Abstract:
In a solid-state image pick-up device  10  in which a microlens layer  16  is provided on a surface of a semiconductor substrate  11  having photoelectric converting units  12 H and  12 L for storing an electric charge corresponding to an amount of incident light arranged vertically and horizontally, a microlens  16 H to be provided on the microlens layer  16  is disposed on only the photoelectric converting unit  12 H to be used as a pixel having a high sensitivity and the microlens layer  16  in a position facing the photoelectric converting unit  12 L to be used as a residual pixel having a low sensitivity has a planar structure  16 L or a perforated structure  16 L.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1.Field of the Invention  
           [0002]    The present invention relates to a solid-state image pick-up device such as a CCD, and more particularly to a solid-state image pick-up device having a wide dynamic range in which a pixel having a high sensitivity and a pixel having a low sensitivity are arranged.  
           [0003]    2.Description of the Related Art  
           [0004]    In a solid-state image pick-up device such as a CCD, a large number of photoelectric converting units (which will be hereinafter referred to as photodiodes) such as minute photodiodes for storing an electric charge corresponding to an amount of incident light are arranged vertically and horizontally and the electric charge stored in each of the photodiodes is read to reproduce the image of light formed on the surface of the solid-state image pick-up device in response to an electric signal.  
           [0005]    However, there is a problem in that the photodiode constituting each pixel of the solid-state image pick-up device has a certain amount of saturation charges so that electric charges that is beyond the constant amount of incident light cannot be stored, by which a dynamic range becomes small. For this reason, there has been made a trial in which both a pixel having a low sensitivity and a pixel having a high sensitivity are arranged in the solid-state image pick-up device to enlarge the dynamic range.  
           [0006]    [0006]FIG. 5 is a typical sectional view showing a conventional solid-state image pick-up device. In FIG. 5, a result obtained by simulating the degree of the refraction of an incident ray is shown together. A large number of minute photodiodes  2 H and  2 L are alternately arranged vertically and horizontally on a silicon substrate  1 , and the photodiode  2 H is used as a pixel having a high sensitivity and the photodiode  2 L is used as a pixel having a low sensitivity. An electrode  3  for transferring an electric charge stored in each pixel and a shielding film  4  covering the electrode  3  are provided on the surface of the silicon substrate  1 .  
           [0007]    A color filter layer  5  and a microlens layer  6  are provided on the silicon substrate  1 . A microlens  6 H for a pixel having a high sensitivity and a large area and a microlens  6 L for a pixel having a low sensitivity and a small area are convexed over a microlens layer  6 , and the microlens  6 H for a pixel having a high sensitivity collects light incident on a large area in the photodiode  2 H and the microlens  6 L for a pixel having a low sensitivity collects light incident on a small area in the photodiode  2 L. The microlens layer  6  having such a structure has been described in JP-A-11-177073, for example.  
           [0008]    In recent years, the number of pixels of a solid-state image pick-up device reaches several millions and the microlens layer  6  to be mounted on the solid-state image pick-up device has also been finer. The microlens layer  6  is generally manufactured by a photoetching technique and it is necessary to change the thicknesses of the microlenses  6 H and  6 L in order to cause the focal lengths of the microlens  6 H for a high sensitivity and the microlens  6 L for a low sensitivity having different areas to be equal to each other. Therefore, there is a problem in that the manufacture cannot be carried out at a one-time photoetching step and the photoetching step is to be carried out many times, resulting in an increase in a manufacturing cost.  
           [0009]    For this reason, conventionally, the manufacture is carried out by setting the thickness of the microlens  6 H for a high sensitivity to be equal to that of the microlens  6 L for a low sensitivity as shown in FIG. 6. To the contrary, the manufacture is carried out by setting the thickness of the microlens  6 L for a low sensitivity to be equal to that of the microlens  6 H for a high sensitivity as shown in FIG. 7. Thus, the manufacturing cost of the microlens layer  6  is reduced.  
