Patent Publication Number: US-6911155-B2

Title: Methods and systems for forming slots in a substrate

Description:
BACKGROUND OF THE INVENTION 
     Ink jet printers have become ubiquitous in society. These printers provide many desirable characteristics at an affordable price. However, the desire for ever more features at ever-lower prices continues to press manufacturers to improve efficiencies. Consumers want ever higher print image resolution, realistic colors, and increased pages or printing per minute. One way of achieving consumer demands is by improving the print head and its method of manufacture. Currently, the print head is time consuming and costly to make. 
     Accordingly, the present invention arose out of a desire to provide fast and economical methods for forming print heads and other fluid ejecting devices having desirable characteristics. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The same components are used throughout the drawings to reference like features and components. 
         FIG. 1  is a front elevational view of an exemplary printer. 
         FIG. 2  is a block diagram that illustrates various components of an exemplary printer. 
         FIGS. 3 and 4  each show a perspective view of a print carriage in accordance with one exemplary embodiment. 
         FIG. 5  is a perspective view of a print cartridge in accordance with one exemplary embodiment. 
         FIG. 6  is a cross-sectional view of a top of a print cartridge in accordance with one exemplary embodiment. 
         FIG. 7  is a top view of a print head in accordance with one exemplary embodiment. 
         FIGS. 8   a - 8   f  each show a cross-sectional view of a substrate in accordance with one exemplary embodiment. 
         FIGS. 9   a - 9   j  each show a cross-sectional view of a substrate in accordance with one exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Overview 
     The embodiments described below pertain to methods and systems for forming slots in a semiconductor substrate. One embodiment of this process will be described in the context of forming fluid feed slots in a print head die substrate. As commonly used in print head dies, the semiconductor substrate often has microelectronics incorporated within, deposited over, and/or supported by the substrate. The fluid feed slot(s) allow fluid, commonly ink, to be supplied to fluid ejecting elements contained in ejection chambers within the print head. The fluid ejection elements commonly comprise heating elements or firing resistors that heat fluid causing increased pressure in the ejection chamber. A portion of that fluid can be ejected through a firing nozzle with the ejected fluid being replaced by fluid from the fluid feed slot. 
     The fluid feed slot can be made in various ways. In one embodiment material is removed from the substrate by dry etching a trench through a first substrate surface. A second trench can be formed by various techniques, such as sand drilling, so that the first and second trenches meet to form a slot through the substrate. In some embodiments, the trenches are formed so that they are about equal depth to ensure that they meet at about the middle of the substrate&#39;s thickness. Slots made this way can be very narrow and as long as desired. Narrow slots remove less material and have beneficial strength characteristics that can reduce die fragility. This, in turn, can allow slots to be positioned closer together on the die. 
     Other embodiments include features that reduce the accumulation of bubbles in the slot. Bubbles can result from the fluid ejection process and can occlude fluid feed if they accumulate in the slot. Various techniques can be utilized to promote bubble migration away from the thin film surface where they are most prone to blocking fluid flow. 
     Although exemplary embodiments described herein are described in the context of providing dies for use in inkjet printers, it is recognized and understood that the techniques described herein can be applicable to other applications where slots are desired to be formed in a substrate. 
     The various components described below may not be illustrated accurately as far as their size is concerned. Rather, the included figures are intended as diagrammatic representations to illustrate to the reader various inventive principles that are described herein. 
     Exemplary Printer System 
       FIG. 1  shows one embodiment of a printer  100 , embodied in the form of an inkjet printer. The printer  100  can be, but need not be, representative of an inkjet printer series manufactured by the Hewlett-Packard Company under the trademark “DeskJet”. The inkjet printer  100  is capable of printing in black-and-white and/or in color. The term “printer” refers to any type of printer or printing device that ejects fluid or other pigmented materials onto a print media. Though an inkjet printer is shown for exemplary purposes, it is noted that aspects of the described embodiments can be implemented in other forms of printing devices that employ inkjet printing elements or other fluid ejecting devices, such as facsimile machines, photocopiers, and the like. 
