Solid-state imaging device and method for manufacturing the same

Abstract

Provided is 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. The solid-state imaging device of the present invention is characterized by including: a lens array in which a plurality of microlenses are arranged in a row; a planarization layer formed on the lens array; and a diffraction grating portion composed of a thermosetting resin, having a plurality of diffraction gratings and disposed on the planarization layer, an angle between a lower surface and a side surface of the diffraction gratings being 80° or more and 100° or less.

Description

Technical Field

[0001] This invention relates to a solid-state imaging element. It also relates to a method for manufacturing the solid-state imaging element. Background Technology

[0002] Both domestically and internationally, there is ongoing development of distance image sensors that capture images containing distance information to objects.

[0003] In recent years, distance image sensors have been used in facial recognition systems such as smartphones, requiring low cost and miniaturization. Therefore, the development of 3D sensing devices utilizing existing CMOS image sensors has also been undertaken.

[0004] Patent document 1 discloses an invention related to a light field imaging device for depth acquisition and 3D imaging.

[0005] Patent Document 1: Japanese Patent No. 7120929 Summary of the Invention

[0006] Diffraction grating patterns are typically made into permanent films by applying a photosensitive resin layer (resist), exposing and developing the film, and then heating (baking) it at high temperatures.

[0007] However, it is known that in this pattern formation, the shape accuracy of the diffraction grating is insufficient, and the optical properties are degraded.

[0008] Patent document 1 does not describe the detailed structure and manufacturing method of the diffraction grating.

[0009] The purpose of this invention is to provide a solid imaging element with a diffraction grating pattern formed on a lens array with high shape accuracy and a method for manufacturing the same.

[0010] One aspect of the solid-state imaging element of the present invention is characterized by having: a lens array having a plurality of microlenses arranged in a row; a planarization layer formed on the lens array; and a diffraction grating portion made of thermosetting resin having a plurality of diffraction gratings disposed on the planarization layer, wherein the angle between the lower surface and the side surface of the diffraction grating is 80° or more and 100° or less.

[0011] One aspect of the solid-state imaging element of the present invention is characterized by having: a lens array having a plurality of microlenses arranged in a row; a planarization layer formed on the lens array; and a diffraction grating portion made of thermosetting resin having a base and a plurality of diffraction gratings protruding from the base, the base covering the upper surface of the planarization layer, wherein the surface roughness Ra of the base between the diffraction gratings is less than 100 Å.

[0012] A method for manufacturing a solid-state imaging element according to one aspect of the present invention is characterized by comprising: step A, forming a planarization layer on a lens array in which a plurality of microlenses are arranged in a row, 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 onto the thermosetting resin layer to form a plurality of diffraction gratings, wherein in step C, the angle between the lower surface and the side surface of the diffraction grating is adjusted to be 80° or more and 110° or less.

[0013] A method for manufacturing a solid-state imaging element according to one aspect of the present invention is characterized by comprising: step A, forming a planarization layer on a lens array in which a plurality of microlenses are arranged in a row, 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 onto the thermosetting resin layer to form 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 remains between the diffraction gratings.

[0014] The effects of the invention

[0015] According to the present invention, a solid imaging element having a diffraction grating pattern formed on a lens array with high shape accuracy and a method thereof can be provided. Attached Figure Description

[0016] Figure 1 This is a schematic cross-sectional view of the solid-state imaging element involved in this embodiment.

[0017] Figure 2 This is a schematic cross-sectional view showing the manufacturing process of a solid-state imaging element in a comparative manner.

[0018] Figure 3 It is a schematic diagram of the pattern shape of the diffraction grating and the diffracted light.

[0019] Figure 4 This is a schematic cross-sectional view showing the cross-sectional shape of the diffraction grating according to the first embodiment.

[0020] Figure 5 This is a schematic cross-sectional view showing the cross-sectional shape of the diffraction grating according to the second embodiment.

[0021] Figure 6 This is a schematic planar view showing the planar shape of the diffraction grating involved in this embodiment.

[0022] Figure 7 This is a schematic cross-sectional view illustrating the manufacturing process of the solid-state imaging element involved in this embodiment.

[0023] Figure 8 This is a schematic cross-sectional view illustrating the manufacturing process of the solid-state imaging element involved in this embodiment.

[0024] Figure 9 This is a schematic cross-sectional view illustrating the manufacturing process of the solid-state imaging element involved in this embodiment.

