Patent ID: 12255260

MODES FOR CARRYING OUT THE INVENTION

In the following, description is given in detail of embodiments of the present disclosure with reference to the drawings. The following description is merely a specific example of the present disclosure, and the present disclosure should not be limited to the following aspects. Moreover, the present disclosure is not limited to arrangements, dimensions, dimensional ratios, and the like of each component illustrated in the drawings. It is to be noted that the description is given in the following order.1. Embodiment (An example of an imaging element including, on a light-receiving surface, a reflectance adjustment layer including a plurality of protrusions of an uneven structure provided on the light-receiving surface and a passivation film embedded in a plurality of recesses of the uneven structure)2. Application Example3. Practical Application Example

1. Embodiment

FIG.1schematically illustrates a cross-sectional configuration example of an imaging element1as an example of a photodetector according to an embodiment of the present disclosure.FIG.2illustrates an overall configuration example of the imaging element1illustrated inFIG.1. The imaging element1is, for example, a CMOS (Complementary Metal Oxide Semiconductor) image sensor or the like to be used for an electronic apparatus such as a digital still camera or a video camera, and includes, as an imaging area, a pixel section (a pixel section100A) in which a plurality of pixels are two-dimensionally arranged in matrix. The imaging element1is, for example, a so-called back-illuminated imaging element configuring one pixel (a unit pixel P) in the CMOS image sensor or the like.

The imaging element1of the present embodiment includes a reflectance adjustment layer10X on a light-receiving surface (a first surface)1051of a semiconductor substrate10in which a photoelectric conversion section11is embedded and formed. The reflectance adjustment layer10X is a pseudo high-reflectance layer including a plurality of protrusions10A1configuring an uneven structure10A provided on the first surface10S1of the semiconductor substrate10and a passivation film12embedded in a plurality of recesses10A2configuring the uneven structure10A. The reflectance adjustment layer10X has a refractive index between those of the semiconductor substrate10and the passivation film12.

[Schematic Configuration of Imaging Element]

The imaging element1takes in incident light (image light) from a subject via an optical lens system (unillustrated), converts the amount of incident light formed as an image on an imaging surface into electric signals on a pixel-by-pixel basis, and outputs the electric signals as pixel signals. The imaging element1includes, on the semiconductor substrate10, the pixel section100A as an imaging area, and also includes, in a peripheral region of the pixel section100A, for example, a vertical drive circuit111, a column signal processing circuit112, a horizontal drive circuit113, an output circuit114, a control circuit115, and an input/output terminal116.

The unit pixels P are provided, for example, with a pixel drive line Lread (specifically, a row selection line and a reset control line) for each of pixel rows, and provided with a vertical signal line Lsig for each of pixel columns. The pixel drive line Lread transmits drive signals for reading signals from the pixels. One end of the pixel drive line Lread is coupled to an output end of the vertical drive circuit111corresponding to each of the rows.

The vertical drive circuit111is a pixel drive section that is configured by a shift register, an address decoder, and the like, and drives the unit pixels P of the pixel section100A on a row-by-row basis, for example. Signals outputted from the respective unit pixels P in the pixel rows selectively scanned by the vertical drive circuit111are supplied to the column signal processing circuit112through the respective vertical signal lines Lsig. The column signal processing circuit112is configured by an amplifier, a horizontal selection switch, and the like provided for each of the vertical signal lines Lsig.

The horizontal drive circuit113is configured by a shift register, an address decoder, and the like. The horizontal drive circuit113drives horizontal selection switches of the column signal processing circuit112in order while scanning the horizontal selection switches. The selective scanning by this horizontal drive circuit113causes signals of the respective pixels transmitted through the respective vertical signal lines Lsig to be outputted to a horizontal signal line121in order, and causes the signals to be transmitted to the outside of the semiconductor substrate10through the horizontal signal line121.

The output circuit114performs signal processing on signals sequentially supplied from the respective column signal processing circuits112via the horizontal signal line121, and outputs the signals. The output circuit114performs, for example, only buffering in some cases, and performs black level adjustment, column variation correction, various kinds of digital signal processing, and the like in other cases.

A circuit portion including the vertical drive circuit111, the column signal processing circuit112, the horizontal drive circuit113, the horizontal signal line121, and the output circuit114may be formed directly on the semiconductor substrate10, or may be provided on an external control IC. In addition, the circuit portion may be formed on another substrate coupled by a cable or the like.

The control circuit115receives a clock supplied from the outside of the semiconductor substrate10, data for an instruction about an operation mode, and the like, and also outputs data such as internal information on the imaging element1. The control circuit115further includes a timing generator that generates a variety of timing signals, and controls driving of peripheral circuits including the vertical drive circuit111, the column signal processing circuit112, the horizontal drive circuit113, and the like on the basis of the variety of timing signals generated by the timing generator.

The input/output terminal116exchanges signals with the outside.

[Circuit Configuration of Unit Pixel]

FIG.3illustrates an example of a readout circuit of the unit pixel P of the imaging element1illustrated inFIG.2. As illustrated inFIG.3, the unit pixel P includes, for example, the photoelectric conversion section11, a transfer transistor TR, a floating diffusion FD, a reset transistor RST, an amplification transistor AMP, and a selection transistor SEL.

The photoelectric conversion section11is, for example, a photodiode (PD). In the photoelectric conversion section11, an anode is coupled to a ground voltage line, and a cathode is coupled to a source of the transfer transistor TR.

The transfer transistor TR is coupled between the photoelectric conversion section11and the floating diffusion FD. A drive signal TRsig is applied to a gate electrode of the transfer transistor TR. When the drive signal TRsig is brought into an active state, a transfer gate of the transfer transistor TR is brought into an electrically-conductive state, and signal charge accumulated in the photoelectric conversion section11is transferred to the floating diffusion FD via the transfer transistor TR.