       FIG. 2  illustrates various components in one embodiment of printer  100  that can be utilized to implement the inventive techniques described herein. Printer  100  can include one or more processors  102 . The processor  102  controls various printer operations, such as media handling and carriage movement for linear positioning of the print head over a print media (e.g., paper, transparency, etc.). 
     Printer  100  can have an electrically erasable programmable read-only memory (EEPROM)  104 , ROM  106  (non-erasable), and/or a random access memory (RAM)  108 . Although printer  100  is illustrated having an EEPROM  104  and ROM  106 , a particular printer may only include one of the memory components. Additionally, although not shown, a system bus typically connects the various components within the printing device  100 . 
     The printer  100  can also have a firmware component  110  that is implemented as a permanent memory module stored on ROM  106 , in one embodiment. The firmware  110  is programmed and tested like software, and is distributed with the printer  100 . The firmware  110  can be implemented to coordinate operations of the hardware within printer  100  and contains programming constructs used to perform such operations. 
     In this embodiment, processor(s)  102  process various instructions to control the operation of the printer  100  and to communicate with other electronic and computing devices. The memory components, EEPROM  104 , ROM  106 , and RAM  108 , store various information and/or data such as configuration information, fonts, templates, data being printed, and menu structure information. Although not shown in this embodiment, a particular printer can also include a flash memory device in place of or in addition to EEPROM  104  and ROM  106 . 
     Printer  100  can also include a disk drive  112 , a network interface  114 , and a serial/parallel interface  116  as shown in the embodiment of FIG.  2 . Disk drive  112  provides additional storage for data being printed or other information maintained by the printer  100 . Although printer  100  is illustrated having both RAM  108  and a disk drive  112 , a particular printer may include either RAM  108  or disk drive  112 , depending on the storage needs of the printer. For example, an inexpensive printer may include a small amount of RAM  108  and no disk drive  112 , thereby reducing the manufacturing cost of the printer. 
     Network interface  114  provides a connection between printer  100  and a data communication network in the embodiment shown. The network interface  114  allows devices coupled to a common data communication network to send print jobs, menu data, and other information to printer  100  via the network. Similarly, serial/parallel interface  116  provides a data communication path directly between printer  100  and another electronic or computing device. Although printer  100  is illustrated having a network interface  114  and serial/parallel interface  116 , a particular printer may only include one interface component. 
     Printer  100  can also include a user interface and menu browser  118 , and a display panel  120  as shown in the embodiment of FIG.  2 . The user interface and menu browser  118  allows a user of the printer  100  to navigate the printer&#39;s menu structure. User interface  118  can be indicators or a series of buttons, switches, or other selectable controls that are manipulated by a user of the printer. Display panel  120  is a graphical display that provides information regarding the status of the printer  100  and the current options available to a user through the menu structure. 
     This embodiment of printer  100  also includes a print engine  124  that includes mechanisms arranged to selectively apply fluid (e.g., liquid ink) to a print media such as paper, plastic, fabric, and the like in accordance with print data corresponding to a print job. 
     The print engine  124  can comprise a print carriage  140 . The print carriage can contain one or more print cartridges  142  that comprise a print head  144  and a print cartridge body  146 . Additionally, the print engine can comprise one or more fluid sources  148  for providing fluid to the print cartridges and ultimately to a print media via the print heads. 
     Exemplary Embodiments and Methods 
       FIGS. 3 and 4  show exemplary print cartridges ( 142   a  and  142   b ) in a print carriage  140 . The print carriages depicted are configured to hold four print cartridges although only one print cartridge is shown. Many other exemplary configurations are possible.  FIG. 3  shows the print cartridge  142   a  configured for an up connect to a fluid source  148   a , while  FIG. 4  shows print cartridge  142   b  configured to down connect to a fluid source  148   b . Other exemplary configurations are possible including but not limited the print cartridge having its own self-contained fluid supply. 