[0025] Figure 10 This is a schematic diagram of a scanning electron microscope image of the diffraction grating section involved in this embodiment.

[0026] Figure 11 yes Figure 10 A schematic diagram.

[0027] Figure 12 This is a cross-sectional profile of the diffraction grating involved in this embodiment.

[0028] Figure 13 This is a cross-sectional profile of the diffraction grating involved in the scale.

[0029] Figure 14 It is image data used to measure the surface roughness Ra between diffraction gratings in the diffraction grating section.

[0030] Figure 15 yes Figure 14 A schematic diagram. Detailed Implementation

[0031] Hereinafter, one embodiment of the present invention (hereinafter referred to as "Embodiment") will be described in detail. Furthermore, the present invention is not limited to the following embodiment and can be implemented with various modifications within its scope. Additionally, the expression "~" includes the values ​​of both the lower limit and the upper limit (boundary value). Furthermore, in the specification, the expressions "upper surface," "above," "lower surface," and "below" are used and 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." Additionally, in each layer, the surface facing the stacking direction is the "upper surface," and the surface opposite to it is the "lower surface." Alternatively, the light-receiving surface is the "upper surface," and the surface opposite to it is the "lower surface."

[0032] <Overview of the solid-state imaging element involved in this embodiment>

[0033] Figure 1 This is a schematic cross-sectional view of the solid-state imaging element according to this embodiment. The solid-state imaging element 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 50, and functions as a distance image sensor as a whole.

[0034] The substrate 20 is, for example, a silicon (Si) substrate. The material of the substrate 20 is not particularly limited, as long as it is a material capable of electrically functioning pixels or light-receiving elements such as the CMOS image sensor 24. Hereinafter, the thickness direction of the substrate 20 is defined as the Z-direction, and the direction from the interior of the substrate 20 toward the surface 20a in the Z-direction is defined as upward. Furthermore, a 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 and Z directions is defined as the Y-direction.

[0035] The solid-state imaging element 10 can have multiple CMOS image sensors 24. The multiple CMOS image sensors 24 are arranged along both the X and Y directions. As described above, by providing multiple CMOS image sensors 24, a pixel array of the solid-state imaging element 10 is formed along the surface 20a of the substrate 20. The number of CMOS image sensors 24 provided on the solid-state imaging element 10 is appropriately set according to the application of the solid-state imaging element 10, etc. Figure 1 At least a portion of the examples are shown in the examples.

[0036] Each CMOS image sensor 24 is embedded in the Z-direction on the surface 20a side of the substrate 20. The light-receiving surface 25 of the CMOS image sensor 24 is exposed from the substrate 20 and is substantially coplanar with the surface 20a. Furthermore, in Figure 1 The detailed structure of the CMOS image sensor 24 is omitted in the illustration, but it is the same as that of a known CMOS image sensor.

[0037] Color filters 28 are disposed above the light-receiving surface 25 of each CMOS image sensor 24 (i.e., above it in the Z direction). Color filters 28 allow light of any of the three primary colors of light—red (R), green (G), and blue (B)—to pass through. The color passing through the color filters 28 is appropriately determined for each of the multiple CMOS image sensors 24 based on their configuration.

[0038] The lens array 30 is formed on the color filter 28 and has a plurality of microlenses 31 arranged in a row corresponding to the color filter.

[0039] Microlenses 31 are disposed on the surface 28a of the color filters 28 on each CMOS image sensor 24. The microlens 31 is a so-called plano-convex lens having a bottom surface and a lens surface. The material of the microlens 31 has a refractive index at least higher than that of air or the planarization layer 40. Specifically, to improve the light-gathering effect of the microlens by obtaining a refractive index difference with the planarization layer 40, the material of the microlens 31 is preferably a high refractive index material, for example, having a refractive index of about 1.6. The curvature or shape of the lens surface is appropriately designed according to the refractive index of the visible wavelength of the material of the microlens 31. Furthermore, the microlenses 31 are formed and configured such that light input from above in the Z-direction and directed in the opposite direction to the Z-direction is focused onto the CMOS image sensor 24 by passing through the color filter 28 below (i.e., below in the Z-direction).

[0040] The planarization layer 40 absorbs the irregularities of the microlens 31 by covering the surface of the lens array 30, thereby forming a generally flat surface 40a for providing the diffraction grating portion 50. The surface 40a of the planarization layer 40 is planarized relative to the surface of the microlens 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 based on the optical path length required for light incident from above the Z direction onto the microlens 31.

