Photoelectric conversion device

Abstract

To induce a crosstalk as stray light by reflecting a light quantum by avalanche light emission with a Si back surface of a moth eye structure.SOLUTION: A photoelectric conversion device has a plurality of avalanche diodes arranged on a semiconductor layer having a first surface and a second surface that is opposite to the first surface. Each of the plurality of avalanche diodes includes: a first conductive type first semiconductor region arranged at a first depth; and a second conductive type second semiconductor region arranged at a second depth deeper than the first depth relative to the second surface. The semiconductor layer comprises an uneven structure provided to the first surface, and an actual period of the uneven structure is smaller than hc / eEa (h: a Planck constant, c: a light velocity, e: an elementary electric amount, and Ea: band gap of the semiconductor layer).SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a photoelectric conversion device and a photoelectric conversion system.

Background Art

[0002] There is a photoelectric conversion device that provides a concavo-convex structure on the light-receiving surface of a photoelectric conversion element and refracts incident light to increase the optical path length of the incident light in the photoelectric conversion element and improve the quantum efficiency. Patent Document 1 describes a single-photon avalanche photodiode (SPAD) having a concavo-convex structure called a moth-eye structure on the light incident surface side of a substrate.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the structure described in Patent Document 1, there is a problem that photons due to avalanche emission are reflected from the Si back surface of the moth-eye structure and induce crosstalk as stray light.

[0005] The present invention has been made in view of the above problems, and aims to reduce crosstalk in a photoelectric conversion device using an avalanche photodiode.

Means for Solving the Problems

[0006] One aspect of the present invention is a photoelectric conversion device having a plurality of avalanche diodes disposed in a semiconductor layer having a first surface and a second surface facing the first surface, wherein each of the plurality of avalanche diodes has a first semiconductor region of a first conductivity type disposed at a first depth and a second semiconductor region of a second conductivity type disposed at a second depth deeper than the first depth with respect to the second surface, the semiconductor layer includes an uneven structure provided on the first surface, and an effective period of the uneven structure is smaller than hc / eEa (h: Planck's constant, c: speed of light, e: elementary charge, Ea: bandgap of the semiconductor layer).

[0007] Another aspect of the present invention is a photoelectric conversion device having a plurality of avalanche diodes disposed in a semiconductor layer having a first surface and a second surface facing the first surface, wherein each of the plurality of avalanche diodes has a first semiconductor region of a first conductivity type disposed at a first depth and a second semiconductor region of a second conductivity type disposed at a second depth deeper than the first depth with respect to the second surface, the semiconductor layer includes an uneven structure provided on the first surface, and an effective period of the uneven structure is smaller than 1.1 μm.

Advantages of the Invention

[0008] According to the present invention, crosstalk of a photoelectric conversion device using an avalanche photodiode can be reduced.

Brief Description of the Drawings

[0009]

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Embodiments for Carrying Out the Invention

[0010] The following embodiments are for embodying the technical idea of the present invention and do not limit the present invention. The sizes and positional relationships of the members shown in each drawing may be exaggerated for clarity of explanation. In the following description, the same components may be denoted by the same reference numerals and the description thereof may be omitted.

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, terms indicating a specific direction or position (for example, "up", "down", "right", "left", and other terms including these terms) are used as necessary. The use of these terms is for facilitating the understanding of the embodiments with reference to the drawings, and the technical scope of the present invention is not limited by the meanings of these terms.

[0012] In this specification, a plan view means viewing from a direction perpendicular to the light incident surface of the semiconductor layer. Further, a cross-sectional view means a plane in a direction perpendicular to the light incident surface of the semiconductor layer. When the light incident surface of the semiconductor layer is a rough surface when viewed microscopically, the plan view is defined based on the light incident surface of the semiconductor layer when viewed macroscopically.

[0013] In the following description, the anode of an avalanche photodiode (APD) is set to a fixed potential, and a signal is taken out from the cathode side. Therefore, the semiconductor region of the first conductivity type having majority carriers with the same polarity as the signal charge is an N-type semiconductor region, and the semiconductor region of the second conductivity type having majority carriers with a polarity different from the signal charge is a P-type semiconductor region. Note that the present invention is also applicable when the cathode of the APD is set to a fixed potential and a signal is taken out from the anode side. In this case, the semiconductor region of the first conductivity type having majority carriers with the same polarity as the signal charge is a P-type semiconductor region, and the semiconductor region of the second conductivity type having majority carriers with a polarity different from the signal charge is an N-type semiconductor region. Hereinafter, the case where one node of the APD is set to a fixed potential will be described, but the potentials of both nodes may vary.

[0014] In this specification, when the term "impurity concentration" is simply used, it means the net impurity concentration obtained by subtracting the amount compensated by the impurity of the opposite conductivity type. That is, the "impurity concentration" refers to the NET doping concentration. A region where the P-type added impurity concentration is higher than the N-type added impurity concentration is a P-type semiconductor region. Conversely, a region where the N-type added impurity concentration is higher than the P-type added impurity concentration is an N-type semiconductor region.

[0015] Configurations common to each embodiment of the photoelectric conversion device and its driving method according to the present invention will be described with reference to FIGS. 1 to 5.

