Abstract:
A light beam is used to cut a slot in a first side of substrate. An optical sensor monitors a surface of a second side of the substrate that is opposite the first side while cutting the slot. If the light beam breaks through the surface of the second side, the sensor detects the light beam.

Description:
RELATED APPLICATION 
   This is a divisional application of U.S. patent application Ser. No. 11/180,369, filed Jul. 13, 2005 now U.S. Pat. No. 7,268,315, titled “MONITORING SLOT FORMATION IN SUBSTRATES,” which application is assigned to the assignee of the present invention and the entire contents of which are incorporated herein by reference. 

   BACKGROUND 
   Fluid-ejection devices, such as ink-jet print heads, usually include a die, e.g., formed on a wafer of silicon or the like using semi-conductor processing methods, such as photolithography or the like. A die normally includes resistors or piezoelectric elements for ejecting fluid, e.g., marking fluids, medicines, drugs, fuels, adhesives, etc., from the die, and a fluid-feed slot (or channel) that delivers the fluid to the resistors or piezoelectric elements so that the fluid covers the resistors or piezoelectric elements. Electrical signals are sent to the resistors or piezoelectric elements for energizing them. An energized resistor rapidly heats the fluid that covers it, causing the fluid to vaporize and be ejected through an orifice aligned with the resistor. An energized piezoelectric element expands to force the fluid that covers it through the orifice. 
   Traditionally, the fluid feed slot has been formed with an abrasive sand blast process. To facilitate the development of smaller parts, the fluid-feed slot in the wafer is now formed using an electromagnetic beam, such as a light or laser beam, which allows much greater dimensional control. Until recently, the fluid-feed slot was formed in the wafer using a laser beam, with a hydrofluorcarbon (HFC) assist gas. However, hydrofluorcarbon (HFC) assist gases are being phased out due to environmental concerns. For some fluid-feed slot formation processes, a water-assist process has replaced HFC assist processes. Some processes involve covering components formed on the wafer prior to forming the slot to protect them during the formation of the slot. However, such coatings are typically water-soluble and cause problems for the water-assist process. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective cutaway view of a portion of an embodiment of a fluid-ejection device, according to an embodiment of the disclosure. 
       FIG. 2  is a top plan view of an embodiment of the fluid-ejection device, according to an embodiment of the disclosure. 
       FIGS. 3A-3C  are cross-sectional views of a portion of an embodiment of a fluid-ejection device during various stages of formation of a fluid feed channel, according to another embodiment of the disclosure. 
       FIG. 4  illustrates an embodiment for monitoring slot formation in a substrate, according to another embodiment of the disclosure. 
   

   DETAILED DESCRIPTION 
   In the following detailed description of the present embodiments, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments that may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice disclosed subject matter, and it is to be understood that other embodiments may be utilized and that process, electrical or mechanical changes may be made without departing from the scope of the claimed subject matter. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the claimed subject matter is defined only by the appended claims and equivalents thereof. 
     FIG. 1  is a perspective cutaway view of a portion of a fluid-ejection device  120 , such as a print head, showing components for ejecting a fluid, according to an embodiment. For one embodiment, fluid-ejection device  120  may be used as a print head, a fuel injector, an IV dispenser, and an inhalation device, such as a nebulizer, as well as to deposit drugs on a substrate, deposit color filters onto display media, deposit adhesives onto substrates, etc. 
   The components of fluid-ejection device  120  are formed on a wafer  122 , e.g., of silicon, that may include a dielectric layer  124 , such as a silicon dioxide layer. Hereafter, the term substrate  125  will be considered as including at least a portion of wafer  122  and at least a portion of dielectric layer  124 . A number of print head substrates may be formed simultaneously on a single wafer die, each having an individual fluid-ejection device. 
   Liquid droplets are ejected from chambers  126 , e.g., often called firing chambers, formed in the substrate  125 , and more specifically, formed in a barrier layer  128  that for one embodiment may be from photosensitive material that is laminated onto substrate  125  and then exposed, developed, and cured in a configuration that defines chambers  126 . 
   The primary mechanism for ejecting a liquid droplet from a chamber  126  is an ejection element  130 , such as a piezoelectric patch or a thin-film resistor. The ejection element  130  is formed on substrate  125 . For one embodiment, ejection element  130  is covered with suitable passivation and other layers, as is known in art, and connected to conductive layers that transmit current pulses, e.g., for heating the resistors or causing the piezoelectric patches to expand. 