       FIG. 5  shows an exemplary print cartridge  142 . The print cartridge is comprised of the print head  144  and the cartridge body  146 . Other exemplary configurations will be recognized by those of skill in the art. 
       FIG. 6  shows a cross-sectional representation of a portion of the exemplary print cartridge  142  taken along line a—a in FIG.  5 . It shows the cartridge body  146  containing fluid  602  for supply to the print head  144 . In this embodiment, the print cartridge is configured to supply one color of fluid or ink to the print head. In this embodiment, a number of different fluid feed slots are provided, with three exemplary slots being shown at  604   a ,  604   b , and  604   c . Other exemplary embodiments can divide the fluid supply so that each of the three fluid feed slots  604   a - 604   c  receives a separate fluid supply. Other exemplary print heads can utilize less or more slots than the three shown here. 
     The various fluid feed slots pass through portions of a substrate  606  in this embodiment. Silicon can be a suitable substrate, for this embodiment. In some embodiments, substrate  606  comprises a crystalline substrate such as single crystalline silicon or polycrystalline silicon. Examples of other suitable substrates include, among others, gallium arsenide, glass, silica, ceramics or a semi conducting material. The substrate can comprise various configurations as will be recognized by one of skill in the art. In this exemplary embodiment, the substrate comprises a base layer, shown here as silicon substrate  608 . The silicon substrate has a first surface  610  and a second surface  612 . Positioned above the silicon substrate are the independently controllable fluid drop generators that in this embodiment comprise firing resistors  614 . In this exemplary embodiment, the resistors are part of a stack of thin film layers on top of the silicon substrate  608 . The thin film layers can further comprise a barrier layer  616 . The barrier layer can comprise, among other things, a photo-resist polymer substrate. Above the barrier layer is an orifice plate  618  that can comprise, but is not limited to a nickel substrate. The orifice plate has a plurality of nozzles  619  through which fluid heated by the various resistors can be ejected for printing on a print media (not shown). The various layers can be formed, deposited, or attached upon the preceding layers. The configuration given here is but one possible configuration. For example, in an alternative embodiment, the orifice plate and barrier layer are integral. 
     The exemplary print cartridge shown in  FIGS. 5 and 6  is upside down from the common orientation during usage. When positioned for use, fluid can flow from the cartridge body  146  into one or more of the slots  604   a - 604   c . From the slots, the fluid can travel through a fluid feed passageway  620  that leads to a firing chamber  622 . A firing chamber can be comprised of a firing resistor, a nozzle, and a given volume of space therein. Other configurations are also possible. When an electrical current is passed through the resistor in a given firing chamber, the fluid can be heated to its boiling point so that it expands to eject a portion of the fluid from the nozzle  619 . The ejected fluid can then be replaced by additional fluid from the fluid feed passageway  620 . 
     The embodiment of  FIG. 7  shows a view from above the thin-film surface of a substrate incorporated into a print head. The substrate is covered by the orifice plate  618  with underlying structures of the print head indicated in dashed lines in this embodiment. The orifice plate is shown with numerous nozzles  619 . Below each nozzle lies the firing chamber  622  that is connected to a fluid feed passageway (feed channel)  620  and then to slot  604   a-c . The slots are illustrated in this embodiment as an elliptical configuration when viewed from above the first surface of the substrate. Other exemplary geometries include rectangular among others. 
     Exemplary Slot Forming Techniques 
       FIGS. 8   a - 8   f  and  9   a - 9   j  show two exemplary embodiments, respectively, in which portions of the substrate are removed to form slots through the substrate. The illustrated substrate  606  has a thickness t. The described embodiments can work satisfactorily with various thicknesses of substrate. For example, in the specific described embodiments, the thickness can range from less than about 100 microns to at least about 2000 microns. The thickness of the substrate t in some exemplary embodiments can be about 675 microns. 