           [0010]    As in the simulation of a pencil of light in FIGS. 6 and 7, however, there is a problem in that a condensation efficiency into the photodiode  2 H for a high sensitivity is reduced in FIG. 6 and a condensation efficiency into the photodiode  2 L for a low sensitivity is reduced in FIG. 7, and the light incident on the solid-state image pick-up device cannot be distributed efficiently into the pixel for a high sensitivity and the pixel for a low sensitivity.  
         SUMMARY OF THE INVENTION  
         [0011]    It is an object of the invention to provide a solid-state image pick-up device which can be manufactured at a low cost and can efficiently distribute incident light into a pixel for a high sensitivity and a pixel for a low sensitivity.  
           [0012]    In order to attain the object, the invention provides a solid-state image pick-up device in which a microlens layer is provided on a surface side of a semiconductor substrate having photoelectric converting units for storing an electric charge corresponding to an amount of incident light arranged vertically and horizontally, wherein a microlens to be provided on the microlens layer is disposed on only the photoelectric converting unit to be used as a pixel having a high sensitivity and the microlens layer in a position facing the photoelectric converting unit to be used as a residual pixel having a low sensitivity has a planar or perforated structure.  
           [0013]    By this structure, the incident light can be distributed efficiently into each of the photoelectric converting units having the pixel for a high sensitivity and the pixel for a low sensitivity, and the incidence efficiency of the light incident on each photoelectric converting unit can be enhanced, and furthermore, the microlens layer can be manufactured at a low cost.  
           [0014]    In the foregoing, it is preferable that a separate convex lens layer from the microlens layer which is provided with a convex lens for collecting, into the photoelectric converting unit, light incident on the photoelectric converting unit to be used as at least the pixel having a low sensitivity should be interposed between the microlens layer and the semiconductor substrate. By this structure, the incidence efficiency of the light incident on the photoelectric converting unit to be used as the pixel for a low sensitivity can further be increased, and furthermore, the microlens layer and the convex lens layer can be manufactured at a low cost.  
           [0015]    In the foregoing, furthermore, it is preferable that the convex lens of the convex lens layer should be provided to be convexed on the semiconductor substrate side and the convex lens of the convex lens layer should be provided to be convexed on the incident light side, and furthermore, the convex lens layers of the lower convex lens and the upper convex lens should be provided and interposed between the microlens layer and the semiconductor substrate. By this structure, it is possible to further reduce the manufacturing cost of the solid-state image pick-up device by utilizing the convex lens layer having a low manufacturing cost. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a typical sectional view showing a solid-state image pick-up device according to a first embodiment of the invention,  
         [0017]    [0017]FIG. 2 is a typical sectional view showing a solid-state image pick-up device according to a second embodiment of the invention,  
         [0018]    [0018]FIG. 3 is a typical sectional view showing a solid-state image pick-up device according to a third embodiment of the invention,  
         [0019]    [0019]FIG. 4 is a typical sectional view showing a solid-state image pick-up device according to a fourth embodiment of the invention,  
         [0020]    [0020]FIG. 5 is a typical sectional view showing a conventional solid-state image pick-up device,  
         [0021]    [0021]FIG. 6 is a typical sectional view showing another conventional solid-state image pick-up device, and  
         [0022]    [0022]FIG. 7 is a typical sectional view showing a further conventional solid-state image pick-up device. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    An embodiment of the invention will be described below with reference to the drawings.  
         [0024]    [0024]FIG. 1 is a typical sectional view showing a solid-state image pick-up device according to a first embodiment of the invention. In FIG. 1, a result obtained by simulating the degree of the refraction of an incident ray is shown together. A solid-state image pick-up device  10  is constituted by a semiconductor substrate  11 , photodiodes  12 H and  12 L arranged vertically and horizontally on the semiconductor substrate  10  (a detailed structure thereof is not shown), an electrode  13  formed on the surface of the semiconductor substrate  11  and serving to transfer stored charges read from the photodiodes  12 H and  12 L, a shielding film  14  for shielding the electrode  13 , a color filter layer  15  provided on the surface side of the semiconductor substrate  11 , and a microlens layer  16  provided thereon.  
