Patent Publication Number: US-2022216258-A1

Title: Image sensor

Description:
CROSS-REFERENCE TO RJELAFED APPLICAIION(S) 
     This application claims priority under 35 USC 119(a) from Korean Patent Application No. 10-2021-0000276, filed on Jan. 4, 2021 in the Korean Intellectual Property Office, the contents of which are herein incorporated by reference in their entirety. 
     BACKGROUND 
     Technical Field 
     Embodiments of the present inventive concept are directed to an image sensor. 
     Discussion of the Related Art 
     I age sensors are semiconductor devices that convert optical images into electrical signals. Among such image sensors, a Complementary Metal Oxide Semiconductor (CMOS) type image sensor is abbreviated as a CMOS image Sensor (CIS). A CIS includes a plurality of pixel areas, and each of the pixel areas includes at least one photodiode (PD) that converts incident light into an electrical signal. On the other hand, a CIS that includes tour photodiodes in one pixel area can have improved autofocusing performance. However, a device isolation film in the pixel area can cause a loss of autofocusing sensitivity. 
     SUMMARY 
     Exemplary embodiments provide an image sensor that reduces light incident on internal device isolation film using an image sensor that includes a color filter that has convex surfaces for each pixel area, and that reduces autofocusing sensitivity loss. 
     According to an exemplary embodiment, an image sensor includes a substrate that includes a first surface and a second surface that oppose each other in a first direction and a plurality of pixel areas arranged in directions parallel to the first surface; a first device isolation film that separates each of the plurality of pixel areas; four photodiodes disposed in each of the plurality of pixel areas inside of the substrate, and arranged in a 2×2 array in directions parallel to the first surface; a second device isolation film that separates the four photodiodes from each other; a color filter disposed on the first surface of the substrate and that includes four regions that correspond to the four photodiodes, respectively, where each of the four regions has a convex upper surface; and a first microlens disposed above the color filter and that corresponds to each of the pixel areas. 
     According to an exemplary embodiment, an image sensor includes a pixel array that includes a plurality of pixel groups arranged in directions parallel to an upper surface of a substrate, where each of the plurality of pixel groups includes a plurality of pixel areas; and a logic circuit that obtains a pixel signal from each of the plurality of pixel areas. Each of the plurality of pixel areas includes four photodiodes arranged in a 2×2 array in directions parallel to the upper surface of the substrate, a color filter disposed on the upper surface of the substrate, and a microlens disposed above the color filter, and the color filter has the same color for each of the plurality of pixel areas and includes four regions that respectively correspond to each of the four photodiodes, wherein each of the four regions has a convex upper surface. 
     According to an exemplary embodiment, an image sensor includes a substrate; a first device isolation film that separates pixel areas disposed in directions parallel to an upper surface of the substrate; four photodiodes disposed in each of the pixel areas inside of the substrate and arranged in a 2×2 array in directions parallel to the upper surface of the substrate; a second device isolation film that separates the four photodiodes from each other; a first microlens disposed above the substrate and that corresponds to each of the pixel areas, where the first microlens primarily refracts incident light; and a color filter disposed on the upper surface of the substrate and below the first microlens, where the color filter includes four regions that respectively correspond to the four photodiodes, and extracts a light component that has a predetermined wavelength from the primarily refracted incident light and produces secondarily refracted light. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram of an image sensor according to an exemplary embodiment. 
         FIG. 2  is a top view of an image sensor according to an exemplary embodiment. 
         FIG. 3  is a cross-sectional view of an image sensor according to an exemplary embodiment. 
         FIGS. 4 to 7  schematically illustrate a pixel array of an image sensor according to exemplary embodiments. 
         FIGS. 8 to 11  are cross-sectional views of image sensors according to exemplary embodiments. 
         FIG. 12  is a flowchart of a process of manufacturing an image sensor illustrated in  FIG. 3 , according to an exemplary embodiment. 
         FIGS. 13A to 13H  are cross-sectional views that illustrate a process of manufacturing an image sensor illustrated in  FIG. 3 , according to an exemplary embodiment. 
         FIGS. 14 and 15  schematically illustrate an electronic device that includes an image sensor according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, exemplary embodiments will be described with reference to the accompanying drawings., 
       FIG. 1  is a block diagram of an image sensor according to an exemplary embodiment. 
     Referring to  FIG. 1 , an image sensor  1  according to an exemplary embodiment includes a pixel array  10  and a logic circuit  20 . 
     In an embodiment, the pixel array  10  includes a plurality of unit pixels PX disposed in an array in a plurality of rows and a plurality of columns. Each of the unit pixels PX includes at least one photoelectric conversion element that generates electric charges in response to light, and a pixel circuit that generates a pixel signal that corresponds to the electric charges generated by the photoelectric conversion element. 
     Then photoelectric conversion device includes a photodiode formed of a semiconductor material, and/or an organic photodiode formed of an organic material. In an exemplary embodiment, each of the unit pixels PX includes two or more photoelectric conversion elements, and the two or more photoelectric conversion elements in one unit pixel PX respond to light of it different colors and generate electric charges. 
     In an exemplary embodiment, each unit pixel PX includes a first photodiode, a second photodiode, a third photodiode, and a fourth photodiode, and the lint to fourth photodiodes respond to light in different wavelength bands and respectively generate electric charges, but embodiments are not limited thereto. 
     Depending on exemplary embodiments, the pixel circuit may include a transfer transistor, a driving transistor, a selection transistor, and a reset transistor. When each of the unit pixels PX includes two or more photoelectric conversion elements, each of the unit pixels PX includes a pixel circuit that processes charges generated by each of the two or more photoelectric conversion elements. For example, when each of the unit pixels PX has four photoelectric conversion elements, the pixel circuit includes four or more of at least one of a transfer transistor, a driving transistor, a selection transistor, and a reset transistor. However, embodiments are not limited to this configuration, and in other embodiments, at least some of the photoelectric conversion elements also share a portion of the transistors. 
     In an embodiment, the logic circuit  20  includes circuits that control the pixel array  10 . For example, the logic circuit  20  includes a row driver  21 , a readout circuit  22 , a column driver  23 , and a control logic  24 . 
     In an embodiment, the row driver  21  drives the pixel array  10  in a row unit. For example, the row driver  21  generates a transmission control signal that controls a transfer transistor of a pixel circuit, a reset control signal that controls the reset transistor, a selection control signal that controls the selection transistor, etc., and inputs the signal to the pixel array  10  in a row unit. 
