Patent Document

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a biochip, and more particularly, to a biochip having an image sensor with a back side illumination photodiode structure which collects light from the back side of a wafer in order to improve capability of sensing light emitted from reaction regions of a biochip. 
     2. Description of the Related Art 
     In general, a biochip is manufactured in a type in which reference samples constituted biological molecules such as DNAs, proteins and the likes are regularly arranged on a substrate made of a material such as glass, silicon and nylon. 
     Biochips are divided into a DNA chip, a protein chip, and so forth, depending upon the kind of reference samples to be arranged. Basically, a biochip uses biochemical reactions between reference samples and target samples which are fixed with respect to a substrate. Representative examples of the biochemical reactions between the reference samples and the target samples include a complementary binding of DNA bases and an antigen-antibody reaction. 
     For the most part, diagnosis by a biochip is implemented by detecting a degree to which a biochemical reaction occurs, through an optical procedure using an image sensor. The optical procedure generally uses a fluorescence or luminescence phenomenon. 
       FIG. 1  is a view illustrating the configuration of a conventional biochip having an image sensor with a front side illumination photodiode structure. 
     Referring to  FIG. 1 , a conventional biochip  100  having an image sensor with a front side illumination photodiode structure includes a biochip layer  100   a  and an image sensor layer  100   b.    
     The biochip layer  100   a  has a plurality of first reaction region  110   a , second reaction region  110   b  and third reaction region  110   c  which have shapes of grooves. The first, second and third reaction regions  110   a ,  110   b  and  110   c  respectively have target samples  111   a ,  111   b  and  111   c  in the upper portions thereof and reference samples  112   a ,  112   b  and  112   c  in the lower portions thereof. 
     The image sensor layer  110   b  has a plurality of first front side illumination photodiode  151   a  (PD 1 ), second front side illumination photodiode  151   b  (PD 2 ) and third front side illumination photodiode  151   c  (PD 3 ) which are formed in an epitaxial layer  150  of a wafer. 
     A plurality of stacked metal wiring lines  131  and  133  are formed in an interlayer dielectric  130  which is formed on the upper surface of the epitaxial layer  150 . 
     However, in the conventional biochip  100  having an image sensor with a front side illumination photodiode structure, light  120 , which is emitted depending upon degrees of biochemical reactions between the target samples  111   a ,  111   b  and  111   c  and the reference samples  112   a ,  112   b  and  112   c  of the plurality of first, second and third reaction regions  110   a ,  110   b  and  110   c , is likely to be absorbed by the metal wiring lines  131  and  132  which are formed over the plurality of first, second and third front side illumination photodiodes  151   a ,  151   b  and  151   c , as a result of which the light sensitivity of the plurality of first, second and third front side illumination photodiodes  151   a ,  151   b  and  151   c  may be degraded. 
     Meanwhile, in the manufacture of the biochip layer, a surface treatment technology is regarded important for the attachment of bio-materials. That is to say, in order to allow the bio-materials to be easily attached to a substrate, surface treatment is performed in such a way as to provide hydrophilicity or hydrophobicity. Such surface treatment is performed mainly using plasma. 
     In the conventional structure adopting the front side illumination (FSI), as the plasma is incident on the photodiodes during the surface treatment, the dark current of the photodiodes may be increased. Further, due to the fact that the biochip layer is formed on the interlayer dielectric, solutions, which are employed in the manufacture and reaction procedures of the biochip layer, may infiltrate into underlying circuits by passing through the interlayer dielectric. As a consequence, problems may be caused in that it is difficult to form the interlayer dielectric and limitations may exist in performing the surface treatment for the biochip layer and using reacting solutions, etc. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has been made in an effort to solve the problems occurring in the related art, and an object of the present invention is to provide a biochip having an image sensor with a back side illumination photodiode structure which can directly collect light with biochemical reaction information, emitted from a biochip layer, so as to improve light sensitivity, and can prevent the characteristics of circuits from deteriorating due to surface treatment conducted during a manufacturing procedure of the biochip layer and infiltration of a solution occurring during a biochemical reaction procedure. 
