JPH07130973A - Integrated light-condensing element for solid-state image sensing element and its manufacture - Google Patents

Abstract

PURPOSE:To miniaturize a solid-state image sensing element having a ring belt-shaped photoelectric conversion part and to make its sensitivity high by a method wherein an incident-light component in a nonsensitive region for the solid-state image sensing element is condensed with good efficiency and a picture element for the solid-state image sensing element is made fine. CONSTITUTION:In a light-condensing element (a macro lens 8), a photoelectric conversion part 9 for a picture element is installed integrally in a nearly ring belt-shaped solid-state image sensing element. In an integrated light-condensing element for a solid-state image sensing element, a lens pattern at least a part of which is protrusion-shaped is provided in a prescribed position, and a refractive index is distributed by the intersection point of the optical axis of the lens pattern and a lens face. A light component which is incident on a nonsensitive region on a signal readout circuit is condensed, by the action of a refractive index on the convex face of the lens, on the photoelectric conversion part 9 through a route indicated by an arrow A. In addition, a light component which is incident from a nonsensitive region on the inside of the inside diameter of the ring belt-shaped photoelectric conversion part 9 is condensed on the photoelectric conversion part 9 through a route indicated by an arrow B due to a bend inside a medium in addition to the action of the refractive index by the convex face.

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 an integrated light-collecting device for a solid-state imaging device, which is formed on a solid-state imaging device in order to improve sensitivity by collecting light on a photoelectric conversion unit, and a manufacturing method thereof.

[0002]

2. Description of the Related Art CCD (Charge Coupled)
Each pixel on a solid-state image sensor such as
It is mainly composed of two regions, a rectangular photoelectric conversion part and a signal reading circuit part. Of these, the area on the signal readout circuit is insensitive to the incident light component. The light component incident on this dead region is condensed on the photoelectric conversion unit to achieve high sensitivity of the image sensor, and as one of the effective means that does not deteriorate other device characteristics, it is transparent on the solid-state image sensor. An integrated convex or concave microlens array has been proposed, in which various lens arrays are arranged so that incident light components that reach the signal readout circuit, which is a dead region, are focused on the photoelectric conversion unit ( JP-A-53-74395). Here, as a method of manufacturing a convex microlens, a method of forming a pattern with a heat-softening material and manufacturing a convex microlens by heat dripping is disclosed.

In addition, CMD (Charge Module)
In a solid-state image pickup device having a ring-shaped photoelectric conversion unit such as an application device, a conical prism is formed inside the inner diameter of the ring-shaped photoelectric conversion unit which is a dead region and right above a portion surrounded by adjacent pixels. Japanese Patent Laid-Open No. 3-150104 discloses a method in which a light beam incident on each insensitive region is wavefront converted into a cone wave radiated at a constant width and a constant angle in a cross section and is efficiently condensed on a ring-shaped photoelectric conversion unit. It is disclosed in the official gazette.

On the other hand, JP-A-2-88433 discloses a method in which a part of the microlens has a refractive index distribution in order to correct various aberrations of light incident on the microlens.

[0005]

At present, a major focus in developing a solid-state image pickup device is miniaturization of a pixel and miniaturization of the device and increase in sensitivity of the device. But,
Such miniaturization of pixels results in a decrease in the light receiving area of the image pickup element, which inevitably causes a problem of a decrease in photosensitivity. In order to solve such a problem, a microlens may be formed on each pixel and a light beam may be condensed on the photoelectric conversion unit (Japanese Patent Laid-Open No. 53-74395). At this time, in the case of a general charge-coupled device (CCD) in which the photoelectric conversion portion of each pixel has a rectangular shape, it is sufficient to use a relatively simple convex or concave microlens array. However, in the case of a solid-state image pickup device (for example, CMD) in which the shape of the photoelectric conversion unit is an annular shape, for example, when a simple convex lens is installed right above the pixel, the light is condensed inside the inner diameter of the pixel. The luminous flux has no influence on the improvement in sensitivity because the inside of the inner diameter is a dead region. Similarly, when a concave lens is provided between each pixel to collect light, it is not possible to use the light incident from directly above the inside of the inner diameter, which is a dead region. That is, for a solid-state imaging device having a ring-shaped photoelectric conversion unit, even if a microlens having a simple convex shape or a concave shape is formed on a pixel, high sensitivity of the element cannot be realized.

In order to solve this drawback, there has been proposed a method of forming a conical prism inside the inner diameter of the ring-shaped photoelectric conversion portion which is a dead area and between each pixel (Japanese Patent Laid-Open No. 5-150104). Gazette), the structure of each pixel is fine, and the dead area inside the photoelectric conversion portion formed therein and the dead area between the pixels is very narrow. Therefore, a conical prism should be formed in this portion. Was very difficult in terms of accuracy.

