Optical element, optical element array, lens group, electronic apparatus, and method of producing optical element

The present technology includes: a substrate, a stepped structure being formed on one surface of the substrate, the stepped structure having a stepped surface having a different height from the one surface; and a coating layer that continuously covers the stepped structure and the one surface on a periphery of the stepped structure and causes light to be transmitted therethrough or reflects the light.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage application under 35 U.S.C. 371 and claims the benefit of PCT Application No. PCT/JP2019/035448 having an international filing date of 10 Sep. 2019, which designated the United States, which PCT application claimed the benefit of Japanese Patent Application Nos. 2018-174754, filed 19 Sep. 2018 and 2019-148765, filed 14 Aug. 2019, the entire disclosures of each of which are incorporated herein by reference.

TECHNICAL FIELD

The present technology relates to an optical element, an optical element array, a lens group, an electronic apparatus, and a method of producing the optical element.

BACKGROUND ART

Conventionally, there has been proposed a lens including a substrate having a plurality of underlying patterns and a coating layer that covers each of the upper surfaces of the underlying patterns and causes light to be transmitted therethrough (see, for example, Patent Literature 1). The lens described in Patent Literature 1 is formed on the upper surface of each of the underlying patterns by forming a lens forming pattern layer on the upper surface of each of the underlying patterns and then thermally reflowing the lens forming pattern layer.

CITATION LIST

Patent Literature

DISCLOSURE OF INVENTION

Technical Problem

However, in the lens described in Patent Literature 1, because a curved structure is formed by utilizing the front surface tension on the upper surface of the underlying pattern, i.e., on the plane, the flexibility of designing is low.

It is an object of the present disclosure to provide an optical element, an optical element array, a lens group, an electronic apparatus, and a method of producing the optical element that have high flexibility of designing.

Solution to Problem

An optical element according to the present disclosure includes: (a) a substrate, a stepped structure being formed on one surface of the substrate, the stepped structure having a stepped surface having a different height from the one surface; and (b) a coating layer that continuously covers the stepped structure and the one surface on a periphery of the stepped structure and causes light to be transmitted therethrough or reflects the light.

Further, an optical element array according to the present disclosure includes: (a) a substrate having a plurality of stepped structures regularly arranged in a two-dimensional array; and (b) a coating layer that continuously covers the plurality of stepped structures and a surface of the substrate on a periphery of the plurality of stepped structures, each of portions of the coating layer covering the plurality of stepped structures causing light to be transmitted therethrough or reflects the light.

Further, an optical element array according to the present disclosure includes: (a) a plurality of first lenses regularly arranged in a two-dimensional array; and (b) a plurality of second lenses that includes a substrate, a plurality of stepped structures being formed on one surface of the substrate, each of the plurality of stepped structures having an annular stepped surface having a different height from the one surface, and a coating layer that continuously covers the plurality of stepped structures and the one surface on a periphery of the plurality of stepped structures and causes light to be transmitted therethrough, and corrects aberrations caused by the plurality of first lenses, light before or after being transmitted through the plurality of first lenses entering the plurality of second lenses.

Further, a lens group according to the present disclosure includes: (a) a first lens; and (b) a second lens that corrects an aberration caused by the first lens, light before or after being transmitted through the first lens entering the second lens, in which

the second lens includes (c) a substrate, a stepped structure being formed on one surface of the substrate, the stepped structure having an annular stepped surface having a different height from the one surface, and (d) a coating layer that continuously covers the stepped structure and the one surface on a periphery of the stepped structure and causes light to be transmitted therethrough.

Further, an electronic apparatus according to the present disclosure includes: (a) a solid-state imaging device that includes a microlens array including a substrate having a plurality of stepped structures of a plurality of stages regularly arranged in a two-dimensional array, and a coating layer that continuously covers the plurality of stepped structures of the plurality of stages and a surface of the substrate on a periphery of the plurality of stepped structures, each of portions of the coating layer covering the plurality of stepped structures having a lens shape; (b) an optical lens that forms an image of image light from a subject onto an imaging surface of the solid-state imaging device; and (c) a signal processing circuit that performs signal processing on a signal output from the solid-state imaging device.

Further, a method of producing an optical element according to the present disclosure includes: (a) a step of forming a stepped structure on a substrate; (b) a step of applying a coating liquid to the substrate on which the stepped structure has been formed; and (c) a step of drying the coating liquid so that a coating layer that continuously covers the stepped structure and a surface of the substrate on a periphery of the stepped structure and causes light to be transmitted therethrough or reflects the light is formed.

Further, a method of producing an optical element according to the present disclosure includes: (a) a step of forming a plurality of stepped structures regularly arranged in a two-dimensional array on a substrate; (b) a step of applying a coating liquid to the substrate on which the plurality of stepped structures has been formed; and (c) a step of drying the coating liquid so that a coating layer that continuously covers the plurality of stepped structures and a surface of the substrate on a periphery of the plurality of stepped structures and causes light to be transmitted therethrough is formed, in which

(d) each of the plurality of stepped structures includes an annular recessed portion for forming a lens, light before or after being transmitted through a color filter entering the lens, and (e) in the step of forming the plurality of stepped structures on the substrate, a width and a diameter of each of the plurality of annular recessed portions are adjusted in accordance with a wavelength range of light transmitted through the color filter corresponding to the annular recessed portion.

MODE(S) FOR CARRYING OUT THE INVENTION

Hereinafter, an example of an optical element, an optical element array, a lens group, an electronic apparatus, and a method of producing the optical element according to an embodiment of the present disclosure will be described with reference toFIG.1toFIG.56. The embodiments of the present disclosure will be described in the following order. Note that the present disclosure is not limited to the following examples. Further, the effects described herein are merely examples and are not limited, and additional effects may be exerted.1. First embodiment: solid-state imaging device1-1 Configuration of entire solid-state imaging device1-2 Configuration of main parts1-3 Method of producing wafer lens2. Second embodiment: solid-state imaging device2-1 Configuration of main parts2-2 Method of producing wafer lens3. Third embodiment: solid-state imaging device3-1 Configuration of main parts3-2 Method of producing correction lens3-3 Modified example4. Fourth embodiment: electronic apparatus5. Application example to moving objects6. Application example to endoscopic surgery system

1. First Embodiment

1-1 Configuration of Entire Solid-State Imaging Device

The solid-state imaging device according to the first embodiment of the present disclosure will be described.FIG.1is a schematic configuration diagram showing the entire solid-state imaging device according to the first embodiment of the present disclosure.

A solid-state imaging device1inFIG.1is a back surface illumination CMOS (Complementary Metal Oxide Semiconductor) image sensor. As shown inFIG.52, the solid-state imaging device1(101) takes in image light (incident light106) from a subject via an optical lens102, and the light amount of the incident light106imaged on the imaging surface is converted into an electrical signal in units of pixels and output as a pixel signal.

As shown inFIG.1, the solid-state imaging device1according to the first embodiment includes a substrate2, a pixel region3, a vertical drive circuit4, a column signal processing circuit5, a horizontal drive circuit6, an output circuit7, and a control circuit8.

The pixel region3includes a plurality of pixels9regularly arranged in a two-dimensional array on the substrate2. The pixel9includes a photoelectric conversion unit23shown inFIG.2and a plurality of pixel transistors (not shown). As the plurality of pixel transistors, for example, four transistors, i.e., a transfer transistor, a reset transistor, a selection transistor, and an amplifier transistor, can be employed. In addition, for example, three transistors excluding the selection transistor may be employed.

The vertical drive circuit4includes, for example, a shift register, selects a desired pixel drive wiring10, and supplies a pulse for driving the pixel9to the selected pixel drive wiring10to drive the respective pixels9on a row-by-row basis. That is, the vertical drive circuit4selectively scans the respective pixels9of the pixel region3on a row-by-row basis sequentially in the perpendicular direction, and supplies a pixel signal based on the signal charges generated in accordance with the amount of received light in the photoelectric conversion unit23of each of the pixels9to the column signal processing circuit5via a vertical signal line11.

The column signal processing circuit5is disposed, for example, for each column of the pixels9, and performs signal processing such as noise removal on a signal output from the pixels9in one row for each pixel column. For example, the column signal processing circuit5performs signal processing such as CDS (Correlated Double Sampling) for removing fixed pattern noise unique to the pixel and AD (Analog Digital) conversion.

The horizontal drive circuit6includes, for example, a shift register, sequentially outputs a horizontal scan pulse to the column signal processing circuit5to select each of the column signal processing circuits5in turn, and causes each of the column signal processing circuits5to output a pixel signal on which signal processing has been performed to a horizontal signal line12.

The output circuit7performs signal processing on a pixel signal sequentially supplied from each of the column signal processing circuits5via the horizontal signal line12and outputs the obtained pixel signal. As the signal processing, for example, buffing, black level adjustment, column variation correction, or various digital signal processing can be used.

