JP3018782B2 - Solid-state imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image sensor, and more particularly, to a solid-state image sensor having a lens on each photodiode.

[0002]

2. Description of the Related Art In a conventional inter-line solid-state imaging device, a transfer register is formed between a photodiode and an adjacent photodiode.
Sufficient sensitivity could not be obtained with only 0%. As a technique that satisfies the above-mentioned need, a technique invented conventionally is a lens patterning technique shown in FIG.

[0003] In the solid-state imaging device shown in FIG.
A P-type layer 2 is formed thereon, and the P-type layer 2 and the N-type diffusion layer 3 constitute a photodiode. The N-type layer 5 operates as a transfer register, and the P ⁺ -type diffusion layer 4 operates as a channel stop for preventing charges accumulated in the N-type layer 5 from entering the adjacent N-type diffusion layer 3. The gate 6 is a polysilicon electrode, on which an interlayer film 7 is formed, and further, a light-shielding film 8 (for example, Al) for defining a photosensitive region is formed. Then, the unevenness due to the light shielding film 8 is flattened by the flattening layer 9, and the lens 10 is formed thereon. The refractive index n ₀ of the flattening layer 9 (for example, phenol novolak resin n ₀ =
1.61) and the refractive index n _{1 of the} lens 10 (for example, phenol-novolak resin n ₁ = 1.61) is n ₀ = n ₁ , so that the optical path of the light incident from the lens 10 is changed at the boundary between the two. In the normal case, the light is condensed on the photodiode as in the optical path 11. In this prior art, since the lens is patterned on the photodiode, the aperture ratio is equivalently increased, and the sensitivity is doubled (1984, 3-17, Television Zendai, Ishihara, Tanigaki, "Resin lens array. High sensitivity CCD image sensor used).

[0004]

However, the optical path 1 shown in FIG.
2, when the reflected light 12 of the lens of the adjacent pixel is incident on the photodiode of the pixel A, signal crosstalk occurs between the pixels C and A, MTF is deteriorated, and a mosaic type color filter is used. The solid-state imaging device has a problem that the degree of color modulation is reduced.

In the case of the optical paths 13 and 14 shown in FIG. 3, that is, an optical path due to a defect deviated from the normal optical axis in manufacturing the lens, and an optical path which does not contribute to the photoelectric conversion by the optical path 15 shown in FIG. The light scattered due to the unevenness on the surface of the surface increases the flare component and the adjacent pixel B or C of the reflected light.
However, there is a problem that the smear component increases due to re-injection into the photodiode, and there is a disadvantage that the image quality is significantly deteriorated when a high-luminance subject is imaged. Further, at the end of the lens, there is a disadvantage that an image is formed on a portion other than the surface of the photodiode as shown by the optical path 16 in FIG. 3 due to aberration of the lens.

[0006]

According to the present invention, a plurality of pixels are provided.
A solid-state imaging device having a lens disposed on each pixel , the lens having a refractive index equal to that of the lens and having a thickness on the lens.
Has an aspheric lens surface layer that is larger at the end than at the center.
In addition, the distance between adjacent lenses is reduced .

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing a first embodiment of the present invention.
The same parts as those in the conventional example described above are denoted by the same reference numerals,
Duplicate description will be omitted. In this embodiment, the refractive index n ₂ (for example, phenol
A lens cover layer 17 made of novolak resin and having a refractive index of 1.61) is laminated. Therefore, the lens on the unit pixel is ultimately constituted by the lens 10 and the lens surface layer 17. Here, in FIG. 1, X represents the distance between adjacent lenses, and t represents the thickness of the lens surface layer 17,
Since t is larger at the end between the center and the end of the original lens 10, the lens shape is an aspherical lens, and the curvature is different between the center of the lens and the end of the lens. The image is formed on the photodiode without causing aberration as shown in FIG. In addition, since the distance X between adjacent lenses is reduced, the amount of light in the optical path 19 that does not contribute to photoelectric conversion is reduced, so that the aperture ratio of the photodiode is equivalently improved, sensitivity and S / N are improved, and the distance between adjacent pixels is reduced. Signal can be significantly reduced. Therefore, MTF
And the degree of color modulation is improved even in a solid-state imaging device using a mosaic type color filter. Further, as the amount of light in the optical path 19 decreases, scattered light on the surface of the light-shielding film 8 decreases, so that a flare component and a smear component can be reduced.

FIG. 2 shows only a lens portion according to a second embodiment of the present invention. In the first embodiment of FIG. 1, the lens is formed after laminating the lens surface coating 17 on the lens 10, but as shown in FIG. A similar aspheric lens can be obtained by forming a lens by laminating 17. In this case, the lens height from the flattening layer 9 (in this case, the height h of the lens pattern 20 and the thickness t of the lens surface layer)
h + t) can be changed freely. When the upper side W2 and the lower side W1 of the lens pattern 20 are equal, the distance X between adjacent lenses can be determined by the relationship between the width and the lens surface layer 17. In FIG. 2, the lens pattern 20 is W1
= W2 is shown, but since W1 and W2 determine the shape of the lens, a trapezoid with a low height h such as W1 ≧ W2 ≧ h> 0 is preferable.

It is needless to say that the present invention can be applied not only to an inter-line solid-state image pickup device but also to all solid-state image pickup devices having a lens on a unit pixel. Further, in the above-described embodiment, an example is shown in which the lens is formed by laminating only one layer of the lens cover layer 17 on the lens 10 or the lens pattern 20, but the present invention is not limited to this. Any number of layers 17 may be laminated to form an aberration-free aspheric lens that effectively guides necessary light to an optical die.

[0010]

As described above, according to the present invention, since the light collection rate on the photodiode is increased, the sensitivity of the solid-state device is improved, and the flare component and the smear component are reduced. As a result, even in a solid-state imaging device using a mosaic type color filter, the degree of color modulation is improved. Further, the image quality does not deteriorate even when a bright object is imaged.

[Brief description of the drawings]

FIG. 1 is a sectional view of a solid-state imaging device according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a lens portion according to a second embodiment of the present invention.

FIG. 3 is a cross-sectional view of a conventional solid-state imaging device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 N-type substrate 2 P-type layer 3 N-type diffusion layer 4 P + -type diffusion layer 5 N-type layer 6 Gate 7 Interlayer film 8 Light-shielding film 9 Flattening layer 10 Lens 11 to 16 Optical path 17 Lens covering layer 20 Lens pattern

Claims (1)

(57) [Claims] 1. A method comprising: a plurality of pixels; a lens on each pixel;
In the arranged solid-state imaging device, on the lens, the refractive index is equal to that of the lens, and the thickness is larger at the end than at the center.
Aspherical lens surface layer, and the distance between adjacent lenses.
A solid-state imaging device characterized in that separation is reduced .