[0041] The planarization layer 40 has a refractive index at least lower than that of the microlens 31. The closer the refractive index of the planarization layer 40 is to that of air, the greater the difference in refractive index between the planarization layer 40 and the microlens 31 can be. As a result, the refraction of light incident on the diffraction grating portion 50 from above in the Z direction to below can be suppressed, ensuring that the path of the light incident on the diffraction grating is oriented in a predetermined direction. Thus, light is well focused by the microlens 31 onto the CMOS image sensor 24, obtaining the desired optical characteristics in the solid-state imaging element 10. The refractive index of the planarization layer 40 can be appropriately adjusted.

[0042] In one example, planarization layer 40 includes hollow filler and a medium. The hollow filler and medium are transparent at visible wavelengths, for example, having a total transmittance of over 90% relative to visible light. The hollow filler helps to reduce the refractive index of planarization layer 40. The medium lies between the particles of the hollow filler, binding the hollow filler together and stabilizing planarization layer 40.

[0043] Silica (SiO2) is a preferred material for hollow fillers. Hollow fillers made of silica are inexpensive and offer high transparency and physical stability for visible wavelengths. By placing the hollow filler in a low-refractive-index layer, air regions are dispersed within the planarization layer 40. As a result, the refractive index of the planarization layer 40 decreases, and as the content of hollow filler increases, its refractive index approaches that of air.

[0044] The diffraction grating portion 50 has a layered base 51 covering the surface 40a of the planarization layer 40 and a plurality of diffraction gratings 52 protruding upward in the Z direction from the base 51. The base 51 and the diffraction gratings 52 are both made of thermosetting resin and are integrally formed.

[0045] The diffraction grating 52 is transparent at visible wavelengths, for example, having a total transmittance of over 90% relative to visible light. The diffraction grating 52 is periodically arranged at predetermined intervals in the X and Y directions. Light incident on the diffraction grating 52 from above and downwards 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 relative to the normal along the Z direction, traveling in a different direction for each wavelength.

[0046] The size or pitch of the diffraction grating 52 can be appropriately set according to the purpose, etc.

[0047] <Technical Background and the Latitude and Longitude of the Solid-State Imaging Element 10 in This Embodiment>

[0048] Previously, 3D sensing devices using CMOS image sensors were developed. To convert 2D images captured by CMOS image sensors into 3D images, diffraction gratings were used. By processing light differentiated by wavelength using the diffraction grating, distances could be determined from the distance image.

[0049] In this 3D device structure, after a color filter 28 and a microlens 31 are formed on a semiconductor substrate with a CMOS image sensor, a planarization layer 40 is formed to planarize the surface of the microlens 31, increase the optical path, and a diffraction grating is formed on the upper surface of the planarization layer 40.

[0050] Figure 2 (a) ~ Figure 2 (c) is a schematic cross-sectional view showing the manufacturing process of a solid-state imaging element for comparison. Furthermore, in Figure 2 The structure below planarization layer 72 is shown in a simplified manner. Figure 2 The reference numeral 70 is a semiconductor substrate with a CMOS image sensor, reference numeral 71 is a microlens, and reference numeral 72 is a planarization layer.

[0051] like Figure 2 As shown in (a), a transparent photosensitive positive resist is used to form a resist coating layer 73 on the entire upper surface of the planarization layer 72. Here, a resist used for microlens applications can be used.

[0052] like Figure 2 (a) shows the formation of a resist coating layer 73, and then... Figure 2 In (b), exposure and development are performed, and multiple diffraction gratings 74 are formed in the pattern. Figure 2 In (c), the diffraction grating 74 is subjected to thermal reflow (baking). Through the above, multiple diffraction gratings 74 can be patterned on the upper surface of the planarization layer 72.

[0053] However, as Figure 2 As shown in (c), by performing thermal reflow (baking), the surface 74a of each diffraction grating 74 will be deformed into a convex curved surface as a whole, and the rectangularity will decrease.

[0054] As mentioned above, if the rectangularity is damaged, the effect of light refraction increases, the light collection efficiency decreases, and thus the optical properties (sensor properties) deteriorate.

[0055] "Optical properties (sensor properties)" refer to the detection accuracy of the distance to an object. A decrease in optical properties leads to a decrease in distance detection accuracy, so it is necessary to improve the rectangularity of the diffraction grating.