     The slots can comprise a first trench  802  that originates from a first side of the substrate, and a second trench  804  (shown  FIG. 8   c ) that originates from the second side of the substrate. For ease of appreciating these trenches, the figures are shown in corresponding pairs. For example,  FIG. 8   a  is a portion of a cross-section taken along line b—b indicated in  FIGS. 5 and 7 , and shows a length l 1  and depth x of the first trench.  FIG. 8   b  is a portion of a cross section taken along line a—a in FIG.  5 .  FIG. 8   b  shows the width w 1  and the same depth x shown in  FIG. 8   a  of the first trench  802 .  FIGS. 8   c  and  8   d  and  FIGS. 8   e  and  8   f  have similar relationships. 
       FIG. 8   a  shows an exemplary embodiment where the first trench  802  has been formed in the substrate from a first side or surface  610 . Here, the first surface can comprise the thin film side of the substrate. The trench can be formed by a dry etch process. The dry etch process is an alternating process that can comprise depositing a passivation layer followed by etching. This alternating sequence can be repeated as desired to remove additional substrate. The dry etch can use SF 6  in the etch step and C 4 F 8  in the depositing step, among others. 
     The trench shown in  FIG. 8   a  extends through approximately 50 percent of the substrate as indicated by x, and thus has a depth of about 335 microns in this particular example. In other embodiments, the trench can be any depth from less than about 40 microns to passing through the entire thickness t. More commonly, the depth x of the trench can be from about 25 percent of the thickness of the substrate to about 75 percent of the thickness of the substrate. 
       FIG. 8   c  shows a partially completed second trench  804  that is formed from the substrate&#39;s second side or surface  612 .  FIG. 8   d  shows a transverse cross section of the partially completed trench  804 . In various embodiments, the second trench can be formed by removing or ablating material through the second surface into the thickness of the substrate. In this example, sand drilling is being used to form the second trench. Sand drilling is a mechanical cutting process where target material is removed by particles such as aluminum oxide delivered from a high pressure air flow system. Sand drilling is also known as sand blasting, abrasive sand machining, and sand abrasion. The sand is removing substrate material until breakthrough occurs between the first trench and the second trench, and then additional substrate material can be removed as desired. 
     In addition to sand drilling, other exemplary embodiments can remove or ablate substrate material to form the second trench using one or more of the following: laser machining, dry etching, wet etching, and mechanical machining. Mechanical machining can include the use of various saws and drills that are commonly used to remove substrate material. 
       FIGS. 8   e - 8   f  show an embodiment where the first trench  802  has been dry etched generally at  820 , and material has been removed to form a second trench  804  generally at  822  to form a slot  604   d . This embodiment shows the finished second trench  804  having a length l 2  and a width w 2  and a depth y. The trench intercepts or otherwise joins with a portion of the first trench. The combination of the two trenches forms a slot  604   d  that extends through the thickness of the substrate and through which a fluid such as ink can flow. So for at least a portion of the substrate, the depths (x and y) of the two trenches equal the thickness t. 
     In the exemplary embodiment shown in  FIGS. 8   e - 8   f , the first trench  802  has generally planar side walls that are generally orthogonal to the first surface  610 . The second trench  804  has generally concave side walls. Other embodiments can have various other side wall configurations. 
     As shown in  FIGS. 8   e - 8   f , in this exemplary embodiment, the second trench intercepts the entire length l 1  of the first trench. Other exemplary embodiments can have less than the entirety of the length of the first trench intercepted by the second trench. Additionally, the second trench can be longer than the first trench so that it encompasses a portion of the first trench for its entire length within the second trench. 
     In the exemplary embodiment shown in  FIG. 8   f , the depth x of the first trench and depth y of the second trench  804  are approximately equal. Other exemplary embodiments can have each trench being shallower or deeper than this embodiment. 
     Although the described embodiments illustrate only removing material from the substrate, intermediate steps in some satisfactory embodiments can add material to the substrate. For example, a material can be deposited as part of the slot formation sequence. 
     The dimensions of the trenches can be modified to make a through slot of any desired length and/or width. For example, the length of the slot can be made small enough that it resembles a hole or via. 
