Abstract:
An image sensor having pixels that include two patterned semiconductor layers. The top patterned semiconductor layer contains the photoelectric elements of pixels having substantially 100% fill-factor. The bottom patterned semiconductor layer contains transistors for detecting, resetting, amplifying and transmitting signals charges received from the photoelectric elements. The top and bottom patterned semiconductor layers may be separated from each other by an interlayer insulating layer that may include metal interconnections for conducting signals between devices formed in the patterned semiconductor layers and from external devices.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 12/684,163 filed on Jan. 8, 2010, which is a divisional of U.S. application Ser. No. 11/524,695 filed on Sep. 21, 2006, which claims priority under 35 U.S.C. §119 of Korean Patent Application 2005-91293 filed on Sep. 29, 2005, the disclosures of which are incorporated by reference herein in their entireties. 
    
    
     BACKGROUND 
     The present invention relates to image sensors, and more particularly to pixels of image sensors. 
     Digital cameras are today one of the most popular consumer electronics. The “MegaPixel” capacity and color sensitivity of image sensors is currently a limiting factor limiting image quality of images captured by digital cameras. Image sensors function to transform (visible) light that is focused onto the image sensor by optical lenses, into electrical signals to capture and display images of high quality. Additionally, a very fast “shutter speed” or “film speed” equivalent in digital image sensors is a strong selling point for high-end digital cameras and can enhance image quality (e.g., reducing blurring due to subject or camera motion). 
     A typical image sensor comprises a pixel array that has a plurality (array) of pixels. Each pixel includes a photodiode for generating signal charges in response to photons (i.e., light) incident thereon, and an electronic element for transferring and outputting the signal charges from the photodiode. Depending upon the manner of transferring and outputting signals charges, image sensors are roughly classified into two kinds, i.e., charge-coupled devices (CCD; hereinafter, ‘CCD image sensors’) and complementary metal-oxide-semiconductor (CMOS) image sensor (hereinafter, ‘CMOS image sensor’). The CCD image sensor uses pluralities of MOS capacitors for accumulating, transferring and outputting charges. By applying appropriate voltages to the electrodes of the MOS capacitors, signal charges of each pixel are successively transferred by way of the MOS capacitors. The CMOS image sensor uses pluralities of transistors, by which signal charges generated by the photodiode are converted into a voltage at each pixel and output therefrom. 
     The CCD image sensors typically have better noise and image quality than CMOS image sensors, but CMOS image sensors typically have lower product cost and lower power consumption than CCD image sensors. In other words, the CMOS image sensor has the advantages of lower power, singularity of voltage and current, compatibility with combined CMOS circuits (e.g., integrated on the same chip), random access of image data, and lower production cost by employing the standard of CMOS technology. Thus, CMOS image sensors are gaining market share in various applications such as digital cameras, smart phones, personal digital assistants (PDA), notebook computers, security cameras, barcode detectors, high-definition television sets, children&#39;s toys, and so on. 
       FIG. 1  is a plane view of a portion of a pixel array of a conventional image sensor. Referring to  FIG. 1 , pixels are formed around active regions  13  of a semiconductor substrate, the active regions being electrically isolated from each other (like “semiconductor islands”), each of which includes a photodiode and pluralities of transistors. Each active region  13  may be sectored into a first active region  13 A including the photodiode, and a second active region  13 B including the plural transistors. On the second active region  13 B are arranged a transfer gate  21 , a reset gate  23 , a source follower gate  25 , and a selection gate  27 . The transfer gate  21  is located adjacent to the first active region  13 A. An impurity region formed in the second active region  13 A between the transfer and reset gates  21  and  23  serves as a floating diffusion region  29  that is electrically connected to the source follower gate  25 . An impurity region formed in the second active region  13 B between the reset and source follower gates  23  and  25  acts as a reset diffusion region  31 . There is an impurity region  33  in the second active region  13 B between the source follower and selection gates  25  and  27 , and an impurity region  35  in the second active region  13 B outside of the selection gate  27 . Each transistor is formed of a gate and the impurity regions at either side of its gate. 
