JP2008017066A - Solid imaging device, solid imaging element, and method of driving solid imaging element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid imaging device capable of suppressing defects such as fixed pattern noise and shading even when the solid imaging device has higher/finer pixels and is made low in operating voltage. <P>SOLUTION: Vertical transfer parts 2 are formed on both sides of each column of photodiode parts 1 formed in an array, and first and second horizontal transfer parts 3 and 4 are formed above and blow an imaging part. Signal charges generated by the respective photodiode parts 1 are equally divided and read out to the vertical transfer parts 2 on both the sides and the respective divided signal charges are transferred in mutually opposite directions. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a solid-state imaging device, a solid-state imaging device, and a driving method of the solid-state imaging device.

  FIG. 6 is a schematic diagram of a planar pattern layout showing a configuration of a typical conventional CCD type solid-state imaging device. As shown in FIG. 6, the CCD solid-state imaging device has a photodiode portion (photoelectric conversion portion) 1 that generates signal charges by photoelectric conversion formed in an array, and the signal charges read from the photodiode portion 1 are An imaging unit having a vertical transfer unit 2 for vertical transfer, a horizontal transfer unit 3 for horizontally transferring signal charges transferred from the vertical transfer unit 2, and an amplifier unit (output unit) formed at one end of the horizontal transfer unit 3 ) 5 and a LOCOS portion 7 formed in a peripheral region surrounding the array constituted by these.

  Light incident on the photodiode unit 1 is converted into a signal charge corresponding to the incident intensity, and is accumulated in the vertical transfer unit 2 by applying a pulse voltage (read voltage) to the read gate electrode (read electrode) of the vertical transfer unit 2. The The signal charges accumulated in the vertical transfer unit 2 are vertically transferred in the direction of the horizontal transfer unit 3 by applying a pulse voltage to the transfer gate electrode (transfer electrode) of the vertical transfer unit 2. The signal charge accumulated in the horizontal transfer unit 3 is horizontally transferred to the amplifier unit 5 by applying a pulse voltage to the transfer gate electrode (transfer electrode) of the horizontal transfer unit 3 and is taken out from the amplifier unit 5 as an output signal.

  Specifically, the vertical transfer unit 2 has independent four gates (transfer gate electrodes) V1 to V4 formed of a first-layer polysilicon film and a second-layer polysilicon film. By applying vertical drive pulses φV1 to φV4, signal charges are transferred in the vertical direction. More specifically, when a pulse voltage (readout voltage) is applied to the transfer gate electrodes V1 and V2 (readout gate electrodes), the potential (potential) of the vertical transfer section 2 is deepened, and the signal charge generated in the photodiode section 1 is vertical. It moves to the transfer unit 2 and is accumulated and mixed (field reading). Thereafter, when the pulse voltages φV1 to φV4 are applied to the transfer gate electrodes V1 to V4 at an appropriate timing, the vertical transfer unit 2 transfers the signal charges in the direction of the horizontal transfer unit 3 (vertical direction). Note that field reading is a reading method in which signal charges read from a plurality of photodiode portions adjacent in the vertical direction are added in the vertical transfer portion.

  Similarly, the horizontal transfer section 3 has independent two gates (transfer gate electrodes) H1 and H2 formed of a first-layer polysilicon film and a second-layer polysilicon film. By applying pulse voltages (two-phase horizontal drive pulses) φH1 and φH2 at timing, signal charges are sequentially transferred in the direction of the amplifier unit 5 (horizontal direction).

  The output signal from the amplifier unit 5 corresponds to each photodiode unit 1 and can be reproduced as an image by restoring the output signal in time series. The above is the structure and driving method of a solid-state imaging device that is normally used (see, for example, Patent Document 1).

