Solid-state imaging device, camera and signal processing method

The solid-state imaging device of the present invention includes: photodiodes which are two-dimensionally arranged; light condensers each of which condenses light and is provided in a position to correspond to two of the photodiodes which are adjacent to each other; and separating units each of which separates the light entering through the light condensers into first light having a wavelength within a predetermined range, and second light having a wavelength out of the predetermined range, and is provided in a position to correspond to one of the light condensers. Each of the separating units includes: a light-selecting unit which selectively allows transmission of one of the first light and the second light and reflect the other one of the first light and the second light, and allow entering of the transmitted light to one of the corresponding two of the photodiodes; and a light-reflecting unit which reflects the light, reflected by the light-selecting unit, towards the other one of the corresponding two of the photodiodes.

BACKGROUND OF THE INVENTION

(1.) Field of the Invention

The present invention relates to a solid-state imaging device and a camera.

(2.) Description of the Related Art

A conventional solid-state imaging device obtains signals of desired colors through color filters in order to obtain pixel signals which correspond to red (R), green (G) and blue (B). Incident light which enters the solid-state imaging device enters photodiodes via microlenses and color filters. An example of an arrangement of is color filters is the Bayer arrangement.

A conventional technology of a solid-state imaging device which enhances sensitivity and improves a color separating characteristic is disclosed in the Japanese Laid-Open Patent Application No. 2000-151933 (Patent Reference 1).

FIG. 1is a plan view showing an imaging element of the above mentioned conventional technology.FIG. 2is a cross-section diagram taken along the line A-A′ inFIG. 1.

The solid-state imaging device shown inFIG. 2includes a red photodiode2, a green photodiode3, and a blue photodiode4which are positioned near a surface of a semiconductor substrate1. The red photodiode2, the green photodiode3, and the blue photodiode4are covered by a transparent film5which is made of silica glass, for example.

The transparent film5is formed in such manner that its top surface, opposite to its lower surface covering the photodiodes2,3and4, has a mountain range-like shape. A filter6, a filter7and a filter8are formed on inclined areas of the top surface of the transparent film5having the mountain range-like shape which are inclined by a fixed angle in the same direction. The filters6,7and8are arranged in positions which correspond to the photodiodes2,3and4, respectively.

The inclination angle of each of the filters6,7and8is preferred to be as close to 45° as possible so that light which enters the filter6from above is reflected towards the right direction of the figure, and is then reflected by the filter7or8to enter the photodiode3or4, respectively.

The filter6has a characteristic that allows transmission of red light R and reflects green light G and blue light B. The filter7has a characteristic that allows transmission of blue light B and reflects green light G. The filter8has a characteristic that reflects any colors of light.

The filters6and7generally include a multilayer film which is called dichroic filter, and are structured in the same manner as the filter which is usually formed on a surface of a dichroic prism of a three charge coupled device (3CCD) video camera and an electric still camera. The filter8includes a total reflection film which includes a metal film made of aluminum, for example.

The filters6,7and8are covered by a transparent film9having a refractive index which is low compared to that of the transparent film5.

On an area of the transparent film9that corresponds to the filter6, there is a concave lens11. The transparent film9is covered by a light-blocking film35. On an area of the light-blocking film35that corresponds to the filter6, there is an aperture36. Through the aperture36of the light-blocking film35and the concave lens11, light enters the filter6only, and unnecessary light does not enter the other filters7and8as the unnecessary light is blocked by the light-blocking film35.

The light-blocking film35and the concave lens11are covered by a transparent film12. On an area of the transparent film12that corresponds to the filter6, there is a convex lens13. Accordingly, for a set of one red photodiode2, one green photodiode3, and one blue photodiode4for three pixels, there is a light condenser which is made up of a pair of one convex lens13and one concave lens11.

Incident light is condensed by the convex lens13and the concave lens11, and enters, as collimated light, the filter6which is an initial stage.

Among the incident light which enters the filter6, red light R enters the red photodiode2through the filter6. Among the incident light which enters the filter6, green light G and blue light B are reflected by the filter6towards the right direction, that is, towards the filter7.

Green light G and blue light B enter the filter7. However, green light G is reflected by the surface of the filter7, and enters the green photodiode3. Blue light B transmits the filter7and enters the filter8. Then blue light B is reflected by the filter8and enters the blue photodiode4.

As described above, the solid-state imaging device of the conventional technology: separates the incident light into red, green and blue as the filters6,7and8reflect and/or allow transmission of the incident light; and allocates the light of each color to the corresponding photodiode2,3or4. As a result, compared to filters having a structure in which specific light among incident light is thermally converted and the remaining light passes, the percentage of the incident light which reaches the photodiodes increases and thus the sensitivity is enhanced.

However, as pixel cells in solid-state imaging devices of recent years become denser and minitualized, the sensitivity is desired to be further enhanced. For example, in the above described conventional technology, separating primary colors from incident light results in a loss of light when light of each primary color transmits or reflects off. For example, inFIG. 2, blue light B reflects off the filter6, transmits the filter7, and reflects off the filter8, and thus causing a loss of light.

The present invention aims at providing a solid-state imaging device and a camera which can enhance a resolution and sensitivity.

SUMMARY OF THE INVENTION

In order to achieve the above mentioned object, the solid-state imaging device of the present invention includes: photodiodes which are two-dimensionally arranged; light condensers each of which condenses light and is provided in a position to correspond to two of the photodiodes which are adjacent to each other; and separating units each of which separates the light entering through the light condensers into first light having a wavelength within a predetermined range, and second light having a wavelength out of the predetermined range, and is provided in a position to correspond to one of the light condensers. Each of the separating units includes: a light-selecting unit which selectively allows transmission of one of the first light and the second light and reflect the other one of the first light and the second light, and allow entering of the transmitted light to one of the corresponding two of the photodiodes; and a light-reflecting unit which reflects the light, reflected by the light-selecting unit, towards the other one of the corresponding two of the photodiodes. With this structure, since the incident light is separated into two light, and each of the separated two light enters a corresponding photodiode, a loss of light in course of separation is reduced, and thus the sensitivity can be enhanced. More specifically, since one of the first light and the second light enters the corresponding photodiode after transmitting the light-selecting unit once, and the other one of the first light and the second light enters the corresponding photodiode after reflecting off twice of the light-selecting unit and the light-reflecting unit, a loss of light caused by the transmission and the reflection can be reduced compared to the case where the incident light is separated into three light, and therefore the sensitivity can be enhanced. Further, a loss of light can be reduced compared to an absorption color filter which includes a pigment or a dye. Furthermore, since each of the light condensers is provided in a position to correspond to two of the photodiodes, it is possible to condense a larger amount of light to each of the photodiodes.

