Patent Publication Number: US-7709871-B2

Title: CMOS image sensor and method for manufacturing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a divisional of U.S. application Ser. No. 11/528,077, filed Sep. 26, 2006 now U.S. Pat. No. 7,488,616, which claims the benefit under 35 U.S.C. §119 of Korean Patent Application No. 10-2005-0090265, filed Sep. 28, 2005, which are hereby incorporated by reference in their entirety. 

   FIELD OF THE INVENTION 
   The present invention relates to a CMOS image sensor and a method for manufacturing the same. 
   BACKGROUND OF THE INVENTION 
   In general, an image sensor is a semiconductor device that converts an optical image into an electrical signal. The image sensors are generally classified into charge coupled devices (CCDs) and complementary metal oxide silicon (CMOS) image sensors (CISs). 
   The CIS includes a photodiode for sensing an irradiated light and a CMOS logic circuit for processing the sensed light into an electric signal for data. As the amount of light in the photodiode increases, the photosensitivity of the image sensor improves. 
   To increase the photosensitivity, one technique is to increase a fill factor (a ratio of a photodiode area to an entire area of the image sensor). Another is a technique in which the path of light incident into a region other than a photodiode is changed to focus the light on the photodiode. 
   A typical example of the focusing technology includes a microlens formation. In the microlens formation, a convex microlens is formed of an excellent light transmission material on the photodiode such that more incident light can be directed onto the photodiode region by refracting the incident light. 
   In this case, the light parallel to an optical axis of the microlens is refracted through the microlens, and thus the focus of the microlens is formed at a predetermined position of the optical axis. 
   Typically, a CIS is classified according to the number of the transistors in a pixel. For example, the CIS can be classified as a 3T, 4T, or 5T type. The 3T includes one photodiode and three transistors. The 4T includes one photodiode and four transistors. 
   Hereinafter, a related art CIS will be described with reference to  FIG. 1 . 
     FIG. 1  is a sectional view of the related art CIS. 
   As illustrated in  FIG. 1 , a photodiode  12 , an interlayer insulation layer  13 , and a color filter layer  14 , and a planarization layer  15  are sequentially formed on a substrate  11 . Then, a microlens  16  is formed on the planarization layer  15 . 
   However, the related art CIS has following problems. 
   For example, as illustrated in  FIG. 1 , incident light in tilt, which is not parallel to an optical axis of the microlens, included in light incident into the color filter  14  through the microlens  16  is induced into the photodiode  12  of another pixel and not the photodiode corresponding to the color filter. Thus, crosstalk occurs such that light becomes mixed and light sensitivity decreases. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention is directed to a CIS and a method for manufacturing the same that addresses and/or substantially obviates one or more problems, limitations, and/or disadvantages of the related art. 
   An object of the present invention is to provide a CIS without crosstalk caused by light incident to a color filter through a microlens that is incident to an irrelevant photodiode and a method for manufacturing the same. 
   Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
   To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided a CIS including: an interlayer insulation layer formed on a substrate having a photodiode and a transistor formed thereon; a plurality of color filters formed on the interlayer insulation layer and spaced a predetermined interval apart from each other; a metal sidewall formed to fill the predetermined interval between the plurality of the color filters; and a microlens formed on each of the plurality of color filters. 
   In another aspect of the present invention, there is provided an CIS including: an interlayer insulation layer formed on a substrate having a photodiode and a transistor formed thereon; a first color filter formed on the interlayer insulation layer; metal sidewalls formed on both side surfaces of the first color filter; a second color filter formed at one side of the first color filter with the metal sidewall interposed therebetween; a third color filter formed at another side of the first color filter with the metal sidewall interposed therebetween; and microlenses formed on the first, second, and third color filters. 
   In a further another aspect of the present invention, there is provided a method for manufacturing a CIS, the method including: forming an interlayer insulation layer on a substrate having a photodiode and a transistor; forming a first color filter on the interlayer insulation layer; forming metal sidewalls on both sides of the first color filter; forming a second color filter on one side of the first color filter with the metal sidewall interposed between the first color filter and the second color filter; forming a third color filter on the other side of the first color filter with the metal sidewall interposed between the first color filter and the third color filter; and forming a microlens on each of the first, second and third color filters. 