     The process of forming a portion of the slot from each side can provide many desirable advantages. One advantage pertains to the dimensions of the slot width. For example, a greatly reduced slot width can be formed using the techniques describes above, as compared with slot widths that are formed entirely from a single side. 
     For example, in one embodiment, on a standard 675 micron thick substrate, a first trench can be dry etched through about one-half of the thickness of the substrate from the front side. The remainder of the thickness of the substrate can be removed from the backside by sand drilling. In one embodiment, the maximum width of the slot can be located on the backside surface. This can be seen in the exemplary embodiment shown in  FIG. 8   f , where the width w 2  of the second trench  804  can be about 240 microns and the width w 1  of the first trench  802  can about 80 microns. This provides a backside trench having a width that is about 300 percent of the width of the front side trench, other embodiments can have larger or smaller relationships. The dimensions described in relation to the embodiment of  FIG. 8   f , provide an aspect ratio (substrate thickness divided by slot width) of about 3. Other embodiments can have other aspect ratios ranging from about 1 to greater than or equal about 20. 
     Other exemplary embodiments can have a trench width of less than about 350 microns. Viewed another way, in some embodiments, the maximum width of the slot  604  is less than or equal to 50 percent of the thickness of the substrate. 
     Conversely, forming a slot using sand drilling alone can form a slot having about a 180 micron thin film width and a backside width of about 650 microns. Thus, the maximum slot width is approximately equal to the substrate thickness, for an aspect ratio of about 1. A slot manufactured in this manner removes a large amount of substrate material making the remaining substrate more fragile. Further, the width of the backside trench requires an undesirably large distance between adjacent slots on a multi-slot substrate or die. 
     Some of the present embodiments, by forming a significant portion of the slot from the front side, not only allow a narrower slot width than sand drilling alone, but can also form a slot of much better quality. For example, a slot that is sand drilled entirely from the backside creates stresses on the underside of the thin film layer before “breakthrough” occurs. Breakthrough is the moment when the entire thickness of a given portion of the substrate has been removed. When breakthrough occurs at the thin film side, large stress forces can weaken the substrate and additionally can cause large chips to be broken from the sides of the slot. This chipping hinders the print quality of the die. 
     When dry etching is conducted from the first side through a significant portion of the substrate, breakthrough from the backside occurs generally in the middle of the substrate where chipping is both minimized and less critical than on the thin film side/surface. Further, the substrate is less susceptible to stress induced breakage when the breakthrough occurs toward the center of the substrate&#39;s thickness. 
       FIGS. 9   a - 9   j  show another exemplary embodiment. Here, multiple dry etch processes are used from the thin film side  610  to form the first trench  802   a  before the backside trench  804   a  is formed to intercept the front side trench to define the slot  604   d . Standard dry etch techniques can be utilized as will be recognized by one of skill in the art. 
     Some exemplary embodiments deposit a masking agent on the substrate and then etch and repeat the process as desired to form a trench. For example, a masking agent such as ep24620 can be used, followed by a dry etchant such as CF 4 . 
     The embodiments of  FIGS. 9   a  and  9   b  show part of a first trench  802   a  formed from the thin film side  610  of the substrate  606 . A subsequent dry etch process forms the first part of the trench having length l 1  and depth x 1 . In the embodiments of  FIG. 9   c , a subsequent dry etch process forms the second part of the trench having the length l 2  which is less than l 1  and increases the trench depth to x 2 . Other embodiments can include multiple etching steps where each etching step covers about the same or greater width and length as the previous one. 
     The embodiments shown in  FIGS. 9   e - 9   f  show the results of a third dry etch process that creates the deepest portions of the trench. In  FIGS. 9   e - 9   f , the deepest portions of the trench are considered to define the depth x 3 . As with the second etch, this dry etch resulted in a trench portion having a length l 3  that is shorter than the one preceding (l 2 ). These multiple dry etches can create a “stair step” pattern on the walls of the trench  802   a  that can be advantageous and will be discussed in more detail below. 