     In an embodiment, the readout circuit  22  includes a correlated double sampler (CDS), an analog-to-digital converter (ADC), etc. The correlated double sampler is connected to the unit pixels PX through column lines. The correlated double samplers performs correlated double sampling by receiving pixel signals from unit pixels PX connected to a row line selected by a row line selection signal of the row driver  21 . The pixel signal is received through the column lines. The analog-to-digital converter converts the pixel signal detected by the correlated double sampler into a digital pixel signal and transmits the digital pixel signal to the column driver  23 . 
     In an embodiment, the column driver  23  includes an amplifying, circuit and a late t or buffer circuit that temporarily stores a digital pixel signal, etc., and processes the digital pixel signal received from the readout circuit  22 , The row driver  21 , the readout circuit  22 , and the column driver  23  are controlled by the control logic  24 . The control logic  24  includes a timing controller that controls the operation timing of the row driver  21 , the readout circuit  22 , and the column driver  23 . 
     In an embodiment, among the unit pixels PX, those unit pixels PX disposed in the same position in the horizontal direction share the same column line. For example, those unit pixels PX disposed in the same position in the vertical direction are simultaneously selected by the row driver  21  and output pixel signals through column lines. In an exemplary embodiment, the readout circuit  22  simultaneously obtains pixel signals from the unit pixels PX selected by the row driver  21  through column lines. The pixel signals include a reset voltage and a pixel voltage. However, embodiments are not the configuration shown in  FIG. 1 , and in other embodiments, the image sensor may additionally include other components and may be driven in other ways.  FIG. 2  is a top view of an image sensor according to an exemplary embodiment. 
     In general, in an image sensor that includes four photodiodes in one pixel area, the four photodiodes share one microlens to increase autofocusing performance by acquiring autofocusing information of all pixel areas. On the other hand, the respective photodiodes are separated by an internal device isolation film, and light incident through the microlens is refracted as the light enters the pixel area. However, due to the structural characteristics of the internal device isolation film, incident light may be concentrated and absorbed by the internal device isolation film. Accordingly, in a general image sensor, autofocusing sensitivity loss may occur. 
     Referring to  FIG. 2 , an image sensor  100  according to an exemplary embodiment of the present inventive concept includes a device isolation film DTI that separates photodiodes PD 1 , PD 2 , PD 3 , and PD 4 . For example, the pixel areas PX are arranged in directions parallel to a first plane, such as an X-Y plane. For example, each of the pixel areas PX includes photodiodes PD 1 , PD 2 , PD 3 , and PD 4  arranged in 2/2 form in directions parallel to the first plane. 
     On the other hand, to prevent the autofocusing sensitivity loss that can occur in a general image sensor that includes four photodiodes in one pixel area, the image sensor  100  according to an exemplary embodiment of the present inventive concept includes color filters  131 ,  132 ,  133  and  134  of color filter  130  that each have a convex upper surface. For example, the color filter  130  includes four regions  131 ,  132 ,  133 , and  134  that correspond to the photodiodes PD 1 , PD 2 , PD 3 , and PD 4 , respectively. For example, each of the four regions  131 ,  132 ,  133 , and  134  has a convex upper surface. Hereinafter, each of the four regions  131 ,  132 ,  133 , and  134  is referred to as the color filter  130 . 
     The image sensor  100  according to an exemplary embodiment includes a first microlens  140  that corresponds to each of the pixel areas PX. For example, the first microlens  140  is disposed above the color filter  130 . In detail, in one pixel area PX, a ratio of the number of first microlenses  140  and the number of areas in die color filter  130  and that have a convex upper surface is 1:4. Accordingly, each of the four regions in the color filter  130  has an area different from that of the first microlens  140 . On the other hand, the first microlens  140  and the convex upper surface in the color filter  130  are circular in a plan view. However, embodiments of the present inventive concept are not limited thereto, and in other embodiments, the first microlens  140  and/or the convex upper surface in the color filter  130  may have a rectangular shape with rounded corners. For example, in the exemplary embodiment illustrated in  FIG. 2 , the first microlens  140  has a relatively large diameter with respect to the optical axis. In addition, a length of the first microlens  140  in a direction parallel to the arrangement direction of the pixel, areas PX is less than the length of the first microlens  140  in a diagonal direction. For example, in a direction parallel to the arrangement direction of the pixel areas PX, the length of the first microlens  140  is twice the diameter of a circular convex upper surface in the color filter  130 . On the other hand, in a direction that is diagonal to the arrangement direction of the pixel areas PX, the length of the first microlens  140  is greater than twice the diameter of a circular convex upper surface in the color filter  130 . However, embodiments are not limited thereto, and in other embodiments, the shapes of the first microlens  140  and the color filter  130  can vary from those illustrated. 
       FIG. 3  is a cross-sectional view of an image sensor according to an exemplary embodiment. 
       FIG. 3  is a cross-sectional view of the image sensor  100  taken along line in  FIG. 2 . Referring to  FIG. 3 , the image sensor  100  according to an exemplary embodiment includes a substrate  110 , a color filter  130 , and a first microlens  140  disposed on the color filter  130  in a first direction, such as a Z direction. For example, the substrate  110  includes a first surface  111  and a second surface  112  that oppose each other in the first direction. In the image sensor  100  according to an exemplary embodiment, the pixel areas PX are arranged in directions parallel to the first surface  111  of the substrate  110 . In addition, other circuits necessary for the operation of the image sensor  100  are disposed on the upper surface of the second surface  112  of the substrate  110 . For example, the substrate  110  can be a semiconductor substrate, and photodiodes PD 1  and PD 2  that receive light are disposed inside of the substrate  110 . However, although two photodiodes PD 1  and PD 2  are illustrated in  FIG. 3 , when referring to  FIG. 2  together, at least four photodiodes PD 1 , PD 2 , PD 3 , and PD 4  are included in one pixel area PX. For example, the four photodiodes PD 1 , PD 2 , PD 3 , and PD 4  are arranged in a  2 x 2  array in directions parallel to the first surface  111 . However, this is only an example and embodiments are not limited to this configuration. 
