Solid-state imaging device and method for fabricating the same

A solid-state imaging device includes: a plurality of light-receiving parts arranged in an array in a substrate and performing photoelectric conversion on incident light; and a plurality of color separators each provided for adjacent four of the light-receiving parts arranged in two rows and two columns. Each of the color separators includes first through fourth color-separating elements and first and second mirror elements.

CROSS-REFERENCE TO RELATED APPLICATION

The disclosure of Japanese Patent Application No. 2006-082882 filed in Japan on Mar. 24, 2006 including specification, drawings and claims is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to solid-state imaging devices and methods for fabricating the devices, and particularly relates to a solid-state imaging device including transmission color filters in a Bayer pattern and a method for fabricating the device.

(2) Background Art

Solid-state imaging devices such as CCD solid-state imaging devices and MOS solid-state imaging devices are used for various image input equipment such as video cameras, digital still cameras and facsimiles.

To obtain a color image in a solid-state imaging device, it is necessary to decompose light incident on the solid-state imaging device into color components and then make the respective color components enter light-receiving parts for performing photoelectric conversion. Color components are generally separated by using absorption color filters (color separators) respectively associated with three colors of red (R), green (G) and blue (B). A green absorption filter, for example, absorbs red light and blue light and transmits only green light. Accordingly, when light passes through the absorption color filter, two-thirds of the light is disadvantageously absorbed, so that the sensitivity of the solid-state imaging device decreases.

On the other hand, transmission color filters are used in, for example, display apparatus. The transmission color filters are formed in combination with dichroic mirrors each of which transmits light with a specific wavelength and reflects light with the other wavelengths (see, for example, Japanese Unexamined Patent Publication No. 8-54623). Accordingly, in the case of applying transmission color filters to a solid-state imaging device, if a dichroic mirror which transmits only green light, for example, is used to separate green light and make the green light enter a light-receiving part and reflected light from which the green light has been separated is further separated and caused to enter other light-receiving parts, light incident on the solid-state imaging device is used without waste.

However, when the conventional transmission color filters are used in a solid-state imaging device, the following problems arise. The solid-state imaging device uses color filters in a Bayer pattern in which four light-receiving parts arranged in two rows and two columns are generally used as a set so that light which has passed through green filters enters two of the light-receiving parts and light which has passed through red and blue filters enters the other two light-receiving parts. This is because human vision has higher sensitivity to green light and, therefore, the number of light-receiving parts which receive green light is increased so as to enhance the resolution of an image. However, the conventional transmission color filters separate incident light into three light beams of red, green and blue. Accordingly, light-receiving parts which respectively receive red, green and blue light beams are arranged in a line, thus making it difficult to arrange color filters in a Bayer pattern.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a solid-state imaging device including transmission color filters in a Bayer pattern.

To achieve the object, according to the present invention, a solid-state imaging device includes four dichroic mirror elements and two mirror elements.

Specifically, a solid-state imaging device according to the present invention includes: a plurality of light-receiving parts arranged in an array in a substrate and performing photoelectric conversion on incident light; and a plurality of color separators each provided for adjacent four of the light-receiving parts arranged in two rows and two columns, wherein the four light-receiving parts are a first light-receiving part, a second light-receiving part, a third light-receiving part and a fourth light-receiving part, each of the color separators includes a first optical element part for guiding incident light to a first optical path entering the first light-receiving part, a second optical element part for guiding incident light to the fourth light-receiving part located in a row and a column which are different from a row and a column on which the first light-receiving part is located, a first color-separating element formed on the first optical path between the first optical element part and the first light-receiving part, reflecting light of one of red, green and blue included in incident light toward the third light-receiving part located in the row on which the first light-receiving part is located and a column different from the column on which the first light-receiving part located, guiding the reflected light to a third optical path crossing the first optical path, and transmitting light of the other two colors, a second color-separating element formed on the second optical path between the second optical element part and the fourth light-receiving part, reflecting light of one of red, green and blue included in incident light toward the second light-receiving part located in the column on which the first light-receiving part is located and a row different from the row on which the first light-receiving part is located, guiding the reflected light to a fourth optical path crossing the second optical path, and transmitting light of the other two colors, a third color-separating element formed on the first optical path between the first color-separating element and the first light-receiving part, reflecting light of one of two colors included in light which has passed through the first color-separating element, guiding the reflected light to a fifth optical path crossing the first optical path, and allowing light of the other color to pass and enter the first light-receiving part, a fourth color-separating element formed on the second optical path between the second color-separating element and the third light-receiving part, reflecting light of one of two colors included in light which has passed through the second color-separating element, guiding the reflected light to a sixth optical path crossing the second optical path, allowing light of the other color to pass and enter the fourth-light-receiving part, a first mirror element formed on the third optical path, reflecting light guided to the third optical path, and guiding the reflected light to a seventh optical path entering the third light-receiving part, and a second mirror element formed on the fourth optical path, reflecting light guided to the fourth optical path, and guiding the reflected light to an eighth optical path entering the second light-receiving part, the color of light reflected by the first color-separating element and the color of light reflected by the second color-separating element differ from each other, and the color of light transmitted through the third color-separating element and the color of light transmitted through the fourth color-separating element are identical.