Here, the light-reflecting unit may reflect only visible light. Further, the solid-state imaging device may further include a removing unit which removes infrared light, and each of the separating units may separate light in which the infrared light is removed by the removing unit into the first light and the second light. With this structure, unnecessary light (for example, infrared light) which is light other than visible light is removed, and thus it is possible to enhance the image quality by enhancing the sensitivity with respect to visible light.

Here, the separating units may include first type separating units and second type separating units. The first light separated by the first type separating units may be first primary color light indicating a first primary color, among red, green and blue, and the second light separated by the first type separating units may be first complementary color light indicating a first complementary color which is a complementary color of the first primary color. The first light separated by the second type separating units may be second primary color light indicating a second primary color which is different from the first primary color, and the second light separated by the second type separating units may be second complementary color light indicating a second complementary color which is a complementary color of the second primary color. Here, the first primary color light, the first complementary color light, the second primary color light, and the second complementary color light may be red light, cyan light, blue light and yellow light, respectively. The first type separating units may be arranged in the same rows or columns, and the second type separating units may be arranged in the same rows or columns. With this structure, since the first primary color, the first complementary color, the second primary color and the second complementary color are used, two combinations of a primary color and a complementary color reduces a loss of light to a minimum. Further, since the first type separating units are arranged in the same rows or columns, and the second type separating units are arranged in the same rows or columns, manufacturing of the separating units can be simplified.

Here, the first primary color light, the first complementary color light, the second primary color light, and the second complementary color light may be red light, cyan light, green light and magenta light, respectively. The first type separating units may be arranged in the same rows or columns, and the second type separating units may be arranged in the same rows or columns. With this structure, in the case where the transmission characteristic (for example, a width at a half value) of the light-selecting unit which corresponds to blue light is inferior to that of the light-selecting unit which corresponds to a different color, the sensitivity can be enhanced.

Here, the solid-state imaging device may further include a converting unit which converts signals respectively indicating the first primary color, the first complementary color, the second primary color, and the second complementary color, obtained from the photodiodes, into a red color signal, a green color signal and a blue color signal. With this structure, since the first primary color, the first complementary color, the second primary color, and the second complementary color are converted into primary color signals, that is, a red signal, a green signal and a blue signal, three primary color signals having an enhanced sensitivity can be obtained.

Here, the light-selecting unit and one of the corresponding two of the photodiodes may be arranged along an optical axis of the light condensed by the corresponding one of the light condensers. Further, the light condensers may be arranged in such manner that the respective centers of the light condensers in a row are shifted from the respective centers of the light condensers in a vertically adjacent row by a distance between the respective centers of two of the photodiodes which are horizontally adjacent. With this structure, shifting the positions of the light condensers allows an enhancement of a spatial resolution to a maximum spatial resolution.

Here, the light-selecting unit may be a multilayer film which includes two types of optical films having different refractive indices. The optical thickness of each of the optical films may be equal to a quarter of a set center wavelength, and the multilayer film may further include an insulator layer having a photonic structure which is structured based on the set center wavelength. With this structure, it is possible to adjust a light transmission characteristic of the multilayer film, as a dichroic filter and a dichroic mirror, which corresponds to the set center wavelength, based on the optical thickness of the insulator layer. As a result, a commonality of forming processes between two types of light-selecting units can be achieved, and the number of manufacturing man-hours can be reduced.

Here, the light-selecting unit may be a multilayer film which includes two types of optical films having different refractive indices. The optical thickness of each of the optical films may be equal to a quarter of a set center wavelength, and the multilayer film may further include an insulator layer having the optical thickness other than the optical thickness equal to a quarter of the set center wavelength. With this structure, it is possible to adjust the light transmission characteristic of the multilayer film, as a dichroic filter and a dichroic mirror, which corresponds to the set center wavelength, based on the optical thickness of the insulator layer. As a result, a commonality of forming processes between two types of light-selecting units can be achieved, and the number of manufacturing man-hours can be reduced.

Furthermore, the camera of the present invention has the same structure as that of the above described solid-state imaging device.

Further, the signal processing method for use in the solid-state imaging device of the present invention is the signal processing method for use in the solid-state imaging device described above. The signal processing method includes: obtaining, from four of the photodiodes, signals respectively indicating the first primary color, the first complementary color, the second primary color, and the second complementary color; and converting the obtained four signals into a red color signal, a green color signal and a blue color signal. With this structure, since the first primary color, the first complementary color, the second primary color and the second complementary color are converted into primary color signals, that is, a red signal, a green signal and a blue signal, it is possible to obtain signals of the three primary colors having an enhanced sensitivity. In addition, in accordance with the arrangement of the light condensers, a resolution in a specific direction (for example, a vertical direction or a horizontal direction) can be made higher than a resolution in another direction.

According to the solid-state imaging device, the camera and the signal processing method of the present invention, it is possible to enhance the sensitivity, and allows simplification in enhancing a resolution due to the suitability for microfabrication. In addition, it is also possible to enhance the resolution in a specific direction.

The disclosure of Japanese Patent Application No. 2006-108035 filed on Apr. 10, 2006 including specification, drawings and claims is incorporated herein by reference in its entirety.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

First Embodiment

A solid-state imaging device according to the present embodiment separates incident light entering through a microlens into first light having a wavelength within a predetermined range, and second light having a wavelength out of the predetermined range. Further, the first light enters a photodiode, and the second light enters a different photodiode. Further, for separating the incident light entering through the microlens, a multilayer film, having an insulator layer (also called a spacer layer) that has a photonic structure which is structured based on the wavelength within the predetermined range, is used. With this, sensitivity of the solid-state imaging device is enhanced.

