JP2008109393A - Imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase a receiving light quantity in an imaging device. <P>SOLUTION: The imaging device includes an optical sensor part 205, a microlens 202 for converging light to the optical sensor part 205, and a transparent film between the microlens 202 and the optical sensor part 205. The transparent film has a region where a refractive index is higher than that of the transparent film around it. In the region, the refractive index is changed from the optical sensor part 205 to the microlens 202. For instance, the refractive index in a second high refractive index region 208 is lower than that in a first high refractive index region 207. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an imaging device in which a transparent film is disposed between a microlens and a photoelectric conversion means.

  In recent years, the resolution of image pickup devices has been increased by increasing the number of pixels, while the price has been reduced by reducing the chip size. For this reason, the size of the pixels constituting the imaging element is decreasing year by year, and the area of the photoelectric conversion unit is also decreasing accordingly. For this reason, it is very important for the imaging device to improve performance that (1) the light is efficiently collected in the optical sensor unit and (2) the interference with the adjacent pixel is reduced.

  In the conventional imaging device, with respect to these two important items, a structure in which a transparent film having a refractive index higher than that of the periphery is formed immediately above the optical sensor part in the transparent film formed above the optical sensor part (hereinafter referred to as “well”). In particular, there is a transparent film region having a higher refractive index than the periphery immediately above the optical sensor portion (referred to as “well structure internal region”) (see Patent Document 1).

By forming a well-type structure, light that does not originally reach the optical sensor portion can be reflected at the refractive index boundary between the inner region of the well structure in the transparent film and the region having a lower refractive index in the periphery. . As a result, light can be guided to the optical sensor unit, and the amount of received light and the light receiving efficiency can be improved, and interference with adjacent pixels can be reduced.
JP 2003-46074 A

  However, in the technique disclosed in Patent Document 1, the light confinement effect due to the increase in the refractive index of the well structure internal region is improved, while the amount of incident light incident on the well structure portion is reduced. This is because the medium in the well structure inner region is uniform, and the interface reflectivity when light enters the well structure portion increases with the increase in the refractive index of the well structure inner region. Conceivable. That is, when the medium in the well structure internal region is uniform, there is a drawback that the light confinement effect by the well structure and the amount of light incident on the well structure have a trade-off relationship.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to increase the amount of received light in an image sensor.

  A preferred embodiment of the present invention relates to a photoelectric conversion means, a microlens for condensing light on the photoelectric conversion means, and an imaging device having a transparent film between the microlens and the photoelectric conversion means, The transparent film has a region having a higher refractive index than the periphery thereof, and the refractive index of the region changes from the photoelectric conversion means toward the microlens.

  According to the present invention, the amount of received light in the image sensor can be increased.

  Hereinafter, an image sensor according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. This embodiment pays attention to the image pick-up element in which the well type structure was formed. The light confinement effect in the well structure in the transparent film and the amount of light incident on the well structure are greatly affected by the refractive index of the high refractive index region constituting the well structure internal region and the incident angle of light incident on the interface. The In the present embodiment, attention is mainly focused on these two phenomena.

  In general, the reflectance of light at the boundary between different media increases as the refractive index difference between the media increases, and increases as the incident angle of incident light on the boundary increases. Therefore, when the well structure is formed of a uniform medium, it is considered that if the refractive index is increased in order to enhance the light confinement effect, the amount of light incident on the well structure portion is reduced during wide-angle incidence. On the other hand, if the refractive index of the medium is lowered uniformly, the light confinement effect due to the well structure is reduced.

  Therefore, in the present embodiment, these trade-offs are solved by forming a refractive index profile in the well structure. For example, a region having a small refractive index is formed in the upper region in the well structure, and a region having a large refractive index is formed as the light receiving region is approached. By adopting such a configuration, it is possible to increase the amount of incident light when entering the well structure and to maintain the light confinement effect. In the following embodiments, the refractive index distribution is formed so as to change stepwise. However, the present invention is not limited to this, and the refractive index distribution may be formed so as to change continuously.

  FIG. 1 is a top view of a general photoelectric conversion unit formed in a two-dimensional manner on a substrate according to a preferred embodiment of the present invention. FIG. 2 is a cross-sectional view taken along the line A-A ′ in the central pixel of FIG. 1.

