JP2008166845A - Solid-state imaging device and driving method of solid-state imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid-state imaging device capable of ensuring full sensitivity and having superior characteristics. <P>SOLUTION: The solid-state imaging device is constituted, such that a transfer electrode of charge transfer portions 2, provided on one side of each sequence of light-receiving sensor portions 1, is constituted of a first transfer electrode formed with electrode layers 3A and 3C of a first layer and a second transfer electrode formed by connecting electrode layers (polysilicon) 3B and 3D of the first layer and an electrode layer (polysilicon) 4 of the second layer by a contact layer 5; the contact layer 5 and the second electrode layer 4 are formed of identical conductive material; the electrode layers 3B and 3D of the first layer of the second transfer electrode are formed independently at each charge transfer portion 2; and in a portion between pixels adjacent in the direction of the charge transfer portions 2, the first transfer electrodes 3A and 3C and the electrode layer 4 of the second layer of the second transfer electrode are laminated. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a solid-state imaging device having a charge transfer unit such as a CCD solid-state imaging device and a driving method of the solid-state imaging device.

  In a CCD solid-state imaging device, a transfer register having a CCD structure is provided as a charge transfer unit, and a signal charge photoelectrically converted and accumulated by a light receiving sensor unit made of a photodiode is read to the transfer register, and the signal charge is transferred to the transfer register. It is configured to be transferred.

  The transfer register is configured by forming a transfer electrode via an insulating film on a transfer channel to which signal charges are transferred. In order to transfer the signal charge, it is necessary to apply voltage pulses having different phases to adjacent transfer electrodes, and it is necessary to prevent the channel from being disconnected. Therefore, the transfer electrode is constituted by two electrode layers of the first layer and the second layer, and the end of the transfer electrode of the second layer slightly overlaps the transfer electrode of the first layer ( For example, see Patent Document 1.)

FIG. 3 shows a schematic configuration diagram (plan view) of the CCD solid-state imaging device in which the transfer electrode is configured by two electrode layers in this way.
As shown in FIG. 3, in this CCD solid-state imaging device, light receiving sensor portions 51 are arranged in a matrix, and on one side of each column of the light receiving sensor portions 51, as a charge transfer portion, in the vertical direction (up and down direction in the figure) An extended vertical transfer register 52 is provided. A horizontal transfer register (not shown) is connected to one end of the vertical transfer register 52.

  3A shows a cross-sectional view of the vertical transfer register 52 in the CCD solid-state imaging device of FIG. 3, and FIG. 4B shows a cross-sectional view between the light receiving sensor portions 51 adjacent in the vertical direction, that is, between the pixels. In FIG. 4A and FIG. 4B, the description of the semiconductor regions (each region of the light receiving sensor portion, the transfer channel region, etc.) in the semiconductor substrate is omitted.

The vertical transfer register 52 includes a transfer electrode 53 and a transfer channel region (not shown) formed in the semiconductor substrate 54, and serves as a charge transfer unit having a CCD structure.
In the transfer electrode 53, transfer electrodes 53B and 53D made of the first electrode layer and transfer electrodes 53A and 53C made of the second electrode layer are alternately arranged in the vertical direction.
In the vertical transfer register 52, the end portions of the second-layer transfer electrodes 53A and 53C are slightly overlapped with the first-layer transfer electrodes 53B and 53D.

Incidentally, miniaturization of pixel cells of solid-state imaging devices has been advanced in response to the increase in the number of pixels and the reduction in size of digital cameras.
Further, since it is demanded that the pixel cell of the solid-state imaging device is miniaturized and has high sensitivity, how to increase the light capturing efficiency becomes a major issue.

However, in the CCD solid-state imaging device shown in FIGS. 3 and 4 in which the transfer electrode 53 composed of the two electrode layers overlaps, the unevenness around the light receiving sensor portion 61 is the overlap portion of the transfer electrode 53. The incident light is partially blocked at this portion.
For this reason, it is difficult to improve the light capturing efficiency.
Since the thickness of the overlap portion of the transfer electrode 53 is usually 1 μm or more, particularly when the size of the pixel cell is 3 μm or less and the opening width on the light receiving sensor portion 51 is reduced to about 1 μm, the overlap portion As a result, the incident light is partially blocked.
JP-A-9-31390

  On the other hand, a CCD solid-state imaging device is also proposed in which the transfer electrodes are formed from a single electrode layer without overlapping the transfer electrodes.

