Patent Document

BACKGROUND OF INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a method for producing an image sensor, and an image sensor produced by the method, with improved imaging quality.  
         [0003]     2. Description of the Prior Art  
         [0004]     As with rapid development of digital image devices, digital image devices have become more popular than traditional analog image devices. However, in order to obtain better quality of digital images with higher resolution, improvement of the image sensor which is used for photoelectric conversion is necessary. In recent years, a solid-state image sensor has been miniaturized, with which a photosensor element is reduced and a drop of the sensitivity is caused.  
         [0005]     Please refer to  FIG. 1  showing a schematic diagram of a conventional digital image-capturing device  10 . The digital image-capturing device  10  comprises a lens  12  and an image sensor  20 . The image sensor  20  comprises a plurality of sensing units  30  each comprising a microlens  24 , a color filter  25  and a photosensor element  22 . When light progresses into the image-capturing device  10 , the light will pass through the lens  12  and project onto the plurality of sensing units  30  through the lens  12 . Each microlens  24  will collect the incident light onto the photosensor element  22  of the sensing unit  30 , after drawing out light with different spectrums by using the color filter  25 . For example, the blue color filter  25   b  is used for drawing out the light in consistent with blue light spectrum, and the green light filter  25   g  is used for drawing out the light in consistent with green light spectrum. Finally, the photosensor element  22  transforms the drawn light into an electrical signal. Generally speaking, the plurality of sensing units  30  are arranged in a regular manner called a Bayer pattern color filter array, as shown in  FIG. 2 . In  FIG. 2 , G, B, R respectively indicates sensing units  30  for sensing green light, blue light, and red light. An area formed by two green sensing units  30 , a blue sensing unit  30  and a red sensing unit  30  is called a pixel  11 . Human eyes have more sensitivity for green light than red and blue light, such that a 2:1:1 arrangement of green, blue, red sensing unit is used to be consistent with real image color. Each sensing unit  30  has a photosensor element  22  formed on a silicon substrate  16 . A transfer electrode  14  formed on the photosensor element  22  is used for transferring the generated electrical signal.  
         [0006]     The higher the image resolution is required, the smaller each pixel area is, and the smaller the area of the sensing unit is. Please refer to  FIG. 3  in conjunction with  FIG. 1 .  FIG. 3  shows a light passing through the sensing unit  30  located at the corner. Generally speaking, a light A progressing to the sensing unit  30  located at the center of the image sensor  20  can be completely sensed by the photosensor element  22 , but a light B progressing to the sensing unit  30  located at a corner of the image sensor  20  has a deviation so that the light B fails to exactly project onto the photosensor element  22 . As shown in  FIG. 3 , theoretically, the light B will pass green color filter  25   g  to draw out the green light constituent, and then be photo-electrically transformed to generate an electrical signal with the photosensor element  22   g . Actually, the large deviation angle of the light B causes the light B to pass through the green color filter  25   g  and the blue color filter  25   b , and is received by the photosensor element  22   b . Therefore, an error occurs due to inconsistent ratio of received light for a pixel at the corner, thereby causing a color shift effect and deterioration of sensing quality. The photosensor element  22  of the sensing unit  30  at the corner will receive less light due to a larger incident angle. Uneven light sensing of the image sensor  20  results in an inconsistent image quality.  
         [0007]     In order to overcome the above-mentioned problem, in U.S. Pat. No. 6,255,640, Endo et al. disclose a solid-state image sensing device having a specific curvature intra-layer color filter and an interlayer film for collecting the emitted light, and in U.S. Pat. No. 6,246,081 and No. 6,312,969, Abe discloses a solid-state image sensor having a light-impervious film formed on a sensor for blocking other light incident from other color filter layer. But such designations result in complicated processes, and are not proper for mass production. Under the trend of lowering the area of the sensing unit, Endo et al.&#39;s solid-state image sensing device is limited to curvature of the specific curvature intra-layer color filter and an interlayer film. A light-impervious film of Abe&#39;s solid-state image sensor cannot block incident light from adjacent pixels. Consequently, an improvement of the image sensor is needed.  
       SUMMARY OF INVENTION  
       [0008]     It is therefore a primary objective of the claimed invention to provide a solid-state image sensor for improving sensing quality and manufacturing method thereof, in order to solve the above-mentioned problems.  
         [0009]     According to the claimed invention, a method of forming a solid-state image sensor is provided. The method includes the steps of forming a plurality of photosensor elements on a substrate; forming a plurality of color filters on the plurality of photosensors; forming a light blocking member between adjacent color filters; and forming a plurality of microlenses on the plurality of color filters. Each photosensor corresponds to each color filter and each microlens is used for receiving an incident light of specific spectrum.  
         [0010]     These and other objectives of the claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0011]      FIG. 1  is a schematic diagram of a digital image-capturing device according to prior art.  
         [0012]      FIG. 2  is a diagram of a Bayer pattern color filter array.  
         [0013]      FIG. 3  shows a light passing through the sensing unit located at the corner.  
