Patent Publication Number: US-2005141104-A1

Title: Image sensor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims the benefit of Korean Application No. P2003-0098107 filed on Dec. 27, 2003, which is hereby incorporated by reference as if fully set forth herein.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to image sensors, and more particularly, to an image sensor in which a light shielding layer is shifted to or located in a circumference of a microlens array, and a thickness of the light shielding layer is greater than a thickness of the microlens array, to prevent a contaminant blocking sealing tape from being brought into direct contact with the microlens array in advance by supporting action of the light shielding layer, and for reducing or avoiding damage to the microlens array easily, for example when a pressure is conventionally applied to the microlens array to press the sealing tape strongly, or during polishing of a back surface of a semiconductor substrate.  
      2. Discussion of the Related Art  
      Recently, as electric and electronic technologies are developed rapidly, a variety of electronic products include image sensor technologies, such as video cameras, digital cameras, PCs with built-in miniature cameras, cellular phones with built-in miniature cameras, and so on, are developed, and spread widely.  
      Traditionally, Charge Coupled Devices (CCD) have been used as the image sensors. However, the CCD has many disadvantages, such as a high driving voltage, and an additional separate supporting circuit is generally required. Thus, the process cost for CCDs is high, and as a result, the present trend in the use of the CCD is decreasing.  
      Recently, as image sensors that can replace the CCD, Complementary Metal Oxide Semiconductor (CMOS) image sensors attract much interest. Different from the present CCD, because the CMOS image sensors are fabricated based on CMOS circuit technologies, the CMOS image sensors have advantages in that low voltage driving is possible, no additional supporting circuit is required, a process cost is low, and so on.  
      Referring to  FIG. 1 , a conventional CMOS image sensor is provided with a microlens array  7  for converging an external light incident thereon, a color filter array  6  for converting the light converged by the microlens array  7  into a color light, a planarizing layer  5  on the color filter array  6  for planarizing a base of the microlens array  7  to induce uniform light transmission, a light transmission layer  4  for transmission of the light converted into the color light at the color filter layer  7  toward a photodiode array  3 , and the photodiode array  3  on an active region of a semiconductor substrate  1  defined by an active cell isolation layer  2 , for receiving the light passed through the light transmission layer  4 , to produce and store photo charges. In addition to this, there is a light shielding layer  8  at an outermost circumference of the color filter array  6  for shielding an external unnecessary light incident on the photodiode array  3 , a signal processing circuit block (not shown), and the like.  
      In a conventional process, in order to fabricate a light, thin, short, and small sized image sensor, a back surface of a semiconductor substrate  1  is spin polished to reduce a total thickness of the image sensor. However, the polishing inevitably produces many silicon particles from the back surface  1   a  of the semiconductor substrate, which move toward a surface of the semiconductor substrate  1  due to static electricity generated during the spin polishing, resulting in contamination of various structures on the image sensor.  
      Referring to  FIG. 2 , for preventing such a problem, a sealing tape  101  is attached to the surface of the image sensor, to block or otherwise prevent the various CMOS image sensor structures from being contaminated with the silicon particles. However, when the back surface  1   a  of the semiconductor substrate  1  is polished, a polishing tool (not shown) applies a pressure to the surface of the image sensor, which sometimes forms a curvature damaged surface  7   a  as shown in  FIG. 3 , if other measures are not taken.  
      Of course, if the curvature damaged surface  7   a  is left as it is without taking any measures, the microlens array  7  fails to perform a regular light converging function, leading to an image reproduction of which quality is poor.  
     SUMMARY OF THE INVENTION  
      Accordingly, the present invention is directed to an image sensor that substantially obviates one or more problems due to limitations and disadvantages of the related art.  
      An object of the present invention is to provide an image sensor, in which a light shielding layer is shifted to or located in a circumference of the microlens array, and a thickness of the light shielding layer is greater than a thickness of the microlens array, to prevent a contaminant blocking sealing tape from being brought into direct contact with the microlens array. The supporting action of the light shielding layer is believed to avoid or reduce damage to the microlens array, even if a pressure is applied to the microlens array to press the sealing tape strongly during polishing of a back surface of the semiconductor substrate.  
      Another object of the present invention is to provide an image sensor, in which damage to a microlens array which may result from polishing of a back surface of a semiconductor substrate and inadvertent contact with a sealing tape is prevented, to maintain or optimize a light converging function of the microlens array and/or substantially improve or maintain a quality of the image reproduced by the image sensor.  
      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 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, as well as variations thereof that are apparent to those skilled in the art.  
      To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, an image sensor includes a microlens array for converging an external light incident thereon, an optional color filter array for converting the light converged by the microlens array into a color light, a photodiode array on a semiconductor substrate at an active region, for receiving the light converged by the microlens array and to produce and store photo charges, an optional light transmission layer over the semiconductor substrate to cover the photodiode array, to support the microlens array and the (optional) color filter array, and to transmit the light converged by the microlens array toward the photodiode array, and a light shielding support layer at a circumference of the microlens array, adapted to shield an external light, support an external particle shielding tape if attached, and prevent or inhibit the microlens array from being brought into physical contact with the tape.  
