Solid-state imaging element and method for manufacturing same

Abstract

The purpose of the present invention is to provide a solid-state imaging element in which a diffraction grating pattern is formed on a lens array with high shape accuracy, as well as a method for manufacturing the same. A solid-state imaging element according to the present invention is characterized by being provided with: a lens array in which a plurality of microlenses are arranged in an aligned manner; a planarization layer formed on the lens array; and a diffraction grating section made of a thermosetting resin, having a plurality of diffraction gratings, and provided on the planarization layer, and is characterized in that the angles between the bottom faces and side faces of the diffraction gratings are 80°-100°.

Description

Solid-state imaging device and its manufacturing method

[0001] The present invention relates to a solid-state imaging device, and also to a method for manufacturing the solid-state imaging device.

[0002] Development of distance image sensors that capture images containing information about the distance to an object is progressing both domestically and internationally.

[0003] In recent years, distance image sensors have been used in face recognition systems on smartphones and other devices, and there is a demand for low-cost, compact 3D sensing devices. To address this demand, development of 3D sensing devices using conventional CMOS image sensors is underway.

[0004] Patent Document 1 discloses an invention relating to a light field imaging device for depth acquisition and three-dimensional imaging.

[0005] Patent No. 7120929

[0006] The diffraction grating pattern is generally formed into a permanent film by applying a photosensitive resin layer (resist), exposing it to light, developing it, and then baking it at a high temperature.

[0007] However, it has been found that such pattern formation does not provide sufficient shape precision for the diffraction grating, resulting in deterioration of optical characteristics. Patent Document 1 does not describe the detailed structure or manufacturing method of the diffraction grating.

[0008] An object of the present invention is to provide a solid-state imaging device in which a diffraction grating pattern is formed on a lens array with high shape accuracy, and a method for manufacturing the same.

[0009] A solid-state imaging element according to one aspect of the present invention comprises a lens array in which a plurality of microlenses are aligned, a planarization layer formed on the lens array, and a diffraction grating portion made of a thermosetting resin, having a plurality of diffraction gratings, and provided on the planarization layer, wherein the angle between the bottom surface and the side surface of the diffraction grating is greater than or equal to 80° and less than or equal to 100°.

[0010] A solid-state imaging element according to one aspect of the present invention comprises a lens array in which a plurality of microlenses are aligned, a planarization layer formed on the lens array, a base made of a thermosetting resin and covering an upper surface of the planarization layer, and a diffraction grating portion having a plurality of diffraction gratings protruding from the base, wherein the surface roughness Ra of the base between the diffraction gratings is 100 Å or less.

[0011] A method for manufacturing a solid-state imaging device according to one aspect of the present invention includes the steps of: Step A: forming a planarization layer on a lens array in which a plurality of microlenses are aligned; and forming a thermosetting resin layer on the planarization layer; Step B: forming a sacrificial pattern corresponding to a diffraction grating on the thermosetting resin layer; and Step C: performing dry etching to transfer the shape of the sacrificial pattern to the thermosetting resin layer, thereby forming a plurality of diffraction gratings; and Step C: adjusting the angle between the bottom surface and the side surface of the diffraction grating to be between 80° and 110°.

[0012] A method for manufacturing a solid-state imaging device according to one aspect of the present invention includes the steps of: Step A: forming a planarization layer on a lens array in which a plurality of microlenses are aligned; and forming a thermosetting resin layer on the planarization layer; Step B: forming a sacrificial pattern corresponding to a diffraction grating on the thermosetting resin layer; and Step C: performing dry etching to transfer the shape of the sacrificial pattern to the thermosetting resin layer, thereby forming a plurality of diffraction gratings; and Step C: leaving a portion of the thermosetting resin layer between the diffraction gratings, the portion having a surface roughness Ra of 100 Å or less.

[0013] According to the present invention, it is possible to provide a solid-state imaging device in which a diffraction grating pattern is formed on a lens array with high shape accuracy, and a method for manufacturing the same.

[0014] 10 is a schematic cross-sectional view of a solid-state imaging element according to the present embodiment. FIG. 11 is a schematic cross-sectional view showing a manufacturing process of a solid-state imaging element according to a comparative example. FIG. 12 is a schematic diagram of a diffraction grating pattern shape and diffracted light. FIG. 13 is a schematic cross-sectional view showing a cross-sectional shape of a diffraction grating according to a first embodiment. FIG. 14 is a schematic cross-sectional view showing a cross-sectional shape of a diffraction grating according to a second embodiment. FIG. 15 is a schematic plan view showing a planar shape of a diffraction grating according to the present embodiment. FIG. 16 is a schematic cross-sectional view showing a manufacturing process of a solid-state imaging element according to the present embodiment. FIG. 17 is a schematic cross-sectional view showing a manufacturing process of a solid-state imaging element according to the present embodiment. FIG. 18 is a schematic view of a scanning electron microscope photograph of a diffraction grating portion according to the present example. FIG. 19 is a schematic diagram of FIG. 10. FIG. 19 is a cross-sectional profile of a diffraction grating according to the present example. FIG. 19 is a cross-sectional profile of a diffraction grating according to a comparative example. FIG. 19 is image data when measuring the surface roughness Ra between diffraction gratings of a diffraction grating portion. FIG. 14 is a schematic diagram of FIG.

