Solid-state image sensor and method for manufacturing the same

Abstract

To provide a solid-state image sensor in which a diffraction grating pattern is formed accurately on a lens array, and a method for manufacturing the solid-state image sensor.SOLUTION: The solid-state image sensor of the present invention includes: a lens array in which a plurality of micro lenses are arranged; a planarized layer formed on the lens array; and a diffraction grating part formed on the planarized layer, the diffraction grating part being made of a thermosetting resin and having a plurality of diffraction gratings. The angle formed by the lower surface and a side surface of the diffraction grating is in the range from 80° to 100°, both inclusive.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a solid-state imaging device. A method for manufacturing this solid-state imaging device will also be mentioned.

Background Art

[0002] The development of distance image sensors that capture images including distance information to an object has been progressing both at home and abroad.

[0003] In recent years, distance image sensors have been used in face recognition systems such as smartphones, and there is a demand for low cost and miniaturization. Therefore, the development of 3D sensing devices using conventional CMOS image sensors has been carried out.

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

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Diffraction grating patterns are generally formed into permanent films through a process of applying a photosensitive resin layer (resist), exposing, developing, and then heating (baking) at a high temperature.

[0007] However, in such pattern formation, it has been found that the shape accuracy of the diffraction grating is not sufficient and the optical characteristics deteriorate. Patent Document 1 does not describe the detailed structure and 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 with high shape accuracy on a lens array, and a method for manufacturing the same.

Means for Solving the Problems

[0009] A solid-state imaging device according to one aspect of the present invention includes a lens array in which a plurality of microlenses are arranged in an array, a planarization layer formed on the lens array, a diffraction grating portion made of a thermosetting resin and having a plurality of diffraction gratings provided on the planarization layer, and an angle between a lower surface and a side surface of the diffraction grating is 80° or more and 100° or less.

[0010] A solid-state imaging device according to one aspect of the present invention includes a lens array in which a plurality of microlenses are arranged in an array, 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, and a 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 a step A of forming a planarization layer on a lens array in which a plurality of microlenses are arranged in an array and forming a thermosetting resin layer on the planarization layer, a step B of forming a sacrificial pattern corresponding to a diffraction grating on the thermosetting resin layer, and a step C of performing dry etching to transfer a shape of the sacrificial pattern to the thermosetting resin layer to form a plurality of diffraction gratings, and in the step C, an angle between a lower surface and a side surface of the diffraction grating is adjusted to be 80° or more and 110° or less.

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

Effect of the Invention

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

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Mode for Carrying Out the Invention

[0015] Hereinafter, an embodiment of the present invention (hereinafter abbreviated as "embodiment") will be described in detail. The present invention is not limited to the following embodiments, and can be variously modified and implemented within the scope of the gist. Note that the notation "~" includes both numerical values (boundary values) of the lower limit and the upper limit. In the specification, the expressions "upper surface", "above", "lower surface", and "below" are used and are defined as follows. That is, the direction in which each functional layer is stacked from the surface of the substrate 20 is "above", and the direction opposite to "above" is "below". Also, in each layer, the surface facing the stacking direction is the "upper surface", and the opposite surface is the "lower surface". Alternatively, the light receiving surface is the "upper surface", and the opposite surface is the "lower surface".

[0016] <Regarding the outline of the solid-state imaging device according to this embodiment> FIG. 1 is a schematic cross-sectional view of the solid-state imaging device according to this 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 portion 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 capable of providing pixels such as the CMOS image sensor 24 and light-receiving elements and enabling them to function electrically. Hereinafter, the thickness direction of the substrate 20 is defined as the Z direction, and the direction from the inside of the substrate 20 toward the surface 20a in the Z direction is defined as the upward direction. Also, one direction parallel to the surface 20a and orthogonal to the Z direction is defined as the X direction, and a direction parallel to the surface 20a and orthogonal to both the X direction and the Z direction is defined as the Y direction.

