Amplifying solid-state image pickup device

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to an amplified solid-state image sensor, and more specifically, to an amplified solid-state image sensor that suppresses a drop in signal level (shading) that occurs in the peripheral portion of an output image.

【0002】

[Conventional technology]

As the solid-state image sensor, a CCD type solid-state image sensor, an amplified solid-state image sensor, and the like are known. In particular, the amplification type solid-state imaging device has an advantage that it can be integrated with a peripheral circuit into a single chip, and is therefore attracting attention as an image input element for a portable device.

【0003】

In these solid-state image sensors, it is an issue to suppress shading that occurs in the peripheral portion of the output image. In a solid-state imaging device, the optical center of the photographing optical system is arranged on the extension line of the center of the imaging region (the region where the pixels are arranged). Therefore, when the exit pupil distance is finite, the light is vertical at the center of the imaging region. However, light is incident from an oblique direction in the peripheral portion of the imaging region. Therefore, in the peripheral portion of the imaging region, the focusing center of the microlens deviates from the center of the light receiving portion, and the focusing rate to the light receiving portion decreases. It is known that such a decrease in the light collection rate in the peripheral portion of the imaging region is the cause of shading.

【0004】

FIG. 6 is a cross-sectional view showing the structure of the CCD type solid-state image sensor. A plurality of light receiving units 22 are arranged in a matrix in the semiconductor substrate 21. Further, although not shown, a charge transfer unit is formed in the semiconductor substrate 21 adjacent to each row of the light receiving unit 22, and a transfer electrode is formed on the charge transfer unit via an insulating film. .. A light-shielding layer 24 is formed on the semiconductor substrate 21, and a plurality of openings are formed in the light-shielding layer 24 corresponding to each of the light-receiving portions 22. An interlayer insulating film 23 is formed on the light-shielding layer 24, and a plurality of microlenses 25 are formed on the interlayer insulating film 23 so as to correspond to each of the light receiving portions 22.

【0005】

In such a CCD type solid-state image sensor, as shown in FIG. 6, it has been proposed to suppress shading by shifting the microlens 25 arranged in the peripheral portion of the imaging region with respect to the light receiving portion 22. (For example, Japanese Patent Application Laid-Open No. 6-140609). The positional deviation (Lm) between the microlens 25 and the corresponding light receiving portion 22 is adjusted so as to gradually increase from the central portion to the peripheral portion of the imaging region. According to such a CCD type solid-state image sensor, shading in the peripheral portion of the output image can be sufficiently suppressed.

【0006】

[Problems to be Solved by the Invention]

In the amplified solid-state image sensor as well, as in the CCD-type solid-state image sensor, as a means of suppressing shading in the peripheral portion of the output image, the microlens arranged in the peripheral portion of the imaging region can be shifted with respect to the light receiving portion. Proposed.

【0007】

FIG. 7 is a cross-sectional view showing the structure of such an amplified solid-state image sensor. A plurality of light receiving units 32 are arranged in a matrix in the semiconductor substrate 31. Further, although not shown, the semiconductor substrate 31 is formed with MOS transistors corresponding to each of the light receiving units 32 to form an amplifier circuit in the pixel. A plurality of light-shielding layers 34 are laminated on the semiconductor substrate 31 with an interlayer insulating film 33 interposed therebetween. Each light-shielding layer 34 is formed with an opening formed corresponding to each of the light-receiving portions 32. Further, a plurality of microlenses 35 are formed above the light receiving unit 32 corresponding to each of the light receiving units 32, and the positional deviation (Lm) between the microlens 35 and the corresponding light receiving unit 32 is the imaging region. It is adjusted so that it gradually increases from the center of the lens to the periphery.

【0008】

However, with such an amplified solid-state image sensor, shading in the peripheral portion of the output image could not be sufficiently suppressed.

【0009】

An object of the present invention is to provide an amplified solid-state image sensor in which shading in the peripheral portion of an output image is suppressed.

【0010】

[Means for solving problems]

In order to achieve the above object, the amplification type solid-state image sensor of the present invention includes a semiconductor substrate, a plurality of light receiving portions formed in the semiconductor substrate, and a plurality of light receiving portions formed above the semiconductor substrate and laminated with each other. An amplification type solid-state imaging device including a light-shielding layer and an interlayer insulating film formed between the light-shielding layers, and the light-shielding layer has a plurality of openings formed corresponding to each of the light-receiving portions. Therefore, in the uppermost light-shielding layer at least the farthest from the semiconductor substrate among the plurality of light-shielding layers, the deviation between the center of the opening and the center of the light-receiving part corresponding thereto is the central portion of the imaging region. It is characterized in that the opening is formed so as to become larger toward the peripheral portion.