     In the image sensor  100  according to an exemplary embodiment, the pixel areas PX are separated by the first device isolation film DTI 1 . On the other hand, the photodiodes PD 1 , PD 2 , PD 3 , and PD 4  in the pixel area PX are separated by the second device isolation film DTI 2 . For example, the first device isolation film DTI 1  is an insulating layer that separates the pixel areas PX from each other, and the second device isolation film DTI 2  is an insulating film that improves the performance of the image sensor  100  by controlling the movement of electrons within one pixel area PX. For example, the first device isolation film DTI 1  and the second device isolation film am respectively extend in the first direction and include an insulating material. On the other hand, the second device isolation film DTI 2  extends between the photodiodes PD 1 , PD 2 , PD 3 , and PD 4  in a second direction, such as an X direction, and a third direction, such as a Y direction, from the first device isolation film DTI 1 , where each of the second and third directions is perpendicular to the first direction. 
     The image sensor  100  according to an exemplary embodiment includes the color filter  130  disposed on le first surface  111  of the substrate  110 . The color filter  130  is divided into four regions  131 ,  132 ,  133  and  134 , and the four regions  131 ,  132 ,  133  and  134  correspond to the four photodiodes PD 1  PD 2 , PD 3  and PD 4 , respectively. In detail, the four regions  131 ,  132 ,  133 , and  134  are also arranged in 2×2 form like the photodiodes PD 1 , PD 2 , PD 3 , and PD 4 , and each of the four regions  131 ,  132 ,  133  and  134  has a convex upper surface. One pixel area PX includes the color filter  130  of the same color. For example, the color of file color filter  130  may be any one of green, red, and blue. However, this is only an example, and the colors of the color filter  130  may be different colors as necessary. 
     In an embodiment, the image sensor  100  includes the first microlens  140  disposed above the. color filter  130 . For example, the first microlens  140  corresponds to the pixel area PX. On the other hand, the first microlens  140  and the four regions  131 ,  132 ,  133 , and  134  in the color filter  130  have different optical axes. For example, the optical axis of the first microlens  140  overlaps the second device isolation film DT 12  in the first direction. in addition, the optical axes of the four regions  131 ,  132 ,  133 , and  134  in the color filter  130  overlap the four photodiodes PD 1 , PD 2 , PD 3 , and PD 4  in the first direction, respectively. 
     In the image sensor  100  according to an exemplary embodiment, the curvature of the first microlens  140  is less than the curvature of each of the four regions  131 ,  132 ,  133 , and  134  in the color filter  130 . Accordingly, the first microlens  140  can collect incident light so that the incident light does not deviate from the pixel area PX of the first microlens  140 . On the other hand, the four regions  131 ,  132 ,  133 , and  134  in the color filter  130  can reduce absorption of incident light into the second device isolation film DTI 2 . However, this is only an example and embodiments are not limited to this configuration, and in other embodiments, the curvatures of the first microlens  140  and the four regions  131 ,  132 ,  133  and  134  in the color filter  130  can vary as necessary. 
     However, a configuration and shape of the image sensor  100  according to an exemplary embodiment are not limited to those illustrated in  FIG. 3 , and other configurations may be added or omitted depending on exemplary embodiments, and the shape can change. For example, in an embodiment, the color filter  130  includes an autofocusing barrier  120  that prevents light incident on the first microlens  140  from entering another pixel area PX. The autofocusing barrier  120  is disposed on the upper surface of the first device isolation film DTI 1 . However, this is only an example and the configuration is not limited thereto, and in other embodiments, the autofocusing barrier  120  can be disposed on a portion of the boundaries of the four regions  131 ,  132 ,  133 , and  134  in the color filter  130 . In addition, a light transmitting layer may be further included between the first microlens  140  and the color filter  130 . 
     In the image sensor  100  according to an exemplary embodiment, light L incident on the image sensor  100  passes through the first microlens  140  and is refracted into first refracted light L′. For example, the first refracted light L′ propagates toward the center of the first microlens  140 . The second device isolation film DTI 2  is disposed on the center of the first microlens  140 . The first refracted light L′ passes through the color filter  130  and is refracted into second refracted light L″. For example, the color filter  130  extracts a component having a predetermined wavelength from the first refracted light L′. The secondly refracted light L″ enters the substrate  110  rather than the second device isolation film DTI 2 . Accordingly, the image sensor  100  according to an exemplary embodiment improves the performance of the image sensor  100  by reducing light absorption by the second device isolation film DTI 2  and by reducing autofocusing sensitivity loss. 
     In an embodiment, a pixel circuit is disposed on the second surface  112  of the image sensor  100 . For example, the pixel circuit includes a plurality of elements  160 , wiring patterns  170  connected to the plurality of elements  160 , and an insulation layer  180  that covers the plurality of elements  160  and the wiring patterns  170 , etc., and that are disposed on the second surface  112  of the substrate  110 . The pixel circuit includes a floating diffusion region  150 . For example, each of the pixel areas PX 1 , PX 2 , PX 3 , and PX 4  includes the floating diffusion region  150  disposed below the plurality of photodiodes PD 1  and PD 2 . For example, the respective floating diffusion regions  150  are electrically connected to each other by at least one of the wiring patterns  170 , and respective locations and areas of the floating diffusion regions  150  can vary depending on exemplary embodiments. In the image sensor  100  according to an exemplary embodiment, the plurality of elements  160  adjacent to the floating diffusion region  150  are transfer transistors. For example, the transfer transistor gate has a vertical structure in which at least a partial region is buried in the substrate  110 . However, this is only an example and the configuration is not limited thereto, and in other embodiments, the transfer transistors share one floating diffusion region  150  within one pixel area. PX. 
       FIGS. 4 to 7  schematically illustrate a pixel array of an image sensor according to exemplary embodiments. 
     First, referring to  FIG. 4 , a pixel array  100 A, of an image sensor according to an exemplary embodiment includes a plurality of pixel areas PX 1 . For example, each of the pixel areas PX 1  includes first to fourth photodiodes. In the exemplary embodiment illustrated in  FIG. 4 , each of the pixel areas PX 1  in the pixel array  100 A is an autofocusing pixel area PX 1 . In the autofocusing pixel area PX 1 , the first to fourth photodiodes, are arranged in 2×2 form, and the first to fourth photodiodes share one microlens. In the pixel array  100 A of an image sensor according to an exemplary embodiment, the autofocusing pixel area PX 1  includes a color filter that includes regions that. have convex upper surfaces that correspond to the first to fourth photodiodes, respectively. However, this is only an example and the configuration is not limited thereto, and in other embodiments, the arrangement of the first to fourth photodiodes and the shape of the color filter in at least a portion of the pixel areas PX 1  can be modified. In addition, according to an exemplary embodiment, only a portion of the pixel areas PX 1  is used for the autofocusing function. 
