Abstract:
Methods of forming a microlens for an image sensor are provided. In one embodiment, the microlens can be oxide film microlens fabricated by forming an oxide film on a substrate; forming a first photoresist pattern on the oxide film; performing a plasma processing with respect to the oxide film using the first photoresist pattern as a mask; removing the first photoresist pattern; and performing an isotropic etching of the plasma processed oxide film. In another embodiment, the oxide film microlens can be fabricated by forming an oxide film on a substrate; forming a first photoresist pattern on the oxide film; implanting ions into the oxide film using the first photoresist pattern as a mask; removing the first photoresist pattern; and performing an isotropic etching of the ion implanted oxide film. Convex shaped microlens can be provided as a result of the etching selectivity to the oxide film.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims the benefit under 35 U.S.C. §119 of Korean Patent Application No. 10-2007-0062013, filed Jun. 25, 2007, which is hereby incorporated by reference in its entirety. 
       BACKGROUND 
       [0002]    A method for forming a microlens during a manufacturing process of an image sensor generally uses a method of performing a micro photo process using a special photoresist for a microlens and then reflowing the special photoresist into convex shaped microlenses. 
         [0003]    However, an amount of the photoresist lost when reflowing the photoresist may be large, causing a gap between the microlenses. The gap can cause an amount of light incident on the photodiode to be reduced by failing to direct the light to the photodiode. 
         [0004]    Also, with the related art special photoresist for a microlens, the microlens of an organic material can create particles during post-processes, such as wafer sawing and bump formation in a chip mounting process. These particles can damage the microlens or are attached to the microlens to cause an image defect. 
         [0005]    In addition, according to the related art, a difference in a focal length may occur along a lateral axis and a diagonal axis of the existing microlens. The difference in focal length can cause crosstalk between adjacent pixels. 
       BRIEF SUMMARY 
       [0006]    Embodiments of the present invention provide a method for manufacturing an image sensor where a microlens is formed using an oxide film. 
         [0007]    According to an embodiment, by omitting the polymer material of the related art microlens, an image sensor can be manufactured with improved yield and reliability. 
         [0008]    In addition, an embodiment of the subject method provides an image sensor capable of minimizing a gap between microlenses. 
         [0009]    In one embodiment, a method for manufacturing an image sensor can include forming a protective layer on a substrate; forming a color filter layer on the protective layer; forming an oxide film on the color filter layer; forming a first photoresist pattern on the oxide film; performing plasma processing on the exposed oxide film using the first photoresist pattern as a mask; removing the first photoresist pattern; and forming an oxide film microlens by an isotropic etching of the plasma processed oxide film. 
         [0010]    In another embodiment, a method for manufacturing an image sensor can include forming a protective layer on a substrate; forming a color filter layer on the protective layer; forming an oxide film on the color filter layer; forming a second photoresist pattern on the oxide film; performing an ion implantation process into the exposed oxide film using the second photoresist pattern as a mask; removing the second photoresist pattern; and forming an oxide film microlens by an isotropic etching of the ion implanted oxide film. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a cross-sectional view of an image sensor according to an embodiment of the present invention. 
           [0012]      FIGS. 2 to 6  are cross-sectional views for describing a method for manufacturing an image sensor according to a first embodiment. 
           [0013]      FIGS. 7 to 11  are cross-sectional views for describing a method for manufacturing an image sensor according to a second embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Hereinafter, a method for manufacturing an image sensor will be described with reference to the accompanying drawings. 
         [0015]    In the description of embodiments, it will be understood that when a layer (or film) is referred to as being ‘on’ another layer or substrate, it can be directly on another layer or substrate, or intervening layers may also be present. Further, it will be understood that when a layer is referred to as being ‘under’ another layer, it can be directly under another layer, or one or more intervening layers may also be present. In addition, it will also be understood that when a layer is referred to as being ‘between’ two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present. 
         [0016]      FIG. 1  is a cross-sectional view of an image sensor according to an embodiment. 
         [0017]    Referring to  FIG. 1 , an image sensor according to one embodiment can include a protective layer  120  formed on a substrate  110 , a color filter layer  130  formed on the protective layer  120 , and an oxide film microlens  140  formed on the color filter layer  130 . 
         [0018]    Embodiments of the subject method can improve yield and reliability by adopting a microlens formed of an oxide film, and not manufacturing the microlens using an existing polymer for the microlens material. 