[0015] An embodiment of the present invention (hereinafter abbreviated as "embodiment") will be described in detail below. The present invention is not limited to the following embodiment, and various modifications can be made within the scope of the gist of the present invention. The notation "to" includes both the lower limit and the upper limit (boundary value). The expressions "upper surface," "upper side," "lower surface," and "lower side" are used in the specification, and are defined as follows: The direction in which each functional layer is stacked from the surface of the substrate 20 is "upper side," and the direction opposite to "upper side" is "lower side." Furthermore, for each layer, the surface facing the stacking direction is the "upper surface," and the surface opposite to that is the "lower surface." Alternatively, the light-receiving surface is the "upper surface," and the surface opposite to that is the "lower surface."

[0016] 1 is a schematic cross-sectional view of a solid-state imaging device according to the present embodiment. The solid-state imaging device 10 includes a substrate 20, a CMOS image sensor 24, a color filter 28, a lens array 30, a planarization layer 40, and a diffraction grating section 50, and functions as a distance image sensor as a whole.

[0017] The substrate 20 is, for example, a silicon (Si) substrate. The material of the substrate 20 is, for example, Si, but is not particularly limited as long as it is a material that can provide pixels and light-receiving elements such as the CMOS image sensor 24 and enable them to function electrically. Hereinafter, the thickness direction of the substrate 20 is referred to as the Z direction, and the direction from the inside of the substrate 20 toward the surface 20a in the Z direction is referred to as the upward direction. Furthermore, a direction parallel to the surface 20a and perpendicular to the Z direction is referred to as the X direction, and a direction parallel to the surface 20a and perpendicular to the X direction and the Z direction is referred to as the Y direction.

[0018] The solid-state imaging device 10 may include a plurality of CMOS image sensors 24. The plurality of CMOS image sensors 24 are arranged along both the X and Y directions. In this manner, by providing a plurality of CMOS image sensors 24, a pixel array of the solid-state imaging device 10 is configured in a direction along the surface 20a of the substrate 20. The number of CMOS image sensors 24 provided in the solid-state imaging device 10 is appropriately set depending on the application of the solid-state imaging device 10, and at least some of them are illustrated in FIG. 1 and the like.

[0019] Each CMOS image sensor 24 is embedded in the surface 20a side of the substrate 20 in the Z direction. A light receiving surface 25 of the CMOS image sensor 24 is exposed from the substrate 20 and is substantially flush with the surface 20a. Note that although the detailed structure of the CMOS image sensor 24 is not shown in Figure 1 etc., it is similar to that of a known CMOS image sensor.

[0020] The color filters 28 are provided above the light receiving surfaces 25 of the respective CMOS image sensors 24 (i.e., above in the Z direction). The color filters 28 have the function of transmitting light in any of the wavelength bands of red (R), green (G), and blue (B), which are the three primary colors of light. The colors transmitted by the color filters 28 are determined appropriately for each of the multiple CMOS image sensors 24, depending on the arrangement of the multiple CMOS image sensors 24, etc.

[0021] The lens array 30 is formed on the color filter 28 and has a plurality of microlenses 31 aligned in correspondence with the color filters.

[0022] The microlenses 31 are provided on the surface 28a of the color filter 28 on each CMOS image sensor 24. The microlenses 31 are so-called plano-convex lenses having a bottom surface and a lens surface. The material of the microlenses 31 has a refractive index at least higher than that of air and the planarization layer 40. In particular, to obtain a refractive index difference with the planarization layer 40 and enhance the light-collecting effect of the microlenses, the material of the microlenses 31 is preferably a high-refractive index material having a refractive index of, for example, approximately 1.6. The curvature and shape of the lens surface are appropriately designed depending on the refractive index of the material of the microlenses 31 at visible wavelengths. Furthermore, the microlenses 31 are formed and positioned so that light incident from above in the Z direction in the opposite direction to the Z direction passes through the color filter 28 below (i.e., downward in the Z direction) and is focused onto the CMOS image sensor 24.

