Patent Publication Number: US-2005127028-A1

Title: Method for fabricating an enlarged fluid channel

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The invention relates to a method for manufacturing a fluid injector; in particular, a method for manufacturing a fluid injector using multiple steps of removing and etching a sacrificial layer to enlarge the fluid channel.  
      2. Description of the Related Art  
      Typically, fluid injectors are applied in an ink-jet printer, a fuel injector, and other devices. Among ink-jet printers presently known and used, injection by thermally driven bubbles has been most successful due to its simplicity and relatively low cost.  
       FIG. 1  is a conventional monolithic fluid injector  1  as disclosed in U.S. Pat. No. 6,102,530. A structural layer  12  is formed on a silicon substrate  10 . A fluid chamber  14  is formed between the silicon substrate  10  and the structural layer  12  to receive fluid  26 . A first heater  20  and a second heater  22  are disposed on the structural layer  12 . The first heater  20  generates a first bubble  30  in the chamber  14 , and the second heater  22  generates a second bubble  32  in the chamber  14  to eject the fluid  26  from the chamber  14 .  
      The conventional method for fabricating a monolithic fluid injector  1  comprises providing a silicon substrate  10 . A patterned sacrificial layer is formed on the first surface of the substrate  10 . A patterned structural layer  12  is formed on the surface of the substrate  10  and covers the patterned sacrificial layer. A fluid actuator is formed on the structural layer. A passivation layer is formed on the structural layer covering the fluid actuator. A fluid channel is formed in the second surface of the substrate, opposing the first surface, and exposing the sacrificial layer. The sacrificial layer is removed to form a fluid chamber, and the fluid chamber is enlarged by anisotropic etching of the silicon substrate. Subsequently, a through hole is formed by sequentially etching the passivation layer and the structural layer, wherein the through hole is communicated with the fluid channel.  
      Additionally, the conventional monolithic fluid injector  1  typically employs a &lt;100&gt; oriented single crystal silicon wafer to serve as a substrate. During anisotropic etching, a pyramid structure is formed along the (111) sidewall at a 54.7° angle with the substrate surface. The aforementioned process is provided to form a fluid channel of a monolithic fluid injector. Due to the nature of silicon anisotropic etching, however, both the entry-end and exit-end of the fluid channel are enlarged when the fluid chamber is enlarged. Hence, if the entry-end of the fluid channel is enlarged, the nozzle density may be reduced and the strength of the fluid injector may be weakened.  
     SUMMARY OF THE INVENTION  
      An object of the present invention is to provide multiple steps of removing and anisotropically etching the sacrificial layer to enlarge the exit-end of the fluid channel instead of enlarging the entry-end of the fluid channel.  
      Accordingly, the invention provides a method for fabricating an enlarged fluid channel. The method comprises providing a substrate having a first surface and a second surface, forming a patterned sacrificial layer on the first surface of the substrate, forming a patterned structural layer on the first surface of the substrate covering the patterned sacrificial layer, forming a fluid channel in the second surface of the substrate, opposite to the first surface, and exposing the sacrificial layer, removing a portion of the sacrificial layer to form a first chamber, and removing the remaining portion of the sacrificial layer to form a second chamber.  
      A fluid actuator, a driving circuit communicating with the fluid actuator and a passivation layer covering the fluid actuator and the driving circuit are formed on the structural layer.  
      It is understood that the sacrificial layer comprises borophosphosilicate glass (BPSG), phosphosilicate glass (PSG), or silicon oxide. The structural layer comprises a silicon oxynitride.  
      The exit-end of the fluid channel is anisotropically etched using KOH, tetramethyl ammonium hydroxide (EDP), or ethylene diamine pyrochatechol (EDP) soluition.  
      The method for fabricating an enlarged fluid channel further comprises multiple steps of removing and etching a portion of the sacrificial layer and enlarging the fluid chamber.  
      A nozzle is formed by etching the structural layer, thereby communicating the enlarged fluid chamber. The fluid is ejected from the nozzle.  
      The present invention improves on the related art in that repeating the steps of removing and anisotropically etching the sacrificial layer to enlarge the exit-end of the fluid channel instead of enlarging the entry-end of the fluid channel. Furthermore, the die density can increase and the strength of the fluid injector can be maintained. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The present invention can be more fully understood by reading the subsequent detailed description in conjunction with the examples and references made to the accompanying drawings, wherein:  
       FIG. 1  is a schematic view of a conventional monolithic fluid injector; and  
       FIGS. 2-7  are schematic views of a method for manufacturing an enlarged fluid chamber according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       FIGS. 2-7  are schematic views of a method for manufacturing a fluid injector using multiple steps of removing and anisotropic etching of the sacrificial layer to enlarge the exit-end of the fluid channel instead of enlarging the entry-end of the fluid channel. Referring to  FIG. 2 , a substrate  100 , such as a single crystal silicon wafer, having a first surface  1001  and a second surface  1002  is provided. A patterned sacrificial layer  110  is formed on the first surface  1101  of the silicon substrate  100 . The sacrificial layer comprises borophosphosilicate glass (BPSG), phosphosilicate glass (PSG), or other silicon oxide material. Sequentially, a patterned structural layer  120  is conformally formed on the first surface  1001  of the substrate  100  covering the patterned sacrificial layer  110 . The structural layer  120  is a low stress silicon oxynitride (SiON) or silicon nitride (SiN). The stress of the silicon oxynitride (SiON) is about 100 to 200 MPa. The low stress silicon oxynitride (SiON) is deposited by chemical vapor deposition (CVD). A low stress silicon oxynitride (SiON)  101  is simultaneously formed on the second surface  1002  of the silicon substrate  100 .  
