JP2009081169A - Solid-state image sensor - Google Patents

Abstract

A solid-state imaging device capable of securing a saturation charge amount of a white pixel while suppressing generation of dark current is provided.
The depths D1, D3, and D4 of the storage layers 19a, 19c, and 19e of the R pixel 12a, the B pixel 12c, and the W pixel 12e are the wavelength length of the light received by the storage layers 19a, 19c, and 19e and the amount of incident light. It is decided by. Since light of almost all wavelengths is incident on the storage layer 19e of the W pixel 12e, the amount of light incident on the storage layer 19e is larger than that of the other storage layers 19a and 19c. In addition, red (R) light has a longer wavelength than each blue (B) light. Therefore, D4>D1> D3. As a result, a sufficient saturation charge amount of the storage layer 19e can be secured, and a useless portion is removed from the storage layer 19c that receives each light of short wavelength blue (B), thereby reducing dark current and white scratches. Can be suppressed.
[Selection] Figure 3

Description

  The present invention relates to a solid-state imaging device, and more particularly to a solid-state imaging device including white pixels in addition to color pixels.

  In a solid-state imaging device such as a CCD, incident light is converted into electric charge by a photodiode, and the accumulated electric charge is converted into a voltage and taken out. On the other hand, by arranging white pixels (W pixels) in addition to general color pixels (R pixels, G pixels, B pixels), color information and luminance information are detected separately, and color dependence of luminance resolution A technique for eliminating the property has been proposed (see Patent Document 1).

A white pixel is a pixel having spectral characteristics correlated with luminance, in which a luminance filter such as a transparent filter having high light transmittance or a white filter is arranged instead of a color filter, and detects luminance information of a subject. In addition, this technology can achieve a high-sensitivity solid-state imaging device while avoiding the color dependency of the luminance resolution, and is used for pixel miniaturization as the number of pixels increases and the density increases in recent years. is there.
JP 2003-318375 A

  In the solid-state imaging device described in Patent Document 1, since light of almost all wavelengths is incident on the white pixel, the amount of light incident on the white pixel is greater than the amount of light incident on the color pixel. For this reason, when strong light hits the solid-state imaging device, the amount of charge generated in the white pixel exceeds the saturation charge amount, and accurate luminance information cannot be obtained. In addition, noise such as smear occurs due to the electric charge overflowing the white pixels.

  However, if the photodiodes of each pixel are formed uniformly deep in the vertical direction to ensure a sufficient amount of saturation charge, dark current noise occurs in the deep part where light does not reach for photodiodes that receive light with a short wavelength. However, the harmful effects such as the increase of so-called white scratches become conspicuous.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a solid-state imaging device that can secure a saturation charge amount of a white pixel while suppressing generation of dark current.

  The solid-state imaging device of the present invention includes a plurality of types of color pixels in which photodiodes that generate signal charges by photoelectrically converting incident light transmitted through any one of a plurality of types of color filters are formed in a semiconductor substrate, In a solid-state imaging device including a white pixel in which a photodiode that photoelectrically converts incident light to generate a signal charge without passing through a filter is formed in a semiconductor substrate, the photodiode of the white pixel from the surface of the semiconductor substrate The depth is made deeper than the depth from the semiconductor substrate surface of the photodiode of the color pixel.

  An additional overflow barrier layer is formed on the overflow barrier layer so that the distance between the overflow barrier layer provided on the back surface side of the semiconductor substrate and each of the photodiodes is almost the same.

  The color pixel includes a red pixel having a red filter for extracting red light, a green pixel having a green filter for extracting green light, and a blue pixel having a blue filter for extracting blue light. It is characterized by becoming.

  According to the solid-state imaging device of the present invention, the depth of the photodiode of the white pixel from the surface of the semiconductor substrate is made deeper than the depth of the photodiode of the color pixel from the surface of the semiconductor substrate. A saturation charge amount of white pixels can be secured.