     The vertically sectional structure of a representative pixel is next described with reference to  FIG. 2 .  FIG. 2  is a cross-sectional view of one pixel taken along section line I-I′ of  FIG. 1 . Referring to  FIG. 2 , the photodiode includes an N-type region  17  and a P-type region  19  formed in the first active region  13 A. The floating diffusion (FD) region  29  is electrically connected to the source follower gate  25  through a local interconnection  37 . 
     In the general structure of a conventional pixel, it is necessary to form the photodiode and gates in the same active region  13  and to allocate a part (e.g.,  13 B) thereof to the transistors. Thus, only a portion, i.e., the first active region  13 A of the active region  13  is used for the photodiode. Thus, there is a limitation of the conventional image sensor due to a fill factor that represents the area occupied in a pixel by the photodiode. 
     The “fill factor” indicates the size of the light sensitive photodiode relative to the entire pixel and is the fraction of the surface that is sensitive to light. A large fill factor is desirable because the larger the fill factor the more light will be captured by the chip up to the maximum of 100%. This helps improve the Signal-to-Noise Ration (SNR). Because of the extra electronics (e.g., transistors) required in each pixel the “fill factor” tends to be quite small, especially for Active Pixel Sensors which have more per pixel transistors. To overcome this limitation, some have proposed an array of microlenses to be placed on top of the sensors, but this increases the production cost. Additionally, in the conventional image sensor, light incident upon a target pixel, especially, light incident from a slanted angle, may be reflected by an interconnection of the target pixel or a gate and may arrive at an adjacent pixel, causing across-talk affect or distortion. 
     SUMMARY OF THE INVENTION 
     Various embodiments of the invention provide image sensors having pixels that include two patterned semiconductor layers. The top (second) patterned semiconductor layer contains the photoelectric elements (e.g., photodiodes) of pixels having substantially 100% fill-factor, and may contain one or more transistors. The bottom (first) patterned semiconductor layer contains transistors for detecting, resetting, amplifying and transmitting signals charges received from the photoelectric elements. The top and bottom patterned semiconductor layers may be separated from each other by an interlayer insulating layer that may include metal interconnections for conducting signals between devices formed in the patterned semiconductor layers and from external devices. 
     Exemplary embodiments of the invention provide a pixel with improved architecture, an image sensor having the pixel, and an image processing system employing the image sensor. 
     Some embodiments of the invention provide an image sensor comprising: first and second semiconductor patterns (i.e., first and second patterned semiconductor layers) with an interlayer insulating layer interposed therebetween; a photoelectric element formed in the second semiconductor pattern; and at least one or more transistors formed in the first semiconductor pattern, electrically connected to the photoelectric element and sensing signal charges generated from the photoelectric element. 
     The photoelectric element may be a photodiode comprising: an N-type region formed in the second semiconductor pattern; and a P-type region formed in the second semiconductor pattern enveloping the N-type region. 
     The image sensor may further comprise first and second charge collection regions (electrically connected to each other) formed in the first and second semiconductor patterns respectively for collecting the signal charges generated in the photoelectric element. The one or more transistors may be operationally coupled with the first and second charge collection regions. The one or more transistors may comprise a first transistor for sensing and a second transistor for resetting signal charges, of the first and second charge collection regions. The first and second transistors are connected with each other by a common drain. A gate of the first transistor is electrically connected to the first and second charge collection regions. The first charge collection region acts as a source of the second transistor. 
     The image sensor may further comprise a transfer gate in the second semiconductor pattern (e.g., beneath the photodiode) for transferring the signal charges to the first and second charge collection region from the photoelectric element. 
     The photoelectric element may be a diode comprising: an N-type region formed in the second semiconductor pattern; and a P-type region, formed in the second semiconductor pattern, enveloping the N-type region. The second charge collection region may be formed in the P-type region outside of the transfer gate, being spaced apart (separated) from the N-type region. 
