JPH04252074A - Solid-state image sensing element - Google Patents

Abstract

PURPOSE:To make it possible to prevent the quantity of incident light from being reduced even in case an F-value is small by a method wherein a focal length of a focal length or longer, which is obtained by the processing limit curvature of a lens array, can be obtained. CONSTITUTION:A solid-state image sensing element provided with a lens array 10 is provided to a photoelectric conversion part 2 and the upper part of this lens array is covered with a substance 11, which has a refractive index smaller than that of the array and has a radius of curvature larger than that of the array.

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 pickup device in which a photoelectric conversion section is provided with a lens array having the same pitch as pixels.

0002

[Background Art] In solid-state image sensors, such as CCD and MOS image sensors, efforts are being made to reduce pixel dimensions or increase the number of pixels in order to achieve smaller size and higher resolution. However, this has led to the problem that the area of the photoelectric conversion section has been reduced and the amount of incident light per unit pixel has been reduced.

[0003] Therefore, a lens array made of a photoresistor or the like is provided to increase the actual amount of incident light by concentrating light on the photoelectric conversion section in an amount larger than the area of the photoelectric conversion section. For example, FIG. 3 is a cross-sectional view of the vicinity of the photoelectric conversion section of a CCD when no lens array is provided, and illustrates the case where parallel light 12 is incident. An N-type layer 2 is formed on a P-type Si substrate 1, and a P-type layer 3 is formed on the surface thereof. These 1 to 3 constitute a photodiode. 4 is the N-type layer of the charge transfer section, 5
6 is a polysilicon electrode, 6 is a SiO2 layer, 7 is a flattening insulating layer, 8 is a light-shielding aluminum, and 9 is a flattening layer. If there is no lens array, light entering the charge transfer section 4 will generate a false signal called smear, so a light shielding aluminum 8 is provided, but the light that originally entered the CCD as a signal is wasted here. Put it away. Therefore, this light is transferred to the photoelectric conversion unit 2.
A lens array was devised for the purpose of guiding. Figure 4 shows
A case in which a lens array is provided is illustrated. Figure 4
By providing the lens array 10 in the photoelectric conversion section as shown by the solid line, it is possible to collect the light that would otherwise hit the charge transfer section 4 in FIG. 3 onto the photoelectric conversion section 2 and increase the amount of incident light. As the amount of incident light increases, the signal charges generated by photoelectric conversion increase, so even though the amount of light incident on the CCD is the same in FIGS. 3 and 4, the signal charges in FIG. 4 are larger. Assuming that the aperture ratio (the ratio of photoelectric conversion parts per pixel) is K,
The maximum sensitivity of the CCD in Figure 4 is 1/K of the sensitivity of the CCD in Figure 3.
You can get twice as close.

0004

[Problem to be Solved by the Invention] When parallel light 12 as shown by the solid line in FIG.
However, when the aperture is opened and the F value is reduced, the incident light is no longer parallel and enters obliquely as shown by the broken line 13 in FIG. The relationship between the maximum incident angle θ and the F value in FIG. 4 is sinθ=
At 1/2 F, the smaller the F value, the larger the incident angle becomes, and as shown by the broken line in FIG. 4, the light spreads out before reaching the photoelectric conversion unit 2, and the amount of incident light decreases. Therefore,
When the aperture opens, the image should become brighter, but because the amount of light incident on the photoelectric conversion unit decreases, the problem arises that the brightness of the image is not as bright as expected when the aperture is opened, or worse, it becomes dark. Therefore, by increasing the focal length of the lens, when the F number is large, the incident light will be focused behind the photoelectric conversion section, and when the F number is small, the incident light will be focused in front of the photoelectric conversion section. Therefore, it is conceivable to make the photoelectric conversion section always have an aperture effect. Therefore, it is conceivable to simply reduce the curvature of the focal lens to increase the focal length, but since there is a limit to the reduction of the curvature of the lens through processing, the focal length cannot be increased beyond a certain limit.

[0005] The present invention prevents the incidence of light from decreasing due to the short focal point of the lens when reducing the F number as described above, that is, when opening the aperture, and reduces the aperture aperture and the brightness of the image. The purpose is to make it proportional.

[0006]

In the present invention, the lens array above the photoelectric conversion portion is covered with a material having a refractive index smaller than that of the lens material, and with a radius of curvature larger than at least the radius of curvature of the lens array.

[0007]

[Effect] By taking such measures, the focal length of the lens array becomes longer without reducing the curvature of the lens array itself, and light that is incident parallel also becomes light that enters obliquely due to the small F value. The light also gathers in the photoelectric conversion section, and prevents a decrease in the amount of incident light due to a decrease in the F value.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a cross section of a CCD solid-state imaging device to which the present invention is applied. The difference from FIGS. 3 and 4 is that a substance 11 having a refractive index smaller than that of the lens array is formed on the lens array 10. In this embodiment, the radius of curvature of the material 11 is infinite, that is, the surface is flat.

FIG. 2 also shows a cross section of a CCD solid-state imaging device to which the present invention is applied. In this case, the radius of curvature of the lens array 11 is larger than the radius of curvature of the lens array, and the antireflection film 14 is further placed on top of the radius of curvature of the lens array.

Although only the CCD is shown in FIGS. 1 and 2, the MO
Of course, it can also be used in the photoelectric conversion section of S-type and other types of solid-state image sensors, and the shape of the covered lens array is
For example, it can be used regardless of whether it is striped or circular. It can also be applied to a solid-state image sensor in which color filters are laminated.

[0011]

[Effects of the Invention] By applying the present invention, it is possible to avoid deterioration in sensitivity when the F number becomes small in a CCD equipped with a lens array and with increased sensitivity. In addition, even if a solid-state image sensor is equipped with a lens array dedicated to a large F-number as shown in Figure 4, it is possible to create a condition where the F-number is small by simply covering it with a material with an appropriate refractive index smaller than the lens array as shown in Figure 1. However, it has the advantage of being usable. Therefore, even the solid-state image sensor on the package can be easily modified. Furthermore, if the present invention is applied, even if the focal length must be increased due to the color filter layer, it is possible to obtain a focal length that is longer than the limit for reducing the curvature of the lens.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view when the present invention is applied to a photodiode, which is a photoelectric conversion portion of a CCD.

FIG. 2 is a sectional view showing another embodiment of the present invention.

FIG. 3 is a cross-sectional view showing a state in which parallel light is incident on a photodiode section of a CCD when a lens array is not used.

FIG. 4 is a cross-sectional view when a lens array is provided in the state shown in FIG. 3;

[Explanation of symbols]

1 P-type layer of Si substrate 2 N-type layer 3 P-type layer 4 N-type layer of CCD charge transfer section 5 Polysilicon electrode 6 Insulating layer SiO2 film 7 Planarization layer 8 Light-shielding aluminum 9 Planarization layer 10 Lens array 11 Substance with a lower refractive index than the lens 12 Parallel incident light 13 Oblique incident light 14 Anti-reflection film

Claims (1)

[Claims] Claim 1: The photoelectric conversion unit is provided with a lens array having the same pitch as the pixels, and the lens array is covered with a material having a smaller refractive index than the lens array and with a radius of curvature larger than that of the lens array. Characteristic solid-state image sensor.