JP2008047608A - Single-plate solid-state image sensing element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve spectral characteristics, particularly, of blue (B) and green (G) in a single-plate solid-state image sensing element while a spectral detecting system is employed utilizing difference in absorption coefficient within a wafer of each wavelength of light. <P>SOLUTION: A color filter is provided only on a green (G) pixel 44b, and color filters of red (R) and blue (B) are eliminated. A part where the color filter is eliminated is formed by embedding a flat film. In the pixels 44a for red (R)/blue (B), incident lights of respective colors are detected through separation with the spectral detecting system utilizing difference of absorption characteristic of the light of each color in a semiconductor substrate. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a single-plate solid-state image sensor that receives red (R), green (G), and blue (B) optical images with a single solid-state image sensor.

A single-plate color solid-state imaging device receives R, G, and B color optical images with a single solid-state imaging device without using a color separation prism.
As a configuration of a single-plate solid-state imaging device, one that uses a color filter for color separation (see Patent Document 1) and a photoelectric conversion characteristic of a photoelectric conversion device without using a color filter is the wavelength of incident light. In addition, by using the property that depends on the position of the semiconductor substrate in the depth direction (that is, the characteristic that the light absorption rate in the wafer varies depending on the wavelength of light), each color is detected separately. (See Patent Document 2). In the latter case, three high-concentration impurity layers separated in the depth direction are provided in the semiconductor substrate.

FIG. 10 illustrates red (R), green (G), and solid (G) in a solid-state imaging device that employs a method in which light of each color is separated and detected using characteristics in which the absorptance of light of each color in the wafer is different. It is a figure which shows an example of the spectral characteristic of blue (B). In FIG. 10, the horizontal axis represents wavelength (nm) and the vertical axis represents sensitivity. As can be seen from FIG. 10, each color of red (R), green (G), and blue (B) can be detected separately without using a color filter. Since they overlap, the separation of each color is not always sufficient.
JP 2002-135792 A Japanese Patent Laid-Open No. 1-134966

In the solid-state imaging device having the above-described three-color filter, the light passing through each color filter is approximately 1/3 of the incident light, so it cannot be denied that the efficiency of photoelectric conversion is deteriorated.
Further, in a solid-state imaging device having a configuration in which no color filter is provided (a configuration in which the absorption rate of light of each color in the wafer is different), when attempting to obtain a higher level of spectral sensitivity of each color, blue ( B) and green (G) may be insufficiently separated (spectral). In other words, in the method that does not use the color filter, the spectral sensitivity is obtained by utilizing the fact that the absorptance in the wafer is different depending on the wavelength of light, but the absorption characteristics are blue (B) and green. (G) is not so different. That is, when the distance at which the light intensity in the silicon single crystal is halved is compared for each color, blue (B: wavelength 460 nm) is 0.32 μm, green (G: wavelength 530 nm) is 0.79 μm, red (R: wavelength 700 nm) is 3.0 μm, and red (R) has a great difference in characteristics from the other two colors, but blue (B) and green (G) are not so different. I understand that. Therefore, in the case of a spectroscopic detection method using the difference in light absorption rate in the wafer depending on the wavelength of light, there is a limit to the spectrum of blue (B) and green (G). It cannot be denied that color mixing occurs.

  The present invention has been made on the basis of such considerations, and an object of the present invention is to adopt a spectroscopic detection method using a difference in light absorption rate in a wafer for each wavelength of light in a solid-state imaging device. The spectral characteristics of blue (B) and green (G) are improved.

The above object of the present invention is achieved by the following configurations.
(1) A single-plate solid-state image sensor that receives optical images of red (R), green (G), and blue (B) with a single solid-state image sensor, and the green light receiving unit for detecting green (G) Only the color filter for (G) is provided, and the red (R) and blue (B) detection light-receiving portions are provided within the semiconductor substrate without providing the color filter. A single-plate solid-state imaging device, wherein the solid-state imaging device is detected by a spectroscopic detection method using a difference in the absorption rate of light of each color.