         [0014]      FIG. 4  shows a cross-sectional view of an image sensor according to the present invention.  
         [0015]      FIG. 5  shows a color filter and a light-impervious film of the image sensor shown in  FIG. 4   
         [0016]      FIG. 6  shows a cross-sectional view of an image sensor of another embodiment according to the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0017]     Please refer to  FIG. 4 , which shows a cross-sectional view of an image sensor  100  according to the present invention. The image sensor  100  comprises a plurality of sensing units arranged in a Bayer pattern color filter array shown in  FIG. 2 . For simplicity, only a green sensing unit  102   g  and a blue sensing unit  102   b  are drawn and labeled. Photosensor elements  122   b ,  122   g  formed on the silicon substrate  116  are used for performing photoelectrical transformation. An insulating layer  106  made of SiO 2  is formed on the substrate  116  by using a thermal oxidation process or a chemical vapor deposition (CVD). Each sensing unit  102   b ,  102   g  includes a transfer electrode (serving as a transfer transistor)  114   b ,  114   g  over the substrate  116 , (i.e. on the insulating layer  106 ) and respectively coupled to photosensor elements  122   b ,  122   g . The transfer electrodes  114   b ,  114   g  are used for transferring electrical signals from the photosensor elements  122   b ,  122   g . In addition, each sensing unit  102   b ,  102   g  contains a color filter  125   b ,  125   g  formed over the photosensor elements  122   b ,  122   g  and the transfer electrode  114   b ,  114   g . A light-shielding film  118  formed between the transfer electrodes  114   b ,  114   g  and the color filters  125   b ,  125   g  is used for isolating the transfer electrode  114   b ,  114   g  and the color filters  125   b ,  125   g . A light-impervious film  130  is formed between the adjacent color filters  125   b ,  125   g  by using a resist etch back process. Then microlenses  124   b ,  124   g  are respectively formed over the color filters  125   b ,  125   g . Notice that the light blocking member  130  can be a light-impervious film made of metal or chemical compound or other light-impervious material, and its height is higher than that of each color filter  125   b ,  125   g.    
         [0018]     Please refer to  FIG. 5 , which shows a color filter and a light blocking member of the image sensor  100  shown in  FIG. 4 . The letter G indicates a color filter  125   g  for green light, B indicates color filter  125   b  for sensing blue light, and R indicates a color filter  125   r  for sensing red light. Each color filter  125   b ,  125   r ,  125   g  comprises a light blocking member  130 .  
         [0019]     The operation of the image sensor  100  is described as follows. Suppose that a light C is emitted into the microlens  124   g  of the sensing unit  102   g , in order to collect light on the surface  132  of the sensing unit  122   g , i.e. the photosensor element  102 , the focal length of the microlens  124   g  is adjusted to proper position to make the incident light project onto the surface  132  of the photosensor element  122   g . As shown in  FIG. 4 , light C through the microlens  124   g  progresses into the green color filter  125   g , and then reflects by means of the light-shielding film  118  to progress into the photosensor element  122   g . Light D through the microlens  124   g  progresses into the green color filter  125   g , and cannot progress toward the photosensor element  122   b  of the adjacent sensing unit  102   b  due to block of the light blocking member  130 . In this way, the photosensor element  122   b  will not sense the green light. Meanwhile the light D will is reflected on the green photosensor element  122   g . Accordingly, the light blocking member  130  set between the color filters  125   b ,  125   g  can not only block light, but can also collect the light. Certainly, a height of the light blocking member  130  can be adjusted as the location of the sensing unit. For example, the height of the sensing unit at corner is higher than that of adjacent color filter  125   b ,  125   g , and even equals to a height of the microlens  124   b ,  124   g , so as to achieve better effect for light isolation.  
         [0020]     Please refer to  FIG. 6 , which shows a cross-sectional view of an image sensor  150  of another embodiment according to the present invention. Differing from the image sensor  100  shown in  FIG. 5 , the light blocking member  130  of the image sensor  150  is formed over the transfer electrode  114  and among the two color filters  125   b ,  125   g  and the two microlenses  124   b ,  124   g.    
         [0021]     The blue sensing unit  102   b  and green sensing unit  102   g  and corresponding elements therein are used to illustrate the present invention, but similar arrangement can be also used in the green sensing unit  102   g  and the red sensing unit  102   r  and corresponding elements therein.  
         [0022]     The present invention image sensor can be applied in a charge-coupled device or a CMOS image sensor.  
         [0023]     In contrast to the prior art, the present invention solid-image sensor provides a light blocking member between the adjacent color filters, which is used for blocking the drawn light with different spectrums from the adjacent color filter, so as to prevent the photosensor element from converting the different spectrum light, resulting in color offset. In addition, the light blocking member is also used for collecting light onto the photosensor element, so as to improve sensing effect of the photosensor element. Using the present invention solid-state image sensor can reduce color coupling effect, and improve the sensing effect of the photosensor element, due to the blocking and reflection of the light blocking member. In addition, the present invention image sensor with a light blocking member is not very complicated and is suitable for mass production.  
         [0024]     Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.

Technology Category: h