Abstract:
The present invention discloses a MEMS (Micro-Electro-Mechanical System) integrated chip with cross-area interconnection, comprising: a substrate; a MEMS device area on the substrate; a microelectronic device area on the substrate; a guard ring separating the MEMS device area and the microelectronic device area; and a conductive layer on the surface of the substrate below the guard ring, or a well in the substrate below the guard ring, as a cross-area interconnection electrically connecting the MEMS device area and the microelectronic device area.

Description:
This is a divisional of a co-pending application Ser. No. 12/464,375, filed on May 12, 2009. 
    
    
     FIELD OF INVENTION 
     The present invention relates to a Micro-Electro-Mechanical System (MEMS) integrated chip and a wiring structure of this system chip. 
     DESCRIPTION OF RELATED ART 
     MEMS devices are used in a wide variety of products such as micro-acoustical sensor, gyro-sensor, accelerometer, etc. A MEMS typically includes a MEMS device and other microelectronic devices which are integrated into an integrated chip.  FIG. 1A  is a top view showing the layout of a prior art MEMS chip. The integrated chip includes a MEMS device area  100  and a microelectronic device area  200  (including, e.g., CMOS devices). The MEMS device area  100  is surrounded by a guard ring  120  to protect the microelectronic device area  200  from damages due to the etching process in manufacturing the MEMS devices. 
     Referring to  1 B, which is a cross-section view along the line A-A of  FIG. 1A . During the manufacturing process of the microelectronic devices and the MEMS device, multiple dielectric layers  20  are deposited (interfaces between layers not shown). In this prior art, a movable MEMS device (not shown) is formed in the MEMS device area by etching the dielectric layer  20 ; thus, a space  10  is left in the MEMS device area  100 . As mentioned earlier, the etching of the dielectric layer  20  should not damage the microelectronic device area  200 . Therefore, a guard ring  120  is provided, which includes a polysilicon layer  12 , a contact layer  13 , a first metal layer  14 , via layers  15   a - 15   c , and other metal layers  16   a - 16   c . The number of the via layers and metal layers may be determined according to the requirement for interconnection of the microelectronic devices and the design of the MEMS device. 
     In order to functionally connect the microelectronic devices and the MEMS device, an electrical connection must be provided therebetween. The foregoing prior art achieves this connection by means of one or more metal layers, such as the first metal layer  14  shown in  FIG. 1B . However, such one or more metal layers must go through the guard ring  120 , and the positions where they go through the guard ring  120  can not form a tightly closed structure with other portions of the guard ring  120  (i.e. the contact layer  13 , via layer  15   a , and the rest of the first metal layer  14  in the drawing); otherwise, it causes short circuit. Therefore, in this prior art, the microelectronic device area  200  can not be completely prevented from being damaged in the etching process for forming the MEMS device. 
     Accordingly, it is highly desired to provide a wiring structure which functionally connects the MEMS device and the microelectronic devices but still maintains the completeness of the guard ring structure. 
     SUMMARY OF THE INVENTION 
     An objective of the present invention is to provide a MEMS integrated chip with specially designed cross-area interconnection for electrically connecting the MEMS device area and the microelectronic device area to solve the foregoing problem. 
     In order to achieve the foregoing objective, in one perspective of the present invention, it provides an integrated MEMS chip with cross-area interconnection, comprising: a substrate; a MEMS device area on the substrate; a microelectronic device area on the substrate; and a guard ring separating the MEMS device area and the microelectronic device area, the guard ring including a structural layer on the substrate and a contact layer on the structural layer, wherein the contact layer is for a cross-area interconnection electrically connecting the MEMS device area and the microelectronic device area. 
     In another perspective of the present invention, it provides a MEMS integrated chip with cross-area interconnection, comprising: a substrate; a MEMS device area on the substrate; a microelectronic device area on the substrate; a guard ring separating the MEMS device area and the microelectronic device area; and a conductive layer on a surface of the substrate below the guard ring, as a cross-area interconnection electrically connecting the MEMS device area and the microelectronic device area. 
     In a third perspective of the present invention, it provides a MEMS integrated chip with cross-area interconnection, comprising: a substrate; a MEMS device area on the substrate; a microelectronic device area on the substrate; a guard ring separating the MEMS device area and the microelectronic device area; and a well in the substrate below the guard ring, as a cross-area interconnection electrically connecting the MEMS device area and the microelectronic device area. 
     The foregoing MEMS integrated chip can include both the aforementioned conductive layer and the aforementioned well. 
     Preferably, the guard ring of the foregoing MEMS integrated chip includes a structural layer with dielectric function on the substrate; a preferable material of the structural layer is undoped polysilicon. 
     In the foregoing MEMS integrated chip, the well can extend under the MEMS device area. 
     The objectives, technical details, features, and effects of the present invention will be better understood with regard to the detailed description of the embodiments below, with reference to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1B  shown the layout and cross section of a prior art MEMS chip. 
         FIGS. 2-7  show six embodiments of the present invention, respectively. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The drawings as referred to throughout the description of the present invention are for illustration only, to show the interrelationships between the process steps and between the layers, but not drawn according to actual scale. 
