Abstract:
A method of manufacturing a solid-state imaging device. Light-receiving sensor portions each constituting a pixel in the form of a matrix is arranged. The matrix has columns aligned in a vertical direction and rows aligned in a horizontal direction. Charge-transfer portions are formed on either side of the columns of said pixels. Transfer electrodes in said charge-transfer portions are formed to include a first transfer electrode formed of a first electrode layer and a second transfer electrode formed by electrically connecting the first electrode layer and a second electrode layer through a contact. The second transfer electrode being disposed in the vertical direction above the charge-transfer portion in a vicinity of the contact to decrease the width of the charge-transfer portions in the horizontal direction and increase the light receiving sensor portions in the vertical direction.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 11/119,138, filed Apr. 30, 2005, the entirety of which is incorporated herein by reference to the extent permitted by law. The present invention contains subject matter related to and claims the benefit of priority from the prior Japanese Patent Application JP 2004-138897, filed in the Japanese Patent Office on May 7, 2004, the disclosure of which is hereby incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a solid-state imaging device including a charge-transfer portion, such as a CCD solid-state imaging device, a method of manufacturing a solid-state imaging device, and a method of driving a solid-state imaging device. 
     2. Description of the Related Art 
     In a CCD solid-state imaging device, a transfer resistor having a CCD structure is provided as a charge-transfer portion, and a signal charge obtained through photoelectric conversion and stored in a light-receiving sensor portion formed of a photodiode is read out to the transfer resistor so that the signal charge is transferred in the transfer resistor. 
     The transfer resistor includes through an insulation film a transfer electrode formed on a transfer channel in which a signal charge is transferred. In order to transfer a signal charge, it is necessary to apply voltage pulses having different phases from each other to the transfer electrodes adjacent to each other, and also it is necessary to prevent a gap from occurring in the channel. Accordingly, the transfer electrode is made to include two electrode layers of a first and second layers, and the edge of the second-layer transfer electrode is made to somewhat overlap the first-layer transfer electrode (refer to Patent Literature 1, for example). 
     A schematic constitutional view (plan view) of a CCD solid-state imaging device including a transfer electrode formed of two electrode layers in this manner is shown in  FIG. 1 . 
     As shown in  FIG. 1 , with respect to this CCD solid-state imaging device, light-receiving sensor portions  51  are arranged in the form of a matrix, and a vertical transfer resistor  52  which extends vertically (in the upward and downward directions in the figure) is provided on one side of each column of the light-receiving sensor portions  51  as a charge-transfer portion. Although not shown in the figure, a horizontal transfer resistor is connected to one end of the vertical transfer resistor  52 . 
     Further, with respect to the CCD solid-state imaging device shown in  FIG. 1 , a sectional view of the vertical transfer resistor  52  is shown in  FIG. 2A , and a sectional view of a portion between light-receiving sensor portions  51  adjacent to each other in the vertical direction, namely a portion between pixels, is shown in  FIG. 2B . Note that in  FIGS. 2A and 2B , description of semiconductor regions (each region in a light-receiving sensor portion, a transfer channel region and the like) in a semiconductor substrate is omitted. 
     The vertical transfer resistor  52  includes a transfer electrode  53  and a transfer channel region (not shown in the figures) formed in a semiconductor substrate  54 , constituting a charge-transfer portion of a CCD structure. 
     Further, as the transfer electrode  53 , transfer electrodes  53 B and  53 D formed of a first electrode layer and transfer electrodes  53 A and  53 C formed of a second electrode layer are alternately disposed in the vertical direction. 
     In addition, the edges of the transfer electrodes  53 A and  53 C of the second layer somewhat overlap the transfer electrodes  53 B and  53 D of the first layer in the vertical transfer resistor  52 . 
     Recently, to cope with the increase in pixel numbers and miniaturization of a digital camera, a pixel cell of a solid-state imaging device has been improved to be minute. 
     Hence, in order to obtain high sensitivity as well as miniaturization of a pixel cell of a solid-state imaging device, higher light-receiving efficiency is desired. 
     However, in the CCD solid-state imaging device including the transfer electrode  53  in which two electrode layers overlap, as shown in  FIG. 1  and  FIGS. 2A and 2B , projections and cavities around the light-receiving sensor portion  51  become large at the overlapped portions of the transfer electrode  53 , so that incident light is partially blocked by the portion. 
