Patent Publication Number: US-2007117367-A1

Title: Fluid injection apparatus and fabrication method thereof

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a fluid injection apparatus and fabrication methods thereof, and in particular relates to a micro fluid injection apparatus and fabrication methods thereof.  
      2. Description of the Related Art  
      Micro fluid injection apparatuses have been widely used in digital apparatuses, such as inkjet printers or others. With development of micro system engineering, micro fluid injection apparatuses are further used in other applications, such as fuel injection systems, cell sorting, drug delivery systems, print lithography or micro jet propulsion systems.  
      FIGS.  1 A˜ 1 C show a conventional monolithic fabrication of a fluid injection apparatus  100 . Referring to  FIG. 1A , a substrate  102  is provided, and a patterned sacrificial layer  104  is formed on a first side  101  thereof. Next, a structure layer  106  is formed to cover the sacrificial layer  104  and the first side  101  of the substrate  102 . A mask layer  108  is formed on a second side  103  of the substrate  102 . Referring to  FIG. 1B , the substrate  102  is etched using the patterned mask layer  108  as a mask to form a manifold  110 , in which the sacrificial layer  104  is exposed. Thereafter, the sacrificial layer  104  is etched through the manifold  110  to form a chamber  112 . Due to the characteristics of dielectric material, the sacrificial layer  104  formed of dielectric materials is unable to achieve sufficient thickness. Consequently, as shown in  FIG. 1C , a further silicon etching process step is required to enlarge the chamber  112 ′.  
      In addition, the sacrificial layer  104  formed of dielectric material is typically formed by chemical vapor deposition, which as a higher cost, and further requires an additional silicon etching process step to enlarge the chamber  112 ′ which also increases fabrication cost and duration. Further, undercutting may occur when the chamber is enlarged by etching the silicon substrate  102 . Thus, the size of the chamber  112 ′ is not easily controlled.  
     BRIEF SUMMARY OF INVENTION  
      A detailed description is given in the following embodiments with reference to the accompanying drawings. These and other problems are generally solved or circumvented, and technical advantages are generally achieved, by preferred illustrative embodiments of the present invention, which provide a fluid injection apparatus.  
      The invention provides a fluid injection apparatus. A chamber wall is disposed overlying the substrate to define an area. A nozzle plate comprising a nozzle is disposed overlying the chamber wall to form a chamber in the area, wherein the chamber wall and the nozzle plate are integrated into a structure layer. A manifold is disposed in the substrate, communicated with the chamber.  
      The invention further provides a method for forming a fluid injection apparatus. A patterned sacrificial layer is formed on the substrate. An electroplate seed layer is formed at least covering the patterned sacrificial layer. A structure layer is electroplated on the electroplate seed layer. The structure layer is patterned to form a nozzle. A portion of the electroplate seed layer within the nozzle is removed. The sacrificial layer is removed to form a chamber. A side of the substrate opposite to the side where the structure layer is disposed is patterned to form a manifold, communicated with the chamber.  
      The invention provides a method for forming a fluid injection apparatus. A polymer sacrificial layer is formed on a portion of the substrate. An isolation layer is formed at least covering the polymer sacrificial layer. A polymer structure layer is formed at least covering the isolation layer. The polymer structure layer is patterned to form a nozzle. A portion of the isolation layer within the nozzle is removed. The polymer sacrificial layer is removed to form a chamber. A side of the substrate opposite to the side is patterned where the structure layer is disposed to form a manifold, communicated with the chamber. 
    
    
     BRIEF DESCRIPTION OF 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:  
       FIG. 1A ˜ 1 C shows a conventional monolithic fabrication of a fluid injection apparatus.  
       FIG. 2A ˜ FIG. 2F  show intermediate cross sections of a fluid injection apparatus of an embodiment of the invention.  