  However, at present, in the solid-state imaging device, an increase in the number of pixels for improving image quality, a finer element pattern, and a lower operating voltage for lower power consumption are progressing, as shown in FIG. When a conventional solid-state image sensor is used, if the number of transfer stages increases due to an increase in the number of pixels and miniaturization, various defects generated in or on the semiconductor substrate along the charge transfer path in the manufacturing process of the solid-state image sensor. There is a problem that the degree of influence on the retention and properties is increased. That is, for example, there is a probability of occurrence of various defects such as pattern defects due to particles (a small amount of dust), pattern defects, electron traps due to crystal defects, and potential pockets due to unevenness of ion implantation (impurity substance implantation). If the number of transfer stages is increased, the probability of occurrence of fixed pattern noise caused by abnormal transfer of signal charges due to these various defects increases, and the output signal deteriorates.

  Further, in the conventional solid-state imaging device, shading failure has been a problem. That is, as shown in FIG. 7, since the signal charge transfer distance (movement distance) from the photodiode unit 1 to the horizontal transfer unit 3 differs depending on the position of the pixel, the signal generated in the photodiode unit 1 far from the horizontal transfer unit 3 During the transfer of charges, the amount of signal charge trapped and reduced at the interface state mainly present at the interface between the semiconductor substrate and the insulating film formed on the surface of the photodiode portion 1 is close to the horizontal transfer portion 3. This is larger than the signal charge amount that decreases during the transfer of the signal charge generated in step. As described above, the amount of signal charge that is reduced in combination with the interface order during transfer differs depending on the position of the pixel, so that there is a problem that unevenness of light and darkness is likely to occur on the image. This defect becomes noticeable especially when the number of transfer stages in the vertical transfer section increases with the increase in pixel size and miniaturization.

  On the other hand, in order to suppress trapping of signal charges at the interface state during transfer, there is a method of deepening the potential and transferring the signal charges deep in the semiconductor substrate, but the drive voltage must be increased, As a result, the capacity of signal charges that can be transferred is reduced.

With the structure and driving method of the conventional solid-state imaging device, when trying to achieve higher pixels, smaller dimensions, and lower operating voltages as described above, various types of fixed pattern noise, shading, etc. There has been a problem that characteristic defects are likely to occur.
JP 2003-234466 A

  In view of the above problems, the present invention forms a vertical transfer unit on each side of each column of a photodiode unit (photoelectric conversion unit), and forms a horizontal transfer unit at the lower and upper portions of the imaging unit, Each signal charge generated in the diode section is equally divided and read to the vertical transfer sections on both sides, and the divided signal charges are transferred in the opposite directions, thereby reducing the number of pixels, miniaturization, and operating voltage. An object of the present invention is to provide a solid-state imaging device, a solid-state imaging device, and a driving method for the solid-state imaging device that can suppress the occurrence of defects such as fixed pattern noise and shading even in a solid-state imaging device that has been turned into a voltage.

  In the solid-state imaging device according to the first aspect of the present invention, photoelectric conversion units that generate signal charges by photoelectric conversion are formed in an array, and vertical transfer units are formed on both sides of each column of the photoelectric conversion units. An image pickup unit, two horizontal transfer units formed at the upper and lower portions of the image pickup unit, an output unit formed at one end of each horizontal transfer unit, and signal charges generated by the photoelectric conversion units, respectively A pulse voltage for dividing and reading out to the vertical transfer units on both sides is applied to the readout electrodes of the vertical transfer units, and the divided signal charges are vertically transferred to the upper and lower sides of the imaging unit. And a circuit for applying the pulse voltage to the transfer electrode of each of the vertical transfer units.

  The solid-state imaging device according to claim 2 of the present invention is the solid-state imaging device according to claim 1, wherein each of the output units is formed at opposite ends of the horizontal transfer units, and And a circuit for applying a pulse voltage for horizontally transferring the signal charges transferred to the horizontal transfer units in opposite directions to transfer electrodes of the horizontal transfer units. A solid-state imaging device according to claim 3 of the present invention is the solid-state imaging device according to claim 1 or 2, wherein the adjacent vertical transfer units are electrically separated. And

  According to a fourth aspect of the present invention, in the solid-state imaging device, photoelectric conversion units that generate signal charges by photoelectric conversion are formed in an array, and vertical transfer units are formed on both sides of each column of the photoelectric conversion units. An image pickup unit, two horizontal transfer units formed at the upper and lower portions of the image pickup unit, and an output unit formed at one end of each horizontal transfer unit.

