Abstract:
An image sensor and a method for fabricating the same having enhanced sensivity. The image sensor enhances sensitivity and minimizes optical loss by isolating color filters from each other using a metal that has superior light reflection properties while having no effect on the color filters during deposition of the metal.

Description:
The present application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2007-0090947 (filed on Sep. 7, 2007), which is hereby incorporated by reference in its entirety. 
     BACKGROUND 
     Image sensors are devices for converting one or two dimensional optical imformation (e.g., optical image) into an electrical signal. Image sensors may be classified into complementary metal-oxide-semiconductor (CMOS) image sensors and charge coupled devices (CCD) image sensors. CCD image sensors exhibit superior photo-sensitivity and noise properties as compared to CMOS image sensors. CCD image sensors, however, are disadvantageous in view of the difficulty obtaining high-integration and also due to its high power consumption. On the other hand, CMOS image sensors (CIS) are advantageous in that they involve simple processes, are suitability for highly integrated devices and exhibit low power consumption. 
     Accordingly, the recent rapid progress in semiconductor device fabrication techniques has brought about great improvement in CIS fabrication techniques and properties. As a result, active research is being made on CIS. In CIS research, sensitivity improvement is the most important reaserch subject. In order to enhance sensitivity, it is important to maximize light absorption while minimizing light loss. To realize sensitivity improvement, various factors including the shape of microlenses, the thicknesses of dielectrics and sensitivity of photodiodes must be taken into consideration. 
     Since general techniques employ color filters made of photoresist materials, they are disadvantages since metals to prevent optical loss cannot be directly deposited on the color filters. Accordingly, there is a limitation in improving sensitivity by isolating color filters from each other. 
     SUMMARY 
     Embodiments relate to an image sensor and a method for fabricating the same with enhanced sensitivity. 
     Embodiments relate to an image sensor and a method for fabricating the same that is suitable for reducing optical loss for the purpose of enhancing sensivity. 
     Embodiments relate to an image sensor and a method for fabricating the same that enhances sensivity and minimizing optical loss by isolating color filters from each other using a metal that has superior reflection properties, while having no effect on the color filters. 
     Embodiments relate to an image sensor that may include at least one of the following: a wafer; a plurality of color filters formed on and/or over the wafer; and a plurality of metal film patterns formed between the color filters to isolate the color filters from each other. In accordance with embodiments, the metal film patterns should be composed of a material which exhibits total light reflection. In accordance with embodiments, the image sensor may further include a dielectric layer contacting the metal film patterns. 
     Embodiments relate to an image sensor that may include at least one of the following: a wafer; first color filters uniformly spaced apart from each other on and/or over the wafer; a dielectric layer formed on and/or over the entire surface of the wafer including the first color filters; metal film patterns formed on and/or over sidewalls of the dielectric layer; and second color filters interposed between the metal film patterns. In accordance with embodiments, the metal films patterns are composed of a material that exhibits total light reflection. In accordance with embodiments, the metal film patterns are composed of at least one of tantalum (Ta) and titamium (Ti). In accordance with embodiments, the second color filters are one of green color filters and red color filters. In accordance with embodiments, the dielectric layer is composed of a low temperature oxide film. 
     Embodiments relate to a method for fabricating an image sensor that may include at least one of the following steps: forming first color filters on and/or over a wafer; and then forming metal film patterns on and/or over sidewalls of the first color filters; and then forming second color filters such that the respective second color filters are in direct contact with the metal film patterns. In accordance with embodiments, the step of forming the metal film patterns may include at least one of: depositing a dielectric layer on and/or over the entire surface of the wafer including the first color filters; and then depositing a metal film exhibiting total light reflection on and/or over the dielectric layer; and then removing a portion of the metal film provided in a region other than the sidewalls of the dielectric layer. In accordance with embodiments, the dielectric layer is composed of a low temperature oxide film and the metal film is deposited using physical vapor deposition (PVD). In accordance with embodiments, the metal films may be partially removed using blanket etching. 
     Embodiments relate to a method for fabricating an image sensor that may include at least one of the following steps: forming first color filters on and/or over a wafer such that the first color filters are uniformly spaced apart from each other; and then forming a dielectric layer on and/or over the entire surface of the wafer including the first color filters; and then forming metal film patterns exhibiting total light reflection on and/or over sidewalls of the dielectric layer; and then forming second color filters between the metal film patterns. In accordance with embodiments, the step of forming the metal films may include one of the following: depositing a metal exhibiting total reflection in a serrated form on and/or over the dielectric layer; and then removing the metal deposited in a region other than the inside walls of the grooves in the dielectric layer. In accordance with embodiments, the step of forming the dielectric layer may include depositing a low temperature oxide film on and/or over the entire surface of the wafer including the first color filters. In accordance with embodiments, the metal film patterns are composed of a material which exhibits total light reflection. In accordance with embodiments, the metal film patterns are composed of at least one of tantalum (Ta) and titamium (Ti). In accordance with embodiments, the step of forming the first color filters includes forming blue color filters spaced apart by a predetermined distance on and/or over the wafer. 
     Embodiments relate to a method that may include at least one of the following steps: forming a plurality of first color filters spaced apart over a wafer; and then forming a low temperature oxide layer over the entire surface of the wafer including the first color filters; forming film patterns which exhibits total reflection of light in spaces between respective first color filters and on sidewalls of the low temperature oxide layer; and then forming second color filters and third color filters in the spaces between respective first color filters and contacting the metal film patterns such that the second color filters and the third color filters are isolated from the first color filters using the film patterns. 
    