FIG. 5 shows a schematic configuration diagram (plan view) of the CCD solid-state imaging device in which the transfer electrode is configured by a single electrode layer.
As shown in FIG. 5, in this CCD solid-state imaging device, the light receiving sensor units 61 are arranged in a matrix, and on one side of each column of the light receiving sensor units 61, as a charge transfer unit in the vertical direction (vertical direction in the figure). An extended vertical transfer register 62 is provided. A horizontal transfer register (not shown) is connected to one end of the vertical transfer register 62.

  Further, in the CCD solid-state imaging device of FIG. 5, a sectional view of the vertical transfer register 62 is shown in FIG. 6A, and a sectional view between pixels adjacent in the vertical direction is shown in FIG. 6B. In FIG. 6A and FIG. 6B, the description of the semiconductor region (each region of the light receiving sensor portion, the transfer channel region, etc.) in the semiconductor substrate is omitted.

The vertical transfer register 62 includes a transfer electrode 63 and a transfer channel region (not shown) formed in the semiconductor substrate 64, and serves as a charge transfer unit having a CCD structure.
The transfer electrode 63 is composed of four transfer electrodes 63A, 63B, 63C, and 63D, each of which is composed of the first electrode layer.
Since the transfer electrodes 63A, 63B, 63C, and 63D are formed of the same electrode layer, there is no overlap portion.

However, in the CCD solid-state imaging device having this structure, as shown in FIG. 6B, in order to adopt a structure in which two electrodes 63A and 63B are passed between pixels adjacent to each other in the vertical direction (charge transfer direction). The inter-pixel width is relatively large.
Therefore, there is a drawback that the area of the light receiving sensor unit 61 is reduced. For example, when compared with the same pixel cell size, the area is reduced by about 30% due to the structure composed of two electrode layers.

Thus, when the area of the light receiving sensor portion is reduced, the amount of charge that can be accumulated in the light receiving sensor portion is reduced, so that the sensitivity is lowered and the dynamic range is reduced. Also, it is greatly affected by shading.
In particular, this problem becomes significant when the pixel size is reduced.

  In order to solve the above-described problems, the present invention provides a solid-state imaging device that can ensure sufficient sensitivity and has good characteristics.

  In the solid-state imaging device according to the present invention and the solid-state imaging device according to the driving method thereof, the light receiving sensor units constituting the pixels are arranged in a matrix, and the charge transfer unit is provided on one side of each column of the light receiving sensor units. The transfer electrode of the charge transfer unit is a first transfer electrode composed of a first electrode layer, and a second transfer electrode formed by electrically connecting the first layer electrode layer and the second layer electrode layer. A contact layer contacting the first and second electrode layers of the second transfer electrode, the first electrode layer and the second electrode layer being polycrystalline silicon; The second electrode layer is formed of the same conductive material, and the first electrode layer of the second transfer electrode is formed independently for each charge transfer unit and is adjacent in the direction of the charge transfer unit. In the inter-pixel portion, the first transfer electrode and the second electrode layer of the second transfer electrode In which are stacked.

According to the above-described configuration of the solid-state imaging device of the present invention, the transfer electrode of the charge transfer unit includes the first transfer electrode including the first electrode layer, the first electrode layer, and the second electrode layer. Are electrically connected to each other, the first electrode layer and the second electrode layer are polycrystalline silicon, and the first transfer electrode layer is the first transfer electrode layer. The contact layer that contacts the electrode layer of the second layer and the electrode layer of the second layer are formed of the same conductive material, and the electrode layer of the first layer of the second transfer electrode is provided for each charge transfer unit. By being formed independently, in the charge transfer portion, the second transfer electrode is mainly composed of the first electrode layer, and there is only a part of the second electrode layer. The degree to which incident light is blocked by the transfer electrode compared to the structure in which two electrode layers overlap. It is significantly less.
Further, in the inter-pixel portion adjacent in the direction of the charge transfer portion, the first transfer electrode (consisting of the first electrode layer) and the second electrode layer of the second transfer electrode are stacked. As a result, it is possible to reduce the width of the inter-pixel portion as compared with the case where the transfer electrode is configured by only the first electrode layer (single-layer electrode structure). Thereby, it is possible to set a large size of the light receiving sensor part in the direction of the charge transfer part.

