Solid-state imaging device

Abstract

To remove parasitic light sensitivity noise and display a high-quality image with high sensitivity.SOLUTION: A solid-state imaging apparatus (18) includes a photoelectric conversion area (3), arranged on the inside of an epitaxial layer (2), a charge retention area (4), arranged on the incident side of light from the photoelectric conversion area (3), a dug-in area (20), dug into the epitaxial layer (2) from the surface of the epitaxial layer (2) toward the photoelectric conversion area (3), and a light-shielding film (8), which covers the charge retention area (4) and extends a side wall of the dug-in area (20).SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a solid-state imaging device having a global shutter function. [Background technology]

[0002] In order to obtain high image quality without increasing the size of the solid-state imaging device, there is a trend to reduce the pixel size of the solid-state imaging device provided in the solid-state imaging device. Patent Document 1 discloses a solid-state imaging device in which a columnar protrusion having a quadrilateral planar shape is provided on a transparent insulating film provided on a wiring layer of the solid-state imaging device, and incident light is refracted to be concentrated on a light receiving section, thereby increasing sensitivity and reducing optical noise. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2017 / 131009 Brochure Summary of the Invention [Problem to be solved by the invention]

[0004] However, the solid-state imaging device of Patent Document 1 has a problem in that it is not possible to remove parasitic photosensitivity noise that occurs when incident light that is refracted and heads toward the light receiving section is diffracted by the light-shielding film and enters the memory section.

[0005] An object of the present invention is to realize a solid-state imaging device capable of removing parasitic photosensitivity noise and displaying a high-quality image with high sensitivity. [Means for solving the problem]

[0006] In order to solve the above problems, a solid-state imaging device according to one embodiment of the present invention is a solid-state imaging device in which a plurality of pixels are arranged in a matrix on a substrate, each of the plurality of pixels comprising: a photoelectric conversion region arranged inside the substrate for converting light incident on the substrate into an electric charge; a charge retention region arranged inside the substrate on the light incident side of the photoelectric conversion region for retaining the electric charge converted in the photoelectric conversion region; a recessed region recessed from the light incident side surface of the substrate toward the photoelectric conversion region to a depth at least corresponding to the charge retention region; and a light-shielding film formed to cover the surface side of the substrate of the charge retention region and extend along the sidewalls of the recessed region. Effect of the Invention

[0007] According to a solid-state imaging device according to an aspect of the present invention, it is possible to remove parasitic photosensitivity noise and display a high-quality image with high sensitivity. [Brief description of the drawings]

[0008] [Figure 1] 1 is a diagram showing a configuration of pixels arranged in a solid-state imaging device according to a first embodiment. [Diagram 2] 1 is a cross-sectional view of the structure of a pixel of a solid-state imaging device according to a first embodiment. [Diagram 3] FIG. 2 is a plan view of a pixel of the solid-state imaging device. [Figure 4] 1 is a cross-sectional view of a pixel structure of a solid-state imaging device according to a comparative example. [Diagram 5] FIG. 11 is a cross-sectional view of a pixel structure of a solid-state imaging device according to another comparative example. [Figure 6] 4 is a graph showing a spectrum of reflectance versus wavelength of a light-shielding film provided in the solid-state imaging device according to the first embodiment. [Figure 7] 4 is a graph showing the relationship between the stress of a passivation film provided in the solid-state imaging device according to the first embodiment and the dark current. [Figure 8] 11 is a cross-sectional view of the structure of a pixel of a solid-state imaging device according to a first modified example of the first embodiment. FIG. [Figure 9]11 is a cross-sectional view of the structure of a pixel of a solid-state imaging device according to Modification 2 of Embodiment 1. FIG. [Figure 10] 13 is a cross-sectional view of the structure of a pixel of a solid-state imaging device according to Modification 3 of Embodiment 1. FIG. [Figure 11] 13 is a cross-sectional view of the structure of a pixel of a solid-state imaging device according to Modification 4 of Embodiment 1. FIG. [Figure 12] 13 is a cross-sectional view of the structure of a pixel of a solid-state imaging device according to a fifth modified example of the first embodiment. FIG. [Figure 13] 13 is a cross-sectional view of the structure of a pixel of a solid-state imaging device according to Modification 6 of Embodiment 1. FIG. [Figure 14] 13 is a cross-sectional view of the structure of a pixel of a solid-state imaging device according to Modification 7 of the first embodiment. FIG. [Figure 15] 13 is a cross-sectional view of the structure of a pixel of a solid-state imaging device according to Modification 8 of Embodiment 1. FIG. [Figure 16] FIG. 15 is a cross-sectional view taken along line AB shown in FIG. [Figure 17] FIG. 2 is a plan view of a pixel of the solid-state imaging device. [Figure 18] 11 is a cross-sectional view of the structure of a pixel of a solid-state imaging device according to a second embodiment. FIG. [Figure 19] 13 is a cross-sectional view of the structure of a pixel of a solid-state imaging device according to a modified example of the second embodiment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] [Embodiment 1] Hereinafter, one embodiment of the present invention will be described in detail.

[0010] Fig. 1 is a diagram showing the configuration of a pixel 21 arranged in a solid-state imaging device 18 according to embodiment 1. Fig. 2 is a cross-sectional view showing the structure of a pixel 21 of the solid-state imaging device 18 according to embodiment 1. Fig. 3 is a plan view of the pixel 21.

[0011] The solid-state imaging device 18 includes a substrate 19. The substrate 19 includes a semiconductor substrate 1 and an epitaxial layer 2 formed on the semiconductor substrate 1.

[0012] The solid-state imaging device 18 includes a plurality of pixels 21 arranged in a matrix on a substrate 19. Each pixel 21 includes a photoelectric conversion region 3 for converting light incident on the substrate 19 into an electric charge, a charge holding region 4 for holding the electric charge converted in the photoelectric conversion region 3, and a pixel transistor region 17 in which transistors necessary for converting a signal charge accumulated in a photoelectric conversion element formed in the photoelectric conversion region 3 into a voltage and for resetting and selecting a pixel are formed.