     Referring to  FIG. 5 , a pixel array  100 B of an image sensor according to an exemplary embodiment includes an autofocusing pixel area PX 1  and a general pixel area PX 2 . A plurality of each of the autofocusing pixel area PX 1  and the general pixel area PX 2  are provided, and the number of autofocusing pixel areas PX 1  and the number of general pixel areas PX 2  can vary. For example, the number of general pixel areas PX 2  is greater than the number autofocusing pixel areas PX 1 . In addition, the positions of the autofocusing pixel areas PX 1  are not limited to those illustrated in  FIG. 5 , and can be modified in other embodiments. 
     Next, referring to  FIG. 6 , a pixel array  100 C according to an exemplary embodiment includes a plurality of pixel groups PG 1  arranged in directions parallel to the upper surface of the substrate. In addition, each of the plurality of pixel groups PG 1  includes pixel areas PX. For example, each of the pixel areas PX includes first to fourth photodiodes. The pixel areas PX may be autofocusing pixel areas or general pixel areas. However, this is only an example and the configuration is not limited thereto. According to exemplary embodiments, only a portion of the pixel areas PX include first to fourth photodiodes, and in other embodiments, the numbers and arrangements of photodiodes in some of the pixel areas PX are different. 
     The pixel array  100 C according to an exemplary embodiment includes a color filter that is arranged to generate an image having a Tetra pattern. For example, the color filter includes regions having a convex upper surface as illustrated in  FIG. 4 . For example, the pixel array  100 C of the image sensor has a 4×4 tetra color filter array FA 1  in which red, green, green, and blue filters are each arranged in a 2×2 form. On the other hand, each of the plurality of pixel groups PG 1  includes 2×2 pixel areas PX. The 2×2 pixel areas PX in the plurality of pixel groups PG 1  include color filters of the same color. For example, each of the pixel areas PX includes four regions that have a convex upper surface, and each of the four legions corresponds to a photodiode. For example, the tetra color filter arrays FA 1  repeatedly arranged as described above constitute the pixel array  100 C. However, this is only an example, and in other embodiments, an arrangement of repetitively configured color filters can vary. 
     On the other hand, referring to FIG,  7 , a pixel array  100 D of an image sensor according to an exemplary embodiment includes a plurality of pixel groups PG 2 , similar to the pixel array  100 C illustrated in  FIG. 6 . The pixel areas PX in each of the pixel groups PG 2  include color filters of the same color. In addition, the color filter includes regions that have a convex upper surface as illustrated in  FIG. 4 . However, unlike the pixel array  100 C illustrated in  FIG. 6 , each of the plurality of pixel groups PG 2  in the pixel array  100 D includes 3×3 pixel areas PX. The pixel array  100 D of the image sensor according to the exemplary embodiment includes a color filter that is arranged to generate an image that has a nona pattern. For example, the pixel array  100 D of the image sensor has a 6×6 nona color filter array FA 2  in which red, green, green, and blue are each arranged in a 3×3 form. However, this is only an example, and in other embodiments, the arrangement of repetitively configured color filters can vary. 
     In exemplary embodiments described with reference to  FIGS. 4 to 7 , each of the pixel areas PX are separated by a first device isolation film, and a second device isolation film is disposed between the first to fourth photodiodes in each of the pixel areas PX. For example, a light-receiving area of each of the first to fourth photodiodes is determined by the first device isolation film and the second device isolation film. For example, if the second device isolation film is not accurately aligned between the first to fourth photodiodes, the light-receiving area of at least one of the first to fourth photodiodes may be different from a light-receiving area of the others, and autofocusing performance of the image sensor can deteriorate. On the other hand, as described above, when the second device isolation film is accurately aligned between the first to fourth photodiodes, incident light is absorbed by the second device isolation film, thereby increasing autofoousing sensitivity loss. 
     In an image sensor that includes the pixel arrays  100 A,  100 B,  100 C, and  100 D, according to an exemplary embodiment of the present inventive concept illustrated in  FIGS. 4 to 7 , include a microlens that produces first refracted light and a color filter that extracts a light component that has a predetermined wavelength from the first refracted light and produces second refracted light to reduce autofocusing sensitivity loss. For example, the difference in the light-receiving area of the first photodiode and the second photodiode can be significantly reduced by accurately aligning an internal separation film of the pixel, and light incident on the second device isolation film can be significantly reduced using the second refraction by a color filter, to allow light to be absorbed by the substrate. Therefore, deterioration of the autofocusing function of the image sensor can be prevented, and the loss of autofocusing sensitivity can be significantly reduced. In addition, an image sensor according to an exemplary embodiment further includes a logic circuit that obtains a pixel signal from the pixel areas PX in the pixel arrays  100 A,  100 B,  100 C, and  100 D, for operation. 
       FIGS. 8 to 11  are cross-sectional views of image sensors according to exemplary embodiments. 
     First, referring to  FIG. 8 , an image sensor  200  according to an exemplary embodiment does not include the autofocusing barrier  120  included in the image sensor  100  illustrated in FIG.  3 . However, other configurations of the image sensor  200  illustrated in  FIG. 8  correspond to the configurations of the image sensor  100 . The image sensor  200  according to an exemplary embodiment secondarily refracts incident light using a curved color filter  230 , so that light leaking to the other pixel areas PX can be reduced. In addition, since the autofocusing barrier  120  is formed by a separate process, process steps may be reduced. 
     Referring to  FIG. 9 , unlike the image sensor  100  illustrated in  FIG. 3 , an image sensor  300  according to an exemplary embodiment includes a. first device isolation film DTI 1  and a second device isolation film DTI 2  that have different thicknesses. For example, the thickness in the second direction of the second device isolation film DTI 2  is less than the thickness of the first device isolation film DTI 1 . However, other configurations of the image sensor  300  illustrated in  FIG. 9  correspond to the configurations of the image sensor  100 . 