In the color separator formed for each four light-receiving parts of the solid-state imaging device, the color of light reflected by the first color-separating element differs from that of light reflected by the second color-separating element, and the color of light transmitted through the third color-separating element is identical to that of light transmitted through the fourth color-separating element. Accordingly, light of the same color enters two of the four light-receiving parts and light of different colors respectively enters the other two light-receiving parts. As a result, transmission color filters are allowed to be arranged in a Bayer pattern, thus implementing a solid-state imaging device with high sensitivity.

Preferably, in the solid-state imaging device, the first color-separating element reflects blue light, the second color-separating element reflects red light, and the third color-separating element and the fourth color-separating element transmit green light. With this configuration, a primary color Bayer pattern is achieved.

In the solid-state imaging device, each of the first optical element part and the second optical element part preferably includes: a microlens element for focusing incident light; and a collimator element for forming light focused by the microlens element into parallel light.

Preferably, in the solid-state imaging device, the fifth optical path and the eighth optical path intersect, the sixth optical path and the seventh optical path intersect, a first halfmirror element for transmitting light traveling on the eighth optical path and for reflecting part of light traveling on the fifth optical path to have the reflected light enter the second light-receiving part is formed at an intersection of the fifth optical path and the eighth optical path, a second halfmirror element for transmitting light traveling on the seventh optical path and for reflecting part of light traveling on the sixth optical path to have the reflected light enter the third light-receiving part is formed at an intersection of the sixth optical path and the seventh optical path, a first light-absorbing part for absorbing light is formed on the fifth optical path at a side opposite the third color-separating element with respect to the first halfmirror element, and a second light-absorbing part for absorbing light is formed on the sixth optical path at a side opposite the fourth color-separating element with respect to the second halfmirror element. With this configuration, light reflected by the third and fourth color-separating elements is also utilized, thus further enhancing the sensitivity of the solid-state imaging device. In addition, color mixture caused by entering of light reflected by the third and fourth color-separating elements into other light-receiving parts is suppressed.

Preferably, in the solid-state imaging device, the fifth optical path and the eighth optical path intersect, the sixth optical path and the seventh optical path intersect, a first beam splitter element is formed at an intersection of the fifth optical path and the eighth optical path, a second beam splitter element is formed at an intersection of the sixth optical path and the seventh optical path, a first polarizer is formed on the fifth optical path between the third color-separating element and the first beam splitter element, a second polarizer is formed on the sixth optical path between the fourth color-separating element and the second beam splitter element, a third polarizer is formed on the seventh optical path between the first mirror element and the second beam splitter element, and a fourth polarizer is formed on the eighth optical path between the second mirror element and the first beam splitter element. With this configuration, light focused in the optical element part is used without waste.

The solid-state imaging device preferably further includes: a first light-blocking film formed around each of the color separators; and a second light-blocking film formed in regions where the color separators are provided and preventing transmission of light in regions other than the first optical path, the second optical path, the third optical path, the fourth optical path, the fifth optical path, the sixth optical path, the seventh optical path and the eighth optical path. With this configuration, occurrence of color mixture is further suppressed.

In this case, the second light-blocking film is preferably made of one of a material which absorbs light and a material which reflects light. Alternatively, a configuration in which an intermediate film transmitting light is formed in regions of each of the color separators serving as the first optical path, the second optical path, the third optical path, the fourth optical path, the fifth optical path, the sixth optical path, the seventh optical path and the eighth optical path, the second light-blocking film is made of a material having a refractive index lower than that of the intermediate film, and the intermediate film serves as a light waveguide may be adopted.

The solid-state imaging device preferably further includes: a first primary-color filter formed between the third color-separating element and the first light-receiving part and associated with the color of light incident on the first light-receiving part; a second primary-color filter formed between the first mirror element and the second light-receiving part and associated with the color of light incident on the second light-receiving part; a third primary-color filter formed between the second mirror element and the third light-receiving part and associated with the color of light incident on the third light-receiving part; and a fourth primary-color filter formed between the fourth color-separating element and the fourth light-receiving part and associated with the color of light incident on the fourth light-receiving part. With this configuration, occurrence of color mixture is suppressed.