   In a still further another aspect of the present invention, there is provided a method for manufacturing a CIS, the method including: forming an interlayer insulation layer on a substrate having a photodiode and a transistor; forming green, red, and blue color filters on the interlayer insulation layer, the green, red, and blue color filters being spaced a predetermined interval apart from each other; forming metal sidewalls on the sides of each of the green, red, and blue color filters; forming a microlens on each of the green, red, and blue color filters. 
   It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings: 
       FIG. 1  is a sectional view of a related art CIS; 
       FIG. 2  is a sectional view of a CIS according to an embodiment of the present invention; 
       FIGS. 3 to 7  are sectional views illustrating a method for manufacturing a CIS according to a first embodiment of the present invention; and 
       FIGS. 8 to 10  are sectional views illustrating a method for manufacturing a CIS according to a second embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
     FIG. 2  is a sectional view of a CIS according to an embodiment of the present invention. 
   As illustrated in  FIG. 2 , a photodiode  102 , which is part of a unit pixel in the CIS, and various transistors (not shown) can be formed on a semiconductor substrate  101 . An interlayer insulation layer  103  can be formed on an entire surface of the semiconductor substrate  101 . Then, a color filter layer can be formed on the interlayer insulation layer  103 . The color filter layer can include a green color filter  104 , a red color filter  106 , and a blue color filter  107  that are spaced a predetermined interval apart from each other. 
   A metal sidewall  105  is formed between the color filters  104 ,  106 , and  107 . 
   In an embodiment, the metal sidewall  105  may be formed on both sides of the green color filter  103 . That is, since the green color filter  104  shares contact points with other color filters  106  and  107 , the metal sidewall  105  is formed between the color filters  104 ,  106 , and  107  when the metal sidewall  105  is formed on both sides of the green filter  104 . 
   In one embodiment, the metal sidewall  105  can be formed of opaque metal. In a specific embodiment, the metal sidewall  105  can be formed to a thickness of 500 to 2000 Å. Thus, light in tilt can be effectively total-reflected. When the thickness of the metal sidewall  105  is less than 500 Å, it may be difficult to perform a total reflection of light. When the metal sidewall  105  is more than 2000 Å, it may be difficult to collect light because the area that the color filters occupy decreases due to the increasing area occupied by the metal sidewall. 
   In one embodiment, the opaque metal may be one selected from the group consisting of Al, Cr, Mo, and Ti. When the opaque metal is formed to a thickness of 1000 Å, light in tilt can be effectively total-reflected. 
   That is, since the metal sidewall  105  is formed of an opaque metal layer between the color filters  104 ,  106 , and  107 , the light incident into the photodiode  102  through a microlens  109  is total-reflected. Therefore, the sensitivity of the image sensor increases by preventing crosstalk when the incident light in tilt is projected. 
   A planarization layer  108  can be formed on an entire surface of the semiconductor substrate  101  having the color filters  104 ,  106 , and  107 . The microlenses  109  can be formed corresponding to each of the color filters  104 ,  106 ,  107 . 
   Hereinafter, a method for manufacturing a CIS will be described according to a first embodiment of the present invention. 
     FIGS. 3 to 7  are sectional views illustrating a method for manufacturing a CIS according to the first embodiment of the present invention. 
   As illustrated in  FIG. 3 , a photodiode  102  and various transistors (not shown) can be formed on a semiconductor substrate  101  to constitute a unit pixel of the CIS. 
   Next, an interlayer insulation layer  103  can be formed on the semiconductor substrate  101  having the photodiode  102 . 
   In an embodiment, the interlayer insulation layer  103  can be formed in a multi-layer structure. In a specific embodiment, after forming one interlayer insulation layer, a light blocking layer (not shown) can be formed for preventing light from being incident into the photodiode  102 , and then another interlayer insulation layer can be formed thereon. 
   In one embodiment, the interlayer insulation layer  103  can be formed of an oxide such as an undoped silicate glass (USG). 
   Next, as illustrated in  FIG. 4 , a green photosensitive material can be applied on the interlayer insulation layer  103 , and then selectively patterned to form green color filters  104  spaced apart a predetermined interval. 