[0013] The photoelectric conversion region 3 is disposed inside the epitaxial layer 2 in order to convert light incident on the substrate 19 into electric charges. The charge retention region 4 is disposed inside the epitaxial layer 2 on the light incident side of the photoelectric conversion region 3.

[0014] Each pixel 21 comprises a recessed region 20 recessed from the light incident surface of the epitaxial layer 2 toward the photoelectric conversion region 3 to a depth at least corresponding to the charge retention region 4, and a light-shielding film 8 formed so as to cover the surface side of the epitaxial layer 2 of the charge retention region 4 and extend along the sidewall of the recessed region 20 in order to block light from reaching the charge retention region 4.

[0015] Each pixel 21 further includes a charge transfer gate electrode 6 for transferring charges from the photoelectric conversion region 3 to the charge retention region 4. The charges converted from light by the photoelectric conversion region 3 are transferred to the charge retention region 4 through a charge transfer path that runs from the photoelectric conversion region 3 through the charge transfer gate electrode 6 to the charge retention region 4.

[0016] In any embodiment, the charge transfer path means the path from the region where the photoelectric conversion region 3 and the charge transfer gate electrode 6 overlap (more precisely, the region with the deepest potential in the photoelectric conversion region 3 when the charge transfer gate electrode 6 is on) to the region with the deepest potential in the charge retention region 4.

[0017] After the charge is transferred to the charge holding region 4, the operation is the same as that of a typical rolling shutter type CIS (CMOS Image Sensor). That is, before the charge is transferred from the charge holding region 4 to the floating diffusion (FD), the FD is reset by a reset transistor, and the charge of the FD at the time of reset is converted to a voltage by a source follower transistor. Then, the reset signal is analog-to-digital converted (AD converted) by selecting a detection pixel by a select transistor, and acquired by a latch circuit. Then, the optical signal charge accumulated in the charge holding region 4 is immediately transferred to the FD, and the charge transferred to the FD is converted to a voltage by a source follower transistor. Then, the optical signal and the reset signal are AD converted via the select transistor in the on state, and acquired by the latch circuit. Then, the reset signal is subtracted from the optical signal and the reset signal by a digital circuit, so that the signal generated by the photoelectric conversion can be correctly acquired.

[0018] 2 and 3, the charge transfer gate electrode 6 overlaps both the deep potential portion of the photoelectric conversion region 3 and the charge retention region 4. As a result, a charge transfer path that transfers charges from the photoelectric conversion region 3 to the charge retention region 4 is formed.

[0019] When the charge transfer gate electrode 6 is on, an electric field is applied below the charge transfer gate electrode 6, and the potential below the charge transfer gate electrode 6 is modulated to the deeper side. At this time, the surface of the epitaxial layer 2 is more strongly affected by the electric field, and furthermore, the potential slope of the charge retention region 4 formed by the impurity implantation and layout is carried over at this time as well, resulting in a potential shape that is deeper by the offset amount than the potential when the charge transfer gate electrode 6 is off.

[0020] Therefore, when the charge transfer gate electrode 6 is on, the region with the deepest potential in the photoelectric conversion region 3 is formed under the region where the photoelectric conversion region 3 and the charge transfer gate electrode 6 overlap. Then, by the amount modulated by the charge transfer gate electrode 6, charges move from there to the deepest potential region of the charge retention region 4, along the potential slope of the charge retention region 4, which is deeper than the deepest potential region of the photoelectric conversion region 3.

[0021] The photoelectric conversion region 3 is formed by extending from the lower side of the carved region 20 to the lower side of the charge holding region 4. The carved region 20 on the photoelectric conversion region 3 is formed by carving to a position deeper than the charge holding region 4. At this time, the charge is transferred vertically from the photoelectric conversion region 3 below the charge holding region 4 to the charge holding region 4 directly above it. Then, in order to appropriately configure the distance between the photoelectric conversion region 3 and the charge holding region 4 at the point where the charge is transferred vertically, a protruding portion that protrudes toward the charge holding region 4 is formed in the photoelectric conversion region 3. Depending on the carved depth of the carved region 20 directly above the photoelectric conversion region 3, the protruding portion may not be formed, or conversely, the distance between the photoelectric conversion region 3 and the charge holding region 4 at the point where the charge is transferred vertically may have to be maintained. The approximate distance between the photoelectric conversion region 3 and the charge holding region 4 in this transfer portion may be about 0.35 μm to 0.45 μm.

[0022] An insulating film 5 is formed on the epitaxial layer 2 .

[0023] Charge transfer gate electrode 6 is formed on insulating film 5 and extends along the sidewall of recessed region 20 until it reaches the bottom of recessed region 20 .

[0024] An antireflection film 7 for reducing the loss of light incident on the substrate 19 is formed on the charge transfer gate electrode 6 and on the recessed region 20. A light shielding film 8 is formed on the antireflection film 7.

[0025] The light shielding film 8 is formed of a single or multiple film structure having a higher light reflectance than a single layer of tungsten.

[0026] Each pixel 21 is provided on a light-shielding film 8 and includes at least one wiring layer 10 in which a plurality of metal wirings are formed, and an interlayer insulating film 9 formed on the light-shielding film 8.

[0027] As the semiconductor substrate 1, a known semiconductor substrate, for example, a silicon substrate, can be used. The photoelectric conversion region 3 only needs to have a structure capable of converting incident light into electric charges, and is constituted, for example, by a photodiode. In a plurality of pixels 21 arranged in a matrix, a charge retention region 4 is provided between the photoelectric conversion regions 3 adjacent to each other along the row direction, as shown in FIG. 1. For example, the charge retention region 4 is constituted by an n-type layer in the epitaxial layer 2, and a potential barrier is formed between the photoelectric conversion region 3 and the charge retention region 4.

[0028] In addition, a recessed region 20 is formed above the photoelectric conversion region 3. A light-shielding film 8 is disposed on the upper side of the charge retention region 4 and on the side walls of the recessed region 20. In addition, a charge transfer gate electrode 6 is disposed so as to cover the upper surface and side surfaces of the charge retention region 4 via the epitaxial layer 2 and the insulating film 5.

