JP2006121105A - Amplification type solid state imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an amplification type solid state imaging device in which occurrence of shading caused by reduction of condensing rate in a peripheral part of an imaging region is suppressed. <P>SOLUTION: This device comprises a semiconductor substrate 1, a plurality of photo-detecting parts 2 formed in the semiconductor substrate, a plurality of laminated light-shielding layers 4 formed above the semiconductor substrate, and an inter-layer insulating film 3 formed between the light-shielding layers. The light-shielding layer has a plurality of opening parts formed while corresponding to the photo-detecting parts. In the uppermost light-shielding layer at least most away from the semiconductor substrate out of the plurality of light-shielding layers, the opening part is so formed that the center of the opening part is displaced from the center of the photo-detecting part corresponding to it. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an amplification-type solid-state imaging device, and more particularly to an amplification-type solid-state imaging device that suppresses signal level drop (shading) that occurs in the periphery of an output image.

  Known solid-state imaging devices include CCD-type solid-state imaging devices and amplification-type solid-state imaging devices. In particular, the amplification type solid-state imaging device has been attracting attention as an image input element of a portable device because it has an advantage that it can be integrated into one chip with a peripheral circuit.

  In these solid-state imaging devices, suppression of shading that occurs in the periphery of the output image is an issue. In the solid-state imaging device, since the optical center of the imaging optical system is arranged on the center extension line of the imaging region (the region where the pixels are arranged), the light is vertical at the center of the imaging region when the exit pupil distance is finite. However, light is incident on the periphery of the imaging region from an oblique direction. For this reason, in the peripheral part of the imaging region, the condensing center by the microlens is shifted from the center of the light receiving part, and the light condensing rate to the light receiving part decreases. It is known that such a decrease in the light collection rate in the periphery of the imaging region is a cause of shading.

  FIG. 6 is a cross-sectional view showing the structure of a CCD type solid-state imaging device. A plurality of light receiving portions 22 are arranged in a matrix in the semiconductor substrate 21. Further, although not shown, a charge transfer portion is formed in the semiconductor substrate 21 adjacent to each column of the light receiving portions 22, and a transfer electrode is formed on the charge transfer portion 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.

In such a CCD type solid-state imaging device, as shown in FIG. 6, it is proposed to suppress shading by shifting the microlens 25 arranged in the periphery of the imaging region with respect to the light receiving unit 22. (For example, refer to Patent Document 1). The positional deviation (Lm) between the microlens 25 and the light receiving unit 22 corresponding to the microlens 25 is adjusted so as to gradually increase from the central part of the imaging region toward the peripheral part. According to such a CCD solid-state imaging device, shading in the peripheral portion of the output image can be sufficiently suppressed.
JP-A-6-140609

  In the amplification type solid-state imaging device, as with the CCD solid-state imaging device, as a means for 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.

  FIG. 7 is a cross-sectional view showing the structure of such an amplification type solid-state imaging device. A plurality of light receiving portions 32 are arranged in a matrix in the semiconductor substrate 31. Further, although not shown in the figure, the semiconductor substrate 31 is formed with MOS transistors constituting an amplifier circuit in the pixel corresponding to each of the light receiving portions 32. On the semiconductor substrate 31, a plurality of light shielding layers 34 are stacked with an interlayer insulating film 33 interposed therebetween. Each light shielding layer 34 has an opening formed corresponding to each of the light receiving portions 32. In addition, a plurality of microlenses 35 are formed in correspondence with each of the light receiving portions 32 above, and the positional deviation (Lm) between the microlens 35 and the light receiving portion 32 corresponding thereto corresponds to the imaging region. It is adjusted so that it gradually increases from the center to the periphery.

  However, such an amplification type solid-state imaging device cannot sufficiently suppress shading in the peripheral portion of the output image.

  That is, in a CCD type solid-state imaging device, only one light-shielding layer is formed, and the distance from the light receiving unit to the microlens is relatively short. Can be suppressed. On the other hand, in the amplification type solid-state imaging device, since the wiring configuring the amplification circuit is used as a light shielding layer, a plurality of light shielding layers are formed. As a result, the distance from the light receiving unit to the microlens is increased. Therefore, as shown in FIG. 7, in the peripheral part of the imaging region, even if the microlens is shifted, it is inevitable that incident light is blocked by the light-shielding layer, and the light collection rate is reduced.

  An object of the present invention is to provide an amplification type solid-state imaging device in which shading in the peripheral portion of an output image is suppressed.