[0018] The solid-state imaging device 10 can include a plurality of CMOS image sensors 24. The plurality of CMOS image sensors 24 are arranged along each of the X direction and the Y direction. In this way, by providing the plurality of CMOS image sensors 24, a pixel array of the solid-state imaging device 10 is configured in the 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 according to the use of the solid-state imaging device 10 and the like, and at least a part of them is illustrated in FIG. 1 and the like.

[0019] Each CMOS image sensor 24 is embedded on the surface 20a side of the substrate 20 in the Z direction. The light-receiving surface 25 of the CMOS image sensor 24 is exposed from the substrate 20 and is substantially flush with the surface 20a. Although the detailed structure of the CMOS image sensor 24 is not shown in FIG. 1 and the like, it is the same as a known CMOS image sensor.

[0020] The color filter 28 is provided above (i.e., in the upward Z direction) the light-receiving surface 25 of each CMOS image sensor 24. The color filter 28 has a function of transmitting light in the wavelength band of any one of the three primary colors of light, red (R), green (G), and blue (B). The color transmitted by the color filter 28 is appropriately determined for each of the plurality of CMOS image sensors 24 according to the arrangement of the plurality of CMOS image sensors 24 and the like.

[0021] The lens array 30 is formed on the color filter 28 and has a plurality of microlenses 31 arranged in alignment corresponding to the color filter.

[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 each having a bottom surface and a lens surface. The material of the microlenses 31 has a refractive index that is at least higher than the refractive index of at least air and the planarization layer 40. In particular, in order to obtain a refractive index difference from the planarization layer 40 and enhance the light condensing action of the microlenses, the material of the microlenses 31 is preferably a high refractive index material having a refractive index of about 1.6, for example. The curvature and shape of the lens surface are appropriately designed according to the refractive index of the material of the microlenses 31 at visible wavelengths and the like. Further, the microlenses 31 are formed and arranged so as to focus light incident from above in the Z direction in the direction opposite to the Z direction through the color filter 28 below (i.e., in the Z direction below) 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 unevenness of the microlenses 31 and forming a substantially flat surface 40a for providing the diffraction grating portion 50. The surface 40a of the planarization layer 40 is planarized with respect to the surface 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 appropriately determined according to the optical path length required for light incident on the microlenses 31 from above in the Z direction and the like.

[0024] The planarization layer 40 has a refractive index that is at least lower than the refractive index of the microlenses 31. The closer the refractive index of the planarization layer 40 is to the refractive index of air, the greater the refractive index difference between the planarization layer 40 and the microlenses 31 can be made. As a result, the refraction of light incident on the diffraction grating of the diffraction grating portion 50 from above in the Z direction downward can be suppressed, and the traveling path of the light incident on the diffraction grating can be directed in a predetermined direction. By this, the light is favorably focused on the CMOS image sensor 24 by the microlenses 31, and desired optical characteristics are 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 hollow fillers and a medium. The hollow fillers and the medium are transparent at visible wavelengths, and for example, have a total light transmittance of 90% or more with respect to light of visible wavelengths. The hollow fillers contribute to lowering the refractive index of the planarization layer 40. The medium is interposed between the particles of the hollow fillers, binds the hollow fillers together, and stabilizes the planarization layer 40.

[0026] As a suitable material for the hollow fillers, silicon dioxide (silica, SiO 2 ) can be exemplified. The hollow fillers made of silica are inexpensive and have high transparency and physical stability with respect to visible wavelengths. When the hollow fillers are located in the low refractive index layer, as a result, air regions are scattered inside the planarization layer 40, the refractive index of the planarization layer 40 decreases, and as the content of the hollow fillers increases, its refractive index approaches the value of air.

[0027] The diffraction grating portion 50 has a layered base 51 that covers the surface 40a of the planarization layer 40, and a plurality of diffraction gratings 52 that protrude upward in the Z direction from the base 51. Both the base 51 and the diffraction gratings 52 are made of a thermosetting resin and are integrated.

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

[0029] <Technical background and the process leading to the solid-state imaging device 10 of the present embodiment> Conventionally, the development of 3D sensing devices using CMOS image sensors has been carried out. In order to convert a 2D image captured by a CMOS image sensor into a 3D image, a diffraction grating is used. Thereby, the distance can be measured from the distance image by performing image processing on the light separated by wavelength 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 provided with a CMOS image sensor, the unevenness on the surface of the microlens 31 is planarized, and a planarization layer 40 is formed to bend the optical path, and a diffraction grating is formed on the upper surface of the planarization layer 40.