FIG. 3is a top view showing a color arrangement of photodiodes in the solid-state imaging device of the first embodiment. As this figure shows, the solid-state imaging device includes photodiodes which are two-dimensionally arranged. The above described first light enters one of two photodiodes which are adjacent to each other, and the above described second light enters the other photodiode. There are two types of pairs of two photodiodes which are adjacent to each other. One of the types of pairs is a pair of a photodiode102B for receiving blue light and a photodiode102Ye for receiving yellow light, the color of which is a complementary color of blue. Another type of pairs is a pair of a photodiode102R for receiving red light and a photodiode102Cy for receiving cyan light, the color of which is a complementary color of red.

As described above, the photodiodes include four types of photodiodes: a photodiode which corresponds to first primary color light indicating a first primary color, that is, one of the colors, red, green and blue; a photodiode which corresponds to first complementary color light indicating a first complementary color, that is, a complementary color of the first primary color; a photodiode which corresponds to second primary color light indicating a second primary color which is different from the first primary color; and a photodiode which corresponds to second complementary color light indicating a second primary color, that is, a complementary color of the second primary color.

FIG. 4is a top view showing an arrangement of microlenses in the solid-state imaging device. As the figure shows, each of a plurality of microlenses109is provided to correspond to a pair of photodiodes, and serves as a light condenser which condenses light. Although the shape of each of the microlenses109is a rounded rhombic shape (a rounded square) as shown in the figure, the shape may be a circle or a square. The optical axis of each of the microlenses109is arranged in such way that it matches the center of a photodiode corresponding to a primary color, that is, a photodiode102B and102R. More specifically, the microlenses109are arranged in such manner that the respective centers of the microlense109in a row are shifted from the respective centers of the microlenses109in a vertically adjacent row by a distance between the respective centers of two of the photodiodes which are horizontally adjacent.

FIG. 5is a diagram showing a cross section of the solid-state imaging device taken along the line A-A shown inFIG. 4. In this figure, the solid-state imaging device includes the photodiode102B and the photodiode102Ye which are positioned near a surface of a semiconductor substrate101. The photodiode102B and the photodiode102Ye are covered by a transparent film103which is made of a silica glass, for example.

The transparent film103is formed in such manner that its top surface, opposite to its lower surface covering the photodiodes102B and104Ye, has a mountain range-like shape. A light-selecting unit104B and a light-reflecting unit104M are formed on inclined areas of the mountain range-like shaped top surface which are inclined by a fixed angle in the same direction. The light-selecting unit104B and the light-reflecting unit104M are positioned to correspond to the photodiode102B and the photodiode102Ye, respectively.

The light-selecting unit104B has a characteristic that selectively: allows transmission of light which has a wavelength of blue light as the light having a wavelength within the predetermined range, among the incident light entering through the corresponding microlens109; and reflects yellow light, the color of which is a complementary color of blue (that is, light having a wavelength which differs from the wavelength of blue light). The light-selecting unit104B is inclined so that the transmitted blue light enters the photodiode102B and that the reflected yellow light enters the light-reflecting unit104M which is positioned above the photodiode102Ye. The inclination angle of the light-selecting unit104B is preferred to be as close to 45° as possible so that the incident light from above is reflected towards the right direction of the figure, and is further reflected by the light-reflecting unit104M to enter the photodiode102Ye.

Furthermore, the light-selecting unit104R has a characteristic that selectively: allows transmission of light which has a wavelength of red light, among the incident light entering through the corresponding microlens109; and reflects cyan light, the color of which is a complementary color of red (that is, light having a wavelength which differs from the wavelength of red light). The light-selecting unit104R is inclined so that the transmitted red light enters the photodiode102R and that the reflected cyan light enters light-reflecting unit104M which is positioned above the photodiode102Cy.

As described above, whether incident light which enters the light-selecting unit104B transmits or reflects off the light-selecting unit104B, and whether incident light which enters the light-selecting unit104R transmits or reflects off the light-selecting unit104R are determined by the wavelength of the incident light. The wavelength range can be set selectively. Generally, for the light-selecting unit104B, a multilayer film called dichroic filter can be used, the dichroic filter being structured in the same manner as the filter formed on a surface of a dichroic prism in an electric still camera, a 3CCD video camera, and the like. However, for the light-selecting unit104B in the present embodiment, a multilayer film including an insulator layer is used, the insulator layer having the photonic structure and being an improved version of the dichroic filter.

The light-reflecting unit104M has a characteristic which reflects incident light, and includes a total reflection film which includes a metal film made of aluminum, for example.

The light-selecting unit104B and the light-reflecting unit104M are covered by a transparent film105having a refractive index which is low compared to that of the transparent film103.

On an area of the transparent film105that corresponds to the light-selecting unit104B, there is a concave lens106. The transparent film105is covered by a light-blocking film107. On an area of the light-blocking film107that corresponds to the light-selecting unit104B, there is an aperture. Through the aperture and the concave lens106, light enters the light-selecting unit104B, and unnecessary light does not enter the light-selecting unit104R and the light-reflecting units104M which are adjacent to the light-selecting unit104B, since the unnecessary light is blocked by the light-blocking film107.

The light-blocking film107and the concave lens106are covered by a transparent film108. On an area of the transparent film108that corresponds to the photodiode102B, the microlens109(a convex lens) is provided. Accordingly, for each pair of one photodiode102B and one photodiode102Ye which are adjacent to each other, there is a light condenser made up of a pair of one microlens109and one concave lens106.

Incident light is condensed by the microlens109and the concave lens106, and enters the light-selecting unit104B as collimated light.

Among the incident light which enters the light-selecting unit104B, blue light B transmits the light-selecting unit104B and enters the blue photodiode102B. Among the incident light which enters the light-selecting unit104B, yellow light Ye, the color of which is a complementary color of blue, is reflected by the light-selecting unit104B towards the light-reflecting unit104M which is positioned above the photodiode102Ye.