  An amplification type solid-state imaging device according to the present invention includes a semiconductor substrate, a plurality of light receiving portions formed in the semiconductor substrate, a plurality of light shielding layers formed above the semiconductor substrate and stacked on each other, and the light shielding layer An amplification type solid-state imaging device including a plurality of openings formed in correspondence with the light receiving unit, the interlayer light-shielding layer including an interlayer insulating film formed between the plurality of light-shielding layers, Of these, at least the uppermost light shielding layer farthest from the semiconductor substrate is characterized in that the opening is formed so as to cause a shift between the center of the opening and the center of the light receiving portion corresponding thereto. And

  An amplification type solid-state imaging device of another configuration 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 so as to correspond to the light receiving portions. An amplification type solid-state imaging device comprising: a light shielding layer having an opening; and a plurality of microlenses formed in correspondence with each of the light receiving parts above the light shielding layer, wherein the microlens and the opening There is a shift between the center and the center of the light receiving unit corresponding to the center, and the microlens and the micro are arranged at the peripheral portion more than the shift between the center of the opening and the center of the light receiving unit corresponding to the opening. The deviation from the center of the light receiving portion corresponding to the lens is larger.

  According to the amplification type solid-state imaging device of the present invention, the opening formed in at least the uppermost light-shielding layer is shifted with respect to the light-receiving part, thereby reducing incident light blocked by the light-shielding layer and collecting light. A decrease in rate can be suppressed. As a result, shading at the periphery of the output image can be suppressed.

  In the amplification type solid-state imaging device of the present invention configured as described above, in the plurality of light shielding layers, the deviation between the center of the opening and the center of the light receiving unit corresponding thereto increases from the lower layer to the upper layer. It is preferable to do.

  In addition, when the incident light to the amplification type solid-state imaging device diverges or converges, the center of the opening is shifted in the direction corresponding to the optical path of the incident light with respect to the center of the light receiving unit corresponding thereto. It is preferable.

  Furthermore, it includes a plurality of microlenses formed in correspondence with each of the light receiving portions above the light shielding layer, and a shift between the center of the microlens and the center of the light receiving portion corresponding thereto corresponds to the imaging region. The microlens is formed so as to increase from the central portion toward the peripheral portion and to be larger than a deviation between the center of the opening in the uppermost light shielding layer and the center of the light receiving portion corresponding thereto. It is preferable to adopt a configuration as described above.

  Further, when the incident light to the amplification type solid-state imaging device diverges or converges, the center of the microlens is shifted in the direction corresponding to the optical path of the incident light with respect to the center of the light receiving unit corresponding thereto. A configuration is preferable. .

  Further, the amount of deviation between the center of the opening in each of the plurality of light shielding layers and the center of the light receiving portion corresponding to the opening is proportional to the distance between the light receiving portion and each of the light shielding layers. It is preferable to do.

  In the center 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 unit are not misaligned.

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

  The amplification type solid-state imaging device 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.

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

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

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

  Although not shown, a plurality of MOS transistors are formed on the semiconductor substrate 1 around each light receiving portion 2. These MOS transistors are electrically connected to each other through a plurality of light shielding films 4 to be described later to constitute an amplifier circuit. Note that the arrangement form 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.

  A plurality of light shielding layers 4 are formed above the semiconductor substrate 1 (hereinafter, each light shielding layer is referred to as “first light shielding layer”, “second light shielding layer”, etc. in order from the semiconductor substrate side). In addition, the light shielding layer farthest from the semiconductor substrate is referred to as “the uppermost light shielding layer”. The number of light shielding layers 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. Moreover, the layer thickness of each light shielding layer 4 is 100 to 1000 nm, for example, Preferably it is 400 to 800 nm. The layer thickness may be the same or different for all the light shielding layers 4.

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

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

  Further, a plurality of microlenses 5 are formed on the uppermost interlayer insulating film so as to correspond to each of the light receiving portions 2. The distance (Hm) from the light receiving unit 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 arrangement of the microlenses 5 will be described later in detail.

  Next, the arrangement of the openings formed in the light shielding layer 4 and the microlenses 5 will be described with reference to FIGS. 1 and 2. FIG. 2 is a plan view schematically showing the arrangement of openings and microlenses formed in the uppermost light shielding layer. In FIG. 1 and FIG. 2, the same parts are denoted by the same reference numerals.

