SOLID-STATE IMAGING DEVICE

A solid-state imaging device according to the present embodiment includes a semiconductor region and an antireflection film. In the semiconductor region, a blue photodiode that detects blue light, a green photodiode that detects green light, and a red photodiode that detects red light are arranged. The antireflection film includes a first insulating film disposed on the semiconductor region and a second insulating film disposed on the first insulating film and having a refractive index higher than a refractive index of the first insulating film. At least one of the first insulating film and the second insulating film has a film thickness in a region through which light received by the blue photodiode is transmitted thinner than a film thickness in a region through which light received by the green photodiode is transmitted.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2022-151885, filed on Sep. 22, 2022; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a solid-state imaging device.

BACKGROUND

A solid-state imaging device includes an antireflection film (AR filter) on a light receiving element (photodiode) of a pixel in order to receive more light and improve sensitivity. However, in the conventional antireflection film, the transmittance of light in a blue wavelength band (for example, light in a wavelength band of about 400 nm to 500 nm) is lower than the transmittance of light having a longer wavelength (green and red light), so that the spectral sensitivity of the entire solid-state imaging device decreases in the blue wavelength band and becomes non-uniform in the entire visible range. Note that, in a case where the antireflection film is adapted to blue light in order to increase the transmittance in the blue wavelength band, the transmittance of light in the green and red wavelength bands decreases. Furthermore, as means for increasing the spectral sensitivity in the blue wavelength band of the solid-state imaging device, for example, there is a method using a microlens, but it is not suitable for increasing an area of the solid-state imaging device.

DETAILED DESCRIPTION

A solid-state imaging device according to the present embodiment includes a semiconductor region and an antireflection film. In the semiconductor region, a blue photodiode that detects blue light, a green photodiode that detects green light, and a red photodiode that detects red light are arranged. The antireflection film includes a first insulating film disposed on the semiconductor region and a second insulating film disposed on the first insulating film and having a refractive index higher than a refractive index of the first insulating film. At least one of the first insulating film and the second insulating film has a film thickness in a region through which light received by the blue photodiode is transmitted thinner than a film thickness in a region through which light received by the green photodiode is transmitted.

Embodiments will now be explained with reference to the accompanying drawings. The embodiments do not limit the present invention. The drawings are schematic or conceptual, and a ratio of each portion and the like are not necessarily the same as actual ones. In the specification and the drawings, the same elements as those described above with respect to the previously described drawings are denoted by the same reference signs, and the detailed description thereof is appropriately omitted.

For convenience of description, an XYZ orthogonal coordinate system is adopted as illustrated in the drawings. A Z-axis direction is a stacking direction (thickness direction) of the solid-state imaging device. Furthermore, in the Z direction, a side of a color filter is also referred to as “upper”, and a side of a semiconductor region2is also referred to as “lower”. However, this expression is for convenience and independent of a direction of gravity.

A solid-state imaging device1according to an embodiment will be described with reference toFIG.1. The solid-state imaging device1may be a linear sensor in which pixels are arranged in a line, or may be an area sensor in which pixels are arranged in both vertical and horizontal directions. Furthermore, the solid-state imaging device1may be a CMOS sensor or a CCD sensor.

As illustrated inFIG.1, the solid-state imaging device1includes a semiconductor region2, a photodiode3b, a photodiode3g, a photodiode3r, an antireflection film7, a blue color filter8b, a green color filter8g, and a red color filter8r. Hereinafter, details of each element will be described with reference toFIG.1.

Note that, in the following description, the photodiode3b, the photodiode3g, and the photodiode3rmay be collectively referred to as a “photodiodes3b,3g, and3r”. Furthermore, the blue color filter8b, the green color filter8g, and the red color filter8rmay be collectively referred to as a “color filter8”.

The semiconductor region2is a region made of a semiconductor, and is made of silicon in the present embodiment. Note that the semiconductor region2may be an epitaxial layer, may be at least a part of a semiconductor substrate, or may include an epitaxial layer and a semiconductor substrate.

The photodiode3is disposed in the semiconductor region2. The photodiode3bis a photodiode that detects blue light (for example, light in a wavelength band of about 400 nm to 500 nm). The photodiode3gis a photodiode that detects green light (for example, light in a wavelength band of about 500 nm to 650 nm). The photodiode3ris a photodiode that detects red light (for example, light in a wavelength band of about 650 nm to 900 nm).

Note that, inFIG.2, the photodiodes3b,3g, and3rare arranged on a straight line, but the present invention is not limited thereto. For example, the photodiode3b, the photodiode3g, and the photodiode3rmay be arranged according to a predetermined arrangement such as a Bayer arrangement.