     Hence, it is difficult to improve the efficiency in receiving light. 
     The overlapped portion of the transfer electrode  53  has normally the thickness of 1 μm or more, so that particularly when the size of a pixel cell is 3 μm or less and the width of an opening on the light-receiving sensor portions  51  is reduced to 1 μm or so, incident light may be partially blocked by the overlapped portions. 
     [Patent Literature 1] Published Japanese Patent Application No. H9-312390 
     SUMMARY OF THE INVENTION 
     On the other hand, a CCD solid-state imaging device in which no overlap occurs in a transfer electrode and the transfer electrode is formed of a single electrode layer has also been proposed. 
     A schematic constitutional view (plan view) of a CCD solid-state imaging device in which a transfer electrode is formed of a single electrode layer as described above is shown in  FIG. 3 . 
     As shown in  FIG. 3 , with respect to this CCD solid-state imaging device, light-receiving sensor portions  61  are arranged in the form of a matrix, and a vertical transfer resistor  62  which extends vertically (in the upward and downward directions in the figure) is provided on one side of each column of the light-receiving sensor portions  61  as a charge-transfer portion. Although not shown in the figure, a horizontal transfer resistor is connected to one end of the vertical transfer resistor  62 . 
     Further, with respect to the CCD solid-state imaging device of  FIG. 3 , a sectional view of the vertical transfer resistor  62  is shown in  FIG. 4A , and a sectional view of a portion between pixels adjacent to each other in the vertical direction is shown in  FIG. 4B . Note that in  FIGS. 4A and 4B , description of semiconductor regions (each region in a light-receiving sensor portion, a transfer channel region, and the like) in a semiconductor substrate is omitted. 
     The vertical transfer resistor  62  includes a transfer electrode  63  and a transfer channel region (not shown in the figures) formed in a semiconductor substrate  64 , constituting a charge-transfer portion of a CCD structure. 
     Further, the transfer electrode  63  includes four transfer electrodes  63 A,  63 B,  63 C and  63 D, all of which are formed of a first electrode layer. 
     Hence, since the transfer electrodes  63 A,  63 B,  63 C and  63 D are formed of the same electrode layer, there is no overlapped portion. 
     However, in the CCD solid-state imaging device thus constructed, as shown in  FIG. 4B , two electrodes  63 A and  63 B are arranged in a portion between pixels adjacent to each other in the vertical direction (in the charge-transfer direction), so that the width between the pixels becomes relatively large. 
     Accordingly, the area of the light-receiving sensor portion may be reduced. For example, when comparing pixel cells having the same size, the area of the portion may be reduced by approximately 30% than that of the former described structure including two electrode layers. 
     If the area of the light-receiving sensor portion is reduced as described above, the amount of electric charge to be stored in the light-receiving sensor portion diminishes, so that sensitivity deteriorates and the dynamic range becomes narrow. Further, the effects of shading become large. 
     In particular, this problem becomes conspicuous when the pixel size is reduced. 
     The present invention addresses the above-identified, and other problems associated with conventional methods and apparatuses and provides a solid-state imaging device capable of securing sufficient sensitivity and of obtaining favorable characteristics. 
     Each of a solid-state imaging device according to an embodiment of the present invention and a solid-state imaging device according to an embodiment of a manufacturing method and a driving method of the present invention includes light-receiving sensor portions, each constituting a pixel, arranged in the form of a matrix and a charge-transfer portion provided on one side of each column of the light-receiving sensor portions; wherein a transfer electrode in a charge-transfer portion includes a first transfer electrode formed of a first electrode layer and a second transfer electrode formed by electrically connecting a first electrode layer and a second electrode layer, the first electrode layer of the second transfer electrode is independently formed in each charge-transfer portion, and the first transfer electrode and the second electrode layer in the second transfer electrode are laminated at a portion between pixels adjacent to each other in the direction of the charge-transfer portion. 