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

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

  Preferably, not only the uppermost light-shielding layer but also other light-shielding layers are similarly set such that the positional deviation between the opening and the light-receiving part gradually increases from the center to the peripheral part 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 unit 2 are located on the same straight line perpendicular to the surface of the semiconductor substrate also in the peripheral part of the imaging region.

  At this time, the positional deviation of the opening corresponding to the same light receiving portion (excluding the light receiving portion at the center of the imaging region) is set to gradually increase from the lower light shielding layer toward the upper light shielding layer. Is done.

  That is, the following relationship is established for the positional deviation of the opening of each light shielding layer 4 corresponding to the same light receiving portion.

      0 ≦ L1 <L2 <... <Ln

  Here, L 1, L 2, and Ln are magnitudes of positional deviations of the openings in the first light shielding layer, the second light shielding layer, and the nth 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 with respect to the direction horizontal to the surface of the semiconductor substrate.

  Furthermore, it is preferable that the following relationship is established for the positional deviation of the openings of the respective light shielding layers 4 corresponding to the same light receiving portion.

        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 nth light shielding layer, respectively.

  The openings can be arranged in a matrix with a constant arrangement pitch, for example. In this case, as shown in FIG. 2, the arrangement pitch of the openings of the light shielding layer 4 is set so that the center of the arrangement of the openings of the light shielding layer 4 coincides with the center of the arrangement of the light receiving parts 2. The above-described positional shift can be achieved by setting the arrangement pitch of the openings of the light shielding layer 4 to be smaller than that of the upper light shielding layer.

  Similar to the opening of the light shielding layer 4, the microlens 5 is arranged such that the positional deviation from the corresponding light receiving unit 2 gradually increases from the central part of the imaging region toward the peripheral part. Further, the positional deviation (Lm) of the micro lens 5 is larger than the positional deviation of the opening corresponding to the same light receiving part (excluding the light receiving part at the center of the imaging region) formed in the uppermost light shielding layer. Is set to be

  For example, the microlenses 5 can be arranged in a matrix with a constant arrangement pitch. In this case, as shown in FIG. 2, the arrangement pitch of the microlenses 5 is set to be larger than the arrangement pitch of the light receiving portions 2 in a state where the center of the arrangement of the microlenses 5 is aligned with the center of the arrangement of the light receiving portions 2. By setting it smaller and smaller than the arrangement pitch of the openings in the uppermost light shielding layer, it is possible to achieve the positional deviation as described above.

  The size of the positional deviation between the opening of the light shielding layer 4 and the microlens 5 includes the exit pupil distance (distance from the exit pupil position to the light receiving unit), and the imaging region size (from the light receiving unit disposed at the center of the imaging region) The distance to the light receiving portion disposed in the portion can be determined as appropriate. As the exit pupil distance is shorter and the imaging region size is larger, it is preferable to set the positional deviation between the aperture and the microlens to be larger.

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

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

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

  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. As the film formation method, 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, for example, a CVD method can be used.

  The same operation is repeated for the desired number of layers to form a plurality of light shielding layers and interlayer insulating films. At this time, in forming the opening of each light shielding layer, an etching mask in which a mask pattern is formed with an array 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 with an arrangement pitch equivalent to that of the light receiving portions.

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

  Next, a resin layer serving 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. Moreover, the layer thickness of a resin layer is 0.5-3 micrometers, for example, Preferably it is 0.5-2 micrometers.

  The resin layer is etched and divided according to the number of pixels. At this time, an etching mask in which a 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 process by heating.

  In the above description, the case where the exit pupil is located above the solid-state imaging device is illustrated, but the present invention can also be applied to the case where the exit pupil is located below the solid-state imaging device (on the semiconductor substrate side). It is.

  FIG. 4 is a cross-sectional view showing an example of the structure of an amplification type solid-state imaging device applicable to such a case. In FIG. 1 and FIG. 4, the same reference numerals are given to the same parts.

  As described above, the direction of displacement 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 imaging device 10. As shown in FIG. 5, when the exit pupil is located below the solid-state imaging device 10, the light incident on the solid-state imaging device 10 is converged light, as opposed to the case where the exit pupil is located above the solid-state imaging device. It becomes.

  In this amplification type solid-state imaging device, the opening of each light shielding layer 4 and the microlens 5 are in the opposite direction to the case where the exit pupil is located above the solid-state imaging device, that is, the imaging region. It arrange | positions so that it may position-shift to the peripheral part side.

  The amplification type solid-state imaging device shown in FIG. 4 has the same structure as that in FIG. 1 except that the direction of positional deviation between the opening of the light shielding layer 4 and the microlens 5 is different.

