     There is a desire to increase the number of nozzles on a printhead for each color. It is also desirable to decrease the spacing between ink feed channels to shrink the size of the printhead for lower cost. Increasing the number of nozzles increases the length of the printhead and therefore the length of the ink feed channels. This long channel in the silicon substrate will weaken the printhead making it more susceptible to stress cracking. Co-pending application (U.S. Publication No. 2008/0136867 A1), discloses the use of anisotropic dry silicon etch, utilizing the “Bosch” process (also known as pulsed or time-multiplexed etching), in which ribs are formed to break up the ink feed channel into sections to increase the strength of the printhead making it more extensible. 
     However, there is also a desire to increase the frequency of drop ejection. One limitation on the frequency of drop ejection is the time required to refill the ink chamber after the previous drop ejection. The frequency of drop ejection can be increased, if the time required to refill the ink chamber is decreased. Co-pending application (U.S. Publication No. 2008/0180485 A1), discloses a dual feed printhead in which the ink feed channel is replaced by multiple ink feed holes for each ink color, with the ink feed holes located on both sides of the ink chamber. In this case, long ink feed channels on both sides of the ink chamber cannot be utilized, as they would result in a considerable decreased strength for the structure. 
     In the dual feed printhead, therefore, the preferred ink feed openings are much smaller than the ink feed channels of the prior art, with lengths extending across 1-2 nozzles corresponding to a length of 20-100 μm and similar width. The use of these multiple feed holes, provide strength and extensibility to the printhead. However these small openings cause fabrication issues. Such small feature sizes cannot be formed using wet etching or laser etching. Instead, a dry anisotropic etch process utilizing the “Bosch” process must be used. For dry etching of small openings with high aspect ratio the etch rate is much slower than for large slots, and slows down further the deeper the etch proceeds, therefore increasing the etch time for formation of these holes. The silicon substrate can be thinned prior to etching to decrease this etch time. It is also desirable to thin the substrate to reduce viscous drag of ink through these small holes, so that ink refill time can be decreased. In fact, silicon substrate thicknesses less than 200 μm are desired to minimize the effect of viscous drag on the ink refill time, and to provide a good aspect ratio for high etch processing throughput during fabrication. However, processing of such thin wafers to pattern and etch the ink feed holes through the back of the wafer is difficult, resulting in wafer breakage and yield loss. It is, therefore, desirable to form ink feed holes along with minimizing the process steps on thin wafers. 
     Another method to decrease the viscous drag is by varying the ink feed opening versus the depth of the feed hole. In the prior art wet etching has been used to provide an anisotropic etch where the feed channel opening is wider at the back of the substrate and narrows down to a smaller opening at the front of the substrate next to the ink chamber. However, the sidewall angle for this, wet etch process of 54.74° is large, and for closely spaced ink feed channels, wet etching is not possible. The anisotropic dry silicon etch, utilizing the “Bosch” process produces openings that typically remain the same width or are reentrant in profile through the substrate in the opposite direction that is desired. It is, therefore, desirable to have a process where the ink feed opening is narrower at the front of the substrate adjacent the ink chamber and wider at the back of the substrate, but where the sidewall angle is significantly less than 54.74°. 
     In the dual feed printhead, to minimize the ink refill time, the ink openings are located very close to the ink chamber. Alignment of the ink feed openings to the ink chamber is critical. In prior art, the patterning of the ink feed channels is performed using back to front wafer alignment of a mask. However, there are issues in fabrication that degrade alignment. If the silicon wafer is warped the ink feed channels will not align precisely with the mask. Also, during the etch process itself, the etch direction is not completely perpendicular to the wafer surface, especially approaching the wafer edge, due to directional variation of the ions. It is also difficult to time the etch process so that there is no over etching causing undercut of the silicon wafer at the device side. It is desirable to have a process that self-aligns the ink feed channel to the ink chamber. 
