JP2012019072A - Solid-state image sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid-state image sensor which can obtain uniform sensitivity in a light receiving element surface.SOLUTION: The solid-state imaging sensor comprises a wiring layer 3 disposed on the side of irradiation light for imaging of a plurality of light receiving elements 2 including photoelectric conversion elements provided in the vicinity of a surface of a semiconductor substrate 1 on the reception side of the irradiation light for imaging 10 so as to surround the light receiving elements 2 in plan view, an insulation layer 41 covering the light receiving elements 2 and the wiring layer 3 and having a recess, and a planarization layer 51 with a flat surface formed by covering and filling the recess. A refraction index of the insulation layer 41 and a refraction index of the planarization layer 51 are approximated.

Description

  The present invention relates to a solid-state imaging device in which a photoelectric conversion device such as a CCD or a CMOS is formed.

  In recent years, imaging devices have been widely used with the expansion of the contents of image recording, communication, and broadcasting. Various types of image pickup devices have been proposed. An image pickup device incorporating a solid-state image pickup device that has been stably manufactured with a small size, light weight, and high performance can be used as a digital camera or digital video. It has become widespread.

  The solid-state imaging device has a plurality of photoelectric conversion elements that receive an optical image from a subject and convert incident light into an electrical signal. The types of photoelectric conversion elements are roughly classified into CCD (charge coupled device) type and CMOS (complementary metal oxide semiconductor) type. In addition, there are two types of photoelectric conversion elements: linear sensors (line sensors) in which photoelectric conversion elements are arranged in a row, and area sensors (surface sensors) in which photoelectric conversion elements are two-dimensionally arranged vertically and horizontally. It is divided roughly into. In any sensor, the larger the number of photoelectric conversion elements (number of pixels), the more accurate the captured image.

  In addition, color sensors that can obtain color information of an object by providing various color filters that selectively transmit light in a specific wavelength region in the path of light incident on the photoelectric conversion element are also widespread. ing. As the color of the color filter, three primary colors composed of three colors of red (R), green (G), and blue (B), cyan (C), magenta (M), and yellow (Y) are used. A complementary color system is generally used.

  The general structure of the solid-state image sensor is shown in the schematic cross-sectional view of FIG. A silicon wafer is generally used as the semiconductor substrate 1, and a general semiconductor process on the wafer surface and a wiring pattern forming process are repeated to form a solid-state imaging device group in which a large number of chips are arranged on the wafer plane. FIG. 2 shows a partially enlarged cross-section of one chip. The light receiving element 2 made of a photoelectric conversion element such as a CCD or CMOS is regularly arranged near the surface of the semiconductor substrate 1 on the side receiving the imaging irradiation light 10. The pattern of the wiring layer 3 using a metal material such as aluminum is provided on the side of the imaging light on the light receiving element 2 so as to surround the light receiving element 2 in plan view. An insulating layer 4 that covers the light receiving element 2 at a low position and a wiring layer 3 having a protruding shape that is usually a multilayer sandwiching an interlayer insulating layer (not shown) constitutes a recess, and covers and fills the recess. It has the planarization layer 5 which formed the flat surface.

  In many cases, in order to use the solid-state imaging device as a color sensor, a colored pixel pattern is formed on the planarizing layer 5 in a one-to-one correspondence with the light-receiving element to protect the colored layer. The protective layer 7 is provided. Further, if necessary, a microlens (not shown) is formed so as to increase the light capturing efficiency for imaging and contribute to the improvement of the sensitivity of the imaging device.

  Like the smoothing layer proposed in Patent Document 1, the flattening layer 5 tends to follow surface irregularities during coating in addition to excellent transparency, adhesion, and chemical resistance. A resin with a small amount is applied to obtain a flattened surface after application. Specifically, by adjusting the material characteristics of the acrylic transparent resin, it is possible to realize a flattened layer excellent in flatness and surface unevenness filling.

