Patent Publication Number: US-7898011-B2

Title: Image sensor having anti-reflection film for reducing crosstalk

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image sensor, and more particularly, to an image sensor with an anti-reflection film for preventing color crosstalk and a smear phenomenon and a method of manufacturing the same. 
     2. Description of the Related Art 
     An image sensor is a device which converts optical energy transmitted through each of red, green, and blue color filters into an electrical signal by using a photo diode and outputs the converted electrical signal by using a metal oxide semiconductor (MOS) transistor. 
       FIG. 1  shows a conventional image sensor. 
     Light transmitted through a micro lens  160  and each of red, green, and blue color filters  170 ,  171 , and  172  reflects from a silicon surface and has a path {circle around ( 1 )} or {circle around ( 2 )} so as to reflect again from an adjacent photodiode  120 , so that the light and a light having a path {circle around ( 3 )} generate crosstalk. In addition, light having a path {circle around ( 4 )} is mixed with an electrical signal of a photo diode, so that noises may occur. 
     Namely, the conventional image sensor has a problem in that light transmitted through a color filter may not be incident perpendicularly on a photodiode disposed below the color filter and may reflect from a metal wire line and be incident on an adjacent photodiode with light transmitted through an adjacent color filter. 
     In addition, light reflecting from the silicon surface may reflect again from the metal wire line disposed above the silicon surface and be incident on an adjacent photodiode, so that color crosstalk may be generated. In addition, the light may be incident on a transmitting pathway of an adjacent MOS transistor for transmitting a carrier generated from the photodiode and may generate an added carrier, so that the added carrier may be mixed with an electrical signal of a photodiode and cause noises. 
     In order to solve the aforementioned problem, a reflection film is formed in an interlayer insulating layer such that light reflecting from a silicon surface of a photodiode reflects from an upper reflection film and is incident on the photodiode in order to improve a light sensitivity. 
       FIG. 2  shows a conventional image sensor having a reflection film. 
     A reflection film  150  is formed between a photodiode  120  and a metal wiring layer. Therefore, light having the path {circle around ( 1 )} transmitted through the micro lens  160  and the color filter  170 ,  171 , or  172  reflects from a silicon surface and reflects again from the reflection film  150  so as to be incident on the photodiode, so that light efficiency increases. 
     However, light having the path {circle around ( 2 )} reflecting from the silicon surface may not reflect from the reflection film  150  and reflect from a metal wire line  140  so as to be incident on an adjacent photodiode  120 , so that the light and light having the path {circle around ( 3 )} may generate crosstalk. In addition, light having the path {circle around ( 4 )} may be mixed with an electrical signal of a photodiode, so that noises may occur. 
     In addition, since the reflection film  150  covers a portion of the photodiode  120 , an effective region of the photodiode  120  is reduced. Therefore, when light is not in focus like light having a path {circle around ( 5 )}, sensitivity may decrease 
     SUMMARY OF THE INVENTION 
     In order to solve the aforementioned problem, the present invention provides an image sensor having an anti-reflection film and a method of manufacturing the same capable of preventing light transmitted through a color filter from being incident on an adjacent photodiode and preventing light which is transmitted through a color filter and is normally incident on a corresponding photodiode but reflects from a silicon substrate and re-reflects from an upper metal layer from being incident on an adjacent photodiode so as not to generate an interference, so that it is possible to reduce color crosstalk and noises. 
     According to an aspect of the present invention, there is provided an image sensor including: a plurality of photodiodes formed in a semiconductor substrate at a predetermined interval; an interlayer insulating layer formed on the semiconductor substrate to cover the semiconductor substrate; an at least two anti-reflection film formed above the surrounding of the photodiode and in the interlayer insulating layer; and a plurality of metal wiring layers which are formed with a predetermined pattern in the interlayer insulating layer and include a plurality of metal wire lines. 
     According to another aspect of the present invention, there is provided a method of manufacturing an image sensor having an anti-reflection film including steps of: (a) forming a plurality of photodiodes in a semiconductor substrate at a predetermined interval; (b) forming an interlayer insulating layer to cover the semiconductor substrate in which a plurality of the photodiodes are formed; (c) forming the anti-reflection film above the surrounding of the formed photodiode and in the interlayer insulating layer; and (d) forming a plurality of metal wiring layers including a plurality of metal wire lines with a predetermined pattern in the formed interlayer insulating layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view showing a conventional image sensor; 
         FIG. 2  is a cross-sectional view showing a conventional image sensor having a reflection film; 
         FIG. 3  is a cross-sectional view showing an image sensor having a anti-reflection film according to the present invention; and 
         FIG. 4  is a top plan view showing a structure of an anti-reflection film of an image sensor having the anti-reflection film according to the present invention. 
     