The antireflection film7includes a first insulating film4, a second insulating film5, and a third insulating film6. The second insulating film5has a higher refractive index than the first insulating film4and the third insulating film6.

As a combination of materials of the first insulating film4, the second insulating film5, and the third insulating film having the above-described refractive index relationship, for example, the first insulating film4is made of silicon oxide (SiO2), the second insulating film5is made of silicon nitride (SiN), and the third insulating film6is made of silicon oxide (configuration example 1). Note that the first insulating film4may be made of aluminum oxide (Al2O3), the second insulating film5may be made of zirconium oxide (ZrO2), and the third insulating film6may be made of silicon oxide (configuration example 2). Furthermore, the first insulating film4may be made of silicon oxide, the second insulating film5may be made of hafnium oxide (HfO2), and the third insulating film6may be made of silicon oxide (configuration example 3).

Tables 1 to 3 show the respective materials and refractive indexes of the configuration examples 1 to 3 of the antireflection film7.

Since the third insulating film6is disposed on the second insulating film5and has a film thickness sufficiently larger than film thicknesses of the first insulating film4and the second insulating film5, the third insulating film6absorbs a difference in the film thickness of the insulating film (the first insulating film4and/or the second insulating film5) in each of the blue, red, and green regions. The third insulating film6has a substantially planar upper surface. The third insulating film6has a refractive index lower than that of the second insulating film5. The third insulating film6is made of, for example, silicon oxide.

The blue color filter8battenuates light in a wavelength band other than the blue wavelength band among light incident on the photodiode3b. The blue color filter8bis disposed on the third insulating film6so as to be positioned above the photodiode3b. The green color filter8gattenuates light in a wavelength band other than the green wavelength band among light incident on the photodiode3g. The green color filter8gis disposed on the third insulating film6so as to be positioned above the photodiode3g. The red color filter8rattenuates light in a wavelength band other than the red wavelength band among light incident on the photodiode3r. The red color filter8ris disposed on the third insulating film6so as to be positioned above the photodiode3r.

The color filter8is formed by depositing a filter material on the third insulating film6by, for example, physical vapor deposition (PVD). The color filter8may be formed by applying (spin coating) a filter material onto the third insulating film6.

Next, a film thickness of the insulating film of the antireflection film7will be described in detail. As illustrated inFIG.1, the first insulating film4has a film thickness T4bin a region through which light received by the photodiode3bis transmitted, a film thickness T4gin a region through which light received by the photodiode3gis transmitted, and a film thickness T4rin a region through which light received by the photodiode3ris transmitted. The film thickness T4b, the film thickness T4g, and the film thickness T4rare examples of a first film thickness, a second film thickness, and a third film thickness in the claims, respectively.

The second insulating film5has a film thickness T5bin a region through which light received by the photodiode3bis transmitted, a film thickness T5gin a region through which light received by the photodiode3gis transmitted, and a film thickness T5rin a region through which light received by the photodiode3ris transmitted. The film thickness T5b, the film thickness T5g, and the film thickness T5rare examples of a fourth film thickness, a fifth film thickness, and a sixth film thickness in the claims, respectively.

In the present embodiment, as can be seen fromFIG.1, a magnitude of each film thickness satisfies a magnitude relationship of T4b<T4g<T4rand T5b<T5g<T5r. This makes it possible to obtain transmittance at an equivalent level between RGB. For example, T4bis 50 Å, T4gis 100 Å, T4ris 150 Å, and T5bis 500 Å, T5gis 550 Å, and T5ris 600 Å. Note that, with regard to the thickness of the second insulating film5, it may be T5b=T5g. That is, the magnitude of each film thickness satisfies a magnitude relationship of T4b<T4g<T4rand T5bT5g<T5r.

In the present embodiment, the film thicknesses of the first insulating film4and the second insulating film5are formed so as to satisfy the above magnitude relationship. As a result, the transmittance of light in the blue wavelength band can be greatly improved. Furthermore, although not as much as the blue wavelength band, the transmittance of light in the green and red wavelength bands is also improved.