     Referring to  FIGS. 10 and 11 , image sensors  400  and  500  according to exemplary embodiments include configurations that correspond to the configurations of the image sensor  100  illustrated in  FIG. 3 . On the other hand, the image sensors  400  and  500  further include second microlenses  445  and  545  disposed between the first microlenses  440  and  540  and the color filters  430  and  530 , respectively. For example, the second microlenses  445  and  545  secondly refract light that has been first refracted while passing through the first microlenses  440  and  540 . Light that is secondarily refracted by the image sensors  400  and  500  according to an exemplary embodiment passes through the color filters  430  and  530 , and are thirdly refracted to enter substrates  410  and  510 . 
     On the other hand, the diameters of the second microlenses  445  and  545  in the image sensors  400  and  500  are not limited to those illustrated, and the diameters are designed for the incident light to pass through the color filters  430  and  530  and to be incident onto the substrates  410  and  510 . For example. as in the second microlens  445  in the image sensor  400  illustrated in  FIG. 10 , the second microlens  445  shares an optical axis with the first microlens  440 . On the other hand, as in the second microlens  545  in the image sensor  500  illustrated in  FIG. 11 , the second microlens  545  share an optical axis with at least one of the four regions  531  and  532  in the color filter  530 . 
     Referring to  FIG. 10 , the second microlens  445  in the image sensor  400  according to an exemplary embodiment has a size that corresponds to the first microlens  440 . For example, the number of first microlenses  440  and the number of second microlenses  445  are the same. In addition, the curvature of the second microlens  445  is the same as the curvature of the first microlens  440 . However, this is only an example and the configuration is not limited thereto, and according to other embodiments, the curvature of the second microlens  445  may be greater or less than the curvature of the first microlens  440 . 
     Referring to  FIG. 11 , the second microlens  545  in the image sensor  500  according to an exemplary embodiment has a size that corresponds to a size of each of the four regions  531  and  532  in the color filter  530 , For example, one pixel area P\corresponds to tow second microlenses  545 . In addition, the curvature of each of the second microlens  545  is the same as the curvature of each of the four regions  531  and  532  in the color filter  530 . However, this is only an example and the configuration is not limited thereto. According to other embodiments, the curvature of each of the second microlens  545  may be greater or less than the curvature of each of the four regions  531  and  532  in the color filter  530 . 
     In exemplary embodiments illustrated in  FIGS. 8 to 11 , the image sensors  200 ,  300 ,  400 , and  500  include curved color filters  230 ,  330 ,  430  and  530 , by way of example, thereby improving performance or yield of the image sensors  200 ,  300 ,  400  and  500 . However, embodiments of the present inventive concept are not limited thereto, and in the image sensors  200 ,  300 ,  400 , and  500  according to exemplary embodiments, autofocusing sensitivity loss is significantly reduced using the curved color filters  230 ,  330 ,  430  and  530 , and other configurations can be variously modified. 
       FIG. 12  is a flowchart of a process of manufacturing an image sensor illustrated in  FIG. 3 , according to an exemplary embodiment. 
     Referring to  FIG. 12 , a method of manufacturing the image sensor  100  illustrated in FIG.  3  according to an exemplary embodiment includes etching a color lens, unlike a manufacturing process of a general image sensor. To manufacture the image sensor  100 , first, an internal device isolation film is formed by filling a trench formed in a substrate with an insulating material (S 11 ). For example, the internal device isolation film includes a first device isolation film that separates pixel areas from each other and a second device isolation film that separates photodiodes from each other. For example, the first device isolation film and the second device isolation film are formed at the same time. However, embodiments of the present inventive concept are not limited thereto, and in other embodiments, the first device isolation film and the second device isolation film are formed in separate processes. 
     In an embodiment, a portion of the substrate is removed through a polishing process, and a pixel circuit that controls the operation of the image sensor  100  is disposed on one surface of the partially removed substrate (S 12 ). in addition, another portion of the substrate is further removed through a polishing process in the opposite direction, and an autofocusing barrier is disposed on the other surface of the partially removed substrate (S 13 ). However, this is only an example, and in other embodiments, as described above, the image sensor does not include an autofocusing barrier. For example, one surface of the substrate is where the internal device isolation film starts to be formed, and the internal device isolation film extends toward the other surface of the substrate. 
     In an embodiment, a color filter that extracts a light component having a predetermined wavelength is formed on the other surface of the substrate (S 14 ). The color filter is formed by a deposition process, and the color filter is divided by an autofocusing barrier. However, embodiments of the present inventive concept are not limited thereto, and in other embodiments, when there is no autofocusing barrier, color filters of different colors can be formed, based on a direction in which the first device isolation film extends as a boundary. In addition, the color of the color filter also varies depending on exemplary embodiments. 
     In an embodiment, thee color filter is initially formed to have a flat upper surface in directions parallel to the upper surface of the substrate, and is subsequently etched to have a convex upper surface that refracts incident light (S 15 ), For example, the color filter includes regions that correspond to respective photodiodes, and each region has a convex upper surface. However, this is only an example, and in other embodiments, the shape of the curved color filter is modified. 
     In an embodiment, a microlens is deposited on the upper surface of the color filter (S 16 ), and the deposited microlens is etched to refract incident light (S 17 ). The shape of the etched microlens is not limited to a particular shape, and can be variously changed in other embodiments. However, the microlens corresponds to one pixel area that includes four photodiodes. The image sensor  100  can be manufactured by the operations S 11  to S 17 , and a detailed form of the image sensor  100  in each operation will be described below. 
       FIGS. 13A to 13H  are cross-sectional views that illustrate a process of manufacturing an image sensor illustrated in  FIG. 3 , according to an exemplary embodiment. 
       FIGS. 13A . to  13 H are cross-sectional views that illustrate a step-by-step manufacturing process of the image sensor  100  according to an exemplary embodiment described in  FIG. 12 . First,  FIG. 13A  is a cross-sectional view of the image sensor  100  in operation S 11  in which internal device isolation films DTI 1  and DTI 2  of device isolation film DTI are formed in trenches on the substrate  110 . For example, to form a trench in a space in which the internal device isolation film DTI is to be formed, a mask layer M is stacked on one surface of the substrate  110 . For example, a trench is not formed in a space covered by the mask layer M, and an insulating material fills the inside of a trench formed in a space not covered by the mask layer M o form the internal device isolation film DTI. The mask layer M is removed together with portions of the substrate  110  and the internal device isolation film DTI by a polishing process. For example, the upper surface of the substrate  110  that remains after portions are removed by the polishing process is the second surface  112 . 