  This single-plate solid-state imaging device uses a color filter only for green (G) in order to improve the spectral sensitivity of green (G) and blue (B). The reason why the color filter is used for green (G) is that when the wavelengths of the three colors of light are compared, green (G) is located in the middle of the three colors. That is, the wavelengths increase in the order of blue (B: wavelength 460 nm), green (G: wavelength 530 nm), and red (R: wavelength 700 nm), but green (G) can be accurately detected using a color filter. If possible, what remains is red (R) and blue (B), and the wavelengths of red (R) and blue (B) are greatly different, so that they can be separated and detected with high accuracy by spectroscopic detection. Therefore, the spectral sensitivity of green (G) and blue (B) is improved and color mixing is reduced as compared with a single-plate type solid-state imaging device having no configuration of a conventional color filter. Further, compared to a configuration using three color filters, incident light can be effectively used for red (R) and blue (B) because there is no color filter, and thus sensitivity is improved. In addition, if the portion where the color filter is omitted is embedded with, for example, a flattening film, no problem occurs. In addition, since the total amount of color resist can be reduced, an effect of reducing material costs can be obtained.

(2) The single-plate solid-state imaging device according to (1), wherein a high concentration impurity layer for red (R), a high concentration impurity layer for green (G), and a blue (G B) high-concentration impurity layers are provided, and the high-concentration impurity layers for red (R) and blue (B) are formed at the same detection position and at different depth positions of the semiconductor substrate. The high concentration impurity layer for green (G) is formed at a detection position different from the high concentration impurity layer for red (R) and blue (B), and the high concentration impurity layer for green (G) A single-plate solid-state imaging device, wherein the green (G) color filter is disposed above.

  This single-plate solid-state imaging device has one pixel in charge of green (G) and one pixel in charge of two colors of red (R) and blue (B) (described as R / B pixels) on a semiconductor substrate. In addition, a green (G) color filter is provided above the green (G) pixel. On the other hand, in the R / B pixel, for each color at a different depth of the semiconductor substrate. A high concentration layer for photoelectric conversion is provided. According to this configuration, pixels for color imaging can be arranged more compactly.

(3) The single-plate solid-state imaging device according to (2), wherein the high concentration impurity layer for blue (B) is formed on a surface portion of the semiconductor substrate, and the high concentration impurity layer for red (R) Is formed in a deeper layer than the blue (B) high-concentration impurity layer.

  In this single-plate solid-state imaging device, signal charges due to blue (B) having a short wavelength are generated on the surface of the semiconductor substrate. Therefore, in the R / B pixel, the high concentration layer for blue (B) is formed on the surface of the semiconductor substrate. The high concentration layer for long wavelength red (R) is provided in a deeper layer.

(4) The single-plate solid-state imaging device according to any one of (1) to (3), wherein a portion where the color filters for red (R) and blue (B) are omitted is embedded with a planarizing film. A single-plate solid-state image pickup device.

  In this single-plate solid-state imaging device, it is clear that the portion where the color filter is omitted is embedded with a planarizing film. This ensures the flatness of the device and does not cause any problems. In addition, the manufacturing process is not particularly complicated. Further, since the color filters for red (R) and blue (B) are omitted, the total amount of color color resists can be reduced. This contributes to cost reduction.

  According to the present invention, by adopting a configuration using a color filter only for green (G), green (G) and blue are compared with a single-plate solid-state imaging device having no conventional color filter. The spectral sensitivity of (B) is improved and color mixing is reduced. Compared to a configuration using three color filters, incident light can be effectively used for red (R) and blue (B) because there is no color filter, and thus sensitivity is improved. Then, if the portion where the color filter is omitted is embedded with, for example, a planarizing film, no problem occurs. Further, since the total amount of color resist can be reduced, the effect of reducing material costs can be obtained. Further, by adopting a pixel configuration in which R / B is one pixel, pixels for color imaging can be arranged more compactly.

Next, preferred embodiments of the single-plate solid-state imaging device of the present invention will be described in detail with reference to the drawings.
(First embodiment)

FIG. 1 is a diagram showing a layout configuration of a solid-state imaging device (CCD) of the present invention.
In FIG. 1, a CCD 36 includes a large number of pixels (light receiving portions) 44 (R / B pixels 44a and G pixels 44b) formed on the surface portion of a semiconductor substrate 43, a vertical transfer path 45, and a horizontal transfer path (HCCD). 46 and an output amplifier (AMP).
The pixels 44 (44 a and 44 b) are arranged in a square lattice pattern on the surface of the semiconductor substrate 43. The vertical transfer path 45 is arranged on the right side of each column of the pixels 44 (44a, 44b). The horizontal transfer path (HCCD) 46 transfers the signal charges read from each pixel 44 and transferred through the vertical transfer path 45 in the horizontal direction.

