Abstract:
An image sensor includes a substrate having adjacent pixel regions and respective photodiode regions therein, and a pixel separation portion including a trench extending into the substrate between the adjacent pixel regions. The trench includes a conductive common bias line therein and an insulating device isolation layer between the common bias line and surfaces of the trench. A conductive interconnection is coupled to the common bias line and is configured to provide a negative voltage thereto. Related fabrication methods are also discussed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation application of and claims priority from U.S. patent application Ser. No. 14/191,670, filed on Feb. 27, 2014, and claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2013-0022858, filed on Mar. 4, 2013, in the Korean Intellectual Property Office, the entire contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     Example embodiments of the inventive concept relate to image sensors and methods of forming the same. 
     Image sensors are semiconductor devices capable of converting electric signals into optical images. Image sensors may be classified into various types, including charge coupled device (CCD) type and complementary metal oxide semiconductor (CMOS) type. A CMOS image sensor (CIS) may include pixels arranged in two dimensions. Each of the pixels may include a photodiode (PD), which converts incident light into electric signal. 
     As semiconductor devices become more highly integrated, image sensors may likewise become highly integrated. Accordingly, the corresponding pixels may be scaled down, such that cross talk may increasingly occur between pixels. 
     SUMMARY 
     Example embodiments of the inventive concept provide highly-integrated image sensors capable of improving dark current properties and methods of fabricating the same. 
     According to example embodiments of the inventive concepts, an image sensor includes a substrate having adjacent pixel regions comprising respective photodiode regions therein, and a pixel separation portion comprising trench extending into the substrate between the adjacent pixel regions. The trench includes a conductive common bias line therein and an insulating device isolation layer between the common bias line and surfaces of the trench. A conductive interconnection is coupled to the common bias line and is configured to provide a voltage thereto. 
     In example embodiments, the trench including the common bias line therein may define a grid including the pixel regions therebetween in plan view. 
     In example embodiments, the trench including the common bias line therein may not extend completely through the substrate. The pixel separation portion may further include a channel stop region between the insulating device isolation layer in the trench and a surface of the substrate. The channel stop region has a conductivity type opposite to that of the respective photodiode regions. 
     In example embodiments, the surface of the substrate may be a light-receiving surface adjacent the respective photodiode regions. The channel stop region may continuously extend from the insulating device isolation layer in the trench to the surface of the substrate. 
     In example embodiments, the trench may have differing depths such that the common bias line therein has a non-planar surface. A distance from the surface of the substrate to the insulating device isolation layer in the trench may be greater in portions of the trench separating two of the adjacent pixel regions than in portions of the trench defining an intersection between four of the adjacent pixel regions. 
     In example embodiments, the surface of the substrate may be opposite a light-receiving surface thereof. 
     In example embodiments, the pixel separation portion may further include a shallow trench isolation region between the channel stop region and the surface of the substrate. The channel stop region may continuously extend from the insulating device isolation layer in the trench to the shallow trench isolation region. A depth of the shallow trench isolation region may be less than that of the insulating device isolation region. 
     According to further example embodiments of the inventive concepts, an image sensor may include a substrate, in which a plurality of pixel regions are provided and which has a first surface and a second surface facing or opposite each other, a photoelectric conversion part formed in each of the pixel regions of the substrate, a gate electrode provided on the photoelectric conversion part, and a pixel separation portion provided in the substrate to separate the pixel regions from each other. The pixel separation portion may include a deep device isolation layer and a common bias line provided in the deep device isolation layer, and the common bias line may be configured to be applied with a negative voltage. Here, light may be incident into the image sensor through the second surface. 
     In example embodiments, in plan view, the common bias line may have a mesh shape. 
     In example embodiments, the common bias line may have a curved top or bottom surface. 
     In example embodiments, the common bias line may be electrically isolated from the substrate. 
     In example embodiments, the common bias line may have a bottom surface positioned adjacent to the first surface and electrically connected to an external-voltage-applying wire. Alternatively, the common bias line may have a top surface positioned adjacent to the second surface and electrically connected to an external-voltage-applying wire. 
