The disclosure of Japanese Patent Application No. 2003-385968 including specifications, claims, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a solid-state image sensing device for reducing noise of electric charge, and a method for controlling the solid-state image sensing device.
2. Description of the Related Art
The CCD (Charge Coupled Device) is an electric charge transfer device capable of transferring signal packets of information charge (electric charge) in good order in one direction at a speed synchronized with external clock pulses.
The frame-transfer-type-CCD solid-state image sensing device includes an image capture section 2i, a storage section 2s, a horizontal transfer section 2h, and an output section 2d as shown in
The light falling on the image capture section 2i generates information charges in the bits of the image capture section 2i. The information charges in a two-dimensional array on the image capture section 2i are transferred to the storage section 2s at high speed by the vertical shift registers of the image capture section 2i. Therefore, the information charges for one frame are stored in he vertical shift registers of the storage section 2s. After this, the information charges are transferred one line after another to the horizontal transfer section 2h. Then, the information charges are transferred in pixel units from the horizontal transfer section 2h to the output section 2d. The output section 2d converts the amount of charge per pixel into a voltage value, and changes in the voltage value are outputs of the CCD.
As shown in
A P-well (PW) 11 is formed in the N-type semiconductor substrate, and an N-well 12 is formed on top of the P-well 11. In other words, a P-well 11 added with P-type impurities is formed in an N-type semiconductor substrate 9. An N-well 12 with high concentration of N-type impurities is formed in the surface portion of the P-well 11. This surface portion indicates a portion that is shallow from the surface.
Separation regions 14 are provided to separate the channel regions of the vertical shift registers. The separation regions 14 formed by P-impurity-doped regions are formed in the N-well by ion implantation of P-type impurity ions arranged mutually in parallel at predetermined intervals. The N-well 12 is electrically partitioned by the adjacent separation regions 14. The spaces placed between the separation regions 14 are channel regions 22, which serve as transfer paths for information charges. Between the adjacent channel regions, the separation regions 14 build up potential barriers to thereby electrically isolate the channel regions 22.
An insulation film 13 is deposited on the surface of the semiconductor substrate 9. A plurality of transfer electrodes 24 made of a polysilicon film are arranged mutually in parallel so as to be at right angles with the extending direction of the channel regions 22 through the intermediary of this insulation film 13. To reduce the resistive components of the transfer electrodes 24, back wires 15 made of tungsten silicide which are connected through openings provided in the same pattern for every certain number of transfer electrodes, are provided in parallel in the extending direction of the channel regions 22. A set of three adjacent transfer electrodes 24-1, 24-2, and 24-3 corresponds to one pixel.
As described above, in a conventional solid-state image sensing device, after information charge is transferred from the image capture section 2i to the storage section 2s, the information charge is output to the output section 2d one line after another by the horizontal transfer section 2h formed continuously with the storage section 2s.
However, in a solid-state image sensing device mounted on an instrument with a function other than capturing images, such as a mobile phone, when using this other function, that is, when talking on the phone, for example, it sometimes happens that the transfer of information charge from the storage section 2s to the horizontal transfer section 2h must be interrupted. While output is interrupted, it is necessary to keep turned on at least one of the transfer electrodes 24-1 to 24-3 of the storage section 2s, and hold information charge in the related potential wells 50. Under the condition that some electrodes are kept turned on, a dark current occurs due to the effect of an interface state resulting from a defect existing at the interface between the insulation film 13 and the semiconductor substrate 9. The dark current caused by this defect-induced interface state is present as noise superimposed on the information charge held in the potential wells 50, and deteriorates the images taken by the CCD solid-state image sensing device.
According to the present invention, a solid-state image sensing device, formed on a semiconductor substrate, includes an image capture section for capturing external light rays and generating information charge (electric charge); and a storage section shielded from incident external light rays and having a plurality of transfer electrodes arranged on a surface of the semiconductor substrate, the storage section being used to transfer the information charges by using the transfer electrodes, the solid-state image sensing device comprising:
According to the present invention, a solid-state image sensing device formed on a semiconductor substrate includes an image capture section for capturing external light rays and generating information charges; a storage section, having a plurality of channel regions arranged mutually in parallel at predetermined intervals on a surface portion of the semiconductor substrate, the surface portion of each of the channel regions being of one electric conductive type and a plurality of transfer electrodes, for transferring the information charges by using the plurality of transfer electrodes, the plurality of transfer electrodes being arranged mutually in parallel in a direction intersecting the plurality of channel regions on a surface of the semiconductor substrate, the solid-state image sensing device comprising;
According to the present invention, there is provided a method of controlling a solid-state image sensing device, which includes an image capture section for capturing external light rays and generating information charges; and a storage section formed on a semiconductor substrate and shielded from incident external light rays, and including a plurality of transfer electrodes arranged on a surface of the semiconductor substrate, a plurality of diodes formed and buried beneath the vicinity of the transfer electrodes, and this controlling method comprises a first process of storing the information charges in the diodes under the condition that the transfer electrodes are all turned off.
As in the solid-state image sensing device in the background technology in
As shown in
The storage section 2s is formed on the surface portion of an N-type semiconductor substrate 9. The surface portion indicates a portion shallow from the surface. For the semiconductor substrate 9, a common semiconductor material, such as a silicon substrate added with N-type impurities, such as arsenic (As), phosphorus (P), or antimony (Sb), may be used. A suitable material for the semiconductor substrate 9 is a silicon substrate with doping concentration of not less than 1×1014/cm3 and not more than 1×1015/cm3.