Yellow light Ye reflects off the light-reflecting unit104M, and enters the photodiode102Ye.

As described above, the light entering through the microlens109is separated into blue light and yellow light as the light-selecting unit104B and the light-reflecting unit104M reflect and/or allow transmission of the incident light. Further, blue light and yellow light are allocated to the corresponding photodiode102B or102Ye. Blue light enters the photodiode102B after transmitting the light-selecting unit104B once. Yellow light enters the photodiode102Ye after reflecting off twice of the light-selecting unit104B and the light-reflecting unit104M. Compared to the conventional case where the light is separated into three light, a loss of light resulted from transmission and reflection is reduced, and thus it is possible to enhance the sensitivity. For every pair of two photodiodes, one microlens is provided, therefore a resolution with respect to incident light becomes a half of the number of the photodiodes. However, when the microlenses are arranged in 45° diagonal lines as shown inFIG. 4, the distance between the respective centers of two of the microlenses which are vertically or horizontally adjacent to each other becomes 1.4 times longer than the distance between the respective centers of two of the photodiodes which are vertically or horizontally adjacent to each other. Further, the vertical resolution and the horizontal resolution can be controlled to be 1/1.4 of the number of the photodiodes.

FIG. 6is a pattern diagram showing directions of the light-selecting units and the light-reflecting units in rows adjacent to each other. A section (a) of the figure is a top view showing two rows which are adjacent to each other. In one of the rows, the blue photodiodes102B and the yellow photodiodes102Ye are alternately aligned. In the other row of the adjacent rows, the cyan photodiodes102Cy and the red photodiodes102R are alternately aligned. A section (b) ofFIG. 6is a pattern diagram showing a cross section taken along the line B-B. In the row shown in the section (b) of the figure in which the photodiodes102B and the photodiodes102Ye (hereinafter referred to as B and Ye, respectively) are alternately aligned, a reflecting surface of the light-selecting unit104B that selectively reflects yellow light having the wavelength different from the wavelength of blue light, faces the right direction of the figure, and a reflecting surface of the light-reflecting unit104M faces the left direction of the figure. The reflecting surface of the light-selecting unit104B and the reflecting surface of the light-reflecting unit104M face each other and both incline in the same direction (45° downward to the right in the figure).

A section (c) ofFIG. 6is a pattern diagram showing a cross section taken along the line C-C. In the section (c) of the figure, the light-reflecting unit104M and the light-selecting unit104R are aligned in the opposite manner to the one shown in the section (b). Therefore, a reflecting surface of the light-reflecting unit104M and a reflecting surface of the light-selecting unit104R face and incline in the opposite directions to the ones shown in the section (b).

FIG. 7AandFIG. 7Bare cross-section diagrams showing more detailed structures of the light-selecting unit104B and the light-selecting unit104R, respectively. AsFIG. 7Ashows, the light-selecting unit104B is a multilayer film including a titanium dioxide layer501a,a silicon dioxide layer501b,a titanium dioxide layer501c,an insulator layer501B, a titanium dioxide layer501e, a silicon dioxide layer501f,and a titanium dioxide layer501g.

More specifically, the light-selecting unit104B is a dielectric multilayer film in which materials such as a silicon oxide layer (SiO2) having a low refractive index and materials such as a titanium oxide layer (TiO2) and a silicon nitride layer (Si3N4) having a high refractive index are alternately layered, and in which the insulator layer501B is also included. All layers except for the insulator layer501B have the same optical thicknesses. The term “optical thickness” refers to a value nd which is a refractive index n of the material of the layer multiplied by the thickness d of the layer. The optical thicknesses of all layers501ato501g,except for the insulator layer501B, are a quarter of a wavelength λ (λ/4) (λ is the wavelength of red light inFIGS. 7A and 7B). The wavelength λ which is set for each layer having the optical thickness of λ/4 is called a set center wavelength.

In contrast, as shown inFIG. 7B, the light-selecting unit104R is different from the light-selecting unit104B in that the light-selecting unit104R includes a silicon dioxide layer501dhaving the optical thickness of λ/4, instead of the insulator layer501B. The light-selecting unit104R does not include the insulator layer501B, and is structured in the same way as the dichroic filter in which each layer has the optical thickness of λ/4. Therefore, the light-selecting unit104R selectively allows transmission of light having a wavelength which is equal to the set center wavelength λ (red light in this case), and reflects light having a different wavelength. Consequently, the light-selecting unit104R shown inFIG. 7Bserves as a dichroic filter and a dichroic mirror which allow transmission of red light and reflect cyan light, the color of which is a complementary color of red. Note that transmission characteristics of the light-selecting unit104B and the light-selecting unit104R are shown in the lower part ofFIG. 15Awhich is described later.

The structure of the insulator layer501B shown inFIG. 7Ahas the photonic structure in which titanium dioxide and silicon dioxide are alternately aligned along the principal surface. The insulator layer501B has a characteristic which allows transmission of light having a wavelength other than λ of the above λ/4. That the light-selecting unit104B includes the insulator layer501B is one of the features of the present embodiment. More specifically, based on the optical thickness of the insulator layer501B, a wavelength range of light which transmits the light-selecting unit104B can be adjusted. In other words, by including the insulator layer501B, the light-selecting unit104B shown inFIG. 7Ashifts the transmission wavelength of the dichroic filter in which each layer has the optical thickness of λ/4, λ being the wavelength of red light. Thus, the light-selecting unit104B is capable of selectively allowing transmission of light within a desired wavelength range (that is, blue light), and reflecting yellow light, the color of which is a complementary color of blue.

As shown inFIG. 7B, the light-selecting unit104R may be a dichroic filter. As shown inFIG. 7A, the light-selecting unit104B includes the dielectric multilayer film which is included in the light-selecting unit104R, and the insulator layer inserted in the dielectric multilayer film. Based on the optical thickness of the insulator layer, the wavelength of light which transmits the light-selecting unit104B is adjusted to the wavelength of blue light. As a result, the light-selecting unit104B and the light-selecting unit104R both include the layers501a,501b,501c,501e,501f,and501g,and therefore, a commonality of manufacturing processes between the light-selecting unit104B and the light-selecting unit104R can be achieved, and the number of manufacturing man-hours can be reduced.