[0029] The solid-state imaging device 18 of this embodiment includes a passivation film 12 that covers the wiring layer 10 and the interlayer insulating film 9 and has a higher refractive index than the interlayer insulating film 9, a planarization film 13 provided on the passivation film 12, and a microlens 15 arranged on the planarization film 13 to cover the photoelectric conversion region 3.

[0030] The passivation film 12 may be made of a silicon nitride material, and the interlayer insulating film 9 may be made of a silicon oxide material. The silicon nitride material means a material containing silicon nitride as a main component, and may contain any impurities. The silicon oxide material means a material containing silicon oxide as a main component, and may contain any impurities, as long as it has insulating properties.

[0031] As shown in FIG. 2, light incident on the solid-state imaging device 18 of this embodiment is refracted by the microlens 15 in the direction of the central axis of the microlens 15 and enters the planarization film 13 and the passivation film 12. The light then passes through the interlayer insulating film 9 and enters the photoelectric conversion region 3. The light incident on the photoelectric conversion region 3 is converted into electric charges. The electric charges generated by this photoelectric conversion are transferred to the charge holding region 4 by applying a voltage to the charge transfer gate electrode 6. The electric charges accumulated in the charge holding region 4 are used as image signals, and a captured image is formed by signal processing. Note that the solid-state imaging device 18 of this embodiment employs a global shutter system, so that photoelectric conversion in the photoelectric conversion region 3 and transfer of electric charges from the photoelectric conversion region 3 to the charge holding region 4 are performed at the same timing for all pixels.

[0032] During the above-mentioned photoelectric conversion, if light is directly incident on the charge holding region 4, parasitic photosensitivity noise occurs. This is because photoelectric conversion also occurs in the charge holding region 4.

[0033] The charge retention region 4 is formed by implanting impurities such as donors As and Ph into the Si-containing epitaxial layer 2, and retains charges mainly by the pn junction capacitance formed thereby in the surface portion. That is, like the photodiode formed in the photoelectric conversion region 3, the charge retention region 4 generates carriers by photoelectric conversion when light is incident on it.

[0034] Even if light does not directly strike the charge retention region 4, some charges photoelectrically converted in the p region (pixel isolation region) below the charge retention region 4 may reach the charge retention region 4 due to diffusion.

[0035] Therefore, in order to prevent light from entering the charge retention region 4, a light-shielding film 8 is provided on the upper and side surfaces of the charge transfer gate electrode 6. A metal such as tungsten is used as the material for this light-shielding film 8. Tungsten has a large light absorption coefficient and has high light-shielding ability even with a thin film thickness, making it a preferable material for the light-shielding film.

[0036] Fig. 4 is a cross-sectional view of a pixel structure of a solid-state imaging device according to a comparative example, and Fig. 5 is a cross-sectional view of a pixel structure of a solid-state imaging device according to another comparative example.

[0037] 2, the recessed region 20 is recessed into the epitaxial layer 2 only to a position shallower than the charge retention region 4. The upper surface of the photoelectric conversion region 3 and the upper surface of the charge retention region 4 are disposed at the same depth in the epitaxial layer 2. The light-shielding film 8 is disposed so as to cover the charge transfer gate electrode 6.

[0038] The solid-state imaging device shown in Fig. 4 has a color filter 14 and an optical waveguide 11. The color filter 14 has a function of coloring the incident light red, green, and blue and converting the light of each dye into an electric signal in the photoelectric conversion region 3. The optical waveguide 11 has a function of collecting the incident light on the central axis of the pixel 21 and allowing the light to efficiently enter the photoelectric conversion region 3. The solid-state imaging device shown in Fig. 5 has an inner lens 16 and the above-mentioned color filter 14.

[0039] 4 and 5, light incident on substrate 19 is incident not only on photoelectric conversion region 3 but also on charge retention region 4, and photoelectric conversion occurs in charge retention region 4 as well. As a result, in the solid-state imaging device of the comparative example, charges other than those photoelectrically converted in photoelectric conversion region 3 are accumulated in charge retention region 4, which retains the signal charge of the previous frame, resulting in parasitic photosensitivity noise.

[0040] In contrast, in the solid-state imaging device 18 of this embodiment, the photoelectric conversion region 3 is set back from the position of the charge retention region 4 toward the semiconductor substrate 1, and the photoelectric conversion region 3 extends along the lower surface of the charge retention region 4. A recessed region 20 is formed in the space created by setting back the photoelectric conversion region 3 toward the semiconductor substrate 1.

[0041] The sidewall of the recessed region 20 faces the side surface of the charge retention region 4. The light-shielding film 8 is formed so as to cover the front surface side of the epitaxial layer 2 of the charge retention region 4 via the antireflection film 7 and the charge transfer gate electrode 6 and extend along the sidewall of the recessed region 20.

[0042] By adopting such a configuration, light that has passed through the interlayer insulating film 9 and entered the epitaxial layer 2 is blocked by the light-shielding film 8 and cannot enter the charge retention region 4. As a result, no photoelectric conversion occurs in the charge retention region 4, and no parasitic photosensitivity noise is generated.

[0043] Furthermore, by extending the photoelectric conversion region 3 to below the charge retention region 4, not only is it possible to minimize the components of charges photoelectrically converted in the p region (pixel isolation region) below the charge retention region 4 that reach the charge retention region 4 due to diffusion, but it is also possible to improve the saturation capacity. Furthermore, due to the elimination of parasitic photosensitivity noise, the solid-state imaging device 18 of this embodiment can optimize the light collecting structure on the substrate solely for improving sensitivity and F-number characteristics (oblique incidence characteristics) and suppressing shading.

[0044] When determining the light collection structure, there is often a trade-off between sensitivity and parasitic photosensitivity noise. For example, if the opening of the light-shielding film 8 on the photoelectric conversion region 3 is widened, the sensitivity improves but the parasitic photosensitivity noise worsens. Conversely, if the opening is narrowed, the sensitivity decreases but the parasitic photosensitivity noise improves.