According to the above-described present invention, it is possible to set a large size of the light receiving sensor unit and ensure a large area of the light receiving sensor unit.
Therefore, according to the present invention, it is possible to realize a solid-state imaging device having a sufficient amount of charge handled by the light receiving sensor unit, sufficient sensitivity and dynamic range, and good characteristics.

  According to the present invention, problems (such as a decrease in sensitivity and a decrease in dynamic range) that occur remarkably with the miniaturization of the solid-state image sensor can be solved. The number of pixels and the density of the image sensor can be increased. It is also possible to reduce the size of the solid-state imaging device.

As an embodiment of the present invention, FIG. 1 shows a schematic configuration diagram (plan view) of a solid-state imaging device.
In the present embodiment, the present invention is applied to a CCD solid-state imaging device.
In this solid-state image sensor, a vertical transfer register 2 is formed on one side of each column of the light-receiving sensor units 1 arranged in a matrix (matrix) to form an imaging region.
Each of the light receiving sensor units 1 constitutes a pixel. In the present embodiment, one light receiving sensor unit 1 is provided for each pixel.
Outside the imaging area, although not shown, a horizontal transfer register is provided by connecting to one end of the vertical transfer register 2, and an output unit is provided at one end of the horizontal transfer register.

Further, FIG. 2A shows a cross-sectional view of the vertical transfer register 2 part of the solid-state image pickup device in FIG. 1, and it is between the light-receiving sensor units 1 adjacent to each other in the vertical direction of the solid-state image pickup device in FIG. That is, FIG. 2B shows a cross-sectional view of the inter-pixel portion.
The vertical transfer register 2 includes a transfer channel region and a gate insulating film (not shown) formed in the semiconductor substrate 11 and a transfer electrode.

Although not shown, a light shielding film is formed to cover the transfer electrode. The light shielding film is configured to have an opening on the light receiving sensor unit 1 so that light enters the light receiving sensor unit 1.
Furthermore, although not shown, an insulating layer, a color filter, an on-chip lens, and the like that cover the light shielding film are provided above the light shielding film, if necessary.

  The solid-state imaging device of the present embodiment is particularly characterized by the configuration of the transfer electrode that constitutes the vertical transfer register 2.

The transfer electrode 3A to which the first-phase transfer pulse φV1 is applied and the transfer electrode 3C to which the third-phase transfer pulse φV3 is applied include an electrode portion extending along the vertical transfer register 2 as shown in FIG. And a wiring portion extending in a portion (inter-pixel portion) between the light receiving sensor portions 1 adjacent in the vertical direction (vertical direction in the drawing).
In addition, the transfer electrode 3A to which the first-phase transfer pulse φV1 is applied and the transfer electrode 3C to which the third-phase transfer pulse φV3 is applied are formed as shown in FIGS. 2A and 2B. It is formed by. The transfer electrode 3A and the transfer electrode 3C are formed in common with the pixels in the same row by the wiring portion.

The transfer electrode 3B to which the second-phase transfer pulse φV2 is applied and the transfer electrode 3D to which the fourth-phase transfer pulse φV4 is applied are formed independently for each vertical transfer register 2 as shown in FIG. Only the electrode portion along the vertical transfer register 2 is provided.
In addition, the transfer electrode 3B to which the second-phase transfer pulse φV2 is applied and the transfer electrode 3D to which the fourth-phase transfer pulse φV4 is applied are formed as shown in FIGS. 2A and 2B. It is formed by.
Further, the transfer electrode 3B to which the second-phase transfer pulse φV2 is applied and the transfer electrode 3D to which the fourth-phase transfer pulse φV4 is applied are connected via the contact layer 5 as shown in FIGS. The transfer electrode 4 formed by the second electrode layer is connected.
A transfer electrode (hereinafter referred to as a second layer transfer electrode) 4 composed of the second electrode layer extends along the vertical transfer register 2 and is connected to the contact layer 5 in the vertical direction (charge transfer). A wiring portion extending in a portion (inter-pixel portion) between the light receiving sensor portions 1 adjacent to each other in the direction).
The transfer electrode 3B and the transfer electrode 3D, which are independently formed for each vertical transfer register 2, are electrically connected to each other in the same row by the wiring portion of the transfer electrode 4, and each vertical transfer pulse φV2, φV4 is supplied.