[0023] The planarization layer 40 is provided so as to cover the surface of the lens array 30, thereby absorbing the irregularities of the microlenses 31 and forming a substantially flat surface 40a on which the diffraction grating section 50 is provided. The surface 40a of the planarization layer 40 is planarized relative to the surfaces of the microlenses 31. The maximum thickness of the planarization layer 40 (i.e., the distance in the Z direction between the surface 40a of the planarization layer 40 and the surface 20a of the substrate 20 (the surface of the CMOS image sensor 24)) is determined appropriately depending on the optical path length required for light incident on the microlenses 31 from above in the Z direction, etc.

[0024] The planarization layer 40 has a refractive index lower than that of at least the microlenses 31. The closer the refractive index of the planarization layer 40 is to the refractive index of air, the greater the difference in refractive index between the planarization layer 40 and the microlenses 31 can be. As a result, refraction of light incident on the diffraction grating of the diffraction grating section 50 from above to below in the Z direction can be suppressed, and the path of light incident on the diffraction grating can be directed in a predetermined direction. This allows the light to be well focused on the CMOS image sensor 24 by the microlenses 31, and the desired optical characteristics can be obtained in the solid-state imaging device 10. The refractive index of the planarization layer 40 can be adjusted as appropriate.

[0025] In one example, the planarization layer 40 contains a hollow filler and a medium. The hollow filler and the medium are transparent at visible wavelengths, for example, having a total light transmittance of 90% or more for light at visible wavelengths. The hollow filler contributes to lowering the refractive index of the planarization layer 40. The medium is present between the hollow filler particles, bonding the hollow fillers together and stabilizing the planarization layer 40.

[0026] Suitable materials for hollow fillers include silicon dioxide (silica, SiO ２ ) can be exemplified. Hollow fillers made of silica are inexpensive and have high transparency at visible wavelengths and physical stability. When hollow fillers are located in the low refractive index layer, air regions are dispersed within the planarization layer 40, resulting in a lower refractive index of the planarization layer 40, and as the hollow filler content increases, the refractive index approaches that of air.

[0027] The diffraction grating section 50 has a layer-like base 51 that covers the surface 40a of the planarizing layer 40, and a plurality of diffraction gratings 52 that protrude upward in the Z direction from the base 51. The base 51 and the diffraction gratings 52 are both made of a thermosetting resin and are integrated together.

[0028] The diffraction grating 52 is transparent at visible wavelengths and has, for example, a total light transmittance of 90% or more for light at visible wavelengths. The diffraction gratings 52 are periodically arranged at predetermined intervals in the X and Y directions. Light incident on the diffraction grating 52 from above downward in the Z direction is diffracted by the diffraction grating 52 at a diffraction angle determined by the wavelength of the light and the pitch of the diffraction grating 52 with respect to a normal along the Z direction, and travels in a different direction for each wavelength. The dimensions, pitch, etc. of the diffraction grating 52 can be set appropriately depending on the purpose, etc.

[0029] <Technical Background and How the Solid-State Imaging Device 10 of the Present Embodiment Was Developed> 3D sensing devices using CMOS image sensors have been developed. A diffraction grating is used to convert a 2D image captured by the CMOS image sensor into a 3D image. This allows distance to be measured from a distance image by performing image processing on the light separated by wavelengths by the diffraction grating.

[0030] In such a 3D device structure, after forming a color filter 28 and a microlens 31 on a semiconductor substrate equipped with a CMOS image sensor, the irregularities on the surface of the microlens 31 are flattened, a planarization layer 40 is formed to increase the optical path, and a diffraction grating is formed on the upper surface of the planarization layer 40.

[0031] 2(a) to 2(c) are schematic cross-sectional views showing the manufacturing process of a solid-state imaging device in a comparative example. Note that in Fig. 2, the structure below a planarization layer 72 is shown in a simplified manner. In Fig. 2, reference numeral 70 denotes a semiconductor substrate equipped with a CMOS image sensor, reference numeral 71 denotes a microlens, and reference numeral 72 denotes a planarization layer.

[0032] 2A, a resist coating layer 73 is formed using a transparent photosensitive positive resist on the entire upper surface of the planarization layer 72. The resist used here may be a resist used for microlenses.

[0033] 2(a), a resist coating layer 73 is formed, and then in FIG. 2(b), exposure and development are performed to form a pattern of a plurality of diffraction gratings 74. In FIG. 2(c), the diffraction gratings 74 are subjected to heat flow (baking). In this manner, a plurality of diffraction gratings 74 can be formed as a pattern on the upper surface of the planarizing layer 72.

[0034] However, as shown in Fig. 2(c), heat flow (baking) caused the surface 74a of each diffraction grating 74 to deform into a convex curved shape overall, reducing the rectangularity. When the rectangularity is reduced in this way, the influence of light refraction increases, reducing the light collection efficiency and thereby reducing the optical characteristics (sensor characteristics).

