Abstract:
The present invention discloses a MEMS device with guard ring, and a method for making the MEMS device. The MEMS device comprises a bond pad and a sidewall surrounding and connecting with the bond pad, characterized in that the sidewall forms a guard ring by an etch-resistive material.

Description:
BACKGROUND 
       [0001]    1. Field of Invention 
         [0002]    The present invention relates to a micro-electro-mechanical system (MEMS) device and a method for making the MEMS device, in particular to a MEMS device with guard ring and a method for making it. 
         [0003]    2. Description of Related Art 
         [0004]    MEMS devices are used in a wide variety of products such as micro-acoustical sensor, gyro-sensor, accelerometer, etc. The MEMS structure of a MEMS device is usually located on top of the wafer, so it should preferably be protected. The present invention thus provides a MEMS device with guard ring and a method for making it. 
       SUMMARY OF THE INVENTION 
       [0005]    It is an objective of the present invention to provide a MEMS device with guard ring. 
         [0006]    It is another objective of the present invention to provide a method for making a MEMS device with guard ring. 
         [0007]    In accordance with the foregoing and other objectives of the present invention, from one aspect, the present invention discloses a MEMS device with guard ring, comprising: a substrate including transistor devices, part of interconnection and MEMS structure; a top dielectric layer formed on the substrate; a top metal layer, part of which forms the bond pad; and a sidewall surrounding and connecting with the bond pad, characterized in that the sidewall is made of an etch-resistive material and forms a guard ring laterally sealing the top dielectric layer. 
         [0008]    The MEMS device may further comprise a shielding layer provided on the top dielectric layer and connected with the sidewall. The shielding layer and the guard ring can each be a single layer or a composite layer. 
         [0009]    In another aspect, the present invention discloses a method for making a MEMS device with guard ring, comprising: providing a substrate including transistor devices, part of interconnection and MEMS structure; forming a top dielectric layer; forming a top metal layer, part of which forms a bond pad; and forming a sidewall guard ring connected with the bond pad by a material which is resistive to an etchant capable of etching the top dielectric layer, wherein the sidewall guard ring laterally seals the top dielectric layer. 
         [0010]    The method may further comprise: forming a shielding layer on the top dielectric layer and connected with the sidewall. 
         [0011]    It is to be understood that both the foregoing general description and the following detailed description are provided as examples, for illustration and not for limiting the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings. 
           [0013]      FIGS. 1A-1C  show an embodiment according to the present invention. 
           [0014]      FIG. 2  shows another embodiment according to the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0015]    The drawings as referred to throughout the description of the present invention are for illustration only, but not drawn according to actual scale. 
         [0016]      FIGS. 1A-1C  shows a bond pad structure according to the first embodiment of the present invention, wherein  FIG. 1B  is a top view taken along the line B-B of  FIG. 1A ;  FIG. 1C  is a top view taken along the line C-C of  FIG. 1A ; and  FIG. 1A  is a cross sectional view taken along the line A-A of  FIG. 1B .  FIG. 1A  shows a substrate  12  which has been processed to include transistor devices, part of the interconnection and MEMS structure (not shown), and also shows a top metal layer  14  which is provided as a bond pad on the substrate  12 . The top metal layer  14  is isolated from the metal of the same level or the level beneath by a top dielectric layer  16 . The top dielectric layer  16  for example can be made of an oxide such as silicon dioxide or a low-K material containing silicon dioxide. 
         [0017]    The dielectric layer  16  needs to be etched during the process for forming the MEMS device. The present invention is characterized in that a guard ring  18  made of an etch-resistive material is formed as a sidewall surrounding the bond pad. The guard ring  18  seals the dielectric layer  16  laterally except the open area  100 . A shielding layer  20  is provided on top of the dielectric layer  16 , which is preferably also made of an etch-resistive material to protect the dielectric layer  16 . The term “etch-resistive” means that the material is resistive to etch of the dielectric layer  16 , that is, resistive to an etchant capable of etching the dielectric layer  16 . 
         [0018]    Depending on the material of the dielectric layer  16 , the guard ring  18  and the shielding layer  20  can be a single or a composite layer made of any etch-resistive material. However, the guard ring  18  and the shielding layer  20  should not be electrically connected with each other; otherwise the bond pad and the surface of the overall device will be shorted together. As long as such premise is met, the guard ring  18  can be made of a material such as metal, amorphous silicon, silicon nitride, silicon oxynitride, or a composite material of two or more of the above materials, and the shielding layer  20  can be made of a material such as metal, amorphous silicon, silicon nitride, silicon oxynitride, or a composite material of two or more of the above materials. 
         [0019]      FIG. 2  shows a second embodiment according to the present invention. This embodiment is characterized in that the shielding layer  20  is a composite layer including an upper layer  20 A and a lower layer  20 B. The lower layer  20 B can be a layer for enhancing the adhesion between the composite shielding layer  20  and the substrate beneath. Or, when the guard ring  18  is made of a conductive material, one of the upper layer  20 A and the lower layer  20 B can be made of an insulating material. In this embodiment, for example, the guard ring  18  can be made of a material such as metal, amorphous silicon, silicon nitride, silicon oxynitride, or a composite material of two or more of the above materials. The upper shielding layer  20 A can be made of a material such as metal, amorphous silicon, silicon nitride, silicon oxynitride, or a composite material of two or more of the above materials. The lower shielding layer  20 B can be made of a material such as metal, amorphous silicon, silicon nitride, silicon oxynitride, or a composite material of two or more of the above materials. “Metal” for example can be, but not limited to, aluminum or copper. 
         [0020]    Although the present invention has been described in detail with reference to certain preferred embodiments thereof, the description is for illustrative purpose and not for limiting the scope of the invention. One skilled in this art can readily think of other modifications and variations in light of the teaching by the present invention. For example, the composite shielding layer  20  can include three or more layers. The guard ring  18  can also be made of a composite material. Therefore, all such modifications and variations should be interpreted to fall within the scope of the following claims and their equivalents.