JP2013030666A - Manufacturing method of microlens and mask for exposure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of microlenses provided on a solid state image sensor so that a high focusing performance is given by narrowing the gap to an adjoining microlens, and each microlens has a uniform shape.SOLUTION: The manufacturing method of microlenses 7 in a solid state image sensor 10 comprises a step for providing a first layer 81 composing the microlenses, laminating a second layer 85 composing the microlenses on the first layer in a shape different from that of the first layer, and forming the microlenses of desired shape by integrating both layers by heat treatment. The first layer has a shape including a radial pattern from the center of each pixel toward the pixel boundary, and the second layer has a shape close to the polygonal shape of each pixel in a convex figure pattern not exceeding the pixel boundary.

Description

  The present invention relates to improving the performance of a microlens provided in a solid-state imaging device.

  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 of the sensors, as the number of photoelectric conversion elements (number of pixels) increases, the captured image becomes more precise. In recent years, in particular, a method for manufacturing a solid-state imaging element having a large number of pixels at low cost has been studied.

  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 an image photographed with a miniaturized solid-state imaging device, it is necessary to miniaturize and highly integrate a photoelectric conversion device 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. And the effective sensitivity decreases.

  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 has been proposed in which a microlens that leads to a light receiving portion of a conversion element is formed on the photoelectric conversion element. By condensing the light with the microlens and guiding it to the light receiving portion of the photoelectric conversion element, the apparent aperture ratio of the light receiving portion can be increased, and the sensitivity of the solid-state imaging device can be improved.

  A microlens manufacturing method is a flow lens type in which a transparent acrylic photosensitive resin, which is a microlens material, is selectively patterned by photolithography, and then the lens shape is created using the thermal reflow characteristics of the material. Also, on the flat layer of acrylic transparent resin that is the material of the microlens, a lens matrix is formed by photolithography and thermal reflow using a resist material having alkali solubility, photosensitivity, and heat flow, and dry etching. There is a transfer type in which a lens shape is transferred to an acrylic transparent resin layer by a method.

In forming a microlens, the microlens has a large light capturing area as much as possible, that is, a gap between adjacent microlenses, even in the case of dealing with pixels miniaturized by any of the above-described manufacturing methods of the flow lens type and the transfer type. It is a necessary condition to keep the effective sensitivity of the solid-state imaging device high to keep the lens shape small and to keep the lens shape good. However, for example, when manufacturing with the flow lens method, it is difficult to maintain a narrow gap and good shape by controlling the thermal reflow behavior of abundant amounts of resin at the boundary between adjacent microlenses. It becomes an unstable factor of quality.
In addition, in a color solid-state imaging device for inputting a color image using a color filter, the size of a microlens provided on a colored pixel corresponding to a pixel for each photoelectric conversion device, a gap with an adjacent microlens, or the lens itself If the light collecting performance varies due to variations in shape, the balance of sensitivity for each color will be lost and defects such as unevenness in color expression will clearly occur, so there is a greater need to improve the performance of microlenses. Become.

  As described above, in order to narrow the gap between adjacent microlenses and to maintain a good lens shape, the process of dividing the target area where the microlens manufacturing process is performed by pixel division and including the photolithography method separately. Has been proposed (see Patent Document 1 and Patent Document 2). FIG. 2 is a partial schematic view for explaining a method of forming a microlens in two stages by such region division by pixel division. FIGS. 2A and 2B illustrate the pattern of the main part of an exposure mask used when forming a microlens, taking as an example the case where a checkered pattern array called a Bayer array is applied to a color filter. (C) is a structure of a color solid-state imaging device as a result of forming a microlens by a two-step photolithography method using each exposure mask shown in (a) and (b). It is a schematic cross section which shows an example.

  In FIG. 2C, the color solid-state imaging device 1 is transparently flattened on the light-receiving surface side surface 4 of the solid-state imaging device pixel portion in which a plurality of photoelectric conversion elements 3 regularly provided on the semiconductor substrate 2 are arranged in a plane. A colored transparent pixel pattern 6 that repeatedly arranges a plurality of colors is provided in a one-to-one correspondence with the plurality of photoelectric conversion elements 3 via the layer 5, and the colored transparent pixel pattern 6 is further formed by the second transparent planarization layer 51. After performing planarization on the arranged planes, the microlenses 71 and 72 are provided.