[0035] "Optical characteristics (sensor characteristics)" refer to the detection accuracy of measuring the distance to an object. Since a decrease in optical characteristics reduces the distance detection accuracy, it is necessary to improve the rectangularity of the diffraction grating.

[0036] FIG. 3 is a schematic diagram of a diffraction grating pattern shape and diffracted light. Each diagram in FIG. 3 is a schematic diagram showing the cross-sectional shape of a diffraction grating, with arrows indicating diffracted light. When the diffraction grating is rectangular, as shown in FIG. 3( a), the refraction of light is small. On the other hand, when the diffraction grating is trapezoidal, as shown in FIG. 3( b), inverted trapezoidal, as shown in FIG. 3( c), or rectangular with one side tilted, as shown in FIG. 3( d), the effect of refraction of light becomes large. Therefore, in this embodiment, the inclination angle of the side surface is specified to reduce the effect of refraction of light.

[0037] <Detailed Description of Solid-State Imaging Device 10 Pertaining to First Embodiment> In the solid-state imaging device 10 pertaining to this embodiment, the rectangularity of the diffraction grating 52 can be improved compared to conventional devices, making it possible to obtain good sensor characteristics. The following mainly describes in detail the shape of the diffraction grating portion 50. Fig. 4 is an enlarged cross-sectional view showing only the diffraction grating 52 portion shown in Fig. 1.

[0038] As shown in Figure 4(a), the diffraction grating 52 has a lower surface 52a on the planarization layer 40 side, a side surface 52c rising upward in the Z direction from a bottom portion 52b of the lower surface 52a, and a flat upper surface 52e facing the lower surface 52a in the thickness direction (Z direction) from the upper end of the side surface 52c via an inflection point 52d.

[0039] The lower surface 52a of the diffraction grating 52 is shown by a virtual line (dotted line) because it is integrated with the base 51. The lower surface 52a is flush with the surface of the base 51, and in FIG. 4(a), the lower surface 52a is shown as being flush with the XY plane.

[0040] In Fig. 4A, the side surface 52c extends parallel to the Z direction, i.e., vertically, and the top surface 52e is formed by a surface parallel to the bottom surface 52a. Therefore, the angle θ1 between the bottom surface 52a and the side surface 52c is 90°. In this way, the diffraction grating 52 shown in Fig. 4A is formed in an ideal rectangular shape.

[0041] In this embodiment, as will be described later, the diffraction grating 52 is formed by dry etching using a thermosetting resin, which can improve the rectangularity of the diffraction grating 52. Therefore, in this embodiment, it is a requirement that the diffraction grating portion 50 be made of a thermosetting resin.

[0042] The thermosetting resin material is not limited, but can be selected from, for example, acrylic resin, epoxy resin, phenol resin, silicone resin, melamine resin, urea resin, etc. The diffraction grating 52 shown in Figure 4(a) is rectangular, and therefore the width dimension W1 of the lower surface 52a and the width dimension W2 of the upper surface 52e are the same length.

[0043] On the other hand, in FIG. 4( b), the side surface 52c is inclined, and the width W2 of the upper surface 52e is smaller than the width W1 of the lower surface 52a. In FIG. 4( b), both side surfaces 52c are inclined at the same inclination angle, and therefore the cross-sectional shape of the diffraction grating 52 is trapezoidal. Here, the term "trapezoidal shape" refers to any shape having an upper base (upper surface) and a lower base (lower surface) that are generally parallel, and does not necessarily include geometric trapezoids. For example, it also includes a shape in which one side surface extends vertically and the other side surface is inclined, as shown in FIG. 3( d). However, having the inclination angles of both side surfaces 52c be the same is preferable because it allows for symmetrical light refraction (see FIG. 3) and is easier to form.

[0044] In this embodiment, the lower limit of the angle θ1 between the lower surface 52a and the side surface 52c of the diffraction grating 52 shown in FIG. 4B is set to 80°.

[0045] In contrast, the diffraction grating 52 shown in Fig. 4(c) has an inverted trapezoidal shape in which the side surface 52c is an inverted tapered surface and the width W2 of the upper surface 52e is greater than the width W1 of the lower surface 52a. In this embodiment, the upper limit of the angle θ1 between the lower surface 52a and the side surface 52c of the diffraction grating 52 shown in Fig. 4(c) is set to 100°.

[0046] For the above reasons, in this embodiment, the angle θ1 between the lower surface 52a and the side surface 52c of the diffraction grating 52 is specified to be equal to or greater than 80° and equal to or less than 100°. However, since the angle θ1 includes manufacturing errors and measurement errors, a difference of ±several degrees is included in the angle θ1 of this embodiment. As a result, when light incident on the side surface 52c is refracted and taken in, it can be diffracted in the same way as light incident on the upper surface 52e, thereby improving the light utilization efficiency. Therefore, by applying this embodiment to the solid-state imaging element 10, various high-performance sensors can be configured, and by applying this to a range image sensor, for example, the distance measurement accuracy can be improved.