The floating diffusion FD is coupled between the transfer transistor TR and the amplification transistor AMP. The floating diffusion FD subjects the signal charge transferred by the transfer transistor TR to charge-voltage conversion into a voltage signal to output the converted voltage signal to the amplification transistor AMP.

The reset transistor RST is coupled between the floating diffusion FD and a power source section. A drive signal RSTsig is applied to a gate electrode of the reset transistor RST. When the drive signal RSTsig is brought into an active state, a reset gate of the reset transistor RST is brought into an electrically-conductive state, and a potential of the floating diffusion FD is reset to a level of the power source section.

The amplification transistor AMP, in which a gate electrode thereof is coupled to the floating diffusion FD and a drain electrode is coupled to the power source section, serves as an input part of a readout circuit of the voltage signal held by the floating diffusion FD or a so-called source follower circuit. That is, a source electrode of the amplification transistor AMP is coupled to the vertical signal line Lsig via the selection transistor SEL to thereby configure the source follower circuit with a constant current source coupled to one end of the vertical signal line Lsig.

The selection transistor SEL is coupled between the source electrode of the amplification transistor AMP and the vertical signal line Lsig. A drive signal SELsig is applied to a gate electrode of the selection transistor SEL. When the drive signal SELsig is brought into an active state, the selection transistor SEL is brought into an electrically-conductive state, and the unit pixel P is brought into a selected state. This allows a readout signal (pixel signal) outputted from the amplification transistor AMP to be outputted to the vertical signal line Lsig via the selection transistor SEL.

[Configuration of Unit Pixel]

The imaging element1has a configuration in which the semiconductor substrate10and a multilayer wiring layer20are stacked. The semiconductor substrate10includes the photoelectric conversion section11embedded and formed therein. The multilayer wiring layer20includes a plurality of wiring layers (e.g., wiring layers21,22, and23). The semiconductor substrate10has the first surface10S1(back surface) and a second surface10S2(front surface). The multilayer wiring layer20is provided on the second surface10S2of the semiconductor substrate10. On the first surface10S1of the semiconductor substrate10, the passivation film12, a first antireflection layer13, a second antireflection layer14, a color filter15and a light-blocking film16that are provided in the same plane, for example, and a lens layer17are stacked in this order.

The semiconductor substrate10is configured by, for example, a silicon (Si) substrate or an indium-gallium-arsenic (InGaAs) substrate. The photoelectric conversion section11is, for example, a PIN (Positive Intrinsic Negative)-type photodiode (PD), and has a p-n junction at a predetermined region of the semiconductor substrate10. As described above, the photoelectric conversion sections11are embedded and formed one by one for each unit pixel P.

The fine uneven structure10A is formed on the first surface10S1of the semiconductor substrate10. The first surface10S1of the semiconductor substrate10is further provided with a separation section10B extending from the first surface10S1toward the second surface10S2.

The uneven structure10A configures the reflectance adjustment layer10X described above, and is configured by the plurality of protrusions10A1and the plurality of recesses10A2provided on the first surface1051of the semiconductor substrate10, which are described later in detail.

The separation section10B is provided between the unit pixels P adjacent to each other. In other words, the separation section10B is provided to surround the unit pixel P, and is provided, in a plan view, in a lattice pattern, for example, across the entire pixel section100A. The separation section10B is provided to electrically separate the adjacent unit pixels P. For example, the separation section10B extends from a side of the first surface1051of the semiconductor substrate10toward the second surface10S2, and has a bottom portion, for example, inside the semiconductor substrate10. In addition, the separation section10B may pass through from the side of the first surface10S1of the semiconductor substrate10to the second surface10S2.

The passivation film12protects a light-receiving surface (first surface1051) of the semiconductor substrate10, and configures the reflectance adjustment layer10X. The passivation film12is stacked on the first surface10S1of the semiconductor substrate10, and fills the plurality of recesses10A2configuring the uneven structure10A and a groove10H configuring the separation section10B. On a front surface of the passivation film12, for example, a waveform structure corresponding to the uneven structure10A is formed, as illustrated inFIG.4.

Examples of a material configuring the passivation film12include a material having a refractive index smaller than that of the semiconductor substrate10. Specific examples of the passivation film12include an oxide film or nitride film including at least one of hafnium (Hf), aluminum (Al), titanium (Ti), zirconium (Zr), tantalum (Ta), yttrium (Y), or strontium (Sr).

The first antireflection layer13is provided to reduce reflection of light incident from a light incident side51at the light-receiving surface (first surface10S1) of the semiconductor substrate10. Similarly to the passivation film12, for example, on a front surface of the first antireflection layer13, a waveform structure corresponding to the uneven structure10A is formed, as illustrated inFIG.4.

Similarly to the passivation film12, examples of a material configuring the first antireflection layer13include a material having a refractive index smaller than that of the semiconductor substrate10. Specific examples of the first antireflection layer13include an oxide film or nitride film including at least one of hafnium (Hf), aluminum (Al), titanium (Ti), zirconium (Zr), tantalum (Ta), yttrium (Y), or strontium (Sr).

The second antireflection layer14is provided to reduce reflection of light incident from the light incident side51at the light-receiving surface (first surface10S1) of the semiconductor substrate10and to planarize a front surface on the light incident side51. Examples of a material configuring the second antireflection layer14include a material having a refractive index smaller than that of a material configuring the first antireflection layer13. Specific examples of the second antireflection layer14include silicon oxide (SiOx), silicon nitride (SiNx), and silicon oxynitride (SiOxNy).

