JP5353356B2 - Solid-state imaging device and manufacturing method thereof - Google Patents

Description

  The present invention relates to a solid-state imaging element in which a photoelectric conversion element composed of a CCD or a CMOS is formed, and a manufacturing method thereof.

  In recent years, imaging devices have been widely used with the expansion of the contents of image recording, communication, and broadcasting. Various types of imaging devices have been proposed, but imaging devices using solid-state imaging devices that have been stably manufactured with small size, light weight, and high performance have 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, a color sensor that can obtain color information of an object by providing various color filters that transmit light of a specific wavelength in the path of light incident on the photoelectric conversion element is also widespread. As the color of the color filter, three primary colors consisting of three colors of red (R), blue (B), and green (G), or cyan (C), magenta (M), and yellow (Y) are used. A complementary color system is generally used.

  One of the important issues in performance required for a solid-state imaging device is to improve the sensitivity to incident light. In order to increase the amount of information of a photographed image, it is necessary to miniaturize and highly integrate a photoelectric conversion element serving as a light receiving unit. However, when the photoelectric conversion element is miniaturized, the area of each photoelectric conversion element is reduced, and the area ratio that can be used as the light receiving unit is also reduced. The amount is reduced and the sensitivity is reduced.

  As a means for preventing such a decrease in sensitivity of the miniaturized solid-state imaging device, in order to efficiently capture light into the light receiving portion of the photoelectric conversion device, the light incident from the object is condensed and photoelectrically A technique for forming a microlens that leads to a light receiving portion of a conversion element has been proposed. By condensing the light with a microlens and guiding it to the light receiving part of the photoelectric conversion element, it becomes possible to increase the apparent aperture ratio (area) of the light receiving part and improve the sensitivity of the solid-state image sensor Become. However, if the solid-state imaging device is further miniaturized, it becomes more difficult to form a miniaturized microlens while maintaining a normal shape with an accurate positional accuracy, so that a sufficient effect may not be obtained. is there.

  On the other hand, the light receiving portion of the photoelectric conversion element provided on the silicon substrate is arranged away from the transistor and the wiring region, so that the aperture ratio of the light receiving portion region is increased particularly when many miniaturized photoelectric conversion elements are arranged. It is difficult. In order to improve this, there is also a technique called a back-illuminated solid-state imaging device in which a photoelectric conversion element is provided on the back side of one side of a silicon substrate on which transistors and wiring layers are formed, and the back side is a light receiving part. It has been proposed (see Patent Document 1).

  The photoelectric conversion element converts the incident light into an electrical signal, but when the light does not enter the predetermined photoelectric conversion element and enters a different photoelectric conversion element (for example, an adjacent photoelectric conversion element), Noise is generated. In particular, in the case of a color sensor provided with a color filter, if light passing through the color filter enters a photoelectric conversion element corresponding to a different color, a problem of color mixing occurs in an obtained image. Such a problem due to erroneous incidence is likely to occur in light incident on the photoelectric conversion element from the boundary portion between adjacent photoelectric conversion elements or from an oblique direction. For this reason, in order to prevent incident light from entering a photoelectric conversion element different from the desired photoelectric conversion element, a technique for providing a light shielding wall between the side edge of the solid-state image sensor and individual color filters has been proposed. ing.

  The situation described above is also the same in the back-illuminated solid-state image sensor, but in the case of the back-illuminated solid-state image sensor, a wiring layer provided on the side opposite to the light receiving portion as viewed from the photoelectric transducer is between the photoelectric transducers. The problem of noise and color mixing is even greater because the incident light is reflected through the gaps and becomes scattered light or stray light inside the solid-state image sensor, causing it to be received by an inappropriate photoelectric conversion element. Influence.

JP 2005-259828 A

  The present invention has been made in view of the above-mentioned problems, and the problem is that in a back-illuminated solid-state imaging device, light incident through a gap between photoelectric conversion elements is reflected by a wiring layer. It is to propose a solid-state imaging device and a method for manufacturing the same that prevent the occurrence of noise and color mixing problems due to reflected light.