  In FIG. 1, “R / B” is written in the pixel 44 a, which is a spectrum in which each pixel 44 of the CCD 36 separately detects red (R) and blue (B) without a color filter. It shows that a detection function is provided (this point will be described later with reference to FIG. 4).

FIG. 2 is a diagram for explaining a layout configuration of pixels and transfer electrodes in the solid-state imaging device of FIG.
The transfer electrodes 47, 48, and 49 of this embodiment have a three-layer polysilicon structure, and constitute an interline CCD that can read all pixels. In the illustrated example, the third polysilicon electrode 49 also serves as a read gate electrode that reads green (G) and blue (B) signal charges, and the second polysilicon electrode 48 reads red (R) signal charges. It is a gate electrode. In FIG. 2, φ1, φ2, and φ3 indicate three-phase clocks.

FIG. 3 is a cross-sectional view of a green (G) pixel taken along line AA in FIG.
As shown in the figure, a P-type impurity layer 50 is formed on an n-type semiconductor substrate 43, and a signal charge storage layer (N ⁺ layer) 58 is formed on the surface portion of the P-type impurity layer 50. . The accumulation layer 58 extends at the end thereof to below the readout gate electrode formed of a part of the transfer electrode 49, and accumulates signal charges generated by the incident light of green (G). The impurity concentration of the N ⁺ layer 58 is about 5 × 10 ^{16 to 17} / cm ³ , and the depth is, for example, about 0.5 to 1.5 μm.

  A silicon oxide film 54 is formed on the surface of the semiconductor substrate, and readout electrodes 48 and 49 are formed on the silicon oxide film 54. A light shielding film 55 is provided so that light does not enter the charge transfer portion 45.

A first planarizing film 56a is provided on the light shielding film 55, and a color filter 8 for green (G) is provided on the planarizing film 56a at a position corresponding to the N ⁺ layer 58. Yes. A second planarization film 56b is further formed thereon, and a microlens 57 is formed on the planarization film 56b.

  4 is a cross-sectional view of a red (R) / blue (B) pixel along the line BB in FIG. In the CCD 36 according to this embodiment, the color signal components of red (R) and blue (B) are separated by utilizing the difference in the light absorption rate of each color in the silicon substrate (the optical properties of the silicon substrate). Unlike FIG. 3, no color filter is provided.

  That is, in this configuration, the light absorption coefficient of the silicon substrate is different in the visible range from red (R), which is long wavelength light, to blue (B), which is short wavelength light. Is absorbed in the shallow region of the silicon substrate and hardly reaches the deep portion of the silicon substrate, but conversely, light in the wavelength region with a small light absorption coefficient reaches the deep region of the silicon substrate, so photoelectric conversion is also performed in the deep portion of the silicon substrate. It makes use of the property that becomes possible.

In FIG. 4, a p-type impurity layer 50 is formed on the surface side of an n-type semiconductor substrate 43. This is shallow part of the P-type impurity layer 50, N ⁺ layer 51 is formed, N ⁺ layer 52 is formed in the deep portion. That is, the high concentration layer is provided at a position in a different depth direction in the semiconductor substrate, and the N ⁺ layer 51 provided in the shallow portion is a high concentration impurity region for blue (B) having a short wavelength. The N ⁺ layer 52 provided in a deep portion is a high concentration region for red (R) having a long wavelength.

The signal charges generated by the blue (B) incident light are accumulated in the N ⁺ layer 51 provided at the shallowest position in the thickness direction of the semiconductor substrate 43. The concentration of the N ⁺ layer 51 (impurity (phosphorus or arsenic (P or As))) forming this signal charge storage portion is about 5 × 10 ^{16 to 17} / cm ³ , and the depth is 0.2 to 0.5 μm: The depth also depends on the impurity concentration (the same applies to the following), so that only the charges generated by the incident light of blue (B) pass through the gate portion and the vertical transfer path 45. Is read out.

The N ⁺ layer 52 formed in the deep part has an N ⁺ region (charge path) 52a that rises to the surface of the semiconductor substrate 43 at the end, and this N ⁺ region 52a is a read gate electrode formed of a part of the transfer electrode. 48 is extended to below. The N ⁺ layer 52 accumulates signal charges generated by red (R) incident light. The N ⁺ layer 52 (impurity concentration is about 5 × 10 ^{16 to 17} / cm ³ , depth 1.0 μm to 2.5 μm) that forms this signal charge accumulating portion extends below the read gate electrode 48, The charges generated by the red (R) incident light are read out to the vertical transfer path 45 through the gate portion.