The color filter15is provided on the light incident side51of the semiconductor substrate10, and includes, for example, color filters15R,15G, and15B that selectively transmit red light (R), green light (G), or blue light (B) for each unit pixel P. As for the color filters15R,15G, and15B, for example, with respect to four unit pixels P arranged in two rows×two columns, two color filters15G each of which selectively transmits green light (G) are arranged on a diagonal line, and the color filters15R and15G that selectively transmit red light (R) and blue light (B) are arranged one by one on the orthogonal diagonal line. The unit pixels P provided with the respective color filters15R,15G, and15B detect corresponding color light beams, for example, in the respective photoelectric conversion sections11. That is, the respective unit pixels P that detect red light (R), green light (G), and blue light (B) have a Bayer arrangement in the pixel section100A.

The light-blocking film16is provided to prevent light obliquely incident on the color filter15from leaking into an adjacent unit pixel P. The light-blocking film16is provided between adjacent color filters15R,15G, and15B in the same plane as the color filter15, for example. That is, the light-blocking film16is provided. in a plan view, in a lattice pattern, for example, across the entire pixel section100A, similarly to the separation section19B. Examples of a material configuring the light-blocking film16include an electrically-conductive material having a light-blocking property. Specific examples thereof include tungsten (W), silver (Ag), copper (Cu), aluminum (Al), and an alloy of Al and copper (Cu).

A lens layer27is provided to cover the entire surface of the pixel section100A, and a front surface thereof is provided with a plurality of on-chip lenses17L provided for the respective unit pixels P, for example. The on-chip lens17L is provided to condense light incident from above on the photoelectric conversion section11. The lens layer27is formed by, for example, an inorganic material such as silicon oxide (SiOx) or silicon nitride (SiNx). In addition thereto, the lens layer27may be formed using an organic material having a high refractive index such as an episulfide-based resin and a thietane compound or a resin thereof. The shape of the on-chip lens17L is not particularly limited, and various lens shapes such as a hemispherical shape and a semi-cylindrical shape can be adopted.

The multilayer wiring layer20is provided on a side opposite to the light incident side51, specifically, on a side of the second surface10S2of the semiconductor substrate10. The multilayer wiring layer20has a configuration, for example, in which a plurality of wiring layers21,22, and23are stacked with an interlayer insulating layer24interposed therebetween. In addition to the readout circuit described above, the multilayer wiring layer20includes, for example, the vertical drive circuit111, the column signal processing circuit112, the horizontal drive circuit113, the output circuit114, the control circuit115, the input/output terminal116, and the like.

The wiring layers21,22, and23are each formed using, for example, aluminum (Al), copper (Cu), tungsten (W), or the like. In addition thereto, the wiring layers21,22, and23may each be formed using polysilicon (Poly-Si).

The interlayer insulating layer34is formed by, for example, a single-layer film including one of silicon oxide (SiOx), TEOS, silicon nitride (SiNx), silicon oxynitride (SiOxNy), or the like, or a stacked film including two or more thereof.

[Configuration of Light-Receiving Surface and its Vicinity]

The imaging element1of the present embodiment includes the reflectance adjustment layer10X having a refractive index of about 3, for example, on the light-receiving surface (first surface10S1). The reflectance adjustment layer10X is provided to suppress reflection and diffraction of incident light at the first surface10S1. As described above, the reflectance adjustment layer10X includes the plurality of protrusions10A1configuring the uneven structure10A provided on the first surface1051of the semiconductor substrate10and the passivation film12embedded in the plurality of recesses10A2configuring the uneven structure10A.

FIG.4illustrates, in an enlarged manner, a cross-sectional configuration of the light-receiving surface (first surface1051) and its vicinity (X in the drawing) of the semiconductor substrate10illustrated inFIG.1. On the first surface1051of the semiconductor substrate10, there is formed the uneven structure10A including the plurality of protrusions10A1and the plurality of recesses10A2each having a predetermined hole diameter (width: w), depth (h), and pitch size (l). As described above, on the first surface10S1of the semiconductor substrate10, the passivation film12is stacked, and the plurality of recesses10A2are filled with the passivation film12.

The reflectance adjustment layer10X is considered as a pseudo layer of a front surface structure of the semiconductor substrate10including the plurality of protrusions10A1configuring the uneven structure10A and the passivation film12embedded in the plurality of recesses10A2configuring the uneven structure10A. For this reason, the reflectance adjustment layer10X has a refractive index averaged by the volume ratio between the semiconductor substrate10and the passivation film12which are components.

In the imaging element1, refractive indexes n10, n13, and n14of the semiconductor substrate10, and the first antireflection layer13and the second antireflection layer14, which are stacked on the light-receiving surface thereof (first surface1051) have a relationship of n10>n13>n14. The numbers at the end correspond to reference numerals of the respective components. As described above, the reflectance adjustment layer10X has a refractive index n10Xaveraged by the volume ratio between the semiconductor substrate10and the passivation film12. That is, the refractive indexes n10, n10X, n13, and n14of the respective layers stacked on the semiconductor substrate10, including the reflectance adjustment layer10X, and the light-receiving surface thereof (first surface10S1) are configured to increase stepwise from the light incident side Si toward the semiconductor substrate10(n10>n10X>n13>n14).

The oxide films listed as the materials for the first antireflection layer13and the second antireflection layer14each have the following refractive indexes: hafnium oxide (HfOx; 1.9), aluminum oxide (AlOx; 1.63), titanium oxide (TiOx; 2.4), zirconium oxide (ZrOx; 2.2), tantalum oxide (TaOx; 2.2), yttrium oxide (YOx; 1.87), strontium oxide (SrOx; 1.9), and silicon oxide (SiOx; 1.3 to 1.5). It is to be noted that numerical values within the parentheses are each a refractive index for a wavelength near 550 nm. As an example, in a case where a silicon substrate (Si; 4.1) is used as the semiconductor substrate10and silicon oxide (SiOx; 1.3 to 1.5) is used as the material configuring the second antireflection layer14, for example, tantalum oxide (TaOx; 2.2) can be selected as the material configuring the first antireflection layer13. Further, for example, aluminum oxide (AlOx;1.63) is selected as the passivation film12configuring the reflectance adjustment layer10X. In that case, the refractive index n10Xof the reflectance adjustment layer10X is a value averaged by the volume ratio between the semiconductor substrate10and the passivation film12as components, and is, for example, 2.6 to 3.7. This suppresses reflection of incident light at the light-receiving surface10S1.

