JP2015133340A - Solid-state imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid-state imaging apparatus having a high sensitivity even at a peripheral part of an imaging region.SOLUTION: The solid-state imaging apparatus comprises: a semiconductor substrate having an imaging region where a plurality of pixels are arranged in a matrix, and a peripheral circuit region; a light receiving part formed on the semiconductor substrate for each pixel; a wiring layer formed on the semiconductor substrate; a light collection element formed on the wiring layer for each pixel. Further, the light collection element consists of a plurality of ark-like light transmission films using an axis vertical to the semiconductor substrate as a center, and divided by a line width equivalent to or shorter than a wavelength of incoming light. Further, in the light collection element in a pixel located at a peripheral part of the imaging region, a first height of the light transmission film at the center part side of the imaging region is higher than a second height of the light transmission film at an opposite side to the center part of the imaging region.

Description

  The present invention relates to a solid-state imaging device, and more particularly to a light collecting element.

  In recent years, with the popularization of digital cameras, camera-equipped mobile phones, and the like, the market for solid-state imaging devices has remarkably expanded. In addition, single-lens reflex digital cameras that exchange and use various optical lenses from wide-angle to telephoto have become widespread. Under such circumstances, there is still a strong demand for thinning digital cameras and the like. In other words, the lens used for the camera portion has a short focal point, and the range of light incident on the solid-state imaging device is a wide angle (a large angle measured from the vertical axis of the incident surface of the solid-state imaging device). Means that.

  In this way, when the angle is wide, incident light becomes oblique in the peripheral part of the imaging region of the solid-state imaging device, and the sensitivity is lowered when the light collecting element is arranged in the same manner as the central part of the imaging region. On the other hand, in FIG. 12B of Patent Document 1, as shown in FIG. 9, in the pixel located in the peripheral part of the imaging region, a high refractive index material is used to shift the refractive index distribution of the condensing element. Has been proposed to shift the image plane toward the center of the imaging region.

JP 2009-15315 A

  However, when a material having a high refractive index is shifted as in the prior art, the distance between the high refractive index materials is narrowed on the shifted side, so that the lithography technique can be restricted and the quantization error increases. As a result, there is a problem that the sensitivity in the peripheral portion of the imaging region is lowered and the captured image is dark in the peripheral portion.

  A solid-state imaging device according to the present invention includes a semiconductor substrate having an imaging region in which a plurality of pixels are arranged in a matrix and a peripheral circuit region, a light receiving unit formed on the semiconductor substrate for each pixel, and an upper surface of the semiconductor substrate. And a light collecting element formed on the wiring layer for each pixel. Furthermore, the condensing element has a plurality of arc-shaped light transmission films divided by a line width equal to or shorter than the wavelength of the incident light so as to be concentric with an axis perpendicular to the semiconductor substrate as a center. Consists of. Furthermore, the light condensing element in the pixel located in the periphery of the imaging region has a first height of the light transmission film on the center side of the imaging region, and the first height of the light transmission film on the side opposite to the center of the imaging region. It is higher than the height of the second.

  With the solid-state imaging device according to the present invention, it is possible to improve the sensitivity of the peripheral portion of the imaging region, and it is possible to obtain a captured image that is brighter than before in the peripheral portion of the captured image.

2 is a plan view of the solid-state imaging device according to Embodiment 1. FIG. (A) is sectional drawing which shows the pixel 14 located in the center part 15 of Embodiment 1, (b) is sectional drawing which shows the pixel 14 located in the peripheral part 16 of Embodiment 1. FIG. (A) is a top view of the condensing element 25 located in the center part 15 of Embodiment 1, (b) is a top view of the condensing element 25 located in the peripheral part 16 of Embodiment 1. FIG. is there. (A) is a figure which shows the calculation result of the conventional condensing characteristic, (b) is a figure which shows the calculation result of the condensing characteristic of this Embodiment. 4 is a graph showing the incident angle dependency of the light collection efficiency of the first embodiment. (A) is sectional drawing which shows the pixel 14 located in the center part 15 of Embodiment 2, (b) is sectional drawing which shows the pixel 14 located in the peripheral part 16 of Embodiment 2. FIG. (A) is a top view of the condensing element 25 located in the center part 15 of Embodiment 2, (b) is a top view of the condensing element 25 located in the peripheral part 16 of Embodiment 2. FIG. is there. (A) is a top view of the condensing element 25 located in the center part 15 of the modification of Embodiment 1, (b) is the condensing located in the peripheral part 16 of the modification of Embodiment 1. FIG. 3 is a plan view of an element 25. FIG. (C) is a top view of the condensing element 25 located in the center part 15 of the modification of Embodiment 2, (d) is the condensing located in the peripheral part 16 of the modification of Embodiment 2. FIG. 3 is a plan view of an element 25. FIG. It is a top view of the conventional condensing element.

