Abstract:
An image sensor and a method for manufacturing the sensor are provided for reducing loss of light reflected from photodiodes, and thus, improving light efficiency. The method of manufacturing an image sensor can include providing a semiconductor substrate having a photodiode; and then forming a reflective film frame on the photodiode, the reflective film frame having sidewalls that are inclined with respect to the uppermost surface of the photodiode; and then forming an opening over the surface of the reflective film frame and corresponding to the photodiode by forming a reflective film on the sidewalls of the reflective film frame.

Description:
[0001]    The present application claims priority under 35 U.S.C. 119 to Korean Patent Application No. 10-2007-0136247 (filed on Dec. 24, 2007), which is hereby incorporated by reference in its entirety. 
       BACKGROUND 
       [0002]    An image sensor is a semiconductor device which converts an optical image into an electrical signal. The image sensor may be classified generally into a charge coupled device (CCD) image sensor and a complementary metal oxide semiconductor (CMOS) image sensor. The CMOS image sensor may include a photodiode for sensing illuminated light and a CMOS logic circuit for processing the detected light into an electrical signal to produce data. 
         [0003]    As the amount of light received by the photodiode becomes larger, the image sensor has more increased photosensitivity. The photosensitivity can be improved by increasing a fill factor representing a ratio of an area of the photodiode to an entire area of the image sensor, or by changing a path of light incident on an area except the photodiode to focus the light on the photodiode. As a representative example of a light focusing technology, a micro lens (generally, a convex micro lens) may be formed on and/or over the photodiode using a highly light-transmissive material. The micro lens refracts incident light to illuminate a larger amount of light on and/or over the photodiode. In this case, light parallel to an optical axis of the micro lens is refracted by the micro lens, and a focus is formed at a specific position on the optical axis. 
         [0004]    Further, in the CMOS image sensor, a portion of the light incident on the photodiode may be reflected by the photodiode, thereby reducing the light focusing efficiency. Accordingly, there is a disadvantage of reducing the photosensitivity of the image sensor. Thus, a reflective film may be formed above the side surface of the photodiode to reduce loss of the reflected light as disclosed in Korean Patent Application No. 10-2005-0134399, filed by the present applicant. 
         [0005]    As illustrated in example  FIG. 1 , a CMOS image sensor may include photodiode  10  and reflective film  12  formed above and parallel to photodiode  10 . By this configuration, it is possible to partially prevent loss of light reflected from photodiode  10 . Meaning, the CMOS image sensor illustrated in example  FIG. 1  may exhibit high light efficiency since light reflected from photodiode  10  is reflected by reflective film  12  to photodiode  10 . However, a large amount of the reflected light is lost out of photodiode  10 . 
       SUMMARY 
       [0006]    Embodiments relate to an image sensor and a method for manufacturing the sensor having improved light focusing efficiency. 
         [0007]    Embodiments relate to an image sensor and a method for manufacturing the sensor that is capable of preventing loss of light by returning light reflected from photodiodes to the photodiodes. 
         [0008]    Embodiments relate to a method of manufacturing an image sensor that can include at least one of the following steps: forming an insulating film on and/or over a semiconductor substrate having a plurality of photodiodes; and then forming a hard mask pattern corresponding to the photodiodes on and/or over the insulating film; and then forming reflective film frames having inclined sidewalls by wet etching the insulating film using the hard mask pattern as an etching mask; and then removing the hard mask pattern; and then forming a reflective film layer on and/or over an entire surface of the semiconductor substrate to cover the reflective film frames; and then forming reflective films having an opening positioned above the photodiodes to receive light by selectively removing the reflective film layer through a photolithography process. 
         [0009]    Embodiments relate to an image sensor that can include at least one of the following: a plurality of photodiodes formed on and/or over a semiconductor substrate; reflective film frames which have a width decreasing from bottom to top and are formed on and/or over the photodiodes; and reflective films which cover the reflective film frames and have openings to receive light. 
         [0010]    Embodiments relate to a method that can include at least one of the following steps: providing a semiconductor substrate having a photodiode; and then forming a reflective film frame on the photodiode, the reflective film frame having sidewalls that are inclined with respect to the uppermost surface of the photodiode; and then forming an opening over the surface of the reflective film frame and corresponding to the photodiode by forming a reflective film on the sidewalls of the reflective film frame. 
         [0011]    In the image sensor and the method of manufacturing the same according to the present invention, the reflective films can be formed to be inclined and bent on and/or over the respective photodiodes, thereby returning light reflected from the photodiodes to the photodiodes to a maximum extent. Thus, there is an effect of reducing loss of light reflected from the photodiodes and improving light efficiency. 
     