  As described above, the light incident on the amplification type solid-state imaging device enters from the vertical direction at the center of the imaging region, but from the oblique direction at the periphery of the imaging region. In addition, since light is incident from an oblique direction, the distance between the light incident point and the center of the light receiving unit becomes larger as the light shielding layer is farther from the light receiving unit.

  In the amplification type solid-state imaging device of the present invention, the position of the opening and the light receiving part 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 part is maximum. The deviation is set to be smaller in the central part where the inclination of the incident light is smaller and larger in the peripheral part where the inclination of the incident light is larger. As a result, for example, as shown in FIG. 1 and FIG. 4, incident light can be condensed to the light receiving part without being blocked by the light shielding layer not only in the central part but also in the peripheral part of the imaging region. Therefore, it is possible to suppress the occurrence of shading in the peripheral portion of the output image.

  According to the amplification type solid-state imaging device of the present invention, shading in the periphery of the imaging region can be suppressed, which is useful as an image input element for a portable device.

It is sectional drawing which shows an example of the structure of the amplification type solid-state imaging device concerning this invention. It is a top view which shows typically an example of arrangement | positioning of the opening part of a light shielding layer, and a microlens. It is a figure for showing the positional relationship of a solid imaging device and an exit pupil. It is sectional drawing which shows another example of the structure of the amplification type solid-state imaging device concerning this invention. It is a figure for showing the positional relationship of a solid imaging device and an exit pupil. It is sectional drawing which shows the structure of a CCD type solid-state imaging device. It is sectional drawing which shows the structure of the conventional amplification type solid-state imaging device.

Explanation of symbols

1, 21, 31 Semiconductor substrate 2, 22, 32 Light receiving part 3, 23, 33 Interlayer insulating film 4, 24, 34 Light shielding layer 5, 25, 35 Micro lens 10 Amplification type solid-state imaging device

Claims (7)

  A semiconductor substrate, a plurality of light receiving portions formed in the semiconductor substrate, a plurality of light shielding layers formed above the semiconductor substrate and stacked on each other, and an interlayer insulating film formed between the light shielding layers Wherein the light shielding layer has a plurality of openings formed in correspondence with the light receiving portion, and is at least the most remote of the plurality of light shielding layers from the semiconductor substrate. An amplification type solid-state imaging device, wherein an opening is formed in an upper light shielding layer so that a deviation between a center of the opening and a center of a light receiving portion corresponding to the opening is formed.   2. The amplification type solid-state imaging device according to claim 1, wherein in the plurality of light shielding layers, a deviation between the center of the opening and the center of the light receiving unit corresponding to the opening increases from the lower layer to the upper layer.   When incident light to the amplification type solid-state imaging device diverges or converges, the center of the opening is shifted in a direction corresponding to the optical path of the incident light with respect to the center of the light receiving unit corresponding thereto. 3. The amplification type solid-state imaging device according to 1 or 2.   Furthermore, it includes a plurality of microlenses formed in correspondence with each of the light receiving portions above the light shielding layer, and a shift between the center of the microlens and the center of the light receiving portion corresponding thereto corresponds to the imaging region. The microlens is formed so as to increase from the central portion toward the peripheral portion and to be larger than a deviation between the center of the opening in the uppermost light shielding layer and the center of the light receiving portion corresponding thereto. The amplification type solid-state imaging device according to claim 1.   When the incident light to the amplification type solid-state imaging device diverges or converges, the center of the microlens is shifted in a direction corresponding to the optical path of the incident light with respect to the center of the light receiving unit corresponding thereto. 5. The amplification type solid-state imaging device according to 4.   The amount of deviation between the center of the opening in each of the plurality of light shielding layers and the center of the light receiving portion corresponding to the opening is proportional to the distance between the light receiving portion and each of the light shielding layers. The amplification type solid-state imaging device according to claim 1. A semiconductor substrate, a plurality of light receiving portions formed in the semiconductor substrate, a light shielding layer having a plurality of openings formed in correspondence with the light receiving portions above the semiconductor substrate, and above the light shielding layer An amplification type solid-state imaging device including a plurality of microlenses formed corresponding to each of the light receiving parts,
Deviation occurs between the center of the microlens and the opening and the center of the light receiving unit corresponding thereto,
In the peripheral part, the deviation between the center of the opening and the center of the light receiving part corresponding to the opening is larger than the deviation between the micro lens and the center of the light receiving part corresponding to the micro lens. A feature of the amplification type solid-state imaging device.

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