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

[0032] As shown in Fig. 2(a), a resist coating layer 73 is formed on the entire upper surface of the planarization layer 72 using a transparent photosensitive positive resist. Here, as the resist to be used, a resist used for microlens applications can be used.

[0033] As shown in Fig. 2(a), after forming the resist coating layer 73, in Fig. 2(b), exposure and development are performed to form a pattern of a plurality of diffraction gratings 74, and in Fig. 2(c), the diffraction gratings 74 are thermally flowed (baked). As described above, a pattern of a plurality of diffraction gratings 74 can be formed on the upper surface of the planarization layer 72.

[0034] However, as shown in Fig. 2(c), by performing thermal flow (baking), the surface 74a of each diffraction grating 74 is deformed into a convex curved surface as a whole, and the rectangularity is reduced. Thus, when the rectangularity is impaired, the influence of light refraction becomes large, and the light collection efficiency decreases, resulting in a decrease in optical characteristics (sensor characteristics).

[0035] "Optical characteristics (sensor characteristics)" refer to the detection accuracy for measuring the distance to an object. Since the detection accuracy of the distance decreases due to the degradation of the optical characteristics, it is necessary to enhance the rectangularity of the diffraction grating.

[0036] FIG. 3 is a schematic diagram of the pattern shape of the diffraction grating and diffracted light. Each figure in FIG. 3 schematically shows the cross-sectional shape of the diffraction grating, and the arrows indicate the diffracted light. As shown in FIG. 3(a), when the diffraction grating is rectangular, the refraction of light is small. On the other hand, as shown in FIG. 3(b), when the diffraction grating is trapezoidal, or as shown in FIG. 3(c), when it is an inverted trapezoid, or as shown in FIG. 3(d), when it has a shape with one side rectangular and the other side inclined, the influence of light refraction becomes large. Therefore, in the present embodiment, in order to reduce the influence of light refraction, the inclination angle of the side surface is defined.

[0037] <Detailed description of the solid-state imaging device 10 according to the first embodiment> In the solid-state imaging device 10 according to the present embodiment, the rectangularity of the diffraction grating 52 can be enhanced compared to the conventional case, enabling good sensor characteristics to be obtained. Hereinafter, mainly, the shape of the diffraction grating portion 50 will be described in detail. FIG. 4 shows an enlarged cross-sectional view in which only the portion of the diffraction grating 52 shown in FIG. 1 is enlarged.

[0038] As shown in FIG. 4(a), the diffraction grating 52 includes a lower surface 52a on the flattening layer 40 side, a side surface 52c that rises upward in the Z direction from the skirt portion 52b of the lower surface 52a, and a flat upper surface 52e that faces the lower surface 52a in the thickness direction (Z direction) via an inflection point 52d from the upper end portion of the side surface 52c.

[0039] Note that since the lower surface 52a of the diffraction grating 52 is integrated with the base 51, it is shown by a virtual line (dotted line). The lower surface 52a is on the same surface as the surface of the base 51, and in FIG. 4(a), the lower surface 52a is shown as the same surface as the X - Y plane.

[0040] In Fig. 4(a), the side surface 52c extends parallel to the illustrated Z direction, that is, in the vertical direction, and the upper surface 52e is formed by a surface parallel to the lower surface 52a. Therefore, the angle θ1 between the lower surface 52a and the side surface 52c is 90°. Thus, the diffraction grating 52 shown in Fig. 4(a) is formed in an ideal rectangular shape.