Japanese Patent Laid-Open No. 5-70735

  As described above, the pattern of the wiring layer 3 using a metal material such as aluminum is provided on the light-receiving element 2 on the imaging irradiation light side so as to surround the light-receiving element 2 in a plan view. And the insulating layer 4 that covers the multi-layered projecting wiring layer 3 constitutes a recess, and the layer formed so as to cover and fill the protrusion corresponding to the recess is the planarizing layer 5. is there. In this structure, since the refractive index of the insulating layer 4 constituting the concave portion and the refractive index of the planarizing layer 5 formed in a shape including the convex portion generally do not coincide with each other, the insulating layer 4 on the side that receives the imaging irradiation light 10. And the planarization layer 5 produce a certain lens effect. For example, in contrast to the insulating layer 4 made of a silicon oxide film having a refractive index n of 1.45 and forming a concave portion, the planarizing layer 5 made of an acrylic transparent resin having a refractive index n of 1.55 and forming a convex portion. Functions as a convex lens toward the light receiving element 2 that receives the irradiation light 10 for imaging.

  When the solid-state imaging device is miniaturized and the period of the unevenness is reduced, the end portion of the metal pattern of the wiring layer 3 approaches the light receiving element 2 in a plan view. Incident light from the outside at the time of imaging is refracted at various positions due to the lens effect described above, and is applied to the end portion of the metal pattern, and reflection of light at the end portion is added. The distribution of the amount of received light changes depending on the positional relationship from the end of the metal pattern in the plane, and the in-plane distribution of sensitivity becomes non-uniform.

  Furthermore, when the wiring layers are formed in multiple layers and misalignment occurs between the wiring layers, asymmetric distortion occurs in the sensitivity distribution. Note that when a microlens is provided in the imaging path so as to contribute to the improvement of the sensitivity of the imaging device, external light can be collected on a pixel basis by the microlens, so that the influence of the above-mentioned sensitivity on the pixel surface is relatively small. can do. However, it is not only a phenomenon that affects the sensitivity distribution of a simple solid-state image sensor that does not use a microlens, but also a problem in the basic performance of the solid-state image sensor, and it imposes certain restrictions on the performance design of the imaging device. Will give.

  The present invention is proposed in view of the above-mentioned problems, and the problem to be solved by the present invention is to provide a solid-state imaging device capable of obtaining uniform sensitivity within the light receiving element plane.

  As a means for solving the above-mentioned problem, the invention according to claim 1 is directed to an imaging illumination on a plurality of light receiving elements comprising photoelectric conversion elements provided in the vicinity of the surface of the semiconductor substrate on the side receiving the imaging illumination light. A flat surface having a wiring layer on the light side so as to surround the light receiving element in a plan view, an insulating layer covering the light receiving element and the wiring layer forming a recess, and covering and filling the recess In the solid-state imaging device having the planarization layer, the refractive index of the insulating layer and the planarization layer is approximated.

  The invention according to claim 2 is characterized in that the refractive index of the planarizing layer is equal to or greater than the refractive index of the insulating layer within a range of 0 to 0.02. It is a solid-state image sensor.

  The invention according to claim 3 is the solid-state imaging device according to claim 1 or 2, wherein the insulating layer is made of a silicon oxide film.

  The invention according to claim 4 is the solid-state imaging element according to claim 1 or 2, wherein the insulating layer is made of a silicon nitride film.

  The present invention relates to a light receiving element by approximating the refractive index of an insulating layer that covers the light receiving element and the wiring layer, and a planarizing layer that covers and fills a recess formed by the insulating layer to form a flat surface. It is possible to provide a solid-state imaging device capable of obtaining in-plane sensitivity uniformly.

It is a cross-sectional schematic diagram for demonstrating the structural example of the solid-state image sensor of this invention. It is a cross-sectional schematic diagram for demonstrating the structural example of the conventional solid-state image sensor.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.
FIG. 1 is a schematic cross-sectional view for explaining a configuration example of a solid-state imaging device of the present invention. Generally, a silicon wafer is used as the semiconductor substrate 1, and by repeating a general semiconductor process on the wafer surface and a wiring pattern formation process, a solid-state imaging element group in which a large number of chips are arranged on the wafer plane is formed. It is the same as the conventional one. The light receiving element 2 composed of a photoelectric conversion element such as a CCD or CMOS is provided in a regular arrangement near the surface of the semiconductor substrate 1 on the side receiving the imaging irradiation light 10, and the imaging irradiation light on the light receiving element 2. On the side, a pattern of the wiring layer 3 using a metal material such as aluminum is provided so as to surround the light receiving element 2 in a plan view. An insulating layer 41 that covers the light receiving element 2 at a low position and a wiring layer 3 having a protruding shape that is usually a multilayer sandwiching an interlayer insulating layer (not shown) constitutes a recess, and covers and fills the recess. It is the same as that of the prior art that the flattening layer 51 having a flat surface is formed.