   The liquid droplets are ejected through orifices  132  (one of which is shown cut away in  FIG. 1 ) formed in an orifice plate  134  that covers most of fluid-ejection device  120 . The orifice plate  134  may be made from a laser-ablated polyimide material. The orifice plate  134  is bonded to the barrier layer  128  and aligned so that each chamber  126  is continuous with one of the orifices  132  from which the liquid droplets are ejected. 
   Chambers  126  are refilled with liquid after each droplet is ejected. In this regard, each chamber is continuous with a channel  136  that is formed in the barrier layer  128 . The channels  136  extend toward an elongated feed channel (or slot)  140  ( FIG. 2 ) that is formed through substrate  125 . Feed channel  140  may be centered between rows of firing chambers  126  that are located on opposite long sides of the feed channel  140 , as shown in  FIG. 2 , according to another embodiment. For one embodiment, the feed channel  140  is made after the fluid-ejecting components (except for the orifice plate  134 ) are formed on substrate  125 . 
   The just mentioned components (barrier layer  128 , resistors  130 , etc.) for ejecting the liquid drops are mounted to a top (or upper surface)  142  of the substrate  125 . For one embodiment, the bottom of the fluid-ejection device  120  may be mounted to a fluid reservoir portion, e.g., of an ink cartridge, or feed channel  140  may be coupled to a separate reservoir, such as an off-axis ink reservoir, e.g., by a conduit, at the bottom so that the feed channel  140  is in fluid communication with openings to the reservoir. Thus, refill liquid flows through the feed channel  140  from the bottom toward the top  142  of the substrate  125 . The liquid then flows across the top  142  (that is, to and through the channels  136  and beneath the orifice plate  134 ) to fill the chambers  126 . 
     FIGS. 3A-3C  are cross-sectional views of a portion of substrate  125  ( FIGS. 1 and 2 ) during various stages of formation of feed channel  140 , according to another embodiment. The above-described components, such as the barrier layer, ejection elements, etc., are shown for simplicity as a single layer  310 . For one embodiment, a protective layer  320  that may be water-soluble (such as a spun and baked ‘universal coating’, based on Isopropanol, Polyvinyl alcohol and de-ionized water mixtures) may cover these components. At least a portion of feed channel  140  is formed in substrate  125  using a light beam  330 , such as a laser beam, e.g., of ultra-violet light, emitted from a light source  340 , starting at a bottom  144 , in  FIG. 3B . As used herein the term “light” refers to any applicable wavelength of electromagnetic energy. For one embodiment, a water-containing jet  350 , e.g., a jet of misted (or aerosolized) water, is directed into feed channel  140 , e.g., from an air/water source  355 , as light beam  330  removes substrate material. For another embodiment, water-containing jet  350  acts to remove debris from feed channel  140 . For another embodiment the light beam  330  is scanned over the surface of substrate  125  using a two mirror galvanometer scan head allowing complex 3D features, such as fluid feed slots, to be formed by removing material with light beam  330  in a preprogrammed spatial pattern (as described in WO03053627). 
   For one embodiment, a controller  360  is connected to light source  340  and air/water source  355 . For another embodiment, controller  360  includes a processor  362  for processing computer/processor-readable instructions. These computer-readable instructions, for performing the methods described herein, are stored on a computer-usable media  364 , and may be in the form of software, firmware, or hardware. As a whole, these computer-readable instructions are often termed a device driver. In a hardware solution, the instructions are hard coded as part of a processor, e.g., an application-specific integrated circuit (ASIC) chip. In a software or firmware solution, the instructions are stored for retrieval by the processor  362 . Some additional examples of computer-usable media include static or dynamic random access memory (SRAM or DRAM), read-only memory (ROM), electrically-erasable programmable ROM (EEPROM or flash memory), magnetic media and optical media, whether permanent or removable. Most consumer-oriented computer applications are software solutions provided to the user on some removable computer-usable media, such as a compact disc read-only memory (CD-ROM). 
   For one embodiment, controller  360  is connected to an optical sensor  370 , such as a photo diode having a nanosecond or faster response time at the wavelength emitted by light source  340 , such as silicon PIN detector model number ET-2030 for wavelengths between 300 and 1100 nm that is available from Electro-Optics Technology, Inc. (Traverse City, Mich., USA) for sensing whether light beam  330  penetrates upper surface  142  forming a “pinhole”  375  in upper surface  142 . If light beam  330  penetrates upper surface  142  and pinhole  375  is sufficiently large, water from water-containing jet  350  can pass through pinhole  375  and reach protective layer  320 , causing protective layer  320  to dissolve, leaving layer  310  unprotected. Portions of the dissolved protective layer  320  may also mix with substrate debris resulting in reduced solubility of the protective layer. Following cleaning, residual debris restricts or completely blocks the various channels  136  ( FIGS. 1 and 2 ). Note that if pinhole  375  is small enough, surface tension and/or viscous effects of the water may act to prevent the water from passing through pinhole  375 . 