[0056] Figure 3 It is a schematic diagram of the pattern shape of the diffraction grating and the diffracted light. Figure 3 The figures illustrate the cross-sectional shape of the diffraction grating schematically, with arrows representing diffracted light. For example... Figure 3 As shown in (a), if the diffraction grating is rectangular, the refraction of light is small. On the other hand, as... Figure 3 (b) In that case, the diffraction grating is trapezoidal, such as Figure 3 (c) is an inverted trapezoid, or like Figure 3 (d) If the shape is a single-sided rectangle with a single-sided tilt, the effect of light refraction will be greater. Therefore, in this embodiment, the tilt angle of the side is specified to reduce the effect of light refraction.

[0057] <Detailed Description of the Solid-State Imaging Element 10 According to the First Embodiment>

[0058] According to the solid-state imaging element 10 of this embodiment, the rectangularity of the diffraction grating 52 can be higher than before, resulting in better sensor characteristics. Hereinafter, the shape of the diffraction grating portion 50 will be described in detail. Figure 4 The text shows only the... Figure 1 The enlarged cross-sectional view shown is a partial magnification of the diffraction grating 52.

[0059] like Figure 4 As shown in (a), the diffraction grating 52 has: a lower surface 52a on the side of the planarization layer 40; a side surface 52c that rises upward in the Z direction from the skirt 52b of the lower surface 52a; and a flat upper surface 52e that is opposite to the lower surface 52a in the thickness direction (Z direction) from the upper end of the side surface 52c via the inflection point 52d.

[0060] Furthermore, the lower surface 52a of the diffraction grating 52 is integrated with the base 51, and is therefore represented by a virtual line (dashed line). The lower surface 52a is coplanar with the surface of the base 51. Figure 4 In (a), the lower surface 52a is shown as the same surface as the X-Y plane.

[0061] exist Figure 4 In (a), the side surface 52c extends parallel to, i.e., perpendicularly along the Z direction shown in the figure, 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°. As described above, Figure 4 (a) shows that the diffraction grating 52 is formed in an ideal rectangle.

[0062] In this embodiment, as described later, a thermosetting resin is used to form the diffraction grating 52 by dry etching. This improves the rectangularity of the diffraction grating 52. Therefore, in this embodiment, it is essential that the diffraction grating portion 50 is made of thermosetting resin.

[0063] Although the materials of thermosetting resins are not limited, they can be selected from, for example, acrylic resins, epoxy resins, phenolic resins, silicone resins, melamine resins, urea resins, etc.

[0064] Figure 4 (a) The diffraction grating 52 shown is rectangular, so the width dimension W1 of the lower surface 52a and the width dimension W2 of the upper surface 52e are the same length.

[0065] On the other hand, Figure 4 In (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. Figure 4 In (b), the two side surfaces 52c are inclined at the same angle, therefore, the cross-sectional shape of the diffraction grating 52 is trapezoidal. Here, "trapezoidal" simply means having an upper base (upper surface) and a lower base (lower surface), and that the upper and lower bases are approximately parallel; it does not only encompass the geometric concept of a trapezoid. For example, it also includes... Figure 3 (d) shows a configuration where one side extends vertically and the other side is inclined. However, by setting the inclination angles of both sides 52c to be the same, the refraction of light can be made symmetrical (see reference). Figure 3 It is easy to form and is therefore preferred.

[0066] In this embodiment, Figure 4 (b) The lower limit of the angle θ1 between the lower surface 52a and the side surface 52c of the diffraction grating 52 shown is set to 80°.

[0067] In contrast, Figure 4 (c) The diffraction grating 52 shown is an inverted trapezoid, that is, the side surface 52c is an inverted cone, and the width dimension W2 of the upper surface 52e is greater than the width dimension W1 of the lower surface 52a.

[0068] In this embodiment, Figure 4 (c) The upper limit of the angle θ1 between the lower surface 52a and the side surface 52c of the diffraction grating 52 shown is set to 100°.

[0069] Based on the above, 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 80° or more and 100° or less. However, the angle θ1 includes manufacturing errors or measurement errors; if the difference is ± a few degrees, it is also included in the angle θ1 of this embodiment. Therefore, when light incident on the side surface 52c is also refracted and guided into the interior, it can be diffracted in the same way as light incident on the upper surface 52e, thereby improving light utilization efficiency. Therefore, by using the solid-state imaging element 10 applied in this embodiment, various high-performance sensors can be constructed; for example, by applying it to a distance image sensor, distance measurement accuracy can be improved.