         [0025]    In the microlens layer  16  according to the embodiment, a microlens  16 H for a pixel having a high sensitivity is formed in the upper position of the photodiode  12 H in such a manner that an area is large and a condensing point is set into the position of the surface of the photodiode  12 H. A small plane region  16 L surrounded by the microlens  16 H for a pixel having a high sensitivity (corresponding to a region in which a microlens  6 L for a pixel having a low sensitivity is to be provided in FIGS.  5  to  7 ) is not provided with a lens and a parallel beam is exactly transmitted to reach the surface of the photodiode  16 L. The plane region  16 L may have such a structure that a hole is formed on the microlens layer  16 .  
         [0026]    In the solid-state image pick-up device  10  mounting the microlens layer  16 , a light collected through the microlens  16 H for a pixel having a high sensitivity is input to the photodiode  12 H and an electric charge corresponding to the amount of the input light is stored. On the other hand, a light incident on the small region  16 L surrounded by the microlens  16 H is input to the photodiode  12 L exactly straight and an electric charge corresponding to the amount of the input light is stored in the photodiode  12 L.  
         [0027]    In the embodiment, a microlens is not provided for the photodiode  12 L and the region  16 L surrounded by the microlens  16 H for a high sensitivity which has a large area is small. Therefore, most of the light transmitted through the region  16 L is incident on the photodiode  12 L and a signal charge for an image having a low sensitivity can be stored efficiently in the photodiode  12 L even if a microlens is not provided for collecting the light.  
         [0028]    [0028]FIG. 2 is a typical sectional view showing a solid-state image pick-up device according to a second embodiment of the invention. A solid-state image pick-up device  20  according to the embodiment is different from the solid-state image pick-up device  10  according to the first embodiment in that a lower convex lens layer  17  is provided between the semiconductor substrate  11  and the color filter layer  15 , and other structures are the same as those of the first embodiment.  
         [0029]    The lower convex lens layer  17  is provided with convex lenses  17 H and  17 L turned in the directions of photodiodes  12 H and  12 L. The convex lenses  17 H and  17 L have thicknesses and diameters which are equal to each other. Therefore, the lower convex lens layer  17  can easily be manufactured. The convex lens  17 H has a smaller diameter than the diameter of a microlens  16 H having a large diameter. Since light collected by the microlens  16 H is transmitted through the convex lens  17 H, the convex lens  17 H having a small diameter is enough.  
         [0030]    By providing the lower convex lens layer  17 , a parallel beam transmitted through a small region  16 L surrounded by the microlens  16 H for a pixel having a high sensitivity is collected by the convex lens  17 L, and rarely collides against a surrounding shielding film  14  and is thus incident on the photodiode  12 L. On the other hand, the light collected by the microlens  16 H for a pixel having a high sensitivity is further collected by the convex lens  17 H. Consequently, a luminous flux expands more greatly over the surface of the photodiode  12 H as compared with that in FIG. 1. However, the luminous flux does not expand up to the outside of the photodiode  12 H so that the incident light can be prevented from being useless.  
         [0031]    It is also possible to employ such a structure that only the convex lens  17 L is provided on the lower convex lens layer  17  and the convex lens  17 H for a pixel having a high sensitivity is not provided.  
         [0032]    [0032]FIG. 3 is a typical sectional view showing a solid-state image pick-up device according to a third embodiment of the invention. A solid-state image pick-up device  30  according to the embodiment is different from the solid-state image pick-up device  20  according to the second embodiment in that an upper convex lens layer  18  is provided in place of the lower convex lens layer  17 , and other structures are the same as those in the second embodiment.  