     Referring to  FIG. 13B , in an embodiment, a pixel circuit is disposed on the second surface  112  that remains after the polishing process is performed in the image sensor  100 . As described above, the pixel circuit includes the plurality of elements  160 , the wiring patterns  170  connected to the plurality of elements  160 , an insulating layer  180  that covers the plurality of elements  160  and the wiring patterns  170 , a floating diffusion region  150 , etc. The pixel circuit controls the operation of the image sensor  100 . On the other hand, portions of the substrate  110  and the internal device isolation film DT 1  on the opposite side of the second surface  112  of the substrate  110  are removed by a polishing process. For example, the opposite upper surface of the substrate  110  that remains after portions are removed by the polishing process is the first surface  111 . Therefore, an internal structure and a pixel circuit of the substrate  110  of the image sensor  100  can be manufactured. 
     Referring to  FIG. 13C , in an embodiment, the first device isolation film DTI 1  and the second device isolation film DT 12  in the image sensor  100  are connected to the second surface  112  and the first surface  111  of the substrate  110 . However, this is only an example and embodiments are not limited to the illustrated configuration. In other embodiments, the first device isolation film DTI 1  and the second device isolation film DTI 2  have different lengths. In detail, extension lengths of the first device isolation film DTI 1  and the second device isolation film DTI 2  differ from each other. 
     In an embodiment, the first device isolation film DTI 1  and the second device isolation film DTI 2  extend from the second surface  112  of the substrate  110  toward the first surface  111 , The first device isolation film DTI 1  and the second device isolation film DTI 2  extend in different directions. The internal device isolation film DTI that extends from the second surface  112  toward the first surface  111  includes polysilicon, and the internal device isolation film DTI that extends from the first surface  111  toward the second surface  112  includes a metal. When light is incident, polysilicon has a higher absorption rate than metal. Accordingly, when the image sensor  100  according to an exemplary embodiment includes the internal device isolation film DTI that includes polysilicon and extends from the second surface  112  toward the first surface  111 , the improvement of the autofocusing sensitivity is enhanced. However, embodiments of the present in concept are not limited thereto, and other embodiments can incorporate the image sensor  100  that includes the internal device isolation film DTI that includes metal and extends from the first surface  111  toward the second surface  112 . 
     Referring to  FIGS. 13D to 13H , in an embodiment, a manufacturing process of the image sensor  100  in steps S 13  to S 17  of  FIG. 12  is illustrated. For example, the autofocusing barrier  120  is formed on the, second surface  112  of the substrate  110 , the color filter  130  is deposited, and the color filter  130  is etched to form the convex upper surfaces. Subsequently, a first mice lens  140  that collects incident light is deposited on the upper surface of the curved color filter  130 , and the first microlens  140  undergoes an etching process to form the convex upper surfaces, thereby it manufacturing the image sensor  100  as illustrated in  FIG. 3 . However, this is only an example and embodiments are not limited to this configuration. in other embodiments, a manufacturing process can vary depending on the configuration and effect of the image sensor  100 . 
       FIGS. 14 and 15  schematically illustrate an electronic device that includes an image sensor according to an exemplary embodiment. 
     Referring to  FIG. 14 , in an embodiment, an electronic device  1000  includes a camera module group  1100 , an application processor  1200 , a power management integrated circuit (PMIC)  1300 , and an external memory  1400 . 
     In an embodiment, the camera module group  1100  includes a plurality of camera modules  1100   a  ,  1100   b  , and  1100   c  Although the drawing shows an embodiment that includes three camera modules  1100   a  ,  1100   b , and  1100   c  , embodiments are not limited thereto. In some embodiments, the camera module group  1100  includes only two camera modules, and in other embodiments, the camera module group  1100  includes n camera modules, where n is a natural number of  4  or more. In addition, in an embodiment, at least one of the plurality of camera modules  1100   a  ,  1100   b  , and  1100   c  in the camera module group  1100  includes an image sensor according to an exemplary embodiment described above with reference to  FIGS. 1 to 13H . 
     Hereinafter, a detailed configuration of the camera module  1100  will be described with reference to  FIG. 15 , but the following description also equally applies to the other camera modules  1100   a  and  1100   b  , according to an exemplary embodiment. 
     Referring to  FIG. 15 , in an embodiment, the camera module  1100   b  includes a prism  1105 , an optical path folding element  1110 , hereinafter referred to as “OPFE”, an actuator  1130 , an image sensing device  1140 , and a storage device  1150 . 
     In an embodiment, the prism  1105  changes the path of externally incident light L and includes a reflective surface  1107  of light reflecting material. 
     In some embodiments, the prism  1105  changes the path of light L incident in a first direction X to a second direction Y perpendicular to the tint direction X. In addition, the prism  1105  rotates the reflective surface  1107  of the light reflective material in the direction A around the central axis  1106 , or rotates in the direction B to change the path of the incident light L to the vertical second direction Y. in addition. the OPFF  1110  can also move in a third direction Z perpendicular to the first direction. X and the second direction Y. 
     In some embodiments, as illustrated, the maximum rotation angle of the prism  1105  in the A direction is less than 15 degrees in the positive (+) A direction, and may be greater than 15 degrees in the negative (−) A direction. However, embodiments are not limited thereto. 
     In some embodiments, the prism  1105  rotates between 20 degrees in the plus (+) or minus (−) B direction, or between 10 degrees and 20 degrees, or between 15 degrees and 20 degrees, where the angle of movement is positive. The prism  105  may rotate at the same angle in the (+) or minus (−) B direction, or it may rotate to almost the same angle in the range of around 1 degree. 
     In some embodiments, the prism  1105  moves the reflective surface  1107  in a third direction, such as the Z direction, parallel to the extension direction of the central axis  1106 . 
     In some embodiments, the OPFE  1110  includes, for example, an optical lens that includes m groups, where m is a natural number. The m lenses cart move in the second direction Y to change the optical zoom ratio of the camera module  1100   b . For example, if the basic optical zoom magnification of the camera module  1100   b  is Z, then moving the m optical lenses in the OPFE  1110  changes the optical zoom magnification of the camera module  1100   b  to, e.g., 3Z or 5Z, or changes the optical zoom magnification to be 5Z or higher. 
     In some embodiments, the actuator  1130  moves the OPFE  1110  or an optical lens, hereinafter referred to as an optical lens, to a specific position. For example, the actuator  1130  adjusts the position of the optical lens so that an image sensor  1142  of the image sensing device  1140  is positioned at a focal length of the optical lens for accurate sensing. 