It is preferable to give a concentration gradient to the storage portion (N ⁺ layer) 52 so that the impurity concentration of the charge passage 52a is high. This facilitates reading of the signal charge from the accumulation unit 52 located in the deep part, and prevents the remaining charge from being read.

A shallow P ⁺ layer 53 is provided on a part of the surface of the semiconductor substrate 43 provided with two kinds of accumulation portions 51 and 52 having different depths, and an SiO ₂ film 54 is provided on the outermost surface. It has been. The impurity (boron) concentration of the P ⁺ layer 53 is about 1 × 10 ¹⁸ / cm ³ and the depth is about 0.1 to 0.2 μm, which reduces the defect level at the oxide film-semiconductor interface on the surface of the pixel. Has contributed. Therefore, the storage part 51 located at the shallowest position in the depth direction of the semiconductor substrate 43 has a P ⁺ N ⁺ P structure. The boron concentration in the P region between the N ⁺ layers 51 and 52 is set to, for example, 1 × 10 ^{14 to 16} / cm ³ , and this P region becomes a potential barrier between the storage unit 51 and the storage unit 52. Thus, charge mixing between the storage unit 51 and the storage unit 52 is prevented, and the probability of color mixing is reduced.

^On the upper surface of the SiO ² film 54, the aforementioned read electrodes (transfer electrodes) 48 and 49 are formed at positions avoiding the light receiving region, and further, a light shielding film 55 having an opening 55a in the light receiving region is provided thereon. Further, a planarizing film 56 (56a, 56b) is formed on the upper portion, and a top lens (microlens) 57 is further formed on the upper portion.

Here, FIG. 5 shows a block diagram of a digital camera (in this example, a digital still camera) according to an embodiment of the present invention.
The digital camera includes a solid-state imaging device (CCD) 36 of the present invention, an analog signal processing circuit 100, an A / D converter 102, a signal processing circuit (signal compression / expansion circuit) 104, a display device 106, The memory 108, various recording media 110, a system microcomputer 112, and a system bus (BUS) are included.

  Since the digital camera of FIG. 5 is equipped with a small solid-state imaging device (CCD) 36 having high spectral sensitivity, high-definition imaging with reduced color mixing is possible.

(Second Embodiment)
In the above-described embodiment, a CCD in which each pixel is arranged in a square lattice has been described as an example. However, for example, in a CCD having a so-called honeycomb pixel arrangement in which each pixel of the CCD is shifted by ½ pitch for each row. The present invention can be realized.

  FIG. 6 is a diagram showing a layout configuration of the solid-state imaging device 60 adopting the honeycomb pixel arrangement. In FIG. 6, the same reference numerals are given to the parts common to FIG. 1.

  Similarly to the first embodiment, the red (R) / blue (B) pixel 44a detects each color signal of red (R) and blue (B) with the same pixel without a color filter. The green (G) pixel 44b detects green (R) incident light that has passed through the color filter. The pixels 44a and 44b are shifted by ½ pitch for each row, and vertical transfer paths meander between the pixels adjacent in the horizontal direction (not shown in FIG. 6).

  FIG. 7 is a diagram illustrating a layout configuration of a pixel portion in the solid-state imaging device of FIG. Each pixel 71 is formed in a rhombus shape by the element isolation band 73, and signal charges are read out from a gate portion 74 provided by cutting out a part of the element isolation band 73 to a vertical transfer path provided between the pixels. On the vertical transfer path, transfer electrodes having a two-layer polysilicon structure are provided so as to overlap each other, and four transfer electrodes 81, 82, 83, 84 are associated with one pixel. As a result, the CCD with the honeycomb pixel arrangement is a CCD that can read out all pixels (progressive operation) with a transfer electrode having a two-layer polysilicon structure.

(Other embodiments)
FIGS. 8A and 8B are diagrams showing a variation (variation) of the arrangement of the green (G) color filter and the arrangement of the pixels of each color.
In FIG. 8 as well, as in the above-described embodiment, only the color filter for green (G) is provided, and red (R) and blue (B) light is absorbed at different positions in R and B, respectively. It is detected by the spectroscopic detection method using the difference in rate.