    
     
       DRAWINGS 
         FIG. 1  illustrates a process of forming blue color filters, in accordance with embodiments. 
         FIG. 2  illustrates a process of forming a dielectric layer, in accordance with embodiments. 
         FIG. 3  illustrates a process of depositing a metal layer, in accordance with embodiments. 
         FIG. 4  illustrates a process of forming a metal film pattern to isolate color filters, in accordance with embodiments. 
         FIG. 5  illustrates a process of forming green color filters and/or red color filters, in accordance with embodiments. 
       Example  FIG. 6  illustrates a phenomenon in which light incident upon the CIS image sensor in accordance with embodiments is totally reflected by a metal film. 
     
    
    
     DESCRIPTION 
     Hereinafter, configurations and operations according to embodiments will be described in detail with reference to the accompanying drawings. Although the configurations and functions of embodiments are illustrated in the accompanying drawings, in conjunction with at least one embodiment, and described with reference to the accompanying drawings and the embodiment, the technical idea of embodiments and the important configurations and functions thereof are not limited thereto. 
     In accordance with embodiments, in order to isolate color filters from each other, a metal film exhibiting total light reflection is formed between the color filters. Prior to forming the metal film, in order to prevent color filters from being damaged, a dielectric layer isolating the color filters from the metal film is formed. As a result, a key aspect of embodiments is to minimize optical loss by isolating color filters from each other using a multi-layered structure including a dielectric layer and a metal film. 
     As illustrated in example  FIG. 1 , color filters  10  (e.g., blue color filters) are formed spaced apart on and/or over a wafer. The wafer may include photodiodes, metal lines and other various films and is to be understood as having the configuration of a general image sensor. Blue color filters  10  are spaced apart from one another by a predetermined distance, such that other color filters, e.g., green color filters and/or red color filter are interposed between blue color filters  10 . Meaning, identical color filters are foomed such that they are not adjacent to each other. When seen from the cross-section of a substrate, blue color filters  10  are uniformly spaced, while when seen from the top side of the substrate, blue color filters  10  are in the form of a lattice pattern. 
     After blue color filters  10  are uniformly spaced, metal films are formed on and/or over sidewalls of blue color filters  10  to isolate blue color filters  10  from each other. The metal films may be formed by depositing a metal exhibiting total light reflection using a method selected from physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD), electroplating and electrolysis plating. However, when taking into consideration the fact that color filters are made of phororesists, embodiments preferably uses PVD to deposite the metal films. Since PVD may cause damage to the color filters, the method in accordance with embodiments can avoid directly depositing the metal film on and/or over the color filters and allow for forming dielectric layer  20  as a buffer film prior to forming the metal films. As illustrated in example  FIG. 2 , after blue color filters ( 10 ) are formed, dielectric layer  20  is formed on and/or over the entire surface of the wafer including blue color filters  10 . Since blue color filters  10  are uniformly spaced apart from each other, dielectric layer  20  has a serrated form. 
     Dielectric layer  20  is preferably made of a low temperature oxide. The low temperature oxide film is formed at a temperature of about 180° C. For reference, blue color filters  10  made of photoresists melt at about 200° C. Accordingly, the formation of the low temperature oxide film has no effect on blue color filters  10 . In particular, dielectric layer  10 , i.e., low temperature oxide film, prevents blue color filters  10  from being damaged upon sputtering to deposite the metal films. 