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

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

[0043] On the other hand, in Fig. 4(b), the side surface 52c is inclined, and the width dimension W2 of the upper surface 52e is smaller than the width dimension W1 of the lower surface 52a. In Fig. 4(b), the side surfaces 52c on both sides are inclined at the same inclination angle. Therefore, the cross-sectional shape of the diffraction grating 52 is trapezoidal. Here, the "trapezoidal shape" means having an upper base (upper surface) and a lower base (lower surface), and it is sufficient that the upper base and the lower base are generally parallel, and it is not a concept including only a geometric trapezoid. For example, a form in which one side surface extends in the vertical direction and the other side surface is inclined as shown in Fig. 3(d) is also included. However, it is more preferable that the inclination angles of the side surfaces 52c on both sides are the same because the refraction of light can be made symmetric (see Fig. 3), and it is also easy to form.

[0044] In the present embodiment, the lower limit value of the angle θ1 between the lower surface 52a and the side surface 52c of the diffraction grating 52 shown in Fig. 4(b) is set to 80°.

[0045] On the other hand, in the diffraction grating 52 shown in FIG. 4(c), the side surface 52c is an inverse tapered surface, and the width dimension W2 of the upper surface 52e is larger than the width dimension W1 of the lower surface 52a, having an inverse trapezoidal shape. In the present embodiment, the upper limit value 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] As described above, in the present embodiment, the angle θ1 between the lower surface 52a and the side surface 52c of the diffraction grating 52 is defined to be 80° or more and 100° or less. However, the angle θ1 includes manufacturing errors and measurement errors, and if the difference is about ± several degrees, it is included in the angle θ1 of the present embodiment. Thereby, the light incident on the side surface 52c can also be diffracted in the same manner as the light incident on the upper surface 52e when refracted and taken into the interior, improving the light utilization efficiency. Therefore, by applying it to the solid-state imaging device 10 of the present embodiment, various sensors with good performance can be configured. For example, by applying it to a distance image sensor, the distance measurement accuracy and the like can be improved.

[0047] A method for measuring the angle θ1 will be described. For example, a cross-sectional file is acquired using an atomic force microscope or the like, and the base portion 52b and the inflection point 52d are determined from the cross-sectional file. The lower surface 52a is determined by drawing a straight line between the base portions 52b on both sides. Further, the side surface 52c is determined by drawing a straight line between the base portion 52b and the inflection point 52d. Then, the angle θ1 between the lower surface 52a and the side surface 52c is measured.

[0048] When the base portion 52b or the inflection point 52d has an R shape, excluding the arc in contact with this R, the lower surface 52a and the upper surface 52e can be determined, and the ends of the lower surface and the upper surface can be connected by a straight line to define the side surface 52c.

[0049] Regarding the lower surface 52a, the surface of the base 51 located on both sides of the diffraction grating 52 or the surface of the planarization layer 40 can be regarded as the lower surface 52a of the diffraction grating 52 to measure the angle θ1.

[0050] Also, in the present embodiment, although not limited, the width dimensions W1 and W2 of the lower surface 52a and the upper surface 52e are approximately 0.50 μm or more and 1.70 μm or less. Also, the distance between the upper surface 52e and the lower surface 52a (the thickness dimension of the diffraction grating 52) is approximately 0.30 μm or more and 0.80 μm or less.

[0051] <Detailed description of the solid-state imaging device 10 according to the second embodiment> The solid-state imaging device 10 of the second embodiment has the stacked structure shown in FIG. 1. As shown in an enlarged view in FIG. 5, the diffraction grating portion 50 includes a base 51 that covers the entire surface 40a of the planarization layer 40, and a plurality of diffraction gratings 52 provided to protrude on the base 51.

[0052] In the present embodiment, the diffraction grating layer formed on the entire surface 40a of the planarization layer 40 can be dug to a certain depth by dry etching, and a remaining film layer can be formed between the respective diffraction gratings 52. This remaining film layer integrally forms a layered base 51 on the lower surface 52a side of each diffraction grating 52. By providing the base 51, the planarization layer 40 can be protected, diffracted light can be appropriately captured, leading to an improvement in sensor characteristics.

[0053] Although not limited, 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 appropriately 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. Thus, by having the above thickness dimension t1, the entire surface 40a of the planarization layer 40 can be surely covered. Note that the "planarization" of the planarization layer 40 means absorbing the unevenness on the surface of the microlens 31 to make the shape flatter than the surface of the microlens 31, and is not limited to being truly flat.