Further, the uneven structure10A of the light-receiving surface (first surface1051) of the semiconductor substrate10preferably has a predetermined shape.

FIG.5illustrates simulation results of a diffraction amount of visible light (e.g., wavelength of 400 nm to 750 nm) depending on the distance (a pitch size1) between a plurality of adjacent recesses10A2configuring the uneven structure10A. Setting the pitch size1of the uneven structure10A to 200 nm or less reduces the diffraction amount of visible light to about 70%, and setting the pitch size1of the uneven structure10A to 150 nm or less reduces the diffraction amount of visible light to about 50%. Further, setting the pitch size1of the uneven structure10A to 100 nm or less reduces the diffraction amount of visible light to 20% or less, and setting the pitch size1of the uneven structure10A to 50 nm or less causes visible light to be hardly diffracted.

FIG.6illustrates simulation results of a relationship between a width w as well as a depth h of each of the plurality of recesses10A2configuring a the uneven structure10A and a reflection characteristics of the light-receiving surface (first surface10S1). For example, by setting the width w of the recess10A2to 15 nm or more and 30 nm or less and by setting the depth h of the recess10A2to 10 nm or more and 60 nm or less, the reflectance of light having a wavelength of 460 nm is 8% or less. Further, for example, by setting the width w of the recess10A2to 20 nm or more and 25 nm or less and by setting the depth h of the recess10A2to 40 nm or more and 50 nm or less, the reflectance of the light having a wavelength of 460 nm is 2% or less.

FIG.7illustrates simulation results of reflection characteristics of the light-receiving surface (first surface10S1) depending on presence or absence of the uneven structure10A. Providing the first surface10S1of the semiconductor substrate10with the uneven structure10A allows the reflectance of light having a short wavelength (e.g., 400 nm), for example, of visible light having a wavelength of 400 nm to 750 nm, to be reduced by about 10%.

From the above simulation results, it is preferable that the pitch size1of the uneven structure10A and the width w as well as the depth h of each of the plurality of recesses10A2configuring the uneven structure10A be set to the following ranges. That is, the pitch size1of the uneven structure10A is preferably, for example, 200 nm or less, and more preferably 100 nm or less. The width w of each of the plurality of recesses10A2configuring the uneven structure10A is preferably, for example, 15 nm or more and 30 nm or less, and more preferably 20 nm or more and 25 nm or less. For example, the depth h of each of the plurality of recesses10A2configuring the uneven structure10A is preferably, for example, 10 nm or more and 60 nm or less, and more preferably 40 nm or more and 50 nm or less. Setting the uneven structure10A to have the above-described predetermined size suppress not only reflection of the incident light at the light-receiving surface10S1but also diffraction of the incident light at the light-receiving surface10S1.

FIG.8illustrates a change in quantum efficiency depending on the thickness of the first antireflection layer13(e.g., a TaOx, film). In a case where the thickness of the first antireflection layer13including a TaOx, film is set to 75 nm, the quantum efficiency is about 63%. Setting the thickness of the first antireflection layer13including a TaOx, film to 55 nm or less improves the quantum efficiency to 65% or more, and setting the thickness, for example, to 35 nm allows for obtainment of a quantum efficiency of 70% or more. Accordingly, the thickness of the first antireflection layer13is preferably set to, for example, 75 nm or less, and more preferably 55 nm or less.

It is to be noted that the cross-sectional shape of the plurality of recesses10A2configuring the uneven structure10A is not limited to the shape, as illustrated inFIG.4, for example, having a side surface substantially perpendicular to the first surface10S1and a bottom surface parallel to the first surface10S1. The cross-sectional shape of the recess10A2may be, for example, a tapered shape that gradually narrows from the first surface10S1toward the second surface10S2, as illustrated inFIG.9A. Alternatively, the cross-sectional shape of the recess10A2may be, for example, a curved shape in which the side surface and the bottom surface of the recess10A2are continuous, as illustrated inFIG.9B. In any of the shapes, each front surface of the passivation film12and the first antireflection layer13has a waving shape depending on the uneven structure10A, thus increasing surface areas of the passivation film12and the first antireflection layer13. Accordingly, when forming the first antireflection layer13by, for example, plasma oxidation, the area of the first antireflection layer13exposed to plasma is enlarged, thus giving a pinning effect to the first antireflection layer13. Thus, it is possible to reduce generation of a dark current on a side of the light-receiving surface (first surface10S1).

In addition, a planar pattern of the plurality of recesses10A2configuring the uneven structure10A may be regularly formed in an X-direction and in a Y-direction, for example, as illustrated inFIG.10A. Alternatively, the planar pattern of the plurality of recesses10A2configuring the uneven structure10A may have a lattice pattern in which the recesses10A2regularly formed in the X-direction and in the Y-direction are continuous to each other, for example, as illustrated inFIG.10B. Further,FIGS.10A and10Beach illustrate the example in which the plurality of recesses10A2are regularly formed; however, the recesses10A2may be randomly formed. At that time, it is sufficient that the average value of the plurality of recesses10A2within a predetermined range such as the unit pixel P satisfy the above-described pitch size1of the uneven structure10A and the width w and the depth h of each of the plurality of recesses10A2configuring the uneven structure10A.