    
     
       DRAWINGS 
         [0012]    Example  FIG. 1  illustrates an enlarged view of a portion including a photodiode in a conventional CMOS image sensor; 
           [0013]    Example  FIGS. 2 to 4  illustrate an image sensor and a method of manufacturing the image sensor, in accordance with embodiments. 
       
    
    
     DESCRIPTION 
       [0014]    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. 
         [0015]    As illustrated in example  FIG. 2 , an image sensor in accordance with embodiments can include a plurality of photodiodes  102  are formed in semiconductor substrate  100  and serve to sense light to produce charges according to the amount of incident light. The image sensor, which can serve as a light sensing device, may employ a plurality of photogates instead of photodiodes  102 . Further, although photodiodes  102  are formed in semiconductor substrate  100 , the image sensor in accordance with embodiments is not limited thereto, and thus, can be disposed on and/or over semiconductor substrate  100 . A plurality of reflective film frames  104  have a width decreasing from bottom to top, i.e., substantially conical-shaped, can be used to form reflective films  106  as will be described later. Reflective film frames  104  can be formed on and/or over photodiodes  102 , respectively. Reflective films  106  can be composed of a metal material and can cover reflective film frames  104  and have openings  107  for receiving light. The size of openings  107  can vary in accordance with the size of photodiodes  102 . In accordance with embodiments, openings  107  can occupy between 70 to 90% of the uppermost surface area of photodiodes  102 . 
         [0016]    The image sensor in accordance with embodiments can also include interlayer insulating film  108 , protective film  110 , a plurality number of color filter layers  112 , planarization layer  114  and a plurality of micro lenses  116  corresponding to a respective photodiode  102 . The image sensor in accordance with embodiments is not limited to such a structure and can include any structure so long as reflective films  106  and reflective film frames  104  are respectively disposed on and/or over photodiodes  102  to have a structure to receive light into photodiodes  102 . Meaning, interlayer insulating film  108 , protective film  110 , color filter layers  112 , planarization layer  114  and micro lenses  116  can be configured differently from the manner illustrated in example  FIG. 2 . 
         [0017]    The respective layers are explained as follows. Interlayer insulating film  108  can be formed on and/or over semiconductor substrate  100  including reflective films  106 . Protective film  110  can be formed on and/or over interlayer insulating film  108  to protect the device from moisture and scratching. Color filter layers  112  can be formed on and/or over protective film  110  at specific intervals. Color filter layers  112  can serve to pass red (R), green (G), and blue (B) light in a specific wavelength band therethrough, respectively. Planarization layer  114  can be formed on and/or over the entire surface of the semiconductor substrate  100  including respective color filter layers  112  and serve to adjust a focal length on and/or over color filter layers  112  and to ensure flatness for forming a lens layer. Micro lenses  116  can be formed having a convex shape of a specific curvature on and/or over planarization layer  114  and can correspond to the respective photodiodes  102 . Micro lenses  116  can serve to concentrate a larger amount of light on and/or over photodiodes  102  through color filter layers  112  according to the wavelength when natural light is illuminated. The curvature and height of micro lenses  116  can be determined with regard to various factors such as a focus of concentrated light. 
         [0018]    As illustrated in example  FIGS. 2 and 3 , light  50  which is projected from a light source onto the image sensor in accordance with embodiments can be collected in micro lenses  116 . The collected light passes through planarization layer  114  and is filtered through color filter layers  112 . Then, the light passes through protective film  110  and interlayer insulating film  108  and reaches photodiodes  102 . Light  105  reflected from photodiodes  102  can return to photodiodes  102  after being reflected by reflective films  106 . 
         [0019]    Hereinafter, a manufacturing method, configuration and operation of the image sensor in accordance with embodiments will be described with reference to the accompanying drawings. 
         [0020]    As illustrated in example  FIG. 4A , a plurality of photodiodes  102  can be formed in semiconductor substrate  100 . Photodiodes  102  can alternatively be formed on and/or over semiconductor substrate  100 . Insulating film  104 A can then be formed on and/or over semiconductor substrate  100  including photodiodes  102 . Insulating film  104 A can be formed of an oxide film. 