      A fluid actuator  130 , a signal transmitting circuit  140  communicating with the fluid actuator  130  and a passivation layer  150  covering the fluid actuator  130  and the signal transmitting circuit  140  are formed on the structural layer  120 . The fluid actuator  130  comprises a thermal bubble actuator or a piezoelectric actuator. The thermal bubble actuator comprises a patterned resist layer. The patterned resist layer is formed on the structural layer  120  to serve as a heater. The resist layer comprises HfB 2 , TaAl, TaN, or TiN. The resist layer can be deposited using PVD, such as evaporation, sputtering, or reactive sputtering.  
      Sequentially, a patterned conductive layer  140 , such as Al, Cu, or Al—Cu alloy, is formed on the structural layer  120  communicating with the resist layer  130  to act as a signal transmitting circuit  140 . The conductive layer  140  may be deposited using PVD, such as evaporation, sputtering, or reactive sputtering. A passivation layer  150  is formed on the substrate  100  covering the structural layer  120  and the signal transmitting circuit  140 . The passivation layer comprises an opening  155  exposing the contact pad of the signal transmitting circuit.  
      Referring to  FIG. 3 , an opening  105  is defined in the low stress silicon oxynitride (SiON) layer  101  exposing the second face  1002  of the single crystal silicon substrate  100 . While forming the fluid channel, the opening  105  serves as a hard mask during etching of the single crystal silicon substrate  100 . The dimensions of the opening  105  are equal to the entry-end of the fluid channel.  
      Referring to  FIG. 4 , The second silicon substrate surface is etched by wet etching to form a fluid channel  500 . The fluid channel  500  exposes the sacrificial layer  110 . Preferably, wet etching is performed using KOH, tetramethyl ammonium hydroxide (EDP), or ethylene diamine pyrochatechol (EDP) solution.  
      Referring to  FIG. 5 , a portion of the sacrificial layer  110  is etched and removed by wet etching or dry etching to form a first fluid chamber  600   a . Wet etching is performed using HF or buffer oxide etching (BOE) solution. The amount of wet etching is determined by real-time control. The entry-end of the fluid channel is dependent on the removed portion of the exit-end of the fluid channel.  
      Referring to  FIG. 6 , The exposed surface of the single crystal silicon substrate is etched and the first chamber  600   a  is enlarged by wet etching. An enlarged first chamber  600   b  is thus formed. The exit-end of the fluid channel  500  is also enlarged to desired dimensions simultaneously. Etching of the exposed surface of the silicon substrate and the first chamber  600   a  is dependent on real-time control. If the etching is complete, the edge of the fluid chamber will be rounded and create an over enlarged fluid channel. The over enlarged fluid channel leads to cross-talk between adjacent fluid chambers during fluid ejection. Preferably, wet etching is performed using KOH, tetramethyl ammonium hydroxide (EDP), or ethylene diamine pyrochatechol (EDP) solution.  
      In another embodiment of the present invention, removing a portion of the sacrificial layer and enlarging the fluid chamber and exit-end of the fluid channel can be repeated twice or more times, depending on the dimensions of the exit-end  500   b  of the fluid channel.  
      Referring to  FIG. 7 , the remaining portion of the sacrificial layer is removed by wet etching or dry etching to form a second fluid chamber  600   c . Etching the remaining portion of the sacrificial layer is performed using HF or buffer oxide etching (BOE) solution. Subsequently, the second fluid chamber  600   c  is enlarged by wet etching. The exit-end of the fluid channel  500  is simultaneously enlarged to desired dimensions. Preferably, wet etching is performed using KOH, tetramethyl ammonium hydroxide (EDP), or ethylene diamine pyrochatechol (EDP) solution.  
      A nozzle  165  is formed by etching the structural layer  120  along the opening  160 . The nozzle  160  communicates with the fluid channel for ejecting micro fluid from the nozzle  160 . The nozzle  160  is preferably formed by plasma etching, chemical dry etching, reactive ion etching (RIE), or laser ablation. A monolithic fluid injector is thus obtained by multiple steps of anisotropic etching and removal of the sacrificial layer with an enlarged exit-end.  
      While the invention has been particularly shown and described with reference to preferred embodiments, it will be readily appreciated by those of ordinary skill in the art that various changes and modifications may be made without departing from the spirit and scope of the invention. It is intended that the claims be interpreted to cover the disclosed embodiment, those alternatives which have been discussed above, and all equivalents thereto.