[Method of Manufacturing Imaging Element]

The imaging element1of the present embodiment can be formed, for example, as follows.

First, as illustrated inFIG.11A, the photoelectric conversion section11is formed inside the semiconductor substrate10. Subsequently, although not illustrated, various transistors configuring the readout circuit and the floating diffusion FD are formed on the side of the second surface10S2of the semiconductor substrate10, and then the multilayer wiring layer20including the wiring layers21,22, and23and the interlayer insulating layer24is formed as illustrated inFIG.11A.

Next, the uneven structure10A and the separation section10B are formed on the first surface10S1of the semiconductor substrate10. The uneven structure10A of the first surface10S1can be formed using, for example, a self-assembly technique (DSA). For example, as illustrated inFIG.11B, a hard mask31and an interlayer32are formed, as films, on the first surface10S1of the semiconductor substrate10. Subsequently, a diblock copolymer is coated on the interlayer32and then annealed, followed by etching. This allows for formation of a mask33having a predetermined pattern on the interlayer32, as illustrated inFIG.11B. The pattern thus formed has, for example, a fine hexagonal structure in a plan view.

Next, as illustrated inFIG.11C, the hard mask31is etched. This allows the pattern of the mask33to be transferred to the hard mask31. Subsequently, as illustrated inFIG.11D, etching of the semiconductor substrate10allows for formation of a plurality of fine recess10A2on the first surface1051of the semiconductor substrate10.

Next, as illustrated inFIG.11E, the groove10H is formed by etching between adjacent photoelectric conversion sections11. Subsequently, as illustrated inFIG.11F, for example, an AlOxfilm is formed as the passivation film12to fill the recess10A2and the groove10H. Next, as illustrated inFIG.11G, for example, a TaOxfilm is formed as the first antireflection layer13, and an SiOxfilm is formed as the second antireflection layer14, sequentially.

Subsequently, for example, CMP (Chemical Mechanical Polishing) is used to planarize a front surface of the second antireflection layer14. Next, as illustrated inFIG.11H, the light-blocking film16is formed on the second antireflection layer14. Thereafter, the color filter15(15R,15G, and15B) and the lens layer17are formed in order. As described above, the imaging element1illustrated inFIG.1is completed.

[Workings and Effects]

In the imaging element1of the present embodiment, the light-receiving surface (first surface1051) of the semiconductor substrate10including the photoelectric conversion section11is provided with the uneven structure10A, and the plurality of recesses10A2configuring the uneven structure10A is filled with the passivation film12. In addition, the first surface10S1is provided with the reflectance adjustment layer10X including the plurality of protrusions10A1configuring the uneven structure10A and the passivation film12embedded in the plurality of recesses10A2. This suppresses reflection and diffraction of wide wavelength bands at the light-receiving surface (first surface10S1). This is described below.

In recent years, the imaging element is required to have a smaller size and a higher definition. Meanwhile, a reduction in size lowers sensitivity, and thus an improvement in sensitivity is required for a high-definition imaging element. For example, in the imaging element, incident light is reflected, for example, at a front surface of an Si substrate. As a result, the intensity of light reaching a light-receiving section is lost, thus leading to lowered sensitivity, and incident light from an unintended optical path causes flare or ghost.

As a method for suppressing reflection of incident light at the front surface of the Si substrate, there has been proposed a technique of providing an antireflection layer having an uneven structure (moth-eye structure) on a top surface thereof, as described above. However, in order to sufficiently suppress the reflection of incident light using the moth-eye structure, it is required to form a deep uneven structure having a thickness of 100 nm or more and a narrow pitch.

In contrast, in the present embodiment, the light-receiving surface (first surface10S1) of the semiconductor substrate10is provided with the uneven structure10A including the plurality of protrusions10A1and the plurality of recesses10A2. Further, the passivation film12is stacked on the first surface10S1of the semiconductor substrate10to fill the plurality of recesses10A2. This allows for formation, on the first surface10S1of the semiconductor substrate10, of the reflectance adjustment layer10X having a refractive index n10Xbetween the refractive index n10of the semiconductor substrate10and the refractive index n13of the first antireflection layer13stacked on the passivation film12.

FIG.12illustrates reflection characteristics of visible light at the light-receiving surface (first surface10S1) depending on presence (Example)/absence (Comparative Example) of the uneven structure10A.FIG.13illustrates relative quantum efficiency of red light (R), green light (G), and blue light (B) depending on presence (Example)/absence (Comparative Example) of the uneven structure10A. In the imaging element1of the present embodiment, the reflectance of blue light (B) on a side of a short wavelength, in particular, of visible light, is greatly reduced, and the quantum efficiency of blue light (B) is improved accordingly.

As described above, it is possible, in the imaging element1of the present embodiment, to suppress reflection of incident light of a wide wavelength band at the first surface10S1while reducing generation of diffracted light at the first surface10S1. Thus, it is possible to improve the sensitivity while suppressing generation of color mixture due to crosstalk. That is, it is possible to provide a highly sensitive photodetector.

In addition, in the imaging element1of the present embodiment, the pitch size1of the uneven structure10A is set to, for example, 200 nm or less, and more preferably 100 nm or less. The width w of each of the plurality of recesses10A2configuring the uneven structure10A is set to, for example, 15 nm or more and 30 nm or less, and more preferably 20 nm or more and 25 nm or less. The depth h of each of the plurality of recesses10A2configuring the uneven structure10A is, for example, 10 nm or more and 60 nm or less, and more preferably 40 nm or more and 50 nm or less. This allows for further suppression of diffraction of incident light at the light-receiving surface10S1, thus making it possible to further reduce the generation of color mixture.