A method for fabricating a solid-state imaging device according to the present invention includes the steps of: forming a plurality of light-receiving parts in an array in a semiconductor substrate; forming a first prism formation film on the semiconductor substrate and then patterning the first prism formation film, thereby forming first prisms having slopes above respective light-receiving parts arranged in every other row and every other column out of the plurality of light-receiving parts; forming a first dielectric film on the slopes of the first prisms, thereby forming a lower color-separating element transmitting light of a first color of the three primary colors of light; forming an interlayer insulating film covering the lower color-separating element on the semiconductor substrate; forming a second prism formation film on the interlayer insulating film and then patterning the second prism formation film, thereby forming second prisms having slopes above the respective light-receiving parts; forming a second dielectric film on the slopes of second prisms formed on the lower color-separating element and located above one of odd-number rows and even-number rows out of the second prisms, thereby forming first upper color-separating elements transmitting light of the first color and a second color of the three primary colors of light and reflecting light of a third color of the three primary colors of light toward a direction entering an adjacent one of the second prisms in a column direction; forming a third dielectric film on the slopes of second prisms formed on the lower color-separating element and located above the other of the odd-number rows and the even-number rows out of the second prisms, thereby forming second upper color-separating elements transmitting light of the first and third colors and reflecting light of the second color toward a direction entering an adjacent one of the second prisms in the column direction; and forming a fourth dielectric film on the slopes of second prisms other than the second prisms formed above the lower color-separating element out of the second prisms, thereby forming mirror elements each for reflecting, in a direction crossing the substrate, light reflected by one of the first upper color-separating element and the second upper color-separating element.

The method for fabricating a solid-state imaging device according to the present invention enables effective formation of color separating elements and mirror elements. Accordingly, a solid-state imaging device including transmission color filters in a Bayer pattern is easily fabricated.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention will be described with reference to the drawings.FIGS. 1 and 2illustrate basic configurations of a solid-state imaging device according to this embodiment.FIG. 1shows a plan configuration andFIG. 2shows a special configuration. InFIG. 2, an intermediate film and other components are not shown for simplicity.

As illustrated inFIGS. 1 and 2, the solid-state imaging device of this embodiment includes a plurality of light-receiving parts21arranged in an array in a substrate11. A color separator (a transmission color filter)22is formed for every four of the light-receiving parts21arranged in two rows and two columns. Four light-receiving parts21and one color separator22constitute a base unit12.

The four light-receiving parts21included in the base unit12are first and fourth light-receiving parts21A and21D for receiving green light, a second light-receiving part21B for receiving red light and a third light-receiving part21C for receiving blue light.

A first optical element part23A is formed above the first light-receiving part21A. A second optical element part23B is formed above the fourth light-receiving part21D. Each of the first optical element part23A and the second optical element part23B includes: an on-chip microlens31for focusing light; and a collimator element32for forming the light focused by the on-chip microlens31into parallel light. The collimator element32may be a concave lens, for example.

The on-chip microlens31of the first optical element part23A is oriented such that the center of the optical axis thereof coincides with the center of the first light-receiving part21A. The on-chip microlens31of the second optical element part23B is oriented such that the center of the optical axis thereof coincides with the center of the fourth light-receiving part21D. For example, it is preferable that the on-chip microlens31is a square in plan view and is inclined 45° with respect to the direction of arrangement of the light-receiving parts21. Then, the entire effective pixel region where the light-receiving parts21are arranged is covered without waste. As illustrated inFIG. 3, the on-chip microlens31may be a rectangular in plan view.

Incident light which has been formed into parallel light by the collimator element32of the first optical element part23A is guided to a first optical path51and enters a first color-separating element35formed on the first optical path51. The first color-separating element35is a dichroic mirror which transmits green light and red light and reflects blue light. Then, blue light is reflected in parallel with the substrate toward the third light-receiving part21C and is guided to a third optical path53crossing the first optical path51.

Incident light which has been formed into parallel light by the collimator element32of the second optical element part23B is guided to a second optical path52and enters a second color-separating element36. The second color-separating element36is a dichroic mirror which transmits green light and blue light and reflects red light. Then, red light is reflected in parallel with the substrate toward the second light-receiving part21B and is guided to a fourth optical path54crossing the second optical path52.

Light transmitted through the first color-separating element35enters a third color-separating element37. The third color-separating element37is a dichroic mirror which transmits only green light and reflects red light. Green light transmitted through the third color-separating element37enters the first light-receiving part21A, and red light is reflected in parallel with the substrate11toward the second light-receiving part21B and is guided to a fifth optical path55.