     The image sensor may further comprise a color filter formed on (e.g., directly on) the second semiconductor pattern. The photoelectric element may directly contact the second semiconductor pattern. The photoelectric element may interpose a buffer layer with the color filter. 
     Other embodiments of the present invention provide an image sensor comprising: first and second semiconductor patterns (i.e., first and second patterned semiconductor layers) with an interlayer insulating layer interposed therebetween; a photoelectric element (e.g., photodiode) in the second semiconductor pattern; a transfer gate below the photoelectric element in the second semiconductor pattern for transferring signal charges from the photoelectric element to a second charge collection region in the second semiconductor pattern; a first charge collection region in the first semiconductor pattern and electrically connected to the second charge collection region; a source follower gate in the first semiconductor pattern and electrically connected to the first and second charge collection regions; first source and drain regions in the first semiconductor pattern at either side of the source follower gate; and a reset gate in the first semiconductor pattern between the first drain region and the first charge collection region. 
     The photoelectric element may be a diode comprising: an N-type region formed in the second semiconductor pattern; and a P-type region formed in the second semiconductor pattern so as to envelop the N-type region. The first charge collection region is formed in the second semiconductor pattern outside of the transfer gate and spaced apart from the N-type region. 
     The interlayer insulating layer may comprise first and second interlayer insulating layers. The first charge collection region is electrically connected to the second charge collection region by: a first contact plug penetrating the first interlayer insulating layer and electrically connected to the second charge collection region; a local conductive pattern formed on the first interlayer insulating layer and electrically connected to the first contact plug; and a second contact plug penetrating the second interlayer insulating layer and electrically connecting the first charge collection region with the local conductive pattern. 
     The local conductive pattern is electrically connected with a third contact plug that penetrates the first interlayer insulating layer and is electrically connected to the source follower gate. 
     The interlayer insulating layer may include metal interconnections for applying bias voltages to the transfer and reset gates. 
     The image sensor may further comprise: a second drain region formed in the first semiconductor pattern; and a selection gate formed in the first semiconductor pattern between the second drain region and the first source region. The interlayer insulating layer may include a metal interconnection for applying a bias voltage to the selection gate. 
     Further other embodiments of the present invention provide an image sensor comprising pixels: each pixel includes a photoelectric element formed in a second semiconductor pattern (i.e., in a first patterned semiconductor layer); and at least one or more transistors formed in a first semiconductor pattern (i.e., in a second patterned semiconductor layer) and operationally coupled to the photoelectric element, the first semiconductor pattern being spaced apart from (separated from) or electrically insulated from the second semiconductor pattern. 
     Still further embodiments of the present invention provide an image processing system comprising: a processor; and an image sensor operationally coupled with the processor. The image sensor comprises a plurality of pixels. Each pixel comprises: a photoelectric element formed in a second semiconductor pattern (i.e., in a second patterned semiconductor layer); and at least one or more transistors formed in a first semiconductor pattern (i.e., in a first patterned semiconductor layer) and operationally coupled to the photoelectric element, the first semiconductor being spaced apart from (separated from) or electrically insulated from the second semiconductor. 
     A further understanding of the nature and advantages of the invention herein may be realized by reference to the remaining portions of the specification and the attached drawings. 
     Exemplary embodiments of the present invention will be described below in more detail with reference to the accompanying drawings. The present invention may, however, be embodied in different forms and should not be construed as 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 scope of the invention to those skilled in the art. 
     In the figures, the size of layers and regions are exaggerated for clarity of illustration. It will also be understood that when a layer (or film) is referred to as being ‘on’ another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may also be present. Further, it will be understood that when a layer is referred to as being ‘under’ another layer, it can be directly under, and one or more intervening layers may also be present. In addition, it will also be understood that when a layer is referred to as being ‘between’ two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present. Like reference numerals refer to like elements throughout. It will be understood that, although the terms for first, second, third, etc. may be used herein to describe various elements such as region, film, layer, etc., these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first layer could be termed a second layer, and, similarly, a second layer could be termed a first layer without depart from the teaching of the disclosure. 