The control circuit8generates clock signals and control signals that serve as a reference for operations of the vertical drive circuit4, the column signal processing circuit5, the horizontal drive circuit6, and the like on the basis of a vertical synchronization signal, a horizontal synchronization signal, and a master clock signal. Then, the control circuit8outputs the generated clock signals and control signals to the vertical drive circuit4, the column signal processing circuit5, the horizontal drive circuit6, and the like.

1-2 Configuration of Main Parts

Next, a detailed structure of the solid-state imaging device1inFIG.1will be described.FIG.2is a diagram showing a cross-sectional configuration of the pixel region3of the solid-state imaging device1according to the first embodiment. InFIG.2, a back surface illumination CMOS image sensor (CMOS type solid-state imaging device) is used as the solid-state imaging device1.

As shown inFIG.2, the solid-state imaging device1according to the first embodiment includes a light receiving layer17obtained by stacking the substrate2, a fixed charge film13, an insulating film14, a light-shielding film15, and a flattening film16in the stated order. Further, on the surface (hereinafter, referred to also as the “back surface S1”) of the light receiving layer17on the side of the flattening film16, a light collection layer20obtained by stacking a color filter18and a wafer lens19(optical element) in the stated order is formed. Here, the wafer lens19is the one referred to also as the on-chip lens or microlens. Further, on the surface (hereinafter, referred to also as the “front surface S2”) of the light receiving layer17on the side of the substrate2, a wiring layer21and a support substrate22are stacked in the stated order. Note that since the back surface S1of the light receiving layer17and the back surface of the flattening film16are the same surface, also the back surface of the flattening film16will be referred to as the “back surface S1” in the following description. Further, since the front surface S2of the light receiving layer17and the front surface of the substrate2are the same surface, also the front surface of the substrate2will be referred to as the “front surface S2” in the following description.

The substrate2includes, for example, a semiconductor substrate formed of silicon (Si), and forms the pixel region3as shown inFIG.1. As shown inFIG.2, the plurality of photoelectric conversion units23formed on the substrate2, i.e., the plurality of pixels9including the plurality of photoelectric conversion units23embedded in the substrate2, are arranged in a two-dimensional array pattern. In the photoelectric conversion unit23, signal charges corresponding to the amount of incident light are generated, and the generated signal charges are accumulated.

The fixed charge film13continuously covers the entire back surface S3side (the entire light receiving surface side) of the substrate2. Further, the insulating film14continuously covers the entire back surface S4side (the entire light receiving surface side) of the fixed charge film13. Further, the light-shielding film15is formed in a lattice pattern on a part of a back surface S5side of the insulating film14(a part of the light receiving surface side) so as to open the light receiving surface of each of the plurality of photoelectric conversion units23. Further, the flattening film16continuously covers the entire back surface S5side (the entire light receiving surface side) of the insulating film14including the light-shielding film15so that the back surface S1of the light receiving layer17is a flat surface without irregularities.

The color filters18are formed on the back surface S1side (light receiving surface side) of the flattening film16corresponding to the respective pixels9. Thus, the color filters18form a color filter array regularly arranged in a two-dimensional array. Each of the color filters18is formed to cause certain wavelengths, such as red, green, and blue, to be transmitted therethrough. Then, the color filter18causes light of a specific wavelength to be transmitted therethrough and causes the transmitted light to enter the photoelectric conversion unit23of the substrate2.

The wafer lenses19are formed on a back surface S6side (light receiving surface side) of the color filter18corresponding to the respective pixels9. Thus, the wafer lenses19form a microlens array24(optical element array) regularly arranged in a two-dimensional array. The wafer lens19collects the image light (the incident light106) from a subject shown inFIG.52, and causes the collected incident light106to be transmitted through the color filter18and then enter the photoelectric conversion unit23.

Note that in the first embodiment, the example in which one wafer lens19is formed corresponding to one pixel9has been shown as shown inFIG.3A, but other configurations may be employed. For example, as shown inFIG.3B,FIG.3C, andFIG.3D, one wafer lens19may be formed corresponding to a plurality of pixels9such as 2×1 pixels, 1×2 pixels, and 2×2 pixels.

As shown inFIG.4, the wafer lens19includes a substrate25and a coating layer26.

The substrate25is formed on the back surface S6side (light receiving surface side) of the color filter18, and includes a plurality of stepped structures27, which is a projecting portion, formed on a back surface S7side (light receiving surface side) of the substrate25. Each of the stepped structures27is formed corresponding to the pixel9and has a stepped surface28of one or more stages. As the stepped surface28, for example, a surface having a height different from that of the back surface S7of the substrate25can be used. For example, a surface in parallel with the back surface S7of the substrate25can be employed.FIG.4illustrates a case where the number of stages of the stepped surface28of the stepped structure27is one.

As shown inFIG.5AandFIG.5B, the number of stages of the stepped surface28of the stepped structure27may be two or more. In the case where the stepped surface28of two or more stages is provided, at least one of a surface perpendicular to the back surface S7(surface on the light receiving surface side) of the substrate25and an inclined surface and a curved surface inclined with respect to the normal direction of the back surface S7can be used as side surfaces29and30in the stepped structure27. The side surface29is a surface for connecting the back surface S7of the substrate25and the stepped surface28. Further, the side surface30is a surface for connecting the two stepped surfaces28and28.FIG.5Aillustrates a case where the number of stages of the stepped surface28of the stepped structure27is two, the side surface29is a perpendicular surface, and the side surface30is a curved surface. Further,FIG.5Billustrates a case where the number of stages of the stepped surface28of the stepped structure27is four, the side surface29is a perpendicular surface, the side surface30of the lowermost part is a perpendicular surface, the side surface30of the intermediate part is a curved surface, and the side surface30of the uppermost part is a curved surface. When the number of stages of the stepped surface28is two or more, the upper surface of the coating layer26can be formed in a smooth curved surface shape, and the wafer lens19having a large curvature can be easily formed.

Note that even if the number of stages of the stepped surface28of the stepped structure27is one, the upper surface of the coating layer26can be formed in a smooth curved surface shape and the wafer lens19having a large curvature can be formed by using, as the side surface29of the stepped structure27, an inclined surface or curved surface inclined with respect to the normal direction of the back surface S7of the substrate25(the surface of the light receiving surface side), as shown inFIG.6AandFIG.6B.FIG.6Aillustrates a case where the number of stages of the stepped surface28is one and the side surface29is an inclined surface. Further,FIG.6Billustrates a case where the number of stages of the stepped surface28is one and the side surface29is a curved surface.

The inclination angle of the inclined surface is favorably within the range of 0 degrees or more and 60 degrees or less with respect to the normal direction of the back surface S7(surface of the light receiving surface side) of the substrate25. In particular, the range of 15 degrees or more and 60 degrees or less is more favorable. Further, the ratio of a width W and a height H of the stepped structure27shown inFIG.4is favorably in the range of 1:10 to 10:1. In particular, the range of 1:5 to 5:1 is more favorable. As the width W, for example, the diameter of the bottom surface of the stepped structure27can be employed in the case where the stepped structure27has a circular shape in plan view. Further, in the case where the stepped structure27has a rectangular shape, the width of the short side of the bottom surface of the stepped structure27can be employed. Further, the width W of the stepped structure27is less than or equal to a pitch p of the stepped structure27(e.g., 50 μm or less).

Further, as the planar shape of the stepped structure27, as shown inFIG.7A,FIG.7B,FIG.7C,FIG.7D, andFIG.7E, a circular shape, a polygonal shape, an elliptical shape, or the like can be used in accordance with the shape of each of the pixels9, the layout of the plurality of pixels9when one wafer lens19corresponds to the plurality of pixels9, and the like. The polygonal shape may be, for example, one in which the corner portions are rounded, as well as one in which the corner portions are angled.FIG.7Aillustrates a case where the planar shape of the stepped structure27is a circular shape. Further,FIG.7Billustrates a case where the planar shape of the stepped structure27is a triangular shape. Further,FIG.7Cillustrates a case where the planar shape of the stepped structure27is a rectangular shape. Further,FIG.7Dillustrates a case where the planar shape of the stepped structure27is a hexagonal shape. Further,FIG.7Eillustrates a case where the planar shape of the stepped structure27is an elliptical shape. Here, in the case where an elliptical shape is used as the planar shape of the stepped structure27, it is favorable that the ratio (aspect ratio) of the long side L and the short side S of the elliptical shape shown inFIG.3Bbe 1 or more and 5 or less.

Further, in the case where the number of stages of the stepped surface28of the stepped structure27is two or more as shown inFIG.8AandFIG.8C, it is favorable to arrange the stepped surfaces28so that the outer peripheries of the stepped surfaces28are separated from each other in plan view as shown inFIG.8BandFIG.8D.FIG.8AandFIG.8Billustrate a case where the stepped surfaces28are arranged such that the outer peripheries of the stepped surfaces28form a plurality of concentric circles in plan view. Further,FIG.8CandFIG.8Dillustrate a case where the stepped surfaces28are arranged such that the outer peripheries of the stepped surfaces28form a plurality of concentric rectangles in plan view.