Light transmitted through the second color-separating element36enters a fourth color-separating element38. The fourth color-separating element38is a dichroic mirror which transmits only green light and reflects blue light. Green light transmitted through the fourth color-separating element38enters the fourth light-receiving part21D, and blue light is reflected in parallel with the substrate11toward the third light-receiving part21C and is guided to a sixth optical path56.

A first mirror element39is formed on the third optical path53above the third light-receiving part21C. Light traveling on the third optical path53is reflected vertically to the substrate toward the third light-receiving part21C and is guided to a seventh optical path57. Then, blue light enters the third light-receiving part21C.

A second mirror element40is formed on the fourth optical path54above the second light-receiving part21B. Light traveling on the fourth optical path54is reflected vertically to the substrate toward the second light-receiving part21B and is guided to an eighth optical path58. Then, red light enters the second light-receiving part21B.

In this embodiment, each of the reflective surfaces of the first color-separating element35, the second color-separating element36, the third color-separating element37, the fourth color-separating element38, the first mirror element39and the second mirror element40is oriented at 45° with respect to the substrate11. Then, light is separated into two directions, i.e., directions horizontal and vertical to the substrate11, so that the thickness of the solid-state imaging device is reduced. It should be noted that if the angle of a reflective surface with respect to the substrate11is in the range from about 30° to about 60°, the thickness of the solid-state imaging device is substantially negligible. On the other hand, the transmission wavelength range of a dichroic mirror as a stack of dielectric films depends on the polarization direction and incident angle of incident light. In consideration of this dependence, the angle of a reflective surface with respect to the substrate11is preferably 30° or less. In this case, though the thickness of the solid-state imaging device is large, the property of separating color components is advantageously enhanced.

In the solid-state imaging device of this embodiment, red light and blue light reflected by the third color-separating element37and the fourth color-separating element38, respectively, travel only in the direction parallel to the substrate11. Accordingly, these red light and blue light are not used and, in addition, might enter light-receiving parts of another adjacent base unit to cause color mixture.

In view of this, as illustrated inFIG. 4, it is preferable that a first halfmirror element41A is formed at an intersection of the fifth optical path55on which red light reflected by the third color-separating element37travels and the eighth optical path58on which red light reflected by the second mirror element40travels and a first light-absorbing part42A is formed on the fifth optical path55at the side opposite the third color-separating element37with respect to the first halfmirror element41A. Likewise, it is also preferable that a second halfmirror element41B is formed at an intersection of the sixth optical path56on which blue light reflected by the fourth color-separating element38travels and the seventh optical path57on which blue light reflected by the first mirror element39travels and a second light-absorbing part42B is formed on the sixth optical path56at the side opposite the fourth color-separating element38with respect to the second light-absorbing part42B.

This configuration allows about a half of light traveling on the fifth optical path55and the sixth optical path56to be used, thus reducing the possibility of color mixture.

Alternatively, a configuration as illustrated inFIG. 5may be employed. In this case, a polarizer44A is formed on the fifth optical path55and a polarizer44B is formed on the eighth optical path58so that polarized electromagnetic radiation of light traveling on the fifth optical path55and polarized electromagnetic radiation of light traveling on the eighth optical path58are orthogonal to each other. In addition, a first polarizing beam splitter element43A is formed at an intersection of the fifth optical path55and the eighth optical path58so that light traveling on the fifth optical path55is reflected toward the second light-receiving part21B and light traveling on the eighth optical path58is transmitted without change. Likewise, a polarizer44C is formed on the sixth optical path56, a polarizer44D is formed on the seventh optical path57and a second polarizing beam splitter element43B is formed at an intersection of the sixth optical path56and the seventh optical path57. This configuration allows all the light focused by the first optical element part23A and the second optical element part23B to enter the light-receiving parts and reduces the possibility of color mixture.

As illustrated inFIGS. 6A and 6B, a light-blocking wall46may be provided between adjacent color separators and a light-blocking wall47may be provided in a portion excluding the optical paths. The light-blocking wall46and the light-blocking wall47may be made of materials which absorb light or materials which reflect light. Each of the light-blocking walls46and47may be made of a material having a refractive index lower than an intermediate film formed in portions serving as the optical paths so that the optical paths have waveguide structures to perform light confinement.