         [0021]    As illustrated in example  FIGS. 4B to 4D , a hard mask pattern corresponding to photodiodes  102  can then be formed on and/or over insulating film  104 A as follows. Layer  200  for hard mask pattern  200 A can be formed on and/or over insulating film  104 A. Layer  200  for hard mask pattern  200 A can be made of silicon nitride (SiN). Photoresist film pattern  300  can then be formed on and/or over layer  200  to expose a region of photodiodes  102 . Hard mask pattern  200 A can then be formed through a photolithography process using photoresist film pattern  300 . When hard mask pattern  200 A has been formed as described above, photoresist film pattern  300  can be removed by ashing. 
         [0022]    As illustrated in example  FIGS. 4E and 4F , insulating film  104 A can then be wet-etched using hard mask pattern  200 A as an etching mask to form reflective film frames  104  having a width decreasing from bottom to top. The wet etching for forming reflective film frames  104  can be performed at a temperature of 80˜160° C. using a phosphoric acid solution of 10 to 90%. When reflective film frames  104  have been formed, hard mask pattern  200 A can be removed. 
         [0023]    As illustrated in example  FIG. 4G , reflective film layer  106 A can then be formed on and/or over entire surface of the semiconductor substrate  100  to cover the reflective film frames  104 . Reflective film layer  106 A can be made of a metal material and can be formed by any metal film deposition method for forming a metal film used in a process of manufacturing a semiconductor device. Preferably, reflective film layer  106 A can be formed by a chemical vapor deposition (CVD) method or a physical vapor deposition (PVD) method. 
         [0024]    As illustrated in example  FIG. 4H , photoresist film pattern  400  for forming reflective films  106  can then be formed on and/or over reflective film layer  106 A. Reflective film layer  106 A can then be selectively removed by a photolithography process using photoresist film pattern  400  as an etching mask, thereby forming reflective films  106  having openings positioned above photodiodes  102  to receive light. When reflective films  106  have been formed, photoresist film pattern  400  can then be removed by ashing. Since reflective film frames  104  are formed by wet etching having a conical shape with bent sidewalls inclined relative to the upper most surface of photodiodes  102  and/or substrate  100 , reflective films  106  can also have a shape conforming or otherwise corresponding to the shape of the sidewalls of reflective film frames  104 . 
         [0025]    As illustrated in example  FIGS. 4A to 4H , after reflective films  106  are formed, the image sensor can be completed by a method of manufacturing an image sensor. For example, in a case where the image sensor is manufactured as illustrated in example  FIG. 2 , the method of manufacturing an image sensor is explained as follows. Interlayer insulating film  108  can be formed on and/or over semiconductor substrate  100  including reflective films  106 . After interlayer insulating film  108  is formed, protective film  110  can then be formed on and/or over interlayer insulating film  108 . After protective film  110  is formed, a plurality of color filter layers  112  can then be formed on and/or over protective film  110  at specific intervals. For example, red, green and blue color filter layers  112  can be formed to filter light according to the wavelength band by performing a coating and patterning process on and/or over protective film  110  using dyeable resist. After color filter layers  112  are formed, planarization layer  114  can then be formed on and/or over entire surface of color filter layers  112 . After planarization layer  114  is formed, micro lenses  116  can be formed on and/or over planarization layer  114  corresponding to photodiodes  102 . There are various methods for forming micro lenses  116 . For example, a material layer for micro lenses, such as resist or SiON, is deposited on and/or over planarization layer  114 , and the deposited material layer for micro lenses is selectively patterned and reflowed corresponding to photodiodes  102 , thereby forming micro lenses  116 . For example, as illustrated in example  FIG. 2 , micro lenses  116  can be formed in a hemispherical shape. In this case, micro lenses  116  can be formed to have an optimal size, thickness and radius of curvature, which are determined according to the size, position and shape of a unit pixel, the thickness of light sensing devices  102 , the height, position and size of a light blocking layer, and the like. 
         [0026]    Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.