Note thatFIG.8AtoFIG.8Dillustrate an example where the stepped surfaces28are arranged so that the outer peripheries of the stepped surfaces28are concentric in plan view, but other configurations may be employed as long as the stepped surfaces28are arranged such that the outer peripheries of the stepped surfaces28are separated from each other. For example, the stepped surfaces28may be arranged such that the center points of the outer peripheries of the stepped surfaces28are shifted in plan view.

Further, as the material of the substrate25, for example, a material that causes light to be transmitted therethrough and has a refractive index of approximately 1.5 can be used. For example, a resin used as a material of a resin-made lens, such as a styrene-based resin and an acrylic-based resin, or an inorganic material having a refractive index close to 1.5, such as silicon oxide (SiO2) and silicon nitride (Si3N), can be employed. As the styrene-based resin, for example, polystyrene, an AS resin, or an ABS resin can be employed. Further, as the acrylic-based resin, for example, poly(meth)acrylonitrile, polymethyl(meth)acrylate, polyethyl(meth)acrylate, polybutyl(meth)acrylate, or polyacrylamide can be employed.

The coating layer26is formed on the back surface S7side (light receiving surface side) of the substrate25, and continuously covers the stepped structure27and the back surface S7(surface on the light receiving surface side) of the substrate25on a periphery of the stepped structure27. That is, the coating layer26is configured to cover the entire back surface S7, i.e., the entire surface having the stepped structure27. The upper surface of the portion covering the stepped structure27is formed in a curved shape of the convex lens.

As described above, in the first embodiment, since the entire surface having the stepped structure27is covered with the coating layer26and the part of the coating layer26covering the stepped structure27is formed in a lens shape (in a convex lens shape), a convex microlens is formed by the stepped structure27and the coating layer26.

Further, as the material of the coating layer26, for example, a material that causes light to be transmitted therethrough and has a refractive index different from the refractive index of the material of the substrate25by ±10% or less of the refractive index of the material of the substrate25can be used. In particular, considering the reduction of the difference in a refractive index, it is favorable to use the same material as the material of the substrate25. By reducing the difference between the refractive index of the coating layer26of incident light and the refractive index of the substrate25, scattering and reflection of incident light on the interface between the coating layer26and the substrate25can be suppressed.

The wiring layer21is formed on the front surface S2side of the substrate2, and includes a wiring32stacked in a plurality of layers (three layers inFIG.2) via an interlayer insulating film31. A pixel transistor constituting the corresponding pixel9is driven via the wiring32of a plurality of layers formed in the wiring layer21.

The support substrate22is formed on a surface of the wiring layer21opposed to the side facing the substrate2. The support substrate22is a substrate for achieving the intensity of the substrate2in the production stage of the solid-state imaging device1. For example, silicon (Si) can be used as the material of the support substrate22.

In the solid-state imaging device1having the above-mentioned configuration, light is applied from the back surface side of the substrate2(the back surface S1side of the light receiving layer17), the applied light is transmitted through the wafer lens19and the color filter18, and the transmitted light is photoelectrically converted by the photoelectric conversion unit23, whereby signal charges are generated. Then, the generated signal charges are output as a pixel signal by the vertical signal line11shown inFIG.1formed of the wiring32via a pixel transistor formed on the front surface S2side of the substrate2.

1-3 Method of Producing Wafer Lens

Next, a method of producing the wafer lens19(optical element according to the first embodiment) of the solid-state imaging device1according to the first embodiment will be described.FIG.9A,FIG.9B,FIG.10A,FIG.10B,FIG.11A,FIG.11B,FIG.12A,FIG.12B,FIG.13A,FIG.13B,FIG.14A,FIG.14B,FIG.15A,FIG.15B,FIG.16A,FIG.16B,FIG.17A,FIG.17B,FIG.18A, andFIG.18Bare plan views and cross-sectional views showing a production step of an optical element according to the first embodiment.FIG.9AtoFIG.18Billustrate a case where the number of stages of the stepped surface28of the stepped structure27of the substrate25is three.

First, as shown inFIG.9AandFIG.9B, a photoresist film33is applied to the entire back surface S8of the substrate25. Subsequently, the photoresist film33is exposed as shown inFIG.10AandFIG.10B, and the photoresist film33is developed as shown inFIG.11AandFIG.11B.

Subsequently, as shown inFIG.12AandFIG.12B, the back surface S8of the substrate25is etched using the developed photoresist film33as an etching mask, and a third-stage (uppermost part) stepped surface28cof the stepped structure27is formed. Subsequently, the photoresist film33is slimmed as shown inFIGS.13A and13B, the third-stage stepped surface28cis etched using the slimmed photoresist film33as an etching mask as shown inFIG.14AandFIG.14B, and a first-stage (lowermost part) stepped surface28aof the stepped structure27is formed. Subsequently, slimming and etching are repeated to form a second-stage (intermediate part) stepped surface28bof the stepped structure27, and thus, the stepped structure27having the stepped surfaces28a,28band28cof three stages is formed.

Subsequently, as shown inFIG.15AandFIG.15B, the photoresist film33is removed from the back surface S8of the substrate25. As a result, the plurality of stepped structures27having the stepped surfaces28a,28b, and28cof three stages regularly arranged in a two-dimensional array is formed on the back surface S7of the substrate25.

Subsequently, as shown inFIG.16AandFIG.16B, a coating liquid34for forming the coating layer26is applied so as to cover the entire back surface S7of the substrate25, i.e., the entire surface having the stepped structure27, and so that the liquid surface is horizontal. Regarding the thickness of the layer including the coating liquid34, the part corresponding to the portion where the stepped structure27is not formed is the thickest, the part corresponding to the first-stage stepped surface28aof the stepped structure27is the second thickest, the part corresponding to the second-stage stepped surface28bof the stepped structure27is the third thickest, and the part corresponding to the third-stage stepped surface28cof the stepped structure27is the thinnest. As the coating liquid34, for example, a coating liquid obtained by dissolving a solute such as a styrene-based resin and an acrylic-based resin in a solvent can be employed. As a method of applying the coating liquid34, for example, a spin coat method can be employed.

Subsequently, as shown inFIG.17AandFIG.17B, the applied coating liquid34is dried. At this time, the solvent volatilizes and the thickness of the layer including the coating liquid34is reduced. Specifically, at an early stage of drying of the coating liquid34, the front surface of the coating liquid34is flat and uniformly reduced in film thickness. However, as the drying of the coating liquid34proceeds, the solute concentration of the coating liquid34in a projecting portion becomes locally high due to the stepped structure27of the substrate25. As a result, the evaporation rate of the solvent of the coating liquid34in the projecting portion becomes slow, and the front surface of the coating liquid34in a recessed portion is recessed. Due to this phenomenon, the amount of reduction in the thickness of the layer becomes larger where the thickness of the layer is thicker. In other words, the reduction amount of the part corresponding to the portion where the stepped structure27is not formed is the greatest, the reduction amount of the part corresponding to the first-stage stepped surface28aof the stepped structure27is the second largest, the reduction amount of the part corresponding to the second-stage stepped surface28bof the stepped structure27is the third largest, and the reduction amount of the part corresponding to the third-stage stepped surface28cof the stepped structure27is the smallest. As a result, the coating layer26having a convex lens shape is formed in the portion covering the stepped structure27.

Subsequently, as shown inFIG.18AandFIG.18B, UV-curing or baking is performed on the coating layer26having a convex lens shape so that the formed coating layer26(coating film) is a permanent film. As a result, the coating layer26is cured and the wafer lens19shown inFIG.4is completed. In the completed wafer lens19, a lens height LH shown inFIG.4is less than or equal to the height H of the stepped structure27. Further, a lens diameter LR is equal to or higher than the width W of the stepped structure27and equal to or lower than the pitch p of the stepped structure27.

Note that in the case where the side surfaces29and30are each an inclined surface, for example, a resist-receding method can be used. In the resist-receding method, as shown inFIG.19AandFIG.19B, when the substrate25is etched, the photoresist film33is also slowly etched using an etching gas mixed with an O2gas or the like. Then, the photoresist film33is gradually reduced, and the region to be etched in the substrate25is gradually widened. As a result, it is possible to form a portion of the substrate25where the etching time is continuously changed, and form an inclined surface on the side surfaces29and30.

As described above, in the wafer lens19(optical element) according to the first embodiment, the substrate25is provided, the stepped structure27being formed on one surface (the back surface S7) of the substrate25, the stepped structure27having the stepped surface28having a different height from the back surface S7. In addition, the coating layer26that continuously covers the stepped structure27and the back surface S7on a periphery of the stepped structure27and causes light to be transmitted therethrough is provided. Therefore, various shapes can be realized in accordance with the shape of the stepped structure27, and the wafer lens19with a high flexibility of designing can be provided.