  The insulating layer 41 desirably has excellent transparency, adhesion, and chemical resistance in addition to electrical insulation, and a silicon oxide film or nitride film used as the semiconductor substrate 1 is formed by using low pressure CVD or plasma. It can be formed by a normal process such as CVD.

  In addition to being excellent in transparency, adhesion, and chemical resistance, the planarizing layer 51 is coated with a resin that is less likely to follow surface irregularities during coating, and the surface after coating is planarized. Get. For example, by adjusting the acrylic transparent resin having low molecular weight and low viscosity material characteristics to a high concentration, it is possible to realize a flattening layer excellent in flatness and surface unevenness filling property.

  In order to use the solid-state imaging device as a color sensor, the colored layer 6 is formed on the planarizing layer 51 as a colored pixel pattern corresponding to the light receiving device in a one-to-one correspondence. A protective layer 7 can be provided. Further, if necessary, a microlens (not shown) can be formed so as to increase the light capturing efficiency for imaging and contribute to the improvement of the sensitivity of the imaging device.

  As the colored pixel pattern to be formed on the colored layer 6, for example, a photosensitive negative resist, which is a green pigment dispersion resin, is applied, and a green pattern is formed through prebaking, selective exposure, development, and heat treatment steps. Thereafter, the same means is repeated to form a blue pattern and a red pattern in order at adjacent positions, and a three-color colored pixel pattern arranged periodically so as to fill the effective area can be obtained.

  The boundary surface between the insulating layer 41 and the planarization layer 51 usually produces a lens effect, and due to the refraction of the imaging irradiation light at the boundary surface, a part of the optical path of the irradiation light is applied to the end of the metal pattern. The reflection of light at the end portion is added, and the distribution of the amount of received light changes depending on the positional relationship from the end portion of the metal pattern in the plane of the light receiving element 2, and the in-plane distribution of sensitivity becomes non-uniform. In order to prevent the above phenomenon, the present invention approximates the refractive indexes of the insulating layer 41 and the planarizing layer 51 and virtually eliminates the interface between the two indicated by the dotted line in an optical sense. It is characterized by.

  If the relationship between the insulating layer 41 that forms the concave portion directly above the light receiving element 2 and the planarization layer 51 that fills the concave portion and forms the convex portion, if the refractive index of the latter is larger than the former, It has the effect of a convex lens with respect to the incidence of imaging irradiation light on the light receiving element, and has the effect of a concave lens in the opposite case. In the case of having the effect of a concave lens, it is clear that the irradiation light spreads and tends to be applied to the end of the metal pattern of the wiring layer 3, which is not preferable. Even in the case of having the effect of a convex lens, if the solid-state imaging device is miniaturized and the period of the unevenness is reduced, undesired reflection at the end of the metal pattern is caused by the degree of light refraction.

  Due to the above circumstances, in the present invention, when the details of approximating the refractive index of the insulating layer 41 and the planarizing layer 51 are further defined, the refractive index of the planarizing layer is 0 than the refractive index of the insulating layer. More preferably, it is characterized by being equal or larger within a range of .about.0.02. Since the planarization layer 51 has no concave lens effect at all for the incidence of the imaging irradiation light to the light receiving element, the irradiation light does not spread and has no clear convex lens effect. Even if the solid-state imaging device is miniaturized so that the period of the unevenness is reduced, undesired reflection at the end of the metal pattern is not caused. As a result, it is possible to avoid the phenomenon that the distribution of the amount of received light changes depending on the positional relationship from the end of the metal pattern in the plane of the light receiving element 2, and to provide a solid-state imaging element that can obtain uniform sensitivity in the surface of the light receiving element. be able to.

