JP2007214351A - Ccd-type solid-state imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the smear caused by the asymmetry of the impurity concentration profile in a CCD-type solid-state imaging device. <P>SOLUTION: This CCD-type solid-state imaging device 20 comprises photoelectric conversion elements 23 formed and arranged in a two-dimensional array form on the surface of a semiconductor substrate 21, a first charge transfer path buried channel 24b formed in one side of the photoelectric conversion element 23 via a readout gate 25, a second charge transfer path buried channel 24a formed in the other side of the photoelectric conversion element 23 via a channel stop 26, and a light-shielding film 36 covering the surface of the semiconductor substrate 21 and formed with an opening 36a directly above the photoelectric conversion elements 23. The opening 36a of the light-shielding film 36 is formed deviated from the second charge transfer path buried channel 24a toward the side of the first charge transfer path buried channel 24b. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a CCD (Charge Coupled Devices) type solid-state imaging device, and more particularly to a CCD type solid-state imaging device with improved smear characteristics.

  FIG. 5 is a schematic cross-sectional view of approximately two pixels of a conventional CCD solid-state imaging device. In the conventional CCD type solid-state imaging device, a pn junction (photodiode) is formed with the p well layer 3 by forming the n region 2 on the surface portion of the semiconductor substrate 1. By forming the high-concentration p-type impurity region 4, a channel stop (element isolation region) is formed, and a vertical transfer path (VCCD) is formed on the other side of the n region 2 via the read gate portion 5 of the p region. A buried channel (n region) 6 is formed.

  A light shielding film 8 is laminated on the surface of the semiconductor substrate 1 via an insulating layer 7, and an opening 8 a of the light shielding film 8 is provided immediately above the n region 2. A transfer electrode film 9 constituting a vertical transfer path is laminated immediately above the buried channel 6 below the light shielding film 8.

  The conventional CCD type solid-state imaging device has a distance W1 from the adjacent pixel side opening end to the far end of the adjacent pixel side channel stop 4 among the light shielding film opening ends of the photodiodes constituting one pixel, and the light shielding film opening end. The distance W2 from the open end on the opposite adjacent pixel side to the far end of the readout gate 5 (the near end of the buried channel 6 that reads the signal charge of its own pixel) is the same distance (W1 = W2). Thus, an opening 8a of the light shielding film 9 is provided.

  In addition, there exist the following patent documents 1 and 2 as a thing relevant to a prior art, for example.

JP-A-9-69621 Japanese Patent Laid-Open No. 2004-6777

  A CCD solid-state imaging device is manufactured by implanting n-type or p-type impurities at various locations on the surface of a semiconductor substrate, and the impurity concentration profile is finely controlled in order to improve the imaging characteristics. As a result, the impurity concentration profile near the opening of the light shielding film is asymmetric.

  Conventionally, the asymmetry of the impurity concentration profile has not been much of a problem, but recent CCD-type solid-state imaging devices have been miniaturized to include more than several million pixels. As a result, the above-described asymmetry is caused. The occurrence of smears can no longer be ignored.

  An object of the present invention is to provide a CCD type solid-state imaging device capable of reducing smear caused by an asymmetry of an impurity concentration profile.

  The CCD solid-state imaging device of the present invention includes a photoelectric conversion element arranged in a two-dimensional array on the surface of a semiconductor substrate, and a first charge formed on one side of the photoelectric conversion element via a readout gate. A transfer path buried channel, a second charge transfer path buried channel formed on the other side of the photoelectric conversion element via a channel stop, and an opening is formed directly above the photoelectric conversion element covering the surface of the semiconductor substrate. In the CCD type solid-state imaging device provided with the light shielding film, the position of the opening of the light shielding film is formed to be deviated from the second charge transfer path buried channel side to the first charge transfer path buried channel side. And

  The CCD type solid-state imaging device of the present invention includes an impurity diffusion layer having a two-layer structure of a conductivity type and a reverse conductivity type of the photoelectric conversion element on a surface portion of the photoelectric conversion element, and a first on the surface side of the impurity diffusion layer. The layer is surrounded by a second layer having a lower concentration than the impurity concentration of the first layer, and the end of the first layer and the read gate are separated from the distance between the end of the first layer and the channel stop. The distance between is long.