An example of applying a checkered pattern arrangement called a Bayer arrangement to a color filter is often used for a color solid-state imaging device. Considering the light condensing by the microlens, it is difficult to elongate the shape of the element, and increasing the number of photoelectric conversion elements corresponding to each of the three miniaturized pixels also has a manufacturing constraint. The reason why the Bayer array is used is to reduce the total number of pixels without reducing the apparent resolution.
In the Bayer array, one pixel corresponds to a color filter pixel of one color, and a set of arrays is repeatedly arranged by four pixels in which two G (green) pixels are arranged diagonally. In this arrangement, the total number of pixels N of the photoelectric conversion elements is N / 2 for G (green) and N / 4 for R (red) and B (blue). A set of N RGB is created by performing an interpolation operation using the output of surrounding pixels for each pixel. Here, the reason why the number of G (green) pixels is twice as large as that of other colors is that the resolution for G, which is highly visible to human eyes, increases the apparent resolution.

  In FIG. 2A, when one set of four pixels of the colored transparent pixel pattern 6 of the Bayer-arranged color filter is enlarged and displayed, it is made to correspond to G (green) pixels that are diagonally arranged and have no R and B display. Then, the micro lens exposure mask pattern 73 is aligned and used in the exposure process of the photolithography method to form the micro lens 71 corresponding to the G (green) pixel shown in FIG. That is, in the example formed by the flow lens type described above, for example, when a positive photosensitive lens material is used, the pattern 73 is used as a light shielding region, and the non-pattern part is used as a transparent region. The microlens 71 is made by utilizing the thermal reflow property of the material. After the microlens 71 corresponding to the G (green) pixel is formed, the same method is repeated using the exposure mask shown in FIG. 2B, whereby R (red) and B (blue) without G display. The microlens 72 is formed by using the exposure mask pattern 74 for the microlens corresponding to the pixel (1).

JP 2000-22117 A JP 2000-269474 A

  As described above, by separately preparing exposure masks for forming microlenses 71 and 72 corresponding to pixels of different colors, and using patterns 73 and 74 having different shapes, gaps between adjacent microlenses can be obtained. It becomes possible to make it narrow. However, in the method of forming microlenses on all pixels in two stages using patterns having different shapes corresponding to the region division by pixel division, even if a narrow gap can be achieved, the shape of the microlens is also included. It is difficult to make them the same, and even if the height is constant, the cross-sectional shape cannot always be the same.Therefore, the condensing performance of the microlens varies, and the color solid-state image sensor has a difference in sensitivity for each color. Arise.

  The present invention is proposed in view of the above-described problems, and the problem to be solved by the present invention is that a microlens provided in a solid-state image sensor is highly condensed by narrowing a gap between adjacent microlenses. In addition to providing performance, a manufacturing method for forming each microlens so that the shape thereof is uniform is provided.

  As means for solving the above-mentioned problem, the invention according to claim 1 has a polygonal pixel corresponding to each of the plurality of photoelectric conversion elements, and one microlens is provided for each pixel. A method of manufacturing a microlens in a solid-state imaging device, wherein after the first layer constituting the microlens is provided, the second layer constituting the microlens is formed in a shape different from that of the first layer. Including a step of forming a microlens of a desired shape by heat-treating and integrating both layers, and the shape of the first layer changes from the center of each pixel to the pixel boundary. A method of manufacturing a microlens, characterized in that the second layer has a convex pattern that includes a radial pattern that faces and the shape of the second layer is close to the shape of each polygonal pixel and does not exceed the pixel boundary.

  According to a second aspect of the present invention, in the microlens according to the first aspect, the first layer and the second layer are made of a material exhibiting the same optical characteristics after the formation of the microlens. It is a manufacturing method.

