JP4724469B2 - Solid-state image sensor - Google Patents

Description

  The present invention relates to a solid-state image sensor mounted on an image input device such as a digital camera or a scanner, and more particularly to a solid-state image sensor capable of accurately correcting a black level.

  When a subject image is reproduced from image data obtained by imaging a subject with a solid-state imaging device, an optical black region (optical black) provided in a peripheral region of the effective imaging area of the solid-state imaging device as described in Patent Document 1 below. Part: OB part) is used to correct the black level.

  FIG. 8 is a schematic diagram of the surface of the solid-state imaging device, and the peripheral region 101 of the effective imaging area 100 of the solid-state imaging device is an optical black portion. A large number of photoelectric conversion elements (photodiodes) are arranged in a matrix in the effective imaging area 100 and the optical black portion 101, and the photoelectric conversion elements in the optical black portion 101 are blocked by a light shielding film. Therefore, it has a structure that cannot receive incident light.

  FIG. 9 is an explanatory diagram showing the output level of the solid-state imaging device. A dummy pixel (not shown in FIG. 8) is provided on the outermost peripheral portion of the solid-state imaging device, an optical black portion 101 is provided on the inner side, and the inner side is an effective imaging area 100. A signal for dark current is output from the optical black unit 101, and this becomes a black level. From the effective imaging area 100, captured image data of the subject is output.

  FIG. 9A shows an ideal output level when the entire surface of the solid-state imaging device is shielded, and the black level output from the optical black unit 101 and the black level output from the effective imaging area 100 are one. I'm doing it. However, in practice, the level output from the optical black unit 101 fluctuates due to a temperature change or the like.

  For example, as shown in FIG. 9B, when the temperature becomes high or the exposure time becomes very long, the output level of the optical black portion 101 fluctuates and becomes larger than the black level output of the effective imaging area 100. The change in black output from the effective imaging area 100 is cut at the black level of the optical black portion 101, and so-called “black crushing” occurs.

  On the other hand, as shown in FIG. 9C, when the temperature is low or the exposure time is very short, the black level output from the effective imaging area becomes larger than the black level of the optical black portion 101. In other words, so-called “black float” occurs. However, since this black float can be dealt with by signal processing, it is not so much a problem.

Japanese Patent No. 2880635

  Since the conventional optical black portion has a structure in which a light shielding film is provided on the photoelectric conversion element, the state shown in FIG. If the black gradation change captured in the effective imaging area is cut off at the output level of the optical black portion and discarded, the black gradation change cannot be restored. For this reason, it is necessary to provide the solid-state image sensor with an optical black portion that does not attain the state of FIG. 9B but at least the state of FIG. 9C so that the black level can be corrected with high accuracy. is there.

  An object of the present invention is to provide a solid-state imaging device capable of accurately correcting a black level.

Solid-state imaging device of the invention, the optical black portion is provided on the periphery of the effective imaging area, in the solid-state imaging device for forming different types of the black level detection pixels of structure in the optical black portion, for the black level detecting One type of pixel has a structure in which a color filter is replaced with a layer that absorbs red light, green light, and blue light, and a microlens is deleted with respect to the pixel structure in the effective imaging area. .

The solid-state imaging device of the present invention is characterized in that the layer that absorbs the red light, the green light, and the blue light is configured by stacking a red filter, a green filter, and a blue filter .

The solid-state imaging device of the present invention is characterized in that another type of the black level detection pixel has a structure in which a light shielding film opening above the photoelectric conversion device is closed with respect to the pixel structure in the effective imaging area. To do.

In the solid-state imaging device of the present invention, another type of the black level detection pixel has a structure in which a photoelectric conversion element is deleted from the pixel structure in the effective imaging area .

In the solid-state imaging device of the present invention, another type of the black level detection pixel has a narrow vertical transfer path formed adjacent to the photoelectric conversion device with respect to the pixel structure in the effective imaging area . It is a structure .