     In forming the ink feed holes through the wafer from the back, the etching of the silicon stops on material used to form the ink chamber. The timing of the endpoint is critical as over etching causes undercut of the ink feed opening at the front surface that causes misalignment of the ink feed opening. Under etching of the area for the ink feed opening could yield a partially formed ink feed opening or even an entirely closed ink feed opening, which is undesirable. Since the etch rate is not uniform across the wafer there will always be ink feed openings that will be overetched. It is desirable to have a process that self aligns the ink feed opening to the ink chamber resulting in uniform ink feed openings with no undercut. 
     There is, therefore, a need for a printhead that has small ink feed holes aligned to the ink feed chambers that are easily fabricated with high yield. This printhead should also be capable of ejecting drops at high frequencies with an ink chamber refill capability to meet this ejection frequency requirement. 
     SUMMARY OF THE INVENTION 
     A method for forming a self-aligned hole through a substrate to form a fluid feed passage is provided by initially forming an insulating layer on a first side of a substrate having two opposing sides; and forming a feature on the insulating layer. Next, etch an opening through the insulating layer, such that the opening is physically aligned with the feature on the insulating layer; and coat the feature with a layer of protective material. Patterning the layer of protective material will expose the opening through the insulating layer. Dry etching from the first side of the substrate forms a blind hole in the substrate corresponding to the location of the opening in the insulating layer, the blind hole including a bottom. Subsequently, grind a second side of the substrate and blanket etch it to form a hole through the entire substrate. 
     Another embodiment of the present invention provides a method for forming a plurality of liquid ejection devices, the method including the steps of: 
     forming an insulating layer on a first side of a silicon wafer having two opposing sides; 
     forming an array of drop forming mechanisms on the insulating layer on the silicon wafer; 
     etching a plurality of openings through the insulating layer on the silicon wafer; 
     forming a chamber layer on the insulating layer on the silicon wafer, the chamber layer including walls between each drop forming mechanism; 
     coating the chamber layer with a layer of photoresist; 
     patterning the layer of photoresist to expose the openings through the insulating layer; 
     dry etching from the first side of the silicon wafer to form blind holes in the silicon wafer corresponding to the locations of the openings in the insulating layer, the blind holes including bottoms; 
     forming a nozzle layer on the chamber layer; 
     patterning the nozzle layer to provide an array of nozzles corresponding to the array of drop forming mechanisms; 
     grinding a second side of the silicon wafer to within a distance of 50 microns from the bottoms of the blind holes; and 
     blanket etching the second side of the silicon wafer to open the blind holes to form a plurality of holes through the entire silicon wafer. 
     A third embodiment of the present invention provides a pinthead that includes a silicon wafer having a first side including a row of chambers and a second side, including a ground surface. Also included are a plurality of self-aligned holes disposed along a first side of the row of chambers and a plurality of self-aligned holes disposed along a second side of the row of chambers, and extending from the first side of the silicon wafer to the second side. Each self-aligned hole is smaller at the first side of the silicon wafer than at the second side of the silicon wafer to form a retrograde profile angle. A drop forming mechanism in the chamber; along with a nozzle plate proximate to the drop forming mechanism; and a source of fluid for supplying fluid to the hole is also included in the printhead. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the detailed description of the preferred embodiments of the invention presented below, reference is made to the accompanying drawings, in which: 
         FIG. 1  is a schematic representation of a liquid ejection system incorporating the present invention; 
         FIG. 2  is a schematic top view of a partial section of a liquid ejection printhead according to the present invention; 
         FIGS. 3-9  show one embodiment of a method for forming a liquid ejection printhead, shown schematically in  FIG. 2 , according to the present invention; 
         FIG. 10  is a schematic top view of a wafer on which liquid ejection printheads are fabricated with dicing marks according to the present invention; 
         FIG. 11  is a schematic top view of a wafer on which liquid ejection printheads are fabricated with trenches formed in the streets according to the present invention; and 
         FIG. 12  is a flow chart describing the steps for fabricating a liquid ejection printhead as shown in  FIGS. 3-9  according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present description will be directed in particular to elements forming part of, or cooperating more directly with, apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art. In the following description, identical reference numerals have been used, where possible, to designate identical elements. 