[0047] A method for measuring the angle θ1 will now be described. For example, a cross-sectional file is obtained using an atomic force microscope or the like, and the skirt 52b and the inflection point 52d are determined from the cross-sectional file. A straight line is drawn between the skirts 52b on both sides to determine the bottom surface 52a. Furthermore, a straight line is drawn between the skirt 52b and the inflection point 52d to determine the side surface 52c. Then, the angle θ1 between the bottom surface 52a and the side surface 52c is measured.

[0048] If the bottom 52b or the inflection point 52d is rounded, the bottom surface 52a and the top surface 52e can be defined excluding the arc tangent to this rounded shape, and a straight line can be drawn between the ends of the bottom surface and the top surface to define the side surface 52c.

[0049] Regarding the lower surface 52 a, the surface of the base 51 located on both sides of the diffraction grating 52 and the surface of the planarizing layer 40 can also be regarded as the lower surface 52 a of the diffraction grating 52 and the angle θ 1 can be measured.

[0050] In the present embodiment, although not limited thereto, the widths W1 and W2 of the lower surface 52a and the upper surface 52e are approximately 0.50 μm to 1.70 μm, and the distance between the upper surface 52e and the lower surface 52a (thickness of the diffraction grating 52) is approximately 0.30 μm to 0.80 μm.

[0051] <Detailed Description of Solid-State Imaging Device 10 According to Second Embodiment> The solid-state imaging device 10 according to the second embodiment has the layered structure shown in Fig. 1. As shown enlarged in Fig. 5, the diffraction grating section 50 has a base 51 that covers the entire surface 40a of the planarizing layer 40, and a plurality of diffraction gratings 52 that are provided on the base 51 and protrude therefrom.

[0052] In this embodiment, the diffraction grating layer formed on the entire surface 40a of the planarization layer 40 is dug to a certain depth by dry etching, and a residual film layer can be formed between each of the diffraction gratings 52. This residual film layer is integrated with the lower surface 52a of each of the diffraction gratings 52 to form a layered base 51. Providing the base 51 protects the planarization layer 40 and allows diffracted light to be appropriately captured, leading to improved sensor characteristics.

[0053] Although not limited thereto, the thickness dimension t1 of the base 51 is preferably approximately 0.3 μm or more and 1.0 μm or less. By ensuring the thickness dimension t1 of the base 51, the surface 40a of the planarization layer 40 can be adequately protected. That is, as described above, the planarization layer 40 contains, for example, a filler. Therefore, the surface 40a of the planarization layer 40 is not truly flat but is roughened. Therefore, by having the above thickness dimension t1, it is possible to reliably cover the entire surface 40a of the planarization layer 40. Note that "planarization" of the planarization layer 40 means absorbing the irregularities on the surface of the microlenses 31 and making it flatter than the surface of the microlenses 31, and is not limited to being truly flat.

[0054] The second embodiment is characterized in that the surface roughness Ra of the surface 51a of the base 51 between the diffraction gratings 52 is 100 Å or less. The surface roughness Ra is an arithmetic mean roughness. The arithmetic mean roughness was measured using an atomic force microscope (AFM) (device name: NX20 300 mm manufactured by Park Systems (the Ra value was confirmed using AFM data analysis software)).

[0055] Although the surface 51a of the base 51 is a surface that is affected by dry etching, the surface roughness Ra of the surface 51a of the base 51 can be reduced to 100 Å or less by adjusting the etching time, etc. In this embodiment, the surface roughness Ra can be reduced to preferably 99.5 Å or less, more preferably 99 Å or less, even more preferably 95 Å or less, and even more preferably 90 Å or less.

[0056] Although the surface 51 a of the base 51 of the diffraction grating unit 50 is an area that scatters light and does not transmit it, if the surface roughness Ra is large, the surface 51 a also has a diffraction grating function, allowing part of the light to transmit and facilitating the spreading of interference fringes. Therefore, in this embodiment, the surface roughness Ra of the surface 51 a of the base 51 is set to 100 Å or less, which makes it possible to suppress the spreading of interference fringes and obtain good sensor characteristics.

[0057] In FIG. 5, the side surface 52c of the diffraction grating 52 is illustrated as a vertical surface. However, as shown in FIGS. 4(b) and 4(c), the side surface 52c may be a forward tapered surface or a reverse tapered surface. In this case, it is preferable that the angle θ1 between the lower surface 52a and the side surface 52c of the diffraction grating 52 is 80° or more and 100° or less.