As a result, the spectral sensitivity characteristic of the solid-state imaging device1can be made uniform. This will be described in detail with reference toFIG.2.FIG.2is a graph illustrating an example of a simulation result regarding wavelength dependency of transmittance of the antireflection film7of the solid-state imaging device1. Here, for example, an item “embodiment (Blue)” indicates wavelength dependency of transmittance of the antireflection film7in a region through which light received by the photodiode3bis transmitted. In the simulation, the configuration of the antireflection film7is the above-described configuration example 1 (SiO2/SiN/SiO2). Furthermore,FIG.2also illustrates a simulation result of wavelength dependence of transmittance of an antireflection film in a solid-state imaging apparatus according to a comparative example. The antireflection film in the comparative example includes two insulating films having different refractive indexes similarly to the antireflection film7, but a thickness of each insulating film is constant regardless of a location (region).

As can be seen from the comparative example illustrated inFIG.2, in a case where a thickness of the insulating film included in the antireflection film is made constant, the transmittance in the blue wavelength band is particularly low. Furthermore, when the thickness of the insulating film included in the antireflection film is adjusted in order to improve the transmittance in the blue wavelength band, the transmittance in the green and red wavelength bands decreases this time. As described above, in the comparative example, it is difficult to improve the transmittance in the blue wavelength band without decreasing the transmittance in the green wavelength band and the red wavelength band.

On the other hand, in the antireflection film7of the present embodiment, the thickness of each insulating film (the first insulating film4and the second insulating film5) is adjusted for each region through which light received by each photodiode is transmitted. That is, by setting the thickness of each insulating film to a thickness suitable for each color wavelength band, as illustrated inFIG.2, higher transmittance than that of the comparative example can be realized in the wavelength bands of all colors. Furthermore, in particular, transmittance higher than that of the comparative example can be realized in the blue wavelength band.

Furthermore, according to the present embodiment, it is possible to increase the transmittance in the blue wavelength band while maintaining the transmittance in the green and red wavelength bands high, and thus, it is possible to improve the uniformity of the transmittance between the wavelength bands. Therefore, it is possible to provide the solid-state imaging device1in which uniformity of spectral sensitivity is improved between the wavelength bands.

Note that, in the description of the above embodiment, the magnitudes of the film thicknesses are in the relationship of T4b<T4g<T4rand T5b<T5g<TSr, but may not necessarily have such a magnitude relationship. For example, in a case where it is only necessary to have a certain degree of transmittance (for example, in a case where it is not necessary to maximize the transmittance in each wavelength band), the film thickness of any one of the first insulating film4and the second insulating film5may be uniform. That is, T4b=T4g=T4ror T5b=T5g=T5rmay be satisfied. Hereinafter, a modification example in a case where either the film thickness of the first insulating film4or the film thickness of the second insulating film5is constant will be described.

Next, two modification examples according to the present embodiment will be described.

First Modification Example

A solid-state imaging device1A according to a first modification example of the embodiment will be described with reference toFIG.3. As illustrated inFIG.3, in the solid-state imaging device1A, a film thickness of the second insulating film5is constant. That is, T5b=T5g=T5r. A film thickness of the first insulating film4has a magnitude relationship of T4b<T4gT4r. For example, in a case where the first insulating film4is silicon oxide and the second insulating film5is silicon nitride, as an example, T4bis 200 Å, T4gand T4rare 475 Å, and T5b, T5gand T5rare 200 Å.

Also in the present modified example, by setting the film thickness of the first insulating film4to have the above magnitude relationship for each photodiode, high transmittance can be achieved in any wavelength band.

Moreover, according to the present modification example, since it is not necessary to change the film thickness of the second insulating film5, a part of a manufacturing process to be described later (seeFIGS.6C(4) to6E(3)) can be omitted.

Second Modification Example

Next, a solid-state imaging device1B according to a second modification example of the embodiment will be described with reference toFIG.4. As illustrated inFIG.4, in the solid-state imaging device1B, a film thickness of the first insulating film4is constant. That is, T4b=T4g=T4r. A film thickness of the second insulating film5has a magnitude relationship of T5b<T5gT5r. For example, in a case where the first insulating film4is silicon oxide and the second insulating film5is silicon nitride, as an example, T4b, T4g, and T4rare 475 Å, and T5bis 100 Å, T5gand T5rare 200 Å.

Also in the present modified example, high transmittance can be achieved in any wavelength band by changing the film thickness of the second insulating film5for each photodiode.

Moreover, since it is not necessary to change the film thickness of the first insulating film4, a part of the manufacturing process to be described later (seeFIGS.6A(3) to6C(2)) can be omitted.

As illustrated in the first modification example and the second modification example, in order to increase the transmittance in the blue wavelength band, at least one of T4b<T4gand T5b<T5gmay be satisfied.