  The invention according to claim 3 is characterized in that the first layer includes a plurality of line segment patterns sharing one end at the center of the pixel and having the other end at each corner of the pixel. A method for producing a microlens according to claim 1 or 2.

  The invention according to claim 4 is the method for manufacturing a microlens according to any one of claims 1 to 3, wherein the first layer is thinner than the second layer.

  The invention according to claim 5 is characterized in that the polygonal shape is a quadrangular shape, and an octagonal layer excluding each corner is laminated as a second layer for each quadrangular pixel. The method for producing a microlens according to claim 1.

  The invention according to claim 6 is characterized in that an end portion closer to the pixel boundary of the first layer is provided closer to the pixel boundary than an end portion of the second layer to be laminated. It is a manufacturing method of the micro lens in any one of 1-5.

The invention described in claim 7 is a mask for exposure used in the method of manufacturing a microlens according to any one of claims 1 to 6, wherein a plurality of pattern shapes corresponding to the pattern of each layer to be stacked are provided. An exposure mask is provided on a sheet.

  The microlens manufacturing method of the present invention uses a two-step photolithography method combining different patterns, but this is not a conventional method corresponding to region division by pixel division, and each microlens is divided into pixel divisions. First, the same processing is performed, and the second layer is laminated by being almost covered with the first layer that becomes the lens-shaped skeleton, and integrated by heat treatment. The gap can be narrowed to give high condensing performance, and each microlens can be formed to have a uniform shape. Therefore, according to the present invention, the condensing performance of the microlens does not vary, and when used in a color solid-state imaging device, there is no difference in sensitivity for each color.

It is a schematic diagram for magnifying partially explaining an example of a pattern of each layer of a microlens divided and formed in a manufacturing method of the present invention, and (a1) and (a2) are the 1st layers which constitute a microlens. FIG. 4B is a plan view showing an example of the pattern of the second layer constituting the microlens, and FIG. 4C is a structural example of a solid-state imaging device provided with the microlens. It is sectional drawing shown. FIG. 4 is a partial schematic diagram for explaining a conventional method for forming a microlens in two stages by dividing an area by pixel division, and FIGS. 4A and 4B are examples in which a Bayer array is applied to a color filter. FIG. 2 is a schematic plan view for explaining a pattern of a main part of an exposure mask used at the time of forming a microlens. FIG. It is a schematic cross section which shows an example of the structure of the color solid-state image sensor as a result of forming a microlens by the photolithographic method of a step. It is a schematic plan view for partially expanding and explaining another example of the pattern of each layer of the microlens formed separately in the manufacturing method of the present invention, wherein (a) and (b) respectively constitute a microlens. The example of the pattern of the 1st layer and the pattern of the 2nd layer is shown, (c) shows the state which laminated | stacked the 1st layer and the 2nd layer, (d) integrated two layers laminated | stacked by heat processing. Shows the state.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.
FIG. 1 is a schematic view for partially explaining an example of a pattern of each layer of a microlens formed separately in the manufacturing method of the present invention. (A1) and (a2) constitute a microlens. The top view which shows the example of two types of patterns of a 1st layer, (b) is a top view which shows the example of the pattern of the 2nd layer which comprises a micro lens, (c) is the solid-state image sensor which provided the micro lens It is sectional drawing which shows the example of a structure.

  The present invention includes a pixel 60 that is defined corresponding to each of a plurality of photoelectric conversion elements 3 arranged in a plane on a semiconductor substrate 2 and that has a polygonal planar shape that clearly defines the corresponding region divided by broken lines in the figure. This is a method of manufacturing the microlens 7 in the solid-state imaging device 10 in which one microlens 7 is provided for each pixel. The pixel 60 in this example may include the colored transparent pixel pattern 6, the transparent flattening layer 5, and the second transparent flattening layer 51 shown in FIG. The element 10 may be a color solid-state imaging element. As an example of the planar arrangement of the polygonal pixels 60, a rectangular shape constituting the checkered pattern arrangement called the Bayer arrangement shown in FIG. 2 will be described below, but the present invention is not limited to this.