     As illustrated in example  FIG. 3 , a metal layer exhibiting total light reflection is deposited on and/or over the serrated form of dielectric layer  20 . The metal layer represented by a shade depends upon the shape of dielectric layer  20 , and thus, also takes a serrated form. The deposited metal may be a metal exhibiting total light reflection. Such a metal may be one of tantalum (Ta) and titanium (Ti). 
     As illustrated in example  FIG. 4 , the serrated metal layer is partially removed to form metal film patterns  30  that isolate the color filters from each other. Meaning, the metal deposited in a region other than the sidewalls of dielectric layer  20  is removed. More specifically, the metal layer formed on and/or over the uppermost surface of dielectric layer  20  and blue color filters  10  and on and/or over the bottommost surface of dielectric layer  20  is removed. Here, the partial removal of the metal layer is carried out using blanket etching. Furthermore, in accordance with embodiments, it is preferable to completely remove the metal without leaving any residue. As a result, metal film patterns  30  which exhibit total light reflection remain on and/or over sidewalls of dielectric layer  20 . 
     As illustrated in example  FIG. 5 , green color filters  40  and/or red color filters  50  are formed in spaces between adjacent blue color filters  10  such that they indirectly contact respective blue color filters  40 . As a result, green color filters  40  and/or red color filters  50  are formed in grooves of the serrated form provided by dielectric  20 , in particular, between metal film patterns  30  formed on the sidewalls of dielectric layer  20 . The CIS image sensor in accordance with embodiments includes a plurality of color filters  10 ,  40  and  50  alternately formed on and/or over a wafer, and metal film patterns  30  formed between color filters  10 ,  40  and  50  to isolate color filters  10 ,  40  and  50  form each other. 
     In accordance with embodiments, one color filter selected from three types of color filters  10 ,  40  and  50  is first formed on and/or over a wafer. Metal film patterns are then formed and the remaining two color filters are then formed at both sides of the formed color filter, respectively. For example, blue color filters  10  are formed on and/or over a wafer, green color filter  40  is formed at one side of blue color filters ( 10 ) and red color filter  50  is formed at the other side thereof. Metal film patterns  30  are formed between color filters  10 ,  40  and  50 . In order to prevent metal film patterns  30  from causing damage to blue color filters  10 , dielectric layer  20  is formed on and/or over blue color filters  10  prior to forming metal film patterns  30 . Accordingly, dielectric layer  20  acts as a buffer film to isolate from the metal film color filters  10 ,  40  and  50 , and particularly, any color filter first formed on and/or over the wafer. Dielectric layer  20  is formed in a serrated form on and/or over the entire surface including blue color filters  10 . The serrated form is caused by blue color filters  10  being spaced apart from each other by a predetermined distance. Accordingly, metal film patterns  30  are formed on and/or over sidewalls of dielectric layer  20 . In addition, other than previously formed blue color filters  10 , green color filters  40  and/or red color filters  50  are formed between adjacent metal film patterns  30  in the spaces or grooves between color filters  10 . 
     As illustrated in example  FIG. 6 , illustrated is a phenomenon in which light incident upon the CIS image sensor is totally reflected in a downward direction by metal film patterns  30 . Since metal film patterns  30  isolate color filters  10 ,  40  and  50  from each other, incident light is totally reflected by metal film patterns  30  and collected on a corresponding photodiode, thereby minimizing optical loss. As a result, the image sensor can exhibit enhanced sensitivity. 
     The method in accordance with embodiments requires a minimized process to deposit the metal film and induces total reflection using metal film patterns, thus enabling considerable enhancement in the sensitivity of the image sensor without negatively affecting an overall process. 
     Although embodiments have been described herein, 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.