Since the transfer electrodes 3A, 3B, 3C, 3D, and 4 are configured in this way, in the portion between the light receiving sensor portions 1 adjacent in the vertical direction, that is, between the pixels, as shown in FIG. The transfer electrodes 3A and 4 are laminated and formed via an interlayer insulating film.
Therefore, the width of the transfer electrode in the inter-pixel portion can be reduced as compared with the case where the transfer electrode is configured by a single electrode layer shown in FIG. 4B.

  For example, in a CCD solid-state imaging device having a pixel cell size of 2.0 μm, in a configuration in which the transfer electrode of the vertical transfer register is composed of a single electrode layer (single layer electrode structure), the width between pixels is about 0.7 μm. In contrast, the stacked structure of this embodiment can be formed with a width of about 0.3 μm, so 0.4 μm is applied to increase the size of the photodiode of the light receiving sensor portion. Can do. As a result, the size of the photodiode can be expanded from 1.0 μm × 1.3 μm of the single-layer electrode structure to 1.0 μm × 1.7 μm, so that the charge amount handled by the light receiving sensor unit is about 30. %, And sufficient sensitivity can be expected.

  On the other hand, the vertical transfer register 2 basically has a single-layer electrode structure composed of transfer electrodes (hereinafter referred to as first-layer transfer electrodes) 3A, 3B, 3C, and 3D composed of first-layer electrode layers. Since only the second-layer transfer electrode 4 is present in the vicinity of the contact portion 5, the degree to which incident light is blocked by the transfer electrode is significantly reduced as compared with the conventional two-layer electrode structure.

  As the material for the transfer electrodes 3A, 3B, 3C, and 3D of the first layer, various conductive materials such as polycrystalline silicon, silicide such as WSi, and metal such as W can be used.

  Various conductive materials can be used for the material of the transfer electrode 4 of the second layer. The transfer electrodes 3A, 3B, 3C, and 3D formed of the first electrode layer may be formed using the same material, but different materials may be used. In the configuration of this embodiment, unlike the case where the transfer electrode is configured by the conventional two-layer electrode layer, the second-layer transfer electrode 4 is not formed immediately above the gate insulating film. Restrictions on the material of the electrode 4 are reduced.

  In the vertical transfer register 2, different vertical transfer pulses φV1, φV2, φV3, and φV4 are applied to the transfer electrodes 3A, 3B, 3C, and 3D adjacent in the vertical direction. Thereby, vertical transfer of signal charges by four-phase driving is performed.

The contact layer 5 is formed by burying a conductive material in a contact hole formed through the interlayer insulating layer 13 between the first-layer transfer electrodes 3B and 3D and the second-layer transfer electrode 4. Yes.
Note that the contact layer 5 and the second-layer transfer electrode 4 may be formed of the same conductive material or may be formed of different conductive materials.

  According to the solid-state imaging device of the present embodiment described above, the transfer electrodes between the pixels are formed by the transfer electrodes 3A and 3C composed of the first electrode layer and the transfer electrode 4 composed of the second electrode layer. The stacked structure enables the width of the inter-pixel portion to be reduced as compared with the case where the transfer electrode is configured only by the first electrode layer (single-layer electrode structure).

Therefore, the vertical dimension of the light receiving sensor unit 1 can be set larger than that of the single-layer electrode structure, and a large area of the light receiving sensor unit can be secured.
As a result, a sufficient charge amount of the light receiving sensor unit 1 is ensured, so that a solid-state imaging device having sufficient sensitivity and dynamic range and good characteristics can be realized.

  Further, according to the solid-state imaging device of the present embodiment, the vertical transfer register 2 basically adopts a single-layer electrode structure composed of the first-layer transfer electrodes 3A, 3B, 3C, and 3D. Since there is only the second layer transfer electrode 4 in the vicinity of the contact portion by the contact layer 5, the degree to which incident light is blocked by the transfer electrode is significantly reduced as compared with the conventional two-layer electrode structure.

In the above-described embodiment, the vertical transfer pulses φV1, φV2, φV3, and φV4 are applied to the transfer electrode 3 of the vertical transfer register 2 to perform four-phase driving. Not only phase driving but also other driving can be supported.
Similarly to the above-described embodiment, the transfer electrode (first stage) composed of the first electrode layer connected to each row is formed independently for each vertical transfer register (for each pixel). The transfer electrodes (second stage) composed of the first electrode layer and the second electrode layer connected for each row are provided at a vertical pitch of one pixel, respectively. It is possible to correspond to each of two-phase driving, four-phase driving, eight-phase driving, and sixteen-phase driving.