[0054] In the second embodiment, the surface roughness Ra of the surface 51a of the base 51 between the diffraction gratings 52 is characterized in that it is 100 Å or less. The surface roughness Ra is the arithmetic mean roughness. For the measurement of the arithmetic mean roughness, an atomic force microscope (AFM) (device name: NX20 300 mm manufactured by park Systems (confirm the Ra value with AFM data analysis software)) was used.

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

[0056] The surface 51a of the base 51 of the diffraction grating section 50 is a region that scatters light and does not transmit it. However, when the surface roughness Ra increases, the surface 51a also has a diffraction grating function, a part of the light is transmitted, and the interference fringes are likely to spread. Therefore, in this embodiment, by reducing the surface roughness Ra of the surface 51a of the base 51 to 100 Å or less, the spread of the interference fringes can be suppressed, and good sensor characteristics can be obtained.

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

[0058] FIG. 6 is a schematic plan view showing the planar shape of the diffraction grating 52 according to the present embodiment. As shown in FIG. 6(a), the plurality of diffraction gratings 52 are formed in a long shape and are regularly arranged at intervals. However, the arrangement shown in FIG. 6(a) is an example and is not limited thereto. That is, in the embodiment shown in FIG. 6(a), the diffraction grating 52 that is long in the Y direction and the diffraction grating 52 that is long in the X direction are included, but it may be composed of only one of them, or the diffraction grating 52 that is inclined obliquely with respect to the X direction and the Y direction may be arranged. Further, the aspect ratios in the X direction and the Y direction are not limited and can be appropriately set according to the required sensor characteristics, applications, etc.

[0059] FIG. 6(b) is an enlarged plan view of the diffraction grating 52 shown in FIG. 6(a). A cross-sectional view taken along line A-A so as to pass through the center C of the diffraction grating 52 shown in FIG. 6(b) and viewed from the arrow direction corresponds to each cross-section of FIG. 4. In FIG. 6(b), the diffraction grating 52 is cut along the short side direction (X direction), but even when it is cut along the long side direction (Y direction) so as to pass through the center C, or when it is cut from an oblique direction with respect to the X direction and the Y direction so as to pass through the center C, the shape appearing in the cross-section is preferably a rectangular shape, a trapezoidal shape, or an inverted trapezoidal shape shown in FIG. 4.

[0060] Note that the numerical values of the width dimensions W1 and W2 listed above are cross-sectional dimensions that appear when cutting along the short side direction, and the width dimensions (W1, W2) of the cross-section that appear when cutting along the long side direction are about 0.3 μm or more and the pixel area size or less.

[0061] <Regarding the manufacturing method of the solid-state imaging device 10 according to the present embodiment> As described in the comparative example of FIG. 2, it was found that the diffraction grating formed by permanently forming the photosensitive resist by baking does not exhibit the performance as designed. That is, in the comparative example, the resist was deformed so as to be convex and rounded, and as a result, the influence of light refraction increased, leading to a decrease in sensor characteristics.

[0062] Therefore, the inventors solved the above problems by adjusting the tilt angle so that the photosensitive resist itself is not used as a diffraction grating and extreme forward or reverse tapered surfaces are not formed.

[0063] In addition, as a result of forming the diffraction grating in the dry etching process, even if the surface roughness Ra of the remaining film layer between the diffraction gratings increases, it leads to a deterioration in sensor characteristics. Therefore, a manufacturing method has also been found that can reduce the surface roughness Ra of the remaining film layer between the diffraction gratings to a predetermined value or less and obtain good sensor characteristics.

[0064] An example of a method for manufacturing the solid-state imaging device 10 according to the present 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 a plurality of microlenses 31 arranged in a two-dimensional array are further formed. As a method for forming the microlenses 31, for example, a high refractive index material that becomes the microlenses 31 is applied in layers on at least the surface 28a of the color filter 28, a photoresist layer is provided thereon, and a lens pattern formed by thermal melting after a photolithography process is etched and transferred to the layer of the lower high refractive index material.