[0070] The method for measuring angle θ1 is explained. For example, a cross-sectional profile is obtained using an atomic force microscope or the like, and the skirt 52b and inflection point 52d are determined from the cross-sectional profile. The lower surface 52a is determined by drawing a straight line between the two sides of the skirt 52b. The side surface 52c is determined by drawing a straight line between the skirt 52b and the inflection point 52d. Then, the angle θ1 between the lower surface 52a and the side surface 52c is measured.

[0071] When the skirt 52b or the inflection point 52d is R (rounded corner) shaped, the lower surface 52a and the upper surface 52e can be defined in addition to the arc tangent to the R, and the ends of the lower surface and the upper surface can be drawn to each other with straight lines to define the side surface 52c.

[0072] Regarding the lower surface 52a, the surfaces of the base 51 located on both sides of the diffraction grating 52 or the surface of the planarization layer 40 can also be regarded as the lower surface 52a of the diffraction grating 52 to determine the angle θ1.

[0073] Furthermore, in this embodiment, although not a limiting statement, 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. Additionally, 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.

[0074] <Detailed Description of the Solid-State Imaging Element 10 According to the Second Embodiment>

[0075] The solid-state imaging element 10 of the second embodiment has Figure 1 The layered structure is shown. For example... Figure 5 As shown in the enlarged view, the diffraction grating portion 50 has: a base 51 that covers the entire surface 40a of the planarization layer 40; and a plurality of diffraction gratings 52 that are disposed protruding on the base 51.

[0076] In this embodiment, the diffraction grating layer integrally formed on the surface 40a of the planarization layer 40 is etched to a certain depth by dry etching, thereby forming a residual film layer between each diffraction grating 52. This residual film layer is integrally formed with the lower surface 52a side of each diffraction grating 52 to constitute a layered base 51. By providing the base 51, the planarization layer 40 can be protected, and the diffracted light can be properly guided, thereby improving the sensor characteristics.

[0077] While not a limiting statement, it is preferable that the thickness t1 of the base 51 is approximately 0.3 μm or more and 1.0 μm or less. By ensuring the thickness t1 of the base 51, the surface 40a of the planarization layer 40 can be adequately protected. That is, the planarization layer 40, as described above, contains, for example, fillers. Therefore, the surface 40a of the planarization layer 40 is not truly flat, but rather roughened. Therefore, by having the aforementioned thickness t1, the entire surface 40a of the planarization layer 40 can be reliably covered. Furthermore, the "planarization" of the planarization layer 40 refers to a shape that absorbs the unevenness of the surface of the microlens 31, making the surface of the microlens 31 flatter, and is not limited to being truly flat.

[0078] In the second embodiment, 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 the arithmetic mean roughness. The arithmetic mean roughness was measured using an atomic force microscope (AFM) (device name: Park Systems NX20 300mm (Ra value was confirmed using AFM data analysis software)).

[0079] The surface 51a of the base 51 is the surface that is affected by dry etching, but by adjusting the etching time, the surface roughness Ra of the surface 51a of the base 51 can be reduced to less than 100 Å. In this embodiment, it is preferable that the surface roughness Ra is 99.5 Å or less, more preferably 99 Å or less, even more preferably 95 Å or less, and more preferably 90 Å or less.

[0080] The surface 51a of the base 51 of the diffraction grating section 50 is a region that scatters light and does not allow light to pass through. However, if the surface roughness Ra increases, the surface 51a also functions as a diffraction grating, allowing some light to pass through and causing interference fringes to diffuse easily. Therefore, in this embodiment, by making the surface roughness Ra of the surface 51a of the base 51 as small as 100 Å or less, the diffusion of interference fringes can be suppressed, and good sensor characteristics can be obtained.

[0081] exist Figure 5 In the diagram, the side surface 52c of the diffraction grating 52 is shown as a vertical plane, but it can also be shown as... Figure 4 As shown in (b) and (c), the surface is either a positive cone or an inverted cone. 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.

[0082] Figure 6 This is a schematic planar view showing the planar shape of the diffraction grating 52 according to this embodiment. For example... Figure 6 As shown in (a), multiple diffraction gratings 52 are formed in elongated strips and arranged regularly at intervals. However, Figure 6 (a) The arrangement shown is an example and is not limited to it. That is, in Figure 6 (a) The embodiment shown includes a strip-shaped diffraction grating 52 in the Y direction and a strip-shaped diffraction grating 52 in the X direction, but it may be composed of only one of them, or the diffraction grating 52 may be arranged obliquely relative to the X and Y directions. In addition, the aspect ratios in the X and Y directions are not limited and can be appropriately set according to the required sensor characteristics or applications.