  The solid-state imaging device according to claim 5 of the present invention is the solid-state imaging device according to claim 4, wherein each of the output units is formed at opposite ends of the horizontal transfer units. Features. A solid-state imaging device according to claim 6 of the present invention is the solid-state imaging device according to claim 4 or 5, wherein the adjacent vertical transfer units are electrically separated. And

  According to a seventh aspect of the present invention, there is provided a method for driving a solid-state imaging device, wherein photoelectric conversion units that generate signal charges by photoelectric conversion are formed in an array and are vertically transferred to both sides of each column of the photoelectric conversion units. A solid-state imaging device driving method comprising: an imaging unit formed with a portion; two horizontal transfer units formed above and below the imaging unit; and an output unit formed at one end of each horizontal transfer unit The signal charges generated by the photoelectric conversion units are divided and read to the vertical transfer units on both sides, and the divided signal charges are vertically transferred to the upper side and the lower side of the imaging unit. It is characterized by that.

  In the solid-state imaging device driving method according to claim 8 of the present invention, the photoelectric conversion units that generate signal charges by photoelectric conversion are formed in an array and are vertically transferred to both sides of each column of the photoelectric conversion units. A solid-state imaging device comprising: an imaging unit formed with a portion; two horizontal transfer units formed on an upper part and a lower part of the imaging unit; and an output unit formed on opposite ends of each horizontal transfer unit The signal charge generated in each photoelectric conversion unit is divided and read to the vertical transfer units on both sides, and the divided signal charges are vertically applied to the upper side and the lower side of the imaging unit. The signal charges transferred to the two horizontal transfer units are horizontally transferred in opposite directions.

  According to the present invention, it is possible to suppress the occurrence of defects such as fixed pattern noise and shading even in a solid-state imaging device in which the number of pixels is increased, the size is reduced, and the operating voltage is reduced.

  Hereinafter, the structure of the solid-state imaging device (solid-state imaging device) and the driving method of the solid-state imaging device in the embodiment of the present invention will be described. FIG. 1 is a schematic diagram of a planar pattern layout showing the configuration of a solid-state imaging device according to an embodiment of the present invention.

  As shown in FIG. 1, in the solid-state imaging device, photodiode portions (photoelectric conversion portions) 1 that generate signal charges by photoelectric conversion are formed in an array, and on both sides of each column of the photodiode portions 1, An imaging unit in which a vertical transfer unit 2 for vertically transferring signal charges read from the photodiode unit 1 is formed; and first and second horizontal transfer units 3 and 4 formed in the upper and lower portions of the imaging unit; , First and second horizontal transfer units 3, 4, first and second amplifier units (output units) 5, 6 formed at opposite ends of the first and second horizontal transfer units 3, 4.

  Specifically, the vertical transfer unit 2 includes four independent transfer gate electrodes (transfer electrodes) V1 to V4 formed of a first-layer polysilicon film and a second-layer polysilicon film. One of these four gates also serves as a read gate electrode (read electrode). In the solid-state imaging device using the solid-state imaging element, the four-phase vertical drive pulses φV1 to φV4 are respectively applied to the four transfer gate electrodes to vertically transfer the signal charges. The transfer direction is opposite on both sides of each column of 1.

  The first and second horizontal transfer gates 3 and 4 have two independent transfer gate electrodes (transfer electrodes) H1 and H2 formed of a first-layer polysilicon film and a second-layer polysilicon film. The solid-state imaging device using the solid-state imaging device applies the two-phase horizontal drive pulses φH1 and φH2 to the two transfer gate electrodes, respectively, and horizontally transfers the signal charges. Is the opposite.

  In addition, a LOCOS section 7 that is an insulating separation area is provided so as to surround the photodiode array area and the first and second horizontal transfer sections 3 and 4. Although not shown, the LOCOS unit is also provided between the pixel columns so that the signal charge accumulated in the photodiode unit of each pixel does not diffuse in the horizontal direction during vertical transfer. In this embodiment, the insulating isolation region is LOCOS. However, for example, groove type insulating isolation (STI) or PN junction isolation may be used.