[0045] When actually designing a light-collecting structure, the opening is designed to balance the sensitivity and the parasitic photosensitivity noise. However, in the light-collecting structure according to this embodiment, the parasitic photosensitivity noise does not occur in principle. Therefore, the opening of the light-shielding film 8 can be widened to the manufacturing limit, so that the light-collecting structure can be designed to improve the sensitivity without any restrictions.

[0046] In addition, the light-collecting structure can be determined without worrying about the trade-off between sensitivity and parasitic photosensitivity noise, or between shading (a phenomenon of variation in sensitivity in which pixels at the edge of the screen generally have lower sensitivity than pixels at the center of the screen because light is incident on the CMOS image sensor via a lens when capturing an image, resulting in angled light incident on the pixels at the edge of the screen) and parasitic photosensitivity noise. Therefore, the light-collecting structure of the solid-state imaging device 18 according to this embodiment can improve sensitivity (optical characteristics).

[0047] 4 and 5 according to the comparative example, the deep potential parts (main charge accumulation parts) of the photoelectric conversion region 3 and the charge retention region 4 are both located on the top surface of the epitaxial layer 2 containing Si, and therefore must be laid out so as to be a certain distance apart. If they are too close to each other, the channel becomes short and the saturation capacity decreases significantly (due to the depletion layers of the photoelectric conversion region 3 and the charge retention region 4 being connected). If they are too close to each other, not only that, but blooming overflowing to the charge retention region 4 side is also significantly deteriorated. Therefore, the layout size of each pixel 21 is limited so that the photoelectric conversion region 3 and the charge retention region 4 are not too close to each other as described above. In addition, a reset transistor that discharges electrons transferred to the pixel transistor (floating diffusion (FD)) in the pixel transistor region 17 of the pixel 21, a source follower transistor that converts charge to potential, a charge discharge transistor that acts as an electronic shutter, and a select transistor that selects the pixel in the case of a pixel structure with a select are present on the top surface of the epitaxial layer 2 containing Si, and the pixel transistor is usually surrounded by shallow trench isolation (STI) to isolate it from the photoelectric conversion region 3 and the charge retention region 4. This is because the depletion layer extends significantly because a high concentration of impurities is injected into the pixel transistor, and if a considerable distance is not taken, the depletion layer will connect to the N-type region such as the photoelectric conversion region 3, becoming a leak source. If the STI is formed, the depletion layer must go around under the STI, so the distance between the pixel transistor and the photoelectric conversion region 3 can be reduced to the width of the STI. In this way, the layout size of the photoelectric conversion region 3 is also limited by the pixel transistor.

[0048] In contrast, the main portion of charge accumulation (the portion with the deep potential, which is preferably as close as possible to the charge holding region 4) of the photoelectric conversion region 3 formed in the solid-state imaging device 18 shown in Fig. 2 is located at a depth that is not affected by either the charge holding region 4 or the pixel transistor. For this reason, this photoelectric conversion region 3 can be expanded to a size that allows sufficient pixel separation from the photoelectric conversion region 3 (adjacent photodiode) formed in the adjacent pixel 21. Therefore, the saturation region of the photoelectric conversion region 3 can be expanded significantly more than in the comparative example.

[0049] FIG. 6 is a graph showing a spectrum of reflectance versus wavelength of the light-shielding film 8 provided in the solid-state imaging device 18 according to the first embodiment.

[0050] Examples of single film structures having a higher light reflectance than the single layer of tungsten (W) of the light-shielding film 8 include an aluminum (Al) / titanium nitride (TiN) film structure, a copper (Cu) / tantalum (Ta) film structure, a W / TiN film structure, and a TiN / Ti / W / TiN film structure.

[0051] The graph in FIG. 6 shows the results of simulating the reflectance spectrum for each of the above film structures. It can be seen that the Al / TiN film structure and the Cu / Ta film structure have significantly higher reflectance than the single-layer tungsten film structure in any wavelength region. Therefore, if only the reflectance is considered, Al and Cu are more suitable materials for the light-shielding film 8 than W. However, the Cu film formation process is restricted by the manufacturing process, since it can only be formed by forming a groove for the light-shielding film wiring, forming a stable metal or metal compound such as Ta or TaN on the insulating film to prevent Cu from diffusing into the insulating film, filling the light-shielding film wiring groove with Cu, and then removing and flattening unnecessary parts by chemical mechanical polishing (CMP). In other words, the degree of freedom of the light-shielding film structure is reduced. Furthermore, if Cu diffuses into the insulating film or onto the substrate surface, it significantly deteriorates device characteristics, such as worsening the white defect peak caused by metal contamination. For these reasons, Cu is not actually used in the light-shielding film.

[0052] From the viewpoint of reliability, the light-shielding film 8 is preferably a W / TiN film structure in which W is formed on a TiN film on an insulating film rather than a single layer of tungsten. The reflectance spectrum of the W / TiN film structure is almost identical to that of a single layer of W. Furthermore, the reflectance can be increased by forming a TiN / Ti film on the W / TiN film. However, as a side effect, the hydrogen absorption property of Ti may work in the direction of interfering with the hydrogen termination effect of the interface state of the substrate, possibly deteriorating the dark characteristics.

[0053] FIG. 7 is a graph showing the relationship between the stress of the passivation film 12 provided in the solid-state imaging device 18 according to the first embodiment and the dark current.

[0054] The passivation film 12 is −5.0×10 -9 dyne / cm 2 It is preferable that the passivation film 12 has a compressive stress of −5.0×10 to 1.0×10. If the film quality of the passivation film 12 is changed, the refractive index also changes. However, if the passivation film 12 has a compressive stress and the warp of the image sensor (substrate 19 of the solid-state imaging device 18) (stress applied to the entire image sensor) is reduced to −5.0×10. -9 dyne / cm 2 The following can be adjusted:

[0055] This makes it possible to cover up side effects caused by the introduction of the optical waveguide 11. The optical waveguide 11 has an overwhelmingly large thermal shrinkage rate compared to the materials of other surrounding components, and as a result, stress acting in a direction that worsens the dark voltage is propagated to the substrate 19 including Si. Therefore, it becomes important to determine the film quality of the passivation film 12 so as to adjust the warp applied to the image sensor in a direction that is favorable for the dark current.