     As described in detail herein below, at least one embodiment of the present invention provides a method for forming an ink feed hole or passage for a liquid drop ejector. The most familiar of such devices are used as printheads in ink jet printing systems. Many other applications are emerging which make use of liquid feed holes in systems similar to ink jet printheads, which emit liquids other than inks, and that need a simple, self-aligned liquid feed hole formation. The terms ink jet and liquid drop ejector will be used herein interchangeably. The inventions described below provide methods for improved fluid feed formation, especially ink, for a liquid drop ejector. 
     Referring to  FIG. 1 , a schematic representation of a liquid ejection system  10 , utilizing a printhead fabricated according to the present invention, is shown. Liquid ejection system  10  includes a source  12  of data (for example, image data), which provides signals that are interpreted by a controller  14  as being commands to eject liquid drops. Controller  14  outputs signals to a source  16  of electrical energy pulses that are sent to liquid ejector printhead die  18  (e.g., an inkjet printhead), a partial section of which is shown in the figure. Typically, a liquid ejector printhead die  18  includes a plurality of liquid ejectors  20  arranged in at least one array, for example, a substantially linear row. During operation, liquid or fluid, for example, ink in the form of ink drops  22 , is deposited on a recording medium  24 . 
     Referring to  FIG. 2 , a schematic representation of a top view of a partial section of a liquid ejector printhead die  18  for ink is shown. Liquid ejector printhead die  18  includes an array or plurality of liquid ejectors  20 , one of which is designated by the dotted line in  FIG. 2 . Liquid ejector  20  includes a structure, for example, having walls  26  extending from a substrate  28  that define a chamber  30 . Walls  26  separate liquid ejectors  20  positioned adjacent to other liquid ejectors  20 . Each chamber  30  includes a nozzle orifice  32  in nozzle plate  31  through which liquid is ejected. A drop forming mechanism, for example, a resistive heater  34  is also located in each chamber  30 . In  FIG. 2 , the resistive heater  34  is positioned above the top surface of substrate  28  in the bottom of chamber  30  and opposite nozzle orifice  32 , although other configurations are permitted. In other words, in this embodiment the bottom surface of chamber  30  is above the top of substrate  28 , and the top surface of the chamber  30  is the nozzle plate  31 . 
     Referring to  FIGS. 1 and 2 , feed holes  36  consist of two linear arrays of feed holes  36   a  and  36   b  that supplies liquid to the chambers  30 . Feed holes  36   a  and  36   b  are positioned on opposite sides of the liquid ejector  20  containing chamber  30  and nozzle orifice  32 . In  FIG. 2  the feed holes  36  are arranged so that feed holes  36   a  are located primarily adjacent a pair of liquid ejectors  20  and feed holes  36   b  are located primarily adjacent the next pair of chambers  30  in the printhead array. Other geometries are also possible as disclosed in co-pending application (U.S. Publication No. 2008/0180485A1), and incorporated herein by reference. 
     Referring to  FIG. 2 , liquid ejectors are formed in a linear array at a high nozzle per inch count. In one exemplary embodiment of the present invention the liquid ejectors  20  are spaced with a period of 20-42 μm. The length L of feed opening  42  can vary from 10 μm to 100 μm, depending on the design. The width W of the feed opening  42  can also vary similarly from 10 μm to 100 μm, and preferably from 50 μm to 60 μm. 
       FIGS. 3-9  illustrate a fabrication method of an exemplary embodiment of the present invention for forming a liquid ejection printhead  18  containing multiple small feed holes  36  aligned to liquid ejectors  20 , for high frequency operation. The fabrication method illustrated in  FIGS. 3-9  is summarized in  FIG. 12  that shows a flow chart of the step sequence for fabricating a liquid ejection printhead  18 . 