A P-well (PW) 11, added with P-type impurities, is formed in the N-type semiconductor substrate 9. As the P-type impurities, boron (B), aluminum (Al), gallium (Ga) or indium (In) may be used. The doping concentration for the P-well is desirably higher than the doping concentration of the semiconductor substrate 9 and a preferable value of the P-well doping concentration is not less than 5×1014/cm3 and not more than 5×1016/cm3. An N-well (NW) 12 added with N-type impurities at a high concentration formed at the surface portion of the P-well 11. The doping concentration of the N-well 12 is desirably higher than the doping concentration of the P-well and a preferable value of the N-well doping concentration is not less than 1×1016/cm3 and not more than 1×1017/cm3. In the N-well, separation regions 14 are formed, which are made up of P-type impurity regions added with a high concentration of P-type impurities and arranged in parallel mutually spaced apart by a specified amount. The doping concentration of the separation regions 14 is preferably not less than 1×1016/cm3 and not more than 5×1017/cm3. The separation regions 14 build potential barriers in the adjacent channel regions 22 to electrically isolate the channel regions from one another.
An insulation film 13 is deposited on the surface of the semiconductor substrate 9. The insulation film 13 may be formed by an insulation material used in semiconductor integrated devices, such as a silicon oxide film (SiO2), a silicon nitride film (SiN), etc.
A plurality of transfer electrodes 24 are arranged mutually in parallel so as to be at right angles with the extending direction of the separation regions 14 with interposition of the insulation film 13. The transfer electrodes 24 may be formed by a polysilicon film, a metal film, or a combination of these materials. According to this embodiment, a set of three adjacent transfer electrodes 24-1, 24-2 and 24-3 corresponds to one pixel.
P+ regions 16 added with a high concentration of P-type impurities are formed in the regions of N-wells 12 placed between the adjacent separation regions 14. Each PN junction between the P+ region 16 and the N-well 12 forms a diode 26. At least one diode is provided to each set of three transfer electrodes 24-1, 24-2 and 24-3, which correspond to one pixel.
Through openings formed by notch regions 28 of the adjacent transfer electrodes 24, ions of P-type impurities are implanted into the surface of the N-well, by which high-density P+-type regions 16 are formed on the surface of the semiconductor substrate 9. At this time, the shape of the high-density P+-type regions is decided in such a way that the transfer electrode 24 is not cut off in the middle of each transfer electrode 24.
By adding P-type impurities to the surface portion through the openings of the notch regions by using the transfer electrodes as the mask, the P+ regions 16 can be formed. In this process, P-type impurities, boron ions for example, are implanted at an acceleration voltage of 20 keV and under an implantation condition of 1×1012/cm2. The doping concentration of the P+-type regions 16 is preferably not less than 1×1016/cm3 and not more than 5×1017/cm3.
The diodes 26 may be formed beneath the vicinity of the transfer electrodes 24 without providing the notch regions 28.
For example, in
As shown in the side sectional view drawing of
Through the openings shown in
The P+-type regions 16 and the N+-type regions 17 may be formed beneath the vicinity of the transfer electrodes 24 by using a resist mask without providing the notch regions 28 as shown in
The P+-type regions 16, used to form diodes 26, are preferably formed to contact the separation regions 14 as shown in
The CCD solid-state image sensing device takes incident light rays and generates information charges according to the intensity of the external light rays by photoelectric conversion. The diodes 26 are used to store information charges from the image capture section 2i for their corresponding pixels.
Of the regions placed between the separation regions 14, the regions where diodes 26 are not formed serve as the channel regions 22 to transfer the information charges. Each channel region 22 is electrically isolated by the separation regions 14.
Description will next be given of a method for controlling the CCD in this embodiment of the present invention.
Before time t0, the information charges were transferred vertically along the channel regions 22. As shown in
Meanwhile, information charge 32 was stored in the potential well 38 formed in the N-well 12. Clock pulses φ1˜φ3 were sequentially applied to the transfer electrodes 24-1˜24-3, and the potential wells 38 formed under the transfer electrodes 24-1˜24-3 moved in the extending direction of the channel regions 22. Accordingly, the information charges 32 were transferred sequentially.
At times t0˜t1, the transfer of information charges 32 at the storage 2s was interrupted. In this process, a negative potential was applied to each of the transfer electrodes 24-1˜24-3, and a negative potential was also applied to the N-type substrate 10. For this reason, the potential distribution along line D-D′ was as indicated by line G in
During the interruption of charge transfer, by applying a negative potential to the transfer electrodes, the interface state between the P+-type region 16 and the N-well 12 or between the P+-type region and the N+-type region 17 is terminated by holes as shown in
At times t1˜t2, the charge transfer that was interrupted is restarted. At this time, a positive potential is applied to either the transfer electrode 24-1 or the transfer electrode 24-2, which is adjacent to the electrode 26, and the N-type substrate 10 is kept at a negative potential. In the timing chart of
After this, in the same manner as before the time t0, by applying clock pulses φ1˜φ3, which are out of phase, to the transfer electrodes 24-1˜24-3, the information charges can be transferred again in a direction towards the channel region 22.
As has been described, according to this embodiment, when the transfer of information charges is interrupted, the charges that occur due to the interface state can be decreased, and the effects of dark current on images can be suppressed. In other words, without sacrificing the sensitivity and the saturation power, noise resulting from the occurrence of the dark current can be reduced. Therefore, it becomes possible to improve the quality of images taken by means of the solid-state image sensing device.
The present invention is not limited to the embodiments described above, and various changes and modifications may be made without departing from the spirit or scope of the invention.
Number | Date | Country | Kind |
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2003-385968 | Nov 2003 | JP | national |