  The configuration of the solid-state image sensor will be described in more detail. 2 is an enlarged plan view of the solid-state imaging device according to the embodiment of the present invention, FIG. 3 is a cross-sectional view taken along line AA ′ in FIG. 2, and FIG. 4 is cut along line BB ′ in FIG. It is sectional drawing of the part which carried out.

  As shown in FIGS. 3 and 4, in the solid-state imaging device, a diffusion layer 9 of the photodiode unit 1 and a diffusion layer 10 of the vertical transfer unit 2 are formed on the semiconductor substrate 8, and a gate insulating film 11 is formed on the semiconductor substrate 8. A first polysilicon film 12 and a second polysilicon film 13 are formed as transfer gate electrodes. The polysilicon films 12 and 13 are formed in separate steps.

  Further, as shown in FIG. 3, the LOCOS unit 7 which is an insulating isolation region provided between the pixel columns is 1 so as to electrically isolate the diffusion layer 10 of the vertical transfer unit belonging to the left and right pixels. It is formed at the boundary between the second layer polysilicon film 12 and the second layer polysilicon film 13. Further, in the solid-state imaging device, as shown in FIG. 4, the second-layer polysilicon film 13 is formed so as to partially overlap the first-layer polysilicon film 12 through a thin insulating film.

  FIG. 5 is a plan view excluding the second-layer polysilicon film 13 that forms part of the transfer gate electrode in FIG. 2, and shows the pattern of the first-layer polysilicon film 12. As apparent from FIG. 5, in this embodiment, transfer gate electrodes V2 and V4 to which vertical drive pulses φV2 and φV4 are applied are formed by the first-layer polysilicon film 12. Similarly, transfer gate electrodes V1 and V3 to which vertical drive pulses φV1 and φV3 are applied are formed by the second-layer polysilicon film 13.

  In FIG. 5, the transfer gate electrodes V2 and V4 to which different vertical drive pulses φV2 and φV4 are applied seem to be in contact with each other, but they are actually separated from each other, and the interval is an actual photolithography process. They are separated by a distance that can be sufficiently separated. Similarly, transfer gate electrodes V1 and V3 to which vertical drive pulses φV1 and φV3 are applied are also separated. However, each transfer gate electrode is continuously connected horizontally to both ends of the pixel array.

  Subsequently, the operation of the solid-state imaging device will be described. The light incident on the photodiode unit 1 is converted into a signal charge corresponding to the incident intensity and accumulated in the photodiode unit 1. Then, the signal charge is divided in half and read out to the vertical transfer units 2 on both the left and right sides. Reading to the vertical transfer unit 2 can be realized by a driving method in which a pulse voltage (read voltage) having the same potential is simultaneously applied to the transfer gate electrodes (read electrodes) V1 and V3 of the vertical transfer unit. The divided signal charges are temporarily accumulated and mixed in the surface portion of the semiconductor substrate immediately below the transfer gate electrode of the adjacent vertical transfer portion divided into left and right by the vertical central axis of the photodiode portion 1 (field). reading). Thereafter, when the pulse voltages φV1 to φV4 are applied to the transfer gate electrodes V1 to V4 at an appropriate timing, the divided signal charges are transferred in opposite directions. Thereafter, the divided signal charges are accumulated in the first and second horizontal transfer units 3 and 4 and horizontally transferred in the opposite directions, respectively, and output divided from the first and second amplifier units 5 respectively. Extracted as a signal.

  Specifically, when a pulse voltage (read voltage) having an appropriate potential is simultaneously applied to the transfer gate electrodes V1 and V3 of the vertical transfer unit 2, that is, when the pulse voltage rises simultaneously, the potential of the diffusion layer 10 of the vertical transfer unit 2 becomes deeper. . As described above, since the diffusion layer 10 extending in the transfer direction, that is, the vertical direction is separately formed on the semiconductor substrate immediately below the transfer gate electrode, the signal charge generated in any photodiode portion 1 is diffused on both the left and right sides. Evenly distributed within the layer 10. The signal charges divided and temporarily accumulated and mixed in the diffusion layers 10 on both sides in this way are transferred in directions opposite to each other by the four-phase vertical drive pulses φV1 to φV4.