     Starting with a substrate  28 , a silicon wafer as described in step  60  of the flow chart of  FIG. 12  is used. As described in step  62  of  FIG. 12  and shown as a partial section of a liquid ejection printhead die  18  in  FIG. 3 , a drop forming mechanism, in this case, an array of resistive heaters  34  are formed on top of an insulating dielectric layer  40 , which is formed on top of the silicon substrate  28 . Fabricated in the liquid ejection printhead  18 , but not shown, are electrical connections to the resistive heaters  34 , as well as power LDMOS and CMOS logic circuitry to control drop ejection. The insulating dielectric layer  40  may also be deposited during these processes. The fabrication of the heater structure is described in co-pending application (U.S. patent application Ser. No. 12/143,880), and incorporated herein by reference. 
     As described in step  64  of  FIG. 12 ,  FIG. 4  shows a partial section of a liquid ejection printhead die  18  after patterning and etching through the insulating dielectric layer  40  to the silicon substrate  28  forming feed openings  42 . 
     As described in step  66  of  FIG. 12 ,  FIG. 5  shows a partial section of a liquid ejection printhead die  18  after formation of the chamber layer  44  that includes walls  26  between each liquid ejector  20  and an outer passivation layer  46  that extends over the rest of the liquid ejection printhead die  18  to protect the circuitry from liquid or fluid, such as ink. The chamber layer  44  can be formed by spin coating, exposure, and development using a photoimageable epoxy such as a novolak resin based epoxy, for example: TMMR resist available from Tokyo Ohka Kogyo. The thickness of the chamber layer  44  is in the range 8-15 μm. 
     As described in step  68  of  FIG. 12 ,  FIG. 6   a  shows a partial section of a liquid ejection printhead die  18  after a layer of photoresist  48  has been coated and patterned. This photoresist layer  48  is patterned to protect the chamber layer  44  from being attacked during etching of the feed holes. The photoresist layer  44  is patterned so that it is pulled back a distance d from feed opening definition  42  patterned in the insulating dielectric layer  40 . In one embodiment this distance d is 0-2 μm.  FIG. 6   b  shows a top view of a partial section of a liquid ejection printhead die  18  after a layer of photoresist layer  48  has been coated and patterned. Section B-B, taken from  FIG. 6   b , is shown in  FIG. 6   c  and illustrates the pull-back distance d of the patterned photoresist layer  48  from the feed opening definition  42  patterned in the insulating dielectric layer  40 . The thickness of photoresist coated is dependent on the thickness of the chamber layer  44  and is designed to provide a thickness on top of the chamber layer  44  to protect it from being attacked during the etching of the feed openings as some thickness of the photoresist is lost during the etch process. 
     As described in step  70  of  FIG. 12 ,  FIG. 7   a  shows a partial section of a liquid ejection printhead die  18  after an anisotropic dry silicon etch has been executed to etch blind feed holes  37  in the silicon substrate  28 . The insulating dielectric layer has a high selectivity to the dry silicon etch so that the blind feed holes are self aligned to the feed openings  42 . This is highly preferable, since the edge of the feed opening is 0-5 μm away from the chamber walls and resistive heater edge. There is no etch stop and etching is timed to provide a blind feed hole depth in the range 50-300 μm deep. The aspect ratio of the blind feed hole in an exemplary embodiment will be less than 5:1. Since there is no etch stop and the aspect ratio is low a high etch rate&gt;20 μm/min. and, therefore, a short etch time can be achieved on commercially available equipment. Such equipment is available from etching equipment manufacture companies such as AVIZA or Surface Technology Systems.  FIG. 7   b  shows section B-B outlined in  FIG. 6   b  after the blind feed hole etch. Commercially available systems with high etch rates use a process that etches the blind feed hole in a manner that gives a retrograde profile with retrograde angle φ that is greater than 1°, and preferably greater than 4°. This retrograde profile (wider toward the back of the substrate  28  and narrower near the front or top surface of the substrate  28 ) is advantageous in that it lowers the impedance for ink flow or other liquids. It also helps in keeping air bubbles from the liquid ejector. For some embodiments, a preferred range for retrograde angle φ is between 1° and 10°. The photoresist layer  48  is then stripped using a liquid solvent. 