  According to the present invention, since a plurality of types of pixels having different structures are provided in the optical black portion as the black level detection pixels, it is possible to select a black level detection pixel and perform black level correction with high accuracy. It becomes possible.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic plan view of an element formed in an effective imaging area and an optical black portion of a solid-state imaging device to which an embodiment of the present invention is applied. The illustrated example is an IT-CCD (interline transfer type charge coupled device), and only two pixels arranged in the vertical direction are illustrated, and a large number of such pixels are arranged in the horizontal and vertical directions. Each pixel has a substantially square shape, a photoelectric conversion element (photodiode) 1 is formed on the left half, and a vertical transfer path 2 is formed on the right half.

FIG. 2 is a schematic cross-sectional schematic view (corresponding to a cross section taken along line AA in FIG. 1) of the pixel 20 in the effective imaging area 100 (see FIG. 8). A P well layer 6 is formed on the surface portion of the n-type semiconductor substrate 5, an N ⁺ region 7 is formed on the surface portion of the P well layer 6, and a P ⁺ layer 8 is formed on the surface of the N ⁺ region 7. Thus, the photodiode 1 is formed.

  An N-type vertical transfer path 2 a is formed adjacent to the photodiode 1 (right side in FIG. 2), and a P-type signal charge read gate portion 9 is provided between the vertical transfer path 2 a and the photodiode 1. On the anti-vertical transfer path side (left side in FIG. 2) of the photodiode 1, a P-type channel stop 10 that separates the vertical transfer paths 2b of adjacent pixels is provided.

  Transfer electrode films 11a and 11b are stacked on the vertical transfer paths 2a and 2b, and a light shielding film 12 is further stacked thereon. The light shielding film 12 includes an opening 12a that opens above the photodiode 1, and allows the incident light to enter the photodiode 1 and prevents the vertical transfer paths 2a and 2b from entering. A color filter 13 is laminated on the light shielding film 12, and a microlens 14 is provided thereon.

  In such a pixel 20, light having the same color as that of the color filter 13 out of the incident light incident on the microlens 14 passes through the color filter 13 and enters the photodiode 1 through the opening 12 a of the light shielding film 12.

  The photodiode 1 generates and accumulates photocharges corresponding to the amount of incident light, and when a read pulse is applied to a read electrode (not shown), the charge accumulated in the photodiode 1 is used as a signal charge as a charge read gate unit 9. And read to the vertical transfer path 2.

  Thereafter, a transfer pulse is applied to the transfer electrode film 11a (φ1, φ2, φ3, φ4 in FIG. 1), so that signal charges are transferred along the vertical transfer path 2 (2a, 2b) to a horizontal transfer path (not shown). ), And then transferred along the horizontal transfer path and output from the solid-state imaging device.

  FIG. 3 is a schematic cross-sectional schematic view of a pixel provided in the optical black portion 101 (corresponding to a cross section taken along line AA in FIG. 1). Since the configuration of the pixel 30 is almost the same as the configuration of the pixel 20 shown in FIG. 2, the same members are denoted by the same reference numerals, description thereof is omitted, and only different portions will be described.

  In the optical black pixel 30 shown in FIG. 3, the light shielding film 12 also covers the upper side of the photodiode 1, and the opening 12 a as shown in FIG. 2 is not provided. As a result, the image data (signal charge) output from the optical black pixel 30 becomes image data indicating “black”, and this image data is transferred to the vertical transfer path and the horizontal transfer path from the solid-state imaging device. Output.

  FIG. 4 is a schematic cross-sectional schematic diagram (corresponding to a cross section taken along the line AA in FIG. 1) of another structure of a pixel provided in the optical black portion 101. Since the configuration of the pixel 40 is almost the same as the configuration of the pixel 20 shown in FIG. 2, the same reference numerals are given to the same members and the description thereof is omitted, and only different portions will be described.