Further, in the imaging element1of the present embodiment, the front surface of each of the passivation film12and the first antireflection layer13has a waveform structure corresponding to the uneven structure10A. This allows the first antireflection layer13to have an increased surface area, thus allowing the first antireflection layer13to have a function as a fixed charge layer. Thus, it is possible to reduce the generation of a dark current on the side of the light-receiving surface (first surface10S1).

Furthermore, it is possible, in the imaging element1according to the present embodiment, to reduce the thickness of the imaging element1, as compared with the case of providing the above-described moth-eye structure. Thus, it is possible to achieve the imaging element having a reduced size and high sensitivity.

2. Application Example

The above-described imaging element1is applicable, for example, to any type of electronic apparatus with an imaging function including a camera system such as a digital still camera and a video camera, a mobile phone having an imaging function, and the like.FIG.14illustrates a schematic configuration of an electronic apparatus1000.

The electronic apparatus1000includes, for example, a lens group1001, the imaging element1, a DSP (Digital Signal Processor) circuit1002, a frame memory1003, a display unit1004, a recording unit1005, an operation unit1006, and a power source unit1007. They are coupled to each other via a bus line1008.

The lens group1001takes in incident light (image light) from a subject, and forms an image on an imaging surface of the imaging element1. The imaging element1converts the amount of incident light formed as an image on the imaging surface by the lens group1001into electric signals on a pixel-by-pixel basis, and supplies the DSP circuit1002with the electric signals as pixel signals.

The DSP circuit1002is a signal processing circuit that processes a signal supplied from the imaging element1. The DSP circuit1002outputs image data obtained by processing the signal from the imaging element1. The frame memory1003temporarily holds the image data processed by the DSP circuit1002on a frame-by-frame basis.

The display unit1004includes, for example, a panel-type display device such as a liquid crystal panel or an organic EL (Electro Luminescence) panel, and records image data of a moving image or a still image captured by the imaging element1in a recording medium such as a semiconductor memory or a hard disk.

The operation unit1006outputs an operation signal for a variety of functions of the electronic apparatus1000in accordance with an operation by a user. The power source unit1007appropriately supplies the DSP circuit1002, the frame memory1003, the display unit1004, the recording unit1005, and the operation unit1006with various kinds of power for operations of these supply targets.

In addition, the above-described imaging element1is applicable to the following electronic apparatuses.

FIG.15illustrates a usage example of the imaging element1according to the foregoing embodiment. In addition to the electronic apparatus having the imaging function described above, the imaging element1is usable in various cases of sensing light such as visible light, an infrared ray, an ultraviolet ray, or an X-ray, for example, as followsApparatuses that shoot images for viewing such as digital cameras or mobile apparatuses each having a camera functionApparatuses for traffic use such as onboard sensors that shoot images of the front, back, surroundings, inside, and so on of an automobile for safe driving such as automatic stop and for recognizing a driver's state, monitoring cameras that monitor traveling vehicles and roads, or distance measurement sensors that measure vehicle-to-vehicle distanceApparatuses for use in home electrical appliances such as televisions, refrigerators, or air-conditioners to shoot images of a user's gesture and bring the appliances into operation in accordance with the gestureApparatuses for medical treatment and health care use such as endoscopes or apparatuses that shoot images of blood vessels by receiving an infrared rayApparatuses for security use such as monitoring cameras for crime prevention or cameras for individual authenticationApparatuses for beauty care use such as skin measurement apparatuses that shoot images of skin or microscopes that shoot images of scalpApparatuses for sports use such as action cameras or wearable cameras for sports applications and the likeApparatuses for agricultural use such as cameras for monitoring the conditions of fields and crops

3. Practical Application Example

Example of Practical Application to Mobile Body

The technology (the present technology) according to the present disclosure is applicable to a variety of products. For example, the technology according to the present disclosure may be achieved as a device mounted on any type of mobile body such as an automobile, an electric vehicle, a hybrid electric vehicle, a motorcycle, a bicycle, a personal mobility, an aircraft, a drone, a vessel, or a robot.

FIG.16is a block diagram depicting an example of schematic configuration of a vehicle control system as an example of a mobile body control system to which the technology according to an embodiment of the present disclosure can be applied.

The vehicle control system12000includes a plurality of electronic control units connected to each other via a communication network12001. In the example depicted inFIG.16, the vehicle control system12000includes a driving system control unit12010, a body system control unit12020, an outside-vehicle information detecting unit12030, an in-vehicle information detecting unit12040, and an integrated control unit12050. In addition, a microcomputer12051, a sound/image output section12052, and a vehicle-mounted network interface (I/F)12053are illustrated as a functional configuration of the integrated control unit12050.

The driving system control unit12010controls the operation of devices related to the driving system of the vehicle in accordance with various kinds of programs. For example, the driving system control unit12010functions as a control device for a driving force generating device for generating the driving force of the vehicle, such as an internal combustion engine, a driving motor, or the like, a driving force transmitting mechanism for transmitting the driving force to wheels, a steering mechanism for adjusting the steering angle of the vehicle, a braking device for generating the braking force of the vehicle, and the like.

The body system control unit12020controls the operation of various kinds of devices provided to a vehicle body in accordance with various kinds of programs. For example, the body system control unit12020functions as a control device for a keyless entry system, a smart key system, a power window device, or various kinds of lamps such as a headlamp, a backup lamp, a brake lamp, a turn signal, a fog lamp, or the like. In this case, radio waves transmitted from a mobile device as an alternative to a key or signals of various kinds of switches can be input to the body system control unit12020. The body system control unit12020receives these input radio waves or signals, and controls a door lock device, the power window device, the lamps, or the like of the vehicle.