[0056] When the stress of the passivation film 12 is controlled in the compressive direction, the stress in the compressive direction of the passivation film 12 propagates to the silicon on the surface of the epitaxial layer 2 including the photoelectric conversion region 3, thereby increasing the band gap of the silicon on the surface of the epitaxial layer 2 including the photoelectric conversion region 3. When this band gap increases, the dark current is exponentially reduced.

[0057] As shown in Figure 7, the compressive stress is -5.0×10 -9 dyne / cm 2 The dark current changes slowly below -5.0×10 -9 dyne / cm 2 If the compressive stress of the passivation film 12 is set as follows, the dark current can be exponentially reduced.

[0058] [Modification 1 of the first embodiment] FIG. 8 is a cross-sectional view showing the structure of a pixel 21 of a solid-state imaging device 18A according to Modification 1 of the first embodiment.

[0059] The difference from the solid-state imaging device 18 of the first embodiment is that an optical waveguide 11 is disposed between the passivation film 12 and the planarization film 13. The other structures and effects are the same as those of the solid-state imaging device 18 of the first embodiment, and therefore the description thereof will be omitted.

[0060] By disposing the optical waveguide 11 in the solid-state imaging device 18A, light incident on the microlens 15 passes through the planarization film 13 and enters the optical waveguide 11. In the optical waveguide 11, the incident light is focused onto a central axis perpendicular to the substrate 19. The focused incident light exits the optical waveguide 11, passes through the interlayer insulating film 9, and enters the photoelectric conversion region 3.

[0061] In this way, the optical waveguide 11 collects and directs light into the photoelectric conversion region 3, so that the amount of light incident on the photoelectric conversion region 3 can be increased compared to a configuration in which the optical waveguide 11 is not provided. The solid-state imaging device 18A of the present embodiment can achieve higher sensitivity.

[0062] In a front side illumination (FSI) structure, a wiring layer 10 is disposed on the light incident side, and a part of the light collected by the microlens 15 is blocked by the wiring layer 10 and lost (metal shading). Furthermore, in a global shutter CIS, a charge retention region 4 (memory node) must also be formed in the pixel 21, so the aperture ratio (fill factor) of the photoelectric conversion region 3 (photodiode portion) relative to the pixel area becomes smaller. As a result, the sensitivity, F-number characteristics (oblique incidence characteristics), and shading characteristics deteriorate.

[0063] One solution to this problem is an optical waveguide structure, and the optical waveguide 11 exhibits the effect of confining light by using a material with a higher refractive index than the interlayer insulating film 9. In other words, as long as the light collected from the microlens 15 enters the entrance (upper opening) of the optical waveguide 11, it is irradiated from the exit (lower opening) without leaking to the surroundings, so that the light incident on the microlens 15 can be efficiently guided to the photoelectric conversion region 3.

[0064] In the configuration of this embodiment in which the area directly above the photoelectric conversion region 3 is dug and the distance from the microlens 15 to the substrate 19 is long, the optical waveguide 11 is particularly effective. As long as the incident light is guided to the dug region 20 by the optical waveguide 11, no parasitic photosensitivity noise (PLS) occurs regardless of the direction in which the light emerging from the optical waveguide 11 is incident on the substrate 19. This allows design without worrying about the taper angle of the optical waveguide 11, increasing the degree of freedom and making it easier to improve sensitivity, F-number characteristics, and shading.

[0065] [Modification 2 of the first embodiment] FIG. 9 is a cross-sectional view showing the structure of a pixel 21 of a solid-state imaging device 18B according to the second modification of the first embodiment.

[0066] The difference from the solid-state imaging device 18 of the first embodiment is that a color filter 14 is disposed between the planarization film 13 and the microlens 15. The other structures and effects are the same as those of the solid-state imaging device 18 of the first embodiment, so the description will be omitted.

[0067] By disposing the color filter 14 on the solid-state imaging device 18B, only light of a specific wavelength is transmitted through the color filter 14 from the light incident on the microlens 15, and other light is absorbed by the color filter 14. Therefore, only light of the specific wavelength is incident on the photoelectric conversion region 3 and is photoelectrically converted.

[0068] In this way, the solid-state imaging device 18B of the present embodiment can convert the three primary colors of light, red, green, and blue, into an electrical signal for each pixel 21 by arranging the color filters 14 that change the wavelength of light transmitted therethrough for each pixel 21. After the three colors of light, red, green, and blue, are converted into electrical signals, the electrical signals are converted back into light to display a color image.

[0069] [Modification 3 of embodiment 1] FIG. 10 is a cross-sectional view showing the structure of a pixel 21 of a solid-state imaging device 18C according to the third modification of the first embodiment.

[0070] The difference from the solid-state imaging device 18 of the first embodiment is that an optical waveguide 11 is disposed between the passivation film 12 and the planarization film 13, and a color filter 14 is disposed between the planarization film 13 and a microlens 15. The other structures and effects are the same as those of the solid-state imaging device 18 of the first embodiment, so a description thereof will be omitted.

[0071] The solid-state imaging device 18C of this embodiment is a combination of the first and second modifications of the first embodiment. By disposing the color filter 14 in the solid-state imaging device 18C, only light of a specific wavelength of light incident on the microlens 15 is transmitted by the color filter 14, and the other light is absorbed by the color filter 14. The light of the specific wavelength transmitted through the color filter 14 is transmitted through the planarization film 13 and enters the optical waveguide 11. In the optical waveguide 11, the incident light of the specific wavelength is focused on a central axis perpendicular to the substrate 19. The focused incident light of the specific wavelength exits the optical waveguide 11, passes through the interlayer insulating film 9, and enters the photoelectric conversion region 3.

[0072] In this way, the solid-state imaging device 18C of the present embodiment can extract only light of a specific wavelength and increase the amount of light incident on the photoelectric conversion region 3. By arranging the optical waveguide 11 and the color filter 14 in the solid-state imaging device 18C, it becomes possible to display a color image with higher sensitivity.