  The CCD type solid-state imaging device of the present invention includes a distance W1 between the second charge transfer path side end of the opening and a near end of the second charge transfer path buried channel, and the first charge transfer of the opening. The ratio W1 / W2 of the distance W2 between the path side end and the near end of the first charge transfer path buried channel is 1 <W1 / W2 ≦ 6/5.

  According to the present invention, it is possible to reduce smear based on the asymmetry of the impurity concentration profile in the vicinity of the opening of the light shielding film.

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

(First embodiment)
FIG. 1 is a schematic cross-sectional view of approximately two pixels of the CCD type solid-state imaging device according to the first embodiment of the present invention. In the solid-state imaging device 20, a large number of pixels (photodiodes) are arranged in an array on the light receiving surface of the n-type semiconductor substrate 21 (substantially at the center of the semiconductor substrate).

  A p-well layer 22 is formed on the surface portion of the n-type semiconductor substrate 21. The n region 23 is formed in the pixel region of the p well layer 22 to form a photodiode (photoelectric conversion element) between the p well layer 22 and the n region 24 is formed in the charge transfer region. A buried channel of the transfer path is formed.

A read gate (p region) 25 for reading the accumulated charge is formed between the n region 23 and the buried channel 24 for transferring the accumulated charge in the n region 23, and the opposite side of the buried channel 24 where the read gate 25 is not provided. An element isolation portion (p ⁺ region (“ ⁺ ” means that the concentration is relatively higher than the surroundings): channel stop) 26 is formed between the n region 24 and the n region 24. A surface p layer (impurity diffusion layer) 27 for suppressing dark current is provided on the surface portion of the n region 23.

  An optical layer is laminated on the upper layer portion of the semiconductor substrate 21 having such a configuration. First, a transparent insulating layer 31 is laminated on the entire surface of the semiconductor substrate 21. The insulating layer 31 has an ONO (oxide film-nitride film-oxide film) structure. On the charge transfer region, the first polysilicon layer 32 and the second polysilicon layer 33 constituting the transfer electrode of the charge transfer path are separated from each other by an interelectrode insulating film 34 such as silicon oxide. Formed.

  Further, a transparent insulating layer 35 is laminated on the entire surface. The insulating layer 35 is made of, for example, a silicon nitride film. Further thereon, a metal film such as tungsten is laminated as a light shielding film 36. The light shielding film 36 has an opening 36 a immediately above the photoelectric conversion region, and light incident in the opening 36 a enters the n region 23 through the silicon nitride film 35 and the insulating layer 31. The silicon nitride film 35 has an antireflection function.

  On the light shielding film 36, an interlayer insulating layer 37 that also serves as a planarization layer is laminated. The interlayer insulating layer 37 is formed of, for example, a BPSG film (borophospho silicate glass) or a PSG film (phospho silicate glass).

  The upper surface of the flattening layer 37 is flattened by CPM or etchback, and a color filter layer 39, a flattening layer 40, and a microlens (top lens) 41 are sequentially stacked thereon.

The impurity concentration in the vicinity of the light-shielding film opening 36a of the CCD type solid-state imaging device 20 shown in the figure is “p” for the surface impurity diffusion layer 27 immediately below the opening 36a, “p ⁺ ” for the channel stop 26, and “p” for the readout gate section 25. It has become.

When viewed from the light shielding film opening 36a as the center, the p-concentration of the channel stop 26 is high and the p-concentration on the read gate 25 side is low, which is asymmetric. The channel stop 26 composed of the high concentration p ⁺ region is formed up to a position in contact with the buried channel 24a for the adjacent pixel (the left channel 24 in FIG. 1).

Here, smear is generated when obliquely incident light of incident light enters the transparent insulating layers 31 and 35 between the light shielding film 36 and the semiconductor substrate 21. Since the diffusion current due to smear propagates through the p layer, smear is more likely to occur in the p ⁺ region, that is, in the channel stop 26 side than in the read gate portion 25 side. That is, a smear current tends to flow toward the channel stop 26 side, and the probability of entering the embedded channel 24a of the adjacent pixel is increased.