(Embodiment 1)
A solid-state imaging device 11 according to a first embodiment will be described with reference to FIGS.

  FIG. 1 is a plan view of the solid-state imaging device according to the present embodiment.

  As shown in FIG. 1, the solid-state imaging device 11 includes an imaging area 12 and a peripheral circuit area 13 located outside the imaging area 12. In the imaging region 12, a plurality of pixels 14 are arranged in a matrix, and each pixel 14 has a light receiving portion (not shown) on a semiconductor substrate. The imaging region 12 can be distinguished into a central portion 15 and a peripheral portion 16. The solid-state imaging device 11 photoelectrically converts the light incident on the light receiving unit into an electrical signal, and the pixel 14 outputs the electrical signal to a processing circuit formed in the peripheral circuit region 13, thereby generating image data. Generate.

  2A is a cross-sectional view showing the pixel 14 located in the central portion 15 in FIG. 1, and FIG. 2B is a cross-sectional view showing the pixel 14 located in the peripheral portion 16 in FIG.

  As shown in FIGS. 2A and 2B, the solid-state imaging device 11 includes a semiconductor substrate 22 in which a plurality of light receiving portions 21 are formed for each pixel 14 and wiring formed on the semiconductor substrate 22. Layer 23. Furthermore, on the wiring layer 23, it has the condensing element 25 formed through the planarization film | membrane on the color filter 24 and the color filter 24 correspondingly formed for every light-receiving part 21. As shown in FIG.

  3A is a plan view of the light collecting element 25 located at the central portion 15 in FIG. 1, and FIG. 3B is a plan view of the light collecting element 25 located at the peripheral portion 16 in FIG. is there.

  As shown in FIG. 3A and FIG. 3B, the condensing element 25 has a concentric circle in which a plurality of light transmission films 26 having a refractive index higher than that of air are centered on an axis perpendicular to the semiconductor substrate 22. A plurality of arc shapes are formed. In the most central portion, a circular light transmission film 26 is formed instead of an arc shape. Each of the light transmission films 26 is formed so that the width and the interval are the same as or smaller than the wavelength of the incident light. In FIG. 3B, the left is the center side of the imaging region 12.

When the fine light transmission film 26 having such a wavelength or less is formed, the light collecting element 25 has a refractive index obtained by averaging the refractive index of the light transmission film 26 and the refractive index of the space located between the light transmission films 26. Function as. The refractive index of the space is smaller than the refractive index of the light transmission film 26. In this embodiment, air is used, and the refractive index is n = 1.0. Air may exist in the space, and it is preferable to use a stable gas such as nitrogen or argon that does not deteriorate the light transmission film 26. The light transmission film 26 is a silicon oxide film, and the refractive index is n = 1.45. As the light transmission film 26, a silicon nitride film having a refractive index of n = 2.0 can be used.

  Furthermore, the condensing element 25 will be described in detail.

  As shown in FIG. 2A and FIG. 2B, the condensing element 25 is formed of a plurality of light transmission films 26 at different heights, and the refractive index is distributed as a whole. The lens functions as a lens having the design refractive index distribution 27.

  In the present embodiment, the height of the light transmission film 26 is set to three stages, which are 1200 nm, 1100 nm, and 800 nm. Further, the width of the light transmission film 26 is equal to or less than the incident light as described above, and in this embodiment, the visible light having a wavelength of 400 nm to 800 nm is set to 100 nm or 150 nm. In addition, the space is formed to have the same width as the light transmission film 26.

  As shown in FIGS. 2A and 3A, in the central portion 15 of the imaging region 12, since the incident light is incident substantially perpendicular to the semiconductor substrate 22, the light transmission film 26 is in a cross section. Also, they are formed symmetrically on the plane. In the figure, the left is the center side of the imaging region 12, and the right is the peripheral circuit region 13 side.

  As shown in FIG. 3B, in the peripheral portion 16 of the imaging region 12, the light transmission film 26 is formed symmetrically on the plane, but as shown in FIG. Is formed asymmetrical.