     In order to achieve the above object, according to one aspect of the present invention, there is provided a biochip having an image sensor with a back side illumination photodiode structure, including: a biochip layer; and an image sensor layer attached to one surface of the biochip layer and configured to sense light with biochemical reaction information, which is emitted from the biochip layer, wherein the image sensor layer includes a plurality of light sensing parts which receive the light directed toward a back side of a wafer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above objects, and other features and advantages of the present invention will become more apparent after a reading of the following detailed description taken in conjunction with the drawings, in which: 
         FIG. 1  is a view illustrating the configuration of a conventional biochip having an image sensor with a front side illumination photodiode structure; and 
         FIG. 2  is a view illustrating the configuration of a biochip having an image sensor with a back side illumination photodiode structure in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference will now be made in greater detail to a preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings. Wherever possible, the same reference numerals will be used throughout the drawings and the description to refer to the same or like parts. 
       FIG. 2  is a view illustrating the configuration of a biochip having an image sensor with a back side illumination photodiode structure in accordance with an embodiment of the present invention. 
     Referring to  FIG. 2 , a biochip  200  having an image sensor with a back side illumination photodiode structure in accordance with an embodiment of the present invention includes a biochip layer  200   a  and an image sensor layer  200   b.    
     The biochip layer  200   a  has a plurality of first reaction region  210   a , second reaction region  210   b  and third reaction region  210   c  which have shapes of grooves. 
     The first reaction region  210   a  has a target sample  211   a  in the upper portion thereof and a reference sample  212   a  in the lower portion thereof. Similarly, the second reaction region  210   b  has a target sample  211   b  in the upper portion thereof and a reference sample  212   b  in the lower portion thereof, and the third reaction region  210   c  has a target sample  211   c  in the upper portion thereof and a reference sample  212   c  in the lower portion thereof. 
     Hereafter, functions of the target sample  211   a  and the reference sample  212   a  of the first reaction region  210   a  will be mainly described in detail. 
     The target sample  211   a  may be used to include a luminescent material which emits light by itself when external illumination is blocked. A representative example of the luminescent material is luciferin. Luciferin becomes active luciferin when activated by ATP (adenosine tri-phosphate). As the active luciferin is oxdidated under the action of luciferase and becomes oxyluciferin, chemical energy is converted into light energy and light is produced. 
     Also, the target sample  211   a  may be used to include a fluorescent material which can generate light of a specified wavelength band by external illumination (not shown). The fluorescent material may be produced in the first reaction region  210   a  as a result of a reaction between the reference sample  212   a  and the target sample  211   a , or may be produced in such a manner that an optional fluorescent material such as GFP (green fluorescence protein) is left in the first reaction region  210   a  after a specified biochemical reaction is induced between the reference sample  212   a  and the target sample  211   a  by binding the optional fluorescent material with the target sample  211   a.    
     The reference sample  212   a  may include different materials depending upon which biochemical reaction is targeted. For example, if the biochemical reaction is an antigen-antibody reaction, the reference sample  212   a  may be an antigen, and if the biochemical reaction is a complementary binding of DNA bases, the reference sample  212   a  may be a gene which is genetically engineered to be capable of complementary binding. 
     The target sample  211   a  is selected depending upon the reference sample  212   a  which is determined according to the kind of the biochemical reaction. For example, if the reference sample  212   a  is an antigen, the target sample  211   a  may be blood, and the like, and if the reference sample  212   a  is a genetically engineered gene, the target sample  211   a  may be a user&#39;s gene, and the like. 
     The image sensor layer  200   b  has a configuration which is placed on the bottom surface of the biochip layer  200   a  and forms a back side illumination (BSI) image sensor. 
     The back side illumination (BSI) image sensor is formed by performing the same processes as the conventional front side illumination (FSI) image sensor and by finally overturning a processed wafer such that the resultantly obtained image sensor can directly collect light. 