  In addition, an additional overflow barrier layer is formed on the overflow barrier layer provided on the back side of the semiconductor substrate so that the distance between each photodiode and the overflow barrier layer is almost the same. The difference in height is suppressed, and variations in the overflow drain potential of each photodiode can be suppressed, thereby preventing adverse effects on the stored charge clearing operation by the overflow drain.

  In addition, the color pixel includes a red pixel having a red filter, a green pixel having a green filter, and a blue pixel having a blue filter, and excellent color reproducibility can be obtained.

  In FIG. 1 showing a solid-state imaging device of the present invention, a solid-state imaging device 10 is configured as an interline transfer type CCD image sensor, and on a semiconductor substrate 11, R pixels 12a, G pixels 12b having the same pixel size, B pixels 12c and W pixels (white pixels) 12e are arranged in a two-dimensional matrix (square lattice) along the row direction (X direction) and the column direction (Y direction) orthogonal thereto.

  The R pixel 12a, the G pixel 12b, and the B pixel 12c are pixels for detecting color information of a subject, and a color filter and a micro lens of a corresponding color are provided on the incident side of the light receiving element (photoelectric conversion element). The signal charges corresponding to the light amounts of the respective colors are generated from the incident light by photoelectric conversion and accumulated. The W pixel 12e is a pixel for detecting luminance information of a subject. A microlens is arranged on the incident side of the light receiving element without a color filter, and a signal charge corresponding to the luminance of incident light is photoelectrically converted. Generate and accumulate with

  As schematically shown in FIG. 2, the color pixels of the R pixel 12a, the G pixel 12b, and the B pixel 12c are arranged at checkered positions, respectively, and the W pixel 12e is arranged at the remaining checkered positions. ing. Specifically, with respect to the row direction and the column direction, lines alternately arranged with the W pixel 12e, the G pixel 12b, the W pixel 12e, and the G pixel 12b, and the B pixel 12c, the W pixel 12e, the R pixel 12a, and the W pixel 12e Each pixel is arranged so that lines repeatedly arranged in order appear alternately. Note that FIG. 2 shows only a range of 8 rows and 8 columns, but actually, a large number of pixels are repeatedly arranged in the row direction and the column direction.

  As shown in FIG. 1, a vertical CCD 13 is provided for each column of pixels in order to transfer signal charges accumulated in the pixels 12a to 12e. The vertical CCD 13 reads signal charges from the light receiving elements of the pixels 12a to 12e and transfers them in the column direction (vertical transfer). A horizontal CCD 14 is connected to the end of each vertical CCD 13 in common.

The horizontal CCD 14 receives the signal charges transferred from each vertical CCD 13 one by one and transfers them in the row direction (horizontal transfer). An output amplifier 15 is provided at the end of the horizontal CCD 14. The output amplifier 15 converts the signal charge transferred from the horizontal CCD 14 into a voltage signal (pixel signal) corresponding to the amount of charge and outputs the voltage signal. Note that in an image processing circuit (not shown) that receives the output from the output amplifier 15 and generates a color image, the pixel signals from the color pixels (R pixel 12a, G pixel 12b, and B pixel 12c) are used as color signals. The pixel signal from the W pixel 12e is used as the luminance signal.

In FIGS. 3 and 4 showing cross-sectional structures of the solid-state imaging device 10 taken along lines II and II-II in FIG. 1, a semiconductor substrate 11 is composed of an n-type silicon substrate 16, and this surface layer has a p-type. A p-type well layer 18 is formed via an overflow barrier layer 17 which is a layer. An n-type storage layer 19 for storing signal charges (electrons) generated by photoelectric conversion is formed in the p-type well layer 18, and a p for preventing dark current is formed on the storage layer 19. ^{A +} type high concentration layer 20 is formed. With this structure, a photoelectric conversion region is generated at the pn junction between the p-type well layer 18 and the storage layer 19, and the embedded photodiode PD that functions as the above-described light receiving element is formed.

  The depths D1, D2, D3, and D4 of the accumulation layers 19a, 19b, 19c, and 19e of the R pixel 12a, the G pixel 12b, the B pixel 12c, and the W pixel 12e are the light received by the accumulation layers 19a, 19b, 19c, and 19e. It is determined by the length of the wavelength and the amount of incident light. Note that the storage layers 19a, 19b, 19c, and 19e are simply referred to as the storage layer 19 when it is not necessary to distinguish between them.