Further, in the wafer lens19(optical element) according to the first embodiment, the number of stages of the stepped surface28has been set to two or more. Alternatively, in the case where the number of stages of the stepped surface28is one, an inclined surface or a curved surface inclined with respect to the normal direction of the back surface S7(surface on the light receiving surface side) of the substrate25has been provided as the side surface29of the stepped structure27. Therefore, the upper surface of the coating layer26can be formed in a smooth curved surface shape, and the wafer lens19having a large curvature can be formed. Therefore, it can be made suitable for further advancing fine pixelization of a CMOS image sensor.

Note that the effects described herein are merely illustrative and not restrictive, and may have other effects.

Further, the method of producing the optical element according to the first embodiment includes: a step of forming the stepped structure27on the substrate25; a step of applying the coating liquid34to the substrate25on which the stepped structure27has been formed; and a step of drying the coating liquid34so that the coating layer26that continuously covers the stepped structure27and the surface (the back surface S7) of the substrate25on a periphery of the stepped structure27and causes light to be transmitted therethrough is formed. Therefore, since the curved surface can be formed only by the application operation, the existing equipment can be used, and the cost can be suppressed. Therefore, it is possible to provide a method of producing an optical element capable of reducing production costs.

Further, in the method of producing the optical element according to the first embodiment, the front surface of the coating layer26can have a gradual curvature portion and the front surface of the coating layer26can be varied with high controllability in accordance with the shape of the stepped structure27. Further, the stepped structure27can be designed to achieve a desired shape of the wafer lens19by simulating the application and drying of the coating liquid34.

Incidentally, for example, as described in Patent Literature 1, in the thermal reflow method of forming a lens by forming a lens forming pattern layer on each of the upper surfaces of the respective stepped structures and then thermally reflowing the lens forming pattern layer, since the curved surface structure is formed by utilizing the front surface tension, only a convex shape can be formed, a concave shape cannot be formed, and thus, the flexibility of designing is reduced.

In contrast, in the method of producing the optical element according to the first embodiment, since any of a projecting shape and a recessed shape can be formed by using the shape of the stepped structure27, it is possible to improve the flexibility of designing. The shape of the optical element can be controlled by controlling the structure (shape and height) of steps and the drying process of the drying rate, and adjusting the physical property values of the coating material, such as the pitch, width, number of steps, inclination angle, curvature, drying rate of the coating liquid, diffusivity, and concentration. Therefore, it is possible to form a curved surface having desired curvature distribution. In addition, for example, a curved surface can be separately formed for each of the pixels9by separately forming a structure of a step or the like for each of the pixels9.

Further, for example, in the thermal reflow method, the material of the lens forming pattern layer needs to have not only photosensitive but also resolving property and thermal reflow property enabling formation of a pattern, and therefore, there are many restrictions on the material.

In contrast, in the method of producing the optical element according to the first embodiment, the photoresist film33does not need to have resolving property or thermal reflow property, and less restrictions on the material of the photoresist film33are required.

Further, for example, in the thermal reflow method, since the lens forming pattern layer is heated, a substrate needs to have heat resistance. Further, as described in, for example, Japanese Patent Application Laid-open No. 2005-349708, in a method of forming a lens by forming a water-repellent film having an opening region on a substrate and then dropping a liquid member corresponding to a lens shape into the opening region, the substrate needs to have hydrophilicity.

In contrast, in the method of producing the optical element according to the first embodiment, the substrate25does not need to have heat resistance or hydrophilicity, and less restrictions on the material of the substrate25of the wafer lens19(optical element) are required.

2-1 Configuration of Main Parts

Next, a solid-state imaging device according to a second embodiment of the present disclosure will be described. The entire configuration of the solid-state imaging device according to the second embodiment and the cross-sectional configuration of the pixel region3are similar to those inFIG.1andFIG.2, and therefore, illustration thereof is omitted.FIG.20is a cross-sectional configuration diagram of main parts of the solid-state imaging device1according to the second embodiment. InFIG.20, portions corresponding to those inFIG.4are denoted by the same reference symbols, and repetitive description thereof is omitted.

The solid-state imaging device1according to the second embodiment is different from the first embodiment in the configuration of the wafer lens19. In the second embodiment, as shown inFIG.20, the stepped structure27is a recessed portion formed from the back surface S7side of the substrate25toward the depth direction. Further, the coating layer26is configured to continuously cover the bottom surface and the inner wall surface of the recessed portion and the back surface S7of the substrate25on a periphery of the recessed portion. The upper surface of the portion covering the bottom surface and the inner wall surface of the recessed portion is formed in a curved shape of the concave lens.

2-2 Method of Producing Wafer Lens

Next, a method of producing the wafer lens19(optical element according to the second embodiment) of the solid-state imaging device1according to the second embodiment will be described.FIG.21A,FIG.21B,FIG.22A,FIG.22B,FIG.23A,FIG.23B,FIG.24A,FIG.24B,FIG.25A,FIG.25B,FIG.26A,FIG.26B,FIG.27A,FIG.27B,FIG.28A,FIG.28B,FIG.29A,FIG.29B,FIG.30A, andFIG.30Bare plan views and cross-sectional views showing a production step of the optical element according to the second embodiment.FIG.21AtoFIG.30Billustrate a case where the number of stages of the stepped surface28of the stepped structure27of the substrate25is three.

First, as shown inFIG.21AandFIG.21B, the photoresist film33is applied to the entire back surface S7of the substrate25. Subsequently, the photoresist film33is exposed as shown inFIG.22AandFIG.22B, and the photoresist film33is developed as shown inFIG.23AandFIG.23B.

Subsequently, as shown inFIG.24AandFIG.24B, the back surface S7of the substrate25is etched using the developed photoresist film33as an etching mask to form a third-stage (lowermost part) stepped surface28fof the stepped structure27. Subsequently, the photoresist film33is slimmed as shown inFIG.25AandFIG.25B, the back surface S7of the substrate25is etched using the slimmed photoresist film33as an etching mask as shown inFIG.26AandFIG.26B, and a second-stage (intermediate part) stepped surface28eof the stepped structure27is formed. Subsequently, slimming and etching are repeated to form a first-stage (uppermost part) stepped surface28dof the stepped structure27, and the stepped structure27having the stepped surfaces28d,28e, and28fof three stages is formed.

Subsequently, as shown inFIG.27AandFIG.27B, the photoresist film33is removed from the back surface S7of the substrate25. As a result, the plurality of stepped structures27having the stepped surfaces28d,28e, and28fof three stages regularly arranged in a two-dimensional array is formed on the back surface S7of the substrate25.

Subsequently, as shown inFIG.28AandFIG.28B, the coating liquid34for forming the coating layer26is applied so as to cover the entire back surface S7of the substrate25, i.e., the entire surface having the stepped structure27, and so that the liquid surface is horizontal. Regarding the thickness of the layer including the coating liquid34, the part corresponding to the third-stage stepped surface28fof the stepped structure27is the thickest, the part corresponding to the second-stage stepped surface28eof the stepped structure27is the second thickest, the part corresponding to the first-stage stepped surface28dof the stepped structure27is the third thickest, and the part corresponding to the portion where the stepped structure27is not formed is the thinnest. As the coating liquid34, for example, a coating liquid obtained by dissolving a styrene-based resin or an acrylic-based resin in an appropriate solvent can be employed. As a method of applying the coating liquid34, for example, a spin coat method can be employed.

Subsequently, as shown inFIG.29AandFIG.29B, the applied coating liquid34is dried. At this time, the solvent volatilizes and the thickness of the layer including the coating liquid34is reduced. Specifically, at an early stage of drying of the coating liquid34, the front surface of the coating liquid34is flat and uniformly reduced in film thickness. However, as the drying of the coating liquid34proceeds, the solute concentration of the coating liquid34in the recessed portion becomes locally low due to the stepped structure27of the substrate25. As a result, the evaporation rate of the solvent of the coating liquid34is increased in the recessed portion, and the front surface of the coating liquid34in the recessed portion is recessed. Due to this phenomenon, the amount of reduction in the thickness of the layer becomes larger where the thickness of the layer is thicker. That is, the reduction amount of the part corresponding to the third-stage stepped surface28fof the stepped structure27is the greatest, the reduction amount of the part corresponding to the second-stage stepped surface28eof the stepped structure27is the second largest, the reduction amount of the part corresponding to the first-stage stepped surface28dof the stepped structure27is the third largest, and the reduction amount of the part corresponding to the portion where the stepped structure27is not formed is the smallest. As a result, the coating layer26having a concave lens shape is formed in the portion covering the stepped structure27.