     In some embodiments, the image sensing device  1140  includes the image sensor  1142 , a control logic  1144 , and a memory  1146 . The image sensor  1142  senses an image of a sensing target using light L received through the optical lens. The control logic  1144  controls the overall operation of the camera module  1100   b . For example, he control logic  1144  controls the operation of the camera module  1100   b  according to a control signal received, through a control signal line CSLb. 
     In some embodiments, the memory  1146  stores information for the operation of the camera module  1100   b  , such as calibration data  1147 . The calibration data  1147  includes information for the camera module  1100   b  to generate image data using light L received from the outside. The calibration data  1147  includes, for example, information on a degree of rotation described above, information on a focal length, information on an optical axis, etc. When the camera module  1100   b  is implemented in the form of a multi-state camera whose focal length changes according to the position of the optical lens, the calibration data  1147  includes the focal length values for each position or state of the optical lens and information related to autofocusing. 
     In some embodiments, the storage unit  1150  stores image data sensed through the image sensor  1142 . The storage unit  1150  is disposed outside of the image sensing device  1140  and is stacked with a sensor chip that constitutes the image sensing device  1140 . In some embodiments, the storage unit  1150  is implemented as an Electrically Erasable Programmable Read-Only Memory (EEPROM), but embodiments are not limited thereto. 
     Referring to  FIGS. 14 and 15  together, in some embodiments, each of the plurality of camera modules  1100   a  ,  1100   b  , and  1100   c  include a an actuator  1130 . Accordingly, each of the plurality of camera modules  1100   a  ,  1100   b , and  1100   c  may include the same or different calibration data  1147  according to the operation of the actuator  1130  included therein. 
     In some embodiments, one of the plurality of camera modules  1100   a  ,  1100   b  and  1100   c  , such as  1100   b  , is a folded lens-type camera module that includes the prism  1105  and OPFE  1110  described above, and the remaining camera modules, such as  1100   a  and  1100   c  , are vertical type camera modules that do not include the prism  1105  and the OPFE  1110 , but embodiments are not limited thereto. 
     In some embodiments, one of the plurality of camera modules  1100   a  ,  1100   b  and  1100   c  , such as camera module  1100   c  , is a vertical type camera module that extracts depth information using, for example, infrared (IR) light, and is a type of depth camera. in this case, the application processor  1200  merges the image data received from the depth camera and the image data received from another camera module, such as camera module  1100   a  or  1100   b  , to generate a 3D depth image. 
     In a some embodiments, at least two of the plurality of camera modules  1100   a  ,  1100   b  , and  1100   c  , such as camera modules  1100   a  and  1100   b  , have different fields of view (view fields). In this case, for example, the optical lenses of at least two of the plurality of camera modules  1100   a  ,  1100   b  , and  1100   c  , such as camera modules  1100   a  and  1100   b  , are different from each other, but embodiments are not limited thereto. 
     In addition, in some embodiments, viewing angles of each of the plurality of camera modules  1100   a  ,  1100   b  , and  1100   c  differ from each other. In this case, the optical lenses in each of the plurality of camera modules  1100   a  ,  1100   b  , and  1100   c  are different from each other, but embodiments of the present disclosure are not limited thereto. 
     In some embodiments, each of the plurality of camera modules  1100   a  ,  1100   b  , and  1100   c  are physically separated from each other. For example, the sensing area of one image sensor  1142  is not divided and shared by the plurality of camera modules  1100   a  ,  1100   b  , and  1100   c  . Rather, an independent image sensor  1142  is disposed inside each of the plurality of respective camera modules  1100   a  ,  1100   b  , and  1100   c.    
     Referring back to  FIG. 14 , in some embodiments, the application processor  1200  includes an image processing device  1210 , a memory controller  1220 , and an internal memory  1230 . The application processor  1200  is implemented separately from the plurality of camera modules  1100   a  ,  1100   b  , and  1100   c  . For example, the application processor  1200  and the plurality of camera modules  1100   a  ,  11001 , and  1100   c  are separated from each other as separate semiconductor chips. 
     In some embodiments, the image processing apparatus  1210  includes a plurality of sub-image processors  1212   a  ,  1212   b  , and  1212   c  , an image generator  1214 , and a camera module controller  1216 . 
     In some embodiments, the plurality of sub-image processors  1212   a  ,  1212   b  , and  1212   c  correspond to the number of the plurality of camera modules  1100   a  ,  1100   b  , and  1100   c  , and each sub-image processors  1212   a  ,  1212   b  , and  1212   c  corresponds to a respective camera module  1100   a  ,  1100   b  , and  1100   c.    
     In some embodiments, image data generated from each of the camera modules  1100   a  ,  1100   b  , and  1100   c  is provided to the corresponding sub-image processors  1212   a  ,  1212   b  , and  1212   c  through separate image signal lines ISLa, ISLb, and ISLc, respectively. For example, image data generated from the camera module  1100   a  is provided to the sub-image processor  1212   a  through image signal line ISLa, and the image data generated from the camera module  1100   b  is provided to the sub-image processor  1212   a  through image signal line ISLb. The image data generated from the camera module  1100   c  is provided to the sub-image processor  1212   c  through image signal line ISLc. Such image data transmission is performed using, for example, a camera serial interface (CSI) based on a Mobile Industry Processor Interface (MIPI), but embodiments are not limited thereto. 
     On the other hand, in some embodiments, one sub-image processor is arranged to correspond to a plurality of camera modules. For example, the sub image processor  1212   a  and the sub image processor  1212   c  are not implemented separately from each other as illustrated, but are integrated into one sub image processor. The image data provided from the camera module  1100   a  and the camera module  1100   c  may be selected through a selection element, such as a multiplexer, etc, and then provided to an integrated sub-image processor. 
     In some embodiments, image data provided to each of the sub-image processors  1212   a  ,  1212   b  , and  1212   c  . is provided to the image generator  1214 . The image generator  1214  generates an output image using image data received from each of the sub-image processors  1212   a  ,  1211   b , and  1212   c  according to image generating information or a mode signal. 
     Specifically, in some embodiments, the image generator  1214  merges at least some of the image data received from the camera modules  1100   a  ,  1100   b  , and  1100   c  , which have different viewing angles, according to the image generation information or the mode signal to generate an output image. On the other hand, the image generator  1214  may generate an output image by selecting image data generated from one of the camera modules  1100   a  ,  1100   b  , and  1100   c  according to the image generation information or the mode signal. 
