Abstract:
A method for fabricating a thin film bulk acoustic resonator (FBAR) is able to simplify the conventional fabricating step. Particularly, a chamber is defined between a substrate and of the resonator without need for a polishing processes and filling processes. Therefore, the present invention is able to have a high fabricating ability, a high production rate and a short fabricating time.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a method for fabricating a thin film bulk acoustic resonator (FBAR) which may be used as a filter used for electronic circuits and more particularly to the method having simple steps to fabricate the FBAR, besides having high production ability of the FBAR.  
           [0003]    2. Description of Related Art  
           [0004]    The high frequency and exact resonance frequency of the FBAR are important elements when fabricating the FBAR. The earlier generation SAW (surface acoustic wave) fabricating method of a resonator employed a pair of parallel fingers on a surface of a substrate. To fabricate a high frequency by the conventional method, a distance of the two adjacent metal fingers has to be reduced. For example, a resonator having 2 GHz frequency is able to use a semiconductor process with less than 0.5 μm. Therefore, fabricating the high frequency resonator is costly and owing to use the surface acoustic property. The power handling is another major limitation for high performance wireless product.  
           [0005]    A present resonator adopting the surface acoustic wave theory is able to solve the above drawbacks incurred in the conventional processing of the resonator. The resonator is fabricated according to the surface acoustic wave theory to have a high frequency and high power factor. That is, a direction of the acoustic wave of the resonator and a surface of the resonator are perpendicular to each other, whereby the resonator needs a relationship of some important elements such as the piezoelectric material and the working frequency of the resonator are inverse proportion to each other, to fabricate an FBAR.  
           [0006]    With reference to FIGS. 6A to  6 E, a conventional fabricating method of a thin film bulk acoustic resonator (FBAR) is shown. The method for fabricating the resonator comprises the following steps:  
           [0007]    defining a recess ( 501 ) in a top face of a Si substrate ( 50 ) and then applying a SiO 2  layer on the top face of the Si substrate;  
           [0008]    applying a phosphorsilica glass layer ( 52 ) on the SiO 2  layer ( 51 );  
           [0009]    chemical machine polishing the phosphorsilica glass layer ( 52 ) to have a portion of the phosphorsilica glass layer ( 52 ) remained in the recess ( 501 );  
           [0010]    sequentially forming a first conductive layer ( 53 ), a piezoelectric material layer ( 55 ) and a second conductive layer ( 54 ) on the phosphorsilica glass layer ( 52 ) remained in the recess ( 501 ); and  
           [0011]    etching away the phosphorsilica glass layer ( 52 ) to expose the recess ( 501 ).  
           [0012]    As per the above steps, a resonator is formed on the recess ( 501 ), that is, after the phosphorsilica glass layer ( 52 ) is etched, the body of the resonator is supported by the edge of the recess ( 501 ). However, the substrate ( 50 ) corresponding to the body of the resonator has to define the recess ( 501 ) for having high frequency filtering ability, so that, before forming the body of the resonator, the recess ( 501 ) has to undergo filling and polishing steps. Therefore, the above complex steps are necessary for the conventional resonator to be able to have high frequency and high power factor, and thus fabricating the FBAR not only takes considerable time but also has a slow production rate.  
           [0013]    To overcome those shortcomings, the present invention provides simple and easy steps and good production ability to mitigate and obviate the aforementioned problems.  
         SUMMARY OF THE INVENTION  
         [0014]    The objective of the present invention is able to provide a simple method for fabricating thin film bulk acoustic resonators (FBAR), and furthermore, the fabrication method of the FBAR does not need a chemical machine polishing(CMP) step. The method for fabricating FBAR comprises the following steps:  
           [0015]    preparing a Si substrate;  
           [0016]    applying an insulating layer on the Si substrate;  
           [0017]    sequentially applying a first conductive layer, a piezoelectric material layer and a second conductive layer on top of the Si substrate;  
           [0018]    partially etching the second conductive layer and the piezoelectric material layer to form an upper electrode and a piezoelectric layer; and  
           [0019]    defining holes in the first conductive layer by etching so as to allow the formation of a chamber under the first conductive layer.  
           [0020]    Therefore, fabricating the FBAR requires only a short working time, and the production rate of the FBAR is accordingly high.  