Further, a method of producing a microlens and forming a distribution of the refractive index therein has been disclosed (Japanese Patent Laid-Open No. HEI-2).
-88433), this method is intended only to correct aberrations, not to focus light on a dead area. In order to focus light on a ring-shaped photoelectric conversion unit such as CMD, the distribution shape must further include the bending of light rays in the medium. As described above, it is difficult to achieve high sensitivity of the device only by the conventional method, by efficiently condensing the incident light component of the dead region of the solid-state image sensor having the annular photoelectric conversion unit. .

The present invention has been made in view of the above conventional problems, and efficiently collects incident light components in a dead region of a solid-state image pickup device having a ring-shaped photoelectric conversion portion to form pixels of the solid-state image pickup device. It is an object of the present invention to provide an integrated light-collecting device for a solid-state image pickup device and a method for manufacturing the same, which can achieve miniaturization and high sensitivity of the device by miniaturization.

[0009]

In order to solve the above problems, the present invention provides an integrated light-collecting device for a solid-state image pickup device, wherein a photoelectric conversion part of a pixel is integrally provided in a substantially annular solid-state image pickup device. A lens pattern having a convex shape, at least a part of which is provided at a predetermined position of the light-collecting element, and a distribution of refractive index is formed from the intersection of the optical axis of the lens pattern and the lens surface.

In manufacturing the integrated light-collecting device for a solid-state image pickup device of the present invention having the above-mentioned structure, glass containing a high refractive index metal component is used as a raw material, and a convex lens pattern is formed for each pixel. After that, a masking process was performed, and a part of the lens pattern was brought into contact with a molten salt of a low refractive index metal component to form a refractive index distribution.

Further, in manufacturing the integrated light-collecting device for a solid-state image pickup device of the present invention having the above structure, a sol containing a high-refractive-index metal component is used as a raw material, and a convex gel lens pattern is formed for each pixel. After the formation, a masking treatment was performed, and a part of the gel lens pattern was brought into contact with a solution containing a low refractive index metal component or an acid to form a refractive index distribution.

[0012]

FIG. 2 shows a sectional perspective view of one pixel in an example of the solid-state image pickup device in which the photoelectric conversion section is composed of pixels in a ring shape. Unlike a general phototransistor, this image pickup device is a CMD having a substantially ring-shaped gate.
Incident light transmitted through the polycrystalline silicon gate 1 formed in the light receiving region generates hole-electron pairs in the n ^- channel layer 3 epitaxially grown on the p ^- substrate 2 made of Si crystal. Of these, the holes 4 are in the region immediately below the polycrystalline silicon gate 1, and the SiO ₂ layer 5 and the n ⁻ channel layer 3 are formed.
Accumulates at the interface with. That is, the potential of the polycrystalline silicon gate 1 changes depending on the presence or absence of incident light, the channel between the n ⁺ source layers 6 increases and decreases, and the electrons supplied from the source 7, that is, the drain current is modulated. As a result,
The signal current amplified by the incident light can be taken out.

In such a solid-state image pickup device having a ring-shaped photoelectric conversion portion, a convex microlens 8 as shown in FIG. 1 is formed for each pixel. Reference numeral 9 is a photoelectric conversion unit. At this time, a distribution is further formed in the refractive index from the top of the convex shape of the microlens 8. The distribution of the refractive index at this time is such that the refractive index is lowest at the top of the convex surface. As a result, the light component incident on the dead area on the signal readout circuit is caused by the refractive index action on the convex surface of the lens.
The light is focused on the photoelectric conversion unit 9 through a path indicated by an arrow A in FIG. Further, the light component incident from the insensitive region on the inside of the inner diameter of the ring-shaped photoelectric conversion unit 9 has a refractive index distribution in the microlens 8. Therefore, in addition to the refraction effect of the convex surface, Along with the bending, the light passes through the path indicated by the arrow B in FIG. 1 and is focused on the photoelectric conversion unit 9. In other words, by forming such a condensing element on each pixel, it is possible to condense light components incident between the pixels and in the insensitive area inside the inner diameter of the annular photoelectric conversion unit to the photoelectric conversion unit. Therefore, it becomes possible to realize high sensitivity of the device.

A method of manufacturing a microlens having a combination of the convex shape and the refractive index distribution described above will be described with reference to FIG. First, as shown in (a), a convex lens pattern 10 is formed by a method utilizing heat sag or the like of glass containing a high refractive index metal component. here,
As shown in (b), the mask 11 is applied to expose only a part of the top of the convex surface. Due to the exposed portion of the surface top, the high refractive index component and the low refractive index component contained in the microlens are exchanged by utilizing the diffusion phenomenon. This allows
As shown in (c), the microlens portion has the lowest refractive index at the apex of its convex shape, and a continuous refractive index distribution in which the refractive index gradually increases is formed radially. (D)
Indicates the state after the mask 11 is removed.