     The embodiments of  FIGS. 9   g - 9   h  show a second partially formed trench  804   a  from the backside  612  of the substrate  606 . In this exemplary embodiment, the second trench  804   a  was formed by sand drilling, though other embodiments can utilize other methods. 
     The embodiments of  FIGS. 9   i - 9   j  show the completed second trench  804   a . It can be seen by comparing the length l 4  with the length l 3  that the backside trench  804   a  intercepts less than the entirety of the length of the front side trench. Such need not, however, be the case. The walls of the second trench in this embodiment are somewhat curved as can be achieved by sand drilling and other methods. Other embodiments can have trenches having different wall shapes from those shown in this embodiment. 
     As shown in this embodiment, the stair step configuration was achieved by making a shallow dry etch having a relatively large length and width (footprint), followed by subsequent dry etches of progressively smaller footprints. Other embodiments can achieve similar results through other techniques. For example, a first dry etch from a first side having a relatively small footprint can be completed to a desired final depth. This etch can then be incorporated into subsequent etches from the front side that have larger footprints but are shallower in depth. The skilled artisan will recognize other satisfactory embodiments. 
     The stair step configuration can reduce the amount of silicon removed from the substrate thus increasing die strength and decreasing manufacturing cost and time. Additionally, this configuration can allow the backside trench to be of less length than the front side trench while substantially avoiding bubble build up in the slot. 
     In some embodiments, gas bubbles can be generated in the fluid ejection process. The bubbles can accumulate in the fluid feed slot or passageways leading to the firing chambers and occlude fluid from reaching some or all of the resistors, thus causing printer failure. Bubbles tend to accumulate on extended horizontal surface instead of migrating up toward the backside surface and into the cartridge body. The stair step configuration can reduce the occurrence of bubble accumulation by reducing areas where bubbles tend to accumulate. 
     Specifically, recall that, as shown in the embodiments of  FIGS. 9   a - 9   j , the substrate is effectively upside down from the configuration in which it is commonly used. The stair step configuration shown in these embodiments can eliminate broad horizontal surfaces where bubbles tend to accumulate. Specifically, by having multiple narrow shelves, bubbles that tend to form and accumulate are allowed, during the fluid ejection process, to migrate upward into the backside trench away from the thin film side, or otherwise dissipate. The stair step configuration can be utilized on both the width and the length of the slot as shown in previous embodiment, or alternatively the stair step configuration can be on either the width or the length. For example, a common width w can be maintained in the multiple dry etches forming the first trench while the lengths l 1 , l 2 , and l 3  are made progressively shorter or longer as desired. 
     In some embodiments, cuts or slots made in the substrate through dry etching can have cleaner side edges with less chipping or variation than other slotting techniques. For example, slots made by dry etching can have sidewalls variations of less than about 5-10 microns, whereas existing sand drilling technology can create chips in excess of about 45-50 microns. This feature of this embodiment, in addition to the increased substrate strength and higher aspect ratio, can further allow slots to be placed closer together on the substrate than existing technologies. 
     The illustrated embodiments describe the first trench being constructed using dry etching followed by various other removal techniques forming the second trench. In other exemplary embodiments, the act of dry etching(s) can be performed after the other act(s) of removal of the substrate. Other exemplary embodiments also can have other intermediary steps. 
     CONCLUSION 
     The described embodiments can provide methods and systems for forming slots in a semiconductor substrate. The slots can be formed by dry etching from a first surface and removing material through the use of various techniques from the other surface. The slots can be inexpensive and quick to form. They can be made as long as desirable and have higher aspect ratios than existing technologies. The resultant substrate can have beneficial strength characteristics that can reduce die fragility and allow slots to be positioned closer together on the die. 
     Although the invention has been described in language specific to structural features and methodological steps, it is to be understood that the invention defined in the appended claims is not necessarily limited to the specific features or steps described. Rather, the specific features and steps are disclosed as preferred forms of implementing the claimed invention.