     In this description, for example, a sentence ‘first element is operationally coupled with second element’ means that a specific terminal or node of the first element is connected to a specific terminal or node of the second element directly or indirectly through a conductive region. For example, the first or/and second elements are not restrictive to embodied descriptions herein in terminology, but may be used for illustrating transistors, impurity regions, or various kinds of conductive interconnections. 
     In the description, for example, a sentence ‘transistor is operationally coupled with photodiode’ may represent that an impurity region of a photodiode acts as a source or drain region of a transistor, an impurity region of a photodiode is electrically connected to the source or drain region of the transistor, or an impurity region of a photodiode is electrically connected to a gate of the transistor. 
     In the description, for example, a sentence ‘first and second transistors are operationally coupled with each other’ may be understood such that a voltage applied to a gate of the first transistor is transferred to a terminal or node of the second transistor, e.g., a gate, a source region, or a drain region, directly or indirectly through a third transistor or a conductor such a metal interconnection. Alternatively, it may indicate that a terminal or node of the first transistor is electrically connected with a terminal or node of the second transistor. 
     In the specification herein, ‘semiconductor substrate’, ‘semiconductor layer’, ‘semiconductor pattern’, or ‘substrate’ will be used to represent a structure based on a semiconductor. This structure based on semiconductor may be comprised of a silicon layer, a silicon-on-insulator (SOI) where a silicon layer is disposed on an insulation layer, a doped or undoped silicon layer, an epitaxial layer formed by a technique of epitaxial growth, or another semiconductor construction. 
     While the exemplary embodiments of the present invention are applicable to all kinds of image sensors, the embodied description herein will be illustrative a CMOS image sensor as an example for appreciation of the features by the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The accompanying figures are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the invention and, together with the description, serve to explain principles of the present invention. In the figures: 
         FIG. 1  is a plane view of a portion of a pixel array of a typical image sensor; 
         FIG. 2  is a cross-sectional view of a pixel taken along section line of  FIG. 1 ; 
         FIG. 3  is a perspective view of a pixel in an image sensor in accordance with an embodiment of the present invention; 
         FIG. 4  is a plane view of a portion of a pixel array of the image sensor of  FIG. 3 ; 
         FIG. 5  is a cross-sectional view of a pixel taken along section line II-II′ of  FIG. 4 ; 
         FIG. 6  is a block diagram of the image sensor including the pixels of  FIGS. 3 ,  4  and  5 ; and 
         FIG. 7  is a block diagram of a system with the image sensor shown in  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 3  is a perspective view of a pixel in an image sensor in accordance with an embodiment of the invention. Referring to  FIG. 3 , a pixel  101  according to the embodiment by the invention comprises a photodiode  115 , and transfer, reset, source follower, and selection transistors operationally coupled with the photodiode  115 . According to this embodiment of the invention, the components of the pixel  101  are arranged in separate first and second semiconductor patterns  111  and  113  that are spaced apart from each other. In this exemplary embodiment of the invention, the photodiode  115  and the transfer transistor are disposed in the second semiconductor pattern  113 , while the reset, source follower, and selection transistors are placed in the first semiconductor pattern  111 . The gate  217  of the transfer transistor is disposed under the photodiode  115 . Thus, the fill factor of the pixel is not affected by the presence or size of the transfer, reset, source follower, and selection transistors therein. 
     According to this embodiment, as the second semiconductor pattern  113  is used entirely for the photodiode  115 , it is possible to achieve the fill factor of substantially 100%. 
     In this embodiment, since the first semiconductor pattern  111  including the transistors does not affect the fill factor, the first semiconductor pattern  111  my be formed in the same size as the second semiconductor pattern  113 . Thus, it is possible to improve the noise characteristic of 1/f and the light-gathering performance (e.g., speed) of the pixel. In addition, the charge collection regions  411 _ 1  and  411 _ 2 , may be enlarged to extend the dynamic range thereof. 