     That is to say, when observed from the standpoint of the conventional front side illumination (FSI) image sensor, the back side illumination (BSI) image sensor according to the present invention collects light from the bottom portions of the photodiodes, that is, the bottom surface of the wafer. 
     The image sensor layer  200   b  has a plurality of first back side illumination photodiode  251   a  (PD 1 ), second back side illumination photodiode  251   b  (PD 2 ), and third back side illumination photodiode  251   c  (PD 3 ) which are formed in an epitaxial layer  250  of the wafer. 
     The first back side illumination photodiode  251   a  (PD 1 ) senses light  220  which is emitted from the first reaction region  210   a  depending upon a degree of a biochemical reaction between the target sample  211   a  and the reference sample  212   a  in the first reaction region  210   a . Similarly, the second back side illumination photodiode  251   b  (PD 2 ) senses light  220  which is emitted from the second reaction region  210   b  depending upon a degree of a biochemical reaction between the target sample  211   b  and the reference sample  212   b  in the second reaction region  210   b , and the third back side illumination photodiode  251   c  (PD 3 ) senses light  220  which is emitted from the third reaction region  210   c  depending upon a degree of a biochemical reaction between the target sample  211   c  and the reference sample  212   c  in the third reaction region  210   c.    
     The light  220 , which is respectively emitted from the first reaction region  210   a , the second reaction region  210   b  and the third reaction region  210   c , directly reaches and is absorbed by the first back side illumination photodiode  251   a  (PD 1 ), the second back side illumination photodiode  251   b  (PD 2 ) and the third back side illumination photodiode  251   c  (PD 3 ), without passing by metal wiring lines which are stacked over the photodiodes in the formation of the conventional front side illumination (FSI) image sensor, whereby light sensitivity can be significantly improved according to the present invention. 
     The light sensed by the first back side illumination photodiode  251   a  (PD 1 ), the second back side illumination photodiode  251   b  (PD 2 ) and the third back side illumination photodiode  251   c  (PD 3 ) is outputted as electrical signals. The electrical signals are processed by a signal processing unit such as an ISP (image signal processor)  255  which is provided in the image sensor layer  200   b.    
     Preferably, the upper portion of the epitaxial layer  250  may include optical filters (not shown) which transmit light of a preselected band and micro lenses (not shown) which focus light on the optical filters. 
     An interlayer dielectric  230  is disposed under the epitaxial layer  250  and a plurality of stacked metal wiring lines  231  and  233  are formed in the interlayer dielectric  230 . This structure is distinguished from the structure of the conventional front side illumination (FSI) image sensor in which the interlayer dielectric  130  is disposed on the epitaxial layer  150  and the metal wiring lines  131  and  133  are formed in the interlayer dielectric  130 . 
     In the conventional structure using front side illumination (FSI), due to the fact that the biochip layer is formed on the interlayer dielectric, the characteristics of the photodiodes are likely to be changed due to surface treatment implemented during a procedure of manufacturing the biochip layer, and reacting solutions may influence underlying circuits by passing through the interlayer dielectric. 
     However, in the present structure using back side illumination (BSI), since the biochip layer is formed on a back side which faces away from a region where circuits are formed, the characteristics of the photodiodes are not influenced by the surface treatment implemented during a procedure of manufacturing the biochip layer, and it is possible to prevent misoperation of circuits from being caused due to infiltration of solutions used in reaction procedures. 
     As is apparent from the above description, in the embodiment of the present invention, due to the fact that light with biochemical reaction information, which is emitted from a biochip layer, is directly collected at the bottom portion of a back side illumination photodiode structure, that is, at the bottom surface of a wafer, light sensitivity can be improved. 
     Also, in the embodiment of the present invention, it is possible to prevent the characteristics of circuits from deteriorating due to surface treatment conducted during a manufacturing procedure of the biochip layer and infiltration of a solution occurring during a biochemical reaction procedure. 
     Although a preferred embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and the spirit of the invention as disclosed in the accompanying claims.

Technology Category: 5