     In example embodiments, the substrate may further include an optical black region provided spaced apart from the pixel regions, and the image sensor may further include an optical black pattern provided on the optical black region. The optical black pattern and the external-voltage-applying wire include the same material. 
     In example embodiments, the substrate may further include a pad region provided spaced apart from the pixel region, and the image sensor may further include a through via provided through the pad region. The through via and the external-voltage-applying wire include the same material. 
     In example embodiments, the pixel separation portion may further include a channel-stop region in contact with the deep device isolation layer. 
     In example embodiments, the image sensor may further include a shallow device isolation layer that is provided in contact with the first surface and spaced apart from the deep device isolation layer. The shallow device isolation layer may have a depth smaller than that of the deep device isolation layer. The channel-stop region may be provided between the deep device isolation layer and the shallow device isolation layer. 
     According to example embodiments of the inventive concepts, a method of fabricating an image sensor may include forming a pixel separation portion in a substrate to define pixel regions. The substrate may have a first surface and a second surface facing each other. Thereafter, a photoelectric conversion part and a gate electrode may be formed in or on each of the pixel regions. The pixel separation portion may be formed to include a deep device isolation layer and a common bias line that is provided in the deep device isolation layer and is applied with a negative voltage. Here, light may be incident into the image sensor through the second surface. 
     In example embodiments, the forming of the pixel separation portion may include etching a portion of the substrate adjacent to the first surface to form a deep trench, forming the deep device isolation layer to cover conformally side and bottom surface of the deep trench, and forming the common bias line to fill the deep trench. 
     In example embodiments, the forming of the pixel separation portion may include etching a portion of the substrate adjacent to the second surface to form a deep trench, forming the deep device isolation layer to cover conformally side and bottom surface of the deep trench, and forming the common bias line to fill the deep trench. 
     In example embodiments, the substrate may further include an optical black region spaced apart from the pixel regions. In this case, the method may further include forming an insulating layer to cover the second surface, and forming an optical black pattern in the insulating layer on the optical black region and an external-voltage-applying wire connected to the common bias line. The optical black pattern and the external-voltage-applying wire may be formed using the same process. 
     In example embodiments, the substrate may further include a pad region spaced apart from the pixel regions. In this case, the method may further include forming an insulating layer to cover the second surface, and forming a through via and an external-voltage-applying wire. The through via may be formed to penetrate the insulating layer and the pad region of the substrate, and the external-voltage-applying wire may be connected to the common bias line. The through via and the external-voltage-applying wire may be formed using the same process. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Example embodiments will be more clearly understood from the following brief description taken in conjunction with the accompanying drawings. The accompanying drawings represent non-limiting, example embodiments as described herein. 
         FIG. 1  is a circuit diagram of an image sensor according to example embodiments of the inventive concept 
         FIG. 2  is a layout illustrating an image sensor according to example embodiments of the inventive concept. 
         FIGS. 3A and 3B  are sectional views taken along lines A-A′ and B-B′, respectively, of  FIG. 2 . 
         FIGS. 4A through 9A  are sectional views taken parallel to the line A-A′ of  FIG. 2  to illustrate a process of fabricating the image sensor of  FIG. 2 . 
         FIGS. 4B through 9B  are sectional views taken parallel to the line B-B′ of  FIG. 2  to illustrate a process of fabricating the image sensor of  FIG. 2 . 
         FIG. 10  is a layout illustrating an image sensor according to other example embodiments of the inventive concept. 
         FIG. 11  is a sectional view taken along a line C-C′ of  FIG. 10  to illustrate the image sensor according to other example embodiments of the inventive concept. 
         FIGS. 12 through 17  are sectional views illustrating a process of fabricating the image sensor of  FIG. 11 . 
         FIG. 18  is a sectional view taken along a line C-C′ of  FIG. 10  to illustrate an image sensor according to still other example embodiments of the inventive concept. 
         FIG. 19  is a block diagram illustrating an electronic device including an image sensor, according to example embodiments of the inventive concept. 