[0065] Next, a coating liquid in which a low refractive index material containing a hollow filler and a medium is dispersed is applied so as to cover the surfaces of the color filter 28 and the microlenses 31 and the surface 20a of the substrate 20 exposed therebetween, and heat is applied to cure it to remove the solvent. Thereby, a planarization layer 40 is formed.

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

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

[0068] The sacrificial pattern 60 is formed through processes of applying the resist in layers, exposure using a photomask, and development, but is not used as a permanent film. Also, in order to keep the sacrificial pattern 60 in a rectangular cross-sectional shape, curing by baking is not performed.

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

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

[0071] Also, by appropriately adjusting the gas species, pressure, time, etc. used when transferring the pattern by a dry etching method, the angle θ1 (see FIG. 4) of the transferred diffraction grating can be adjusted. Although not limited, for example, as the thermosetting resin, an epoxy resin is used, the thickness (thickness dimension t1 + t2 shown in FIG. 1) of the thermosetting resin layer 50A is about 1.4 ± 0.1 μm, and as the gas species, CF 4 Or CHF 3 is used, and the chamber pressure during dry etching is 6 Pa~ 10 about Pa, and the time of dry etching is 2.5 minutes~ 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, and the diffraction grating 52 is formed. The dry etching is terminated so that the thermosetting resin layer 50A at the site without the sacrificial pattern 60 remains without being completely removed. 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 a plurality of diffraction gratings 52 protrude on the base 51 that covers the planarization layer 40 without gaps. Then, the sacrificial pattern 60 shown in FIG. 9 is removed.

[0073] In the present 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 within the range of 80° or more and 100° or less. Further, the surface roughness Ra of the surface 51a of the base 51 left between the diffraction gratings 52 can be adjusted to 100 Å or less.

[0074] Since the diffraction grating according to the present embodiment can diffract the incident light as designed, by applying it to the solid-state imaging device 10, various sensors with good performance can be configured. For example, by applying the solid-state imaging device according to the present embodiment to a distance image sensor, the distance measurement accuracy and the like can be improved.

[0075] When the refractive index is low, the planarization layer 40 has a porous structure with many voids as described above. However, in the configuration according to the present embodiment, since the planarization layer 40 is completely covered by the base 51, the planarization layer 40 is preferably protected, and there is also an advantage that the filler does not fall off and the liquid does not penetrate.

[0076] As described above, one embodiment of the present invention has been described in detail. However, the present invention is not limited to a specific embodiment, and includes configuration changes, combinations, etc. within the range not departing from the gist of the present invention. Some changes are exemplified below, but these are not all, and other changes are also possible. These changes may be appropriately combined with two or more.

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

Example

[0078] Hereinafter, the present invention will be described in detail with reference to examples implemented to clarify the effects of the present invention. Note that the present invention is not limited by the following examples at all.

[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 the present embodiment manufactured by the above-described manufacturing method, and FIG. 11 shows a schematic diagram thereof. FIG. 10(a) is an SEM photograph viewed from a plane, 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 viewed obliquely from above, and FIG. 11(c) is a schematic diagram thereof. As shown in FIGS. 10(a)(c) and FIGS. 11(a)(c), it was found that a plurality of diffraction gratings 52 can be regularly arranged.

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

[0081] Also, the upper surface 52e of the diffraction grating 52 was found to be substantially flat and substantially parallel to the upper surfaces of the base 51 and the planarization layer 40. Also, the side surface 52c in the cross section was found to be a steep inclined surface.

[0082] FIG. 12 is a cross-sectional profile of the diffraction grating manufactured by the manufacturing method of the present example, and FIG. 13 is a cross-sectional profile of the diffraction grating manufactured by the manufacturing method of the comparative example shown in FIG. 2.

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

[0084] The width dimension W1 of the lower surface 52a of the diffraction grating of the example shown in FIG. 12 was about 1.1 μm, and the width dimension W2 of the upper surface 52e was about 0.9 μm. Also, the angle θ1 of the side surface 52c of the diffraction grating 52 was about 80°. Thus, the inclination angle of the side surface 52c could be obtained from the cross-sectional profile. Note that a measurement error is allowed within a certain range (for example, about ± several %).