         [0033]    In the upper convex lens layer  18 , convex lenses  18 H and  18 L turned toward the incident light side are formed in positions corresponding to photodiodes  12 H and  12 L. Since the thicknesses of the convex lenses  18 H and  18 L are equal to each other, the upper convex lens layer  18  can easily be manufactured. The reason why the diameter of the convex lens  18 H for a pixel having a high sensitivity of the upper convex lens layer  18  is set to be larger than the diameter of the convex lens  17 H for a pixel having a high sensitivity of the lower convex lens layer  17  (FIG. 2) is that a distance between the surface of the convex lens  18 H and a microlens  16 H is small and light transmitted through the microlens  16 H is to be always incident on the convex lens  18 H.  
         [0034]    By providing the upper convex lens layer  18 , a parallel beam transmitted through a small region  16 L surrounded by the microlens  16 H for a pixel having a high sensitivity is collected by the convex lens  18 L and is incident on the photodiode  12 L without colliding against a surrounding shielding film  14 . On the other hand, the light collected by the microlens  16 H for a pixel having a high sensitivity is further collected by the convex lens  18 H. In the same manner as in the second embodiment, consequently, a luminous flux expands over the surface of the photodiode  12 H. However, the luminous flux does not expand up to the outside of the photodiode  12 H so that the incident light can be prevented from being useless.  
         [0035]    In the same manner as in the second embodiment, it is also possible to employ such a structure that only the convex lens  18 L is provided on the upper convex lens layer  18  and the convex lens  18 H for a pixel having a high sensitivity is not provided.  
         [0036]    [0036]FIG. 4 is a typical sectional view showing a solid-state image pick-up device according to a fourth embodiment of the invention. A solid-state image pick-up device  40  according to the embodiment is different from the solid-state image pick-up device  10  according to the first embodiment in that the lower convex lens layer  17  according to the second embodiment and the upper convex lens layer  18  according to the third embodiment are superposed and interposed between the semiconductor substrate  11  and the color filter layer  15 , and other structures are the same as those in the first embodiment.  
         [0037]    The lower convex lens layer  17  is provided with convex lenses  17 H and  17 L turned toward photodiode  12 H and  12 L sides. Since the convex lenses  17 H and  17 L have thicknesses and diameters which are equal to each other, the lower convex lens layer  17  can easily be manufactured.  
         [0038]    In the upper convex lens layer  18 , the convex lenses  18 H and  18 L turned toward the incident light side are formed in positions corresponding to the photodiodes  12 H and  12 L. Since the convex lenses  18 H and  18 L have thicknesses equal to each other, the upper convex lens layer  18  can also be manufactured easily.  
         [0039]    While the lower convex lens layer  17  and the upper convex lens layer  18  are manufactured separately and both of them are superposed and provided in the embodiment, the lower convex lens layer  17  and the upper convex lens layer  18  may be formed together over one sheet. Moreover, the convex lenses  17 H and  18 H may be omitted as described in the second and third embodiments.  
         [0040]    By providing the lower convex lens layer  17  and the upper convex lens layer  18 , a parallel beam transmitted through a small region  16 L surrounded by a microlens  16 H for a pixel having a high sensitivity is collected by the convex lenses  17 L and  18 L and is incident on the photodiode  12 L without colliding against a surrounding shielding film  14 .  
         [0041]    According to each of the embodiments described above, the incidence efficiency of the light incident on each of the photodiode constituting a pixel for a high sensitivity and the photodiode constituting a pixel for a low sensitivity can be enhanced with a microlens structure at a low cost (the microlens layer  16  and the convex lens layers  17  and  18 ). Thus, it is possible to provide a high performance solid-state image pick-up device.  
         [0042]    According to the invention, the structure of a microlens for distributing incident light into a pixel having a high sensitivity and a pixel having a low sensitivity can be manufactured at a low cost. Consequently, it is possible to inexpensively manufacture a solid-state image pick-up device having a pixel for a high sensitivity and a pixel for a low sensitivity.