Note that the International Patent Publication WO 2005/069376 A1 discloses a technique of adjusting the transmission wavelength in such manner that the transmission wavelength is shifted from the set center wavelength, by providing an insulator layer in a dielectric multilayer film in which each layer has the optical thickness of λ/4. The light-selecting units104B and104R can be manufactured based on this publication.

FIGS. 8A and 8Bare cross-section diagrams of the light-reflecting units104M. The light-reflecting unit104M shown inFIG. 8Aincludes an aluminium layer601a. By including the aluminium layer601a, the light-reflecting unit104M completely reflects the incident light entering from the light-selecting unit104B or the light-selecting unit104R towards the photodiode102Ye or the photodiode102Cy, respectively. The light-reflecting unit104M shown inFIG. 8Bcompletely reflects visible light only, and serves as a removing unit which removes ultraviolet light and infrared light. Therefore, the light-reflecting unit104M shown inFIG. 8Bis formed by a component such as a multilayer film having layers601b-601gwhich absorbs ultraviolet light and infrared light.

As described above, the solid-state imaging device of the present invention is structured in such way that it separates incident light entering through the microlens109into the first primary color light having the wavelength within the predetermined range, and the first complementary color light having a wavelength out of the predetermined range. The first primary color light enters one of the photodiodes, and the first complementary color light enters another one of the photodiode. Further, for separating the incident light entering through the microlens109, the light-selecting units104B and104R are used, the light-selecting units104B and104R including the multilayer film having the insulator layer that has the photonic structure which is structured based on the wavelength of the predetermined range. Accordingly, sensitivity of the solid-state imaging device can be enhanced, and a commonality of the manufacturing processes can be achieved, and thus the manufacturing cost can be reduced.

Next, a number of variations are described.

FIG. 9AandFIG. 9Bare diagrams showing cross-sections of the light-selecting unit104B and the light-selecting unit104R as a first variation of the light-selecting units104B and104R. The light-selecting unit104B shown inFIG. 9Ais a dichroic filter structured by a multilayer film which includes a titanium dioxide layer701a, a silicon dioxide layer701b, a titanium dioxide layer701c, a silicon dioxide layer701d, a titanium dioxide layer701e, a silicon dioxide layer701f, and a titanium dioxide layer701g. The set center wavelength of the light-selecting unit104B is the wavelength of blue light. The light-selecting unit104R shown inFIG. 9Bis different from the light-selecting unit104B shown inFIG. 9Ain that there is an insulator layer701R having the photonic structure instead of the silicon dioxide layer701d. Based on the optical thickness of the insulator layer701R, the transmission wavelength of the light-selecting unit104R is adjusted to the wavelength of red light. With these structures of the light-selecting unit104B and the light-selecting unit104R, too, the common layers701a,701b,701c,701e,701fand701gin the light-selecting unit104B and in the light-selecting unit104R share the same optical thicknesses, and thus these common layers can be manufactured at the same time for both types of the light-selecting units. Consequently, a commonality of the manufacturing processes is achieved, and thus the manufacturing cost can be reduced.

FIG. 10AandFIG. 10Bare diagrams showing cross-sections of the light-selecting unit104B and the light-selecting unit104R as a second variation of the light-selecting units104B and104R. The light-selecting unit104B shown inFIG. 10Ais a multilayer film which includes a titanium dioxide layer801a, a silicon dioxide layer801b, a titanium dioxide layer801c, an insulator layer801B, a titanium dioxide layer801e, a silicon dioxide layer801f, and a titanium dioxide layer801g. The set center wavelength of all layers except for the insulator layer801B, that is, the set center wavelength of the layers801a,801b,801c,801e,801fand801g, is, for example, the wavelength of green light rather than the wavelength of blue light or red light (the optical thickness of λ/4, λ being the wavelength of green light). The light-selecting unit104R shown inFIG. 10Bis different from the light-selecting unit104B shown inFIG. 10Ain that there is an insulator layer801R instead of the insulator layer801B. The insulator layer801B has the optical thickness which shifts the wavelength of light that transmits the light-selecting unit104B from the wavelength of green light to the wavelength of blue light, and the wavelength of light that transmits the light-selecting unit104B is adjusted to the wavelength of blue light. The insulator layer801R has the optical thickness which shifts the wavelength of light that transmits the light-selecting unit104R from the wavelength of green light to the wavelength of red light, and the wavelength of light that transmits the light-selecting unit104R is adjusted to the wavelength of red light.

With these structures of the light-selecting unit104B and the light-selecting unit104R, too, the common layers801a,801b,801c,801e,801fand801gin the light-selecting unit104B and in the light-selecting unit104R share the same optical thicknesses, and thus these common layers can be manufactured at the same time for both types of the light-selecting units. Consequently, a commonality of the manufacturing processes is achieved, and thus the manufacturing cost can be reduced. In addition, although there is a difference in the optical thicknesses, both the light-selecting unit104B and the light-selecting unit104R have an insulator layer. Therefore, the thickness of the light-selecting unit104B and the thickness of the light-selecting unit104R can be made equal to each other.

Note that although, in the above embodiment, the pairs (B, Ye) and (R, Cy) are described as examples of pairs of a primary color and a complementary color, any two arbitrary pairs may be selected from among the pairs (B, Ye), (R, Cy) and (G, Mg).

FIG. 11is a diagram showing a first variation of a color arrangement of the photodiodes in pairs of a primary color and a complementary color. In this figure, in one of any two rows adjacent to each other, photodiodes102G and photodiodes102Mg which correspond to (G, Mg), respectively, are alternately arranged. In the other row of the adjacent rows, the photodiodes102Cy and the photodiodes102R which correspond to (Cy, R), respectively, are alternately arranged.