         FIGS. 20 through 24  show examples of multimedia devices, to which image sensors according to example embodiments of the inventive concept can be provided. 
     
    
    
     It should be noted that these figures are intended to illustrate the general characteristics of methods, structure and/or materials utilized in certain example embodiments and to supplement the written description provided below. These drawings are not, however, to scale and may not precisely reflect the precise structural or performance characteristics of any given embodiment, and should not be interpreted as defining or limiting the range of values or properties encompassed by example embodiments. For example, the relative thicknesses and positioning of molecules, layers, regions and/or structural elements may be reduced or exaggerated for clarity. The use of similar or identical reference numbers in the various drawings is intended to indicate the presence of a similar or identical element or feature. 
     DETAILED DESCRIPTION 
     Example embodiments of the inventive concepts will now be described more fully with reference to the accompanying drawings, in which example embodiments are shown. Example embodiments of the inventive concepts may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of example embodiments to those of ordinary skill in the art. In the drawings, the thicknesses of layers and regions are exaggerated for clarity. Like reference numerals in the drawings denote like elements, and thus their description will be omitted. As used herein the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Other words used to describe the relationship between elements or layers should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” “on” versus “directly on”). 
     It will be understood that, although the terms “first”, “second”, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of example embodiments. 
     Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes” and/or “including,” if used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof. 
     Example embodiments of the inventive concepts are described herein with reference to cross-sectional illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of example embodiments. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, example embodiments of the inventive concepts should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, an implanted region illustrated as a rectangle may have rounded or curved features and/or a gradient of implant concentration at its edges rather than a binary change from implanted to non-implanted region. Likewise, a buried region formed by implantation may result in some implantation in the region between the buried region and the surface through which the implantation takes place. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of example embodiments. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments of the inventive concepts belong. It will be further understood that terms, such as those defined in commonly-used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
       FIG. 1  is a circuit diagram of an image sensor according to example embodiments of the inventive concept. 
     Referring to  FIG. 1 , the image sensor may include a plurality of unit pixels, each of which includes a photoelectric conversion region PD, a transfer transistor Tx, a source follower transistor Sx, a reset transistor Rx, and a selection transistor Ax. The transfer transistor Tx, the source follower transistor Sx, the reset transistor Rx, and the selection transistor Ax may include a transfer gate TG, a source follower gate SF, a reset gate RG, and a selection gate SEL, respectively. A photoelectric conversion portion may be provided in the photoelectric conversion region PD. The photoelectric conversion portion may be a photodiode including an n-type impurity region and a p-type impurity region. The transfer transistor Tx may include a drain region serving as a floating diffusion region FD. The floating diffusion region FD may also serve as a source region of the reset transistor Rx. The floating diffusion region FD may be electrically connected to the source follower gate SF of the source follower transistor Sx. The source follower transistor Sx may be connected to the selection transistor Ax. The reset transistor Rx, the source follower transistor Sx, and the selection transistor Ax may be shared by adjacent pixels, and this makes it possible to increase an integration density of the image sensor. 
     Hereinafter, an operation of the image sensor will be described with reference to  FIG. 1 . In particular, when in a light-blocking state, a power voltage VDD may be applied to a drain region of the reset transistor Rx and a drain region of the source follower transistor Sx to turn on the reset transistor Rx and discharge electric charges from the floating diffusion region FD. Thereafter, if the reset transistor Rx is turned-off and external light is incident into the photoelectric conversion region PD, electron-hole pairs may be generated in the photoelectric conversion region PD. Holes may be moved toward the p-type doped region, and electrons may be moved toward and accumulated in the n-type doped region. If the transfer transistor Tx is turned on, the electric charges (e.g., electrons) may be transferred to and accumulated in the floating diffusion region FD. A change in amount of the accumulated charges may lead to a change in gate bias of the source follower transistor Sx, and this may lead to a change in source potential of the source follower transistor Sx. Accordingly, if the selection transistor Ax is turned on, an amount of the charges may be transmitted or read out as a signal through a column line. 