   At substantially the same time as pinhole  375  is formed, a portion of light beam  330  passes through pinhole  375 , passes through an optional filter  372 , e.g., an ultra-violet filter, and is sensed by optical sensor  370 . For one embodiment, optional filter  372  may be selected to limit the amount of laser light reaching the optical sensor  370  to reduce the likelihood of signal saturation or damage to sensor  370 . For another embodiment, may be chosen to selectively block any extraneous light generated by the laser removal process (e.g., a narrow band-pass filter centered on the wavelength of light source  340 ), such as laser generated plasma emissions. Optical sensor  370  converts the sensed light beam into a signal indicative of the light beam and transmits the signal to controller  360 . For one embodiment, controller  360  keeps track of the number of pinholes, and compares the number to a predetermined (or acceptable) number of pinholes. If the number of pinholes exceeds the predetermined number, an indication of too many pinholes is given, e.g., in the form of an audible and/or visual alarm, and/or light source  340  and water-containing jet  350  are stopped. 
   In some embodiments, optical sensor  370  is mounted off a central axis of light beam  330 , e.g., off a central axis of a likely location of a pinhole  375 , so that it senses the pinhole  375  at an angle relative to light beam  330 , as shown in  FIG. 4 . Note that for one embodiment, a lens  410  may be interposed between optical sensor  370  and filter  372 . For this configuration, optical sensor  370  senses scattered light and/or plasma light generated by light beam  330  to enable detection of pinholes  375 . More specifically, light beam  330  heats a portion of substrate  125 , causing some of the heated portion to vaporize. The vaporized substrate material is heated further by light beam  330  that generates a plasma  420  that radiates broadband radiation. When light beam  330  just breaks through, the pressure of the vapor and plasma is sufficient for it to blow out of a pinhole  375 , causing light beam  330  and plasma  420  to issue from pinhole  375  that can be detected by the off-axis configuration of optical sensor  370 . The plasma and any silicon debris may also scatter the laser light that can be detected by the off-axis configuration of optical sensor  370 . 
   For another embodiment, the amount of light, and thus a size of the pinhole, is related to an amplitude, e.g., voltage, of the signal. For some embodiments, the amplitude is compared to a predetermined (or an acceptable) amplitude corresponding to an acceptable pinhole size. If the amplitude exceeds the predetermined amplitude, an indication that the pinhole is too large is given, e.g., in the form of an audible and/or visual alarm, and/or light source  340  and water-containing jet  350  are stopped. For some embodiments, the predetermined number of pinholes depends on the size of the pinholes. For these embodiments, a collective size of the pinholes is determined by summing the size of each pinhole over the number of pinholes. The collective size may then be compared to a predetermined collective pinhole size. If the collective size exceeds the predetermined collective size, an indication of this is given, e.g., in the form of an audible and/or visual alarm, and/or light source  340  and water-containing jet  350  are stopped. For one embodiment, forming feed channel  140  with light beam  330  and water-containing jet  350  proceeds until a pinhole is sensed, thereby establishing a depth limit for feed channel  140  for which the water-containing jet  350  can be used. 
   In a further embodiment, optical sensor  370  may include a camera, e.g., an analog or digital camera, with a video card and a processor for converting and monitoring the output of individual video lines of the analog camera or individual pixels of the digital camera. For one embodiment, controller  360  may process signals from the camera. For another embodiment, a field of view of the camera can be adjusted by a correct choice of camera lens so that only the area being scanned directly with light beam  330  is monitored, thereby increasing the sensitivity. 
   After feed channel  140  reaches a predetermined depth, such as when a pinhole is sensed, water-containing jet  350  is turned off, any remaining water is removed from feed channel  140 , and, as shown in  FIG. 3C , an air jet  380  is directed into feed channel  140 , e.g., from air/water source  355 . Air jet  380  is then used in conjunction with light beam  330  to finish feed channel  140 , i.e., so that feed channel  140  passes through upper surface  142  at a desired size, as shown in  FIG. 3C  for an embodiment. After finishing feed channel  140 , protective layer  320  is removed, e.g., using commercial wafer cleaning equipment, such as ONTRAK model DSS-200 Post CMP Wafer Scrubber System available from Axus Technology, Chandler, Ariz., USA. 
   CONCLUSION 
   Although specific embodiments have been illustrated and described herein it is manifestly intended that the scope of the claimed subject matter be limited only by the following claims and equivalents thereof.