      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 which are incorporated in and which 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  illustrates a cross-section showing an example of a conventional image sensor;  
       FIG. 2  illustrates a cross-section showing an example of a contact state of a conventional image sensor to a sealing tape;  
       FIG. 3  illustrates a cross-section conceptually showing an example of a damaged state of a conventional microlens array;  
       FIG. 4  illustrates a section showing an example of an image sensor in accordance with a preferred embodiment of the present invention;  
       FIG. 5A  illustrates a perspective view showing an example of a contact state of an image sensor to a sealing tape in accordance with a preferred embodiment of the present invention; and  
       FIG. 5B  illustrates a section along a line A 1 -A 2  in  FIG. 5A , with the sealing tape in place along the periphery of the microlens array.  
    
    
     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.  
      Referring to  FIG. 4 , the image sensor, for an example, a CMOS image sensor, includes a microlens array  17  for converging an external light incident thereon, a color filter array  16  for converting the light converged by the microlens array  17  into a color light, a light transmission layer  14  for transmission of the light converted into the color light at the color filter layer  17  toward a photodiode array  13 , and the photodiode array  13  on an active region of a semiconductor substrate  11  defined by an active cell isolation layer  12 , for receiving the light passed through the light transmission layer  14  and producing and storing photo charges. The light transmission layer  14  is formed over the semiconductor substrate  11  to cover the photodiode array  13  and to support the microlens array  17  and the color filter array  16 .  
      In the present invention, as described before, in order to fabricate a light, thin, short, and small sized image sensor on the whole, a back surface  11   a  of the semiconductor substrate  11  is spin polished to reduce a total thickness of the image sensor. Of course, the polishing inevitably produces many silicon particles from the back surface  11   a  of the semiconductor substrate  11 , which may move toward a surface of the semiconductor substrate  11  due to static electricity generated during the spin polishing, resulting in contamination of various structures of the image sensor.  
      Referring to  FIGS. 5A and 5B , for preventing such a problem in the present invention, a particle blocking sealing tape  201  is attached to the surface of the image sensor, to prevent and/or block the various structures from being contaminated with the silicon particles. In this instance, as described before, if the back surface  11   a  of the semiconductor substrate  11  is polished when the sealing tape  201  covers the surface of the image sensor, the polishing tool applies a pressure to the surface of the image sensor, which may form a curvature damaged surface on microlenses in microlens array  17 , if other measures are not taken.  
      As shown in the drawings, in the present invention, a light shielding support layer  18  is formed in a circumference region of the microlens array  17 , surrounding the microlens array  17 . The light shielding support layer  18  is adapted to shield external light incident on the photodiode array  13 , and generally comprises (i) a conventional thermoplastic resin that does not deform substantially at a temperature less than about 300° C. and (ii) a colored pigment selected to absorb light of a wavelength or wavelength band from which circuitry is to be shielded. Light shielding support layer  18  may further shield a signal processing block and/or other structures and/or circuits located under the circumference region of the microlens array  17 .  
      Referring back to  FIG. 4 , in this instance, a planarizing layer  15  on an underside of the light shielding supporting layer  18  may be adapted or configured to cover the light transmission layer  14 , and planarize a base of the microlens array  17  and the light shielding supporting layer  18 . Thus, planarizing layer  15  preferably has a planar upper surface on which microlens array  17  and light shielding supporting layer  18  may be formed adjacent to one another. Furthermore, planarizing layer  15  preferably is formed (e.g., deposited) such that it covers the upper and side surfaces of color filter array  16 .  
      As shown in the drawings, different from the related art light shielding layer  8  (see  FIGS. 1-3 ), the light shielding supporting layer  18  of the present invention (see  FIG. 4 ) has a thickness relatively greater than the microlens array  17 , preferably by 1.5˜2.5 times.  
      In this instance, referring to  FIG. 5B , different from the related art, the sealing tape  201  is attached to the light shielding support layer  18  of the CMOS image sensor for blocking external particles. Thus, the sealing tape  201  does not contact with the microlens array  17  directly, but is supported by the light shielding support layer  18 , with a gap ‘S’ between the sealing tape  201  and, the microlens array  17 . In this state, when the back surface  11   a  of the semiconductor substrate  11  is polished, and a pressure is applied to the upper surface of the image sensor from the polishing tool, the microlens array  17  can avoid direct physical contact with the sealing tape  201  easily, minimizing and/or avoiding damage that may be caused by contact with the sealing tape  210 .  
      By improving the related art image sensor, damage to the microlens array  17  that may be caused by polishing of the back surface of the semiconductor substrate  11  and/or by contact of the sealing tape  201  may be reduced or avoided. Thus, the light converging function of the microlens array  17  can be optimized naturally (e.g., without accounting or adjusting for damage to the lenses in microlens array  17 ), leading to an improved quality of reproduced images.  
      Once the total thickness of the image sensor is reduced by polishing (sometimes called “back grinding” in the art), the sealing tape may be removed, various structures of the image sensor may be connected to outside parts electrically, and an outside exposure lens may be fitted, to complete fabrication of the image sensor or (micro)camera containing the same.  
      As has been described, by positioning the light shielding layer in a circumference of the microlens array and/or adjacent to the microlens array, and forming the light shielding layer such that its thickness is greater than a corresponding thickness of the microlens array, the contaminant blocking sealing tape may be supported by the light shielding layer and prevented from directly contacting the microlens array, thereby reducing or avoiding damage to the microlens array when pressure is applied to the image sensor to press the sealing tape and/or during polishing of the back surface of the semiconductor substrate. If such damage to the microlens array is reduced or prevented, the light converging function of the microlens array may be optimized, and the quality of the image reproduced by the image sensor can be improved.  
      It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. 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.