     The photodiode  115  includes a first conductive region (e.g., an N-type region)  113   n  formed in the second semiconductor pattern  113  and a second conductive region (e.g., a P-type region)  113   p  enveloping the first conductive region  113   n . In this embodiment, electron-hole pairs as signal charges are generated in response to photons incident upon the second semiconductor pattern  113 , and electrons are accumulated in the N-type region  113   n . Since the N-type region  113   n  is entirely enclosed (enveloped) by the P-type region  113   p , the leakage of electrons out of the N-type region  113   n  is minimized. 
     The transfer gate  217  is disposed under a gate insulation layer  317  adjacent to the N-type region  113   n , interposed between the gate insulation layer  317  and the N-type region  113   n . It can be seen that the transfer transistor includes the transfer gate  217 , and that the second charge collection region  411 _ 2  and the N-type region  113   n  are positioned at either side of the transfer gate  217 . If a bias voltage is applied to turn ON the transfer gate  217 , the charges (e.g., electrons) accumulated in the N-type region  113   n  are transferred to the second charge collection region  411 _ 2  functioning as a floating diffusion region. The second charge collection region  411 _ 2  is formed in the second semiconductor pattern  113  outside of the transfer gate  217 , being doped with N-type impurities. 
     On the first semiconductor pattern  111 , a reset gate  211 , a source follower gate  213 , and a selection gate  215  are formed on gate insulation layers  311 ,  313 , and  315  formed on the first semiconductor pattern  111 . Impurity regions in the first semiconductor pattern  111 , are source/drain regions. The gate and the impurity regions at either side of a gate constitute a transistor. For instance, a reset transistor includes the reset gate  211  and the impurity regions  411 _ 1  and  413  at either side of the reset gate  211 . A source follower transistor includes the source follower gate  213  and the impurity regions  413  and  415  at either side of the source follower gate  213 . A selection transistor includes the selection gate  215  and the impurity regions  415  and  417  at either side of the selection gate  215 . A VDD voltage (from a power supply not shown) is applied to the impurity region  413  between the reset and source follower gates  211  and  213 . 
     The impurity region  411 _ 1  of the reset transistor is electrically connected to the second charge collection region  411 _ 2 , acting as a floating diffusion region (similar to the second charge collection region  411 _ 2 ). In other words, the impurity region  411 _ 1  of the reset transistor accumulates charges transferred from the photodiode  115  (which hereinafter will be referred to as the first charge collection region in recognition of the fact that signal charges are first accumulated therein). When a bias voltage is applied to the reset gate  211 , a conductive channel is formed under the reset gate  211  in the first semiconductor pattern  111  and signal charges remaining in the first and second charge collection regions  411 _ 1  and  411 _ 2  flow into a power source (not shown) connected to the impurity region  413  of the reset transistor. The pixel is thereby initialized. 
     The source follower gate  213  (of the source follower transistor) is electrically connected to the first and second charge collection regions  411 _ 1  and  411 _ 2 . The first and second charge collection regions,  411 _ 1  and  411 _ 2 , and the source follower gate  213  are electrically connected with each other by way of a local conductive pattern  611  and contact plugs  511 ,  513 , and  711 , forming a common node. Thus, a signal voltage, corresponding to (e.g., proportionate with) the amount of signal charges accumulated in the first and second charge collection regions  411 _ 1  and  411 _ 2 , appears at the impurity region  415  of the source follower transistor. When a bias voltage is applied to the selection gate  215  of the selection transistor, the signal voltage (at the impurity region  415 ) is transferred to an output terminal of the selection transistor, i.e., to the impurity region  417 . The signal transferred to the output terminal  417  of the selection transistor is detected and processed by a peripheral circuit (not shown). The signal processing operations performed by peripheral circuits are well known to persons skilled in the art and will be described with reference to  FIG. 6  below. 
