Patent Publication Number: US-2007105382-A1

Title: Fluid ejection device and method of fabricating the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This application is a division of U.S. patent application Ser. No. 10/980,958, filed Nov. 4, 2004. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a semiconductor device, and more specifically to a fluid ejection device and a method of fabricating the same.  
      2. Description of the Related Art  
      Strong basic solutions, such as TMAH, KOH, or NaOH, are commonly used as etching solutions in silicon fabrication processes. Such solutions offer different etching performance for various monosilicon crystal planes. Although etching performance for various crystal planes may have slight distinctions due to different kinds or concentration of etching solution, or different etching temperatures, the etching rates for various crystal planes is approximately (111)&lt;(110)&lt;(100), specifically, the etching rate for crystal plane (111) is far slower than for others.  
       FIG. 1  and  FIG. 2  illustrate the etching performance of a strong basic solution for various crystal planes. Referring to  FIG. 1 , the crystal plane (100) is etched to form an anisotropic etching track with an included angle of 54.7° in substrate  10 . In  FIG. 2 , which shows the etching result of the crystal plane (111), a vertically anisotropic etching track is formed in substrate  10 .  
      Therefore, a manifold with a back opening larger than a front opening is formed in the chip (100) while etching the back thereof is performed, for example, a back opening width of a manifold with a front opening width of about 200 μm is enlarged to about 1100˜1200 μm during etching the back of the chip. Thus, the manifold formed in chip (100) occupies the majority of a wafer, and substantially reduces the available area thereon.  
      Additionally, during assemble, a chip must provide sufficient space for binding with a cartridge. Generally, the width of the binding region at the left and right sides of a chip is about 1200 μm respectively. Thus, a chip should provide a bottom region width of at least 3500˜3600 μm for fabricating a fluid ejection device, thereby reducing availability in the bottom area thereon.  
      Currently, the original substrate (100) is replaced by a substrate (111) to reduce the back opening size of a manifold. Nevertheless, although the back opening width thereof can be reduced due to specific etching performance, the manifold shape may slant to result in an unexpected chamber shape, deteriorating the dispersion effect of the device.  
      Referring to  FIG. 3 , a conventional fluid ejection device comprises a silicon substrate  10 , a manifold  20  used to transport fluid, chambers  30  formed in both sides of the manifold  20  to store fluid, and a plurality of nozzles  40  installed on the device surface to ejection fluid.  
      According to the above device structure, the back opening is larger than the front opening of the manifold, thus the back opening occupies the majority of the wafer, and substantially reduces the available area thereon.  
      Additionally, a conventional fabrication method for a fluid ejection device is disclosed in the following description, and illustrated in  FIGS. 4   a  to  4   b . Referring to  FIG. 4   a , a substrate  10 , such as a silicon substrate with crystal orientation (100) is provided. A patterned sacrificial layer  20  is formed on the substrate  10 . The sacrificial layer  20  is composed of BPSG, PSG, or silicon oxide, preferably PSG. Subsequently, a patterned structural layer  30  is formed on the substrate  10  to cover the patterned sacrificial layer  20 . The structural layer  30  includes silicon oxide nitride formed by chemical vapor deposition (CVD).  
      Next, a patterned resist layer  40  is formed on the structural layer  30  as an actuator, such as a heater. The resist layer  40  comprises HfB 2 , TaAl, TaN, or TiN. A patterned isolation layer  50  is then formed to cover the substrate  10  and the structural layer  30 , and a heater contact  45  is formed thereon. Subsequently, a patterned conductive layer  60  is formed on the structural layer  30  to fill the heater contact  45  to form a signal transmission line  62 . Finally, a protective layer  70  is formed on the isolation layer  50  and the conductive layer  60 , exposing the conductive layer  60  to form a signal transmission line contact  75 , thereby facilitating the subsequent packaging process.  
      Subsequently, referring to  FIG. 4   b , the back of the substrate  10  is etched by wet etching using KOH as an etching solution to form a manifold  80 , and exposes the sacrificial layer  20 . The sacrificial layer  20  is then etched by HF to form a chamber  90 . Finally, the protective layer  70 , the isolation layer  50 , and the structural layer  30  are then etched in order to form a nozzle  95  connecting the chamber  90 .  
      The back opening is larger than the front opening of the manifold  80  due to the specific crystal orientation (100) of the substrate  10 , and thereby occupies excessive bottom area on the wafer.  
     SUMMARY OF THE INVENTION  
      In order to solve the conventional problems, an object of the invention is to provide a fluid ejection device to effectively reduce the size of a back opening of a manifold, and control a chamber shape by providing a double substrate layer.  
      To achieve the above objects, the invention provides a fluid ejection device including a first substrate having a first crystal orientation, a second substrate having a second crystal orientation, bound to the first substrate, wherein the first crystal orientation is different from the second crystal orientation, a manifold through the first and second substrates, a chamber formed in the second substrate, connected with the manifold, and a plurality of nozzles connecting the chamber.  
      Based on the device structure of the invention, the substrate (111) is first etched to form a vertical etching track therein, as it will reduce the back opening width of the manifold. The substrate (100) is then etched to form another etching track therein, controlling the shape of the subsequently formed chamber.  
