JPH05150104A - Integral type condensing element for solid-state image pickup element - Google Patents

Abstract

PURPOSE:To improve the sensitivity of a solid-state image pickup element by efficiently condensing the light arriving at the blind region of the solid-state image pickup element having annular band-shaped photoelectric conversion parts, to a photoelectric conversion parts. CONSTITUTION:The condensing element used by being integrally provided on the solid-state image pickup element having nearly the annular band shape in the shape of the photoelectric conversion parts 1 of respective picture elements is provided with circular conical prisms 2, 3 right above the inside of the bore of the annular band-shaped photoelectric conversion parts 1 which are optoelectrically blind of the respective picture elements and right above the central part of the optoelectrically blind regions enclosed by the adjacent picture elements on a transparent layer 6 formed on the surface of the image pickup element. The light arriving at the signal reading out circuit, etc., which are the blind regions of the solid-state image pickup element is introduced to the photoelectric conversion parts 1, by which the sensitivity is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element for improving the sensitivity of a solid-state image pickup device composed of pixels having a ring-shaped photoelectric conversion portion, and more particularly, to an incident light to a dead region of the solid-state image pickup device. The present invention relates to a light-collecting device formed on the surface of a transparent layer on a solid-state image pickup device in order to improve sensitivity by collecting light on a photoelectric conversion unit.

[0002]

2. Description of the Related Art At present, the major focus of solid-state image pickup device development is miniaturization of pixels by miniaturization of pixels and high sensitivity of the devices. However, such miniaturization of pixels results in a reduction in the light-receiving area of the entire image sensor, which inevitably causes a problem of a decrease in photosensitivity.

Therefore, as one of effective means for solving such a problem and achieving high sensitivity and not deteriorating other device characteristics, a transparent lens array is arranged on a solid-state image pickup device, There has been proposed an integrated convex or concave microlens array in which an incident light component arriving on a signal reading circuit, which is a dead region, is condensed on a photoelectric conversion unit (Japanese Patent Laid-Open No. 53-74395). ..

[0004]

In the case of a general charge-coupled device (CCD) in which the photoelectric conversion part of each pixel has a rectangular shape, a relatively simple convex or concave microlens array is used as a light-collecting device. Is sufficient. However, in the case of a solid-state image sensor in which the photoelectric conversion region has an annular shape, when the convex lens is installed directly above the pixel, the inside of the inner diameter is a dead region, so the light is condensed inside the inner diameter. The light does not contribute to the sensitivity improvement at all, and when trying to collect the amount of light by providing a concave lens between each pixel, the light incident from directly above the inner diameter, which is the dead area, is also used. Can not do it.

The present invention has been made in view of such a situation, and an object thereof is to eliminate the above-mentioned structural defects of the conventional light-collecting element and to efficiently convert the light reaching the insensitive region. An object of the present invention is to provide an integrated light-collecting device for a solid-state image sensor, which can improve the sensitivity of the solid-state image sensor by condensing light on the conversion unit.

[0006]

In order to solve the above-mentioned problems, an integrated light-collecting device for a solid-state image pickup device of the present invention has a photoelectric conversion part of each pixel integrated into a substantially annular-shaped solid-state image pickup device. In the light-collecting element to be provided and provided, the transparent layer formed on the surface of the image pickup element is surrounded by an adjacent pixel immediately above the inner diameter of the annular photoelectric conversion section which is photoelectrically insensitive. In addition, a conical prism is provided right above the center of the photoelectrically insensitive area.

[0007]

According to the present invention, the transparent layer formed on the surface of the solid-state image pickup device is surrounded by the adjacent pixel immediately above the inner diameter of the ring-shaped photoelectric conversion portion which is photoelectrically insensitive to each pixel. Since the conical prism is provided right above the center of the photoelectrically insensitive area, the light flux incident on each insensitive area is converted into a conical wave radiated at a constant width and a constant angle in the cross section, It is possible to make the light incident on the annular photoelectric conversion unit. In this way, it is possible to guide the light that has reached the signal readout circuit, which is a dead region of the solid-state image pickup device having the ring-shaped photoelectric conversion unit, to the photoelectric conversion unit, and to improve the sensitivity.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the integrated light-collecting device for a solid-state image pickup device of the present invention will be described below with reference to the accompanying drawings.
First, FIG. 4 shows a perspective cross-sectional view of one pixel of a solid-state image sensor of one example in which the photoelectric conversion portion is composed of annular pixels.
Unlike a general phototransistor, this solid-state imaging device has a gate having a substantially annular shape as shown in the figure. That is, the incident light transmitted through the polycrystalline silicon gate electrode, which is the light receiving region, generates a hole-electron pair in Si. The holes are accumulated at the interface of Si—SiO ₂ of the gate electrode, and the drain current indicated by the arrow is modulated by the change of the gate potential to be an amplified signal current. In this way, if the light-receiving region has a substantially annular shape, as described above, even if a convex lens is installed right above the pixel, the inside of the inner diameter of the light-receiving ring is a dead region. The light collected inside the inner diameter does not contribute to sensitivity improvement at all, and even if a concave lens is provided between each pixel to collect the amount of light, similarly, the light is directly above the inner area, which is a dead area. It is not possible to use the light that comes in from.