  In FIG. 2, incident light 201 is refracted by the microlens 202 and enters the optical sensor unit 205 as a photoelectric conversion unit through the color filter 203. The optical sensor unit 205 is formed inside the semiconductor substrate 206, and senses incident light 201 to generate electric charges. A transparent film is disposed between the microlens 202 and the optical sensor unit 205. The transparent film includes a low refractive index region 204 having a low refractive index, a high refractive index region including a first high refractive index region 207 and a second high refractive index region 208 having a refractive index higher than that of the low refractive index region 204. , Is composed of. The refractive index of the low refractive index region 204 is, for example, about 1.45. The first high refractive index region 207 has a refractive index higher than that of the second high refractive index region 208. For example, the refractive index of the first high refractive index region 207 is about 1.9, and the second high refractive index region 207 The refractive index of the refractive index region 208 is about 1.75.

  In FIG. 2, the high refractive index region in the well structure inner region is, for example, two stages, and the ratio between the thickness of the first high refractive index region and the thickness of the second high refractive index region is 1: 1. Represents. In the present embodiment, the lower region is called a first high refractive index region, and the upper region is called a second high refractive index region. In the case of three stages described later, the lowermost region is called a first high refractive index region, the central region is called a second high refractive index region, and the uppermost region is called a third high refractive index region.

  Here, the microlens 202 is a lens configured above each pixel, has a width of about a unit pixel, and has a function of efficiently guiding light to each photosensor unit.

For example, SiO ₂ can be used as the transparent film having a low refractive index, and SiN can be used as the high refractive index region in the transparent film.

In addition, as the optical sensor unit 205, for example, an n ⁻ region formed by ion implantation of an n-type dopant into a Si substrate can be used.

  In the present embodiment, the refractive index in the well structure is changed continuously and step by step so that the refractive index distribution in the well structure is determined for each target pixel position. Say.

  The above-described embodiment is an example as means for realizing the present invention, and the elements, conditions, the number of regions, the material of the constituent elements, etc. constituting the imaging device and unit pixel to which the present invention is applied are appropriately modified. , Changes, additions, etc. Therefore, the present invention is not limited only to the above-described embodiment.

  EXAMPLES Hereinafter, although this invention is demonstrated based on an Example, this invention is not limited to these Examples, As long as it is contained in the concept of this invention, the structure and manufacturing method can be changed suitably.

(Example 1)
In this example, an image sensor having a structure in which the refractive index value is changed in the well structure inner region is simulated. As shown in FIG. 2, in this embodiment, two high refractive index regions in the well structure inner region are provided so that the thickness ratio becomes 1: 1 from the optical sensor unit 205 toward the microlens 202. It is divided into.

  The calculation conditions when the simulation is performed are shown below. The incident light wavelength was set to 0.55 μm, the depth of the optical sensor unit was set to 5.0 μm, and the amount of received light was calculated assuming that the light reaching the optical sensor unit 205 was received.

  FIG. 3 is a diagram illustrating the relationship between the amount of received light and the incident angle of the incident light 201 when the refractive indexes of the first high refractive index region 207 and the second high refractive index region 208 in the central pixel of the present embodiment are changed. It is. The horizontal axis represents the incident angle of the incident light 201 with respect to the image sensor, and the vertical axis represents the amount of light received at that time. The graph line in which only one number is shown in the graph indicates that the first high refractive index region 207 and the second high refractive index region 208 have the same refractive index, that is, an imaging element having a uniform refractive index. Indicates. In the graph line in which two numbers are shown in the graph, the left number represents the refractive index of the second high refractive index region 208, and the right number represents the refractive index of the first high refractive index region 207.

  In this embodiment, the well structure is formed in the inner region of the well structure so that the ratio of the thicknesses of the high refractive index regions is 1: 1 from the optical sensor unit 205 toward the microlens 202. The refractive index is changed from the optical sensor unit 205 toward the microlens 202 in these high refractive index regions. Accordingly, as shown in FIG. 3, it can be seen that the amount of received light is improved when the incident angle of the incident light 201 is between 0 and 13 °. In addition, at the time of wide-angle incidence, it can be seen that the image pickup device having the two high refractive index regions 207 and 208 has substantially the same performance as the image pickup device having a uniform refractive index.

