Abstract:
A method of making a silicon-based miniaturized microphone by means of the application of a combination of processes including a semiconductor manufacturing process and a silicon micro-machining technology. A silicon-based miniaturized microphone made by means of this method has a silicon substrate, which defines a resonance cavity, a diaphragm, a backplate having sound holes, and solder pads. This method is easy to perform, and suitable for a mass production to reduce the manufacturing cost.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to miniaturized microphones and more particularly, to a method of making silicon-based miniaturized microphone, which is practical for making high sensitivity and high reliability miniaturized thin type microphones through a mass production.  
         [0003]     2. Description of the Related Art  
         [0004]     It is the market tendency to provide compact and sophisticated mobile electronic devices such as MP3 players, cell phones, PDAs, etc. A microphone is an important part commonly seen in regular mobile electronic devices. It is important to provide a high-performance microphone having light, thin, short and small characteristics.  
         [0005]      FIG. 1  shows a miniaturized microphone  7  constructed according to U.S. Pat. No. 5,573,679. According to this design, the diaphragm  71  and backplate  72  of the microphone  7  are respectively made by silicon nitride. Because silicon nitride is electrically insulative, electrically conductive layers  73  and  74  must be provided at the diaphragm  71  and the backplate  72  to work as electrodes. These electrically conductive layers  73  and  74  relatively increase the size and manufacturing cost of the microphone  7 .  
         [0006]      FIG. 2  shows a miniaturized microphone  8  constructed according to U.S. Pat. No. 5,888,845. According to this design, epitaxy wafers are used to make the diaphragm  81  of the microphone  8 . Therefore, the material cost of this structure of microphone  8  is high. Further, the backplate  82  of the microphone  8  is made by using a metal layer  83  as a seed layer and then using a micro plating technique to form a metal thick film  84  on the top surface of the metal layer  83  to enhance the stiffness of the backplate. However, it is difficult to control the uniformity of the thickness of the metal thick film  84 . Further, because the backplate has no passivation for protection, the quality of the product is not guaranteed.  
         [0007]      FIG. 3  shows a miniaturized microphone  9  constructed according to U.S. Pat. No. 6,140,689. According to this design, the microphone  9  has the backplate  92  set at an inner side and the diaphragm  91  set at the outer side. Further, because the diaphragm  91  has a small thickness, it tends to be affected by external environmental conditions. Due to the said drawbacks, the yield rate of this design is low.  
         [0008]     Therefore, it is desirable to provide a method of making microphone, which is practical for making miniaturized, high-performance microphones at a high yield rate.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention has been accomplished under the circumstances in view. It is the primary objective of the present invention to provide a method of making silicon-based miniaturized microphone, which is practical for making high sensitivity and high reliability miniaturized microphones.  
         [0010]     It is another objective of the present invention to provide a method of making silicon-based miniaturized microphone, which is practical for mass production of high sensitivity and high reliability miniaturized microphones to reduce the manufacturing cost.  
         [0011]     To achieve these objectives of the present invention, the method of making a silicon-based miniaturized microphone comprising the steps of: a) preparing a silicon substrate having a dielectric layer respectively covered on top and bottom surfaces thereof and depositing a polysilicon material on the dielectric layer at the top surface of the silicon substrate to form a diaphragm, and then doping the diaphragm with baron ions or phosphor ions, and then annealing the diaphragm, and then etching the diaphragm by a photo lithographic process subject to a predetermined pattern; b) depositing a sacrificial layer on the diaphragm; c) depositing an insulative layer on the sacrificial layer; d) depositing a polysilicon film on the insulative layer and then doping the polysilicon film with baron ions or phosphor ions and then annealing the polysilicon film to form a backplate, and then etching the backplate subject to a predetermined pattern; e) depositing a passivation on the backplate and then etching the passivation to provide a contact window; f) using a sputtering coating technology or an evaporation coating technology to form two solder pads, which are respectively and electrically connected to the backplate and the diaphragm, within the contact window; g) etching the passivation, the backplate and the insulative layer, so as to form a plurality of sound holes; h) stripping off the dielectric layer at the bottom surface of the silicon substrate, and then etching the silicon substrate, and then stripping off a part of the dielectric layer at the top surface of the silicon layer so as to form a resonance cavity; and i) stripping off the sacrificial layer. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a schematic drawing showing the structure of a miniaturized microphone according to the prior art.  
         [0013]      FIG. 2  is a schematic drawing showing another structure of miniaturized microphone according to the prior art.  
         [0014]      FIG. 3  is a schematic drawing showing still another structure of miniaturized microphone according to the prior art.  
         [0015]      FIGS. 4A-4I  show a silicon-based miniaturized microphone processing process according to a preferred embodiment of the present invention.  
         [0016]      FIG. 5  is a schematic drawing showing the structure of a silicon-based miniaturized microphone constructed according to another preferred embodiment of the present invention.  
         [0017]      FIG. 6  is a schematic drawing showing an alternate form of the silicon-based miniaturized microphone constructed according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     Referring to  FIG. 4I , a silicon-based miniaturized microphone  1  is shown comprised of a silicon substrate  1   a , a backplate  4 , a diaphragm  2 , and two metal solder pads  51 ,  52 .  