  Therefore, in the CCD type solid-state imaging device 20 of the present embodiment, the entrance where obliquely incident light enters, that is, the position of the opening 36a on the channel stop side of the opening 36a is separated from the channel stop 26. Then, the read gate side opening end 36c is shifted to the read gate 25 side, and the size of the opening 36a itself is not changed.

  That is, the distance W1 between the opening end 36b of the opening 36a and the far end of the channel stop 26 is longer than the distance W2 between the opening end 36c of the reading gate 36a and the far end of the reading gate 25 ( W1> W2).

  FIG. 2 is a comparison diagram of the CCD type solid-state imaging device (FIG. 2A) of the present embodiment and the conventional CCD type solid-state imaging device (FIG. 2B). In this embodiment, the position of the light shielding film opening 36a is as follows. Conventionally, the charge transfer path is formed so as to be separated from the adjacent charge transfer path (VCCD) 24a, that is, the channel stop 26, and approach the charge transfer path 24b of itself.

  Like the CCD type solid-state imaging device 20 of the present embodiment, by increasing the distance W1, the probability that the smear diffusion current flows into the embedded channel 24a of the adjacent pixel is reduced, and the influence of smear can be suppressed. It becomes. Further, by shortening the distance W2, it is not necessary to reduce the size of the opening 36a, and as a result, a decrease in light receiving sensitivity is suppressed.

  FIG. 3 is a graph showing the result of simulating the relationship between smear (standard value) and the position of the light shielding film opening 36a (W1 / W2). The smear characteristic I with respect to the opening position of the light shielding film is asymmetric with respect to the position of W1 / W2 = 1. This is due to the asymmetry of the impurity concentration profile.

  The reason why the smear characteristic rapidly deteriorates as the light shielding film opening position shifts in the direction of W1 / W2 <1 is that it approaches the channel stop 26 formed by the high concentration impurity region. In this embodiment, the light shielding film opening end 36c is brought close to the charge transfer path 24b on the charge reading side in order to maintain the size of the light shielding film opening. However, if it is too close, the smear characteristic is also deteriorated. This is because the probability that a smear diffusion current due to light incident from the opening end 36c side flows into the charge transfer path 24b is increased.

  As can be seen from FIG. 3, the smear characteristic I takes a minimum value in the range of 1 <W1 / W2 ≦ 6/5. For this reason, the smear characteristic can be improved by shifting the opening of the light shielding film within the range where the minimum value is obtained.

  The light-shielding film opening has a minute size and manufacturing variation exists. For this reason, even if the light shielding film opening is manufactured at the position of W1 / W2 = 1, the position varies back and forth around W1 / W2 = 1. CCD type solid-state imaging devices that vary in the direction of W1 / W2 <1 are inferior due to poor smear characteristics, which causes a reduction in manufacturing yield.

  On the other hand, when the light shielding film opening position is manufactured at a position where the smear characteristic takes the minimum value as in this embodiment, even if the opening position is shifted to the channel stop side due to manufacturing variation, the smear characteristic is not deteriorated, and therefore it is not necessary. It will not be a good product, and the manufacturing yield will be improved. That is, it is possible to reduce both the manufacturing cost and the smear characteristic.

(Second Embodiment)
FIG. 4 is a schematic cross-sectional view of approximately two pixels of a CCD solid-state imaging device according to the second embodiment of the present invention. The difference between the CCD solid-state imaging device 50 of the present embodiment and the CCD solid-state imaging device 20 of the first embodiment is the structure of the impurity diffusion layer 27 provided on the surface of the n region 23, and the other structures are the first embodiment. Since the configuration is the same as that of the embodiment, the same members are denoted by the same reference numerals, and the description thereof is omitted.

  The impurity diffusion layer 27 of the first embodiment shown in FIG. 1 (in FIG. 1, the thickness is shown to be about the same as that of the n region 23, but actually it is manufactured thin. The same applies to FIG. 4). Is composed of a p-layer of uniform concentration.

In contrast, the impurity diffusion layer 27 of the present embodiment is provided on the surface of the p ⁻ layer (“ ⁻ ” means that the impurity concentration is relatively lower than the surroundings) 27a and the p ⁻ layer 27a. The p layer 27b has a two-layer structure.

