JP6520400B2 - Microlens for solid-state imaging device and method of forming microlens for solid-state imaging device - Google Patents

Description

  The present invention relates to a microlens formed on an on-chip color filter provided on an imaging device and a method of forming the same.

  In recent years, imaging devices have come to be widely used along with the expansion of the contents of image recording, communication, and broadcasting. Although various types of imaging devices have been proposed as imaging devices, imaging devices incorporating a solid-state imaging device that has been stably manufactured with small size, light weight and high performance have been proposed as digital cameras and digital video. It has become widespread.

  The solid-state imaging device has a plurality of photoelectric conversion devices that receive an optical image from a photographic subject and convert incident light into an electrical signal. The types of photoelectric conversion elements are roughly classified into CCD (charge coupled device) types and CMOS (complementary metal oxide semiconductor) types.

  In addition, two types of linear sensors (line sensors) in which the photoelectric conversion elements are arranged in one row and area sensors (surface sensors) in which the photoelectric conversion elements are two-dimensionally arrayed in the vertical and horizontal directions It is divided roughly.

  In any of the sensors, the more the number of photoelectric conversion elements (the number of pixels), the denser the captured image becomes. In recent years, therefore, a method for manufacturing a solid-state image sensor having a large number of pixels at low cost has been studied. .

  In addition, a color filter function of transmitting light of a specific wavelength is provided in the path of light incident on the photoelectric conversion element. By doing so, a color solid-state imaging device as a single-plate type color sensor capable of obtaining color information of an object is also widely used. In the color solid-state imaging device, one pixel is patterned by a specific colored transparent pixel corresponding to one photoelectric conversion device.

  By arranging a large number regularly, color separated image information can be collected. The color of the colored transparent pixel is a three-primary color system consisting of three colors of red (R), green (G) and blue (B), or cyan (C), magenta (M) and yellow (Y) Complementary color systems are generally used, and in particular, three primary color systems are widely used.

  One of the important issues in the 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 captured by a miniaturized solid-state imaging device, it is necessary to miniaturize the photoelectric conversion device to be a light receiving portion to achieve high integration.

  However, when the photoelectric conversion elements are highly integrated, the area of each photoelectric conversion element is reduced, so that the area ratio that can be used as the light receiving unit is also reduced. Therefore, the amount of light that can be taken into the light receiving portion of the photoelectric conversion element is reduced, and the effective sensitivity of the solid-state imaging element is reduced.

  As a means for preventing such a decrease in sensitivity of the miniaturized solid-state imaging device, the layer closer to the light receiving region is made of a material having a larger refractive index for the purpose of efficiently taking light into the light receiving portion of the photoelectric conversion device. It has been proposed to include a multi-layered (at least two or more layers) micro lens and to refract light incident on the micro lens to the light receiving area side with a larger refractive index layer as it gets closer to the photoelectric conversion element. However, light can be received well, and the sensitivity of the solid-state imaging device is improved (Patent Document 1).

  However, the solid-state imaging device in recent years has been increased in the number of pixels, and a high-definition solid-state imaging device having more than several million pixels has been required. The change in refractive index at the interface of each layer adversely affects the sensitivity of the microlens attached to the high-definition solid-state imaging device and the image quality degradation due to the increase of noise such as flare.

JP 2007-165713 A

  SUMMARY OF THE INVENTION The object of the present invention is to improve image quality degradation caused by noise reduction such as sensitivity reduction and flare, which are caused by microlenses in which materials having different refractive indexes are multilayered, which are being carried out with high definition of solid-state imaging devices. It is an object of the present invention to provide a method of forming a microlens for a solid-state imaging device and a microlens for a solid-state imaging device.

As means for solving the above-mentioned problems, the invention according to claim 1 is a microlens for a solid-state imaging device provided in a solid-state imaging device for focusing incident light,
The solid-state imaging device is configured by laminating a plurality of photoelectric conversion devices formed on the surface of a semiconductor substrate, and a color filter transmitting light of a predetermined wavelength band on each surface of the photoelectric conversion device,
The microlens for a solid-state imaging device has different refractive indexes at the inner core and the outer periphery, and the refractive index is continuously reduced from the inner core to the outer periphery ,
The microlens is a microlens for a solid-state imaging device, wherein the microlens is formed of two or more transparent resins having different refractive indexes .

The invention according to claim 2 is the microlens for a solid-state imaging device according to claim 1, characterized in that the microlens is formed of two transparent resins having different refractive indexes.