As a basic manufacturing process of the microlens, as described above, any of a flow lens type and a transfer type is possible. In the present invention, the microlens is divided and designed in two stages, a first layer corresponding to the skeleton structure and a second layer corresponding to the outer structure, and each is performed by a basic manufacturing process and laminated, After that, they are integrated by heat treatment, and in the following description, a flow lens type manufacturing process will be unified for the sake of simplicity.

  In the present invention, after providing the first layer corresponding to the skeleton structure of the microlens, the second layer corresponding to the outer structure of the microlens is laminated on the first layer in a shape different from that of the first layer. And then forming a microlens having a desired shape by heat-treating and integrating both layers.

The process of forming the first layer and the second layer separately is possible, for example, by repeating the process of selectively patterning a transparent acrylic photosensitive resin by a photolithography method. After forming the layer, a prior heat treatment can be performed once using the thermal reflow properties of the material.
Since the first layer and the second layer integrally form a microlens after being deformed by heat treatment, it is desirable that the optical characteristics after heat treatment be the same. As the material constituting each layer, for example, the same kind of transparent acrylic photosensitive resin can be used, but it is desirable that the optical properties of the constituent parts by each layer are not different by the final treatment after lamination. The original material can be slightly adjusted according to the detailed conditions of the process process.

In the present invention, the shape of the first layers 81 and 82 includes a radial pattern from the center of each polygonal pixel toward the pixel boundary, and the shape of the second layer 85 is the shape of each polygonal pixel. It is a convex pattern that is close to the pixel boundary and does not exceed the pixel boundary indicated by the alternate long and short dash line. The first layer and the second layer are formed separately by the photolithography method, and correspond to the shape of a selective pattern of transmission / non-transmission in the exposure mask used in the exposure process. For example, if the acrylic photosensitive resin forming the microlens is a positive type having photodegradability, the selective pattern may be formed as a non-transparent or light-shielding pattern in a transmissive or transparent background.
The first layer is mainly composed of a radial pattern for creating the skeleton structure of the microlens. In addition, the first layer is partially responsible for the function of the second layer for creating the outer structure of the microlens. Is not excluded.
The convex figure indicating the shape of the second layer refers to a figure in which points on a line segment connecting any two points on the figure always exist on the same figure. In this example, a planar figure is used. It is.

In this example, the first layers 81 and 82 share one end at the center of each pixel 60 and the other end at each corner of the pixel, as shown in FIGS. 1 (a1) and (a2). The same isolated radial line segment pattern on each pixel including a plurality of line segment patterns having a portion can be formed in an array that repeats at the same relative position on the pixel array. In particular, the line segment pattern as described above is as wide as possible in the region of the pixel 60, that is, the gap between the adjacent microlenses is made as narrow as possible to create a skeleton structure for defining the final microlens shape. Become. Further, as shown in FIG. 1B, the second layer 85 is formed by repeatedly arranging the same isolated convex pattern on each pixel 60 at the same relative position on the pixel array. Can do. The isolated convex pattern is close to the shape of each polygonal pixel, can substantially cover each pixel region, and does not cross the pixel boundary. Therefore, the overall shape of the microlens is the planar shape of each pixel. It is appropriate to decide according to Moreover, since the fluidity control in the contact state by the lamination and heat treatment with the first pattern for forming the skeleton structure acts on the second pattern, it is easy to control the external structure of the microlens. Accordingly, the gap between adjacent microlenses can be narrowed to provide high light condensing performance, and each microlens can be formed to have a uniform shape.
In addition, a microlens having a more appropriate shape can be obtained by a simple method by the device described below.

  The layer to be laminated is not limited to two layers. For example, it is possible to form another layer with the same kind of material between the first layer and the second layer. In order to shorten the length, a structure composed of two layers is desirable. When the microlens manufacturing method of the present invention is implemented with a two-layer structure, it is preferable to form the lower layer, that is, the first layer that forms the skeletal structure, thinner than the second layer that forms the outer structure. By providing the first layer constructed in advance relatively thin compared to the upper layer, it is possible to suppress the amount of resin flowing and to achieve a precisely controlled end position. It can be optimally used to guide the behavior of the second layer that creates the outer structure.