         [0019]     As shown in  FIGS. 4A-4I , the method of making the aforesaid silicon-based miniaturized microphone  1  comprises the steps of:  
         [0020]     a) preparing a N type or P type silicon substrate  1   a  having the crystal orientation &lt;100&gt; and a dielectric layer  1   b  of silicon dioxide or silicon nitride respectively covered on the top and bottom surfaces, and depositing a polysilicon material in the dielectric layer  1   b  at the top side of the silicon substrate  1   a  by a low pressure CVD (Chemical Vapor Deposition) process to form a diaphragm  2 , and then doping the diaphragm  2  with baron ions or phosphor ions, and then annealing the diaphragm  2  to form a P type or N type, low stress, semiconductor diaphragm of thickness about 0.1-0.4 μm, for enabling of processing the diaphragm with a photo lithographic process to have the designed pattern (see  FIG. 4A );  
         [0021]     b) growing a sacrificial layer  3  of LTO (Low Temperature Oxide), for example, PSG (phosphorous silicon glass) about 0.5-5.0 μm thick from the diaphragm  2  by a low pressure CVD or PECVD (Plasma Enhanced Chemical Vapor Deposition) process, and then employing a photo lithographic process (see  FIG. 4B ), where LOT is used for the sacrificial layer  3  for the advantage of relatively lower density relative to HTO (High Temperature Oxide) for rapid etching and further silicon micro-machining (see  FIG. 4B );  
         [0022]     c) growing an insulative layer  41  of silicon nitride having a thickness about 0.1-2.0 μm from the sacrificial layer  3  by a low pressure CVD or PECVD (Plasma Enhanced Chemical Vapor Deposition) process (see  FIG. 4C );  
         [0023]     d) growing a polysilicon film having a thickness about 1.0-6.0 μm from the top surface of the insulative layer  41  by a low pressure CVD (Chemical Vapor Deposition) process, and then doping the polysilicon film with baron ions or phosphor irons and then annealing the film to form a backplate  4  having protruding structures  4   a , and then etching the backplate  4  subject to the desired pattern (see  FIG. 4D );  
         [0024]     e) growing a passivation  42  of silicon nitride of thickness about 0.1-2.0 μm from the top surface of the backplate  4  by a low pressure CVD or PECVD (Plasma Enhanced Chemical Vapor Deposition) process to provide the effects of protection, electricity insulation and stiffness reinforcement, and then etching the passivation  42  by photo lithography to provide contact windows  50  (see  FIG. 4E );  
         [0025]     f) using a semiconductor sputtering or evaporation coating technology to cover the top side of the backplate  4  with a layer of metal material, for example, aluminum, gold, chrome, platinum, titanium, nickel, copper, silver, or the alloy thereof of thickness about 0.1-1.5 μm, and then using a semiconductor lift-off or wet etching technology to define the pattern of the metal coating, so as to form two solder pads  51  and  52  within the contact windows  50  that are respectively electrically connected to the backplate  4  and the diaphragm  2  (see  FIG. 4F );  
         [0026]     g) using a lithographic technology to define the pattern, and then using an etching technology to etch the passivation  42 , the backplate  4  and the insulator layer  41  subject to the defined pattern, so as to form a plurality of sound holes  43  and etching holes  43   a  (see  FIG. 4G );  
         [0027]     h) using a photo lithographic technology to define an etching window  6  at the bottom side of the silicon substrate  1   a  (see  FIG. 4G ), and then using the dielectric layer of the silicon substrate  1   a  as an etching mask to selectively etch the etching window  6  with KOH or TMAH solution by an anisotropic chemical wet etching process to form a notch  5 , and then stripping off the dielectric layer  1   b  from the top side of the silicon substrate  1   a  so that the notch  5  forms a resonance cavity  5  and the diaphragm  2  is kept suspending in the resonance cavity  5  (see  FIG. 5H ); and  
         [0028]     i) using HF (Hydrofluoric Acid), BOE (Buffered Oxide Etchant), or HF (Hydrofluoric Acid) vapor to strip off the sacrificial layer  3  (see  FIG. 41 ), thereby obtaining the desired silicon-based miniaturized microphone  1 .  
         [0029]     Referring to  FIG. 4I  again, the silicon-based miniaturized microphone  1  has arranged one above another in proper order the silicon substrate  1   a , the diaphragm  2 , the insulative layer  41 , the backplate  4 , the passivation  42 , and the two solder pads  51  and  52 , wherein the silicon substrate  1   a  defines a resonance cavity  5 ; the insulative layer  41  and the backplate  4  and the passivation  42  define a plurality of sound holes  43 .  
         [0030]     Therefore, the backplate  4  and diaphragm  2  of the silicon-based miniaturized microphone  1  work as top and bottom electrodes such that vibration of the diaphragm  2  upon a sound pressure causes a variation of the capacitance value.  
         [0031]     Further, the protruding structure  4   a  of the backplate  4  of the silicon-based miniaturized microphone  1  prevents stiction between the diaphragm  2  and the backplate  4 , thereby improving the yield rate of the product.  
         [0032]     Further, when employing another anti-stiction technology to strip off the sacrificial layer  3  during step i), for example, sacrificial layer dry etching, hydrofluoric acid vapor etching, or organic drying technology, the design of the protruding structure  4   a  can be eliminated, thereby obtaining another structure of silicon-based miniaturized microphone  10  as shown in  FIG. 5 .  
         [0033]     In the aforesaid first preferred embodiment of the present invention, an anisotropic chemical wet etching process is employed to etch the etching window  6  to form a resonance cavity  5  having the &lt;111&gt; orientation of the peripheral walls during step h). An ICP (Inductively Coupled Plasma) etching process may be employed instead of the anisotropic chemical wet etching process, thereby forming a resonance cavity  55  having vertical peripheral walls as shown in  FIG. 6 .  
         [0034]     Therefore, changing the aforesaid steps (h) and (i) can obtain another structure of silicon-based miniaturized microphone  20  as shown in  FIG. 6 .  
         [0035]     The silicon-based miniaturized microphone manufacturing process of the present invention is a combination of a semiconductor manufacturing process and a silicon micro-machining technology. Although particular embodiments of the invention have been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.