       FIG. 2  is a layout illustrating an image sensor according to example embodiments of the inventive concept,  FIGS. 3A and 3B  are sectional views taken along lines A-A′ and B-B′, respectively, of  FIG. 2 . 
     Referring to  FIGS. 1, 2, 3A and 3B , a substrate  2  may be provided to include unit pixel regions UP. The substrate  2  may be a silicon wafer, a silicon-on-insulator (SOI) substrate, or a substrate including a semiconductor epitaxial layer. The substrate  2  may include a first surface  2   a  and a second surface  2   b  opposite each other. The second surface  2   b  may be arranged or configured in the image sensor such that light may be incident thereon, and is also referred to herein as a light-receiving surface  2   b.    
     A pixel separation portion  12  may be provided in the substrate  2  to separate the unit pixel regions UP from each other. In plan view, the pixel separation portion  12  may be shaped like a mesh or grid. In example embodiments, the pixel separation portion  12  may have a height that is substantially equivalent to a thickness of the substrate  2 . The pixel separation portion  12  may be formed through the substrate  2  to connect or otherwise extend between the first and second surfaces  2   a  and  2   b . The pixel separation portion  12  may include an insulating deep device isolation layer  11  and a conductive common bias line  13  therein. The deep device isolation layer  11  and the common bias line  13  may be in contact with each other. The pixel separation portion  12  may further include a channel-stop region  10  that is in contact with the deep device isolation layer  11 . The deep device isolation layer  11  may be formed of an insulating material, whose refractive index is different from that of the substrate  2 . For example, the deep device isolation layer DTI may be formed of at least one of a silicon oxide layer, a silicon nitride layer, or a silicon oxynitride layer. In the present embodiment, the deep device isolation layer  11  may be provided in contact with the first surface  2   a  and spaced apart from the second surface  2   b . A top surface of the deep device isolation layer  11  adjacent to the second surface  2   b  may have a curved or uneven structure. A distance from the second surface  2   b  to a top surface  6  of the deep device isolation layer  11  may be a first distance D 1  between two adjacent pixel regions UP, and a second distance D 2  (which is less than or equal to D 1 ) at an intersection of four adjacent pixel regions UP. 
     The common bias line  13  may be formed of at least one of an undoped or doped polysilicon layer, a metal silicide layer, or a metal-containing layer. Since the deep device isolation layer  11  has the curved or uneven top surface, the common bias line  13  may have a curved or uneven top surface. A line-shaped edge or linear portion  13   a  may be provided at an end portion of the common bias line  13 . The line-shaped edge  13   a  may be electrically connected to an edge contact  130  and an external-voltage-applying wire  132  that are provided adjacent to the first surface  2   a . The common bias line  13  may be applied with a negative voltage via the external-voltage-applying wire  132 . The negative voltage applied to the common bias line  13  may fix or attract holes to a surface of the deep device isolation layer  11 , and this makes it possible to improve a dark current property of the image sensor. 
     The channel-stop region  10  may be in contact with the second surface  2   b . For example, the photoelectric conversion part PD may be doped with n-type impurities, and the channel-stop region  10  may be doped with p-type impurities. Since the pixel separation portion  12  is formed to penetrate and extend through the substrate  2  from the first surface  2   a  to the second surface  2   b , each of the unit pixel regions UP can be electrically or optically isolated from the others, and thus, it is possible to reduce or prevent cross talk between the unit pixel regions UP from occurring by a slantingly incident light (that is, in response to incident light at oblique angles relative to the light-receiving surface  2   b ). Further, the photoelectric conversion part PD may be formed to be in contact with the sidewall of the pixel separation portion  12  and may have the same area as the unit pixel region UP, which can allow the image sensor to have an increased light-receiving area and/or an increased fill factor. 