[0083] Figure 6 (b) is to Figure 6 (a) shows a magnified planar view of the diffraction grating 52. (From...) Figure 6 (b) The cross-sectional view shown, which is cut along line A-A and viewed from the direction of the arrow, with the center C of the diffraction grating 52 passing through it, is equivalent to... Figure 4 Each section. In Figure 6In (b), the diffraction grating 52 is cut along the short side direction (X direction). However, if the cut is made along the long side direction (Y direction) in a manner passing through the center C, or if the cut is made in a direction inclined relative to the X and Y directions in a manner passing through the center C, the shape appearing in the cut is preferably as follows: Figure 4 The rectangle, trapezoid, or inverted trapezoid shown.

[0084] Furthermore, the width dimensions W1 and W2 mentioned above are the cross-sectional dimensions displayed when cut along the short side direction. The width dimensions (W1 and W2) of the cross-section displayed when cut along the long side direction are greater than 0.3μm and less than or equal to the pixel area size.

[0085] <Regarding the manufacturing method of the solid-state imaging element 10 according to this embodiment>

[0086] like Figure 2 As illustrated in the comparative examples, the designed performance was not achieved in the diffraction grating formed by permanently coating the photoresist with a baking process. Specifically, in the comparative examples, the resist was convex and deformed into a rounded shape, increasing the effect of light refraction and resulting in a deterioration in sensor characteristics.

[0087] Therefore, the inventors solved the above problems by not setting the photoresist itself as a diffraction grating and by adjusting the tilt angle to avoid forming an extreme positive or negative conical surface.

[0088] Furthermore, even if the surface roughness Ra of the residual film layer between the diffraction gratings increases, the sensor characteristics will degrade as a result of forming diffraction gratings via dry etching. Therefore, a manufacturing method has been discovered that can reduce the surface roughness Ra of the residual film layer between the diffraction gratings to below a specified value, thereby obtaining good sensor characteristics.

[0089] Using the accompanying drawings, an example of a method for manufacturing the solid-state imaging element 10 of this embodiment will be described.

[0090] 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. As a method for forming the microlenses 31, for example, a high refractive index material that will become the microlens 31 is coated in layers on at least the surface 28a of the color filter 28, a photoresist layer is provided thereon, and the lens pattern obtained by thermal melting after the photolithography process is etched and transferred onto the lower high refractive index material layer.

[0091] Next, a coating liquid containing a low-refractive-index material, including hollow filler and a medium, is applied to cover the surfaces of the color filter 28 and the microlens 31, as well as the exposed surface 20a of the substrate 20 between them. The mixture is then heated to cure, thereby removing the solvent. This forms a planarization layer 40.

[0092] Next, as Figure 7 As shown, a thermosetting resin layer 50A is formed on the planarization layer 40 (step A). ​​The thickness of the thermosetting resin layer 50A is set as the sum of the thickness of the base 51 and the diffraction grating 52. Figure 1 The thickness dimension shown is above t1+t2.

[0093] Furthermore, using a transparent photoresist, such as Figure 8 As shown, 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, for example, made of... Figure 6 (a) shows the formation of the planar pattern.

[0094] The sacrificial pattern 60 is formed by applying a layer of resist and then exposing and developing it using a photomask. However, it is not used as a permanent film, and in order to keep the sacrificial pattern 60 in a rectangular cross-section, it is not cured by baking.

[0095] like Figure 8 As shown, the side 60a of the preferred sacrificial pattern 60 is formed in the vertical direction along the Z direction, but it is only necessary to have an inclination angle θ2 between 80° and 100°.

[0096] In this embodiment, when forming the sacrificial pattern 60 using a photoresist, the depth of focus (focal point) during exposure is appropriately adjusted. This allows the tilt angle θ2 of the side surface 60a of the sacrificial pattern 60 to be adjusted to 80° or more and 100° or less. The tilt angle θ2 is defined by the angle between the lower surface 60b of the sacrificial pattern 60 and the side surface 60a.