Subsequently, as shown inFIG.30AandFIG.30B, the coating layer26having a concave lens shape is UV-cured or baked so that the formed coating layer26(coating film) is a permanent film. As a result, the coating layer26is cured and the wafer lens19shown inFIG.20is completed. In the completed wafer lens19, the lens height LH shown inFIG.20is less than or equal to the height of the stepped structure27. Further, the lens diameter LR is equal to or higher than the width W of the stepped structure27and equal to or lower than the pitch p of the stepped structure27.

As described above, in the wafer lens19(optical element) according to the second embodiment, the substrate25is provided, the stepped structure27being formed on one surface (the back surface S7) of the substrate25, the stepped structure27having the stepped surface28having a different height from the back surface S7. In addition, the coating layer26that continuously covers the stepped structure27and the back surface S7on a periphery of the stepped structure27and causes light to be transmitted therethrough is provided. Therefore, various shapes can be realized in accordance with the shape of the stepped structure27, and the wafer lens19with a high flexibility of designing can be provided.

3-1 Configuration of Main Parts

Next, a solid-state imaging device according to a third embodiment of the present disclosure will be described. Since the entire configuration of the solid-state imaging device according to the third embodiment is similar to that inFIG.1, illustration thereof is omitted.FIG.31is a diagram showing a cross-sectional configuration of the pixel region3according to the third embodiment. InFIG.31, portions corresponding to those inFIG.2are denoted by the same reference symbols, and repetitive description thereof is omitted.

As shown inFIG.31, the solid-state imaging device1according to the third embodiment is different from the first embodiment in that a complicated aspherical lens having a large curvature in the center portion and a gradual curvature in the outer periphery portion is realized by combining the wafer lens19having a spherical lens shape and a large curvature in the center portion and a correction lens35having a gradual curvature in the outer periphery portion to obtain a lens group. That is, the correction lens35is configured to receive the light that has been transmitted through the wafer lens19.

The correction lenses35are formed in the flattening film16between the insulating film14and the color filter18corresponding to the pixels9. Thus, the correction lenses35form a correction lens array (optical element array) regularly arranged in a two-dimensional array. The correction lens35is optically designed to correct the aberrations caused by the wafer lens19. Examples of the aberrations caused by the wafer lens19include Seidel five aberrations (spherical aberration, astigmatism, coma aberration, field curvature aberration, and distortion aberration) and chromatic aberrations (magnification chromatic aberration and on-axis chromatic aberration).

Here, in the case where the wafer lens19is a lens that produces a magnification chromatic aberration, when light enters the wafer lens19obliquely to the optical axis, the imaging position of the light by the wafer lens19is a different position in the plane perpendicular to the optical axis for each color (wavelength range) included in the incident light. Further, in the case where the wafer lens19is a lens that produces an on-axis chromatic aberration, when light enters the wafer lens19in parallel with the optical axis, the imaging position of the light by the wafer lens19is a different position on the optical axis for each color (wavelength range) included in the incident light. Therefore, in accordance with the wavelength range (color) of the light transmitted through the color filter18corresponding to the wafer lens19, there is a possibility that a part of the light by the wafer lens19deviates from the photoelectric conversion unit23corresponding to the wafer lens19and enters the light-shielding film15on a periphery of the photoelectric conversion unit23or a different photoelectric conversion unit23. Then, when a part of the light enters the light-shielding film15, there is a possibility that the sensitivity of the photoelectric conversion unit23corresponding to the wafer lens19is reduced. Further, when a part of the light enters the different photoelectric conversion unit23, there is a possibility that not only the sensitivity of the photoelectric conversion unit23corresponding to the wafer lens19is reduced but also color mixing occurs in the photoelectric conversion unit23.

Therefore, in the case where the correction lens35is used as a lens for correcting chromatic aberrations, the correction lens35is designed so that substantially all of the light that has entered the wafer lens19enter the photoelectric conversion unit23corresponding to the wafer lens19, as shown inFIG.32A,FIG.32B, andFIG.32C. That is, the correction lens35is configured to increase the light collection ratio and the accuracy of the imaging point of the aspherical lens realized by combining the wafer lens19and the correction lens35.FIG.32Aillustrates the collection state of a light53by the correction lens35(hereinafter, referred to also as the “red correction lens”) disposed in the pixel9including the color filter18that causes light of red wavelengths to be transmitted therethrough.FIG.32Billustrates the collection state of the light53by the correction lens35(hereinafter, referred to also as the “green correction lens”) disposed in the pixel9including the color filter18that causes light of green wavelengths to be transmitted therethrough.FIG.32Cillustrates the collection state of the light53by the correction lens35(hereinafter, referred to also as the “blue correction lens”) disposed in the pixel9including the color filter18that causes light of blue wavelengths to be transmitted therethrough.

By correcting the chromatic aberration caused by the wafer lens19, it is possible to prevent the sensitivity of the photoelectric conversion unit23from being reduced and prevent the color mixing from occurring. In addition, since substantially all of the light that has entered the wafer lens19enter the photoelectric conversion unit23, the inter-pixel light shielding region between the photoelectric conversion units23can be reduced, the size of the photoelectric conversion unit23can be increased, and the sensitivity of the photoelectric conversion unit23can also be improved.

Further, as the correction lens35for correcting chromatic aberrations such as a magnification chromatic aberration and an on-axis chromatic aberration, for example, a lens having an annular recessed portion36, which has an annular shape along the outer periphery portion of the correction lens35in plan view can be used as shown inFIG.33A,FIG.33B,FIG.34A,FIG.34B,FIG.35A, andFIG.35B.FIG.33AandFIG.33Billustrate a red correction lens,FIG.34AandFIG.34Billustrate a green correction lens, andFIG.35AandFIG.35Billustrate a blue correction lens.

Further, the width of the annular recessed portion36is smaller in the order of, for example, the width of the annular recessed portion36of the red correction lens<the width of the annular recessed portion36of the green correction lens<the width of the annular recessed portion36of the blue correction lens. Further, the diameter of the annular recessed portion36is smaller in the order of, for example, the diameter of the annular recessed portion36of the blue correction lens<the diameter of the annular recessed portion36of the green correction lens<the diameter of the annular recessed portion36of the blue correction lens. As the diameter of the annular recessed portion36, for example, the average value of the inner diameter and the outer diameter of the annular recessed portion36can be used.

Note that in the third embodiment, a thermal reflow method can also be employed as a method of forming the wafer lens19. By employing the thermal reflow method, when the wafer lens19is formed to have a spherical lens, the stepped structure27of the wafer lens19only needs to have a relatively simple shape. Therefore, the labor required for forming the stepped structure27can be reduced, and the production costs of the wafer lens19can be reduced.

Next, a detailed structure of the correction lens35inFIG.31will be described.FIG.36is a diagram showing a cross-sectional configuration of the correction lens35.

As shown inFIG.36, the correction lens35includes a substrate37and a coating layer38.

The substrate37is formed on a back surface S10side (surface on the color filter18side) of a portion16aon the insulating film14side of the flattening film16, and includes a plurality of stepped structures39, which is a recessed portion formed from a back surface S11side (surface on the color filter18side) of the substrate37toward the depth direction, similarly to the substrate25according to the second embodiment. Each of the stepped structures39is formed corresponding to each of the pixels9and has a stepped surface40of one or more stages. As the stepped surface40, for example, a surface having a height different from that of the back surface S11of the substrate37can be used. For example, a surface parallel to the back surface S11of the substrate37can be used.FIG.36illustrates a case where the number of stages of the stepped surface40of the stepped structure27is one. Further, as another structure or material of the substrate37, for example, a structure and a material similar to those of the substrate25according to the first and second embodiments can be employed.

Note that in the case where the correction lens35is a lens having the annular recessed portion36shown inFIG.33A,FIG.33B,FIG.34A,FIG.34B,FIG.35A, andFIG.35B, for example, an annular recessed portion, which has an annular shape along the outer periphery portion of the correction lens35in plan view, can be used as the stepped structure39of the substrate37. That is, the plurality of stepped structures39having the annular stepped surface40having a different height from the back surface S11may be formed on the back surface S11of the substrate37. In the following description, the annular recessed portion, which has an annular shape, of the stepped structure39is also denoted by the reference symbol “39”. Further, for example, in the case where the width of the annular recessed portion36of the correction lens35is adjusted in the order shown inFIG.33A,FIG.33B,FIG.34A,FIG.34B,FIG.35A, andFIG.35B, the width of the annular recessed portion39of the substrate37is favorably smaller in the order of the width of the annular recessed portion39corresponding to the red correction lens<the width of the annular recessed portion39corresponding to the green correction lens<the width of the annular recessed portion39corresponding to the blue correction lens.

In the case where such a lens is used, the diameter of the annular recessed portion39of the substrate37is favorably smaller in the order of, for example, the diameter of the annular recessed portion39corresponding to the blue correction lens<the diameter of the annular recessed portion39corresponding to the green correction lens<the diameter of the annular recessed portion39corresponding to the blue correction lens. As the diameter of the annular recessed portion39, for example, the average value of the inner diameter and the outer diameter of the annular recessed portion39can be employed. Further, the depth of the annular recessed portion39of the substrate37is favorably the same in all the annular recessed portions39.

