Abstract:
An image sensor structure, which comprises: a pixel; a first metal line; a second metal line, located under the first metal line; a conductive region, located under the second metal line; and at least one dummy contact, provided between the second metal line and the conductive region, wherein the second metal line and the conductive region are not electrically connected to each other via the dummy contact

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an image sensor structure, and particularly relates to an image sensor structure utilizing at least a dummy via or al least a dummy contact. 
         [0003]    2. Description of the Prior Art 
         [0004]    An image sensor may suffer from optical crosstalk, which degrades the image quality (resolution and color fidelity). Optical crosstalk here refers to light intended for a particular pixel enters into neighboring pixels. However, optical crosstalk can not be trivial from the pixel layout since the pixel layout is 2D while the real structure is 3D. Metal routings are usually drawn to improve optical crosstalk issue such that optical crosstalk can be controlled and at the same time sensitivity tradeoff is minimized. However, large gaps still exist between polysilicon and different metal routings, thus optical signal may “leak” or “crosstalk” to its neighbor. 
         [0005]    Contacts and vias can help reduce optical cross talk but they are utilized only where an interconnect between two layers is necessary. Accordingly, there is usually only a few contacts/vias and they might not exist in optimal locations to reduce optical crosstalk. 
         [0006]      FIG. 1  is a top view diagram illustrating a prior art image sensor structure. As shown in  FIG. 1 , a plurality of contacts  101 ,  103 ,  105  and  107  (only parts of them are marked) are provided between metal lines  109  and  111 . Also, a plurality of contacts  109 ,  111 ,  113  and  115  (only parts of them are marked) are provided between the metal line  109  and conductive regions (not shown) such as a diffusion region or a poly region. 
         [0007]      FIG. 2  is a section view of the image sensor structure in  FIG. 1 . In  FIG. 2 ,  FIG. 2(   a ) is a section view corresponding to cross section line AA′ and  FIG. 2(   b ) is a section view corresponding to the cross section line BB′. As shown in  FIG. 2(   a ), at the right side, the optical signal NL from a neighbor pixel can be blocked since there is a contact  201  located between metal lines  203  and  205 . However, at the left side, the optical signal NL from a neighbor pixel can not be blocked and will enter the pixel  211  to generate optical cross talk, since there is no contact located under the metal lines  207  and  209 . Also, desired optical signal L, which is represented by dotted lines, may lose due to the incident angle. 
         [0008]    Similarly, at the right side of  FIG. 2(   b ), the optical signal NL from a neighbor pixel can be blocked since there is a via  213  located between the metal line  215  and the diffusion region  217 . However, at the left side, the optical signal NL from a neighbor pixel can not be blocked and will enter the pixel  219  to generate optical cross talk, since there is no via located under the metal lines  221  and  223 . Also, desired optical signal L may lose due to the incident angle. 
       SUMMARY OF THE INVENTION 
       [0009]    One embodiment discloses an image sensor structure, which comprises: a pixel; a first metal line; a second metal line, located under the first metal line; at least one dummy via, provided between the first metal line and the second metal line, wherein the first metal line and the second metal line are not electrically connected to each other via the dummy via. 
         [0010]    Another embodiment discloses an image sensor structure, which comprises: a pixel; a first metal line; a second metal line, located under the first metal line; a conductive region, located under the second metal line; and at least one dummy contact, provided between the second metal line and the conductive region, wherein the second metal line and the conductive region are not electrically connected to each other via the dummy contact. 
         [0011]    According to above-mentioned embodiments, dummy vias and dummy contacts can be provided at suitable locations to avoid undesired neighbor optical signals entering pixels. Also, the desired optical signal can be reflected to the pixel. Therefore, the issue described in the prior art can be improved. 
         [0012]    These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a top view diagram illustrating a prior art image sensor structure. 
           [0014]      FIG. 2  is a cross section view of the image sensor structure in  FIG. 1 . 
           [0015]      FIG. 3  is a top view diagram illustrating an image sensor structure according to one embodiment of the present application. 
           [0016]      FIGS. 4 ,  5 ,  6  are examples for cross section views of the image sensor structure shown in  FIG. 3 . 
           [0017]      FIG. 7  is a top view diagram illustrating an image sensor structure according to one embodiment of the present application. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Certain terms are used throughout the description and following claims to refer to particular components. As one skilled in the art will appreciate, electronic equipment manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following description and in the claims, the terms “include” and “comprise” are used in an open-ended fashion, and thus should be interpreted to mean “include, but not limited to . . . ”. 
         [0019]      FIG. 3  is a top view diagram illustrating an image sensor structure according to one embodiment of the present application. Comparing with the top view shown in  FIG. 1  and  FIG. 3 ,  FIG. 3  further comprises dummy vias, which are symbolized as circles include right slant lines such as dummy vias  303 ,  305  and  307 , and dummy contacts, which are symbolized as circles including two direction slant lines such as dummy contacts  313  and  315 , besides the vias and contacts shown in  FIG. 1 . Please note that the marks utilized in  FIG. 3  to indicate dummy contacts and dummy vias are only for the convenience to identify vias, contacts, dummy vias and dummy contacts, and do not mean to limit the structures or materials of dummy vias and dummy contacts. 