As described above, in order to increase the transmittance in the blue wavelength band, it is sufficient that at least one of the first insulating film4and the second insulating film5has a film thickness in a region through which light received by the photodiode3bis transmitted thinner than a film thickness in a region through which light received by the photodiode3gis transmitted.

Next, specific numerical ranges of the film thickness (film thickness T4b) of the first insulating film4and the film thickness (film thickness T5b) of the second insulating film5in the blue wavelength band, which can achieve higher transmittance than that of the comparative example, will be described.

FIG.5illustrates a simulation result of the transmittance of blue light when the film thicknesses of the first insulating film4and the second insulating film5are changed. That is,FIG.5illustrates the transmittance of blue light when the film thickness T4band the film thickness T5bare changed. InFIG.5, as an example of a reference, a portion where the transmittance is 90% or more is shaded. The transmittance was obtained from a multilayer film interference spectrum in which light polarization (S-polarized light and P-polarized light) was also taken into consideration using a thin film interference model in which the second insulating film5was a thin film. As simulation conditions, the semiconductor region2, the first insulating film4, the second insulating film5, and the third insulating film6are made of silicon (Si), silicon oxide, silicon nitride, and silicon oxide, respectively.

In a case where it is attempted to obtain a transmittance of 90% or more in the blue wavelength band, as can be seen fromFIG.5, for example, the film thickness T4bmay be 50 Å or more and 100 Å or less, and the film thickness T5bmay be 400 Å or more and 600 Å or less. Furthermore, the film thickness T4bmay be 100 Å or more and 150 Å or less, and the film thickness T5bmay be 350 Å or more and 500 Å or less. Alternatively, the film thickness T4bmay be 150 Å or more and 200 Å or less, and the film thickness T5bmay be 300 Å or more and 450 Å or less.

Next, an example of a method of manufacturing the solid-state imaging device1will be described with reference toFIGS.6A to6E.FIGS.6A to6Eare process cross-sectional views for explaining the method of manufacturing the solid-state imaging device1.

First, as illustrated inFIG.6A(1), the semiconductor region2is prepared. For the semiconductor region2, for example, a semiconductor substrate made of silicon (Si), silicon carbide (SiC), or the like may be used.

Next, as illustrated inFIG.6A(1), the photodiode3b, the photodiode3g, and the photodiode3rare formed in the semiconductor region2. Note that an arrangement order of the photodiodes3b,3g, and3ris not limited to the illustrated order, and may be any order.

Next, as illustrated inFIG.6A(2), the first insulating film4is formed on the photodiodes3b,3g, and3r. The first insulating film4is formed by, for example, depositing a first material on the photodiodes3a,3b, and3cby physical vapor deposition (PVD), chemical vapor deposition (CVD), or thermal oxidation. For example, 200 Å of the first material is deposited. The first material is, for example, silicon oxide, aluminum oxide, or the like.

Next, as illustrated inFIG.6A(3), a photoresist is applied onto the photodiodes3b,3g, and3r, and selectively exposed and developed to form a resist mask R1on the first insulating film4above the photodiode3r.

Next, as illustrated inFIG.6A(4), etching for removing the first insulating film4in a portion (that is, a portion above the photodiodes3band3g) not covered with the resist mask R1is performed. The etching is, for example, wet etching using an etching solution. Note that all of the portions of the first insulating film4not covered with the resist mask may not be removed by etching.

Next, as illustrated inFIG.6B(1), the resist mask R1is removed using, for example, a developer.

Next, as illustrated inFIG.6B(2), the first material is deposited again on the first insulating film4and the photodiodes3band3g. For example, 150 Å of the first material is deposited.

Next, as illustrated inFIG.6B(3), a photoresist is applied onto the first insulating film4, and selectively exposed and developed to form a resist mask R2on the first insulating film4above the photodiodes3gand3r.

Next, as illustrated inFIG.6B(4), etching for removing the first insulating film4of a portion not covered with the resist mask R2(that is, a portion on the photodiode3b) is performed by, for example, wet etching using an etching solution. Note that all of the portions of the first insulating film4not covered with the resist mask may not be removed by etching.

Next, as illustrated inFIG.6C(1), the resist mask R2is removed using, for example, a developer.

Next, as illustrated inFIG.6C(2), the first material is deposited again on the first insulating film4and the photodiode3b. For example, 150 Å of the first material is deposited. As a result, the final first insulating film4is formed. The final film thickness is T4b=150 Å, T4g=300 Å, and T4r=500 Å.