The coating layer38is formed on a back surface S11side of the substrate37(a portion16bside of the flattening film16on the color filter18side), and continuously covers the stepped structure39and the back surface S11of the substrate37on a periphery of the stepped structure39, similarly to the coating layer26according to the first and second embodiment. That is, the coating layer38is configured to cover the entire back surface S11, i.e., the entire surface having the stepped structure39. The upper surface of the portion covering the stepped structure39is formed in a curved shape of the outer periphery portion of the aspherical lens.

Further, as the material of the coating layer38, for example, a material that causes light to be transmitted therethrough and has a refractive index different from the refractive index of the material of the substrate37by ±10% or less of the refractive index of the material of the substrate37can be used. In particular, considering the reduction of the difference in the refractive index, it is favorable to use the same material as the material of the substrate37. By reducing the difference between the refractive index of the coating layer38of incident light and the refractive index of the substrate37of incident light, scattering and reflection of incident light on the interface between the coating layer38and the substrate37can be suppressed.

3-2 Method of Producing Correction Lens

Next, a method of producing the correction lens35(optical element according to the third embodiment) of the solid-state imaging device1according to the second embodiment will be described.FIG.37A,FIG.37B,FIG.38A,FIG.38B,FIG.39A,FIG.39B,FIG.40A,FIG.40B,FIG.41A,FIG.41B,FIG.42A,FIG.42B,FIG.43A,FIG.43B,FIG.44A, andFIG.44Bare plan views and cross-sectional views showing a production step of the optical element according to the second embodiment.FIG.37AtoFIG.44Billustrate the case where the correction lens35is a lens having the annular recessed portion36shown inFIG.33AandFIG.33B.

First, as shown inFIG.37AandFIG.37B, a photoresist film41is applied to the entire back surface S11of the substrate37. Subsequently, the photoresist film41is exposed as shown inFIG.38AandFIG.38B, and the photoresist film41is developed as shown inFIG.39AandFIG.39B.

Subsequently, as shown inFIG.40AandFIG.40B, the back surface S11of the substrate37is etched by using the developed photoresist film41as an etching mask to form the plurality of stepped structures39having an annular recessed shape to be irradiated with the light that has been transmitted through the color filter18. Subsequently, as shown inFIG.41AandFIG.41B, the photoresist film41, i.e., the etching mask of the back surface S11is removed from the back surface S11of the substrate37. As a result, the plurality of stepped structures39having an annular recessed shape regularly arranged in a two-dimensional array on the back surface S11of the substrate37is formed.

Subsequently, as shown inFIG.42AandFIG.42B, a coating liquid42for forming the coating layer38is applied so as to cover the entire back surface S11of the substrate37, i.e., the entire surface having the stepped structure39, and so that the liquid surface is horizontal. Regarding the thickness of the layer including the coating liquid42, the part corresponding to the stepped surface40(bottom surface of the annular recessed portion) of the stepped structure39is the thickest, and the part corresponding to the portion where the stepped structure39is not formed is the thinnest. As the coating liquid42, for example, a coating liquid obtained by dissolving a styrene-based resin or an acrylic-based resin in an appropriate solvent can be employed, similarly to the coating liquid34according to the first and second embodiments. As a method of applying the coating liquid42, for example, a spin coat method can be employed.

Subsequently, as shown inFIG.43AandFIG.43B, the applied coating liquid42is dried. At this time, the solvent volatilizes and the thickness of the layer including the coating liquid42is reduced. Specifically, at an early stage of drying of the coating liquid42, the front surface of the coating liquid42is flat and uniformly reduced in film thickness. However, as the drying of the coating liquid42proceeds, the solute concentration of the coating liquid42in the recessed portion becomes locally low due to the stepped structure39of the substrate37. As a result, the evaporation rate of the solvent of the coating liquid42is increased in the recessed portion, and the front surface of the coating liquid42in the recessed portion is recessed. Due to this phenomenon, the amount of reduction in the thickness of the layer becomes larger where the thickness of the layer is thicker. That is, the reduction amount of the part corresponding to the stepped surface40(bottom surface of the annular recessed portion) of the stepped structure39is the largest, and the reduction amount of the part corresponding to the portion where the stepped structure39is not formed is the smallest. As a result, the coating layer38having a lens shape and an annular recessed portion is formed in a portion covering the stepped structure39. Subsequently, as shown inFIG.44AandFIG.44B, the coating layer38having a concave lens shape is UV-cured or baked so that the formed coating layer38is a permanent film. As a result, the coating layer38is cured and the correction lens35shown inFIG.33AandFIG.33Bis completed.

Note that in the case where the correction lens35is a lens for correcting chromatic aberrations, i.e., in the case where the correction lens35is a lens having the annular recessed portion36shown inFIG.33A,FIG.33B,FIG.34A,FIG.34B,FIG.35A, andFIG.35B, it is favorable to design the width and diameter of the annular recessed portion39of the substrate37in accordance with the shape of the annular recessed portion36. That is, in the step of forming the plurality of stepped structures39(the annular recessed portions39) on the substrate37described above, the width and diameter of the annular recessed portion39are adjusted in accordance with the wavelength range (color) of light transmitted through the color filter18corresponding to the annular recessed portion39as shown inFIG.33A,FIG.34A, andFIG.35A. Specifically, first, the position given with a curvature and the magnitude of the curvature are designed by the annular recessed portion36of the correction lens35so as to correct the chromatic aberration caused by the wafer lens19. Subsequently, the width and diameter (position) of the annular recessed portion39are optimized as parameters so that the shape of the correction lens35having the designed curvature can be realized by simulating the application and drying of the coating liquid42. In this case, it is favorable that the depth of the annular recessed portion39of the substrate37is the same in all the annular recessed portions39. As a result, all the annular recessed portions39of the substrate37can be formed simultaneously in one process flow while the shape of the correction lens35is made different for each wavelength region (color) of the light transmitted through the color filter18.

As described above, in the correction lens35(optical element) according to the third embodiment, the substrate37is provided, the stepped structure39being formed on one surface (the back surface S11) of the substrate37, the stepped structure39having the stepped surface40having a different height from the back surface S11. In addition, the coating layer38that continuously covers the stepped structure39and the back surface S11on a periphery of the stepped structure39and causes light to be transmitted therethrough is provided. Therefore, various shapes can be realized in accordance with the shape of the stepped structure39, and the correction lens35with a high flexibility of designing can be provided.

Further, in the lens group according to the third embodiment, the wafer lens19(“first lens” in a broad sense) and the correction lens35(“second lens” in a broad sense) for correcting aberrations caused by the wafer lens19are provided, light that has been transmitted through the wafer lens19entering the correction lens35. Then, the correction lens35includes the substrate37, the stepped structure39being formed on one surface (the back surface S11), the stepped structure39having the stepped surface40having an annular shape and a different height from the back surface S11, and the coating layer38that continuously covers the stepped structure39and the back surface S11on a periphery of the stepped structure39and causes light to be transmitted therethrough. Therefore, a lens with optical performance equivalent to that of a complex aspherical lens can be realized relatively easily.

Further, in the lens group according to the third embodiment, the correction lens35(second lens) is a lens for correcting chromatic aberrations caused by the wafer lens19(first lens). Therefore, it is possible to prevent the sensitivity of the photoelectric conversion unit23corresponding to the wafer lens19from being reduced, and prevent the color mixing in the photoelectric conversion unit23on a periphery of the photoelectric conversion unit23from occurring.

Further, the method of producing the optical element according to the third embodiment includes: a step of forming the plurality of stepped structures39regularly arrayed in a two-dimensional array on the substrate37; a step of applying the coating liquid42to the substrate37on which the plurality of stepped structures39has been formed; and a step of drying the coating liquid42so that the coating layer38that continuously covers the plurality of stepped structures39and the surface of the substrate37on a periphery of the plurality of stepped structures39and causes light to be transmitted therethrough is formed. Then, each of the stepped structures39includes the annular recessed portion39for forming a lens that the light that has been transmitted through the color filter18enters. Further, in the step of forming the plurality of stepped structures39on the substrate37, the width and diameter of each of the plurality of annular recessed portions39are adjusted in accordance with the wavelength range (color) of light transmitted through the color filter18corresponding to the annular recessed portion39. Therefore, the depth of the annular recessed portion39of the substrate37can be the same and all the annular recessed portions39can be formed simultaneously in one process flow.

Incidentally, for example, as described in Patent Literature 1, in the thermal reflow method of forming a lens by forming a lens forming pattern layer on each of the upper surfaces of the respective stepped structures and then thermally reflowing the lens forming pattern layer, since the curved surface structure is formed by utilizing the front surface tension, it is difficult to make a lens have a gentle curvature portion, and an aberration correction lens cannot be formed.