[0097] Furthermore, by appropriately adjusting the type of gas, pressure, and time used when transferring patterns via dry etching, the angle θ1 of the transferred diffraction grating can be adjusted (refer to...). Figure 4 While not limiting, for example, as a thermosetting resin, epoxy resin is used, with a thermosetting resin layer thickness of 50A ( Figure 1 The thickness dimension (t1 + t2) shown is set to approximately 1.4 ± 0.1 μm. CF4 or CHF3 is used as the gas type. The chamber pressure during dry etching is set to approximately 6 Pa to 10 Pa, and the dry etching time is set to 2.5 to 3.5 minutes.

[0098] Next, as Figure 9As shown, dry etching using the sacrificial pattern 60 is performed (step C). The shape of the sacrificial pattern 60 is thus transferred onto the thermosetting resin layer 50A, forming a diffraction grating 52. The dry etching is then stopped so that the thermosetting resin layer 50A in areas without the sacrificial pattern 60 remains intact. At this point, 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. Thus, as... Figure 9 As shown, the thermosetting resin layer 50A becomes a diffraction grating portion 50 protruding from the base 51 of the planarization layer 40, where multiple diffraction gratings 52 are seamlessly covered. Then, Figure 9 The sacrifice pattern 60 shown is removed.

[0099] In this embodiment, the diffraction grating is formed under the aforementioned dry etching conditions, thereby enabling high-precision adjustment of the angle θ1 of the side surface 52c of the diffraction grating 52 within a range of 80° to 100°. Furthermore, 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.

[0100] The diffraction grating described in this embodiment enables incident light to diffract as designed, and therefore, by applying it to the solid-state imaging element 10, various high-performance sensors can be constructed. For example, by applying the solid-state imaging element described in this embodiment to a distance image sensor, distance measurement accuracy can be improved.

[0101] When the refractive index is low, the planarization layer 40 becomes a porous structure with many voids as described above. However, in the structure of this embodiment, the planarization layer 40 is completely covered by the base 51, so it also has the advantages of properly protecting the planarization layer 40 and preventing filler from falling off or liquid from seeping in.

[0102] The foregoing has described one embodiment of the present invention in detail, but the present invention is not limited to this specific embodiment and also includes structural changes, combinations, etc., without departing from the spirit of the present invention. Several changes are illustrated below, but these are not exhaustive, and other changes are also possible. Two or more of the above-described changes may also be combined.

[0103] In the above embodiments, an on-chip solid-state imaging element with a color filter directly formed on a substrate is shown. However, the application scope of the technical concept involved in this invention is not limited to this. For example, it can also be applied to diffraction gratings disposed on organic EL (OLED).

[0104] Example

[0105] The present invention will now be described in detail through embodiments implemented to demonstrate its effects. However, the present invention is not limited to these embodiments.

[0106] <Experiments related to the angle of the side surface of the diffraction grating>

[0107] Figure 10 The image is a scanning electron microscope (SEM) image of the diffraction grating portion 50 according to this embodiment, produced by the manufacturing method described above. Figure 11 This is a schematic diagram. Figure 10 (a) is a SEM photograph viewed from a planar perspective. Figure 11 (a) is its schematic diagram. Figure 10 (b) is a cross-sectional SEM image. Figure 11 (b) is its schematic diagram. Figure 10 (c) is a SEM image viewed from an oblique angle above. Figure 11 (c) is its schematic diagram. For example... Figure 10 (a) (c) and Figure 11 As shown in (a) and (c), it can be seen that multiple diffraction gratings 52 can be arranged regularly.

[0108] like Figure 10 (b) Figure 11 As shown in (b), the diffraction grating 52 is approximately rectangular or approximately trapezoidal. In addition, the multiple diffraction gratings 52 are convex shapes on the layered base.

[0109] Furthermore, it can be seen that the upper surface 52e of the diffraction grating 52 is generally flat and roughly parallel to the upper surface of the base 51 or the planarization layer 40. Additionally, it can be seen that the side surface 52c in the cross-section is a steeply inclined surface.

[0110] Figure 12 This is a cross-sectional profile of the diffraction grating manufactured using the method described in this embodiment. Figure 13 Through Figure 2 The cross-sectional profile of the diffraction grating produced by the comparative manufacturing method is shown.

[0111] Measured using atomic force microscopy (AFM). Figure 12 and Figure 13 The cross-sectional profile shown. Figure 12 The diffraction grating of the illustrated embodiment is approximately trapezoidal. Figure 13 The surface of the diffraction grating shown in the comparative example is elliptical in shape.