    
    
     DESCRIPTION OF REFERENCE NUMERALS INDICATING PRIMARY ELEMENTS IN THE DRAWINGS 
     
         
         
           
               110 ,  210 : semiconductor substrate 
               120 , 220 : photodiode region 
               130 ,  230 : interlayer insulating layer 
               140 ,  240 : metal wire line 
               150 : reflection film 
               160 ,  260 : micro lens 
               170 ,  270 : green color filter region 
               171 ,  271 : red color filter region 
               172 ,  272 : blue color filter region 
               250 : anti-reflection film 
           
         
       
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the attached drawings. 
       FIG. 3  shows an image sensor having an anti-reflection film according to an embodiment of the present invention. The image sensor includes a semiconductor substrate  210 , a plurality of photodiodes  220 , an interlayer insulating layer  230 , at least two metal wiring layers  240 - 1 ,  240 - 2 , and at least two anti-reflection films  250 - 1 ,  250 - 2 . 
     A plurality of the photodiodes  220  is formed in the semiconductor substrate  210  at a predetermined interval down to a predetermined depth. The interlayer insulating layer  230  is formed on the semiconductor substrate  210  so as to cover the semiconductor substrate  210  in which a plurality of the photodiodes  220  are formed. At least one of the metal wiring layers  240 - 1 ,  240 - 2  includes a plurality of metal wire lines and is formed in the interlayer insulating layer  230  with a predetermined pattern. 
     The first anti-reflection film  250 - 1  is formed between the lowest metal wiring layer  240 - 1  and the semiconductor substrate  210 . The second anti-reflection film  250 - 2  is form between the lowest metal wiring layer  240 - 1  and the second metal wiring layer  240 - 2  located above the lowest metal wiring layer  240 - 1 . The anti-reflection films  250 - 1 ,  250 - 2  include at least one of poly silicon, amorphous silicon, tungsten (W), and TiN. 
     In addition, in terms of a size, a conventional reflection film is larger than the metal wire line. On the contrary, the anti-reflection films  250 - 1 ,  250 - 2  according to the present invention are smaller than the metal wire line. 
     Light path is described with reference to  FIG. 3 . 
     Even though light transmitted through a micro lens  260  and a red, green, or blue color filter  270 ,  271 , or  272  having a path {circle around ( 1 )} or {circle around ( 2 )} reflects from the silicon surface and re-reflects from the metal wire lines of the metal wiring layers  240 - 1 ,  240 - 2 , an intensity of the light is lessened by the anti-reflection films  250 - 1 ,  250 - 2  having high absorbance. Therefore, the light cannot be incident on an adjacent photodiode  220 . 
     In addition, although the light is incident on the photodiode  220 , the light has a small amount of optical energy, so that the crosstalk caused from the incident light and light having a path {circle around ( 3 )} can be removed. In addition, light having a path {circle around ( 4 )} is prevented from being incident into a transmission path of the MOS transistor. Therefore, an improved image quality can be obtained in comparison with a structure of the conventional image sensor. 
       FIG. 4  is a top plan view showing an image sensor having an anti-reflection film according to an embodiment of the present invention. The anti-reflection film is formed between a first metal wiring layer M 1  and a second metal wiring layer M 2  to surround a photodiode PD. 
     A method of manufacturing an image sensor having an anti-reflection film according to the present invention will be described. 
     Polysilicon gates and the photodiodes  220  are formed on the semiconductor substrate  210 , and the interlayer insulating layer  230  is deposited thereon. 
     Before the metal wiring layer  240  is formed, a material having high absorbance serving as the anti-reflection film  250  is formed in the interlayer insulating layer  230 . The anti-reflection film  250  may surround the photodiode  220  as shown in  FIG. 3 . The anti-reflection film  250  may be made of a material of polysilicon, amorphous silicon, tungsten (W), TiN, or the like. 
     Next, the metal wiring layer  240 , the color filters  270 ,  271 , and  272 , and the micro lenses  260  are formed, so that the image sensor capable of solving the color crosstalk problem can be manufactured. [ 271 , 272 , 273 → 270 , 271 , 272 ] 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims. 
     An image sensor having an anti-reflection film according to the present invention can reduce color crosstalk and noises in comparison with a conventional image sensor by using the anti-reflection film formed above the surrounding of a photodiode.