In view of the above, in the present invention, a position immediately above the inner diameter of the ring-shaped pixel, which is a photoelectrically insensitive region, and a position directly above the center of a portion surrounded by adjacent pixels, which is also a dead region, are provided.
By arranging two kinds of conical prism (axicon) arrays provided in a concave shape having a circular opening surface and having a conical conical surface having the opening surface as a bottom surface as an entrance surface,
It is intended to improve the sensitivity of the solid-state image pickup device by condensing the incident light heading for the dead region on the ring-shaped light receiving region.

FIG. 1 is a partial plan view of an embodiment of a solid-state image pickup device having an integrated light-collecting device according to the present invention, and FIG. 2 is a partial sectional view taken along the line AA 'in FIG. Indicates. In the plan view of FIG. 1, 1 is a ring-shaped photoelectric conversion region of each pixel, and 2 is a diameter 2a provided so that the apex angle is located just above the center inside the inner diameter of the ring-shaped photoelectric conversion region 1. _{1 is} a first conical prism (axicon) having an apex angle 2θ ₁ , and 3 is a diameter 2a provided so that the apex angle is located right above the center of a dead region surrounded by four adjacent pixels. _{2 is} a second conical prism (axicon) having an apex angle 2θ ₂ . As shown in the cross-sectional view of FIG. 2, a transparent conical prism forming layer 6 which is also transparent is formed on a transparent intermediate layer 5 formed on the solid-state imaging device. An array of two types of conical prisms, the second conical prism 3, is provided.

As is apparent from the cross-sectional view of FIG. 2, the parallel light incident on the first conical prism 2 provided right above the inner diameter of the ring-shaped photoelectric conversion portion 1 in the dead region is The light is refracted by the conical surface of the conical prism 2, converted into a conical wave radiated at a constant width and at a constant angle in the cross section, and enters the ring-shaped photoelectric conversion unit 1.

Further, the parallel light incident on the second conical prism 3 provided right above the insensitive area surrounded by the four adjacent pixels is refracted by the conical surface of the conical prism 3 and becomes constant. The wavefront is converted into a cone wave that is radiated at a certain angle in the width,
Part of the conical wave is incident on each of the photoelectric conversion units 1 of the four adjacent pixels. As shown in FIG. 3, the conical wave generated by the second conical prism 3 illuminates the area 40 on the imaging surface. Since this irradiation area 40 overlaps with the four photoelectric conversion units 1 adjacent to each other in the area 41, the light reaching the dead area surrounded by the four pixels adjacent to the shaded area 41 is distributed and condensed. Will be done.

Further, since no conical prism is provided directly above the ring-shaped photoelectric conversion unit 1, the photoelectric conversion unit 1 is not provided.
The light heading for reaches directly there.

Due to the above-mentioned structure, in the ring-shaped photoelectric conversion portion 1, the direct light traveling toward the photoelectric conversion portion 1 is directed toward the dead area inside the inner diameter of the photoelectric conversion area 1 by the first conical prism 2. Since the light having the wavefront converted into a wave and a part of the light having the wavefront converted into the conical wave by the second conical prism 3 are incident on the dead region surrounded by the four adjacent pixels, the solid light is solid. The light reaching the insensitive area of the image pickup element is also incident on the light receiving area, and the sensitivity of the solid-state image pickup element is improved.

In order to manufacture such conical prisms 2 and 3, for example, a pattern transfer method using a stamper is suitable, and the material of the conical prism forming layer 6 is
Examples include organic materials and inorganic materials. In each case, one example of the manufacturing method is shown below.

In the case of an organic material, the transparent intermediate layer 5 is formed on the surface of the solid-state image pickup device with quartz glass or the like to a required thickness, and then an ultraviolet curable resin is applied on the transparent intermediate layer 5 to form the conical prisms 2 and 3. A glass stamper engraved with a pattern is brought into contact with this ultraviolet curable resin layer, and the resin is cured by irradiating ultraviolet rays from the stamper side, and then the glass stamper is removed to form the desired conical prism 2, 3 pattern on the surface. Can be produced.