  The invention according to claim 3 is characterized in that the refractive index of the micro lens is 1.5 or more in the inner core portion and 1.4 or more in the outer peripheral portion. These are microlenses for solid-state imaging devices.

  In the invention according to claim 4, the shape of the microlens for a solid-state imaging device is any one of a spherical shape, a parabola shape, and a sine wave shape. 1 is a microlens for a solid-state imaging device according to item 1.

According to the solid-state imaging device of the present invention, the refractive index in the microlens is continuously reduced from the inner core to the outer periphery, thereby reducing the sensitivity of the microlens attached to the high-definition solid-state imaging device, flare, etc. It has been possible to provide a microlens for a solid-state imaging device and a method for forming a microlens for a solid-state imaging device, capable of capturing a bright image with high light collection efficiency without deterioration in image quality due to increased noise.

It is the conceptual sectional view which showed the structure of the solid-state image sensor using the microlens for solid-state image sensors of this invention. It is the conceptual diagram which showed the refractive index distribution in the microlens for solid-state image sensors of this invention. It is the conceptual diagram which showed the refractive index distribution in the microlens for solid-state image sensors of this invention. It is a conceptual diagram showing an optical path of perpendicular incidence light. It is the conceptual diagram which showed the optical path of oblique incidence light. It is the conceptual diagram which showed the formation method of the microlens for solid-state image sensors of this invention.

  Hereinafter, modes for carrying out the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view of a solid-state imaging device 7 according to an embodiment of the present invention, showing a configuration of a microlens for a solid-state imaging device in which changes in refractive index in the microlens 5 are continuously distributed. The solid-state imaging device includes a semiconductor substrate 1, a photoelectric conversion device 2, a flattening layer 3, a color filter layer 4, and a microlens 5. The semiconductor substrate 1 is a substrate for mounting the photoelectric conversion element 2.

  The photoelectric conversion element 2 converts light incident through the microlens 5 into a charge. The planarization layer planarizes the micro lens mounting surface. The color filter layer 4 has a role of transmitting light of a specific wavelength in the path of light incident on the photoelectric conversion element 2.

  The microlens 5 is formed of two or more transparent resins different in refractive index, and the refractive index has a distribution that decreases continuously from the inner core to the outer peripheral.

  FIG. 2 shows an example of the refractive index distribution of the microlens 5 for a solid-state imaging device according to the present invention, which has a refractive index distribution which continuously changes from the inner core portion to the outer peripheral portion.

  FIG. 3 shows another example of the refractive index distribution of the microlens 5 for a solid-state imaging device of the present invention, but in both examples, the refractive index of the inner core portion is 1.5 or more and the refractive index of the outer peripheral portion is 1 .4 or more.

  FIG. 4 is a conceptual view showing the optical path of the vertically incident light, but the light enters the micro lens 5, travels in the micro lens 5, passes through the color filter layer 4 and the flattening layer 3, and the photoelectric conversion element 2 is to go into.

  FIG. 5 is a conceptual view showing an optical path of oblique incident light, but as in the case of oblique incidence also in the case of vertical incidence, the oblique incidence also travels inside the microlens 5 and passes through the color filter layer 4 and the flattening layer 3 to form the photoelectric conversion element 2. to go into.

  In the solid-state imaging device 7 of the present embodiment, incident light can be efficiently condensed on the photoelectric conversion device 2 by the above-described configuration of the microlens 5, and the condensing efficiency can be enhanced.

  A method of forming the above-described microlens 5 will be described.

FIG. 6 is a conceptual view showing a method of forming a microlens according to an embodiment of the present invention. First, on the semiconductor substrate 1 on which the photoelectric conversion element 2 is formed on the surface portion, a planarization layer 3 and color The filter layers 4 are sequentially laminated.

  Next, a photosensitive high refractive index transparent resin 8 is applied (a), exposure and development are performed, and a first microlens 9 is formed in the upper central portion of the light receiving portion of the photoelectric conversion element (b).

  Furthermore, the photosensitive low refractive index transparent resin 10 having photosensitivity is coated on the first microlens 9 (c), exposed and developed, and the second microlens 12 is formed right above the first microlens 9 (D)).

  Here, the transparent resin used for the micro lens 5 is a material whose refractive index is diffused by heat flow. For example, it is an acrylic type, an epoxy type, an acrylic urethane type, a polyamide type etc.

  After forming the first microlens 9 and the second microlens 12, the refractive index of the first microlens 9 and the second microlens 12 is diffused by heat treatment, and the inner core to the outer periphery of the microlens 5 are diffused. (E) to be continuously smaller.