  Specifically, when the light transmission films 26 having the same distance from the center of the light collecting element 25 are compared with each other, the height of the light transmission film 26 on the center side of the imaging region 12 is 1100 nm, and the peripheral circuit region of the imaging region 12 There is a portion where the height on the 13th side is 800 nm. Further, although the light transmission film 26 exists on the center side of the imaging region 12, there is a portion that does not exist on the peripheral circuit region 13 side of the imaging region 12. The center side of the imaging region 12 is a first zone 31, and the peripheral circuit region 13 side of the imaging region 12 is a second zone 32.

  The first zone 31 is smaller than the second zone 32, and the condensing element 25 is shifted to the central portion 15 side as a whole.

  In other words, for the rings having different heights, the distance between the light transmitting film having the first height and the axis is equal to the distance between the light transmitting film having the second height and the axis.

  Thereby, the refractive index distribution of the condensing element 25 can be shifted toward the center side of the imaging region 12. At this time, in the present invention, since the intervals between the plurality of light transmission films 26 are made equal between the center side and the outside of the imaging region 12, the lithography technique can be controlled to the same degree and a highly reliable refractive index distribution is realized. it can.

  One method for setting the height of the light transmission film 26 of the present embodiment will be described.

  As shown in FIG. 2B, an ideal refractive index distribution of the condensing element 25 in the peripheral portion 16 of the imaging region 12 is a design refractive index distribution 27, and the designed refractive index distribution 27 at both ends of the pixel 14 is a straight line. Tie at 28. In the peripheral portion 16, the straight line 28 is ideally a straight line 28 inclined with respect to the semiconductor substrate 22 because the refractive index distribution is shifted toward the center of the imaging region 12. The height difference of the light transmission film 26 can be set so as to match the inclined straight line 28.

  Next, the design refractive index profile 27 of the present embodiment will be described.

  The design refractive index distribution 27 in FIG. 2B is expressed by the following (Equation 1).

Δn (x) = Δn _max [(Ax ² + Bxsinθ) / 2π + C] (Formula 1)
(A, B, C: constant)
Here, Δn _max is a difference in refractive index between SiO ₂ and air in the light transmission film material (this time 0.45).
In addition, in the above equation (1), the parameters when the refractive index of the incident side medium is n ₀ and the refractive index of the emission side medium is n ₁ are the following (Expression 2) to (Expression 4).

A = − (k ₀ n ₁ ) / 2f (Formula 2)
B = −k ₀ n ₀ (Formula 3)
k ₀ = 2π / λ (Equation 4)
This makes it possible to optimize the lens for each target focal length f, target incident light incident angle, and wavelength. In the above equation (1), the condensing component is represented by a quadratic function of the distance x from the center of the pixel to the peripheral direction, and the deflection component is represented by the product of the distance x and a trigonometric function.

  Next, the light collection characteristics of the present embodiment will be described.

  FIG. 4A is a diagram illustrating a calculation result of a conventional light collection characteristic, and FIG. 4B is a diagram illustrating a calculation result of the light collection characteristic of the present embodiment.

  These calculation results show that the light generated from the set light source is incident on the surface of the solid-state imaging device and propagates throughout the solid-state imaging device including the light receiving unit by electromagnetic field simulation using the finite element method. . The incident light has a wavelength of 540 nm, and the incident angle is set to be parallel to the surface of the solid-state imaging device.

  Comparing FIG. 4 (a) and FIG. 4 (b), the condensing distribution by the condensing element of the present invention is efficiently condensed on the light receiving part, compared to the condensing distribution by the conventional condensing element. Can be confirmed. Specifically, conventionally, a part of the incident light is blocked by the light-shielding film in the solid-state imaging device, thereby causing a condensing loss. In the present embodiment, the light-receiving unit is not blocked by the light-shielding film. The light is collected efficiently. This is a difference in reproducibility of the refractive index distribution occurring between the prior art and the present invention, and shows that the light collection performance can be improved by reducing the quantization error.

  Next, the incident angle characteristic of the present embodiment will be described.

  FIG. 5 is a graph showing the incident angle dependence of the light collection efficiency of the present embodiment. Reference numeral 51 indicates the normalized sensitivity according to the conventional method, and is represented by a short broken line. Reference numeral 52 denotes an ideal normalized sensitivity, which is represented by a long broken line. Reference numeral 53 indicates the normalized sensitivity according to the present embodiment, and is represented by a solid line.