【0011】

In the CCD type solid-state image sensor, only one light-shielding layer is formed, and the distance from the light-receiving part to the microlens is relatively short. Therefore, simply shifting the position of the microlens with respect to the light-receiving part sufficiently suppresses shading. be able to. On the other hand, in the amplification type solid-state image sensor, since the wiring constituting the amplifier circuit is used as the light-shielding layer, a plurality of light-shielding layers are formed, and as a result, the distance from the light receiving portion to the microlens becomes long. Therefore, as shown in FIG. 7, in the peripheral portion of the imaging region, even if the microlens is shifted, it is inevitable that the incident light is blocked by the light-shielding layer, and the focusing rate is lowered.

【0012】

However, according to the amplification type solid-state image sensor of the present invention, the opening formed in at least the uppermost light-shielding layer is arranged so as to be offset from the light-receiving part in the peripheral portion of the imaging region, so that the light-shielding layer shields the image. It is possible to reduce the incident light and suppress the decrease in the focusing rate. As a result, shading in the peripheral portion of the output image can be suppressed. In the central portion of the imaging region, it is preferable that the center of the opening formed in the light-shielding layer and the center of the light-receiving portion are not misaligned.

【0013】

In the amplification type solid-state image sensor, it is preferable that the deviation between the center of the opening and the center of the corresponding light receiving portion in the plurality of light-shielding layers increases from the lower layer to the upper layer. This is because shading can be reliably suppressed even when the number of light-shielding layers is large.

【0014】

Further, in the amplified solid-state image sensor, when the incident light to the amplified solid-state image sensor diverges or converges, the center of the opening is the center of the light receiving portion corresponding to the divergence or convergence of the incident light. It is preferable that the direction is shifted according to the optical path. This is because shading can be suppressed more reliably.

【0015】

For example, when the incident light to the amplified solid-state image sensor is diverged, the center of the opening may be deviated from the center of the light receiving portion corresponding to the light in the direction toward the center of the imaging region. preferable. Further, when the incident light to the amplified solid-state image sensor converges, the center of the opening may be deviated from the center of the light receiving portion corresponding to the center in the direction toward the peripheral portion of the imaging region. preferable.

【0016】

The amplification type solid-state image sensor further includes a plurality of microlenses formed above the light-shielding layer corresponding to each of the light-receiving portions, and the center of the microlenses and the light-receiving portion corresponding thereto. The deviation from the center increases from the central portion to the peripheral portion of the imaging region, and is larger than the deviation between the center of the opening in the uppermost light-shielding layer and the corresponding center of the light receiving portion. It is preferable that the microlens is formed so as to be. According to this preferred example, shading can be reliably suppressed.

【0017】

In this preferred example, when the incident light on the amplified solid-state image sensor diverges or converges, the center of the microlens is directed with respect to the corresponding center of the light receiving portion according to the optical path of the incident light. It is preferable that the lens is deviated to. This is because shading can be suppressed more reliably.

【0018】

For example, when the incident light to the amplified solid-state image sensor is diverged, the center of the microlens may be deviated from the center of the light receiving portion corresponding to the incident light in the direction toward the center of the imaging region. preferable. Further, when the incident light on the amplified solid-state image sensor converges, the center of the microlens may be deviated from the center of the light receiving portion corresponding to the center of the microlens in the direction toward the peripheral portion of the imaging region. preferable.

【0019】

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an example of the amplification type solid-state image sensor of the present invention will be described.

【0020】

The amplified solid-state image sensor includes an imaging region in which a plurality of pixels are arranged and a non-imaging region in which peripheral circuits for driving the pixels are arranged. Hereinafter, the structure of the imaging region will be described.

【0021】

As described above, a plurality of pixels are arranged in the imaging region. Each of the pixels includes a light receiving unit for performing photoelectric conversion and an amplifier circuit for amplifying a signal generated by the photoelectric conversion of the light receiving unit. Further, the amplifier circuit usually includes a plurality of MOS transistors.

【0022】

FIG. 1 is a cross-sectional view showing an example of the amplified solid-state image sensor of the present invention, and shows the structure of an imaging region.

【0023】

A plurality of light receiving units 2 are formed in the semiconductor substrate 1 according to the number of pixels. The light receiving units 2 are arranged in a matrix on the surface of the semiconductor substrate 1 with a constant arrangement pitch.