[0073] [Variation 4 of the First Embodiment] FIG. 11 is a cross-sectional view showing the structure of a pixel 21 of a solid-state imaging device 18D according to the fourth modification of the first embodiment.

[0074] The difference from the solid-state imaging device 18 of the first embodiment is that an inner lens 16 is disposed between the passivation film 12 and the planarization film 13. The other structures and effects are the same as those of the solid-state imaging device 18 of the first embodiment, so the description will be omitted.

[0075] By disposing the inner lens 16 in the solid-state imaging device 18D, incident light that has passed through the microlens 15 passes through the planarization film 13, enters the inner lens 16, and is focused toward the central axis perpendicular to the substrate 19. The focused incident light passes through the passivation film 12 and the interlayer insulating film 9 and enters the photoelectric conversion region 3. By disposing the inner lens 16, it is possible to focus incident light from outside and make it enter the photoelectric conversion region 3.

[0076] This allows external incident light to be efficiently converted into electrons in the photoelectric conversion region 3, thereby further improving the sensitivity.

[0077] As mentioned above, the FSI type global shutter CIS has a problem that the light collection efficiency deteriorates due to a decrease in the fill factor. In addition to the optical waveguide structure described above, the use of such an inner lens 16 allows the light incident from the microlens 15 to be efficiently collected on the substrate 19.

[0078] [Fifth Modification of First Embodiment] FIG. 12 is a cross-sectional view showing the structure of a pixel 21 of a solid-state imaging device 18E according to the fifth modification of the first embodiment.

[0079] The difference from the solid-state imaging device 18 of the first embodiment is that an inner lens 16 is disposed between the passivation film 12 and the planarization film 13, and a color filter 14 is disposed between the planarization film 13 and the microlens 15. The other structures and effects are the same as those of the solid-state imaging device 18 of the first embodiment, so a description thereof will be omitted.

[0080] The solid-state imaging device 18E of this embodiment is a combination of the second and fourth modifications of the first embodiment. By disposing the color filter 14 in the solid-state imaging device 18E, only light of a specific wavelength is transmitted through the color filter 14 from the light incident on the microlens 15, and the other light is absorbed by the color filter 14. The light of the specific wavelength transmitted through the color filter 14 is transmitted through the planarizing film 13 and enters the inner lens 16. In the inner lens 16, the incident light of the specific wavelength is focused on a central axis perpendicular to the substrate 19. The focused incident light of the specific wavelength exits the inner lens 16, passes through the interlayer insulating film 9, and enters the photoelectric conversion region 3.

[0081] In this way, the solid-state imaging device 18E of the present embodiment can extract only light of a specific wavelength and increase the amount of light incident on the photoelectric conversion region 3. By arranging the inner lens 16 and the color filter 14 in the solid-state imaging device 18E, it becomes possible to display a color image with higher sensitivity.

[0082] [Variation 6 of the First Embodiment] FIG. 13 is a structural cross-sectional view of a pixel 21 of a solid-state imaging device 18F according to the sixth modification of the first embodiment.

[0083] The difference from the solid-state imaging device 18 of the first embodiment is that an optical waveguide 11 and an inner lens 16 are disposed between the passivation film 12 and the planarization film 13. The other structures and effects are the same as those of the solid-state imaging device 18 of the first embodiment, and therefore the description thereof will be omitted.

[0084] Light incident on the microlens 15 passes through the planarization film 13 and enters the inner lens 16, where it is focused toward a central axis perpendicular to the substrate 19. The focused incident light enters the optical waveguide 11. In the optical waveguide 11, the incident light of a specific wavelength is focused onto a central axis perpendicular to the substrate 19. The focused incident light of a specific wavelength exits the optical waveguide 11, passes through the interlayer insulating film 9, and enters the photoelectric conversion region 3.

[0085] [Seventh Modification of the First Embodiment] FIG. 14 is a cross-sectional view showing the structure of a pixel 21 of a solid-state imaging device 18G according to the seventh modification of the first embodiment.

[0086] The difference from the solid-state imaging device 18 of the first embodiment is that the optical waveguide 11 and the inner lens 16 are disposed between the passivation film 12 and the planarization film 13, and the color filter 14 is disposed between the planarization film 13 and the microlens 15. The other structures and effects are the same as those of the solid-state imaging device 18 of the first embodiment, so the description will be omitted.

[0087] Of the light incident on the microlens 15, only light of a specific wavelength is transmitted through the color filter 14, and the other light is absorbed by the color filter 14. The light of the specific wavelength that has transmitted through the color filter 14 passes through the planarization film 13 and enters the inner lens 16. In the inner lens 16, the incident light of the specific wavelength is focused on a central axis perpendicular to the substrate 19. The focused incident light of the specific wavelength exits the inner lens 16 and enters the optical waveguide 11. In the optical waveguide 11, the incident light of the specific wavelength is focused on a central axis perpendicular to the substrate 19. The focused incident light of the specific wavelength exits the optical waveguide 11, passes through the interlayer insulating film 9, and enters the photoelectric conversion region 3.

[0088] [Eighth Modification of First Embodiment] Fig. 15 is a structural cross-sectional view of a pixel 21 of a solid-state imaging device 18H according to Modification 8 of Embodiment 1. Fig. 16 is a cross-sectional view taken along line AB shown in Fig. 15. Fig. 17 is a plan view of the pixel 21.

[0089] The difference from the solid-state imaging device 18 of the first embodiment is that the charge transfer gate electrode 6H is embedded in the epitaxial layer 2 so as to cover both side surfaces of the charge retention region 4 and sandwich the charge retention region 4. The other structure and effects are the same as those of the solid-state imaging device 18 of the first embodiment, so a description thereof will be omitted.

[0090] Light incident on the solid-state imaging device 18H is refracted by the microlens 15 in the direction of the central axis of the microlens 15 and enters the planarization film 13 and the passivation film 12. The light then passes through the interlayer insulating film 9 and enters the photoelectric conversion region 3.