[0085] <Experiment on surface roughness Ra between diffraction gratings> FIG. 14k is the image data used in the experiment on the surface roughness Ra between diffraction gratings. FIG. 15 is a schematic diagram of FIG. 14. From this image data, a 3D image etc. can be obtained based on the acquired image (SEM photograph) shown in FIG. 14(b).

[0086] The portion surrounded by the frames shown in FIGS. 14(a) and 15(a) is the base remaining between the diffraction gratings, and the surface roughness Ra of this base was measured using an atomic force microscope (AFM) (device name: NX20 300mm manufactured by park Systems (confirm the Ra value with AFM data analysis software)). When the surface roughness Ra was obtained from the average roughness of the entire portion surrounded by the frames shown in FIGS. 14(a) and 15(a), the surface roughness was 99.14 Å.

[0087] Note that the dry etching time required to obtain the diffraction grating shown in FIG. 14 was 2 minutes and 45 seconds. Since the surface roughness Ra increases and the optical characteristics deteriorate as the dry etching time becomes longer, based on this example, the dry etching time was set to 2.5 minutes to 3.5 minutes. As a result, it was found that the surface roughness Ra between the diffraction gratings can be made 100 Å or less, preferably 99.5 Å or less.

Industrial Applicability

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

Explanation of Signs

[0089] 10: Solid-state imaging device 20: Substrate 24: CMOS image sensor 25: Light-receiving surface 28: Color filter 30: Lens array 31: Microlens 40: Planarization layer 50: Diffraction grating section 50A: Thermosetting resin layer 51: Base 52: Diffraction grating 60: Sacrificial pattern 72: Planarization layer 73: Resist coating layer 74: Diffraction grating θ1: Angle θ2: Tilt angle

Claims

1. A lens array in which a plurality of microlenses are arranged in alignment, A planarization layer formed on the lens array, A diffractive grating portion made of a thermosetting resin, having a plurality of diffractive gratings, and provided on the planarization layer, wherein an angle between a lower surface and a side surface of the diffractive grating is 80° or more and 100° or less, A solid-state imaging device characterized by this.

2. Side surfaces on both sides of the diffractive grating are formed at substantially the same angle, The solid-state imaging device according to claim 1, characterized by this.

3. The diffractive grating portion has a base covering an upper surface of the planarization layer, and the diffractive grating is provided to protrude on the base, The solid-state imaging device according to claim 1, characterized by this.

4. A surface roughness Ra of the base between the diffractive gratings is 100 Å or less, The solid-state imaging device according to claim 3, characterized by this.

5. A lens array in which a plurality of microlenses are arranged in alignment, A planarization layer formed on the lens array, A diffractive grating portion made of a thermosetting resin, having a base covering an upper surface of the planarization layer and a plurality of diffractive gratings protruding from the base, Comprising, A surface roughness Ra of the base between the diffractive gratings is 100 Å or less, A solid-state imaging device characterized by this.

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

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

8. Step A of forming a planarization layer on a lens array in which a plurality of microlenses are arranged in alignment, and forming a thermosetting resin layer on the planarization layer, Step B of forming a sacrificial pattern corresponding to a diffractive grating on the thermosetting resin layer, Step C of performing dry etching to transfer a shape of the sacrificial pattern to the thermosetting resin layer to form a plurality of diffractive gratings, Having, In step C, an angle between a lower surface and a side surface of the diffractive grating is adjusted to be 80° or more and 110° or less, A method for manufacturing a solid-state imaging device characterized by this.

9. Step A of forming a planarization layer on a lens array in which a plurality of microlenses are arranged in alignment, and forming a thermosetting resin layer on the planarization layer, Step B of forming a sacrificial pattern corresponding to a diffractive grating on the thermosetting resin layer, Performing dry etching to transfer the shape of the sacrificial pattern to the thermosetting resin layer to form a plurality of diffraction gratings, step C; having; In step C, a part of the thermosetting resin layer having a surface roughness Ra of 100 Å or less is left between the diffraction gratings; A method for manufacturing a solid-state imaging device, characterized by the above.

Images