  The vertically transferred signal charge reaches the first and second horizontal transfer units 3 and 4. The first and second horizontal transfer portions 3 and 4 also have transfer gate electrodes formed of a first-layer polysilicon film and a second-layer polysilicon film that partially overlap each other. By applying pulse voltages (two-phase horizontal drive pulses) φH1 and φH2 to the two gates at an appropriate timing, the signal charges accumulated in the first and second horizontal transfer units 3 and 4 are sequentially reversed in the opposite directions. It is transferred and taken out as an output signal from the first and second amplifier sections 5 and 6.

  Here, the output signal from each amplifier is a half signal, but the output signal corresponds to a specific photodiode unit 1 and is synthesized by signal processing using a memory or the like. It can be reproduced as an image signal. For example, since each output signal is transferred in the opposite direction from each photodiode unit, the image signals output from the first and second amplifier units 5 and 6 are opposite to each other in time series. Therefore, each image signal is stored in two memories, and the output from one of the memories is reversed and synthesized, whereby the image can be reproduced.

  In addition to the solid-state imaging device shown in FIG. 1, the solid-state imaging device using the solid-state imaging device divides the signal charge generated by each photodiode unit 1 and vertically transfers the both sides. 2 is applied to the transfer gate electrodes (read gate electrodes) V1 and V3 of the vertical transfer unit 2, and the divided signal charges are vertically transferred to the upper and lower sides of the imaging unit. For applying the four-phase vertical drive pulses φV1 to φV4 to the transfer gate electrodes V1 to V4 of the vertical transfer unit 2 and the signal charges transferred to the two horizontal transfer units 3 and 4 in opposite directions. A circuit for applying two-phase horizontal drive pulses φH1 and φH2 for horizontal transfer to the transfer gate electrodes H1 and H2 of the horizontal transfer units 3 and 4, respectively. Reading by dividing the load by transferring in opposite directions.

  As described above, in the present embodiment, the signal charges generated in the respective photodiode units 1 are equally divided and read out to the vertical transfer units 2 on both sides, and the divided signal charges are output to the upper side of the imaging unit. The signal charges transferred vertically to the two horizontal transfer units 3 and 4 are horizontally transferred in opposite directions.

  According to the present embodiment, signal charges generated in the same photodiode section are transferred in half, so signal charge transfer abnormalities due to various defects such as pattern defects, pattern defects, potential pockets, etc. It is possible to reduce the probability of occurrence of fixed pattern noise caused by.

  That is, when it is assumed that various defects such as pattern defects, pattern defects, and potential pockets are generated, in the conventional solid-state imaging device, if a defect exists in one place of the vertical transfer unit, it is strongly fixed. Pattern noise occurs. However, according to the present embodiment, since the signal charge is divided into two, even if there is a defect in one place of the vertical transfer unit, the remaining half of the charge is output via a path having no defect. Therefore, it is settled with fixed pattern noise of half intensity.

  In addition, since the signal charge is transferred in half, the potential depth on the surface of the semiconductor substrate that can transfer all charges is reduced even if the pulse voltage of the four-phase vertical drive pulse of the vertical transfer unit is reduced. Since it can be ensured, the voltage can be lowered.

  Further, the shading has a correlation with the charge movement distance (transfer distance) in the vertical transfer unit. That is, the longer the moving distance, the larger the signal charge loss due to shading. In this embodiment, since the signal charges generated in the same photodiode portion are halved and vertically transferred in opposite directions to each other, the total movement distance of the signal charges is equal in all the photodiode portions, so The unevenness of becomes difficult to occur. Note that the horizontal transfer has a very high transfer frequency compared to the vertical transfer, and the signal charge is transferred before being trapped at the interface state, so that the influence is small.

  In the present embodiment, the solid-state imaging device and the solid-state imaging device in which the amplifier units 5 and 6 are formed at the opposite ends of the two horizontal transfer units 3 and 4 have been described. The structure formed only in the end of one side of one horizontal transfer part may be sufficient.