  In the optical black pixel 40 shown in FIG. 4, an opening 12a is provided in the light shielding film 12, but a red (R) filter 13R, a green (G) filter 13G, and a blue (B) filter are used as color filters. 13B is laminated. In order to reduce the incident efficiency of incident light, no microlens is mounted.

  That is, in this pixel structure, all of the light incident on the filter is absorbed by the filters 13R, 13G, and 13B, and the light is not incident on the photodiode 1. As a result, the image data output from the optical black pixel 40 becomes image data indicating “black”, and this image data is transferred to the vertical transfer path and the horizontal transfer path to be output from the solid-state imaging device.

  The structure of the optical black pixel 30 shown in FIG. 3 is configured to block light with the light shielding film 12. The light shielding film 12 is usually composed of a metal film (for example, a tungsten film). When light enters the metal film, the dark current generated in the photodiode 1 varies, which is a factor that varies the “black” level. It is considered to be. Therefore, in the structure of the optical black pixel 40 shown in FIG. 4, the incident light is absorbed by the color filters 13 </ b> R, 13 </ b> G, and 13 </ b> B above the opening 12 a of the light shielding film 12.

  In FIG. 4, three layers of color filters are laminated. However, a structure in which one layer of black color filter is provided may be used, or a structure in which the opening 12a is not provided in the light shielding film 12 may be used. good.

  FIG. 5 is a schematic cross-sectional schematic diagram (corresponding to a cross section taken along the line AA in FIG. 1) of still another structure of a pixel provided in the optical black portion 101. Since the configuration of the pixel 50 is almost the same as the configuration of the pixel 30 shown in FIG. 3, the same members are denoted by the same reference numerals, description thereof is omitted, and only different portions will be described.

  The optical black pixel 50 shown in FIG. 5 employs a configuration in which incident light is blocked by the light shielding film 12 without providing the opening 12a in the light shielding film 12, as in FIG. The structure is such that the photodiode that is the factor is eliminated (not formed).

  FIG. 6 is a schematic sectional schematic view (corresponding to a section taken along line AA in FIG. 1) of still another structure of the pixel provided in the optical black portion 101. FIG. Since the configuration of the pixel 60 is almost the same as the configuration of the pixel 30 shown in FIG. 3, the same members are denoted by the same reference numerals, description thereof is omitted, and only different portions will be described.

  In the optical black pixel 60 shown in FIG. 6, the width of the channel stop 10 is widened, and the widths of the vertical transfer paths 2a and 2b are narrowed. A dark current is generated in both the photodiode 1 and the vertical transfer path 2, but the dark current generated in the vertical transfer path 2 is predominantly larger, so the vertical transfer path 2 is formed narrow.

  The four types of optical black pixels 30 (FIG. 3), 40 (FIG. 4), 50 (FIG. 5), and 60 (FIG. 6) having different structures have been described above. With a conventional solid-state imaging device, FIG. Only the pixel 30 having the structure was formed in the optical black portion 101. However, the solid-state imaging device according to the present embodiment is characterized in that at least two of the four types of pixels 30, 40, 50, and 60 are provided in the optical black region 101.

  For example, the pixel 30 shown in FIG. 3 is provided in the left optical black portion 101L in FIG. 8, and the pixel 40 shown in FIG. 4 is provided in the right optical black portion 101R in FIG. Alternatively, the pixel 30 shown in FIG. 3 and the pixel 40 shown in FIG. 4 may be provided in the right optical black portion 101R in which about 30 pixels are arranged. Alternatively, two types of optical black pixels may be provided on the upper side and the lower side of the optical black portion.

  Then, the optical black pixel that corrects the black level of the image data output from the pixel in the effective imaging area 100 (FIG. 2) is switched between the normal imaging and the imaging under the condition that the dark current increases.

  That is, during normal shooting, the black level of the image data output from the effective imaging area 100 is corrected with the output level of the optical black pixel shown in FIG. 3 as the black level, and when the temperature becomes higher than the predetermined temperature, When the dark current increases, such as when the shooting mode is higher than the sensitivity or when the exposure time is longer than the predetermined time, the effective imaging area is set with the output level of the optical black pixel shown in FIG. 4 as the black level. The black level of the image data output from 100 is corrected.