  As means for solving the above problems, the invention according to claim 1 is a thin film plate-like silicon layer, a wiring layer provided on one side of the silicon layer, and the wiring of the silicon layer. A plurality of photoelectric conversion elements formed on the surface opposite to the layer facing the light receiving portion, and the surface on which the photoelectric conversion elements of the silicon layer are formed, and formed in a gap between adjacent light receiving portions Protruding portions made of silicon, flattening transparent layers that cover the protruding portions made of silicon and forming a flat surface, and provided on the upper surface of the flattening transparent layer in correspondence with each of the photoelectric conversion element light receiving portions And a color filter.

  The invention according to claim 2 is characterized in that a microlens is provided on the upper surface of the color filter corresponding to each of the light receiving portions of the photoelectric conversion element. It is.

  The invention according to claim 3 is a method of manufacturing the solid-state imaging device according to claim 1 or 2, wherein the convex portion made of silicon is integral with the silicon layer, and the convex portion made of silicon. The step of forming the portion is a method of manufacturing a solid-state imaging device, wherein one side of the thin film plate-like silicon layer is selectively etched.

  According to the solid-state imaging device of the present invention, in the back-illuminated solid-state imaging device, the projected portion made of silicon blocks the incident light from passing through the gap between the photoelectric conversion devices, so that the light reflected by the wiring layer is given. As a result, a phenomenon that part of incident light is received by an inappropriate photoelectric conversion element does not occur. For this reason, it is possible to provide a solid-state imaging device that does not cause noise and color mixing problems.

  Further, according to the method for manufacturing a solid-state imaging device of the present invention, the step of forming the convex portion made of silicon selectively etches one surface of the thin film plate-like silicon layer. Since the position accuracy of the planar arrangement of the projections made of silicon and the uniformity of the height can be obtained well, the positional relationship with the color filter and microlens formed in the subsequent process is highly accurate. The overall height of the solid-state imaging device can be controlled well. For this reason, a high quality solid-state image sensor can be manufactured.

  Furthermore, according to the method for manufacturing a solid-state imaging device of the present invention, the convex portion made of silicon is a portion that remains after being selectively etched from the thin film plate-like silicon layer. Compared with the case where the portion is provided, not only the process is simple, but also those having stable material characteristics that affect the reliability of the element can be used. For this reason, a high-quality solid-state imaging device can be manufactured at low cost.

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

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings. It should be noted that the following schematic cross-sectional views are all enlarged views of a part of the solid-state imaging device, and needless to say, are appropriately connected to the left and right in the drawing. FIG. 1 is a schematic cross-sectional view for explaining an example of a solid-state imaging device according to the present invention. An insulating layer 90 is arranged on one surface side of a thin-film silicon layer 10 made of a silicon substrate. 20 is provided. The wiring layer 20 usually has a multilayer wiring structure made of a metal such as aluminum, and transmits an electrical signal from a photoelectric conversion element described later. A plurality of photoelectric conversion elements 30 formed on the surface of the silicon layer 10 opposite to the wiring layer 20 so as to face the light receiving section, and a plurality of light receiving section gaps on the surface of the silicon layer 10 on the photoelectric conversion element light receiving section side. A convex portion 40 made of silicon disposed on the top, a flattened transparent layer 50 covering the convex portion made of silicon and forming a flat surface, and an upper surface of the flattened transparent layer 50 of the photoelectric conversion element light receiving portion. Color filters 61, 62, 63 provided corresponding to each of them. The color filters 61, 62, and 63 represent a series of adjacent pixels of different colors.

  FIG. 3 is a schematic cross-sectional view for explaining another example of the solid-state imaging device of the present invention. A microlens 70 is provided on the upper surface of each pixel of the color filters 61, 62, and 63 shown in FIG. In this example, the microlens 70 is provided corresponding to each of the photoelectric conversion element light receiving portions. However, in the drawing, the microlens 70 is provided only on the upper surface of the central color filter pixel 62 for the sake of simplicity. Was written. Although the incident light 81 and 82 indicated by arrows are only partially shown, the light from the image to be imaged is also a color filter in FIGS. 1 and 3 and FIGS. 2 and 4 described later. This means pouring over the entire top surface. 3 and 4 show that the incident light 81 reaches the light receiving surface of the photoelectric conversion element 30 while being focused by the microlens 70. On the other hand, the incident light 82 passes through a pixel 63 different from the pixel 62 through which the incident light 81 passes in the vicinity of the gap between the color filter pixels, and is blocked by the convex portion 40 made of silicon in FIGS.