[0058] FIG. 6 is a schematic plan view showing the planar shape of a diffraction grating 52 according to this embodiment. As shown in FIG. 6A, multiple diffraction gratings 52 are formed in elongated shapes and regularly arranged at intervals. However, the arrangement shown in FIG. 6A is merely an example and is not limited thereto. That is, the embodiment shown in FIG. 6A includes diffraction gratings 52 elongated in the Y direction and diffraction gratings 52 elongated in the X direction. However, only one of the diffraction gratings 52 may be configured, or diffraction gratings 52 inclined with respect to the X and Y directions may be arranged. Furthermore, the aspect ratios in the X and Y directions are not limited and can be set appropriately depending on the desired sensor characteristics, application, and the like.

[0059] Fig. 6(b) is an enlarged plan view of the diffraction grating 52 shown in Fig. 6(a). The cross-sectional view of the diffraction grating 52 shown in Fig. 6(b) taken along line A-A passing through the center C of the diffraction grating 52 and viewed from the direction of the arrow corresponds to each cross section in Fig. 4. In Fig. 6(b), the diffraction grating 52 is cut along the short length direction (X direction). However, even when the diffraction grating 52 is cut along the long length direction (Y direction) passing through the center C, or when the diffraction grating 52 is cut from a direction oblique to the X and Y directions passing through the center C, the shape that appears in the cross section is preferably the rectangular, trapezoidal, or inverted trapezoidal shape shown in Fig. 4.

[0060] The width dimensions W1 and W2 listed above are the cross-sectional dimensions that appear when cut along the short dimension, and the cross-sectional width dimensions (W1, W2) that appear when cut along the long dimension are approximately 0.3 μm or more and approximately the pixel area size or less.

[0061] 2, it was found that a diffraction grating formed by baking a photosensitive resist to form a permanent film did not exhibit the performance as designed. That is, in the comparative example, the resist was deformed to have a convex and rounded shape, which increased the influence of light refraction, leading to a deterioration in sensor characteristics.

[0062] Therefore, the inventors solved the above problem by not using the photosensitive resist itself as a diffraction grating and by adjusting the inclination angle so that an extremely forward tapered surface or an extremely reverse tapered surface would not be formed.

[0063] In addition, even if the surface roughness Ra of the residual film layer between the diffraction gratings increases as a result of forming the diffraction gratings using a dry etching process, this leads to a deterioration in sensor characteristics. Therefore, we have discovered a manufacturing method that can reduce the surface roughness Ra of the residual film layer between the diffraction gratings to a predetermined value or less, thereby obtaining good sensor characteristics.

[0064] An example of a manufacturing method for the solid-state imaging device 10 of this embodiment will be described with reference to the drawings. First, a color filter 28 is provided on a substrate 20 on which a CMOS image sensor 24 is formed, and then a plurality of microlenses 31 arranged in a two-dimensional array are formed. One method for forming the microlenses 31 is to apply a layer of a high refractive index material that will become the microlenses 31 at least on the surface 28a of the color filter 28, provide a photoresist layer thereon, and etch-transfer the lens pattern formed by thermal melting after a photolithography process onto an underlying layer of high refractive index material.

[0065] Next, a coating liquid containing a dispersed low refractive index material containing hollow filler and a medium is applied so as to cover the surfaces of the color filters 28 and the microlenses 31 and the surface 20a of the substrate 20 exposed therebetween, and the solvent is removed by applying heat to harden the coating liquid, thereby forming the planarization layer 40.

[0066] 7, a thermosetting resin layer 50A is formed on the planarization layer 40 (Step A). ​​The thickness of the thermosetting resin layer 50A is equal to or greater than the sum of the thicknesses of the base 51 and the diffraction grating 52 (thickness dimension t1+t2 shown in FIG. 1).

[0067] Furthermore, a sacrificial pattern 60 corresponding to the diffraction grating 52 is formed on the thermosetting resin layer 50A using a transparent photosensitive resist (step B), as shown in Fig. 8. The sacrificial pattern 60 is formed, for example, in the planar pattern shown in Fig. 6(a).

[0068] The sacrificial pattern 60 is formed by applying a layer of resist and then going through a process of exposure and development using a photomask, but since it is not used as a permanent film and the sacrificial pattern 60 maintains its rectangular cross section, it is not hardened by baking.

[0069] As shown in FIG. 8, the side surface 60a of the sacrificial pattern 60 is preferably formed vertically along the Z direction, but may have an inclination angle θ2 between 80° and 100°.