FIGS. 9A to 9C are cross-sectional views showing pixel structures corresponding to the respective colors (B, R, and G) in the CCD shown in FIGS. 8A and 8B.
As shown in FIG. 9A, a high impurity concentration layer (n ⁺ layer) 96 is provided on the surface of the P-type impurity 95 at the pixel position responsible for blue (B). As shown in FIG. 9B, a high impurity concentration layer (n ⁺ layer) 97 is provided at a deep position of the P-type impurity 95 at the pixel position responsible for red (R). As shown in FIG. 9C, a color filter 8 for green (G) is provided above the pixel position responsible for green (G), and the surface of the P-type impurity 95 is A high impurity concentration layer (n ⁺ layer) 99 is provided.

  The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the technical idea of the present invention. In the above-described embodiment, the example in which the CCD is used as the solid-state imaging device has been described. However, a CMOS image sensor can also be used.

  As described above, according to the present invention, by adopting a configuration that uses a color filter only for green (G), compared to a single-plate solid-state imaging device that does not use a conventional color filter at all, Spectral sensitivity of blue (B) and green (G) is improved, color mixing can be reduced, and since the color filter can be omitted, incident light can be used effectively and the total amount of color resist can be reduced. The effect of reduction can also be obtained. Further, by adopting a pixel configuration in which R / B is one pixel, the pixels can be arranged more compactly.

  The present invention has the effects of improving the spectral sensitivity of the solid-state imaging device, effectively using incident light, and reducing the material cost, and is therefore useful as a single-plate solid-state imaging device.

1 is a block configuration diagram of a digital camera (a digital still camera in this example) according to an embodiment of the present invention. FIG. 2 is a diagram for explaining a layout configuration of pixels and transfer electrodes in the solid-state imaging device of FIG. 1. FIG. 3 is a cross-sectional view of a green (G) pixel along the line AA in FIG. 2. It is sectional drawing of a red (R) / blue (B) pixel which follows the BB line of FIG. 1 is a block configuration diagram of a digital camera (a digital still camera in this example) according to an embodiment of the present invention. It is a figure which shows the layout structure of the solid-state image sensor which employ | adopted honeycomb pixel arrangement | positioning. It is a figure which shows the layout structure of the pixel part in the solid-state image sensor of FIG. (A), (b) is a figure which shows the modification (variation) of arrangement | positioning of the color filter for green (G), and arrangement | positioning of the pixel of each color. (A)-(c) is sectional drawing which shows the structure of the pixel corresponding to each color (B, R, G) in CCD shown by Fig.8 (a), (b). Red (R), green (G), and blue (B) in a solid-state imaging device that employs a method of separating and detecting light of each color by utilizing the characteristic that light absorptance of each color in the wafer is different. It is a figure which shows an example of the spectral characteristic of this.

Explanation of symbols

8 Green (G) color filter 36 Solid-state imaging device 40 N-type semiconductor substrate 44 (44a, 44b) Pixel 45 Vertical transfer path 46 Horizontal transfer path 48 Read electrode (transfer electrode)
50 P-type impurity layer 51, 52, 58 High-concentration impurity layer 54 Silicon oxide film (insulating film)
55 Light-shielding film 56 (56a, 56b) Flattening film 57 Micro lens 60 CCD
AMP output amplifier

Claims (4)

A single-plate solid-state imaging device that receives optical images of red (R), green (G), and blue (B) with a single solid-state imaging device,
Only the green (G) color filter is provided in the light receiving part for detecting green (G), and the red (R), blue (B) detecting light receiving part is provided without a color filter. A single-plate solid-state imaging device, wherein blue (B) light is detected by a spectroscopic detection method using a difference in light absorptance of each color in a semiconductor substrate. The single-plate solid-state imaging device according to claim 1,
A high concentration impurity layer for red (R), a high concentration impurity layer for green (G), and a high concentration impurity layer for blue (B) are provided in the same semiconductor substrate,
The high concentration impurity layers for red (R) and blue (B) are formed at the same detection position and at different depth positions of the semiconductor substrate,
The high concentration impurity layer for green (G) is formed at a detection position different from the high concentration impurity layer for red (R) and blue (B), and the high concentration impurity for green (G) A single-plate solid-state imaging device, wherein the green (G) color filter is disposed above the layer. The single-plate solid-state imaging device according to claim 2,
The high concentration impurity layer for blue (B) is formed on the surface portion of the semiconductor substrate, and the high concentration impurity layer for red (R) is formed deeper than the high concentration impurity layer for blue (B). A single-plate solid-state imaging device. A single-plate solid-state imaging device according to any one of claims 1 to 3,
A single plate type solid-state image pickup device, wherein a portion where the color filters for red (R) and blue (B) are omitted is embedded with a planarizing film.

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