FIG. 12is a pattern diagram showing an arrangement of the microlenses109and cross sections of the rows adjacent to each other inFIG. 11. As shown in a section (a) ofFIG. 12, the microlenses109are arranged in such manner that the center of each of the microlenses109matches the center of a photodiode which corresponds to a primary color, that is, the photodiode102G and102R. As shown in sections (b) and (c) ofFIG. 12, the light-selecting units104and the light-reflecting units104M in one of any two rows adjacent to each other incline in the opposite direction to the direction in which the light-selecting units104and the light-reflecting units104M in the other row of the adjacent rows incline. Note that in the case where transmission characteristics of the light-selecting units104R,104G and104B are the characteristics shown in the lower part ofFIG. 15A, the color arrangement shown inFIG. 11is the most preferable color arrangement. This is because inFIG. 15A, a width at a half value of blue light is narrower that that of green light and of red light. In other words, by using the light-selecting units104R and104G which transmit red light and green light, respectively, and which have a better transmission characteristic than blue light, the sensitivity of the solid-state imaging device can be further enhanced.

Second Embodiment

The present embodiment describes an example of adjusting the optical thickness based on the physical thickness, instead of adjusting the optical thickness based on an insulator layer having the photonic structure in the light-selecting units104.

FIG. 13is a cross-section diagram of a solid-state imaging device of the second embodiment. The arrangement of photodiodes shown inFIG. 13is assumed to be the arrangement shown inFIG. 11in which the rows of (G, Mg) and the rows of (Cy, R) are alternately arranged.

The cross-section diagram shown inFIG. 13is different from the cross-section diagram shown inFIG. 5in that the cross-section diagram ofFIG. 13includes the photodiode102Mg and the photodiode102G instead of the photodiode102Ye and the photodiode102B, and includes a light-selecting unit904G instead of the light-selecting unit104B. Hereinafter, a description on points which are the same inFIG. 5is omitted, and a description mainly on different points is provided.

The photodiode102Mg and the photodiode102G have the same structures as the photodiode102Ye and the photodiode102B in a physical sense, however there is a difference in light which enters.

The light-selecting unit904G is different from the light-selecting unit104B in that the insulator layer does not have the photonic structure.

FIG. 14AandFIG. 14Bare cross-section diagrams showing more detailed structures of the light-selecting unit904R and the light-selecting unit904G, respectively. AsFIG. 14Ashows, the light-selecting unit904R is a multilayer film including a titanium dioxide layer201a, a silicon dioxide layer201b, a titanium dioxide layer201c, an insulator layer201R, a titanium dioxide layer201e, a silicon dioxide layer201f, and a titanium dioxide layer201g. All layers except for the insulator layer201R have the same optical thicknesses. All layers201ato201gexcept for the insulator layer201R have the set center wavelength which is the wavelength of green light. The insulator layer201R shown inFIG. 14Ais made of silicon dioxide, and has the optical thickness different from λ/4, λ being the wavelength of green light. Based on the optical thickness of the insulator layer201R, a wavelength range of light which transmits the light-selecting unit904R can be adjusted. In other words, by including the insulator layer201R, the light-selecting unit904R shown inFIG. 14Ashifts the transmission wavelength of the dichroic filter in which each layer has the optical thickness of λ/4, λ being the wavelength of green light. Thus, the light-selecting unit904R is capable of selectively allowing transmission of light within a desired wavelength range (that is, red light), and reflecting cyan light, the color of which is a complementary color of red.

In contrast, the light-selecting unit904G shown inFIG. 14Bis different from the light-selecting unit104B in that the light-selecting unit904G includes a silicon dioxide layer201dwhich has the optical thickness of λ/4. Since the light-selecting unit904G does not include the insulator layer201R, it means that the light-selecting unit904G has the same structure as the dichroic filter in which each layer has the optical thickness of λ/4, provided that the wavelength of green light is set as the set center wavelength. Therefore, the light-selecting unit904G allows transmission of light which has the wavelength equal to the set center wavelength λ (green light in this case). Accordingly, the light-selecting unit904G shown inFIG. 14Bserves as a dichroic filter and a dichroic mirror which allow transmission of green light, and which reflect magenta light, the color of which is a complementary color of green.

Next, spectral characteristics of the light-selecting units904of the present embodiment are described.

FIG. 15Ais a diagram showing spectral characteristics of the light-selecting units904B,904G and904R. The light-selecting unit904G shown in the figure is the light-selecting unit904G shown inFIG. 14B. The thickness of the insulator layer (spacer layer) is 0 nm. The light-selecting unit904B shown inFIG. 15Ahas a structure in which an insulator layer (spacer layer) having the thickness of 200 nm is added to the multilayer film of the light-selecting unit904G shown inFIG. 14B. The light-selecting unit904R shown inFIG. 15Ahas a structure in which an insulator layer (spacer layer) having the thickness of 50 nm is added to the multilayer film of the light-selecting unit904G shown inFIG. 14B.

Note that the spectral characteristics of the light-selecting units904B,904G and904R are derived using a characteristic matrix method. Further, the spectral characteristics are derived with an assumption that the refractive index of titanium dioxide (material having a high refractive index) is 2.5, the refractive index of silicon dioxide (material having a low refractive index) is 1.45, and the optical thickness and physical thickness of the insulator layer (spacer layer) are 200 nm and 80 nm for the light-selecting unit904B, 50 nm and 20 nm for the light-selecting unit904R, and 0 nm for the light-selecting unit904G.

As shown inFIG. 15A, it is possible to change the wavelength of light which transmits the spacer layer by adjusting the thickness of the spacer layer.

Note that instead of the above mentioned titanium dioxide, such material as silicon nitride, tantalum pentoxide, and zirconium dioxide may be used as the material having a high refractive index. Further, a material other than silicon dioxide may be used as the material having a low refractive index.

Next, transmission characteristics of the light-selecting units904are described.

FIGS. 15B and 15Care graphs showing a transmission characteristic of a dielectric multilayer film which changes depending on whether or not a spacer layer is included in the film. Note that the transmission characteristics shown inFIGS. 15B and 15Care derived using a matrix method in which a Fresnel coefficient is used, and are the transmission characteristics of vertical incident light only which are derived with an assumption that the pair number is 10 and the set center wavelength is 550 nm. The vertical axis of each of the graphs indicates transmittance, and the horizontal axis indicates a wavelength of incident light which enters the dielectric multilayer film.