In contrast, in the method of producing the optical element according to the third embodiment, the front surface of the coating layer38can have a gradual curvature portion and the front surface of the coating layer38can be varied with high controllability in accordance with the shape of the stepped structure39. Further, the stepped structure39can be designed so that a desired shape of the correction lens35can be realized by simulating the application and drying of the coating liquid42.

3-3 Modified Example

(1) In the solid-state imaging device1according to the first and second embodiments, the case where the optical element according to the present disclosure is used for the wafer lens19has been described as an example, but the optical element according to the present disclosure is applicable also to an inner lens43formed on the flattening film16as shown inFIG.45, for example. Further, for example, as shown inFIG.46, the optical element according to the present disclosure is applicable also to a reflector44used for a display device or the like.FIG.46illustrates a case where a reflector lens45(reflective layer) that reflects light, a light-emitting layer46that emits light, an interlayer film47that forms a flat surface having no irregularities, and a color filter48formed corresponding to the wavelength of light to be displayed are staked on a front surface S9of the coating layer26having a concave lens shape in the stated order. InFIG.46, a reflected light49reflected by the reflector44is indicated by an arrow.

(2) Further, the present disclosure is not limited to the solid-state imaging device where the distribution of the incident light amount of visible light is detected and imaged as an image as in the solid-state imaging device1according to the first and second embodiments. For example, the present disclosure is applicable to a solid-state imaging device where distribution of the incident light amount of infrared rays, X-rays, particles, or the like is imaged as an image. Further, the present disclosure is applicable also to a general solid-state imaging device (physical quantity distribution detecting device), such as a fingerprint detecting sensor that detects distribution of another physical quantity such as pressure and electrostatic capacity and images it as an image.

(3) The present disclosure is not limited to the solid-state imaging device where each of the pixels9of the pixel region3is sequentially scanned on a row-by-row basis to read a pixel signal from each of the pixels9as in the solid-state imaging device1according to the first and second embodiments. For example, the present disclosure is applicable also to an X-Y address-type solid-state imaging device where an arbitrary pixel9is selected in units of pixels to read a signal from the selected pixel9in units of pixels.

(4) Further, in the solid-state imaging device1according to the third embodiment, the case where the correction lens35is disposed in the flattening film16has been described as an example, but the correction lens35may be disposed on the light receiving surface side of the wafer lens19so that light before being transmitted through the wafer lens19enters the correction lens35, for example.

(5) In the solid-state imaging device1according to the third embodiment, the case where an annular recessed portion having an annular shape is formed as the stepped structure39of the substrate37constituting the correction lens35has been described as an example, but an annular projecting portion having an annular shape may be formed as shown inFIG.47AandFIG.47B, for example.

(6) Further, in the solid-state imaging device1according to the third embodiment, the case where the aspherical lens is realized by combining the wafer lens19and the correction lens35to form a lens group has been described as an example, but the methods of producing the optical element according to the first, second, and third embodiments may be combined to form the wafer lens19having an aspherical lens shape as shown inFIG.48A,FIG.48B,FIG.49A, andFIG.49B, for example.FIG.48AandFIG.48Billustrate the case where the stepped structure27(“first stepped structure” in a broad sense), which is a recessed portion, and the stepped structure39(“second stepped structure” in a broad sense), which is an annular recessed portion and has the annular stepped surface40surrounding the periphery of the stepped structure27, are formed on the back surface S7of the substrate25constituting the wafer lens19. Further,FIG.49AandFIG.49Billustrate a case where the stepped structure27(first stepped structure), which is a projecting portion, and the stepped structure39(second stepped surface), which is an annular projecting portion and has the annular stepped surface40surrounding the periphery of the stepped structure27, are formed on the back surface S7of the substrate25constituting the wafer lens19. In this case, the coating layer26continuously covers the stepped structure27, the stepped structure39, and the back surface S7on a periphery of the stepped structure27and the stepped structure39and causes light to be transmitted therethrough.

(7) Further, in the solid-state imaging device1according to the third embodiment, an example where a lens group is configured by combining the wafer lens19and the correction lens35has been shown, but an inner lens may also be combined in addition to the wafer lens19and the correction lens35to form a lens group, for example. Specifically, as shown inFIG.50A,FIG.50B, andFIG.50C, an inner lens50may be provided between the correction lens35and the photoelectric conversion unit23and a lens group obtained by combining the wafer lens19, the correction lens35, and the inner lens50may be configured.FIG.50Aillustrates the collection state of the light53by a lens group configured in the pixel9corresponding to the color filter18that causes light of red wavelengths to be transmitted therethrough. Further,FIG.50Billustrates the collection state of the light53by a lens group configured in the pixel9corresponding to the color filter18that causes light of green wavelengths to be transmitted therethrough. Further,FIG.50Cillustrates the collection state of the light53by a lens group configured in the pixel9corresponding to the color filter18that causes light of blue wavelengths to be transmitted therethrough.

Further, for example, as shown inFIG.51A,FIG.51B, andFIG.51C, an inner lens51may be provided between the wafer lens19and the correction lens35and a lens group obtained by combining the wafer lens19, the inner lens51, and the correction lens35may be configured.FIG.51Aillustrates the collection state of the light53by a lens group configured in the pixel9corresponding to the color filter18that causes light of red wavelengths to be transmitted therethrough. Further,FIG.51Billustrates the collection state of the light53by a lens group configured in the pixel9corresponding to the color filter18that causes light of green wavelengths to be transmitted therethrough. Further,FIG.51Cillustrates the collection state of the light53by a lens group configured in the pixel9corresponding to the color filter18that causes light of blue wavelengths to be transmitted therethrough. In the case where such a lens group is formed, the correction lens35is designed so that substantially all of the light that has entered the wafer lens19enters the photoelectric conversion unit23corresponding to the lens group by being transmitted via the lens group.

(8) Further, in the solid-state imaging device1according to the third embodiment, the case where the correction lens35for correcting chromatic aberrations caused by the wafer lens19is formed corresponding to each of all the wafer lenses19has been shown as shown inFIG.31,FIG.32A,FIG.32B, andFIG.32C, but the correction lens35may be formed corresponding to only a part of the wafer lenses19, for example. For example, in the case where the imaging position of light by the wafer lens19corresponding to the color filter18that causes light of blue wavelengths to be transmitted therethrough deviates most from the central portion of the photoelectric conversion unit23corresponding to the wafer lens19, the correction lens35may be formed corresponding only to the wafer lens19.

(9) Further, in the solid-state imaging device1according to the third embodiment, the case where the correction lens35is configured to increase the light collection rate of the aspherical lens realized by combining the wafer lens19and the correction lens35has been described as an example, but the correction lens35may be configured to decrease the light collection rate of the aspherical lens, for example. For example, in the case where a filter that shields infrared light is provided corresponding to each of the plurality of pixels9, there is a possibility that the pixel9in which the amount of received infrared light is larger than that of other photoelectric conversion units23is generated due to variations in the light shielding performance of the filter. In contrast, by configuring the correction lens35so that the light collection rate of the infrared light in the aspherical lens is lowered, even if the pixel9in which the amount of received infrared light is large is generated, it is possible to reduce the amount of infrared light entering the photoelectric conversion unit23corresponding to the pixel9.

Next, an electronic apparatus according to a fourth embodiment of the present disclosure will be described.FIG.52is a schematic configuration diagram of an electronic apparatus100according to a fourth embodiment of the present disclosure.

The electronic apparatus100according to fourth embodiment includes a solid-state imaging device101, an optical lens102, a shutter device103, a drive circuit104, and a signal processing circuit105. The electronic apparatus100according to the fourth embodiment shows an embodiment in the case where the solid-state imaging device1according to the first embodiment of the present disclosure is used for an electronic apparatus (e.g., camera) as the solid-state imaging device101.

The optical lens102images the image light (the incident light106) from a subject onto the imaging surface of the solid-state imaging device101. As a result, signal charges are accumulated in the solid-state imaging device101for a certain time. The shutter device103controls a period in which the solid-state imaging device101is irradiated with light and a period in which light is shielded. The drive circuit104supplies drive signals for controlling the transfer operation of the solid-state imaging device101and the shutter operation of the shutter device103. In accordance with the drive signal (timing signal) supplied from the drive circuit104, signal transfer of the solid-state imaging device101is performed. The signal processing circuit105performs various types of signal processing on a signal (pixel signal) output from the solid-state imaging device101. The video signal on which signal processing has been performed is stored in a storage medium such as a memory, or is output to a monitor.

Note that the electronic apparatus100to which the solid-state imaging device1can be applied is not limited to a camera, and the solid-state imaging device1can be applied to other electronic apparatuses. For example, the solid-state imaging device1may be applied to an imaging device such as a camera module for mobile devices such as mobile phones and tablet terminals.