【0024】

Although not shown, a plurality of MOS transistors are formed around each light receiving unit 2 on the semiconductor substrate 1. These MOS transistors are electrically connected to each other via a plurality of layers of light-shielding films 4 described later to form an amplifier circuit. The form of arrangement of the MOS transistors is not particularly limited, and can be appropriately determined according to the circuit structure of the amplifier circuit formed in the pixel and the like.

【0025】

A plurality of light-shielding layers 4 are formed above the semiconductor substrate 1 (hereinafter, each light-shielding layer is referred to as a "first light-shielding layer", a "second light-shielding layer", etc. in order from the semiconductor substrate side. The light-shielding layer farthest from the semiconductor substrate is called the "top light-shielding layer"). The number of layers of the light-shielding layer 4 can be appropriately determined according to the circuit structure of the amplifier circuit formed in the pixel, and is, for example, 2 to 5 layers, preferably 3 layers. The layer thickness of each light-shielding layer 4 is, for example, 100 to 1000 nm, preferably 400 to 800 nm. The layer thickness may be the same or different for all the light-shielding layers 4.

【0026】

Each light-shielding layer 4 is formed with a plurality of openings corresponding to each of the light-receiving portions 2. The form of arrangement of the openings will be described in detail later.

【0027】

An interlayer insulating film 3 is formed on each light-shielding layer 4. The layer thickness of each interlayer insulating film 3 is, for example, 300 to 1200 nm, preferably 600 to 1000 nm. Further, the layer thickness may be the same or different for all the interlayer insulating films 3.

【0028】

Further, a plurality of microlenses 5 are formed on the interlayer insulating film of the uppermost layer so as to correspond to each of the light receiving portions 2. The distance (Hm) from the light receiving portion 2 (the surface of the semiconductor substrate 1) to the microlens 5 is, for example, 2 to 10 μm, preferably 3 to 7 μm. The form of arrangement of the microlens 5 will be described in detail later.

【0029】

Next, the form of the arrangement of the opening and the microlens 5 formed in the light-shielding layer 4 will be described with reference to FIGS. 1 and 2. Note that FIG. 2 is a plan view schematically showing the arrangement of the openings and the microlenses formed in the uppermost light-shielding layer. Further, in FIGS. 1 and 2, the same parts are designated by the same reference numerals.

【0030】

At least the opening in the uppermost light-shielding layer and the microlens 5 are arranged so as to cause a displacement with respect to the light receiving portion 2 in the peripheral portion of the imaging region. The direction of misalignment can be determined according to the optical path of the light incident on the solid-state image sensor. For example, as shown in FIG. 3, when the exit pupil is located above the solid-state image sensor 10 (microlens side), the light incident on the solid-state image sensor 10 is divergent light. Hereinafter, such a case will be described as an example.

【0031】

The opening formed in the light-shielding layer of the uppermost layer is arranged so that the center of the opening and the center of the light receiving portion 2 are located on the same straight line perpendicular to the surface of the semiconductor substrate 1 in the central portion of the imaging region. In the peripheral portion of the imaging region, the center of the opening is arranged so as to be located closer to the center portion of the imaging region than the center of the light receiving portion 2. The positional deviation between the opening and the light receiving portion 2 is set so as to gradually increase from the central portion to the peripheral portion of the imaging region.

【0032】

Preferably, not only the uppermost light-shielding layer but also the other light-shielding layers are set so that the positional deviation between the opening and the light-receiving portion gradually increases from the central portion to the peripheral portion of the imaging region. .. However, regarding the first light-shielding layer, it is preferable that the center of the opening and the center of the light receiving portion 2 are located on the same straight line perpendicular to the surface of the semiconductor substrate even in the peripheral portion of the imaging region.

【0033】

At this time, the positional deviation of the openings corresponding to the same light receiving portion (excluding the light receiving portion in the center of the imaging region) is set so as to gradually increase from the light-shielding layer on the lower layer side to the light-shielding layer on the upper layer side. Will be done.

【0034】

That is, the following relationship is established for the positional deviation of the openings of the light-shielding layers 4 corresponding to the same light-receiving part.

【0035】

0 L1 <L2 <... <Ln Here, L1, L2, and Ln are the magnitudes of the misalignment of the openings in the first light-shielding layer, the second light-shielding layer, and the n-th light-shielding layer, respectively. The magnitude of the positional deviation is an amount representing the deviation between the center of the light receiving portion and the center of the opening in the direction horizontal to the surface of the semiconductor substrate.