         [0019]    A gap between the microlenses can be minimized by adopting the microlens formed using the oxide film. 
         [0020]    According to certain embodiments, the microlenses of an image sensor can be formed by performing an isotropic etching utilizing the effects of etching selectivity during forming the oxide film microlens. 
         [0021]    It should be noted that the number of color filters corresponding to the microlens is not limited to the number described in the disclosed embodiments. For example, one microlens can correspond to one color filter. As an alternative example, one microlens can correspond to three or five color filters. 
         [0022]      FIGS. 2 to 6  illustrate a method for manufacturing an image sensor according to a first embodiment. 
         [0023]    Referring to  FIG. 2 , a protective layer  120  can be formed on a substrate  110 . The substrate  110  can further be provided with a photodiode (not shown) or other structures (not shown). 
         [0024]    The protective layer  120  is used to protect a device from moisture and scratch. In certain embodiments, the protective layer  120  can be formed of, for example, an oxide film or a nitride film. 
         [0025]    A color filter layer  130  can be formed on the protective layer  130 . In one embodiment, the color filter layer can be formed by applying a dyeable resist to the substrate and subjecting the dyeable resist to exposure and development processes. The color filter layer  130  can include red, green, and blue color filter layers filtering light corresponding to a wavelength band. 
         [0026]    A planarization layer (not shown) can be formed on the color filter layer  130  for a control of the focal length and an assurance of a planarized surface when forming a lens layer. Here the figures show the color filter  130  having equal sized color filters. However, this is for illustrative purposes only and is not meant to indicate that the color filters of the color filter layer are necessarily the same size and shape. 
         [0027]    An oxide film  142  can be formed on the planarization layer or color filter layer  130 . 
         [0028]    In one embodiment, the oxide film  142  can be deposited at a temperature of about 200° C. or less. The oxide film  142  can be SiO 2 , but embodiments are not limited thereto. In certain embodiments, the oxide film  142  can be formed through chemical vapor deposition (CVD), physical vapor deposition (PVD), or plasma enhanced chemical vapor deposition (PECVD). 
         [0029]    Next, according to an embodiment, a first photoresist pattern  210  can be formed on the oxide film  142 . 
         [0030]    The first photoresist pattern  210  can be provided to expose a central portion of a region of the oxide film  142  from which a microlens will be formed. For example, in one embodiment, the first photoresist pattern  210  can expose a region of the oxide film  142  corresponding to a center portion of a microlens and a region extending from the center portion in a first direction to about 10 to 30% of the microlens. For example, the total diameter can be about 20% to about 60% of the microlens. 
         [0031]    The oxide film  142  can be provided to form the microlenses. Here, the oxide film  142  can be patterned to form a microlens. According to preferred embodiments, the microlenses are formed having a convex shape. However, if a rapid ion etching (RIE) process is performed directly on the oxide film  142 , a rectangular lens without a slope may be manufactured. 
         [0032]    Accordingly, a slope should be formed in the oxide film  142  to manufacture the lens in a convex form. Therefore, in order to have an isotropic etching selectivity in a process such as the RIE, a photo etching process (PEP) can be performed with respect to the oxide film such that a portion of the oxide film for forming the microlens is subjected to a plasma treatment process. 
         [0033]    In other words, the oxide film  142  can be subjected to a plasma process using the first photoresist pattern  210  as the mask. Referring to  FIG. 3 , a plasma process can be performed with respect to the exposed oxide film  142 . 
         [0034]    The central portion on which the microlens will be formed can be subjected to the plasma processing by performing the plasma processing on the exposed oxide film  142 . 
         [0035]    According to an embodiment, the plasma process can be an N 2  plasma treatment. The central portion of the oxide film, from which the microlens is formed, can be provided with a nitride film  145  by the plasma processing. 
         [0036]    In one embodiment, the plasma processing on the oxide film  142  can be performed under conditions of Power: 200 W-1500 W, Gas: N 2 , Gas Flow Rate: 10˜60 sccm, N 2  Plasma Treatment Time: 10˜30 sec, Pressure: 5˜10 mtorr, and using PVD equipment. 
         [0037]    Then, referring to  FIG. 4 , the first photoresist  210  can be removed. Referring to  FIG. 5 , the plasma processed oxide film  142  can then be subjected to an isotropic etching process to form the oxide microlens  140  as shown in  FIG. 6 . 