[0070] In this embodiment, when forming the sacrificial pattern 60 using photoresist, the depth of focus (focus) during exposure is appropriately adjusted. This allows the inclination angle θ2 of the side surface 60a of the sacrificial pattern 60 to be adjusted to between 80° and 100°. The inclination angle θ2 is defined as the angle between the bottom surface 60b and the side surface 60a of the sacrificial pattern 60.

[0071] Furthermore, by appropriately adjusting the type of gas, pressure, time, etc. used when transferring the pattern by dry etching, the angle θ1 of the transferred diffraction grating (see FIG. 4) can be adjusted. For example, without being limited thereto, an epoxy resin is used as the thermosetting resin, the thickness of the thermosetting resin layer 50A (thickness dimension t1+t2 shown in FIG. 1) is set to about 1.4±0.1 μm, and CF is used as the gas type. ４ Or CHF ３ The chamber pressure during dry etching was set to about 6 Pa to 10 Pa, and the dry etching time was set to 2.5 minutes to 3.5 minutes.

[0072] Next, as shown in FIG. 9 , dry etching is performed using the sacrificial pattern 60 (Step C). As a result, the shape of the sacrificial pattern 60 is transferred to the thermosetting resin layer 50A, forming the diffraction grating 52. The dry etching is terminated so that the thermosetting resin layer 50A in the areas where the sacrificial pattern 60 is not present is not completely removed but remains. At this time, the depth dimension t2 is adjusted according to the dry etching conditions. This depth dimension t2 is the thickness dimension of the diffraction grating 52. As a result, as shown in FIG. 9 , the thermosetting resin layer 50A becomes a diffraction grating portion 50 in which multiple diffraction gratings 52 protrude from a base 51 that tightly covers the planarization layer 40. Then, the sacrificial pattern 60 shown in FIG. 9 is removed.

[0073] In this embodiment, by forming the diffraction grating under the above-described dry etching conditions, the angle θ1 of the side surface 52c of the diffraction grating 52 can be accurately adjusted to within a range of 80° to 100°. In addition, the surface roughness Ra of the surface 51a of the base 51 remaining between the diffraction gratings 52 can be adjusted to 100 Å or less.

[0074] The diffraction grating according to the present embodiment can diffract incident light as designed, and therefore can configure various high-performance sensors by applying it to the solid-state imaging device 10. For example, by applying the solid-state imaging device according to the present embodiment to a range image sensor, the accuracy of distance measurement can be improved.

[0075] If the refractive index is low, the planarization layer 40 will have a porous structure with many voids as described above, but in the configuration of this embodiment, the planarization layer 40 is completely covered by the base 51, which has the advantage of providing good protection for the planarization layer 40 and preventing the filler from falling off and liquid from seeping in.

[0076] Although one embodiment of the present invention has been described in detail above, the present invention is not limited to a specific embodiment, and includes configuration changes and combinations within the scope of the gist of the present invention. Some examples of changes are shown below, but these are not all inclusive, and other changes are also possible. Two or more of these changes may be combined as appropriate.

[0077] In the above-described embodiment, an on-chip type solid-state imaging device in which a color filter is formed directly on a substrate is shown, but the scope of application of the technical concept of the present invention is not limited to this, and it can also be applied to, for example, a diffraction grating disposed on an organic EL (OLED).

[0078] The present invention will be described in detail below with reference to examples carried out to clarify the effects of the present invention, but the present invention is not limited to the following examples.

[0079] <Experiment on the angle of the side surface of the diffraction grating> Fig. 10 is a scanning electron microscope (SEM) image of the diffraction grating portion 50 according to this embodiment, which was produced by the manufacturing method described above, and Fig. 11 is a schematic diagram thereof. Fig. 10(a) is an SEM photograph taken from a plan view, Fig. 11(a) is a schematic diagram thereof, Fig. 10(b) is an SEM photograph of a cross section, Fig. 11(b) is a schematic diagram thereof, Fig. 10(c) is an SEM photograph taken from diagonally above, and Fig. 11(c) is a schematic diagram thereof. As shown in Figs. 10(a) and 11(a) and 11(c) , it was found that a plurality of diffraction gratings 52 could be regularly arranged.

[0080] As shown in FIGS. 10(b) and 11(b), it was found that the diffraction grating 52 has a substantially rectangular or trapezoidal shape, and that the plurality of diffraction gratings 52 are shaped to protrude from a layered base.

[0081] It was also found that the top surface 52e of the diffraction grating 52 was substantially flat and generally parallel to the top surfaces of the base 51 and the planarizing layer 40. It was also found that the side surface 52c in cross section was a steeply inclined surface.

[0082] FIG. 12 shows a cross-sectional profile of a diffraction grating fabricated by the manufacturing method of this example, and FIG. 13 shows a cross-sectional profile of a diffraction grating fabricated by the manufacturing method of the comparative example shown in FIG.