In addition, the p layer 27 b is formed inside the p ⁻ layer 27 a so that the side end of the p layer 27 b does not contact the channel stop 26 and the read gate portion 25. Then, between the channel stop 26 ends and the p layer 27b end p ^- the width d of the layer 27a, p between the readout gate unit 25 ends and the p layer 27b end ^- the width of the layer 27a It is formed so that t becomes wide.

The p layer 27b is provided so as to be surrounded by the p ⁻ layer 27a for the following reason. The reason why the p layer 27b is provided on the surface portion of the n region 23 is to suppress dark current. By providing the p layer 27b, free electrons generated as a dark current component are trapped in holes in the p layer 27b. Generation of white scratches on the captured image is suppressed.

However, when the p layer 27b is provided, the electric field between the p layer 27b and the read gate portion 25 or between the p layer 27b and the n region 23 becomes strong, and the leak current flowing by this electric field increases. Therefore, the p layer 27b is surrounded by the p ⁻ layer 27a to weaken the electric field.

  Also in the CCD solid-state imaging device 50 of the present embodiment, as shown in FIG. 4, the distance W2 is shortened as in the first embodiment. Therefore, in the present embodiment, the distance t between the end portion of the p layer 27b and the read gate portion 25 is made longer than the distance d between the end portion of the p layer 27b and the channel stop 26, thereby weakening the electric field on the read gate portion 25 side. The leakage current to the reading side is further reduced.

  The CCD solid-state imaging device according to the present invention is useful as an image sensor mounted on a digital camera or the like because smear characteristics are improved.

It is a principal part cross-sectional schematic diagram of the CCD type solid-state image sensor which concerns on 1st Embodiment of this invention. It is a comparison figure of the CCD type solid-state image sensor concerning a 1st embodiment of the present invention, and the conventional CCD type solid-state image sensor. It is the graph which simulated the correlation with a smear characteristic and a light shielding film opening position. It is a principal part cross-sectional schematic diagram of the CCD type solid-state image sensor concerning 2nd Embodiment of this invention. It is a principal part cross-sectional schematic diagram of the conventional CCD type solid-state image sensor.

Explanation of symbols

20, 50 CCD type solid-state imaging device 21 Semiconductor substrate 22 P well layer 23 n region (charge storage region)
24 buried channel (VCCD)
25 Read gate (p region)
26 channel stop (p ⁺ region)
27 Surface impurity diffusion layer (p layer)
27a p ^- layer 27b p layer 36 shielding film 36a shielding film opening 36b shielding film opening channel stop end 36c light shielding film opening the read gate end

Claims (3)

  Photoelectric conversion elements arranged in a two-dimensional array on the surface of a semiconductor substrate, a first charge transfer path buried channel formed on one side of the photoelectric conversion element via a read gate, and the photoelectric conversion element CCD type solid-state imaging device comprising: a second charge transfer channel embedded channel formed on the other side of the semiconductor substrate via a channel stop; and a light shielding film covering the surface of the semiconductor substrate and having an opening formed immediately above the photoelectric conversion element. In the device, a CCD solid-state imaging device, wherein the position of the opening of the light shielding film is deviated from the second charge transfer path buried channel side to the first charge transfer path buried channel side.   The surface of the photoelectric conversion element is provided with an impurity diffusion layer having a two-layer structure having a conductivity type opposite to that of the photoelectric conversion element, and the first layer on the surface side of the impurity diffusion layer is defined by the impurity concentration of the first layer. A structure in which the second layer having a low concentration is enclosed, and the distance between the end of the first layer and the read gate is longer than the distance between the end of the first layer and the channel stop. The CCD solid-state imaging device according to claim 1.   The distance W1 between the second charge transfer path side end of the opening and the near end of the second charge transfer path buried channel, the first charge transfer path side end of the opening, and the first charge transfer path 3. The CCD type solid-state imaging device according to claim 1, wherein a ratio W1 / W2 with respect to a distance W2 from the near end of the buried channel is 1 <W1 / W2 ≦ 6/5. element.

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