     As described in step  72  of  FIG. 12 ,  FIG. 8  shows a partial section of a liquid ejection printhead die  18  after a photoimageable nozzle plate layer  31  has been laminated, and patterned to form nozzles  32 . The photoimageable nozzle plate layer  31  can be formed using a dry film photoimageable epoxy such as a novolak resin based epoxy, for example: TMMF dry film resist available from Tokyo Ohka Kogyo. The thickness of the photoimageable nozzle plate layer  31  is in the range 5-15 μm and in a preferred embodiment is 10 μm. The use of a dry film laminate for the nozzle plate enables the formation of the nozzle plate  31  on the liquid ejection printhead containing high topography features such as the ink feed holes  36 . Also since the ink feed openings are not all the way through the substrate, but are still blind holes  37  at this point, there are no difficulties in applying vacuum to hold down the substrate during lamination. 
     As described in step  74  of  FIG. 12 , the substrate  28  containing liquid ejection printhead die  18  is then mounted on a tape frame and ground from the back.  FIGS. 9   a  and  9   b  show section B-B as outlined in  FIG. 6   b , before grinding in  FIG. 9   a  and after grinding in  FIG. 9   b . The substrate is ground to within a distance t of 0-40 μm of the feed openings. In a preferred embodiment the distance t is 20 μm for the following reasons. Firstly the grinding process can leave residue in the feed openings if the grinding process is used to fully open the feed lines. Secondly, the grinding process typically results in microcracks causing damage for a thickness of 10-20 μm deep into the substrate. This damage will cause a weakness of the substrate resulting in cracking if not removed. Thirdly, the feed opening etch depth varies across the substrate as well as thickness variation of the substrate after the grinding process. The combination of the variation of the feed opening etch depth and the variation of the substrate thickness is typically about 12 μm. 
     As described in step  76  of  FIG. 12 , the substrate is then left on the tape frame and exposed, unmasked, to a plasma containing etchant gas Sulfur hexafluoride. Such blanket etch systems are commercially available from, for example, TEPLA and are used to remove damage in the silicon substrate after grinding. The system is maintained so that the substrate temperature stays below 70° C. This ensures that the tape frame will not be affected and the chamber  44  and nozzle plate  31  polymer layers will not be etched. This system performs a blanket etch on the substrate  28 , removing silicon from the substrate  28  until the feed openings are exposed.  FIG. 9   c  shows section B-B as outlined in  FIG. 6   b  with opened feed openings. The advantages of this method are as follows: First, the etch provides clean opening of the feed openings with no residue. Second, damage that was formed during wafer grinding is removed by this step, as is well known in the art. Third, the substrate is mounted on a tape frame so handling of a thin wafer is much easier. Fourth, no patterning of the substrate back is necessary making the process much simpler. The substrate can be taken from this step straight to dicing so that handling of thin wafers is minimized. The final thickness of the silicon substrate  28  is less than or equal to the depth of the feed hole  36  and in a preferred embodiment is in the range 50-300 μm. 
     WORKING EXAMPLE 
     Devices were fabricated according to the present invention. Starting with a silicon substrate, an insulating dielectric layer consisting of 1 μm silicon oxide was deposited using plasma enhanced chemical vapor deposition. A resistive heater layer 600 Å thick consisting of a tantalum silicon nitride alloy was deposited using physical vapor deposition and patterned to form an array of heaters. A 0.6 μm aluminum layer was next deposited using physical vapor deposition and patterned to form connections to the resistive heater layer. Next a 0.25 μm silicon nitride layer was deposited using plasma enhanced chemical vapor deposition and a 0.25 μm tantalum layer was deposited using physical vapor deposition. These layers are used to protect the resistive heater material from the ink. 
     A 1.7 μm resist layer was then coated and patterned and a dry etch was used to form feed openings etched through the silicon oxide and silicon nitride layer. TMMR photoimageable permanent resist was spin coated to a thickness of 12 μm and patterned using a mask with UV light to form the chamber layer. The TMMR resist was then cured at 200° C. for 1 hour. 