     In some embodiments, the image generation information includes a zoom signal or a zoom factor. Further, in some embodiments, the mode signal is, for example, a signal based on a mode selected by a user. 
     In some embodiments, when the image generation information is a zoom signal or zoom factor, and each camera module  1100   a  ,  1100   b  ,  1100   c  has a different viewing field or viewing angle, the image generator  1214  operates differently according to the type of the zoom signal. For example, when the zoom signal is a first signal, then, after merging the image data received from two camera modules, such as camera module  1100   a  and camera module  1100   c  , an output image is generated by the merged image signal and the image data output from the camera module not used for merging an output image, in this case camera module ( 1100   b ). If the zoom signal is a second signal different from the first signal, the image generator  1214  does not perform such image data merging, and converts image data received from any one of the camera module  1100   a  ,  1100   b  ,  1100   c  , to create an output image. However, embodiments are not limited thereto, and in other embodiments, a method of processing image data can be modified and implemented as needed. 
     In some embodiments, the image generator  1214  receives high dynamic range (HDR) image data that has a different exposure time from at least one of the plurality of sub-image processors  1212   a  ,  1212   b  , and  1212   c  , and generates merged image data with an increased dynamic range. 
     In some embodiments, the camera module controller  1216  provides a control signal to each of the camera modules  1100   a  ,  1100   b  , and  1100   c  , The control signal generated from the camera module controller  1216  is transmitted to the corresponding camera modules  1100   a  ,  1100   b  , and  1100   c  through separate control signal lines CS 1   a , CS 1   b , and CSLc, respectively, 
     In some embodiments, any one of the plurality of camera modules  1100   a  ,  1100   b  ,  1100   c  can be designated as a master camera, such as camera module  1100   b  , according to the image generation information which includes a zoom signal, or the mode signal, and the remaining camera modules (such as camera modules  1100   a  and  1100   c  are designated as slave cameras. Such information is included in the control signal and transmitted to the corresponding camera modules  1100   a  ,  1100   b  , and  1100   c  through the respective control signal lines CSLa, CSLb, and CSLc. 
     In an embodiment, the selection of camera modules that operate as masters and slaves can be changed according to the zoom factor or the operation mode signal. For example, when the viewing angle of the camera module  1100   a  is wider than that of the camera module  1100   b  and the zoom factor shows a low zoom magnification, the camera module  1100   b  operates as a master, and the camera module  1100   a  is a slave. Conversely, when the zoom factor indicates a high zoom magnification, the camera module  1100   a  operates as a master and the camera module  1100   b  operates as a slave. 
     In some embodiments, a control signal provided from the camera module controller  1216  to each of the camera modules  1100   a  ,  1100   b  , and  1100   c  includes a sync enable signal. For example, when the camera module  1100   b  is a master camera and the camera modules  1100   a  and  1100   c  are slave cameras, the camera module controller  1216  transmits a sync enable signal to the camera module  1100   b  . The camera module  1100   b  that receives the sync enable signal generates a sync signal based on the received sync enable signal, and transmits the generated sync signal to the camera modules  1100   a  and  1100   c  . The camera module  1100   b  and the camera modules  1100   a  and  1100   c  are synchronized by the sync signal to transmit image data to the application processor  1200 . 
     In some embodiments, the control signal provided from the camera module controller  1216  to the plurality of camera modules  1100   a  ,  1100   b  , and  1100   c  includes mode information according to the mode signal. Based on this mode information, the plurality of camera modules  1100   a  ,  1100   b , and  1100   c  can operate in a first operation mode or a second operation mode, depending on the sensing speed. 
     In some embodiments, in the first operation mode, the plurality of camera modules  1100   a  ,  1100   b  , and  1100   c  generate an image signal at a first rate, such as a first frame rate, and encode the image signal at a second rate that is higher than the first rate, and transmit the encoded image signal to the application processor  1200 . In this case, the second speed may be  30  times or greater than the first speed. 
     In some embodiments, the application processor  1200  stores the received image signal, for example, the encoded image signal, in the memory  1230  provided therein or the external storage  1400 , and then, the encoded image signal is read from the memory  1230  or the storage  1400  and decoded, and the image data generated from the decoded image signal is displayed. For example, a corresponding subprocessor of the plurality of subprocessors  1212   a  ,  1212   b  , and  1212   c  performs decoding and performs image processing on the decoded image signal. 
     In some embodiments, in me second operation mode, the plurality of camera modules  1100   a  ,  1100   b  , and  1100   c  generate an image signal at a third frame rate that is lower than the first frame rate and transmits the image signal to the application processor  1200 . The image signal provided to the application processor  1200  is an unencoded signal. The application processor  1200  may perform image processing on the received image signal, or may store the image signal in the memory  1230  or the storage  1400 . 
     In some embodiments, the PMIC  1300  supplies power, such as a power voltage, to each of the plurality of camera modules  1100   a  ,  1100   b  , and  1100   c  . For example, the MC  1300 , under the control of the application processor  1200 , supplies a first power to the camera module  1100   a  through the power signal lino PSLa, supplies a second power to the camera module  1100   b  through the power signal line PSLb, and supplies a third power to the camera module  1100   c  through the power signal line PSLc. 
     In some embodiments, the PMIC  1300  generates power for each of the plurality of camera modules  1100   a  ,  1100   b  , and  1100   c  in response to a power control signal PCON received from the application processor  1200 , and also adjusts the power level. The power control signal PCON includes a power adjustment signal for each operation mode of the plurality of camera modules  1100   a  ,  1100   b  , and  1100   c  . For example, the operation mode includes a low power mode, and in this case, the power control signal PCON includes information on a camera module that operates in a low power mode and a set power level. Levels of power signals provided to each of the plurality of camera modules  1100   a  ,  1100   b  , and  1100   c  may be the same or different from each other. In addition, the level of power signals can be dynamically changed. 
     As set forth above, an image sensor according to an exemplary embodiment includes a color filter that has convex upper surfaces for respective pixel areas. On the other hand, light that is refracted and incident through a microlens passes through the color filter and is refracted again to enter the substrate. Accordingly, loss of autofocusing sensitivity according to the structure of an internal device isolation film is reduced. 
     While exemplary embodiments have been illustrated and described above, it will be apparent to those skilled in the art that modifications and variations could be made without departing from the scope of embodiments of the present invective concept as defined by the appended claims.