At this time, the lens in the peripheral portion exhibits the same effect as a simple convex lens, and collects light. But,
At the top of the convex surface of the lens, the refractive index at the intersection of the optical axis and the surface is the lowest, and since it is a gradient index optical element in which the refractive index increases toward the periphery, this paraxial region Has the same effect as the concave lens, and the incident light is diverged without being condensed. That is, the light in the lens peripheral part (corresponding to the signal reading part) is condensed and the light in the lens center part (corresponding to the inner diameter of the ring-shaped photoelectric conversion part) is diverged to enter from any part on the pixel. The generated light component is also focused on the ring-shaped photoelectric conversion unit. This makes it possible to greatly improve the sensitivity of the device.

The formation of the distribution of the refractive index here is carried out by exchanging the metal component contained in the glass by utilizing the diffusion phenomenon, and by the ion exchange method of immersing the glass in the molten salt. It may be carried out, or after the sol made from the metal alkoxide is gelled, the metal component may be eluted with an acid, or the sol-gel method of exchanging with another metal species in a solvent such as alcohol may be used. It has no effect on the effect of the invention. That is, a gel consisting of a silicon alkoxide and a high refractive index metal component alkoxide is immersed in an acid to elute the high refractive index metal component, or a gel consisting of a silicon alkoxide and a metal salt of a high refractive index metal component, The sol-gel method of exchanging the high-refractive-index component and the low-refractive-index component by immersing it in the alcohol solution containing the salt of the low-refractive-index metal component, and the glass containing the high-refractive-index metal component of the low-refractive-index metal component An ion exchange method can be used in which the high refractive index metal component and the low refractive index metal component are exchanged by immersing in a molten salt. However, since monovalent metal ions have a large diffusion coefficient during the semiconductor manufacturing process and affect the characteristics of the semiconductor, it is more preferable to use divalent or higher-valent metal ions. The sol-gel method that can easily diffuse divalent or higher valent metal ions is suitable for this. In general, the ion exchange method is not used for metal ions having a valence of 2 or more because the diffusion coefficient of the ions in the glass is small, but this is not always the case for a microscopic light-collecting element, and it is impossible in principle. Not a thing.

Further, the light condensing element here is an element for condensing the light flux on the photoelectric conversion part, and does not necessarily have to form an image. Therefore, the convex shape of the lens has a considerable degree of freedom. be able to. For example, as shown in FIG. 4A, it is possible to flatten the upper surface portion 12a of the convex microlens 12 and form the refractive index distribution in the flat portion.

[0018]

Example 1 50 ml of ethanol was added to 83.3 g of Si (OC ₂ H ₅ ) ₄ and 60 ml of 0.01N HCl was added to carry out partial hydrolysis. 1m of lead acetate
100 ml of an ol / l aqueous solution was added to form a sol. This sol was coated on a glass substrate having a mask formed of an organic photoresist. This is to form a hemispherical pattern by utilizing the water-repellent effect of the organic photoresist. After the sol was gelled, the mask was removed to form a convex gel lens pattern. Masking was formed on the obtained substrate so that part of the top surface of the convex gel lens pattern was exposed, and the substrate was coated with 0.5 mol / l of barium acetate methanol: H ₂ O = 2: 8 (vol). Ratio) Soak in the solution for a few seconds,
Then, it was gradually dried in a semi-closed methanol atmosphere. By heat-treating the obtained substrate, a light-collecting element in which a refractive index distribution was formed from the tops of the respective surfaces of the matrix-shaped convex lens pattern was obtained. When this condensing element was used as a ring-shaped photoelectric conversion unit for the image pickup element, high sensitivity was realized.

[0019]

Example 2 0.09 in 59.1 g of Si (OC ₂ H ₅ ) ₄
A hydrolysis reaction was carried out by adding 42 ml of 2N HCl aqueous solution. Here, 0.5 mol / l TlNO ₃ aqueous solution 1
00 ml was added, and 10.0 g of fine silica powder having an average particle diameter of 200 angstrom was added, and ultrasonic waves were applied to form a uniform sol. A 0.2N ammonia solution was added thereto to adjust the pH of the sol to 4.5. This sol was dip-coated on a glass substrate having a mask formed of an organic photoresist. At this time, since the organic photoresist has a water repellent effect, the sol rises in a hemispherical shape. After the sol gelled, the mask material was removed, and then heat treatment was performed to vitrify the sol and form a matrix-shaped convex surface. Further, masking was performed here so that only the top of the convex surface was exposed. This board is N
It was immersed in a molten salt of aNO ₃ to exchange Tl ⁺ for Na ⁺ . After that, the mask was removed to manufacture a microlens having a desired shape and refractive index distribution. When this microlens was used as a light-collecting element of an image sensor having a ring-shaped photoelectric conversion unit, high sensitivity could be realized.