In the case of an inorganic material, the so-called sol-gel method is used. In the sol-gel method, a metal alkoxide solution is hydrolyzed at room temperature or a temperature close to it to form a sol (a colloid using a liquid as a dispersion medium) by a polycondensation reaction, and the reaction is further promoted to form a gel (the colloid solution is a jelly-like solution). It is a method of producing glass by heating it to a certain high temperature and vitrifying it. In this case, on the solid-state image sensor having a transparent intermediate layer 5 such as quartz glass having a required thickness provided on the surface, adjustment is performed so that shrinkage during drying and heating is sufficiently small and a required film thickness is obtained after the treatment. The metal alkoxide solution (sol) is applied, and the stamper having the pattern is brought into contact with the solution, and the solution is gelated in that state. After that, the stamper is removed, the gel is dried, and heat treatment is performed at several hundred degrees. Through the above steps, desired patterns of the conical prisms 2 and 3 can be formed on the surface.

As a method of manufacturing the stamper required here, for example, the following method can be considered. The first method is to create a desired conical pattern group on an electron beam resist on a substrate by drawing while changing the electron dose by an electron beam drawing method, and pattern this using a nickel electroforming method. It is to be transferred and used as a stamper master.
If one such master is produced, a large number of replicas can be produced by the ultraviolet curing resin and the electroforming process based on this. A glass stamper is produced from the master and the duplicate by using the sol-gel method described above. When the element is manufactured by the sol-gel method, the stamper does not need to be transparent, and thus the duplicate manufactured in the nickel electroforming step may be used as it is as the stamper.

The second method is to manufacture a stamper master by an ultraprecision cutting method. Based on the method of directly producing a master of equal size and a mold in which a pattern of several tens of times is engraved, the pattern transfer by positively utilizing the shrinkage during drying and heating of the gel in the sol-gel method, There is a method in which heat shrinkage is repeated until a desired pattern size is obtained, and the glass replica thus produced is used as a stamper master. In the latter case, the shrinkage rate can be varied by adjusting the composition ratio of water and alcohol contained in the metal alkoxide solution, and the shrinkage rate can be about 60 to 50% of the pattern to be the mold.
In addition, in the case of this method, since it is impossible to manufacture it as a substrate-shaped thin film due to a large shrinkage ratio, it is manufactured as a block. The subsequent manufacturing method of the stamper is the same as the first method.

Although one embodiment of the integrated light-collecting device for a solid-state image pickup device of the present invention has been described above, the present invention is not limited to this embodiment and various modifications can be made. For example,
Even if a convex conical prism is used instead of the concave conical prism, the wavefront can be converted into a conical wave radiated at a constant width and a constant angle in the cross section.
The conical prism can also be formed by forming a concave conical pattern on the surface of the transparent layer and filling it with a transparent body having a high refractive index or a transparent body having a small refractive index.

[0021]

As is apparent from the above description, according to the integrated light-collecting device for a solid-state image pickup device of the present invention, the transparent layer formed on the surface of the solid-state image pickup device is photoelectrically insensitive to each pixel. Since a conical prism is provided right above the inner diameter of a ring-shaped photoelectric conversion unit and right above the center of the photoelectrically insensitive area surrounded by adjacent pixels, the light flux incident on each insensitive area can be It becomes possible to convert the wavefront into a conical wave radiated at a constant width and a constant angle in the cross section and make it enter the annular photoelectric conversion unit. In this way, it is possible to guide the light that has reached the signal readout circuit, which is a dead region of the solid-state image pickup device having the ring-shaped photoelectric conversion unit, to the photoelectric conversion unit, and to improve the sensitivity.

Therefore, according to the present invention, the light utilization factor is remarkably improved as compared with the conventional one which does not use the light condensing element. As a result, in the solid-state image pickup device, it is possible to simultaneously achieve miniaturization of the device due to miniaturization of pixels and high sensitivity.

[Brief description of drawings]

FIG. 1 is a partial plan view of an embodiment of a solid-state image pickup device having an integrated light-collecting device according to the present invention.

FIG. 2 is a partial cross-sectional view taken along the line AA ′ in FIG.

FIG. 3 is a diagram showing how a conical wave from a conical prism provided immediately above between adjacent pixels is incident on a ring-shaped photoelectric conversion unit.

FIG. 4 is a perspective cross-sectional view of one pixel of a solid-state image sensor in which a photoelectric conversion portion is composed of pixels in a ring shape.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Ring-shaped photoelectric conversion area 2 ... 1st conical prism 3 ... 2nd conical prism 5 ... Transparent intermediate layer 6 ... Conical prism preparation layer 40 ... Irradiation area | region by 2nd conical prism 41 ... 2nd conical prism Area where irradiation area and photoelectric conversion part overlap

Claims (1)

[Claims] 1. A condensing element used integrally with a solid-state image pickup device having a photoelectric conversion portion of each pixel in a substantially annular shape, wherein a photoelectric layer of each pixel is provided on a transparent layer formed on the surface of the image pickup device. The solid-state imaging device is characterized in that a conical prism is provided just above the inner diameter of the ring-shaped photoelectric conversion unit, which is insensitive to, and just above the center of the photoelectrically insensitive region surrounded by adjacent pixels. Integrated light-collecting device for devices.