  As shown in FIG. 5, in the present embodiment, high-efficiency (80% or more) light can be collected with respect to a wide range of incident light having an incident angle of about 0 ° to 40 °. Compared to the element, a wider angle of incidence angle is realized. It can be seen that the light condensing element of the present invention has sufficiently obtained the effect of reducing the quantization error.

(Embodiment 2)
Next, a solid-state imaging device according to the second embodiment will be described. Note that the description of matters overlapping with those of the first embodiment is omitted, and only different items will be described.

  6A is a cross-sectional view showing the pixel 14 located in the central portion 15 of the present embodiment, and FIG. 6B is a cross-section showing the pixel 14 located in the peripheral portion 16 of the present embodiment. FIG.

  FIG. 7A is a plan view of the light collecting element 25 located in the central portion 15 of the present embodiment, and FIG. 7B is a light collecting element 25 located in the peripheral portion 16 of the present embodiment. FIG.

  The present embodiment is different from the first embodiment in that the line width of the light transmission film 26 is further varied. As shown in FIG. 6B and FIG. 7B, for example, the line width of the region where the light transmission film 26 is present can be increased. Further, in FIG. 2B, for example, the two outer rings from the center are lower in the second zone 32 than in the first zone 31 and are different in height. As shown in FIG. 5, the refractive index difference can be increased by making the line width of the ring of the first zone 31 wider than the line width of the ring of the second zone 32. In the first embodiment, the ring width is set to 100 nm. However, in the second embodiment, there is a portion in which the ring width of the second zone 32 is 150 nm. As described above, in the present invention, since the height of the light transmission film 26 can be adjusted, it is not necessary to set the ring width until the accuracy of the lithography technique is reduced, and the quantization error can be reduced.

  In other words, the light transmitting film 26 having the first height constitutes the first zone, the light transmitting film 26 having the second height constitutes the second zone, and the light condensing element 25 corresponds to the pixel 14. It consists of multiple zones.

  The first zone 31 is smaller than the second zone 32, and the condensing element 25 is shifted to the central portion 15 side as a whole.

  As described above, the line width may be equal to or smaller than the incident light as described above, and may be 100 nm or 150 nm. In addition, since the height of the light transmission film 26 can be adjusted without reducing the line width to such an extent that the accuracy of the lithography technique is lowered, it is possible to reduce the quantization error.

(Modification of Embodiments 1 and 2)
In the first and second embodiments, all the rings are circles. However, in all the embodiments, it is not necessary to be a complete circle.

  FIG. 8A is a plan view of the light collecting element 25 located at the central portion 15 of the present modification of the first embodiment, and FIG. 8B is a peripheral portion of the present modification of the first embodiment. FIG. 16 is a plan view of the light collecting element 25 located at 16; FIG. 8C is a plan view of the light collecting element 25 located at the central portion 15 of the present modification of the second embodiment, and FIG. 8D is a peripheral portion of the present modification of the second embodiment. FIG. 16 is a plan view of the light collecting element 25 located at 16;

  As shown in FIGS. 8B and 8D, the central portion 15 on the left side of the drawing may have a shape close to an ellipse in the direction in which the major axis faces. At this time, the center position of each ellipse may be different. Also at this time, as in the first embodiment, the light condensing element 25 with a reduced quantization error can be realized by changing the height of the light transmission film 26 so that the design refractive index distribution 27 is obtained. Moreover, since the zones are not uniform, it may have a so-called egg-like shape with one side extended.

As described above, in the present application, even when referred to as a circle or an arc shape, the circle does not have to be a complete circle, but shows a curve like an arc. Also, in the present application, when called a ring, it is not necessary to be a complete ring for one round, and a partial ring may be used. Furthermore, although the innermost ring is formed like a plate without holes, this is also included in the ring in this application.

(Embodiment 3)
Next, a method for manufacturing the light transmission film 26 according to the present embodiment will be described.

  In the present embodiment, the case where the height of the light transmission film 26 is three steps and a region where the light transmission film does not exist will be described. First, the light transmission film 26 is formed with a certain thickness above the color filter 24. By adjusting the film thickness to the height of the highest light transmission film 26, the subsequent etching process can be simplified.

  Next, the light transmission film 26 is removed by etching with a first mask having an opening in a region where the light transmission film 26 does not exist.

  Next, the light transmission film 26 is removed by etching using a second mask having an opening in a region where the lowest light transmission film 26 exists. The opening of the second mask may include the opening of the first mask.