     According to an embodiment of the structure of the above-described solid-state imaging device of the present invention, the transfer electrode in the charge-transfer portion includes the first transfer electrode formed of the first electrode layer and the second transfer electrode formed by electrically connecting a first electrode layer and a second electrode layer and the first electrode layer of the second transfer electrode is independently formed in each charge-transfer portion, so that in the charge-transfer portion, the second transfer electrode is mainly formed of the first electrode layer with only part of the second electrode layer, and therefore the extent to which incident light is blocked by the transfer electrode is greatly reduced in comparison with a structure in related art in which two electrode layers are overlapped. 
     Further, in a portion between pixels adjacent to each other in the direction of the charge-transfer portion, the first transfer electrode (formed of the first electrode layer) and the second electrode layer in the second transfer electrode are laminated, so that the width of the portion between pixels can be made narrow in comparison with the case in which the transfer electrode includes only a first electrode layer (single-layer electrode structure). Thus, the size of the light-receiving sensor portion can be set large in the direction of the charge-transfer portion. 
     According to the above-described embodiment of the present invention, the size of the light-receiving sensor portion can be set large to obtain the large area of the light-receiving sensor portion. 
     Therefore, according to an embodiment of the present invention, a solid-state imaging device having favorable characteristics can be obtained in which a sufficient amount of electric charge can be received by light-receiving sensor portions, and sufficient sensitivity and sufficient dynamic range are secured. 
     Further, according to an embodiment of the present invention, problems (deterioration in sensitivity, a narrow dynamic range, and the like) conspicuously occurred when a solid-state imaging device is made minute can be solved, so that a solid-state imaging device can be made minute and the increase in the number of pixels and high density of a solid-state imaging device can be obtained. Furthermore, the miniaturization of a solid-state imaging device can also be achieved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic constitutional view (plan view) of a CCD solid-state imaging device in which a transfer electrode includes two layers; 
         FIG. 2A  is a sectional view of a vertical transfer resistor portion in the CCD solid-state imaging device of  FIG. 1  and  FIG. 2B  is a sectional view of a portion between pixels in the CCD solid-state imaging device of  FIG. 1 ; 
         FIG. 3  is a schematic constitutional view (plan view) of a CCD solid-state imaging device in which a transfer electrode is formed of a single layer; 
         FIG. 4A  is a sectional view of a vertical transfer resistor portion in the CCD solid-state imaging device of  FIG. 3  and  FIG. 4B  is a sectional view of a portion between pixels in the CCD solid-state imaging device of  FIG. 3 ; 
         FIG. 5  is a schematic constitutional view (plan view) of a solid-state imaging device according to an embodiment of the present invention; and 
         FIG. 6A  is a sectional view of a vertical transfer resistor portion in the CCD solid-state imaging device of  FIG. 5  and  FIG. 6B  is a sectional view of a portion between pixels in the CCD solid-state imaging device of  FIG. 5 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 5  is a schematic constitutional view (plan view) showing a solid-state imaging device according to an embodiment of the present invention. 
     This embodiment is a case in which the present invention is applied to a CCD solid-state imaging device. 
     In this solid-state imaging device, a vertical transfer resistor  2  is formed on one side of each column of light-receiving sensor portions  1  arranged in the form of a matrix to constitute an imaging area. 
     Each light-receiving sensor portion  1  constitutes a pixel, and in this embodiment, one portion is provided per pixel. 
     Outside the imaging area, although not shown in the figure, a horizontal transfer resistor is provided to be connected to one end of the vertical transfer resistor  2 , and an output portion is provided at one end of the horizontal transfer resistor. 
     Further,  FIG. 6A  is a sectional view of the vertical transfer resistor  2  of the solid-state imaging device shown in  FIG. 5 ; and  FIG. 6B  is a sectional view of a portion between light-receiving sensor portions  1 , namely between pixels, adjacent to each other in the vertical direction of the solid-state imaging device (in the charge-transfer direction of the vertical transfer resistors  2 ) shown in  FIG. 5 . 
     The vertical transfer resistor  2  includes a transfer channel region and a gate insulation film, which are not shown in the figures and which are formed in a semiconductor substrate  11 , and a transfer electrode. 
     Further, although not shown in the figures, a light shielding film is formed covering the transfer electrode. The light shielding film has openings on the light-receiving sensor portions  1  to make light enter the light-receiving sensor portions  1 . 
     Further, although not shown in the figures, above the light shielding film are provided an insulation layer covering the light shielding film, a color filter, on-chip lenses and the like, if necessary. 