     SPR220-7 photoresist was then spin coated to a thickness of 10 μm on top of the chamber layer giving a thickness of ˜22 μm over the feed opening. The resist was then exposed, leaving a 0.25 μm gap between feed opening and resist edge. The exposed silicon in the feed opening was then etched to a depth of 230 μm using DRIE silicon etching system manufactured by Surface Technology Systems. The resist was then stripped in a solvent ALEG-310 manufactured by Baker chemicals. 
     TMMF photoimageable permanent dry film resist with a thickness of 10 μm was laminated onto the chamber layer using a dry film laminator manufactured by Teikoku Taping Company. The dry film resist was exposed using a mask with UV light and developed to form nozzles. 
     Protective tape was then applied to the front side of the wafer and the wafer was ground from the backside to a thickness of 250 μm. The wafer was then put into an inductively, coupled plasma etch system manufactured by Oxford Instruments Ltd. and blanket etched using a SF 6 /Ar gas chemistry until the feed holes were opened in the back of the wafer. 
     The wafer was then diced by sawing and single liquid ejection printheads were packaged into ink jet printheads. The packaging yield was very high demonstrating the robustness of the dual feed structure. The printhead was filled with ink and drop ejection was measured. The liquid ejection printhead ejected 2.5 pL drops at frequencies&gt;60 kHz. 
     Another embodiment of the present invention includes the dicing of the wafer from the backside. Typically in the dicing process the wafer needs to be mounted front side up so alignment of the dicing can be performed. It would be preferable for the present invention to dice the wafer from the backside since at the final step that is how the wafer is mounted. However dicing marks need to be provided to align the dicing streets to the chips. 
       FIG. 10  shows a schematic view of the top of a silicon wafer  54  containing many liquid ejection printhead die  18  after the feed hole  36  etch described in  FIG. 7 . Shown on the wafer are the streets  52  where dicing is to occur. During the formation of the feed openings  42  and feed holes  36  dicing marks  50  patterned at the intersections of the streets are also formed. The opening of these dicing marks  50  are designed so that they will be etched to the same depth as the feed holes  36 . When the feed holes  36  are exposed during the blanket plasma etch as shown in  FIG. 9   c , these dicing marks  50  will also be exposed. These dicing marks  50  can then be used during dicing to align the dicing saw to the streets. 
     In another embodiment of the present invention, liquid ejection printhead die  18  are separated into individual chips (sometimes termed as “singulated” by industry artisans) or, in other words, diced from the wafer without the need for sawing.  FIG. 11  shows a schematic view of the top of a silicon wafer  54  containing many liquid ejection printhead die  18 , after the feed hole  36  etch described in  FIG. 7 . Shown on the wafer are the streets  52  where dicing is to occur. During the formation of the feed openings  42  and feed holes  36  trenches  56  patterned along the streets  52  are also to be formed. The open area of these trenches  56  are designed so that they will be etched to the same depth as the feed holes  36 . When the feed holes  36  are opened during the blanket plasma etch as shown in  FIG. 9   c , these trenches  56  will also be opened. At this point each liquid ejection printhead die  18  is separated without the need for sawing. The liquid ejection printhead die  18 , can then be picked off the dicing tape directly for packaging into a liquid ejection printhead. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
     PARTS LIST 
     
         
           10  liquid ejection system 
           12  data source 
           14  controller 
           16  electrical pulse source 
           18  liquid ejection printhead die 
           20  liquid ejector 
           22  ink drop 
           24  recording medium 
           26  wall 
           28  substrate 
           30  chamber 
           31  nozzle plate 
           32  nozzle orifice 
           34  resistive heater 
           36  feed holes 
           37  blind feed holes 
           40  insulating dielectric layer 
           42  feed openings 
           44  chamber layer 
           46  outer passivation layer 
           48  photoresist layer 
           50  dicing marks 
           52  streets 
           54  silicon wafer 
           56  trenches