  As described above, the insulating layer 41 can be formed of a silicon oxide film or nitride film used as the semiconductor substrate 1 by a normal process such as low pressure CVD or plasma CVD. A silicon oxide film having a refractive index of about 1.45 can be obtained. In the silicon nitride film, the ratio of nitrogen to silicon in the film changes depending on the film forming conditions such as the substrate temperature, and films having different optical characteristics can be obtained in the range of refractive index of about 1.75 to 2.0.

  When the planarizing layer 51 is made of an acrylic transparent resin having a refractive index of 1.55 as a base as described above, the refractive index of the resin base is increased or decreased according to the refractive index of the insulating layer 41 described above. It is necessary. For example, when the silicon oxide film is used as the insulating layer 41, the refractive index of the planarizing layer is decreased by 0.08 to 0.1. Although it is most desirable to make the refractive index of the planarization layer 51 coincide with the refractive index of 1.45 of the insulating layer 41, it is also preferable to reduce the original 1.55 to 0.046 to 1.46.

  As in the above example, as a method of reducing the refractive index of the original resin, a method of adding fluorine is possible. For example, the transparency, adhesion, chemical resistance, and flatness without following the surface irregularities during coating can be obtained by adjusting the acrylic transparent resin having low molecular weight and low viscosity material properties to a high concentration. It can be adjusted to add the low refractive index characteristic of fluorine while maintaining the coating characteristics excellent in surface irregularity filling property.

  When the silicon nitride film is the insulating layer 41 and the refractive index of the insulating layer is 1.75, it is appropriate to adjust the refractive index of the planarizing layer 51 to 1.75 to 1.77. As in the previous example, when an acrylic transparent resin having a refractive index of 1.55 is used as a base, the refractive index of the planarizing layer 51 is increased by 0.2 to match the refractive index of the insulating layer 41 of 1.75. Is most desirable, but it is also preferable to increase the original 1.55 by 0.21 to 1.76.

  As a method of increasing the refractive index of the original resin as in the above-described example, a technique of adding fine refractive index ceramics that does not cause light scattering loss is possible. For example, the transparency, adhesion, chemical resistance, and flatness without following the surface irregularities during coating can be obtained by adjusting the acrylic transparent resin having low molecular weight and low viscosity material properties to a high concentration. It can be adjusted to add the high refractive index characteristics of the high refractive index fine-particle ceramics that do not cause light scattering loss while maintaining the coating characteristics excellent in surface irregularity filling properties.

  As the high-refractive-index fine-particle ceramics that do not cause light scattering loss, various metal oxides such as titanium oxide, zirconium oxide, chromium oxide, and zinc oxide can be used as fine particles. Since the suitability for addition to the resin depends on detailed conditions, it must be optimized.

DESCRIPTION OF SYMBOLS 1 ... Semiconductor substrate 2 ... Light receiving element 3 ... Wiring layer 4, 41 ... Insulating layer 5, 51 ... Flattening layer 6 ... Colored layer 7 ... Protective layer 10 ... Imaging light

Claims (4)

  A wiring layer is provided on the plurality of light-receiving elements on the plurality of light-receiving elements including photoelectric conversion elements provided in the vicinity of the surface of the semiconductor substrate on the side receiving the irradiation light for image pickup so as to surround the light-receiving elements in a plan view. In a solid-state imaging device having a flattening layer in which an insulating layer covering the element and the wiring layer forms a concave portion and a flat surface is formed by covering and filling the concave portion, the refractive index of the insulating layer and the flattening layer is A solid-state imaging device characterized by being approximated.   2. The solid-state imaging device according to claim 1, wherein a refractive index of the planarizing layer is equal to or greater than a refractive index of the insulating layer within a range of 0 to 0.02.   The solid-state imaging device according to claim 1, wherein the insulating layer is made of a silicon oxide film.   The solid-state imaging device according to claim 1, wherein the insulating layer is made of a silicon nitride film.

Images