     A plurality of transistors Tx 1 , Tx 2 , Rx, Dx, and Sx and a plurality of wires may be provided on the first surface  2   a . A well region PW may be provided on the photoelectric conversion part PD. In example embodiments, the well region PW may be doped with p-type impurities. Shallow device isolation layers STI may be provided on the well region PW to define active regions AR of the transistors Tx 1 , Tx 2 , Rx, Dx, and Sx. The shallow device isolation layer STI may be formed to have a depth smaller than the deep device isolation layer  11 . In example embodiments, the shallow device isolation layer STI and the deep device isolation layer  11  may be connected to each other, thereby constituting or defining a single body or region. For example, as shown in  FIG. 3A , the shallow device isolation layer STI and the deep device isolation layer  11  may be formed between the unit pixel regions UP to have an inverted ‘T’ shape. 
     In each of the unit pixel regions UP, the transfer gate TG serving as the gate electrode of the transfer transistor Tx 1  may be provided on the first surface  2   a  of the substrate  2 . A gate insulating layer  24  may be interposed between the transfer gate TG and the substrate  2 . A top surface of the transfer gate TG may be higher than the first surface  2   a  of the substrate  2 , and a bottom surface thereof may be positioned in the substrate  2  or the well PW. For example, the transfer gate TG may include a protruding portion  21  positioned on the substrate  2  and a buried portion  22  inserted into the substrate  2 . The floating diffusion region FD may be formed in a portion of the substrate  2  between an upper sidewall of the buried portion  22  and the shallow device isolation layer STI. The floating diffusion region FD may be doped with impurities having a different conductivity type from that of the well region PW. For example, the floating diffusion region FD may be doped with n-type impurities. 
     A doped ground region  26  may be formed in a portion of the active region AR, which is spaced apart from the transfer gate TG by the shallow device isolation layer STI. The doped ground region  26  may be doped with impurities having the same conductivity type as that of the well region PW. For example, the doped ground region  26  may be doped with p-type impurities. In example embodiments, an impurity concentration of the doped ground region  26  may be higher than that of the well region PW. The floating diffusion region FD and the doped ground region  26  may be electrically connected to at least one of contact plugs and wires  30  that are disposed on the first surface  2   a . The first surface  2   a  may be covered with a plurality of interlayered insulating layers  32 . 
     An anti-reflecting layer  38  may be formed to cover wholly the second surface  2   b . In each of the unit pixel regions UP, a color filter  42  and a micro-lens  44  may be provided on the anti-reflecting layer  38 . The color filter  42  may be a portion of a color filter array including a plurality of color filters arranged in the form of matrix. In example embodiments, the color filter array may be provided to form the Bayer pattern including a red filter, a green filter, and a blue filter; however, embodiments of the present inventive concept are not limited to particular filter colors. For example, in other embodiments, the color filter array may be configured to include a yellow filter, a magenta filter and a cyan filter. In certain embodiments, the color filter array may further include a white filter. 
       FIGS. 4A through 9A  are sectional views taken parallel to the line A-A′ of  FIG. 2  to illustrate a process of fabricating the image sensor of  FIG. 2 , and  FIGS. 4B through 9B  are sectional views taken parallel to the line B-B′ of  FIG. 2  to illustrate a process of fabricating the image sensor of  FIG. 2 . 
     Referring to  FIGS. 4A and 4B , the substrate  2  including first and second opposing surfaces  2   a  and  2   b  is prepared. The substrate  2  may be a silicon wafer, a silicon-on-insulator (SOI) substrate, and/or a substrate including a semiconductor epitaxial layer. The substrate  2  may be doped with, for example p-type impurities. An ion implantation process may be performed to form the photoelectric conversion part PD and the well region PW in the substrate  2 . The photoelectric conversion part PD may be doped with, for example, n-type impurities, and the well region PW may be doped with, for example, p-type impurities. The photoelectric conversion part PD and/or the well region PW may be formed after the formation of the pixel separation portion  12  is complete. A first mask pattern  3  may be formed on the first surface  2   a . The substrate  2  adjacent to the first surface  2   a  may be etched using the first mask pattern  3  as an etch mask, thereby forming the first trench  4  with a first depth D 3 . 