The outside-vehicle information detecting unit12030detects information about the outside of the vehicle including the vehicle control system12000. For example, the outside-vehicle information detecting unit12030is connected with an imaging section12031. The outside-vehicle information detecting unit12030makes the imaging section12031image an image of the outside of the vehicle, and receives the imaged image. On the basis of the received image, the outside-vehicle information detecting unit12030may perform processing of detecting an object such as a human, a vehicle, an obstacle, a sign, a character on a road surface, or the like, or processing of detecting a distance thereto.

The imaging section12031is an optical sensor that receives light, and which outputs an electric signal corresponding to a received light amount of the light. The imaging section12031can output the electric signal as an image, or can output the electric signal as information about a measured distance. In addition, the light received by the imaging section12031may be visible light, or may be invisible light such as infrared rays or the like.

The in-vehicle information detecting unit12040detects information about the inside of the vehicle. The in-vehicle information detecting unit12040is, for example, connected with a driver state detecting section12041that detects the state of a driver. The driver state detecting section12041, for example, includes a camera that images the driver. On the basis of detection information input from the driver state detecting section12041, the in-vehicle information detecting unit12040may calculate a degree of fatigue of the driver or a degree of concentration of the driver, or may determine whether the driver is dozing.

The microcomputer12051can calculate a control target value for the driving force generating device, the steering mechanism, or the braking device on the basis of the information about the inside or outside of the vehicle which information is obtained by the outside-vehicle information detecting unit12030or the in-vehicle information detecting unit12040, and output a control command to the driving system control unit12010. For example, the microcomputer12051can perform cooperative control intended to implement functions of an advanced driver assistance system (ADAS) which functions include collision avoidance or shock mitigation for the vehicle, following driving based on a following distance, vehicle speed maintaining driving, a warning of collision of the vehicle, a warning of deviation of the vehicle from a lane, or the like.

In addition, the microcomputer12051can perform cooperative control intended for automated driving, which makes the vehicle to travel automatedly without depending on the operation of the driver, or the like, by controlling the driving force generating device, the steering mechanism, the braking device, or the like on the basis of the information about the outside or inside of the vehicle which information is obtained by the outside-vehicle information detecting unit12030or the in-vehicle information detecting unit12040.

In addition, the microcomputer12051can output a control command to the body system control unit12020on the basis of the information about the outside of the vehicle which information is obtained by the outside-vehicle information detecting unit12030. For example, the microcomputer12051can perform cooperative control intended to prevent a glare by controlling the headlamp so as to change from a high beam to a low beam, for example, in accordance with the position of a preceding vehicle or an oncoming vehicle detected by the outside-vehicle information detecting unit12030.

The sound/image output section12052transmits an output signal of at least one of a sound and an image to an output device capable of visually or auditorily notifying information to an occupant of the vehicle or the outside of the vehicle. In the example ofFIG.57, an audio speaker12061, a display section12062, and an instrument panel12063are illustrated as the output device. The display section12062may, for example, include at least one of an on-board display and a head-up display.

FIG.17is a diagram depicting an example of the installation position of the imaging section12031.

InFIG.17, the imaging section12031includes imaging sections12101,12102,12103,12104, and12105.

The imaging sections12101,12102,12103,12104, and12105are, for example, disposed at positions on a front nose, sideview mirrors, a rear bumper, and a back door of the vehicle12100as well as a position on an upper portion of a windshield within the interior of the vehicle. The imaging section12101provided to the front nose and the imaging section12105provided to the upper portion of the windshield within the interior of the vehicle obtain mainly an image of the front of the vehicle12100. The imaging sections12102and12103provided to the sideview mirrors obtain mainly an image of the sides of the vehicle12100. The imaging section12104provided to the rear bumper or the back door obtains mainly an image of the rear of the vehicle12100. The imaging section12105provided to the upper portion of the windshield within the interior of the vehicle is used mainly to detect a preceding vehicle, a pedestrian, an obstacle, a signal, a traffic sign, a lane, or the like.

Incidentally,FIG.17depicts an example of photographing ranges of the imaging sections12101to12104. An imaging range12111represents the imaging range of the imaging section12101provided to the front nose. Imaging ranges12112and12113respectively represent the imaging ranges of the imaging sections12102and12103provided to the sideview mirrors. An imaging range12114represents the imaging range of the imaging section12104provided to the rear bumper or the back door. A bird's-eye image of the vehicle12100as viewed from above is obtained by superimposing image data imaged by the imaging sections12101to12104, for example.

At least one of the imaging sections12101to12104may have a function of obtaining distance information. For example, at least one of the imaging sections12101to12104may be a stereo camera constituted of a plurality of imaging elements, or may be an imaging element having pixels for phase difference detection.

For example, the microcomputer12051can determine a distance to each three-dimensional object within the imaging ranges12111to12114and a temporal change in the distance (relative speed with respect to the vehicle12100) on the basis of the distance information obtained from the imaging sections12101to12104, and thereby extract, as a preceding vehicle, a nearest three-dimensional object in particular that is present on a traveling path of the vehicle12100and which travels in substantially the same direction as the vehicle12100at a predetermined speed (for example, equal to or more than 0 km/hour). Further, the microcomputer12051can set a following distance to be maintained in front of a preceding vehicle in advance, and perform automatic brake control (including following stop control), automatic acceleration control (including following start control), or the like. It is thus possible to perform cooperative control intended for automated driving that makes the vehicle travel automatedly without depending on the operation of the driver or the like.