     The solid-state imaging device according to the embodiment particularly has characteristics in the structure of the transfer electrode constituting the vertical transfer resistor  2 . 
     Each of a transfer electrode  3 A to which a transfer pulse φV 1  of a first phase is applied and a transfer electrode  3 C to which a transfer pulse φV 3  of a third phase is applied has, as shown in  FIG. 5 , an electrode portion extending along the vertical transfer resistor  2  and a wiring portion extending between light-receiving sensor portions  1  (between pixels) adjacent to each other in the vertical direction (in the upward and downward directions in the figure). 
     Further, the transfer electrode  3 A to which a transfer pulse φV 1  of a first phase is applied and the transfer electrode  3 C to which a transfer pulse φV 3  of a third phase is applied are formed of a first electrode layer, as shown in  FIGS. 6A and 6B . Those transfer electrodes  3 A and  3 C are formed in common with respect to pixels in the same row by means of the wiring portion. 
     A transfer electrode  3 B to which a transfer pulse φV 2  of a second phase is applied and a transfer electrode  3 D to which a transfer pulse φV 4  of a fourth phase is applied are, as shown in  FIG. 5 , formed independently in each vertical transfer resistor  2 , and each of the electrodes has only an electrode portion extending along the vertical transfer resistor  2 . 
     Further, the transfer electrode  3 B to which a transfer pulse φV 2  of a second phase is applied and the transfer electrode  3 D to which a transfer pulse φV 4  of a fourth phase is applied are formed of a first electrode layer, as shown in  FIGS. 6A and 6B . 
     Furthermore, as shown in  FIGS. 5 and 6A , a transfer electrode  4  formed of a second electrode layer is through a contact layer  5  connected to each of the transfer electrode  3 B to which a transfer pulse φV 2  of a second phase is applied and the transfer electrode  3 D to which a transfer pulse φV 4  of a fourth phase is applied. 
     This transfer electrode  4  formed of a second electrode layer (hereinafter referred to as a second-layer transfer electrode) has a portion extending along a vertical transfer resistor  2  and being connected to the contact layer  5 , and a wiring portion extending between light-receiving sensor portions (between pixels) adjacent to each other in the vertical direction (in the charge-transfer direction). 
     By means of the wiring portion of the transfer electrode  4 , transfer electrodes  3 B and  3 D independently formed in each of the vertical transfer resistors  2  are electrically connected with respect to those electrodes formed in the same row, and respective vertical transfer pulses φV 2  and φV 4  are provided thereto. 
     Since the transfer electrodes  3 A,  3 B,  3 C,  3 D and  4  are thus constructed, the transfer electrode  3 A and the transfer electrode  4  of two layers are, as shown in  FIG. 6B , laminated through an interlayer insulation film  6  in a portion between light-receiving sensor portions  1 , namely between pixels, adjacent to each other in the vertical direction. 
     Accordingly, the width of each transfer electrode between pixels can be reduced in comparison with the case shown in  FIG. 4B  in which the transfer electrode is formed of a single electrode layer. 
     For example, with respect to a CCD solid-state imaging device, whose size of a pixel cell is 2.0 μm, having a structure in which the transfer electrode of the vertical transfer resistor is formed of a single electrode layer (single-layer electrode structure), the width of a portion between pixels becomes approximately 0.7 μm, whereas the width of the portion in the laminated structure according to this embodiment becomes approximately 0.3 μm, so that 0.4 μm can be used to increase the size of a photodiode in each light-receiving sensor portion. Thus, the dimensions of a photodiode can be enlarged from 1.0 μm×1.3 μm of a single-layer electrode structure to 1.0 μm×1.7 μm, so that the amount of electric charge received by each light-receiving sensor portion increases by approximately 30%, which enables sufficient sensitivity and sufficient dynamic range to be obtained. 
     On the other hand, the vertical transfer resistor  2  basically employs the single-layer electrode structure including the transfer electrodes  3 A,  3 B,  3 C and  3 D formed of one electrode layer (hereinafter referred to as the first-layer transfer electrode) and the transfer electrode  4  of a second layer only provided in the vicinity of the contact portion  5 , and therefore, the extent to which incident light is blocked by those transfer electrodes is greatly reduced in comparison with a two-layer electrode structure in related art. 