In the case where the entire dielectric multilayer film which includes silicon nitride and silicon dioxide is a multilayer film having the optical thickness of λ/4, light having the wavelength within a wavelength range is reflected asFIG. 15Bshows, the wavelength range having the set center wavelength as the center of the range. Note that the larger the difference is between the refractive index of a multilayer film material having a high refractive index and the refractive index of a multilayer film material having a low refractive index, the larger the reflection bandwidth expands.

In contrast, in the case where the dielectric multilayer film is formed in such manner that multilayer films having the optical thickness of λ/4 are provided to sandwich the spacer layer having the optical thickness other than λ/4 and are symmetric to each other with respect to the spacer layer, it is possible to obtain the light-selecting units904which allow transmission of only light that has the wavelength near the set center wavelength in the reflection band of the multilayer film which has the optical thickness of λ/4, as shown inFIG. 15C.

As described above, a change in the thickness of the spacer layer results in a change in the transmission peak wavelength. In the present embodiment, with a focus on such a characteristic, the dielectric multilayer film is used, and thus, the thicknesses of the light-selecting units904can be approximately the wavelength of incident light (approximately 500 nm). Therefore, it is possible to minitualize the solid-state imaging device.

Further, the characteristics shown inFIGS. 15A to 15Calso apply to the insulator layer having the photonic structure in the first embodiment. This is because in the case where the insulator layer having the photonic structure is used, instead of adjusting the physical thickness, the refractive index is adjusted based on a pitch and an arrangement of the photonic structure, which results in an adjustment of the optical thickness.

As described above, the light-selecting unit904R and the light-selecting unit904G both include the common layers201a,201b,201c,201e,201fand201g. Therefore, a commonality of manufacturing processes between the light-selecting unit904R and the light-selecting unit904G can be achieved, and the number of manufacturing man-hours can be reduced.

Note that the International Patent Publication WO 2005/069376 A1 discloses the technique of adjusting the transmission wavelength in such manner that the transmission wavelength is shifted from the set center wavelength, by providing an insulator layer in a dielectric multilayer film in which each layer has the optical thickness of λ/4 and by adjusting the optical thickness of the provided insulator layer. The light-selecting units904R and904G can be manufactured based on this publication.

Next, a number of variations are described.

FIG. 16is a diagram showing a second variation of a color arrangement of the photodiodes which are in pairs of a primary color and a complementary color. In this figure, in one of any two rows adjacent to each other, the photodiodes102B and the photodiodes102Ye, as the pairs (B, Ye), are alternately arranged. In the other row of the adjacent rows, the photodiodes102R and the photodiodes102Cy, as the pairs (R, Cy), are alternately arranged. The position of the pair of the photodiodes in one of any two rows which are adjacent to each other is shifted from the position of the pair of the photodiodes in the other row of the adjacent rows by one photodiode (by one pixel). Thus, a photodiode102X which is at the head of each (R, Cy) row (shown as X in the figure) is not used.

FIG. 17is a pattern diagram, corresponding toFIG. 16, showing an arrangement of the microlenses109, and cross sections of rows adjacent to each other. As shown in a section (a) ofFIG. 17, the shape of each of the microlenses109is a rounded rhombic shape (square). The microlenses109are arranged in such manner that the center of each of the microlenses109matches the center of a photodiode which corresponds to a primary color, that is, the photodiode102B and102R. As shown inFIG. 16, shifting the position of the pair of the photodiodes in one of any two rows adjacent to each other from the position of the pair of photodiodes in the other row of the adjacent rows by one pixel (by one photodiode) allows both the light-selecting units104and the light-reflecting units104M in any two rows adjacent to each other to incline in the same direction, as shown in sections (b) and (c) ofFIG. 17. Therefore, it is possible to enhance manufacturing reliability.

FIG. 18is a diagram showing a third variation of the color arrangement of the photodiodes in the solid-state imaging device. In the figure, the photodiode which corresponds to a primary color and the photodiode which corresponds to another primary color are positioned in the same columns. In one of any two rows adjacent to each other, the photodiodes102Ye and the photodiodes102B, as the pairs (Ye, B), are alternately arranged. In the other row of the adjacent rows, the photodiodes102Cy and the photodiodes102R, as the pairs (Cy, R), are alternately arranged.

FIG. 19is a pattern diagram, corresponding toFIG. 18, showing an arrangement of the microlenses109, and cross-sections of rows adjacent to each other. As shown in a section (a) ofFIG. 19, the shape of each of the microlenses109is almost a rectangular. The microlenses109are arranged in such manner that the center of each of the microlenses109matches the center of a photodiode which corresponds to a primary color, that is, a photodiode102B and102R. As shown inFIG. 18, placing the photodiodes which, among the photodiodes in pairs, correspond to primary colors in the same columns allows both the light-selecting units104and the light-reflecting units104M in any two rows adjacent to each other to incline in the same direction as shown in sections (b) and (c) ofFIG. 19. Therefore, it becomes easy to uniform inclination degrees of all light-selecting units104and all light-reflecting units104M. The arrangement of the microlenses109shown inFIG. 19enables an increase in the resolution in a specific direction with respect to incident light. More specifically, with the solid-state imaging device of the present embodiment, the vertical arrangement pitch and the horizontal arrangement pitch of the microlenses109differ from each other. The vertical arrangement pitch is ½ of the horizontal arrangement pitch. As a result, this structure allows the vertical resolution to be twice the horizontal resolution.

FIG. 20is a pattern diagram showing a fourth variation of an arrangement of the microlenses109and cross-sections of rows adjacent to each other. This figure corresponds to the color arrangement of the photodiodes shown inFIG. 18, however, as shown in sections (b) and (c) ofFIG. 20, the position of the pair of the photodiodes in one of any two rows adjacent to each other is shifted from the position of the pair of the photodiodes in the other row of the adjacent rows by one photodiode. In other words, the photodiodes102X are not used. With this arrangement, the light-selecting unit104and the light-reflecting unit104M in one of any two rows adjacent to each other incline in the opposite direction to the direction in which the light-selecting unit104and the light-reflecting unit104M in the other row of the adjacent rows incline.