[0091] Light incident on the photoelectric conversion region 3 is converted into electric charges. The electric charges generated by this photoelectric conversion are transferred to the charge holding region 4 by applying a voltage to the charge transfer gate electrode 6H.

[0092] 15 to 17, the charge transfer gate electrode 6H overlaps both the deep potential portion of the photoelectric conversion region 3 and the charge retention region 4. As a result, a charge transfer path for transferring charges from the photoelectric conversion region 3 to the charge retention region 4 is formed.

[0093] In this way, if the charge transfer gate electrode 6H is embedded in the epitaxial layer 2 so as to cover both side surfaces of the charge retention region 4 and sandwich the charge retention region 4, it becomes possible to transfer charges from the photoelectric conversion region 3 to the charge retention region 4 even if the charge transfer gate electrode 6H is not formed between the sidewall of the recessed region 20 and the charge retention region 4.

[0094] Such an embedded structure of the charge transfer gate electrode 6H tends to form a potential that is advantageous for the transfer of charges from the photoelectric conversion region 3 to the charge retention region 4. This makes it possible to increase the opening size of the light-shielding film 8 extending along the side wall of the recessed region 20 by the amount of the charge transfer gate electrode 6H not being present between the side wall of the recessed region 20 and the charge retention region 4. This increases the light collection rate of the photoelectric conversion region 3, improving the sensitivity of the solid-state imaging device 18H.

[0095] In this manner, by etching Si in the same manner as shallow trench isolation (STI) and embedding a polysilicon gate electrode in the epitaxial layer 2, charge transfer gate electrodes 6H are embedded on both sides of the charge retention region 4, and a voltage is applied to the charge retention region 4 so as to sandwich the charge retention region 4 from both sides, thereby assisting the charge transfer.

[0096] 16 and 17 show a structure in which the charge holding region 4 is sandwiched between the charge transfer gate electrodes 6H from both sides, but the charge transfer gate electrode 6H may be provided on only one side of the charge holding region 4.

[0097] [Embodiment 2] Other embodiments of the present invention will be described below. For ease of explanation, the same reference numerals are given to members having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0098] 18 is a structural cross-sectional view of a pixel 21 of a solid-state imaging device 18I according to embodiment 2. The difference from the solid-state imaging device 18 of embodiment 1 is that the depth of the carved region 20 directly above the photoelectric conversion region 3 is shallower than the depth of the lower end of the charge retention region 4, and that the photoelectric conversion region 3 is formed only below the carved region 20, and does not extend below the charge retention region 4.

[0099] If the photoelectric conversion region 3 were to be extended to the charge retention region 4, the photoelectric conversion region 3 and the charge retention region 4 would become connected, and therefore the photoelectric conversion region 3 cannot be extended to the charge retention region 4, resulting in this configuration.

[0100] The charge transfer gate electrode 6 is formed on the epitaxial layer 2 so as to cover the charge retention region 4, extends along the sidewalls of the recessed region 20 to reach the bottom surface, and extends along a portion of the bottom surface to overlap the photoelectric conversion region 3 and the charge retention region 4.

[0101] When a voltage is applied to the charge transfer gate electrode 6 , the charges converted by the photoelectric conversion region 3 are transferred from the photoelectric conversion region 3 through the charge transfer gate electrode 6 to the charge retention region 4 .

[0102] [Eighth Modification of the Second Embodiment] 19 is a structural cross-sectional view of a pixel 21 of a solid-state imaging device 18J according to a modification of embodiment 2. The difference from solid-state imaging device 18I of embodiment 2 is that the deeper region of the photoelectric conversion region 3 (photodiode) is extended to below the charge retention region 4 (memory node).

[0103] In this photoelectric conversion region 3, a potential slope is formed from the deep side to the shallow side, and the impurity implantation is adjusted so that the charge generated on the deep side also flows to the shallow side and is accumulated. This makes it possible to increase the saturation capacity of the photoelectric conversion region 3 more than the configuration shown in FIG.

[0104] 〔summary〕 Solid-state imaging devices 18·18A to 18J according to aspect 1 of the present invention are solid-state imaging devices 18·18A to 18J in which a plurality of pixels 21 are arranged in a matrix on a substrate 19, and each of the plurality of pixels 21 comprises: a photoelectric conversion region 3 arranged inside the substrate 19 for converting light incident on the substrate 19 into an electric charge; a charge retention region 4 arranged inside the substrate 19 on the light incident side of the photoelectric conversion region 3 for retaining the electric charge converted in the photoelectric conversion region 3; a recessed region 20 recessed from the light incident side surface of the substrate 19 toward the photoelectric conversion region 3 to a depth corresponding to at least the charge retention region 4; and a light-shielding film 8 formed so as to cover the surface side of the substrate 19 of the charge retention region 4 and extend along the sidewalls of the recessed region 20.

[0105] According to the above configuration, a charge retention region for retaining charges converted in the photoelectric conversion region is disposed on the light incident side of the photoelectric conversion region inside the substrate. A carved region that is carved from the surface of the substrate on the light incident side is disposed toward the photoelectric conversion region to a depth at least corresponding to the charge retention region. A light-shielding film for blocking light from reaching the charge retention region is formed so as to cover the surface side of the substrate of the charge retention region and extend along the sidewall of the carved region.

[0106] Therefore, not only the top surface of the charge retention region but also the side surface of the charge retention region are covered with the light-shielding film, and as a result, it is possible to provide a solid-state imaging device that, in principle, does not generate parasitic photosensitivity noise caused by light that is diffracted and leaks into the charge retention region out of the light incident on the substrate.

[0107] Solid-state imaging devices 18·18A-18J according to aspect 2 of the present invention, in accordance with aspect 1 above, further include charge transfer gate electrodes 6·6H for transferring the charges from the photoelectric conversion region 3 to the charge retention region 4, and it is preferable that the charges are transferred to the charge retention region 4 through a charge transfer path that runs from the photoelectric conversion region 3 through the charge transfer gate electrodes 6·6H to the charge retention region 4.

[0108] According to the above configuration, by applying a voltage to the charge transfer gate electrode, charges converted from light incident on the substrate can be transferred from the photoelectric conversion region to the charge retention region.