  In the above-described embodiment, the present invention is applied to a CCD solid-state imaging device having a charge transfer section having a CCD structure. However, the present invention is also applied to a solid-state imaging element having a charge transfer section having another structure. Can be applied.

  The present invention is not limited to the above-described embodiment, and various other configurations can be taken without departing from the gist of the present invention.

1 is a schematic configuration diagram (plan view) of a solid-state imaging device according to an embodiment of the present invention. A is a cross-sectional view of a vertical transfer register portion of the solid-state imaging device of FIG. B is a cross-sectional view of an inter-pixel portion of the solid-state imaging device of FIG. It is a schematic block diagram (plan view) of a CCD solid-state imaging device having a two-layer transfer electrode. A is a cross-sectional view of a vertical transfer register portion of the CCD solid-state imaging device of FIG. B is a cross-sectional view of an inter-pixel portion of the CCD solid-state imaging device of FIG. It is a schematic block diagram (plan view) of a CCD solid-state imaging device having a transfer electrode having a single layer structure. FIG. 6A is a cross-sectional view of a vertical transfer register portion of the CCD solid-state image sensor of FIG. B is a cross-sectional view of an inter-pixel portion of the CCD solid-state imaging device of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Photosensitive sensor part, 2 Vertical transfer register, 3A, 3B, 3C, 3D 1st layer transfer electrode (consisting of an electrode layer) 4 Second layer transfer layer (consisting of an electrode layer) 5 Contact layer

Claims (6)

The light receiving sensor portions constituting the pixels are arranged in a matrix,
A charge transfer unit is provided on one side of each row of the light receiving sensor unit,
The transfer electrode of the charge transfer unit is a first transfer electrode formed of a first electrode layer, and a second transfer electrode formed by electrically connecting the first electrode layer and the second electrode layer. And
The electrode layer of the first layer and the electrode layer of the second layer are polycrystalline silicon,
The contact layer that contacts the electrode layer of the first layer and the electrode layer of the second layer of the second transfer electrode, and the electrode layer of the second layer are formed of the same conductive material,
The electrode layer of the first layer of the second transfer electrode is formed independently for each charge transfer unit,
Solid-state imaging characterized in that the first transfer electrode and the electrode layer of the second layer of the second transfer electrode are stacked in an inter-pixel portion adjacent in the direction of the charge transfer portion. element.   The first transfer electrode includes an electrode portion extending along the vertical transfer portion and a wiring portion extending between pixels between the light receiving sensor portions adjacent to each other in a direction in which the vertical transfer portion transfers charges vertically. The solid-state imaging device according to claim 1.   The electrode layer of the second layer of the second transfer electrode extends along the vertical transfer portion and is connected to the contact layer, and adjacent to the light transfer direction in which the vertical transfer portion transfers charges vertically. The solid-state imaging device according to claim 1, further comprising a wiring portion extending between the pixels of the sensor portion.   2. The solid-state imaging device according to claim 1, wherein the first electrode layer of the second transfer electrode is electrically connected to the same row by the second electrode layer. 3. . The light receiving sensor portions constituting the pixels are arranged in a matrix,
A charge transfer part is formed on one side of each row of the light receiving sensor part,
The transfer electrode of the charge transfer unit is a first transfer electrode formed of a first electrode layer, and a second transfer electrode formed by electrically connecting the first electrode layer and the second electrode layer. And
The electrode layer of the first layer of the second transfer electrode is formed independently for each charge transfer unit,
In the inter-pixel portion adjacent in the direction of the charge transfer unit, the solid-state imaging device driving method in which the first transfer electrode and the second electrode layer of the second transfer electrode are stacked. There,
The electrode layer of the first layer and the electrode layer of the second layer are polycrystalline silicon,
The contact layer that contacts the electrode layer of the first layer and the electrode layer of the second layer of the second transfer electrode, and the electrode layer of the second layer are formed of the same conductive material,
A first-phase transfer pulse is applied to one of the first transfer electrodes comprising the first electrode layer,
A third-phase transfer pulse is applied to the other of the first transfer electrodes formed of the first electrode layer. A method for driving a solid-state imaging device, comprising: A second-phase transfer pulse is applied to one of the first electrode layers of the second transfer electrode, and a fourth phase is applied to the other of the first electrode layers of the second transfer electrode. The solid-state imaging device driving method according to claim 5, wherein the transfer pulse is applied.

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