【0036】

Further, it is preferable that the following relationship is established for the misalignment of the openings of the light-shielding layers 4 corresponding to the same light-receiving part.

【0037】

L2: H2 = L3: H3 = ... = Ln: Hn Here, H2, H3, and Hn are distances from the light receiving portion (semiconductor substrate surface) to the second light-shielding layer, the third light-shielding layer, and the n-th light-shielding layer, respectively.

【0038】

The openings can be arranged in a matrix with a constant arrangement pitch, for example. In this case, as shown in FIG. 2, with the center of the arrangement of the openings of the light-shielding layer 4 aligned with the center of the arrangement of the light-receiving part 2, the arrangement pitch of the openings of the light-shielding layer 4 is set to the light-receiving part 2. By setting the arrangement pitch of the opening of the light-shielding layer 4 to be smaller than the arrangement pitch of the light-shielding layer 4 and to be smaller as the light-shielding layer of the upper layer, the above-mentioned misalignment can be achieved.

【0039】

Similar to the opening of the light-shielding layer 4, the microlens 5 is arranged so that the positional deviation from the corresponding light-receiving portion 2 gradually increases from the central portion to the peripheral portion of the imaging region. Further, the misalignment (Lm) of the microlens 5 is larger than the misalignment of the opening corresponding to the same light receiving portion (excluding the light receiving portion in the center of the imaging region) formed in the uppermost light-shielding layer. Is set to be.

【0040】

The microlenses 5 can be arranged in a matrix with a constant arrangement pitch, for example. In this case, as shown in FIG. 2, with the center of the array of the microlens 5 and the center of the array of the light receiving unit 2 aligned, the array pitch of the microlens 5 is set to be higher than the array pitch of the light receiving unit 2. By setting it to be small and further smaller than the arrangement pitch of the openings in the uppermost light-shielding layer, the misalignment as described above can be achieved.

【0041】

The size of the misalignment between the opening of the light-shielding layer 4 and the microlens 5 is the exit pupil distance (distance from the exit pupil position to the light receiving part) and the imaging area size (the end from the light receiving part arranged in the center of the imaging area). It can be appropriately determined according to the distance to the light receiving portion arranged in the portion) and the like. It is preferable that the shorter the exit pupil distance and the larger the imaging region size, the larger the displacement between the aperture and the microlens.

【0042】

Next, an example of a method for manufacturing the amplification type solid-state image sensor as described above will be described.

【0043】

First, a p-type impurity such as boron is injected into a silicon substrate to form a p-type well. Next, an n-type impurity such as phosphorus is injected into the p-type well to form a light receiving portion. At this time, an injection mask in which the mask pattern is arranged with a constant arrangement pitch is used.

【0044】

In addition, a plurality of MOS transistors are formed around the light receiving portion. In a MOS transistor, for example, an n-type impurity is injected into a p-type well to form a source and a drain, and then a silicon oxide film is formed on a silicon substrate by thermal oxidation. It can be formed by forming a polysilicon film by the CVD method) and patterning it to form a gate electrode. Further, a silicon oxide film is formed by the CVD method, and an insulating film is formed so as to cover the gate electrode.

【0045】

A first light-shielding layer is formed on the insulating film. As the first light-shielding layer, for example, a metal such as aluminum or tungsten can be used, and as the film-forming method thereof, for example, a sputtering method can be used. Next, an opening is formed in the first light-shielding layer by etching, and then an interlayer insulating film is formed on the first light-shielding layer. As the interlayer insulating film, for example, a silicon oxide film or the like can be used, and as the film forming method thereof, for example, a CVD method can be used.

【0046】

The same operation is repeated for the desired number of layers to form a plurality of light-shielding layers and an interlayer insulating film. At this time, in forming the openings of the light-shielding layers, an etching mask in which the mask pattern is formed with an arrangement pitch smaller than that of the light-receiving portion is used. However, for the first light-shielding layer, it is also possible to use an etching mask in which a mask pattern is formed at an arrangement pitch equivalent to that of the light receiving portion.

【0047】

Further, in forming the openings of each light-shielding layer, an etching mask in which the mask pattern is arranged at a pitch smaller than the arrangement pitch of the openings in the light-shielding layer of the lower layer is used.

【0048】

Next, a resin layer as a constituent material of the microlens is formed on the interlayer insulating film. As the resin, for example, an acrylic resin or the like can be used. The thickness of the resin layer is, for example, 0.5 to 3 μm, preferably 0.5 to 2 μm.