       FIG. 3A ˜ FIG. 3F  show intermediate cross sections of a fluid injection apparatus of an embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF INVENTION  
      The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. Embodiments of the invention, which provides a fluid injection apparatus, will be described in greater detail by referring to the drawings that accompany the invention. It is noted that in the accompanying drawings, like and/or corresponding elements are referred to by like reference numerals. The invention is not limited to any particular fluid driving device or driving method, which is not particularly mentioned in the specification. Any fluid driving device or driving method, such as thermal bubble driven or piezoelectric actuator can be applied to the invention.  
       FIG. 2A ˜ FIG. 2F  show intermediate cross sections of a fluid injection apparatus of an embodiment of the invention. Referring to  FIG. 2A , a substrate  200 , such as silicon substrate or glass substrate, is provided. Preferably, the substrate  200  is a silicon substrate. A gate  202 , for example comprising polysilicon or metal, is formed on the substrate  200 . Next, a first dielectric layer  204 , such as silicon oxide, silicon nitride or silicon oxynitride, is formed to cover the gate  202  and a portion of the substrate  200 . A first conductive layer  206 , such as Al or Cu, is formed on the first dielectric layer  204  and a portion of the substrate  200 , wherein portions of the first conductive layer  206  on opposite sides of the gate  202  acts a source  207  and a drain  209 . The gate  202  and related elements thereof constitute a fluid control device  213  of an embodiment of the invention.  
      Thereafter, a second dielectric layer  208 , such as silicon oxide, silicon nitride or silicon oxynitride, is formed on a portion of the first conductive layer  206 , the first dielectric layer  204  and the substrate  200 . It is noticed that the second dielectric layer  208  exposes a portion of the first conductive layer  206  and the drain  209  to form a via. A electric resistance layer  216  is formed to cover a portion of the first conductive layer  206  and the source  207 . Next, a second conductive layer  218 , such as Al or Cu, is formed on the electric resistance layer  216 , wherein the second conductive layer  218  directly contacts the electric resistance layer  216 . The second conductive layer  218  and the electric resistance layer  216  are patterned by, for example lithography and etching. Next, a portion of the second conductive layer  218  overlying the heating device area is etched to expose a portion of the electric resistance layer  216 . Thus, the electric resistance layer  216  and the first conductive layer  206  thereunder constitute a heating device  215 . A passivation layer  220 , such as SiC or SiN, is formed on the second conductive layer  218  and the electric resistance layer  216 , and a metal protective layer  222 , such as Ta, is formed on a portion of the electric resistance layer  216  overlying the heating device  215 . Thereafter, the passivation layer  222  is patterned to form a contact pad  217 .  
      Next, a sacrificial layer  224  is formed on the first side  201  of the substrate  200  by, for example deposition or coating, and then patterned by lithography and etching. In an embodiment of the invention, the fluid controlling device  213  is disposed on the first side. In this embodiment, the sacrificial layer  224  can comprise dielectric materials, such as an oxide, or a macromolecular compound, such as a resist. In a preferred embodiment of the invention, the thickness of the sacrificial layer  224  can be about 5 μm˜100 μm.  
      Referring to  FIG. 2B , a electroplate seed layer  226  is formed on the passivation layer  220  and the sacrificial layer  224  by, for example plasma vapor deposition. Preferably, the electroplate seed layer  226  comprises a Ti layer and an Au layer on the Ti layer. The Ti layer, preferably has a thickness of less than about 1000 Å, is for increasing adhesion. The Au layer, preferably has a thickness of about 1000 Å˜8000 Å, is for electroplate seeding. Alternatively, in another embodiment of the invention, the electroplate seed layer  226  comprises a Ti layer and an Ni layer on the Ti layer.  
      Referring to  FIG. 2C , a patterned resist layer  228  is formed on a portion of the electroplate seed layer  226  predetermined to form a nozzle, and the pad  217 .  