Further, in the fourth embodiment, the solid-state imaging device1according to the first embodiment is used for an electronic apparatus as the solid-state imaging device101, but other configurations may be used. For example, the solid-state imaging device1according to the second embodiment, the solid-state imaging device1according to the third embodiment, or the solid-state imaging device1according to the modified example may be used for an electronic apparatus.

5. Application Example to Moving Objects

The technology according to the present disclosure (the present technology) is applicable to various products. For example, the technology according to the present disclosure may be realized as an apparatus mounted on any type of moving objects such as an automobile, an electric car, a hybrid electric vehicle, a motorcycle, a bicycle, personal mobility, an airplane, a drone, a ship, and a robot.

InFIG.54, the vehicle12100includes as the imaging section12031, imaging sections12101,12102,12103,12104, and12105.

An example of a vehicle control system to which the technology according to the present disclosure can be applied has been described above. The technology according to the present disclosure can be applied to the imaging section12031or the like among the configurations described above. Specifically, the solid-state imaging device1inFIG.1can be applied to the imaging section12031. By applying the technology according to the present disclosure to the imaging section12031, it is possible to obtain a captured image that is easier to see, so that fatigues of the drivers can be reduced.

6. Application Example to Endoscopic Surgery System

The technology according to the present disclosure (present technology) is applicable to various products. For example, the technology according to the present disclosure may be applied to an endoscopic surgery system.

The endoscope11100includes a lens barrel11101having a region of a predetermined length from a distal end thereof to be inserted into a body lumen of the patient11132, and a camera head11102connected to a proximal end of the lens barrel11101. In the example depicted, the endoscope11100is depicted which includes as a hard mirror having the lens barrel11101of the hard type. However, the endoscope11100may otherwise be included as a soft mirror having the lens barrel11101of the soft type.

The lens barrel11101has, at a distal end thereof, an opening in which an objective lens is fitted. A light source apparatus11203is connected to the endoscope11100such that light generated by the light source apparatus11203is introduced to a distal end of the lens barrel11101by a light guide extending in the inside of the lens barrel11101and is irradiated toward an observation target in a body lumen of the patient11132through the objective lens. It is to be noted that the endoscope11100may be a direct view mirror or may be a perspective view mirror or a side view mirror.

FIG.56is a block diagram depicting an example of a functional configuration of the camera head11102and the CCU11201depicted inFIG.55.

An example of an endoscopic surgery system to which the technology according to the present disclosure can be applied has been described above. The technology according to the present disclosure can be applied to, for example, the endoscope11100, the image pickup unit11402of the camera head11102, or the like among the configurations described above. Specifically, the solid-state imaging device1inFIG.1can be applied to the image pickup unit10402. By applying the technology according to the present disclosure to the image pickup unit11402, it is possible to obtain a clearer surgical site image, so that the operator can reliably check the surgical site.

Note that the endoscopic surgery system has been described here as an example, but the technology according to the present disclosure may be applied to, for example, a microscopic surgery system or the like.

It should be noted that the present technology may also take the following configurations.

a substrate, a stepped structure being formed on one surface of the substrate, the stepped structure having a stepped surface having a different height from the one surface; anda coating layer that continuously covers the stepped structure and the one surface on a periphery of the stepped structure and causes light to be transmitted therethrough or reflects the light.
(2) The optical element according to (1) above, in whichthe stepped structure has, as a side surface for connecting the one surface and the stepped surface, an inclined surface or a curved surface inclined with respect to a normal direction of the one surface.
(3) The optical element according to (1) above, in whichthe stepped structure has the stepped surface, the stepped surface including stepped surfaces of two or more stages.
(4) The optical element according to (3) above, in whichthe stepped structure has, as a side surface for connecting the one surface and the stepped surface and as a side surface for connecting the stepped surfaces, the stepped surfaces being two stepped surfaces of two stages, at least one of a perpendicular surface parallel to a normal direction of the one surface and an inclined surface and a curved surface inclined with respect to the normal direction of the one surface.
(5) The optical element according to (2) or (4) above, in whichan inclination angle of the inclined surface is 0 degrees or more and 60 degrees or less with respect to the normal direction of the one surface.
(6) The optical element according to any one of (1) to (5) above, in whicha ratio of a width and a height of the stepped structure is in a range of 1:10 to 10:1
(7) The optical element according to any one of (1) to (6) above, in whichthe stepped structure has at least one of a circular shape, a polygonal shape, or an elliptical shape in plan view.
(8) The optical element according to (7) above, in whichan aspect ratio of the elliptical shape is 1 or more and 5 or less.
(9) The optical element according to (3) above, in whichouter peripheries of the stepped surfaces of the stepped structure are separated from each other in plan view.
(10) The optical element according to any one of (1) to (9) above, in whicha difference between a refractive index of a material of the substrate and a refractive index of a material of the coating layer is ±10% or less of the refractive index of the material of the substrate.
(11) The optical element according to any one of (1) to (10) above, in whichthe stepped structure forms a projecting portion, andthe coating layer continuously covers an upper surface and a side wall surface of the projecting portion and the one surface on a periphery of the projecting portion, and causes light to be transmitted therethrough or reflects the light.
(12) The optical element according to any one of (1) to (10) above, in whichthe stepped structure forms a recessed portion, andthe coating layer continuously covers a bottom surface and an inner side wall surface of the recessed portion and the one surface on a periphery of the recessed portion and causes light to be transmitted therethrough or reflects the light.
(13) The optical element according to any one of (1) to (5) and (10) above, in whichthe stepped structure includes a first stepped structure and a second stepped structure having an annular stepped surface surrounding a periphery of the first stepped structure, andthe coating layer continuously covers the first stepped structure, the second stepped structure, and the one surface on a periphery of the first stepped structure and the second stepped structure and causes light to be transmitted therethrough.
(14) An optical element array, including:a substrate having a plurality of stepped structures regularly arranged in a two-dimensional array; anda coating layer that continuously covers the plurality of stepped structures and a surface of the substrate on a periphery of the plurality of stepped structures, each of portions of the coating layer covering the plurality of stepped structures causing light to be transmitted therethrough or reflects the light.
(15) An optical element array, including:a plurality of first lenses regularly arranged in a two-dimensional array; anda plurality of second lenses that includes a substrate, a plurality of stepped structures being formed on one surface of the substrate, each of the plurality of stepped structures having an annular stepped surface having a different height from the one surface, and a coating layer that continuously covers the stepped structure and the one surface on a periphery of the stepped structure and causes light to be transmitted therethrough, and corrects aberrations caused by the plurality of first lenses, light before or after being transmitted through the plurality of first lenses entering the plurality of second lenses.
(16) The optical element array according to (15) above, in whicheach of the plurality of second lenses is a lens for correcting chromatic aberrations caused by the plurality of first lenses.
(17) A lens group, including:a first lens; anda second lens that corrects an aberration caused by the first lens, light before or after being transmitted through the first lens entering the second lens, in whichthe second lens includesa substrate, a stepped structure being formed on one surface of the substrate, the stepped structure having an annular stepped surface having a different height from the one surface, anda coating layer that continuously covers the stepped structure and the one surface on a periphery of the stepped structure and causes light to be transmitted therethrough.
(18) The lens group according to (17) above, in whichthe second lens is a lens for correcting a chromatic aberration caused by the first lens.
(19) An electronic apparatus, including:a solid-state imaging device that includes a microlens array including a substrate having a plurality of stepped structures of a plurality of stages regularly arranged in a two-dimensional array, and a coating layer that continuously covers the plurality of stepped structures of the plurality of stages and a surface of the substrate on a periphery of the plurality of stepped structures, each of portions of the coating layer covering the plurality of stepped structures having a lens shape;an optical lens that forms an image of image light from a subject onto an imaging surface of the solid-state imaging device; anda signal processing circuit that performs signal processing on a signal output from the solid-state imaging device.
(20) A method of producing an optical element, including:a step of forming a stepped structure on a substrate;a step of applying a coating liquid to the substrate on which the stepped structure has been formed; anda step of drying the coating liquid so that a coating layer that continuously covers the stepped structure and a surface of the substrate on a periphery of the stepped structure and causes light to be transmitted therethrough or reflects the light is formed.
(21) A method of producing an optical element, including:a step of forming a plurality of stepped structures regularly arranged in a two-dimensional array on a substrate;a step of applying a coating liquid to the substrate on which the plurality of stepped structures has been formed; anda step of drying the coating liquid so that a coating layer that continuously covers the plurality of stepped structures and a surface of the substrate on a periphery of the plurality of stepped structures and causes light to be transmitted therethrough is formed, in whicheach of the plurality of stepped structures includes an annular recessed portion for forming a lens, light before or after being transmitted through a color filter entering the lens, andin the step of forming the plurality of stepped structures on the substrate, a width and a diameter of each of the plurality of annular recessed portions are adjusted in accordance with a wavelength range of light transmitted through the color filter corresponding to the annular recessed portion.

REFERENCE SIGNS LIST