     Referring to  FIGS. 5A and 5B , an insulating layer is formed to fill the first trench  4  and is planarized to expose the first surface  2   a  and the shallow device isolation layer STI. 
     Referring to  FIGS. 6A and 6B , a second mask pattern  5  may be formed to cover the first surface  1   a  and define the pixel regions UP. The shallow device isolation layer STI and the substrate  2  may be etched using the second mask pattern  5  as an etch mask to form the second trench  6  having a second depth D 4 . The second trench  6  may be formed to include a plurality of grooves intersecting to each other, thereby having a grid- or mesh-like shape in plan view. Here, an amount of the substrate  2  that is etched is greater at an intersection between four adjacent pixel regions UP than between two adjacent pixel regions UP. That is, the etch amount of the substrate  2  may be larger at the intersection of the grooves, when compared with at each of the grooves. Accordingly, at this stage, the second trench  6  may have a third depth D 5  that is equivalent to or greater than the second depth D 4 . Further, the second trench  6  may have a curved or uneven bottom surface. For example, a distance from the second surface  2   b  to the bottom surface of the second trench  6  may be a first height H 1  between two adjacent unit pixel regions UP and a second height H 2 , which is equivalent to or smaller than the first height H 1 , between four adjacent unit pixel regions UP. An ion implantation process P 1  may be performed to the substrate  2  covered with the second mask pattern  5 , and thus, the channel-stop region  10  may be formed in portions of the substrate  2  exposed by the second trench  6 . The channel-stop region  10  may be doped with, for example, p-type impurities. 
     Referring to  FIGS. 7A and 7B , the second mask pattern  5  may be removed, and then, the insulating layer  11  may be conformally deposited to cover the side and bottom surfaces of the second trench  6 . The conductive layer  13  may be deposited to fill the second trench  6 . A planarization process may be performed to expose the first surface  2   a , and thus, the deep device isolation layer  11 , the common bias line  13 , and the line-shaped edge  13   a  may be formed in the second trench  6 . As a result, the pixel separation portion  12  including the deep device isolation layer  11 , the channel-stop region  10 , and the common bias line  13  may be formed to separate the unit pixel regions UP from each other. 
     Referring to  FIGS. 8A and 8B , the gate insulating layer  24  and the transfer gate TG may be formed on the first surface  2   a , and the floating diffusion region FD and the doped ground region  26  may be formed. The contact plugs and wires  30  and the interlayered insulating layers  32  may be formed on the first surface  2   a . In example embodiments, the edge contact  130  and the external-voltage-applying wire  132 , which are connected to the line-shaped edge  13   a , may be formed using the process of forming the contact plugs and wires  30 . 
     Referring to  FIGS. 8A, 8B, 9A, and 9B , the substrate  2  may be inverted or rotated in such a way that the second surface  2   b  faces upward. A grinding or CMP process may be performed to remove a portion of the substrate  2  adjacent to the second surface  2   b  by a first thickness T 1  and thereby to expose the channel-stop region  10 . Meanwhile, a variation in depth of the bottom surface of the deep device isolation layer  11  may be determined by that of the second trench  6 . Thus, if the pixel separation portion  12  included only the deep device isolation layer  11 , the polished surface of the substrate  2  (after the grinding or CMP process) may have a deteriorated surface flatness or uniformity, owing at least to the variation in depth of the bottom surface of the deep device isolation layer  11 . Further, during the grinding or CMP process, a stress may be exerted to an interface between the substrate  2  and the deep device isolation layer  11  to create many defects. The deterioration in surface uniformity or the increase of defects may result in increased variation in color between pixels or a deteriorated dark current property. In contrast, according to example embodiments of the inventive concept, the grinding or CMP process may be perform to expose the channel-stop region  10 , not the deep device isolation layer  11 , and thus, it is possible to improve the surface uniformity and reduce the number of defects in the grinding or CMP process. As a result, it is possible to realize the image sensor with an improved dark current property and a high image quality. 