  Finally, the light transmission film 26 is removed by etching with a third mask having an opening in a region where the light transmission film 26 having an intermediate height exists. The opening in the third mask may include the opening in the first mask and the second mask.

  Note that the etching amount of each etching is performed in consideration of the height of the light transmission film 26 to be finally formed. For example, when the opening of the second mask includes the opening of the first mask, the light transmission film 26 in the region where the light transmission film 26 does not finally exist is etched twice.

  The light transmission film 26 may be three or more heights high. The mask may be formed in a lump using a gray scale mask or the like.

(Other matters)
In the embodiment, the first zone and the second zone have been described as being divided into two, but it is also possible to divide into more zones. For example, the height of the concentric arc-shaped light-transmitting film can be changed in four zones by further dividing in the vertical direction. In this way, the refractive index distribution can be optimized and the sensitivity can be improved for the pixels 14 located in the peripheral portion 16 obliquely from the center of the imaging region 12.

  Further, in the present embodiment, the invention is carried out with respect to the light condensing element 25 positioned above the color filter 24. However, such a light condensing element is also disposed under the color filter 24 as an in-layer lens. Thus, the sensitivity can be further improved.

  That is, the wiring layer 23 further includes an intra-layer lens for each pixel 14, and the intra-layer lens is divided by a line width that is about the axis perpendicular to the semiconductor substrate 22 and that is approximately equal to or shorter than the wavelength of incident light. The inner lens in the pixel 14 located in the peripheral portion 16 of the imaging region 12 is composed of a plurality of arc-shaped light transmitting films 26 and the third height of the light transmitting film 26 on the central portion 15 side of the imaging region 12 is. However, it is higher than the fourth height of the light transmission film 26 on the opposite side to the central portion 15 of the imaging region 12.

  Further, in the present embodiment, when the size of the pixel 14 is 3.75 μm × 3.75 μm or the like, and the present invention is used for a large sensor used for a single-lens reflex camera or the like, the effect of the present invention becomes more remarkable.

  Further, these embodiments can be combined within a range where there is no contradiction.

The solid-state imaging device of the present invention can be used for a digital still camera, a digital video camera, a camera-equipped mobile phone, and the like, and is useful.

DESCRIPTION OF SYMBOLS 11 Solid-state imaging device 12 Imaging area 13 Peripheral circuit area 14 Pixel 15 Central part 16 Peripheral part 21 Light receiving part 22 Semiconductor substrate 23 Wiring layer 24 Color filter 25 Condensing element 26 Light transmission film 27 Design refractive index distribution 28 Straight line 31 First Zone 32 Second zone

Claims (6)

A semiconductor substrate including an imaging region in which a plurality of pixels are arranged in a matrix and a peripheral circuit region;
For each pixel, a light receiving portion formed on the semiconductor substrate;
A wiring layer formed on the semiconductor substrate;
A light-collecting element formed on the wiring layer for each pixel;
The light-collecting element is composed of a plurality of arc-shaped light transmission films divided by a line width that is equal to or shorter than the wavelength of incident light, with an axis perpendicular to the semiconductor substrate as a center,
The light condensing element in the pixel located in the peripheral part of the imaging region has the first light transmission film on the central part side of the imaging region in which the light transmission is opposite to the central part of the imaging region. A solid-state imaging device that is higher than the second height of the film.   The solid-state imaging device according to claim 1, wherein the axis is located closer to a center side of the imaging region than a center of the pixel.   3. The solid-state imaging device according to claim 1, wherein a distance between the light transmitting film having the first height and the axis is equal to a distance between the light transmitting film having the second height and the axis.   4. The solid-state imaging device according to claim 1, wherein a line width of the light transmissive film at the first height is larger than a line width of the light transmissive film at the second height. The light transmission film of the first height constitutes a first zone,
The light transmission film at the second height constitutes a second zone,
The solid-state imaging device according to claim 1, wherein the condensing element includes a plurality of zones of the pixels. The wiring layer further includes an inner lens for each pixel,
The intra-layer lens is composed of a plurality of arc-shaped light transmission films that are divided by a line width that is equal to or shorter than the wavelength of incident light, with an axis perpendicular to the semiconductor substrate as a center,
The intra-layer lens in the pixel located in the periphery of the imaging area has the third height of the light transmission film on the center side of the imaging area, and the light transmission on the side opposite to the center of the imaging area. The solid-state imaging device according to claim 1, wherein the solid-state imaging device is higher than a fourth height of the film.

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