Next, as illustrated inFIG.6C(3), the second insulating film5is formed on the first insulating film4. The second insulating film5is formed by, for example, depositing a second material on the first insulating film4by chemical vapor deposition (CVD). For example, 50 Å of the second material is deposited. The second material is, for example, silicon nitride, hafnium oxide, or zirconium oxide.

Next, as illustrated inFIG.6C(4), a photoresist is applied onto the second insulating film5, and selectively exposed and developed to form a resist mask R3on the second insulating film5above the photodiode3r.

Next, as illustrated inFIG.6D(1), etching is performed to remove the second insulating film5of the portion (that is, a portion above the photodiodes3band3g) not covered with the resist mask R3. The etching is, for example, wet etching using an etching solution. Note that the entire portion of the second insulating film5not covered with the resist mask may not be removed by etching.

Next, as illustrated inFIG.6D(2), the resist mask R3is removed using, for example, a developer.

Next, as illustrated inFIG.6D(3), the second material is deposited again on the second insulating film5and the first insulating film4located on the photodiodes3band3g. For example, 50 Å of the second material is deposited.

Next, as illustrated inFIG.6D(4), a photoresist is applied onto the second insulating film5, and selectively exposed and developed to form a resist mask R4on the second insulating film5above the photodiodes3gand3r.

Next, as illustrated inFIG.6E(1), etching for removing the second insulating film5of the portion not covered with the resist mask R4(that is, the portion above the photodiode3b) is performed. Note that the entire portion of the second insulating film5not covered with the resist mask may not be removed by etching.

Next, as illustrated inFIG.6E(2), the resist mask R4is removed using, for example, a developer.

Next, as illustrated inFIG.6E(3), the second material is deposited again on the second insulating film5and the first insulating film4located on the photodiode3b. For example, 250 Å of the second material is deposited. As a result, the final second insulating film5is formed. Furthermore, the final film thickness of the second insulating film5is T5b=250 Å, T5g=300 Å, and T5r=350 Å.

Next, as illustrated inFIG.6E(4), the third insulating film6is formed on the second insulating film5. The third insulating film6is formed by, for example, depositing a third material on the second insulating film5by physical vapor deposition (PVD) or chemical vapor deposition (CVD). The third material is, for example, silicon oxide. Note that the film thickness of the third insulating film6is sufficiently larger than the film thickness of the first insulating film4and the film thickness of the second insulating film5, and absorbs a difference in film thickness in each region of the first insulating film4and the second insulating film5.

Next, the color filters8b,8g, and8rare formed on the third insulating film6. The color filters are formed by, for example, depositing a filter material on the third insulating film6by physical vapor deposition (PVD). The color filter8may be formed by applying (spin coating) a filter material onto the third insulating film6. Specifically, the blue color filter8bis formed on the third insulating film6in the portion located above the photodiode3b, the green color filter8gis formed on the third insulating film6in the portion located above the photodiode3g, and the red color filter8ris formed on the third insulating film6in the portion located above the photodiode3r.

Through the above steps, the solid-state imaging device1according to the embodiment is manufactured. Note that the above description is merely an example of a method of manufacturing the solid-state imaging device1, and the solid-state imaging device1can be manufactured by other methods.

In the solid-state imaging device according to the present embodiment described above, the film thickness in the region of each color is adjusted so as to satisfy at least one of T4b<T4gand T5b<T5gwith respect to the magnitude relationship of the film thicknesses of the first insulating film4and the second insulating film5. Thus, the transmittance of the blue wavelength band can be improved. Furthermore, the film thickness in the region of each color is adjusted so as to satisfy at least one of T4g<T4rand T5g<T5rwith respect to the magnitude relationship of the film thicknesses of the second insulating film5and the third insulating film6. Thus, the transmittance in the green wavelength band can be improved. As a result, according to the present embodiment, the transmittance can be improved in any of the blue wavelength band, the green wavelength band, and the red wavelength band, and the transmittance can be made uniform among the wavelength bands. Thus, the spectral sensitivity can be made uniform between the wavelength bands.

Moreover, since the antireflection film7suitable for each wavelength band can be provided, the spectral sensitivity in each wavelength band can be freely controlled.

Furthermore, the present embodiment can be similarly applied to increase the area of the solid-state imaging device, and the increase in area can be more easily realized as compared with a structure such as a microlens. Therefore, the cost of the solid-state imaging device can be reduced as compared with the case of increasing the spectral sensitivity using the microlens.

Furthermore, particularly, when at least one of T4b<T4gand T5b<T5gis satisfied, the spectral sensitivity in the blue wavelength band can be improved. As a result, an SN ratio of the optical signal in the blue wavelength band can be improved.