FIG. 21is a diagram showing a fifth variation of a color arrangement of the photodiodes in pairs of a primary color and a complementary color. In this figure, two types of pairs, that is the pairs (B, Ye) and the pairs (Cy, R) are alternately aligned in each row. In any two rows adjacent to each other, different pairs are vertically adjacent to each other.

FIG. 22is a pattern diagram, corresponding toFIG. 21, showing an arrangement of the microlenses109and cross-sections of rows adjacent to each other. As shown in a section (a) ofFIG. 22, the center of each of the microlenses109does not match the center of the photodiode102which corresponds to a primary color nor the center of the photodiode102which corresponds to a complementary color. The microlenses109need to be formed in such manner that each of the microlenses109condenses incident light in a direction towards the photodiode102which corresponds to a primary color or the photodiode102which corresponds to another primary color. As shown in sections (b) and (c) ofFIG. 22, the light-selecting unit104and light-reflecting unit104M in one of any two rows adjacent to each other incline in the opposite direction to the direction in which the light-selecting unit104and the light-reflecting unit104M in the other row of the adjacent rows incline.

FIG. 23is a diagram showing a sixth variation of a color arrangement of the photodiodes in pairs of a primary color and a complementary color. In this figure, in one of any two columns adjacent to each other, pairs (R, Cy) are aligned, and in the other column of the adjacent columns, pairs (Ye, B) are aligned.

FIG. 24is a pattern diagram, corresponding toFIG. 23, showing an arrangement of the microlenses109, and cross-sections of rows adjacent to each other. As shown in a section (a) ofFIG. 24, the center of each of the microlenses109matches the center of the photodiode102which correspond to a primary color. A section (b) ofFIG. 24is a pattern diagram showing a vertical cross section taken along the line O-O. A section (c) ofFIG. 24is a pattern diagram showing a vertical cross section taken along the line P-P. As shown in the figure, each pair may be a pair of two photodiodes which are vertically adjacent to each other. Further, when the photodiodes having almost rectangular microlenses109as shown inFIG. 19, are rearranged in such way that the photodiodes in pairs are vertically aligned rather than horizontally aligned, the microlenses109are also rearranged in such way that the long sides of the rectangles are vertically aligned. As a result, this arrangement allows the horizontal resolution to be twice the vertical resolution.

Note that in each embodiment described above, the light-selecting unit104selectively allows transmission of primary color light and reflects complementary color light. However, the light-selecting unit104may selectively allow transmission of the complementary color light and reflect the primary color light. In such case, the microlenses109may be arranged in such manner that the center of each of the microlenses109matches the center of the photodiode102which corresponds to a complementary color. Further, the microlenses109may be arranged in such manner that each of the microlenses109in one of any two rows adjacent to each other matches the photodiode102which corresponds to a primary color, and the center of each of the microlenses109in the other row of the adjacent rows matches the photodiode102which corresponds to a complementary color.

Third Embodiment

The present embodiment describes signal processing for converting color signals which are obtained by the solid-state imaging device of each of the above described embodiments into signals of three primary colors.

FIG. 25is a block diagram showing configuration of a camera according to the third embodiment. As the figure shows, a camera401of the present embodiment includes a signal processing unit410, a solid-state imaging device411, a driving unit412, a controlling unit414, a mechanical shutter415, a lens416and a displaying unit420.

The signal processing unit410includes a color converting unit413, and performs color conversion by obtaining signals of each of the photodiodes outputted by the solid-state imaging device411.

The solid-state imaging device411is the solid-state imaging device of the above described first and second embodiments. Light from an imaging subject enters the solid-state imaging device via the lens416and the mechanical shutter415. As an imaging result, the solid-state imaging device411outputs, in sequence, signals respectively indicating the first primary color, the first complementary color, the second primary color, and the second complementary color obtained from four photodiodes to the signal processing unit410. A pair of the first primary color signal and the first complementary color signal represents one of the following pairs: (B signal, Ye signal), (R signal, Cy signal) and (G signal, Mg signal). A pair of the second primary color signal and the second complementary color signal represents one of the other pairs mentioned above.

The driving unit412outputs various driving signals for driving the solid-state imaging device411.

The controlling unit414controls the entire camera401.

The displaying unit420makes a display on a monitor and a display of a captured image.

FIG. 26is an explanatory diagram of the color converting unit413. The color converting unit413converts the first primary color signal, the first complementary color signal, the second primary color signal and the second complementary color signal into a red signal, a green signal, and a blue signal. This color conversion can be performed using a well-known operation.

Note that for the mechanical shutter415, a filter may be provided to serve as a removing unit which removes ultraviolet light and infrared light.

Further, in each of the above described embodiments, the solid-state imaging device may be a Charge Coupled Device (CCD) type solid-state imaging device or a Metal Oxide Semiconductor (MOS) type solid-state imaging device.

Furthermore, as a material having a high refractive index, such material as silicon nitride, tantalum pentoxide, and zirconium dioxide may be used instead of using the above described titanium dioxide. Further, as a material having a low refractive index, a material other than silicon dioxide may be used.

Note that the number of layers in the multilayer film of the light-selecting units is not limited to the number shown in the above described embodiments, and may be any number. It is needless to say that a material of each layer is not limited to the above mentioned titanium dioxide, silicon dioxide, and magnesium oxide. Instead, tantalum oxide (Ta2O5), zirconium oxide (ZrO2), silicon nitride (SiN), silicon nitride (Si3N5), aluminium oxide (Al2O3), magnesium fluoride (MgF2) and hafnium oxide (HfO3) may be used.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a solid-state imaging device having photodiodes which are formed on a semiconductor substrate, and to a camera having such a solid-state imaging device. For example, the present invention is applicable to a CCD image sensor, a MOS image sensor, a digital still camera, a camera equipped mobile phone, a monitoring camera, a camera built in a laptop computer, a camera unit connected to an information processing apparatus and the like.