  Since the long wavelength red (R) light reaches the deep part of the storage layer 19a constituting the photodiode PD of the R pixel 12a, the storage layer 19a is used to validate the charge generated in the deep part. It is desirable to form the depth D1 sufficiently deep.

  On the other hand, short-wavelength green (G) and blue (B) light does not reach as deep as red (R) light (or because the arrival rate is small), so Even if the depths D2 and D3 of the storage layers 19b and 19c are increased as in the photodiode PD that receives light, the sensitivity is not directly improved, but instead the surface area is increased unnecessarily and the dark current is increased. Therefore, it is preferable that D1> D2 and D1> D3. Similarly, it is preferable that D2> D3 from the relationship of wavelengths.

  Further, since light of almost all wavelengths is incident on the storage layer 19e constituting the photodiode PD of the W pixel 12e, not only light having a long wavelength is incident, but also the amount of incident light becomes very large. For this reason, it is desirable that the depth D4 of the storage layer 19e be formed deeper than the depth D1 of the storage layer 19a of the R pixel 12a.

  Therefore, the depths D1, D2, D3, and D4 of the storage layers 19a, 19b, 19c, and 19e are adjusted so that the relationship D4> D1> D2> D3 is established. The accumulation layers 19 having different depths can be formed, for example, by appropriately controlling acceleration energy at the time of ion implantation. The depth of the storage layer 19 can also be controlled by injecting counter ions into the deep portion of the storage layer 19.

  Additional overflow barrier layers 21a, 21b, and 21c are formed immediately below the storage layer 19a and the storage layers 19b and 19c that are shallower than the storage layer 19e. The additional overflow barrier layers 21 a to 21 c are integrated with the underlying overflow barrier layer 17.

  The depths D5, D6, and D7 of the additional overflow barrier layers 21a, 21b, and 21c are adjusted so that D5 <D6 <D7 corresponding to D4> D1> D2> D3. This suppresses variations in the distances CL1 to CL4 between the bottoms of the storage layers 19a, 19b, 19c, and 19e and the overflow barrier layer 17 and the additional overflow barrier layers 21a to 21c, thereby reducing variations in the overflow drain voltage. Can be suppressed. The additional overflow barrier layers 21a to 21c can be formed by adjusting the acceleration energy of ion implantation.

On the surface layer of the p-type well layer 18, an n-type charge transfer channel 22 is formed that extends in the column direction (direction perpendicular to the paper surface) and transfers charges. The charge transfer channel 22 is separated from the storage layer 19 via the p-type well layer 18 and the channel stop 23. The channel stop 23 is an element isolation layer (P ⁺ ) that is electrically isolated from the charge transfer channel 22 of the adjacent pixel.

  A gate insulating film 24 made of silicon oxide or the like is formed on the entire surface of the semiconductor substrate 11. A transfer electrode 25 is formed above the charge transfer channel 22 via the gate insulating film 24 to control reading of the signal charge from the storage layer 19 and vertical transfer in the charge transfer channel 22. The transfer electrode 25 is made of conductive silicon such as polysilicon. As described above, the charge transfer channel 22 and the transfer electrode 25 constitute the vertical CCD 13 described above.

  An interlayer insulating film 26 made of silicon oxide or the like is formed so as to cover the surfaces of the transfer electrode 25 and the gate insulating film 24. A light shielding film 27 made of tungsten or the like is formed above the transfer electrode 25 via the interlayer insulating film 26. In the light shielding film 27, an opening 27a is formed only above the storage layer 19 constituting the light receiving element PD. Light enters the light receiving element PD through the opening 27a.

  A planarization layer 28 is formed on the surfaces of the opening 27 a and the light shielding film 27. For example, BPSG (Boron Phosphorous Silicate Glass) is vapor-deposited, reflowed (heat treatment), coated with a transparent resin material and developed, and then planarized 28 is subjected to CMP (Chemical Mechanical Polishing). Is formed by planarizing the surface. In addition, the formation material and formation method of the planarization layer 28 are not restricted to this.