     Various conductive materials including polycrystalline silicon, silicide such as WSi, metals such as W can be used for the transfer electrodes  3 A,  3 B,  3 C and  3 D of the first layer. 
     For the transfer electrode  4  of the second layer as well, various conductive materials can be used. The same material as that of the transfer electrodes  3 A,  3 B,  3 C and  3 D formed of the first electrode layer may be used, or a different material may be used to form the transfer electrode  4 . Differently from the case in related art in which the transfer electrode is formed of two electrode layers, in the structure according to this embodiment, the transfer electrode  4  of the second layer is not formed right above the gate insulation film, so that there are fewer restrictions on the material of the transfer electrode  4  of the second layer. 
     Then, in the vertical transfer resistor  2 , different vertical transfer pulses φV 1 , φV 2 , φV 3  and φV 4  are applied to the transfer electrodes  3 A,  3 B,  3 C and  3 D vertically adjacent to each other, respectively. Thus, vertical transfer of a signal charge by means of four-phase drive is executed. 
     That is, electric signals generated in the light-receiving sensor portions  1  are read out to vertical transfer resistors under the transfer electrode  3 A,  3 B,  3 C or  3 D by the vertical transfer pulse φ V 1 , φ V 2 , φ V 3  or φ V 4  applied to the transfer electrode  3 A,  3 B,  3 C or  3 D. The vertical transfer pulse φ V 1 , φ V 2 , φ  3  or φ  4  is applied the transfer electrode  3 A,  3 B,  3 C or  3 D in order of one alignment and the electric signals in vertical transfer resistors are transferred vertically. 
     The contact layer  5  is formed by burying a conductive material into a contact hole made through an interlayer insulation layer  13  between the transfer electrodes  3 B and  3 D of the first layer and the transfer electrode  4  of the second layer. 
     Note that the contact layer  5  and the transfer electrode  4  of the second layer can be formed of the same conductive material or different conductive materials. 
     According to the above-described solid-state imaging device of this embodiment, since the transfer electrode between pixels has a laminated structure in which the transfer electrodes  3 A and  3 C formed of the first electrode layer and the transfer electrode  4  formed of the second electrode layer are laminated, the width of a portion between pixels can be reduced in comparison with the case in which transfer electrodes are formed only of a first electrode layer (single-layer electrode structure). 
     Therefore, the size in the vertical direction of the light-receiving sensor portion  1  can be set large to secure the large area for the light-receiving sensor portion, in comparison with a single-layer electrode structure. 
     Thus, since a sufficient amount of electric charge can be dealt with by the light-receiving sensor portions  1 , a solid-state imaging device having favorable characteristics of having sufficient sensitivity and a sufficient dynamic range can be obtained. 
     Further, according to the solid-state imaging device of this embodiment, the vertical transfer resistor  2  basically employs the single-layer electrode structure including the transfer electrodes  3 A,  3 B,  3 C and  3 D formed of one electrode layer and the transfer electrode  4  of a second layer only provided in the vicinity of the contact portion  5  formed by the contact layer  5 , and therefore, the extent to which incident light is blocked by those transfer electrodes is greatly reduced in comparison with a two-layer electrode structure in related art. 
     It should be noted that although in the above-described embodiment a structure is employed in which four-phase drive is executed by applying the vertical transfer pulses φV 1 , φV 2 , φV 3  and φV 4  to the transfer electrode  3  of the vertical transfer resistor  2 , the present invention can be applied to other drive methods than that of the four-phase drive. 
     Similarly to the above-described embodiment, the present invention can be applied to one-phase drive, two-phase drive, four-phase drive, eight-phase drive and 16-phase drive, by providing at a vertical pitch of each pixel both the (first-stage) transfer electrode formed of a first electrode layer connected between rows, and the (second-stage) transfer electrode formed of the first electrode layer independently formed in each vertical transfer resistor (each pixel) and the second electrode layer connected between rows. 
     Further, in the above-described embodiment, the present invention is applied to a CCD solid-state imaging device including a charge-transfer portion of a CCD structure, however, the present invention can be applied to solid-state imaging devices including charge-transfer portions of other structures. 
     The present invention is not limited to the above-described embodiment, and various other structures will be acceptable without departing from the gist of the present invention. 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.