FIG. 2 is a schematic cross-sectional view for explaining an example of a conventional solid-state imaging device, and FIG. 4 is a schematic cross-sectional view for explaining another example of a conventional solid-state imaging device. 2 and 4, there is no convex portion 40 made of silicon, and a relatively thin silicon layer 1 compared to the convex portion 40 made of silicon.
Since the shielding effect by 0 is not sufficient, a certain percentage of the incident light 82 enters the surface of the wiring layer and is reflected by the surface of the wiring layer 20 on the incident light side. As described above, in the back-illuminated solid-state image sensor, light incident through the gap between the photoelectric conversion elements is reflected by the wiring layer, and this reflected light becomes scattered light or stray light inside the solid-state image sensor, resulting in noise. And easily cause color mixing problems.

  The convex portion 40 made of silicon is originally integral with the thin film plate-like silicon layer 10 made of a silicon substrate. That is, when the photoelectric conversion element 30 is formed in the silicon substrate according to a normal photodiode manufacturing process and then the light receiving surface of the photoelectric conversion element 30 is opened, the periphery of each photoelectric conversion element 30 By leaving only the silicon layer located at the part, the remaining part of the silicon layer is used as a convex part, and is formed by utilizing a part of the original silicon layer.

The formation process of the convex part 40 made of silicon will be described with reference to the drawings.
FIG. 5 is a schematic cross-sectional view for explaining an example of the manufacturing method of the solid-state imaging device of the present invention, which is shown in the order of steps (a) and (b). The silicon layer 11 shown in FIG. 5A is the same as the silicon layer 10 of FIGS. 1 to 4, but the silicon layer region as the formation region of the photoelectric conversion element 30 is replaced with another processed silicon layer region. Represented separately. The light receiving part is directed to the surface (the back side of the silicon substrate) opposite to the surface on which the wiring layer 20 is formed (the front side of the silicon substrate), and on the side close to the wiring layer 20 inside the silicon substrate of the material, The photoelectric conversion elements 30 are arranged and provided by a normal semiconductor wafer process. In addition, an insulating layer 90 is disposed on the surface (front side) opposite to the surface on which the photoelectric conversion element of the silicon substrate is formed. The wiring layer 20 is formed in the insulating layer 90 and a photolithography step. To form. In the case where the wiring layer 20 is a multilayer wiring layer, an interlayer insulating layer and a conductive portion are included in the configuration, but this is performed by a normal method, and detailed description in the drawings is omitted. Thereafter, a predetermined amount of silicon is polished from the back surface of the silicon substrate using a grinder. Polishing is performed so that at least the height of the convex portion made of silicon, which will be described later, is a thickness that allows a desired height to be obtained. FIG. 5B shows a process of processing the silicon layer 12 above the light receiving portion in which the photoelectric conversion elements 30 are arranged except for the silicon layer 13 in the polishing removal region.

  The silicon layer 12 can be patterned by etching to obtain a convex portion 40 made of silicon. The etching can be performed by either wet etching using sulfuric acid, hydrochloric acid or hydrofluoric acid, or dry etching using fluorine or other halogen gas. Specific means is selected depending on the etching rate ratio with the masking material for etching and the low undercut at the time of etching, but the use of dry etching is generally suitable for forming a fine pattern. The region of the silicon layer 14 becomes a region finally removed by dry etching. The region 14 where the silicon layer is removed by dry etching is a region where the light receiving portion of the photoelectric conversion element 30 is opened. The convex portion 40 made of silicon is desirably formed so as to cover the gap between adjacent photoelectric conversion elements.