      Next, a structure layer  230 , for example comprising Au, is formed on the electroplate seed layer  226  by, for example an electroplating process, wherein the portion of the electroplate seed layer  226  covered by the resist layer  228  is not reacted in the electroplating solution during the electroplating process. Thus, the structure layer  230  is formed on a portion of the electroplate seed layer  226  uncovered by the resist layer  228 . The structure layer  230  can have a thickness of about 5 μm˜100 μm. Referring to  FIG. 2D , the resist layer  228  is removed by, for example development, stripper or plasma ashing. Subsequent to removal of the resist layer  228 , a nozzle  232  in the structure layer  226  is formed. Next, a portion of the electroplate seed layer  226  within the nozzle  232  is removed by, for example etching. It is noticed that formation of the nozzle  232  is not limited to the described method. The nozzle  232  can also be form by patterning the structure layer  230  with lithography and etching.  
      Referring to  FIG. 2E , the second side  203  of the substrate  200  is patterned by, for example, lithography and etching, or sand blasting to form a manifold  234 , wherein the sacrificial layer  224  is exposed. Next, the sacrificial layer  224  is removed through the manifold  234  by, for example etching, to form a chamber  236  connected to the manifold  234 . When the sacrificial layer  234  is formed of macromolecular compound, it can be removed by plasma ashing or stripper. The invention, however, is not limited thereto. The sacrificial layer  234  can be removed through the nozzle  232 . Next, the manifold  234  is formed in the substrate  200 . It is noticed that the structure layer  230  comprises a sidewall portion  230   a  and a nozzle plate portion  230   b  on the sidewall portion  230   a . In the preferred embodiment of the invention, since the structure layer  230  is formed by electroplating, the sidewall portion  230   a  and a nozzle plate portion  230   b  are formed as a whole. The entire structure layer  230  is formed as a whole. The chamber wall  230   a  and the nozzle plate  230   b  are integrated into a structure layer.  
      Next, the electroplate seed layer  226  in the chamber  236  and neighboring the structure layer  230  is removed by isotropic etching, such as wet etching. Referring to  FIG. 2F , a structure protective layer  238 , such as Au with thickness of about 3000 Å˜8000 Å thick, is formed to cover the structure layer  230 . Preferably, the structure protective layer  238  is formed by electroless plating, in which the structure protective layer  238  can selectively cover the structure layer  230 . In this embodiment of the invention, since the structure layer  230 , comprising the sidewalls and the nozzle plate, is formed as a whole, the structure layer could be more rigid. In addition, due to formation of the nozzle  232  by a monolithic process, a distance between the nozzle  232  and the heater  215  could be precisely controlled.  
       FIG. 3A ˜ FIG. 3F  show intermediate cross sections of a fluid injection apparatus of an embodiment of the invention. Referring to  FIG. 3A , a substrate  300 , such as silicon substrate or glass substrate, is provided. Preferably, the substrate  300  is a silicon substrate. A gate  202 , for example comprising polysilicon or metal, is formed on the substrate  300 . Next, a first dielectric layer  204 , such as silicon oxide, silicon nitride or silicon oxynitride, is formed to cover the gate  202  and a portion of the substrate  300 . A first conductive layer  206 , such as Al or Cu, is formed on the first dielectric layer  204  and a portion of the substrate  300 , wherein portions of the first conductive layer  206  on opposite sides of the gate  202  acts a source  207  and a drain  209 . The gate  202  and related elements thereof constitute a fluid control device  213  of an embodiment of the invention.  
      Thereafter, a second dielectric layer  208 , such as silicon oxide, silicon nitride or silicon oxynitride, is formed on a portion of the first conductive layer  206 , the first dielectric layer  204  and the substrate  300 . It is noticed that the second dielectric layer  208  exposes a portion of the first conductive layer  206  and the drain  209  to form a via. An electric resistance layer  216  is formed to cover a portion of the first conductive layer  206  and the source  207 . Next, a second conductive layer  218 , such as Al or Cu, is formed on the electric resistance layer  216 , wherein the second conductive layer  218  directly contacts the electric resistance layer  216 . The second conductive layer  218  and the electric resistance layer  216  are patterned by, for example lithography and etching. Next, a portion of the second conductive layer  218  overlying the heating device area is etched to expose a portion of the electric resistance layer  216 . Thus, the electric resistance layer  216  and the first conductive layer  206  thereunder constitute a heating device  215 . A passivation layer  220 , such as SiC or SiN, is formed on the second conductive layer  218  and the electric resistance layer  216 . A metal protective layer  222 , such as Ta, is formed on a portion of the electric resistance layer  216  overlying the heating device  215 . Thereafter, the passivation layer  222  is patterned to form a contact pad  217 .  