     The first semiconductor pattern  111 , including the reset, source follower, and selection transistors, may be a P-type silicon semiconductor substrate. The transistors formed in the first semiconductor pattern  111  may be formed by, for example, depositing and patterning each of a gate insulation layer and a conductive layer, and implanting ionic impurities to form the impurity regions. A conductive layer for the gate is not restricted to this exemplary embodiment and may be formed of other materials or in other structures, for example, polysilicon, or a multi-layer of polysilicon and silicide. When the first semiconductor pattern  111  is a P-type, N-type ionic impurities are injected to form source/drain regions of the transistors. 
     An interlayer insulating layer ( 911 , see  FIG. 5 , not shown in  FIG. 3 ) is interposed between the first and second semiconductor patterns  111  and  113 , as will be detailed with reference to  FIG. 5 . 
     The transfer gate  217  may be formed by depositing a conductive layer on the interlayer insulating layer ( 911  shown in  FIG. 5 ) and patterning the conductive layer. Patterning of the conductive layer may be conducted by a photolithography process. The gate insulation layer  317  covering (insulating) the transfer gate  217  may be formed by a film deposition technique. The second semiconductor pattern  113  disposed on the second interlayer insulating layer ( 813  shown in  FIG. 5 ), covering the transfer gate  217  and the gate insulation layer  317  thereon, may be formed by means of a film deposition technique such as chemical vapor deposition (CVD) or plasma-enhanced CVD, or epitaxial growth, the methods of formation not being restricted to those examples. 
     The photodiode  115  may be formed by conducting ion implantation into the second semiconductor pattern  113 . For instance, the photodiode  115  may be produced (after forming the second semiconductor pattern  113  doped with P-type impurities), by implanting ionic impurities to form the N-type region  113   n  and implanting ionic impurities to form the top P-type region  113   p . According to this embodiment, the photodiode  113  constitutes a vertical PNP structure, thereby avoiding the effect of image lag. 
     The second charge collection region  412 _ 2  acting as the floating diffusion region may be formed by implanting ionic impurities into the second semiconductor pattern  113  and using the transfer gate  217  as an ion injection mask. 
     The steps of ion implantation for the photodiode  115  and the second charge collection region  411 _ 2  may proceed in an appropriate order. 
     The contact plugs,  511 ,  513 , and  517 , may be formed by patterning the interlayer insulating layer(s) ( 811 ,  813  as shown in  FIG. 5 ) to form contact holes and then filling the contact holes with a conductive material. The local conductive pattern  611  is may be formed by depositing and patterning a conductive layer (upon interlayer insulating layer  811 ). The contact plugs  511  and  513  connected each to the first charge collection region  411 _ 1  and the source follower gate  213  may be formed at the same time through the interlayer insulating layer  811 . 
     Interconnections not shown are disposed between the first and second semiconductor patterns  111  and  113  in order to apply bias voltages to the reset gate  211 , the selection gate  215 , and the transfer gate  217 . The interconnections not shown may be formed while forming the local conductive pattern  611 . 
     While forming the contact plugs  511  and  513  connected to the first charge collection region  411 _ 1  and the source follower gate  213  respectively, a contact plug (not shown) connected to the selection gate  215  may be formed at the same time. And, at the same time that the contact plug  711  is formed to connect the local conductive pattern  611  with the second charge collection region  411 _ 2 , a contact plug (not shown) for connecting the transfer gate  217  with an interconnection that conducts a bias voltage to the transfer gate  217  may be also be formed. 
     A processing sequence for forming the contact plugs, the interconnections, and the local conductive pattern may be varied in alternative modes. According to this embodiment, as the interconnections for applying bias voltage to the plural gates are formed under the photodiode  115 , it is possible to secure misalignment margins for the interconnections, providing flexibility in arranging the interconnections. 
     In this exemplary embodiment, a color filter may be disposed over the photodiode, so to minimizes optical and electrical cross-talk therein. In addition, since the photodiode is very close to or contacts with the color filter and has a large fill-factor, it may not require a micro-lens for condensing light. 
     A light shielding pattern can be formed under the photodiode without degrading the fill factor of the pixel, and it is possible to minimize electrical interference more effectively. 