     Thereafter, as shown in  FIGS. 3A and 3B , the anti-reflecting layer  38 , a first insulating layer  39 , a second insulating layer  40 , the color filter  42 , and the micro-lens  44  may be formed on the second surface  2   b  of the substrate  2 . 
       FIG. 10  is a layout illustrating an image sensor according to other example embodiments of the inventive concept.  FIG. 11  is a sectional view taken along a line C-C′ of  FIG. 10  to illustrate the image sensor according to other example embodiments of the inventive concept. 
     Referring to  FIGS. 10 and 11 , according to other example embodiments of the inventive concept, the image sensor may include the substrate  2  with the pixel region PR, the optical black region OB, the pad region TR, and the edge region ER. The unit pixel regions UP may be provided in the pixel region PR, and the optical black region OB and the pad region TR may be provided spaced apart from the pixel region PR. The line-shaped edge  13   a  may be provided in the edge region ER. The pixel separation portion  12  may include the deep device isolation layer  11 , the common bias line  13 , the channel-stop region  10 , and the shallow device isolation layer STI. In example embodiments, the deep device isolation layer  11  may be provided in contact with the second surface  2   b  and spaced apart from the first surface  2   a . The channel-stop region  10  may be provided between the shallow device isolation layer STI and the deep device isolation layer  11 . Each or at least one of the deep device isolation layer  11  and the common source line  13  may have a curved or uneven bottom surface. An optical black pattern  50  may be provided on the optical black region OB. A through via  52  may be provided in the pad region TR to penetrate the first insulating layer  39 , the anti-reflecting layer  38 , and the substrate  2 . An insulating spacer  46  may be interposed between the through via  52  and the substrate  2 . A solder ball  54  may be attached to the through via  52 . The edge contact  130  and the external-voltage-applying wire  132  may be provided in the first insulating layer  39  of the edge region ER to be in contact with the line-shaped edge  13   a . The through via  52 , the optical black pattern  50 , and the external-voltage-applying wire  132  may be formed of the same material (e.g., tungsten) in some embodiments. 
     The optical black pattern  50  may reduce or prevent light from being incident on or into a reference pixel provided thereunder. Since the reference pixel is in the light-blocking state, an amount of electric charges generated in the reference pixel (hereinafter, referred as to a reference charge amount) can be used to compare an amount of electric charges from the unit pixel regions UP (hereinafter, referred as to a unit charge amount), and to calculate a difference between the unit and reference charge amounts. This may make it possible to obtain more accurate signals from each unit pixel UP. 
     Except for the above described differences, the image sensor according to other example embodiments of the inventive concept may be configured to have substantially similar features as those of the previously-described embodiments. 
       FIGS. 12 through 17  are sectional views illustrating a process of fabricating the image sensor of  FIG. 11 . 
     Referring to  FIG. 12 , the first trench  4  may be formed, as shown in  FIG. 4A , and then, the second mask pattern  5  may be formed to cover the first mask pattern  3  and define a region for the channel-stop region  10 . The substrate  2  may be doped with impurities using the second mask pattern  5  as an ion injection mask to form the channel-stop region  10 . The channel-stop region  10  may be doped with, for example, p-type impurities. 
     Referring to  FIG. 13 , the first and second mask patterns  3  and  5  may be selectively removed to expose the first trench  4 . An insulating layer may be deposited to fill the first trench  4 , and then, the insulating layer may be etched to form the shallow device isolation layer STI having a flat or planar top surface. 
     Referring to  FIG. 14 , as described with reference to  FIG. 9A , the gate insulating layer  24 , the transfer gate TG, the floating diffusion region FD, the doped ground region  26 , the contact plugs and wires  30 , and the interlayered insulating layers  32  may be formed on or in the first surface  2   a  of the substrate  2 . In contrast to  FIG. 9A , the edge contact  130  and the external-voltage-applying wire  132  may not be formed at this stage. 