A manufacturing method from the formation of the convex portion 40 made of silicon to the completion of the solid-state imaging device will be described below.
In order to provide a color filter corresponding to the arrangement of the photoelectric conversion elements 30 provided with the convex portions 40 made of silicon on the gap, so as to cover the entire effective area of the photoelectric conversion elements 30 and the convex portions 40 made of silicon, A flattened transparent layer 50 is formed. Since the flattening transparent layer 50 is provided for flattening the base surface on which the color filters 61, 62 and 63 are formed, unlike the conventional case without the convex portion 40 made of silicon, the flattening transparent layer 50 is sufficient in the present invention. Thickness and flatness are required. When forming a flattened transparent layer 50 by applying a transparent resin, depending on the viscosity of the transparent resin, if a sufficient thickness cannot be obtained by a single application, the transparent resin is divided into a plurality of times. It can be formed by applying and laminating.

  The color filters 61, 62, and 63 select a colored photosensitive resin according to a predetermined color, perform pattern exposure and development, and repeat a photolithography method using the remaining colored photosensitive resin film as each color layer. Form.

  When the microlens 70 is provided, a resin pattern is formed at a position corresponding to each pixel of the photoelectric conversion element 30 and the color filters 61, 62, and 63 by a photolithography method, and then the surface tension of the molten resin is increased by a thermal reflow method. It can be used to form a lens.

  As described above, according to the solid-state imaging device of the present invention, in the back-illuminated solid-state imaging device, the projections made of silicon block the incident light from passing through the gaps between the photoelectric conversion elements, or the thickness of the silicon is thick. As a result, the attenuation when light passes through the silicon part including the convex part is increased, so that the light reflected by the wiring layer is not given, and as a result, a part of the incident light becomes an inappropriate photoelectric conversion element. The phenomenon that light is received does not occur. In particular, a linear sensor (line sensor) with photoelectric conversion elements arranged in a row is different from an area sensor (surface sensor) in which photoelectric conversion elements are arranged two-dimensionally vertically and horizontally, and there is another photoelectric conversion element next to it. Since the incident light from the vicinity of the side that is not to be blocked can be blocked by the convex portion made of silicon, a particularly great effect can be obtained.

  Further, the back-illuminated solid-state imaging device of the present invention mainly prevents incident light from passing through the gaps between the photoelectric conversion elements and preventing the reflected light from being generated on the wiring layer by the projections made of silicon. However, even in a general solid-state imaging device that is not a back-illuminated type, it can be easily considered that the convex portion made of silicon can be used as a light-shielding wall between pixels by arranging the convex portions made of silicon in the gaps between the photoelectric conversion devices. .

10 ... Silicon layer 11 ... Silicon layer (photoelectric conversion element formation region)
12 ... Silicon layer (Silicon protrusion formation region)
13 ... Silicon layer (polishing removal area)
14 ... Silicon layer (dry etching removal region)
DESCRIPTION OF SYMBOLS 20 ... Wiring layer 30 ... Photoelectric conversion element 40 ... Convex part 50 which consists of silicon ... Flattening transparent layers 61, 62, 63 ... Color filter 70 ... Micro lens 81, 82. ..Incoming light 90 ... insulating layer

Claims (3)

  A thin film plate-like silicon layer, a wiring layer provided on one side of the silicon layer, and a plurality of photoelectric conversions formed on the surface of the silicon layer opposite to the wiring layer with the light receiving portion facing On the surface side of the element and the photoelectric conversion element of the silicon layer, a convex part made of silicon formed in a gap between adjacent light receiving parts, and a flat surface covering the convex part made of silicon are formed A solid-state imaging device comprising: a flattening transparent layer to be formed; and a color filter provided on an upper surface of the flattening transparent layer in correspondence with each of the photoelectric conversion element light receiving portions.   2. The solid-state imaging device according to claim 1, wherein a microlens is provided on the upper surface of the color filter corresponding to each of the photoelectric conversion element light receiving portions.   3. The method of manufacturing the solid-state imaging device according to claim 1, wherein the convex portion made of silicon is integrated with the silicon layer, and the step of forming the convex portion made of silicon is the thin film plate shape. A method for manufacturing a solid-state imaging device, wherein one side of a silicon layer is selectively etched.

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