     The photodiode may be formed after completing almost all of metal interconnections. Thus, since there is no metal contact on the photodiode, a dark level thereof can be minimized. 
       FIG. 4  is a plane view illustrating part of the pixel array of the image sensor of  FIG. 3 , and  FIG. 5  is a cross-sectional view of a pixel in the array of  FIG. 4  taken along section line II-IF in  FIG. 4 . 
     Referring to  FIG. 4 , the first semiconductor pattern  111 , including the reset gate  211 , the source follower gate  213 , and the selection gate  215 , is located under the second semiconductor pattern  113  and is entirely covered by the second semiconductor pattern  113 . Therefore, the dimensions of the pixel are determined by the size of the second semiconductor pattern  113  including the photodiode  115 . The second semiconductor pattern  113  can be used entirely as the photodiode  115 . As illustrated in  FIG. 4 , a gate width (or the width of the active region) can be enlarged in by extension of the first semiconductor pattern  111  along the y axis, by which enlarged width the performance of transistor becomes improved. The width of the first semiconductor pattern  111  may be extended so as to make the first semiconductor pattern  111  the same size as the second semiconductor pattern  113 . Further, since the first semiconductor pattern  111  is disposed under the second semiconductor pattern  113  including the photodiode  115 , it is permissible to variously modify the configuration of the first semiconductor pattern  111  without reducing the fill factor. For instance, upon altering the configuration of the first semiconductor pattern  111  in various ways, it is possible to design channel patterns suitable for the optimum performance of the transistors without reducing the fill factor. 
     In addition, because the transfer gate  127  is disposed under the photodiode  115 , the gate length of the transfer gate  127  may be variously designed for the optimum transfer efficiency. 
     A cross-section of the pixel of  FIGS. 3  and  FIG. 4  can be seen from  FIG. 5 . In  FIG. 5 , the reference numerals  811  and  813  denote first and second interlayer insulating layers and are collectively referred to by the reference numeral  911 . The reference numeral  1111  indicates a color filter. The first and second interlayer insulating layers  811  and  813  may be formed of, for example, borophospho-silicate glass (BPSG) doped with boron (B) and phosphorous (P), boro-silicate glass (BSG) doped with boron, phosphor-silicate glass (PSG) doped with phosphorous, undoped silicate glass (USG), or vapor-deposited silicon oxide. The color filter may be formed by a conventional process. 
     Referring to  FIG. 5 , the color filter  1111  is arranged close or in direct contact with the top of the photodiode  115 . In the conventional image sensor shown in  FIG. 1  or  2 , because various kinds of interconnections are arranged over the photodiode, the color filter is inevitably spaced apart from (above) the photodiode. And the conventional image sensor uses microlenses to raise the efficiency of light sensing. Further, due to the distance between the color filter and the photodiode in the conventional image sensor, the light passing through the color filter may arrive at an adjacent pixel as well as a target pixel. In exemplary embodiments of the present invention, since the color filter  1111  is disposed close to or in direct contact with the photodiode  115 , light passing through the color filter is entirely incident on the photodiode  115  in substance. Moreover, because, in exemplary embodiments of the invention, the photodiode is located directly under the color filter, a microlens need not be formed in the pixel. 
       FIG. 6  is a block diagram of the image sensor  2080  including the pixel of  FIGS. 3 ,  4  and  5 . Referring to  FIG. 6 , the pixel array  2000  includes a plurality of pixels arranged in a matrix. The matrix of the pixel array  2000  includes rows and columns of pixels. A row driver  2100  selects a specific row of pixels in the pixel array  2000  in response to an output of a row decoder  2200 , and a column driver  2600  selects a specific column of pixels in the pixel array  2000  in response to an output of a column decoder  2700 . The CMOS image sensor is controlled by a controller  2500 . The controller  2500  controls the row decoder  2200 , the row driver  2100 , the column decoder  2700 , and the column driver  2600 . 