【0049】

The resin layer is etched and divided according to the number of pixels. At this time, an etching mask in which the mask pattern is arranged at an arrangement pitch smaller than the arrangement pitch of the openings in the uppermost light-shielding layer is used. Then, the divided resin layer is formed into a lens shape by performing a reflow treatment by heating.

【0050】

In the above description, the case where the exit pupil is located above the solid-state image sensor has been illustrated, but the present invention can also be applied to the case where the exit pupil is located below the solid-state image sensor (semiconductor substrate side). Is.

【0051】

FIG. 4 is a cross-sectional view showing an example of the structure of an amplification type solid-state image sensor that can be applied in such a case. In addition, in FIG. 1 and FIG. 4, the same reference numerals are given to the same parts.

【0052】

As described above, the direction of the misalignment of the opening of the light-shielding layer and the microlens is determined according to the optical path of the light incident on the solid-state image sensor 10. As shown in FIG. 5, when the exit pupil is located below the solid-state image sensor 10, the light incident on the solid-state image sensor 10 is convergent light as opposed to the case where the exit pupil is located above the solid-state image sensor 10. It becomes.

【0053】

In this amplified solid-state image sensor, the opening of each light-shielding layer 4 and the microlens 5 are in the direction opposite to the case where the exit pupil is located above the solid-state image sensor with respect to the corresponding light-receiving part, that is, the imaging region. It is arranged so as to be displaced to the peripheral side of the.

【0054】

The amplified solid-state image sensor shown in FIG. 4 has the same structure as that of FIG. 1 except that the opening of the light-shielding layer 4 and the misalignment direction of the microlens 5 are different.

【0055】

As described above, the light incident on the amplified solid-state image sensor is incident from the vertical direction at the center of the image pickup region, but from an oblique direction at the peripheral portion of the image pickup region. Further, since the light is incident from an oblique direction, the distance between the light incident point and the center of the light receiving portion becomes larger as the light shielding layer is farther from the light receiving portion.

【0056】

In the amplified solid-state imaging device of the present invention, the positions of the opening and the light receiving portion in at least the uppermost light shielding layer among the plurality of light shielding layers, that is, the light shielding layer in which the deviation between the incident point and the center of the light receiving portion is maximized. The deviation is set so as to be smaller in the central portion where the inclination of the incident light is small and larger in the peripheral portion where the inclination of the incident light is large. As a result, for example, as shown in FIGS. 1 and 4, not only the central portion of the imaging region but also the peripheral portion can collect the incident light to the light receiving portion without being blocked by the light shielding layer. Therefore, it is possible to suppress the occurrence of shading in the peripheral portion of the output image.

【0057】

[Effect of the invention]

As described above, according to the amplification type solid-state imaging device of the present invention, the semiconductor substrate, the plurality of light receiving portions formed in the semiconductor substrate, and each of the light receiving portions formed above the semiconductor substrate. A plurality of light-shielding layers having a plurality of openings corresponding to the above, and at least in the uppermost light-shielding layer farthest from the semiconductor substrate among the plurality of light-shielding layers, the center of the opening and the corresponding light-shielding layer correspond to the center of the light-shielding layer. Since the opening is formed so that the deviation from the center of the light receiving portion increases from the center portion of the imaging region toward the peripheral portion, shading in the peripheral portion of the imaging region can be suppressed.

[Simple explanation of drawings]

[Figure 1]

It is sectional drawing which shows an example of the structure of the amplification type solid-state image sensor which concerns on this invention.

[Figure 2]

It is a top view which shows typically an example of the opening of a light-shielding layer and the arrangement of microlenses.

[Fig. 3]

It is a figure for showing the positional relationship between a solid-state image sensor and an exit pupil.

[Fig. 4]

It is sectional drawing which shows another example of the structure of the amplification type solid-state image sensor which concerns on this invention.

[Fig. 5]

It is a figure for showing the positional relationship between a solid-state image sensor and an exit pupil.

[Fig. 6]

It is sectional drawing which shows the structure of the CCD type solid-state image sensor.

[Fig. 7]

It is sectional drawing which shows the structure of the conventional amplification type solid-state image sensor.

[Explanation of symbols]

1, 21, 31 Semiconductor substrate 2, 22, 32 light receiving part 3, 23, 33 interlayer insulating film 4, 24, 34 shading layer 5, 25, 35 micro lenses 10 Amplified solid-state image sensor