  FIG. 3 is a schematic plan view for explaining another example of the pattern of each layer of the microlens divided and formed in the manufacturing method of the present invention by partially enlarging the minimum unit of one pixel 60. a) and (b) show examples of the pattern of the first layer and the pattern of the second layer constituting the microlens, respectively, and (c) shows a state in which the first layer and the second layer are laminated. (D) shows a state in which the two laminated layers are integrated by heat treatment.

  In this example, the polygonal shape representing the planar shape of the pixel is a square shape, and as shown in FIG. 3B, an octagonal layer excluding each corner for each square pixel is a second layer. Stack as 85. At each corner of each quadrangular pixel, it is difficult to control the shape of the second layer alone, so it is designed to make the final shape of the microlens dependent on the first layer. is there.

  Also, as shown in FIG. 3A, a diagram showing a state in which an end portion closer to the pixel boundary 61 indicated by the dotted line of the radial pattern which is the first layer 81 is as close as possible to the pixel boundary and the upper layer is laminated. As apparent from FIG. 3C, the end of the first layer 81 can be provided closer to the pixel boundary 61 than the end of the second layer 85. When the microlenses 7 are formed by heat-treating the laminated layers in this state, as shown in FIG. 3 (d), the gap between the adjacent microlenses is narrowed to give high condensing performance. The shape of the microlens can be formed uniformly.

  The exposure mask used in the method for manufacturing a microlens of the present invention is a plurality of masks each having the first layer and the second layer separately, and the exposure masks are sequentially used. To realize a laminated pattern. The plurality of exposure masks provide a set of exposure masks aligned by a common mark.

DESCRIPTION OF SYMBOLS 1 ... Color solid-state image sensor 2 ... Semiconductor substrate 3 ... Photoelectric conversion element 4 ... Light-receiving surface side surface 5 ... Transparent planarization layer 51 ... Second transparent planarization layer 6 ..Colored transparent pixel pattern 60... Pixel 61... Pixel boundaries 7, 71, 72... Microlens 73 .. pattern for exposure mask (for microlens corresponding to green pixel)
74 ... Mask pattern for exposure (for microlenses for red and blue pixels)
81, 82 ... first layer 85 ... second layer 10 ... solid-state imaging device

Claims (7)

A method of manufacturing a microlens in a solid-state imaging device having polygonal pixels corresponding to each of a plurality of photoelectric conversion elements, and providing one microlens for each pixel,
After providing the first layer constituting the microlens, the second layer constituting the microlens is provided on the first layer in a shape different from the first layer, and then both layers are heat-treated. Forming a microlens having a desired shape by integrating the first layer, the shape of the first layer includes a radial pattern from the center of each pixel toward the pixel boundary, and the shape of the second layer is A method of manufacturing a microlens, characterized in that it is a convex figure pattern that is close to the shape of each polygonal pixel and does not cross the pixel boundary.   The method for manufacturing a microlens according to claim 1, wherein the first layer and the second layer are made of a material that exhibits the same optical characteristics after the microlens is formed.   3. The micro of claim 1, wherein the first layer includes a plurality of line segment patterns sharing one end at the center of the pixel and having the other end at each corner of the pixel. Lens manufacturing method.   The method for manufacturing a microlens according to claim 1, wherein the first layer is thinner than the second layer.   The polygonal shape is a quadrangular shape, and an octagonal layer excluding each corner is laminated as a second layer for each quadrangular pixel. Microlens manufacturing method.   6. The microlens according to claim 1, wherein an end portion of the first layer closer to the pixel boundary is provided closer to the pixel boundary than an end portion of the second layer to be laminated. Manufacturing method.   The exposure mask used in the method for manufacturing a microlens according to claim 1, wherein the exposure mask has a pattern shape corresponding to the pattern of each layer to be laminated on a plurality of separate sheets. .