  According to the solid-state imaging device microlens 5 of the present invention, the light collection efficiency is increased by continuously reducing the refractive index in the microlens 5 from the inner core to the outer periphery, and a bright image is captured. It becomes possible.

  Hereinafter, the present embodiment will be described. After forming the light shielding layer and the flattening layer 3 on the semiconductor substrate 1 in which the photoelectric conversion element 2 is formed on the upper surface, a color resist of red (R), green (G) and blue (B) is used. The color filter layers 4 of three colors are sequentially formed by photolithography.

  The film thickness of each of the red (R), green (G) and blue (B) color filter layers is 0.5 to 0.8 μm, and after forming the color filter layers, the planarizing layer is made of 0. It is formed to a thickness of 1 μm.

  Next, a photosensitive resin high refractive index transparent resin material (photosensitive acrylic resin) is coated with a film thickness of 0.6 μm on the formed color filter layer, exposed and developed, and the light receiving portion of the photoelectric conversion element A first microlens is formed in the upper center portion. The first microlens here has a hemispherical shape with a height of 0.5 μm.

  Next, a photosensitive low refractive index transparent resin material (photosensitive acrylic resin) having a film thickness of 1.5 μm is coated on the first microlens, exposed and developed, and then directly on the first microlens. Form a second microlens. The second microlens here has a hemispherical shape with a height of 1.2 μm.

  Next, after forming the first microlens and the second microlens, heat flow treatment is performed at 200 ° C. for 300 seconds using a hot plate of a size capable of mounting the semiconductor substrate, and solid-state imaging with a microlens of Example 1 A device was produced.

Comparative Example 1
The microlens attached solid-state imaging device of Comparative Example 1 was produced under the same conditions as Example 1 except that the heat flow treatment was not performed.

<Light receiving efficiency evaluation>
When the standard light source (light source: xenon lamp) was irradiated to the solid-state imaging device with microlenses of Example 1 and Comparative Example 1 and the light receiving efficiency was measured, the output of Comparative Example 1 was 80.9% (visible region) However, the output of Example 1 was 86.0%, and the heat-flow-treated solid-state imaging device with a microlens had a result that was about 5% better.

<Refractive index distribution evaluation>
The refractive index profiles of the microlenses of Example 1 and Comparative Example 1 were measured by an ellipsometer. In the micro lens of Example 1, the refractive index decreases continuously from the inner core portion (1.52) to the outer peripheral portion (1.43), but in Comparative Example 1, the refractive index is 0.5 μm from the center There was an interface where the refractive index changed from 1.51 to 1.43.

  The evaluation results are shown in Table 1.

  In the solid-state imaging device according to the present invention, the light receiving efficiency is improved by using the micro lens in which the heat flow processing is performed and the refractive index is continuously reduced from the inner core to the outer peripheral, and high sensitivity can be achieved. The

DESCRIPTION OF SYMBOLS 1 ... semiconductor substrate 2 ... photoelectric conversion element 3 ... planarization layer 4 ... color filter layer 5 ... micro lens 6 ... optical path 7 ... solid-state image sensor 8 ... photosensitivity High refractive index transparent resin 9 ... First micro lens 10 ... Photosensitive low refractive index transparent resin 11 ... Exposure light 12 ... Second micro lens

Claims (4)

A microlens for a solid-state imaging device provided on a solid-state imaging device for focusing incident light, comprising:
The solid-state imaging device is configured by laminating a plurality of photoelectric conversion devices formed on the surface of a semiconductor substrate, and a color filter transmitting light of a predetermined wavelength band on each surface of the photoelectric conversion device,
The microlens for a solid-state imaging device has different refractive indexes at the inner core and the outer periphery, and the refractive index is continuously reduced from the inner core to the outer periphery ,
The microlens for a solid-state imaging device, wherein the microlens is formed of two or more transparent resins different in refractive index . The microlens for a solid-state imaging device according to claim 1, wherein the microlens is formed of two transparent resins having different refractive indexes.   The microlens for a solid-state imaging device according to claim 1 or 2, wherein the refractive index of the microlens is 1.5 or more in the inner core portion and 1.4 or more in the outer peripheral portion. The micro-lens for a solid-state imaging device according to any one of claims 1 to 3, wherein the shape of the micro-lens for a solid-state imaging device is any one of a spherical shape, a parabola shape, and a sine wave shape. lens.