[0112] Figure 12The width W1 of the lower surface 52a of the diffraction grating in the illustrated embodiment is approximately 1.1 μm, and the width W2 of the upper surface 52e is approximately 0.9 μm. Furthermore, the angle θ1 of the side surface 52c of the diffraction grating 52 is approximately 80°. As described above, the tilt angle of the side surface 52c can be determined from the cross-sectional profile. Moreover, a measurement error within a certain range (e.g., approximately ±100%) is permissible.

[0113] <Experiments related to surface roughness Ra between diffraction gratings>

[0114] Figure 14 These are image data used in experiments related to surface roughness Ra between diffraction gratings. Figure 15 yes Figure 14 A schematic diagram. This image data can be based on... Figure 14 (b) shows the acquisition of images (SEM photos) and the acquisition of 3D images, etc.

[0115] Figure 14 (a) Figure 15 (a) The portion enclosed by the frame shown is the base remaining between the diffraction gratings, the surface roughness Ra of which was measured using atomic force microscopy (AFM) (instrument name: Park Systems NX20 300mm (Ra value confirmed by AFM data analysis software)). When based on Figure 14 (a) Figure 15 (a) shows that the average roughness of the entire portion enclosed by the frame is used to obtain the surface roughness Ra, which is 99.14 Å.

[0116] In addition, Figure 14 The dry etching time required for the diffraction grating shown is 2 minutes and 45 seconds. If the dry etching time is longer, the surface roughness Ra increases, and the optical properties deteriorate. Therefore, based on this embodiment, the dry etching time is set to 2.5 minutes to 3.5 minutes. It is understood that this allows the surface roughness Ra between the diffraction gratings to be below 100 Å, preferably below 99.5 Å.

[0117] Industrial applicability

[0118] According to the present invention, a solid-state imaging element with excellent sensor characteristics can be obtained, which can be advantageously applied to 3D sensing devices.

[0119] This application is based on Japanese Patent Application No. 2023-194069, filed on November 15, 2023. Its entire contents are incorporated herein by reference.

Claims

1. A solid-state imaging element, characterized in that, have: A lens array, in which multiple microlenses are arranged in a row; A planarization layer is formed on the lens array; and The diffraction grating section, made of thermosetting resin, has multiple diffraction gratings disposed on the planarization layer. The angle between the lower surface and the side surface of the diffraction grating is greater than 80° and less than 100°.

2. The solid-state imaging element according to claim 1, characterized in that, The two sides of the diffraction grating are formed at approximately the same angle.

3. The solid-state imaging element according to claim 1, characterized in that, The diffraction grating portion has a base that covers the upper surface of the planarization layer, and the diffraction grating is provided protrudingly on the base.

4. The solid-state imaging element according to claim 3, characterized in that, The surface roughness Ra of the base between the diffraction gratings is less than 100 Å.

5. A solid-state imaging element, characterized in that, have: A lens array, in which multiple microlenses are arranged in a row; A planarization layer is formed on the lens array; and The diffraction grating portion, made of thermosetting resin, has a base and a plurality of diffraction gratings protruding from the base, the base covering the upper surface of the planarization layer. The surface roughness Ra of the base between the diffraction gratings is less than 100 Å.

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

7. The solid-state imaging element according to claim 1 or 5, characterized in that, The refractive index of the planarization layer is lower than that of the microlens.

8. A method for manufacturing a solid-state imaging element, characterized in that, have: Step A: A planarization layer is formed on a lens array in which multiple microlenses are arranged in a row, and a thermosetting resin layer is formed on the planarization layer. Step B: A sacrificial pattern corresponding to the diffraction grating is formed on the thermosetting resin layer; as well as Step C involves dry etching to transfer the shape of the sacrificial pattern onto the thermosetting resin layer, forming multiple diffraction gratings. In step C, the angle between the lower surface and the side surface of the diffraction grating is adjusted to be above 80° and below 110°.

9. A method for manufacturing a solid-state imaging element, characterized in that, have: Step A: A planarization layer is formed on a lens array in which multiple microlenses are arranged in a row, and a thermosetting resin layer is formed on the planarization layer. Step B: A sacrificial pattern corresponding to the diffraction grating is formed on the thermosetting resin layer; as well as Step C involves dry etching to transfer the shape of the sacrificial pattern onto the thermosetting resin layer, forming multiple diffraction gratings. In step C, a portion of the thermosetting resin layer with a surface roughness Ra of less than 100 Å remains between the diffraction gratings.

Images