   Next, an opaque metal layer  105   a  (e.g., Al, Cr, Mo, Ti, etc.) can be formed on an entire surface of the semiconductor substrate  101  having the green color filter  104  to a thickness of 500 to 2000 Å. 
   Next, as illustrated in  FIG. 5 , a blanket etch process can be performed on the opaque metal layer  105   a  to form metal sidewalls  105  on both sides of the green color filters  104 . 
   That is, the metal sidewalls  105  can be formed on both sides of the green color filter  104 . Accordingly, because the green color filter  104  shares contact points with other color filters  106  and  107 , the metal sidewalls  105  are formed between the color filters  104 ,  106 , and  107  when the metal sidewalls  105  are formed on both sides of the green filter  104 . 
   Although the metal sidewall  105  is formed on both sides of the green color filter  104  in the first embodiment described above, the present invention is not limited to this. 
   As illustrated in  FIG. 6 , after a red photosensitive material is applied to an entire surface of the semiconductor substrate  101  having the metal sidewall  105  and green color filter  104 , it can be selectively patterned to form a red color filter  106  on a side of a green color filter  104 . 
   Next, a blue photosensitive material can be applied to an entire surface of the semiconductor substrate  101 . The blue photosensitive material can be selectively patterned using a photo and exposure process to form a blue color filter  107  on another side of the green color filter  104 . 
   Next, as illustrated in  FIG. 7 , a planarization layer  108  can be formed on an entire surface of the semiconductor substrate  101  having the color filters  104 ,  106 , and  107 . 
   Next, a microlens material layer can be applied on the planarization layer  108 , and then selectively patterned and reflowed to form a hemispherical microlens  109  to correspond to each of the color filters  104 ,  106 , and  107 . 
   In embodiments, an insulation layer such as an oxide layer or a photoresist may be used for the microlens material layer. 
   Additionally, the reflow process can use a hot plate or furnace. According to a contracting and heating method, the microlenses can have a different curvature. Concentration efficiency varies according to the curvature. 
   Next, ultraviolet rays can be irradiated on the microlens  109  for hardening. In one embodiment, a laser can be used to harden the microlens  109 . Since the microlens  109  is hardened, it maintains an optimal radius for curvature. 
   Although a planarization layer  108  is formed in the embodiments described above, microlenses  109  may be directly formed on each of the color filters  104 ,  106 , and  107  without forming the planarization layer  108 . 
   In the method for manufacturing the CIS according to the first embodiment of the present invention, since the metal sidewall  105  of an opaque metal layer is formed between the color filters  104 ,  106 , and  107 , the light incident into the photodiode  102  through the microlens  109  is total-reflected. Therefore, the sensitivity of the image sensor increases by preventing crosstalk from incident light in tilt. 
   A method for manufacturing a CIS according to a second embodiment of the present invention will be described. 
   The method for the second embodiment may incorporate elements of the method for the first embodiment described in various embodiments above. 
   Characteristics of the method of the second embodiment are as follows. 
   In the first embodiment, after forming the green color filter  104 , metal sidewalls  105  can be formed on both sides of the green color filter  104 . 
   In contrast, in the second embodiment, as illustrated in  FIG. 8 , the color filters  104 ,  106 , and  107  can first be formed in a predetermined interval T from each other. 
   Then, as illustrated in  FIG. 9 , a metal layer can be deposited on the semiconductor substrate  101  having the color filters  104 ,  106 , and  107  to fill the predetermined interval T. Then, a blanket etch or chemical mechanical polishing (CMP) process can be performed to form a metal sidewall  105  between the color filters  104 ,  106 , and  107 . 
   Next, as illustrated in  FIG. 10 , a planarization layer  108  and a microlens  109  can be sequentially formed on the color filters  104 ,  106 , and  107  having the interposed metal sidewall  105 . 
   In the method for the second embodiment, since the metal sidewall  105  of an opaque metal layer is formed between the color filters  104 ,  106 , and  107 , the light incident into the photodiode through a microlens is total-reflected. Therefore, the sensitivity of the image sensor increases by preventing crosstalk due to incident light in tilt. 
   It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.