           [0021]    Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    [0022]FIG. 1 is a cross section view of making an insulating layer step of the method in accordance with the present invention;  
         [0023]    [0023]FIG. 2 is a cross section view of making three elements on the insulating layer step of the method in accordance with the present invention;  
         [0024]    FIGS.  3 A˜ 3 C are two cross section views of making an upper body of a resonator step of the method in accordance with the present invention;  
         [0025]    FIGS.  4 A˜ 4 C are three cross section views of making a chamber defining between the substrate and the first metal layer step of the method in accordance with the present invention;  
         [0026]    [0026]FIGS. 5A and 5B are cross section views of making a lower body of the resonator step of the method in accordance with the present invention; and  
         [0027]    FIGS.  6 A˜ 6 E are cross section views of the conventional steps of fabricating an FBAR. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0028]    With reference to FIGS. 1 and 2, the method for fabricating a thin film bulk acoustic resonator comprises the following steps:  
         [0029]    preparing a Si substrate ( 10 );  
         [0030]    applying an insulating layer ( 11 ) on the Si substrate ( 10 ), wherein a thickness of the insulating layer ( 11 ) is 1000˜10000 angstrom;  
         [0031]    applying a first conductive layer ( 12 ) on the insulating layer ( 11 ), wherein a thickness of the first conductive layer ( 12 ) is 1000˜10000 angstrom;  
         [0032]    applying a piezoelectric material layer ( 13 ) on the first conductive layer ( 12 ), and a thickness of the piezoelectric material layer ( 13 ), such as an AlN and a ZnO, is 0.5˜5 μm;  
         [0033]    applying a second conductive layer ( 14 ) on the piezoelectric material layer ( 13 ) wherein a thickness of the second conductive layer ( 14 ) is 1000˜10000 angstrom;  
         [0034]    forming a first photo-resistant layer ( 20 ) on the second conductive layer ( 14 ), as shown in FIG. 3A;  
         [0035]    etching the second conductive layer ( 14 ) to leave the second conductive layer ( 14 ) covered by the first photo-resistant layer ( 20 ) on the piezoelectric material layer ( 13 ) to form an upper electrode ( 14   a ) of the resonator, as shown in FIG. 3B;  
         [0036]    etching the piezoelectric material layer ( 13 ) to leave the piezoelectric material layer ( 13 ) covered by first photo-resistant layer ( 20 ) and the upper electrode ( 14   a ) on the first conductive layer ( 12 ) and then removing the first resistant layer ( 20 ) to form a piezoelectric layer ( 13   a ) of the resonator, as shown in FIG. 3C;  
         [0037]    forming a second photo-resistant layer ( 21 ) on the first conductive layer ( 12 ), as shown in FIG. 4A;  
         [0038]    etching the first conductive layer ( 12 ) to leave the first conductive layer ( 12 ) covered by the second photo-resistant layer ( 21 ) on the insulating layer ( 11 ) to define multiple through holes ( 120 ) in the first conductive metal layer ( 12 ), as shown in FIG. 4B;  
         [0039]    etching the insulating layer ( 11 ) through the multiple through holes ( 120 ) to defined a chamber ( 110 ) on the first conductive layer ( 12 ), as shown in FIG. 4C;  
         [0040]    forming a third photo-resistant layer ( 22 ) on the first conductive layer ( 12 ), as shown FIG. 5A; and  
         [0041]    etching the first conductive layer ( 12 ) to leave the first conductive layer ( 12 ) covered by the third photo-resistant layer ( 22 ), and then removing the third photo-resistant layer ( 22 ) to forming the lower electrode ( 12   a ) of the resonator, as shown FIG. 5B.  
         [0042]    The chamber ( 110 ) is defined between the resonator and the substrate ( 10 ) after forming the upper and lower electrode ( 12   a ,  14   a ) and the piezoelectric layer ( 13   a ) of the resonator for supporting the resonator without undergoing the filling and the polishing steps, so that the method has simple fabricating processes and a short working time  
         [0043]    With reference to FIG. 5B, the body of the resonator supported on the substrate ( 10 ) comprises the substrate ( 10 ), at least two insulating layers ( 11 ) formed on an upper surface of the substrate ( 10 ), at least one lower electrode ( 12   a ) formed on the two adjacent insulating layers ( 11 ), at least one piezoelectric layer ( 13   a ) corresponded to form on each lower electrode ( 12   a ), and at least one upper electrode ( 14   a ) formed on the piezoelectric layer ( 13   a ). In order to support the resonator the lower electrode ( 12   a ) is larger than the upper electrode ( 14   a ), however the upper and lower electrodes otherwise have the same characteristics.  
         [0044]    As perthe above description about the invention, the method has simple processes to fabricate the FBAR, especially, the chamber defined after forming the all amounts of the resonator. Therefore, the method does not have the CMP processes, and the filling processes to forming the chamber, so that the present method has the following advantages:  
         [0045]    1. Simple steps of method for fabricating the FBAR;  
         [0046]    2. Reduction of the fabricating time in comparison to the conventional method; and  
         [0047]    3. Increase in the production of fabrication the FBAR in comparison to the conventional method.  
         [0048]    Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.