     Referring to  FIG. 15 , the substrate  2  may be inverted or turned-over, and a grinding or CMP process may be performed to remove a portion of the substrate  2  adjacent to the second surface  2   b  by a predetermined thickness. Here, the deep device isolation layer  11  may not be exposed during the grinding or CMP process, and thus, it is possible to reduce or prevent a polished surface of the substrate from having a reduced or lowered flatness or uniformity and to suppress surface defects from occurring. A portion of the substrate  2  adjacent to the second surface  2   b  may be etched to form the second trench  6  exposing the channel-stop region  10 . Thereafter, an insulating layer and a conductive layer may be sequentially formed to fill the second trench  6 , and may be planarized to form the deep device isolation layer  11 , the common bias line  13 , and the line-shaped edge  13   a . Due to the presence of the channel-stop region  10 , it is possible to reduce a depth of the second trench  6 , which may make it possible to prevent or suppress an etch damage from occurring. 
     Referring to  FIG. 16 , the anti-reflecting layer  38  and the first insulating layer  39  may be sequentially stacked on the second surface  2   b . The first insulating layer  39 , the anti-reflecting layer  38 , and the substrate  2  may be patterned to form a through-via hole  51   a  exposing the wire  30  on the pad region TR. The first insulating layer  39  may be patterned to form a first recess region  51   b  on the optical black region OB. The first insulating layer  39  and the anti-reflecting layer  38  may be patterned to form a second recess region  51   c  on the edge region ER. 
     Referring to  FIG. 17 , a conductive layer may be deposited and planarized to form the through via  52 , the optical black pattern  50 , and the edge contact and external-voltage-applying wire  130  and  132  filling the through-via hole  51   a , the first recess region  51   b , and the second recess region  51   c , respectively. 
     Subsequent processes may be performed in the same or similar manner as that described in example embodiments of the inventive concept. 
       FIG. 18  is a sectional view taken along a line C-C′ of  FIG. 10  to illustrate an image sensor according to still other example embodiments of the inventive concept. 
     Referring to  FIG. 18 , structural features of the image sensors according to the aforementioned embodiments may be combined to realize an image sensor according to still other example embodiments of the inventive concept. For example, according to still other example embodiments of the inventive concept, the image sensor may be configured to include the pixel separation portion  12 , whose structure is similar to that of  FIGS. 3A and 3B , and the edge contact  130  and the external-voltage-applying wire  132 , whose disposition is similar to that of  FIG. 11 . 
       FIG. 19  is a block diagram illustrating an electronic device having an image sensor, according to example embodiments of the inventive concept. The electronic device may be any of various types of devices, such as a digital camera or a mobile device, for example. Referring to  FIG. 19 , an illustrative digital camera system includes an image sensor  100 , a processor  230 , a memory  300 , a display  410  and a bus  500 . As shown in  FIG. 19 , the image sensor  100  captures an external image under control of the processor  230 , and provides the corresponding image data to the processor  230  through the bus  500 . The processor  230  may store the image data in the memory  300  through the bus  500 . The processor  230  may also output the image data stored in the memory  300 , e.g., for display on the display device  410 . 
       FIGS. 20 through 24  show examples of multimedia devices, to which image sensors according to example embodiments of the inventive concept can be applied. Image sensors according to example embodiments of the inventive concept can be applied to a variety of multimedia devices with an imaging function. For example, image sensors according to example embodiments of the inventive concept may be applied to a mobile phone or a smart phone  2000  as shown in  FIG. 20 , to a tablet PC or a smart tablet PC  3000  as shown in  FIG. 21 , to a laptop computer  4000  as shown in  FIG. 22 , to a television set or a smart television set  5000  as shown in  FIG. 23 , and/or to a digital camera or a digital camcorder  6000  as shown in  FIG. 24 . 
     According to example embodiments of the inventive concept, the image sensor may include a common bias line, to which a negative voltage can be applied, and which is disposed in a deep device isolation layer. Accordingly, it may be possible to fix or otherwise attract holes in a sidewall of deep device isolation layer and thereby improve a dark current property of the image sensor. 
     While example embodiments of the inventive concepts have been particularly shown and described, it will be understood by one of ordinary skill in the art that variations in form and detail may be made therein without departing from the spirit and scope of the attached claims.