  FIG. 4 is a diagram showing a list of simulation results when the refractive indexes of the first high refractive index region 207 and the second high refractive index region 208 are changed in this embodiment. In the list, the double circle indicates that the light receiving amount of the image sensor having two high refractive index regions 207 and 208 is particularly greatly improved as compared with the image sensor in which the well structure inner region has a uniform refractive index. Shows things. From this result, by setting the difference in refractive index between the high refractive index regions to about 0.15 or less, it has two high refractive index regions 207 and 208 as compared with an imaging element having a uniform refractive index. It can be seen that the amount of light received by the image sensor can be greatly improved.

(Example 2)
In this example, an image sensor having a structure in which the refractive index value is changed in the well structure inner region is simulated. As shown in FIG. 5, in this embodiment, the high refractive index regions 501 to 503 in the well structure inner region have a thickness ratio of 2 from the optical sensor unit 205 toward the microlens 202. It is divided into three so as to be 1: 1. The simulation calculation conditions are the same as those in the first embodiment.

  FIG. 6 is a diagram showing the relationship of the amount of received light with respect to the incident angle of light when the refractive indexes of the first to third high refractive index regions 501 to 503 in the central pixel of this embodiment are changed. The horizontal axis represents the incident angle of the incident light 201 with respect to the image sensor, and the vertical axis represents the amount of light received at that time. In the graph, a graph line in which only one number is shown indicates an imaging element in which the first to third high refractive index regions 501 to 503 have the same refractive index, that is, have a uniform refractive index. In the graph line in which three numbers are shown in the graph, the left number is the refractive index of the third high refractive index region 503, the middle number is the refractive index of the second high refractive index region 502, and the right number Represents the refractive index of the first high refractive index region 501.

  In the present embodiment, the high refractive index regions are formed in the well structure internal region from the optical sensor unit 205 toward the microlens 202 so that the ratio of the thicknesses of the high refractive index regions is 2: 1: 1. The refractive index is changed from the optical sensor unit 205 toward the microlens 202 in these high refractive index regions. As a result, as shown in FIG. 6, it can be seen that the amount of received light is improved when the incident angle of the incident light 201 is between 0 and 13 °. In addition, at the time of wide-angle incidence, it can be seen that the image sensor having the three high refractive index regions 501 to 503 maintains substantially the same performance as the image sensor having a uniform refractive index.

  FIG. 7 shows that, in this embodiment, the refractive index of the first high refractive index region 501 is fixed at 1.9, and the refractive indexes of the second high refractive index region 502 and the third high refractive index region 503 are changed. A list of simulation results is shown. In the list, the double circle indicates that the amount of light received by the image pickup device having three high refractive index regions 501 to 503 is greatly improved as compared with the image pickup device in which the well structure inner region has a uniform refractive index. Shows things. From this result, by setting the difference in refractive index between the high refractive index regions to about 0.1 or less, it has three high refractive index regions 501 to 503 as compared with an imaging element having a uniform refractive index. It can be seen that the amount of light received by the image sensor can be greatly improved.

(Example 3)
In this example, an image sensor having a structure in which the refractive index value is changed in the well structure inner region is simulated. As shown in FIG. 8, in this embodiment, the high refractive index regions 801 and 802 in the well structure inner region have a thickness ratio of 3: 1 from the optical sensor unit 205 toward the microlens 202. It is divided into two. The simulation calculation conditions are the same as those in the first embodiment.

  FIG. 9 is a diagram showing the relationship between the incident angle of the incident light 201 and the amount of received light when the refractive indexes of the first high refractive index region 801 and the second high refractive index region 802 in the central pixel of this embodiment are changed. It is. The horizontal axis represents the incident angle of the incident light 201 with respect to the image sensor, and the vertical axis represents the amount of light received at that time. In the graph, a graph line in which only one number is shown indicates an imaging element in which the refractive indexes of the two high refractive index regions 801 and 802 are the same, that is, have a uniform refractive index. In the graph line in which two numbers are shown in the graph, the left number represents the refractive index of the second high refractive index region 802, and the right number represents the refractive index of the first high refractive index region 801.

  In this embodiment, the high refractive index regions are formed in the well structure inner region from the optical sensor unit 205 toward the microlens 202 so that the ratio of the thicknesses of the high refractive index regions is 3: 1. The refractive index is changed from the optical sensor unit 205 toward the microlens 202 in these high refractive index regions. Accordingly, as shown in FIG. 9, it can be seen that the amount of received light is improved when the incident angle of the incident light 201 is between 0 and 13 °. In addition, at the time of wide-angle incidence, it can be seen that the image pickup device having the two high refractive index regions 801 and 802 maintains substantially the same performance as the image pickup device having a uniform refractive index.