[0109] In the solid-state imaging devices 18 , 18 A to 18 H, and 18 J according to the third aspect of the present invention, the photoelectric conversion region 3 is preferably formed extending from below the recessed region 20 to below the charge retention region 4 .

[0110] According to the above configuration, the saturation capacity of the photoelectric conversion region can be increased.

[0111] In a solid-state imaging device 18H according to the fourth aspect of the present invention, it is preferable that the charge transfer gate electrode 6H is embedded in the substrate (epitaxial layer 2) so as to cover the side surface of the charge retention region 4.

[0112] According to the above-mentioned configuration, it is not necessary to provide a charge transfer gate electrode on the recessed region side of the charge retention region, and the opening of the light-shielding film can be enlarged, which increases the light collection rate of the photoelectric conversion region and improves the sensitivity of the solid-state imaging device.

[0113] In the solid-state imaging devices 18 and 18A to 18J according to the fifth aspect of the present invention, the light-shielding film 8 is preferably formed of a single or multiple film structure having a higher light reflectance than a single layer of tungsten.

[0114] According to the above configuration, the reflectance of the light shielding film toward the charge retention region can be increased, thereby improving the light shielding performance of the light shielding film, and at the same time, the amount of light toward the photoelectric conversion region can be increased, thereby improving the sensitivity.

[0115] It is preferable that the solid-state imaging devices 18A, 18C, 18F, and 18G of aspect 6 of the present invention further include an interlayer insulating film 9 formed on the light-shielding film 8, and an optical waveguide 11 formed on the interlayer insulating film 9 using a material having a refractive index different from that of the interlayer insulating film 9, in order to guide the light to the photoelectric conversion region 3.

[0116] According to the above configuration, light incident on the substrate can be efficiently guided by the optical waveguide to the photoelectric conversion region arranged below the carved region.

[0117] The solid-state imaging devices 18D, 18E, 18F, and 18G of aspect 7 of the present invention further include an interlayer insulating film 9 formed on the light-shielding film 8, and an inner lens 16 formed on the interlayer insulating film 9 to collect the light so as to guide the light to the photoelectric conversion region 3, and it is preferable that the inner lens 16 is formed of the same material as the material constituting the interlayer insulating film 9 or at least one material having a refractive index different from that of the material constituting the interlayer insulating film 9.

[0118] According to the above configuration, the light incident on the substrate can be efficiently guided by the inner lens to the photoelectric conversion region arranged below the recessed region.

[0119] The solid-state imaging devices 18A, 18C, 18D, 18E, 18F, and 18G according to an eighth aspect of the present invention further include a passivation film 12 formed between the interlayer insulating film 9 and the optical waveguide 11 or the inner lens 16, and the passivation film 12 has a refractive index of −5.0×10 -9 dyne / cm 2 It is preferred to have a compressive stress of:

[0120] According to the above configuration, the dark current of the solid-state imaging device can be exponentially reduced.

[0121] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. The technical scope of the present invention also includes embodiments obtained by appropriately combining the technical means disclosed in the different embodiments. Furthermore, new technical features can be formed by combining the technical means disclosed in the respective embodiments. [Explanation of symbols]

[0122] 1. Semiconductor substrate (substrate) 2 Epitaxial layer (substrate) 3 Photoelectric conversion area 4 Charge retention area 5. Insulating film 6 Charge transfer gate electrode 7 Anti-reflection coating 8. Light-shielding film 9 Interlayer insulating film 10 wiring layers 11 Optical waveguide 12 Passivation film 13 Planarization film 14 Color Filters 15 Microlenses 16 Inner Lens 17 Pixel transistor area 18 Solid-state imaging device 19 Substrate 20 Excavation Area 21 pixels

Claims

1. A solid-state imaging device in which a plurality of pixels are arranged in a matrix on a substrate, Each of the plurality of pixels is a photoelectric conversion region disposed within the substrate for converting light incident on the substrate into an electric charge; a charge retention region disposed inside the substrate on the light incident side of the photoelectric conversion region for retaining charges converted in the photoelectric conversion region; a recessed region that is recessed from the surface of the substrate on the light incidence side toward the photoelectric conversion region to a position at least deeper than the charge retention region and that guides the light to the photoelectric conversion region; a light-shielding film formed so as to cover the front surface side of the substrate of the charge retention region and extend along a side wall of the recessed region; the photoelectric conversion region is formed to extend from below the recessed region along a lower surface of the charge retention region, 13. A solid-state imaging device, comprising: a photoelectric conversion region having a protruding portion protruding toward the charge retention region.

2. a charge transfer gate electrode for transferring the charge from the photoelectric conversion region to the charge retention region; 2. The solid-state imaging device according to claim 1, wherein the charges are transferred to the charge holding region through a charge transfer path that extends from the photoelectric conversion region through the charge transfer gate electrode to the charge holding region.

3. A solid-state imaging device as described in claim 2, wherein the charge transfer gate electrode is embedded in the substrate so as to cover the side surface of the charge retention region.

4. A solid-state imaging device described in any one of claims 1 to 3, wherein the light-shielding film is formed of a single or multiple film structures having a higher light reflectance than a single layer of tungsten.

5. An interlayer insulating film formed on the light-shielding film; 5. The solid-state imaging device according to claim 1, further comprising an optical waveguide formed on the interlayer insulating film and made of a material having a refractive index different from that of the interlayer insulating film, in order to guide the light to the photoelectric conversion region.

6. An interlayer insulating film formed on the light-shielding film; an inner lens formed on the interlayer insulating film to condense the light so as to guide the light to the photoelectric conversion region; 6. The solid-state imaging device according to claim 5, wherein the inner lens is formed of at least one material having the same refractive index as the material constituting the interlayer insulating film or a refractive index different from that of the material constituting the interlayer insulating film.

7. The semiconductor device further includes a passivation film formed between the interlayer insulating film and the optical waveguide or the inner lens, 7. The solid-state imaging device according to claim 6, wherein the passivation film has a compressive stress of −5.0×10 −9 dyne / cm 2 or less.

Images