       FIG. 2  illustrates the first embodiment of the present invention. In this embodiment, a contact layer  13  is provided as a cross-area interconnection between a MEMS device and a microelectronic device (such as a CMOS device), and a lowest structural layer  12   a  is used for electrical isolation to prevent short circuit between the contact layer  13  and the substrate  11 . The structural layer  12   a  for example can be an undoped polysilicon layer or a layer made of any other material capable of providing electrical isolation. In a preferred embodiment, the contact layer  13  is used as a conducting wire (connection line, not only a plug) in the MEMS device area  100  or the microelectronic device area, or both. 
       FIG. 3  illustrates the second embodiment of the present invention. In this embodiment, the contact layer  13   a  is used as a conducting wire (connection line, not only a plug) in the MEMS device area  100 , and the structural layer  12   a  (such as an undoped polysilicon layer or a layer made of any other material capable of providing electrical isolation) is provided for electrical isolation between the contact layer  13   a  and the substrate  11 . Yet, the cross-area connection between the MEMS device and the microelectronic device is achieved by a conductive layer  17  on the surface of the substrate  11 ; the conductive layer  17  for example can be made of cobalt silicide (CoSi 2 ), titanium silicide (TiSi 2 ), or other materials commonly used in the bottom of a contact layer to increase conductivity thereof. Since the cross-area interconnection does not go through the guard ring  120  but goes under it, the contact layer  13   b  and the structural layer  12   b  in the guard ring  120  can form a tightly closed structure with other portions thereof. The structural layer  12   b  is preferably a dielectric layer or a layer with dielectric function, so that the guard ring  120  is not short-circuited to the conductive layer  17 ; but it should be formed by a material other than that for the dielectric layer  20 . For example, the dielectric layer  20  can be made of silicon dioxide, and the structural layer  12   b  can be made of silicon nitride, silicon oxynitride, etc. In a preferable embodiment, the structural layer  12   b  is made of undoped polysilicon, for better process integration. In the microelectronic device area  200 , the conductive layer  17  can be electrically connected to the microelectronic devices through interconnection formed by the contact layer  13   c , the metal layer  14 , etc. 
       FIG. 4  illustrates the third embodiment of the present invention. In this embodiment, the contact layer  13   a  is also used as the conducting wire in the MEMS device area  100 , and the structural layer  12   a  (such as an undoped polysilicon layer or a layer made of any other material capable of providing electrical isolation) is provided as the electrical isolation between the contact layer  13   a  and the substrate  11 . Yet, the cross-area interconnection of the MEMS device and the microelectronic device is achieved by a well  18  in the substrate  11 . The well  18  for example includes an N type well  18   a  and a heavily doped N+ well  18   b  above the N type well  18   a , and the substrate  11  for example can be a P type substrate. A junction diode is formed between the N type well  18  and the P type substrate  11  to avoid short circuit. Similarly, since the cross-area interconnection does not go through the guard ring  120  but goes under the guard ring  120 , the contact layer  13   b  and the structural layer  12   b  (such as an undoped polysilicon layer) in the guard ring  120  can form a tightly closed structure with other portions thereof. 
       FIG. 5  illustrates the fourth embodiment of the present invention. In this embodiment, other than the conductive layer  17  for cross-area interconnection between the MEMS device and microelectronic device, an N type well  18  is also provided to form a junction diode with the P type substrate for avoiding short circuit. Similarly, since the cross-area interconnection does not go through the guard ring  120  but goes under the guard ring  120 , the contact layer  13   b  and the structural layer  12   b  (such as an undoped polysilicon layer) in the guard ring  120  can form a tightly closed structure with other portions thereof. 
       FIG. 6  illustrates the fifth embodiment of the present invention. In this embodiment, the junction diode formed between the N type well  18  and the P type substrate  11  extends to the MEMS device area  100 ; therefore, the undoped polysilicon layer for electrical isolation may not be required in the MEMS device area  100 . The contact layer  13   a  can contact the N type well  18  directly. 
       FIG. 7  illustrates the sixth embodiment of the present invention. This embodiment is similar to the former embodiment. The junction diode formed between the N type well  18  and P type substrate  11  extends to the MEMS device area  100 ; hence, the undoped polysilicon layer for electrical isolation may not be required in the MEMS device area  100 . The cross-area interconnection between the MEMS device and microelectronic device further includes the conductive layer  17 . 
     The present invention has been described in considerable detail with reference to certain preferred embodiments thereof. It should be understood that the description is for illustrative purpose, not for limiting the scope of the present invention. Those skilled in this art can readily conceive variations and modifications within the spirit of the present invention. For example, the materials, number of the metal layers, etc. of each foregoing embodiment can be modified without departing from the spirit of the present invention. Furthermore, the microelectronic devices integrated with the MEMS device are not limited to CMOS devices; they can include bipolar junction transistors (BJTs) and other devices. In view of the foregoing, the spirit of the present invention should cover all such and other modifications and variations, which should be interpreted to fall within the scope of the following claims and their equivalents.