[Comparative Example 1] A microlens was manufactured in the same manner as in Example 2. However, the ion exchange operation was not performed. When this microlens was used as a light-collecting element of an image pickup device having a ring-shaped photoelectric conversion unit, the sensitivity was low.

[0021]

Example 3 A sol similar to that of Example 1 was prepared, and Example 1 was prepared.
A gel-like lens pattern was produced by the same operation as in. This substrate was immersed in an ethanol solution of potassium acetate (0.15 mol / l) for several seconds with the surface on which the convex pattern was formed facing downward, and then the substrate was lifted as it was and allowed to stand in an ethanol atmosphere. By this process, the solution of potassium acetate accumulated on the top of the convex surface of the lens is exchanged with the lead component in the gel, but the exchange amount is limited to the exchange with a small amount of potassium / ethanol accumulated on the top of the lens surface. Lead in the microlens portion does not elute too much. On the contrary, when the exchange amount is too small, the number of steps may be increased. By drying and heat-treating the obtained substrate, a microlens having a desired shape and refractive index distribution could be manufactured.

[0022]

Example 4 A sol prepared in the same manner as in Example 2 was applied on a substrate, and then contacted with a stamper having a pattern as shown in FIG. Photolithography was performed here to fabricate a substrate in which only the optical axis portion of each microlens was exposed. This was immersed in the same solvent salt as in Example 2 to exchange Tl ⁺ for Na ⁺ . As a result, a microlens having a shape and a refractive index distribution as shown in FIG. 4B could be manufactured. When this condensing element was used as a condensing element of an image pickup element having a ring-shaped photoelectric conversion part, high sensitivity was realized. In this example, since the region where the refractive index of the microlens has a distribution has a flat surface and does not have a bending action of light, the distribution shape can be easily controlled.

[0023]

Example 5 Si (OCH ₃ ) ₄ and Ti (O ⁿ C
₄ H ₉ ) ₄ was used as a raw material to form a gel lens pattern. The substrate was masked so that a part of the top of the surface was exposed. This substrate was treated in 1N sulfuric acid to elute the Ti component. The substrate was dried and heat-treated to obtain a matrix light-collecting device. When this condensing element was used as a condensing element of an image pickup element having a ring-shaped photoelectric conversion part, high sensitivity was realized.

[0024]

As described above, according to the integrated light-collecting device for a solid-state image pickup device and the method for manufacturing the same of the present invention, the light incident on the insensitive region on the solid-state image pickup device having the annular photoelectric conversion portion is prevented. It is possible to collect light efficiently, and by doing so, it is possible to achieve miniaturization of the element of the solid-state image sensor and miniaturization of the element and high sensitivity at the same time.

[Brief description of drawings]

FIG. 1 is an optical path diagram showing an optical path of a condensing element having a distribution of refractive index from a convex surface top portion of the present invention.

FIG. 2 is a cross-sectional perspective view of one pixel of a solid-state image sensor in which a photoelectric conversion unit is formed of annular pixels.

FIG. 3 is a process drawing showing an example of the manufacturing method of the present invention.

4A is a front view showing a microlens manufactured in Example 3 of the present invention, and FIG. 4B is a sectional view showing the shape of a stamper used in Example 3 of the present invention.

[Explanation of symbols]

1 Polycrystalline Silicon Gate 2 p ^- Substrate 3 n ^- Channel Layer 4 Holes 5 SiO ₂ Layer 6 n ⁺ Source Layer 7 Source 8, 12 Microlens 9 Photoelectric Conversion Section 10 Lens Pattern 11 Mask

Claims (3)

[Claims] 1. A condensing element for use as a photoelectric conversion part of a pixel integrally provided in a substantially annular solid-state imaging device, wherein a lens pattern, at least a part of which has a convex shape, is provided at a predetermined position of the condensing element. An integrated light-collecting device for a solid-state imaging device, characterized in that a distribution is formed in a refractive index from an intersection of an optical axis of the lens pattern and a lens surface. 2. In manufacturing the integrated light-collecting device for a solid-state image pickup device according to claim 1, after forming a convex lens pattern for each pixel using glass containing a high refractive index metal component as a raw material. A method for manufacturing an integrated light-collecting device for a solid-state image pickup device, which comprises performing a masking process and forming a refractive index distribution by bringing a part of the lens pattern into contact with a molten salt of a low-refractive-index metal component. . 3. In manufacturing the integrated light-collecting device for a solid-state imaging device according to claim 1, a sol containing a high refractive index metal component is used as a raw material, and a convex gel lens pattern is formed for each pixel. After that, a masking process is performed, and a part of the gel lens pattern is brought into contact with a solution containing a low refractive index metal component or an acid to form a refractive index distribution. A method for manufacturing a body type light condensing element.