[0083] The cross-sectional profiles shown in Fig. 12 and Fig. 13 were measured using an atomic force microscope (AFM). The diffraction grating of the example shown in Fig. 12 was approximately trapezoidal, while the entire surface of the diffraction grating of the comparative example shown in Fig. 13 was elliptical.

[0084] The width W1 of the lower surface 52a of the diffraction grating in the example shown in Figure 12 was approximately 1.1 µm, and the width W2 of the upper surface 52e was approximately 0.9 µm. The angle θ1 of the side surface 52c of the diffraction grating 52 was approximately 80°. In this way, the inclination angle of the side surface 52c could be determined from the cross-sectional profile. A certain range of measurement error (e.g., approximately ± a few percent) is allowed.

[0085] <Experiment on Surface Roughness Ra Between Diffraction Gratings> Figure 1k4 shows image data used in an experiment on the surface roughness Ra between diffraction gratings. Figure 15 is a schematic diagram of Figure 14. This image data can be used to obtain 3D images, etc., based on the obtained image (SEM photograph) shown in Figure 14(b).

[0086] The framed areas in Figures 14(a) and 15(a) are the bases remaining between the diffraction gratings, and the surface roughness Ra of these bases was measured using an atomic force microscope (AFM) (apparatus name: NX20 300 mm manufactured by Park Systems (the Ra value was confirmed using AFM data analysis software)). The surface roughness Ra was obtained from the average roughness of the entire framed areas in Figures 14(a) and 15(a), and was found to be 99.14 Å.

[0087] The dry etching time required to obtain the diffraction grating shown in Figure 14 was 2 minutes and 45 seconds. Since a longer dry etching time increases the surface roughness Ra and deteriorates the optical characteristics, the dry etching time was set to 2.5 to 3.5 minutes based on this example. It was found that this makes it possible to reduce the surface roughness Ra between the diffraction gratings to 100 Å or less, and preferably to 99.5 Å or less.

[0088] According to the present invention, a solid-state imaging element with excellent sensor characteristics can be obtained, and can be preferably applied to a 3D sensing device.

[0089] This application is based on Japanese Patent Application No. 2023-194069, filed November 15, 2023, the entire contents of which are incorporated herein by reference.

Claims

1. A solid-state imaging device comprising: a lens array in which a number of microlenses are aligned; a planarization layer formed on the lens array; and a diffraction grating section made of a thermosetting resin, having a number of diffraction gratings, and provided on the planarization layer, wherein the angle between the bottom surface and the side surface of the diffraction grating is greater than or equal to 80° and less than or equal to 100°.

2. The solid-state imaging device according to claim 1, wherein both side surfaces of said diffraction grating are formed at substantially the same angle.

3. The solid-state imaging device according to claim 1, characterized in that the diffraction grating portion has a base covering an upper surface of the planarizing layer, and the diffraction grating is provided so as to protrude above the base.

4. The solid-state imaging device according to claim 3, wherein the surface roughness Ra of the base between the diffraction gratings is 100 Å or less.

5. A solid-state imaging device comprising: a lens array having a plurality of aligned microlenses; a planarization layer formed on the lens array; and a diffraction grating section made of a thermosetting resin and having a base covering an upper surface of the planarization layer and a plurality of diffraction gratings protruding from the base, wherein the surface roughness Ra of the base between the diffraction gratings is 100 Å or less.

6. The solid-state imaging device according to claim 4 or 5, characterized in that the surface roughness Ra is 99.5 Å or less.

7. A solid-state imaging device according to claim 1 or claim 5, wherein the refractive index of the planarization layer is lower than the refractive index of the microlenses.

8. A method for manufacturing a solid-state imaging device, comprising: step A: forming a planarizing layer on a lens array in which a plurality of microlenses are aligned, and forming a thermosetting resin layer on the planarizing layer; step B: forming a sacrificial pattern corresponding to a diffraction grating on the thermosetting resin layer; and step C: performing dry etching to transfer the shape of the sacrificial pattern to the thermosetting resin layer, thereby forming a plurality of diffraction gratings, wherein in step C, an angle between the bottom surface and the side surface of the diffraction grating is adjusted to be between 80° and 110°.

9. A method for manufacturing a solid-state imaging device, comprising: step A: forming a planarization layer on a lens array in which a plurality of microlenses are aligned, and forming a thermosetting resin layer on the planarization layer; step B: forming a sacrificial pattern corresponding to a diffraction grating on the thermosetting resin layer; and step C: performing dry etching to transfer the shape of the sacrificial pattern to the thermosetting resin layer, thereby forming a plurality of diffraction gratings, wherein in step C, a portion of the thermosetting resin layer having a surface roughness Ra of 100 Å or less is left between the diffraction gratings.

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