(Comparative example)
The comparative example is a simulation of a conventional imaging device having a structure with a uniform refractive index in the well structure internal region. As shown in FIG. 10, in this comparative example, the high refractive index region 1001 in the well structure internal region is uniform from the optical sensor unit 205 toward the microlens 202. The simulation calculation conditions are the same as those in the first embodiment.

  FIG. 11 is a diagram illustrating the relationship between the incident angle of the incident light 201 and the amount of received light when the refractive index of the high refractive index region 1001 in the central pixel of this comparative example is changed. The horizontal axis represents the incident angle of the incident light 201 with respect to the image sensor, and the vertical axis represents the amount of light received at that time. The numbers in the graph represent the refractive index of the high refractive index region 1001.

  In this comparative example, the refractive index of the high refractive index region 1001 is uniform from the photosensor portion 205 toward the microlens 202 in the well structure internal region. Accordingly, as shown in FIG. 11, it can be seen that the amount of received light is reduced as compared with the first to third embodiments when the incident angle of the incident light 201 is between 0 and 13 °. In particular, it can be seen that as the refractive index of the high refractive index region 1001 is lower, the amount of received light decreases more significantly, and the incident angle of the incident light 201 at which the amount of received light decreases compared to Examples 1 to 3 is increased. .

It is a top view of the photoelectric conversion part formed two-dimensionally with respect to the board | substrate which concerns on suitable embodiment of this invention. FIG. 2 is a cross-sectional view taken along the line A-A ′ in the center pixel of FIG. 1. It is a figure which shows the relationship of the light reception amount with respect to the incident angle of light in the case of changing the refractive index of the 1st, 2nd high refractive index area | region in the center pixel of a present Example. It is a figure which shows the list of the simulation result when changing the refractive index of the 1st, 2nd high refractive index area | region in Example 1. FIG. FIG. 6 is a cross-sectional view taken along the line A-A ′ at the center pixel in FIG. 1 in the second embodiment. FIG. 10 is a diagram illustrating a relationship between an incident angle of light and a received light amount at a central pixel in the second embodiment. FIG. 10 is a diagram showing a list of results of characteristics with respect to refractive index fluctuations in a central pixel in Example 2. FIG. 9 is a cross-sectional view taken along the line A-A ′ in the center pixel of FIG. 1 in Example 3. FIG. 10 is a diagram illustrating the relationship between the incident angle of light and the amount of received light at the central pixel in the third embodiment. It is sectional drawing of the conventional image pick-up element which has a well type structure in a comparative example. In a comparative example, it is a figure which shows the relationship between the incident angle of light and the light reception amount in the center pixel of the conventional image pick-up element which has a well-type structure.

Explanation of symbols

205 Photosensor unit 202 Micro lens 204, 207, 208 Transparent film

Claims (9)

A photoelectric conversion means; a microlens for condensing light on the photoelectric conversion means; and an imaging device having a transparent film between the microlens and the photoelectric conversion means,
The transparent film has a region having a higher refractive index than its surroundings,
The imaging device, wherein the refractive index of the region changes from the photoelectric conversion means toward the microlens.   The imaging element according to claim 1, wherein a refractive index of the region is gradually decreased from the photoelectric conversion unit toward the microlens.   The region includes a first region having a first refractive index from the photoelectric conversion means toward the microlens, and a second region having a second refractive index lower than the first refractive index. The imaging device according to claim 2, wherein the two regions are arranged in this order.   The image sensor according to claim 3, wherein the ratio of the thickness of the first region to the thickness of the second region is 1: 1.   The image sensor according to claim 3, wherein the ratio of the thickness of the first region to the thickness of the second region is 3: 1.   The region includes a first region having a first refractive index from the photoelectric conversion means toward the microlens, and a second region having a second refractive index lower than the first refractive index. 3. The image pickup device according to claim 2, wherein the second region and the third region having a third refractive index lower than the second refractive index are arranged in this order. .   The imaging device according to claim 6, wherein a ratio of the thickness of the first region, the thickness of the second region, and the thickness of the third region is 2: 1: 1.   The imaging device according to any one of claims 3 to 7, wherein a difference in refractive index between the regions arranged in the region is 0.15 or less.   The imaging element according to claim 1, wherein a refractive index of the region continuously decreases from the photoelectric conversion unit toward the microlens.

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