      Another object of the invention is to provide a method of fabricating the fluid ejection device, including the following steps. A first substrate having a first crystal orientation is provided. A second substrate having a second crystal orientation is provided to bind to the first substrate, wherein the first crystal orientation is different from the second crystal orientation. Subsequently, a patterned sacrificial layer is formed on the second substrate, as a predetermined region where at least one chamber is subsequently formed.  
      Next, a patterned structural layer is formed on the second substrate to cover the patterned sacrificial layer. A manifold through the first and second substrates is then formed to expose the patterned sacrificial layer. Subsequently, the sacrificial layer is removed to form the chamber. The chamber is continuously etched to enlarge the volume thereof so as to occupy a portion of the second substrate. Finally, the structural layer is etched to form at least one nozzle connecting the chamber.  
      A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:  
      FIGS.  1 ˜ 2  are cross sections illustrating etching performance for various crystal planes.  
      FIGS.  3  is a cross section of a conventional fluid ejection device.  
       FIGS. 4   a ˜ 4   b  are cross sections illustrating fabrication of a conventional fluid ejection device.  
       FIGS. 5   a ˜ 5   c  are cross sections illustrating the method of fabricating a fluid ejection device in an embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       FIGS. 5   a ˜ 5   c  illustrate the method of fabricating the fluid ejection device according to the invention.  
      In  FIG. 5   a , in which the initial step of the invention is illustrated, a first substrate  500  and a second substrate  510  are provided, wherein the first substrate  500  is a silicon substrate with crystal orientation (111) and the second substrate  510  is a silicon substrate with crystal orientation (100). The thickness ratio of the first substrate  500  and the second substrate  510  is about 10:1, wherein the thickness of the first substrate  500  is about 500˜675 μm, and the thickness of the second substrate  510  is about 30˜50 μm.  
      The second substrate  510  binds to the first substrate  500  by direct binding or medium binding, wherein the direct binding temperature is about above 1000° C., and the medium is oxide.  
      Subsequently, referring to  FIG. 5   b , a patterned sacrificial layer  520  is formed on a first plane  5001  of the second substrate  510 . The sacrificial layer  520  is composed of BPSG, PSG, or silicon oxide, preferably PSG. The thickness of the sacrificial layer  520  is about 5000˜20000 Å. The sacrificial layer  520  is a predetermined region where at least one chamber is subsequently formed.  
      Next, a patterned structural layer  530  is formed on the second substrate  510  to cover the patterned sacrificial layer  520 . The structural layer  530  may include silicon oxide nitride formed by CVD. The thickness of the structural layer  530  is about 0.5˜2 μm. Additionally, the structural layer  530  comprises a low-stress material, and the stress thereof is about 50˜200 MPa.  
      Subsequently, a patterned resist layer  540  is formed on the structural layer  530 , as a fluid ejection actuator, such as a heater, thereby driving fluid out of subsequently formed nozzles. The resist layer  540  comprises HfB 2 , TaAl, TaN, or TiN, and is preferably TaAl.  
      A patterned isolation layer  550  is then formed to cover the structural layer  530 , and a heater contact  555  is formed. Subsequently, a patterned conductive layer  560  is formed on the isolation layer  550  to fill the heater contact  555  to form a signal transmission line. Finally, a protective layer  570  is formed on the second substrate  510  to cover the isolation layer  550  and the conductive layer  560 , exposing the conductive layer  560  to form a signal transmission line contact  580 , thereby facilitating the subsequent packaging process.  
      Subsequently, referring to  FIG. 5   c , a series of etching steps are performed. First, a second plane  5002  of the first substrate  500  is etched to form a portion of the manifold  590  by anisotropic wet etching using TMAH, KOH, or NaOH as an etching solution.  
      During the above etching, the substrate  500  with crystal orientation (111) is etched to form a vertical etching track therein, thus reducing the back opening width of the manifold, and significantly increasing the available area on the first substrate  500 .  
      Next, the second substrate  510  with crystal orientation (100) is etched to achieve the manifold fabrication, and exposes the sacrificial layer  520 . The shape of subsequently formed chambers can be controlled by the manifold structure through the first and second substrates.  
      The narrow opening width of the manifold  590  is about 160˜200 μm. Compared to the related art wherein the back opening width is about 1100˜1200 μm, the occupied area on the chip bottom of the present invention is significantly reduced. Additionally, the manifold  590  connects to a fluid storage tank.  
      Next, the sacrificial layer  520  is etched to form chambers  600  by HF, and subsequently etched by a basic etching solution, such as KOH or NaOH, to enlarge the volume thereof, thus occupying a portion of the second substrate  510 .  
      Finally, the protective layer  570 , the isolation layer  550 , and the structural layer  530  are etched in order by laser or reactive ion etching (RIE) to form nozzles  610  connecting to the chambers  600  which are connected to the manifold  590 .  
      Additionally, if the resolution of a single row of chambers is 300 dpi, resolution can be increased to 600˜1200 dpi by staggering each row of chambers in the embodiment.  
      In conclusion, the double substrate layer structure of the present invention can reduce the occupied area on a chip bottom, and provide preferable chamber shape to stably eject fluid.  
      While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.