  In the formation region of the R pixel 12a, the G pixel 12b, and the B pixel 12c on the surface of the flattening layer 28, the R filter 29c that extracts red light and the G filter 29b that extracts green light, respectively, as the color filters described above. A B filter 29c for extracting blue light is formed. Each of the filters 29a to 29c is formed of a resin material containing a specific pigment and has substantially the same thickness. On the other hand, in the formation region of the W pixel 12e on the surface of the planarization layer 28, a transparent filter 29e that transmits light of almost all wavelengths is formed. A microlens 30 is formed on the color filters 29a to 29c and the transparent filter 29e.

  In the solid-state imaging device 10 configured as described above, the depth D4 of the storage layer 19e of the W pixel 12e is set to a depth that can secure a sufficient saturation charge amount. Even when strong light is applied, the amount of charge generated in the W pixel 12e does not exceed the saturation charge amount, and accurate luminance information can be obtained. Further, since the depths D1 to D3 of the storage layers 19a to 19c of the color pixels are set to such depths that there is no useless portion, dark current can be reduced and the occurrence of white scratches can be suppressed.

  In the embodiment described above, an example is shown in which pixels are arranged in a square lattice pattern along the XY direction. However, the present invention is not limited to this, and as shown in FIG. A pixel array (so-called honeycomb array) rotated by 45 ° with respect to the XY direction may be used.

  In the above embodiment, the color pixel is configured as a pixel that detects light of three primary colors of red (R), green (G), and blue (B), but the present invention is not limited to this, The color pixels may be configured as pixels that detect complementary color light of cyan (C), magenta (M), and yellow (Y).

  In the above embodiment, the depths D1 to D4 of the storage layers constituting the photodiodes PD of white pixels and color pixels satisfy the relationship of D4> D1> D2> D3, but the present invention is limited to this. For example, the relationship of D4> D1 = D2 = D3 may be satisfied.

  In the above embodiment, the solid-state imaging device is configured as an interline transfer type CCD image sensor. However, the present invention is not limited to this, and a frame transfer type CCD image sensor or a CMOS type image sensor. The present invention can be applied to all solid-state imaging devices of a single plate color imaging system such as

It is a schematic plan view which shows the structure of a solid-state image sensor. It is a schematic diagram which shows a square lattice-like pixel arrangement | sequence. It is a longitudinal cross-sectional view which follows the II line | wire of FIG. It is a longitudinal cross-sectional view which follows the II-II line | wire of FIG. It is a schematic diagram which shows a honeycomb arrangement | sequence.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Solid-state image sensor 11 Semiconductor substrate 12a R pixel 12b G pixel 12c B pixel 12e W pixel 17, 21a-21c Overflow barrier layer 19a, 19b, 19c, 19e Storage layer 29a R filter 29b G filter 29c B filter 29e Transparent filter CL1 CL4 Distance D1 to D7 Depth PD Photodiode (light receiving element)

Claims (3)

A photodiode that photoelectrically converts incident light that has passed through one of a plurality of types of color filters to generate signal charges, and a plurality of types of color pixels formed in a semiconductor substrate, and incident light that does not pass through the color filters. In a solid-state imaging device including a white pixel in which a photodiode that generates a signal charge by photoelectric conversion is formed in a semiconductor substrate,
A solid-state imaging device, wherein a depth of the photodiode of the white pixel from the surface of the semiconductor substrate is made deeper than a depth of the photodiode of the color pixel from the surface of the semiconductor substrate.   The additional overflow barrier layer is formed on the overflow barrier layer so that the distance between the overflow barrier layer provided on the back surface side of the semiconductor substrate and each of the photodiodes is almost the same. Item 10. A solid-state imaging device according to Item 1.   The color pixel includes a red pixel having a red filter for extracting red light, a green pixel having a green filter for extracting green light, and a blue pixel having a blue filter for extracting blue light. The solid-state imaging device according to claim 1, wherein:

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