     An output signals from each of the pixels include a pixel reset signal Vrst and a pixel image signal Vsig. The pixel reset signal Vrst corresponds with the potential of the charge collection region when the pixel is in a reset state. The pixel image signal Vsig corresponds with the potential of the charge collection region after signal charges generated from an image have been transferred to the charge collection region. The pixel reset signal Vrst and the pixel image signal Vsig are read out by a sampling/holding circuit  2610 . An amplifier (AMP)  2620  generates a difference signal Vrst−Vsig from the reset and image signals Vrst and Vsig. The difference signal is transformed into a digital signal by an analog-digital converter (ADC)  2750 . An image processor  2800  generates a digital image from the digitized differential signals. The image sensor  2080  may be included in a semiconductor chip (e.g., a wafer  3000 ). 
       FIG. 7  is a block diagram of a processor-based system  4000  including the image sensor of  FIG. 6 . The processor-based system  400  may be, any digital circuit that may employ the image sensor  4080 . The processor-based system is not limited hereto, but may be a computer system, a camera system, a cell-phone, a scanner, a videophone, a surveillance system, a machine vision system, a vehicle navigation system, an automatic focus system, a star tracking system, a motion detection system, an image stabilization system, a data compression system, or other system compatible with an image sensor. 
     The system  4000  includes a processor (e.g., central processor unit, CPU)  4020  communicating with plural devices or peripherals via a bus  4040 . The devices (peripherals) coupled to bus  4040 , are e.g., an input/output unit  4060  and the image sensor  4080 , provide the system  4000  with input/output communication. The devices coupled to bus  4040 , include at least one peripheral memories, such as a RAM  4100 , a hard disc driver (HDD)  4120 , a floppy disc driver (FDD)  4140 , and a compact disc (CD) driver  4160 . The image sensor  4080  receives control signals as data from the processor  4020  or from another device of the system  4000 . The image sensor  4080  provides the processor  402  with a data signal defining an image on basis of the received control signals or data, and the processor  4020  processes the signal supplied from the image sensor  4080 . 
     Accordingly in exemplary embodiments of the invention, a fill factor of substantially 100% can be attained because the second semiconductor pattern  113  is used entirely for the photodiode. 
     In exemplary embodiments of the invention, (see  FIGS. 3 ,  4 ,  5 ) the first semiconductor pattern  111  including the transistors does not affect the fill factor, and may be formed at the same size (area) as the second semiconductor pattern  113 . Thus, it is possible to improve the noise characteristic of 1/f and also the performance of light-sensing operations. In addition, exemplary embodiments of the invention facilitate enlargement of charge collection regions  411 _ 1  and  411 _ 2 , to extend dynamic range. 
     In exemplary embodiments of the invention, the photodiode  113  constitutes a vertical PNP structure that avoids an effect of image lag. Image lag occurs in conventional image sensors when traces of a previous frame (image) remain in future frames, i.e. when the pixel is not fully reset. 
     In exemplary embodiments of the invention, since the first semiconductor pattern  111  is disposed under the second semiconductor pattern  113  including the photodiode  115 , it is permissible to variously modify the configuration of the first semiconductor pattern  111  without reducing the fill factor. For instance, by altering the configuration of the first semiconductor pattern  111  in various forms, it is possible to design channel patterns suitable for the optimum performance of the transistors. 
     In exemplary embodiments of the invention, since the color filter is disposed close to or directly contacting the photodiode, light passing through the color filter is entirely incident upon the target photodiode. 
     In exemplary embodiments of the invention, since the photodiode is located directly under the color filter, the microlens provided in conventional image sensors may be omitted entirely. 
     In exemplary embodiments of the invention, forming a light shielding pattern under the photodiode does not degrade the fill factor of the pixel, and it is possible to minimize electrical interference more effectively. 
     In this embodiment, the photodiode is formed after formation of almost all of the metal interconnections. Thus, since there is no metal contact on the photodiode, it is able to minimize a dark level thereof. 
     The above-disclosed subject matter is to be considered illustrative, and not limiting, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments, which fall within the true spirit and scope of the present invention. Thus, to the maximum extent allowed by law, the scope of the present invention is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.