         [0020]    Dummy vias are vias that are provided between metal layers  314  and  316 , but the metal layers  314  and  316  are not electrically connected to each other via dummy vias.  FIG. 4  is an example for a cross section view of the image sensor structure shown in  FIG. 3 . The cross section view shown in  FIG. 4  corresponds to the cross section line AA′ shown in  FIG. 3 . As shown in  FIG. 4 , a plurality of dummy vias  401 ,  403 , and  405  are provided between the upper metal lines  409 - 415  and the lower metal line  417 , and the dummy vias  401 ,  403 , and  405  are only connected to upper metal lines  409 - 413  but not connected to the lower metal line  417 . Please note that the device  407  shown in  FIG. 4  is a via rather than a dummy via. Accordingly, the upper metal lines  409 - 413  are not electrically connected to the lower metal line  409  via the dummy vias  401 ,  403 , and  405 . In the structure shown in  FIG. 4 , the desired optical signal L can still be reflected by the dummy via  405  to enter the pixel  419 , but the neighbor optical signal NL will be blocked by the dummy vias  401  and  403 . Thus, the problem disclosed in prior art can be solved. 
         [0021]    Besides the structure shown in  FIG. 4 , the distribution of the dummy vias can be as shown in  FIG. 6 . In the structure shown in  FIG. 6 , the via  601  is connected between the upper metal line  611  and the lower metal line  615 . Also, the dummy via  603  is still connected to the upper metal line  613 . However, the dummy vias  605  and  609  are only connected to the lower metal lines  617  and  619 . Also, the dummy via  607  connects to neither the upper metal lines  611  and  613  nor the lower lines  615 ,  617 , 619 . Accordingly, the dummy vias can be designed to be connected to the lower metal line, or connected to neither the upper metal line nor the lower metal line. 
         [0022]      FIG. 5  is an example for a cross section view of the image sensor structure shown in  FIG. 3 . The cross section view shown in  FIG. 5  corresponds to the cross section line BB′ shown in  FIG. 3 . 
         [0023]    As shown in  FIG. 5 , a plurality of dummy contacts  501 ,  503 , and  505  are provided between the lower metal lines  509 - 515  and the conductive region  517  (diffusion region in this embodiment), and the dummy contacts  501 ,  503 , and  505  are only connected to lower metal lines  509 - 513  but not connected to the conductive region  517 . Please note that the device  507  shown in  FIG. 5  is a contact rather than a dummy contact. Accordingly, the lower metal lines  509 - 515  are not electrically connected to the conductive region  517  via dummy contacts  501 - 505 . In the structure shown in  FIG. 5 , the desired optical signal L can be reflected by the dummy contact  503  to enter the pixel  519 , but the neighbor optical signal NL will be blocked by the dummy contacts  501 ,  503  and  505 . Thus, the problem disclosed in prior art can be solved. 
         [0024]    Besides the structure shown in  FIG. 5 , the distribution of the dummy contacts can be as shown in  FIG. 6 . In the structure shown in  FIG. 6 , the contact  621  is connected between the lower metal line  617  and the conductive region  623  (diffusion region in this embodiment). Also, the dummy contacts  625  and  627  are still connected to the lower metal line  619 . However, the dummy contact  633  is only connected to the conductive region  631 . Also, the dummy contact  629  connects to neither the lower metal lines  615 ,  617 ,  619  nor the conductive region  631 . Accordingly, the dummy vias can be designed to be only connected to the conductive region, or connected to neither the lower metal line nor the conductive region. Please note that the structure shown in  FIG. 6  also indicates that the dummy vias and the dummy contacts can be jointly utilized in the image sensor structure. 
         [0025]    The dummy contact can be extended to a dummy contact side wall, and the dummy via can be extended to a dummy via side wall.  FIG. 7  is a top view diagram illustrating an image sensor structure according to another embodiment of the present application. As shown in  FIG. 7 , a dummy contact and a contact can be combined to form a dummy contact side wall such as the dummy contact side wall  705 . Also, two dummy vias can be combined to form a dummy via side wall such as the dummy via side walls  707  and  709 . Additionally, two dummy contacts can be combined to form a dummy contact side wall such as the dummy contact side walls  701  and  703 . Via the structure shown in  FIG. 7 , the function of the dummy contacts or vias can also be reached. 
         [0026]    According to above-mentioned embodiments, dummy vias and dummy contacts can be provided at suitable locations to avoid undesired neighbor optical signals entering pixels. Also, the desired optical signal can be reflected to the pixel. Therefore, the issue described in the prior art can be improved. 
         [0027]    Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.