  FIG. 7 is an explanatory diagram of the black level output from the solid-state imaging device according to the present embodiment. Even when the black level a output from the optical black pixel 30 increases due to an increase in dark current due to an increase in temperature or the like and becomes larger than the black level b of the effective imaging area 100, the optical black pixel having a different structure Since the black level c output from 40 is a level c different from the black level a, there is a high possibility that the black level can be corrected by the state shown in FIG.

  Although four types of optical black pixels having different structures have been described above, it is impossible to predict which pixels 30, 40, 50, and 60 have the smallest dark current under various shooting conditions. For this reason, in this embodiment, a plurality of types of optical black pixels having different structures are provided.

  In the above-described embodiment, two types of optical black pixels are provided. However, three, four, or more types of optical black pixels are provided in the optical black unit 101, and the output black level is the same. It is also possible to adopt a configuration that employs the lowest optical black pixel and uses it for black level correction.

  The embodiment described above is a CCD solid-state imaging device, but the above-described embodiment can also be applied to a CMOS solid-state imaging device except for a pixel structure (FIG. 6) that changes the vertical transfer path width.

  According to the present invention, since a plurality of types of optical black pixels are provided, it is possible to perform high-precision black level correction of captured image data by selecting optical black pixels to be used for black level correction. It is useful as a solid-state imaging device mounted on an image input device such as a scanner.

It is a plane schematic diagram of the pixel which comprises the solid-state image sensor which concerns on one Embodiment of this invention. It is a cross-sectional schematic diagram of the pixel in an effective imaging area among the solid-state image sensors shown in FIG. It is a cross-sectional schematic diagram of the pixel provided in an optical black part among the solid-state image sensors shown in FIG. It is a cross-sectional schematic diagram of the pixel of another structure provided in an optical black part among the solid-state image sensors shown in FIG. It is a cross-sectional schematic diagram of the pixel of another structure provided in an optical black part among the solid-state image sensors shown in FIG. It is a cross-sectional schematic diagram of the pixel of another structure provided in an optical black part among the solid-state image sensors shown in FIG. It is a schematic diagram which shows the output level of the signal output from the optical black part and effective imaging area of the solid-state image sensor which concerns on one Embodiment of this invention. It is a surface schematic diagram of a solid-state image sensor. It is a schematic diagram which shows the output level of the signal output from the optical black part and effective imaging area of the conventional solid-state image sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photodiode 2, 2a, 2b Vertical transfer path 12 Light-shielding film 12a Opening part 13 Color filter 13R Red filter 13G Green filter 13B Blue filter 14 Micro lens 20 Pixel 30, 40, 50, 60 in effective imaging area For black level detection Pixel

Claims (5)

The optical black portion is provided on the periphery of the effective imaging area, in the solid-state imaging device for forming different types of the black level detection pixels of structure in the optical black portion, one of the black level detection pixels, the effective A solid-state imaging device having a structure in which a color filter is replaced with a layer that absorbs red light, green light, and blue light, and a microlens is removed from a pixel structure in an imaging area . The solid-state imaging device according to claim 1, wherein the layer that absorbs the red light, the green light, and the blue light is configured by stacking a red filter, a green filter, and a blue filter . Another one of the black level detection pixels, claim 1 or claim 2, wherein the relative pixel structure of the effective imaging area is closed structure in which a light shielding film opening of the photoelectric conversion elements above The solid-state image sensor described in 1. Another one of the black level detection pixels, to any one of claims 1 to 3, wherein the relative pixel structure of the effective imaging area is a structure in which remove the photoelectric conversion element The solid-state imaging device described. Another type of the black level detection pixel is a structure in which a vertical transfer path formed adjacent to a photoelectric conversion element is narrower than a pixel structure in the effective imaging area. The solid-state image sensor of any one of Claim 1 thru | or 4 .

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