The solid-state imaging device, the solid-state imaging device, and the driving method of the solid-state imaging device according to the present invention can increase the number of pixels, miniaturize, and lower the voltage, and can reduce fixed pattern noise and shading defects peculiar to the solid-state imaging device. This is possible, and is useful for electronic equipment equipped with a solid-state imaging device.

Schematic of a planar pattern layout showing the configuration of a solid-state imaging device in an embodiment of the present invention Schematic enlarged plan view of a solid-state imaging device in an embodiment of the present invention FIG. 2 is a schematic cross-sectional view taken along line A-A ′ of FIG. 2. FIG. 2 is a schematic cross-sectional view taken along line B-B ′ in FIG. 2. 1 is a schematic enlarged plan view showing a pattern of a first-layer polysilicon film of a solid-state imaging device in an embodiment of the present invention. Schematic of a planar pattern layout showing the configuration of a conventional CCD type typical solid-state imaging device The figure for demonstrating the cause of the shading defect of the conventional solid-state imaging device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photodiode part 2 Vertical transfer part 3, 4 Horizontal transfer part 5, 6 Amplifier part 7 LOCOS part 8 Semiconductor substrate 9 Diffusion layer of photodiode part 10 Diffusion layer of vertical transfer part 11 Gate insulating film 12 1st layer polysilicon film 13 Second layer polysilicon film

Claims (8)

An imaging unit in which photoelectric conversion units that generate signal charges by photoelectric conversion are formed in an array, and vertical transfer units are formed on both sides of each column of the photoelectric conversion unit, and
Two horizontal transfer units formed at the top and bottom of the imaging unit;
An output unit formed at one end of each horizontal transfer unit;
A pulse voltage for dividing the signal charge generated in each photoelectric conversion unit and reading it to the vertical transfer units on both sides is applied to the readout electrode of each vertical transfer unit, and the divided signal charges are A circuit for applying a pulse voltage for vertical transfer to the upper side and the lower side of the imaging unit to the transfer electrode of each vertical transfer unit;
A solid-state imaging device comprising: The solid-state imaging device according to claim 1,
Each output unit is formed at opposite ends of each horizontal transfer unit,
The solid-state imaging device further comprises a circuit for applying a pulse voltage for horizontally transferring the signal charges transferred to the horizontal transfer units in opposite directions to transfer electrodes of the horizontal transfer units. .   The solid-state imaging device according to claim 1, wherein the adjacent vertical transfer units are electrically separated. An imaging unit in which photoelectric conversion units that generate signal charges by photoelectric conversion are formed in an array, and vertical transfer units are formed on both sides of each column of the photoelectric conversion unit, and
Two horizontal transfer units formed at the top and bottom of the imaging unit;
An output unit formed at one end of each horizontal transfer unit;
A solid-state imaging device comprising:   5. The solid-state imaging device according to claim 4, wherein the output units are formed at opposite ends of the horizontal transfer units.   The solid-state imaging device according to claim 4, wherein the adjacent vertical transfer units are electrically separated. An imaging unit in which photoelectric conversion units that generate signal charges by photoelectric conversion are formed in an array, and vertical transfer units are formed on both sides of each column of the photoelectric conversion unit, and
Two horizontal transfer units formed at the top and bottom of the imaging unit;
An output unit formed at one end of each horizontal transfer unit;
A method for driving a solid-state imaging device comprising:
Dividing the signal charges generated by the photoelectric conversion units into the vertical transfer units on both sides and vertically transferring the divided signal charges to the upper side and the lower side of the imaging unit,
A method for driving a solid-state imaging device. An imaging unit in which photoelectric conversion units that generate signal charges by photoelectric conversion are formed in an array, and vertical transfer units are formed on both sides of each column of the photoelectric conversion unit, and
Two horizontal transfer units formed at the top and bottom of the imaging unit;
An output unit formed at opposite ends of each horizontal transfer unit;
A method for driving a solid-state imaging device comprising:
The signal charges generated by the photoelectric conversion units are respectively divided and read out to the vertical transfer units on both sides, and the divided signal charges are vertically transferred to the upper side and the lower side of the imaging unit, so that the two horizontal The signal charges transferred to the transfer unit are horizontally transferred in opposite directions.
A method for driving a solid-state imaging device.

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