For example, the microcomputer12051can classify three-dimensional object data on three-dimensional objects into three-dimensional object data of a two-wheeled vehicle, a standard-sized vehicle, a large-sized vehicle, a pedestrian, a utility pole, and other three-dimensional objects on the basis of the distance information obtained from the imaging sections12101to12104, extract the classified three-dimensional object data, and use the extracted three-dimensional object data for automatic avoidance of an obstacle. For example, the microcomputer12051identifies obstacles around the vehicle12100as obstacles that the driver of the vehicle12100can recognize visually and obstacles that are difficult for the driver of the vehicle12100to recognize visually. Then, the microcomputer12051determines a collision risk indicating a risk of collision with each obstacle. In a situation in which the collision risk is equal to or higher than a set value and there is thus a possibility of collision, the microcomputer12051outputs a warning to the driver via the audio speaker12061or the display section12062, and performs forced deceleration or avoidance steering via the driving system control unit12010. The microcomputer12051can thereby assist in driving to avoid collision.

At least one of the imaging sections12101to12104may be an infrared camera that detects infrared rays. The microcomputer12051can, for example, recognize a pedestrian by determining whether or not there is a pedestrian in imaged images of the imaging sections12101to12104. Such recognition of a pedestrian is, for example, performed by a procedure of extracting characteristic points in the imaged images of the imaging sections12101to12104as infrared cameras and a procedure of determining whether or not it is the pedestrian by performing pattern matching processing on a series of characteristic points representing the contour of the object. When the microcomputer12051determines that there is a pedestrian in the imaged images of the imaging sections12101to12104, and thus recognizes the pedestrian, the sound/image output section12052controls the display section12062so that a square contour line for emphasis is displayed so as to be superimposed on the recognized pedestrian. The sound/image output section12052may also control the display section12062so that an icon or the like representing the pedestrian is displayed at a desired position.

Description has been given hereinabove referring to the embodiment, the application example, and the practical application example; however, the present technology is not limited to the foregoing embodiment and the like, and may be modified in a wide variety of ways. For example, an image plane phase difference pixel may be formed in addition to an imaging pixel in the pixel section100A, and the unit pixel P may serve also as the image plane phase difference pixel. The imaging pixel photoelectrically converts a subject image formed by an imaging lens in the photodiode PD to generate a signal for image generation. The image plane phase difference pixel divides a pupil region of the imaging lens and photoelectrically converts a subject image from the divided pupil region to generate a signal for phase difference detection.

It is to be noted that the effects described herein are merely exemplary and should not be limited to the description, and may further include other effects.

It is to be noted that the present disclosure may also have the following configuration. According to the present technology of the following configurations, the light-receiving surface of the semiconductor substrate including the light-receiving section is provided with the uneven structure, and the passivation film filling the plurality of recesses configuring the uneven structure is stacked on the light-receiving surface. This suppresses reflection and diffraction of incident light of a wide wavelength band at the light-receiving surface. Thus, it is possible to provide a highly sensitive photodetector.

(1)

A photodetector including:a substrate having a first surface that serves as a light-receiving surface and a second surface opposed to the first surface, the substrate including an uneven structure provided on the first surface and a light-receiving section that performs photoelectric conversion to generate electric charge corresponding to an amount of light reception for each pixel;a passivation film stacked on the first surface of the substrate; anda reflectance adjustment layer including a plurality of protrusions configuring the uneven structure and the passivation film embedded in a plurality of recesses configuring the uneven structure, the reflectance adjustment layer having a refractive index between the substrate and the passivation film.
(2)

The photodetector according to (1), in which a pitch size of the plurality of recesses is 200 nm or less.

(3)

The photodetector according to (1), in which a pitch size of the plurality of recesses is 100 nm or less.

(4)

The photodetector according to any one of (1) to (3), in which a width of each of the plurality of recesses is 15 nm or more and 30 nm or less.

(5)

The photodetector according to any one of (1) to (3), in which a width of each of the plurality of recesses is 20 nm or more and 25 nm or less.

(6)

The photodetector according to any one of (1) to (5), in which a depth of each of the plurality of recesses is 10 nm or more and 60 nm or less.

(7)

The photodetector according to any one of (1) to (5), in which a depth of each of the plurality of recesses is 40 nm or more and 50 nm or less.

(8)

The photodetector according to any one of (1) to (7), further including:a first antireflection layer provided on the passivation film; anda second antireflection layer provided on the first antireflection layer.
(9)

The photodetector according to (8), in which the refractive index of the reflectance adjustment layer is lower than the substrate and higher than refractive indexes of the first antireflection layer and the second antireflection layer.

(10)

The photodetector according to (8) or (9), in which the refractive index of the first antireflection layer is higher than the refractive index of the second antireflection layer.

(11)

The photodetector according to any one of (1) to (10), in which the substrate includes a silicon substrate or an indium-gallium-arsenic substrate.

(12)

The photodetector according to any one of (1) to (11), in which the passivation film includes an oxide film or a nitride film including at least one of hafnium, aluminum, titanium, zirconium, tantalum, yttrium, or strontium.

(13)

The photodetector according to any one of (1) to (12), in which the plurality of recesses has a tapered shape that gradually narrows from the first surface toward the second surface.

(14)

The photodetector according to any one of (8) to (13), further including an optical member above the second antireflection layer, the optical member condensing incident light on the light-receiving section.

(15)

A photodetector including:a substrate having a first surface that serves as a light-receiving surface and a second surface opposed to the first surface, the substrate including an uneven structure provided on the first surface and a light-receiving section that performs photoelectric conversion to generate electric charge corresponding to an amount of light reception for each pixel; anda passivation film stacked on the first surface of the substrate and filling a plurality of recesses configuring the uneven structure, the passivation film having, on a front surface thereof, a waveform structure corresponding to the uneven structure.
(16)

The photodetector according to (15), further including a first antireflection layer on the passivation film, the first antireflection layer having, on a front surface thereof, a waveform structure corresponding to the uneven structure.

This application claims the benefit of U.S. patent application No. 63/054,373 filed with the United States Patent and Trademark Office on Jul. 21, 2020, the entire contents of which are incorporated herein by reference.

It should be understood by those skilled in the art that various modifications, combinations, sub-combinations, and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.