      Next, a polymer sacrificial layer  302  is formed on the first side  301  of the substrate  300  by, for example deposition or coating, and then patterned by lithography and etching. In an embodiment of the invention, the fluid controlling device  213  is disposed on the first side  301  of the substrate. The polymer sacrificial layer  302  can comprise light sensitive materials, such as photoresist, or non light sensitive materials. Thickness of the polymer sacrificial layer  302  can be about 5 μm˜100 μm. Preferably, the thickness of the polymer sacrificial layer  302  is more than about 10 μm, thus, a chamber defined by the polymer sacrificial layer  302  has sufficient volume.  
      Referring to  FIG. 3B , an isolation layer  304  is formed on the passivation layer  220  and the polymer sacrificial layer  302  by, for example plasma vapor deposition. The isolation layer  304  can be macromolecular compound or metal. Preferably, the isolation layer  304  is Ti and more preferably is about 1500 Å˜2500 Å thick. In this embodiment, the isolation layer  304  is for preventing the polymer sacrificial layer  304  from reaction with a polymer structure layer formed in following steps.  
      Next, referring to  FIG. 3C , a polymer structure layer  306  is formed to cover the isolation layer  304  by, for example coating, and lithography and etching thereafter, and the polymer structure layer are then patterned to form a nozzle  308 . The polymer structure layer  306  can comprise light sensitive materials, such as photoresist, or non light sensitive materials. Referring to  FIG. 3D , a portion of the isolation layer  304  within the nozzle  308  is removed through the nozzle  308 .  
      In another embodiment of the invention, the polymer sacrificial layer  302  and the polymer structure layer  306  are formed of different high macromolecular materials. The polymer sacrificial layer  302  and the polymer structure layer  306  can contact directly without the isolation layer  304  therebetween when suitable materials are chosen for the polymer sacrificial layer  302  and the polymer structure layer  306  to not react with each other.  
      Referring to  FIG. 3E , the second side  303  of the substrate  300  is patterned by, for example lithography and etching, or sand blasting to form a manifold  310 , wherein the polymer sacrificial layer  302  is exposed. Next, the polymer sacrificial layer  302  is removed through the manifold  310  by, for example etching, to form a chamber  312  connected to the manifold  310 . In this embodiment of the invention, the polymer sacrificial layer  302  can be removed by plasma ashing or stripper. The invention, however, is not limited thereto. The polymer sacrificial layer  302  can also be removed through the nozzle  308 . Next, the manifold  310  is formed in the substrate  300 . It is noticed that the isolation layer  304  can be used as an etching stop when the polymer sacrificial layer  302  is etched. Due to the difference in etching selectivity between the polymer sacrificial layer  302  and the isolation layer  304 , etching of the polymer sacrificial layer  302  can be stopped at the isolation layer  304 , thus, the polymer sacrificial layer  302  should not be over etched. In addition, since the polymer sacrificial layer  302  is a macromolecular compound, it can be removed by solvent. Thus, process steps for forming the fluid injection apparatus could be simpler, and cost could be reduced. Next, the isolation layer  304  in the chamber  312  and neighboring the structure layer  306  is removed by isotropic etching, such as wet etching.  
      Referring to  FIG. 3F , a structure protective layer  314 , such as Ni with a thickness of about 3000˜8000 Å, is formed to cover the structure layer  306 . In this embodiment of the invention, due to the characteristics of the polymer sacrificial layer  302 , the polymer sacrificial layer  302  can achieve a thickness of more than about 10 μm. Thus, the chamber  312  can have sufficient volume, and enlargement of the chamber  312  could be eliminated. Consequently, cost and process duration is reduced. In addition, undercutting generated during chamber enlargement could be eliminated, and chamber size can be controlled more precisely.  
      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.