         [0038]    According to an embodiment, the etching selectivity of the nitride film  145  and the oxide film  142  can be about 1:5 to about 1:6 (1:5˜6). This etching selectivity can be used to create the sloping sides of the microlens because the oxide film portion has the about 5 to 6 times the etching rate as that of the nitride film portion. 
         [0039]    In one embodiment, the isotropic etching can be performed under conditions of RF Power: 1400 W (source)/0V (bias), Gas (Flow Rate (sccm)): CF 4 (90)/O 2 (10)/Ar(100), Process Time: 60˜90 sec, Pressure: 70˜100 mtorr, and using CVD equipment. 
         [0040]    Accordingly, a method of manufacturing an image sensor adopting a microlens using an oxide film can be provided. 
         [0041]    Also, embodiments of the subject method for manufacturing an image sensor can improve yield and reliability by adopting the microlens using the oxide film. 
         [0042]    In addition, embodiments of the subject method can minimize the gap between the microlenses. 
         [0043]    Furthermore, according to embodiments of the present invention, the microlenses are not formed of a polymer as typically provided in the related art. 
         [0044]      FIGS. 7 to 11  illustrate a method for manufacturing an image sensor according to a second embodiment. 
         [0045]    The image sensor according to second embodiment can include many of the same features as the image sensor according to the first embodiment. For example, the method according to the second embodiment can include forming a protective layer  120  on a substrate  110 , forming a color filter layer  130  on the protective layer  120 , and forming an oxide film  142  on the color filter layer  130 . 
         [0046]    Referring to  FIG. 7 , a second photoresist pattern  220  can be formed on the oxide film  142 . 
         [0047]    The second photoresist pattern  220  can expose outer portions of a region of the oxide film  142  from which a microlens will be formed. That is, the second photoresist pattern  220  can be formed covering regions of the oxide film  142  corresponding to a central portion of a microlens to be formed from the oxide film  142 . 
         [0048]    In one embodiment, the second photoresist pattern  220  can expose a region of the oxide film  142  corresponding to outer edges of a portion of the microlens formed from the oxide film  142  by about 10 to 30% of the microlens. For example, the total diameter of the exposed region can be 20 to 60% of the diameter of the microlens. 
         [0049]    Thereafter, an ion implantation into the oxide film  142  can be performed using the second photoresist pattern  220  as a mask. 
         [0050]    The ion implantation can occur in the oxide film  142  at regions of the oxide film corresponding to outer edge portions of a microlens to be formed from the oxide film  142 . 
         [0051]    According to one embodiment, the ion implantation can be performed using any suitable element having a heavy mass under conditions of Energy: 10˜20 KeV, Dose: 2˜5.0E13, and Angle: 0˜10°. According to certain embodiments, the elements having a heavy mass can include elements with atomic weight of 10 or more. In one embodiment, germanium (Ge) can be used for the ion implantation. 
         [0052]    The step of performing the ion implantation into the oxide film using the second photoresist pattern  220  as the mask can be used to damage the exposed portions of the oxide film  142  from which the microlens will be formed. 
         [0053]    Referring to  FIG. 8 , the ion implantation creates a ‘damaged’ implanted portion  147 . The etching selectivity of the damaged portion  147  and the oxide film  142  can be about 4:1 to about 5:1 (4˜5:1). In other words, the implanted portion  147  damages the oxide film by making the implanted portion thermodynamically unstable so that it can be etched relatively faster than the undamaged oxide film  142 . 
         [0054]    Referring to  FIG. 9 , the second photoresist pattern  220  can be removed. Then, referring to  FIG. 10 , the ion implanted oxide film  142  can be subjected to isotropic etching to form an oxide film microlens  140  as shown in  FIG. 11 . 
         [0055]    The isotropic etching of the ion implanted oxide film  142  can be performed under conditions of RF Power: 1400 W(source)/0V(bias), Gas (Flow Rate (sccm)): CF 4 (90)/O 2 (10)/Ar(100), Process Time: 60˜90 sec, Pressure: 70˜100 mtorr, and using CVD equipment. 
         [0056]    Accordingly, a method of manufacturing an image sensor adopting a microlens using an oxide film can be provided. 
         [0057]    Any reference in this specification to “one embodiment,” “an embodiment,” “example embodiment,” etc., means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with any embodiment, it is submitted that it is within the purview of one skilled in the art to effect such feature, structure, or characteristic in connection with other ones of the embodiments. 
         [0058]    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.