As illustrated inFIGS. 7A and 7B, a configuration in which first primary-color filters48A for green are formed between the third color-separating element37and the first light-receiving part21A and between the fourth color-separating element38and the fourth light-receiving part21D, a second primary-color filter48B for blue is formed between the first mirror element39and the third light-receiving part21C and a third primary-color filter48C for red is formed between the second mirror element40and the second light-receiving part21B may be employed. This configuration suppresses occurrence of color mixture. Formation of the primary-color filters and the light-blocking walls may be combined.

Hereinafter, a method for fabricating a solid-state imaging device according to this embodiment will be described with reference to the drawings.FIGS. 8A through 8C,FIGS. 9A through 9CandFIGS. 10A and 10Bare cross-sectional views showing respective process steps of the method for fabricating a solid-state imaging device of this embodiment in the order of fabrication.FIG. 10Ais a cross-sectional view taken along the line Xa-Xa inFIG. 9C.FIG. 10Bis a cross-sectional view taken along the line Xb-Xb inFIG. 9C.

First, as shown inFIG. 8A, a plurality of light-receiving parts21are formed in an array in a semiconductor substrate11. Then, a transparent first prism formation film61made of, for example, silicon dioxide (SiO2) is formed on the substrate11. Thereafter, a synthetic resin film62made of, for example, acrylic resin containing melamine as a binder is formed on the first prism formation film61. The synthetic resin film62may be formed by, for example, spin coating.

Next, as shown inFIG. 8B, the synthetic resin film62is dried at low temperature, and then is irradiated with ultraviolet light such as a g-line (wavelength: 436 nm) or an i-line (wavelength: 365 nm) to be patterned, thereby forming a mask in the shape of prisms having slopes above the respective light-receiving parts21which are to receive green light.

Then, as shown inFIG. 8C, the entire surface is etched back so that the pattern of the synthetic resin film62is transferred onto the first prism formation film61, thereby forming first prisms63on the light-receiving parts21which are to receive green light.

Thereafter, as shown inFIG. 9A, a first dielectric film81as a stack of SiO2and TiO2is formed by, for example, CVD on the slopes of the first prisms63, thereby forming lower color separating elements64serving as a third color-separating element37and a fourth color-separating element38. The first dielectric film81is formed as a dichroic mirror which transmits only green light by controlling the amounts of SiO2and TiO2.

Subsequently, as shown inFIG. 9B, a first intermediate film65made of, for example, borophosphosilicate glass (BPSG) and a second prism formation film66made of, for example, SiO2are sequentially formed by, for example, CVD to cover the lower color separating elements64. Thereafter, a synthetic resin film67is formed on the second prism formation film66.

Then, as shown inFIG. 9C, the synthetic resin film67is patterned and then the entire surface is etched back, thereby forming second prisms68above the respective light-receiving parts21.

Thereafter, as shown inFIGS. 10A and 10B, a second dielectric film82as a stack of SiO2and TiO2is deposited on the slopes of the second prisms68which are formed above the light-receiving parts21for receiving green light and have their slopes located adjacent to the light-receiving parts21for receiving blue light. The amount of the second dielectric film82is adjusted such that the second dielectric film82serves as a dichroic mirror which transmits green light and red light and reflects blue light. In this manner, first upper color-separating elements69A which are first color-separating elements35are formed.

In addition, a third dielectric film83as a stack of SiO2and TiO2is deposited on the slopes of the second prisms68which are formed above the light-receiving parts21for receiving green light and have their slopes located adjacent to the light-receiving parts21for receiving red light. The amount of the third dielectric film83is adjusted such that the third dielectric film83serves as a dichroic mirror which transmits green light and blue light and reflects red light. In this manner, second upper color-separating elements69B which are second color-separating elements are formed.

Furthermore, a fourth dielectric film84as a stack of SiO2and TiO2is deposited on the slopes of the second prisms68which are formed above the light-receiving parts21for receiving blue light and red light. The amount of the fourth dielectric film84is adjusted such that the fourth dielectric film84serves as a total-reflection mirror which reflects light of all colors. In this manner, mirror elements70which are a first mirror element39and a second mirror element40are formed.

Thereafter, a second intermediate film71covering the first upper color-separating elements69A, the second upper color-separating elements69B and the mirror elements70is formed, and then a collimator element32and an on-chip microlens31are formed by known methods.

In this embodiment, the stack of SiO2and TiO2is used as the first through fourth dielectric films81through84. Alternatively, a stack of a low-refractive-index material such as magnesium fluoride (MgF2) and a high-refractive-index material such as tantalum oxide (Ta2O5) may be used.

As described above, the present invention provides a solid-state imaging device including transmission color filters in a Bayer pattern and a method for fabricating the device. The present invention is useful for a solid-state imaging device including transmission color filters in a Bayer pattern and a method for fabricating the device, for example.