[0016] FIG. 1 is a diagram showing the configuration of a stacked type photoelectric conversion device 100 according to an embodiment of the present invention. The photoelectric conversion device 100 is configured by laminating and electrically connecting two substrates, a sensor substrate 11 and a circuit substrate 21. The sensor substrate 11 has a first semiconductor layer having a photoelectric conversion element 102 described later and a first wiring structure. The circuit substrate 21 has a second semiconductor layer having circuits such as a signal processing unit 103 described later and a second wiring structure. The photoelectric conversion device 100 is configured by laminating the second semiconductor layer, the second wiring structure, the first wiring structure, and the first semiconductor layer in this order. The photoelectric conversion device described in each embodiment is a back-illuminated type photoelectric conversion device in which light is incident from the first surface and the circuit substrate is disposed on the second surface.

[0017] Hereinafter, the sensor substrate 11 and the circuit substrate 21 will be described as diced chips, but are not limited to chips. For example, each substrate may be a wafer. Further, each substrate may be diced after being laminated in a wafer state, or chips may be laminated and joined after being chipped.

[0018] A pixel region 12 is arranged on the sensor substrate 11, and a circuit region 22 for processing a signal detected in the pixel region 12 is arranged on the circuit substrate 21.

[0019] FIG. 2 is a diagram showing an arrangement example of the sensor substrate 11. Pixels 101 each having a photoelectric conversion element 102 including an avalanche photodiode (hereinafter, APD) are arranged in a two-dimensional array in a plan view to form a pixel region 12.

[0020] The pixel 101 is typically a pixel for forming an image, but when used for TOF (Time of Flight), it does not necessarily have to form an image. That is, the pixel 101 may be a pixel for measuring the arrival time and the amount of light of light.

[0021] FIG. 3 is a configuration diagram of the circuit board 21. It has a signal processing unit 103 that processes the charges photoelectrically converted by the photoelectric conversion element 102 in FIG. 2, a readout circuit 112, a control pulse generation unit 115, a horizontal scanning circuit unit 111, signal lines 113, and a vertical scanning circuit unit 110.

[0022] The photoelectric conversion element 102 in FIG. 2 and the signal processing unit 103 in FIG. 3 are electrically connected via connection wirings provided for each pixel.

[0023] The vertical scanning circuit unit 110 receives the control pulses supplied from the control pulse generation unit 115 and supplies control pulses to each pixel. Logic circuits such as a shift register and an address decoder are used for the vertical scanning circuit unit 110.

[0024] The signal output from the photoelectric conversion element 102 of the pixel is processed by the signal processing unit 103. The signal processing unit 103 is provided with a counter, a memory, etc., and digital values are held in the memory.

[0025] The horizontal scanning circuit unit 111 inputs control pulses for sequentially selecting each column to the signal processing unit 103 in order to read signals from the memories of the respective pixels in which digital signals are held.

[0026] Signals are output from the signal processing unit 103 of the pixels selected by the vertical scanning circuit unit 110 to the signal lines 113 for the selected columns.

[0027] The signals output to the signal lines 113 are output to a recording unit or a signal processing unit outside the photoelectric conversion device 100 via the output circuit 114.

[0028] In FIG. 2, the arrangement of the photoelectric conversion elements in the pixel region may be arranged in a one-dimensional manner. Also, even if there is only one pixel, the effects of the present invention can be obtained, and the case where there is one pixel is also included in the present invention. The functions of the signal processing unit do not necessarily have to be provided one by one for all the photoelectric conversion elements. For example, one signal processing unit may be shared by a plurality of photoelectric conversion elements and signal processing may be performed sequentially.

[0029] As shown in FIGS. 2 and 3, a plurality of signal processing units 103 are arranged in a region overlapping the pixel region 12 in a plan view. Then, in a plan view, a vertical scanning circuit unit 110, a horizontal scanning circuit unit 111, a column circuit 112, an output circuit 114, and a control pulse generation unit 115 are arranged so as to overlap between the edge of the sensor substrate 11 and the edge of the pixel region 12. In other words, the sensor substrate 11 has a pixel region 12 and a non-pixel region arranged around the pixel region 12, and a vertical scanning circuit unit 110, a horizontal scanning circuit unit 111, a column circuit 112, an output circuit 114, and a control pulse generation unit 115 are arranged in a region overlapping the non-pixel region in a plan view.

[0030] FIG. 4 is an example of a block diagram including the equivalent circuits of FIGS. 2 and 3.

[0031] In FIG. 2, the photoelectric conversion element 102 having the APD 201 is provided on the sensor substrate 11, and the other members are provided on the circuit substrate 21.

[0032] The APD 201 generates charge pairs corresponding to incident light by photoelectric conversion. A voltage VL (first voltage) is supplied to the anode of the APD 201. Also, a voltage VH (second voltage) higher than the voltage VL supplied to the anode is supplied to the cathode of the APD 201. A reverse bias voltage is supplied between the anode and the cathode so that the APD 201 performs an avalanche multiplication operation. By supplying such a voltage, the charges generated by the incident light cause avalanche multiplication, and an avalanche current is generated.

[0033] In addition, when a reverse bias voltage is supplied, there are a Geiger mode in which the potential difference between the anode and the cathode operates at a potential difference greater than the breakdown voltage, and a linear mode in which the potential difference between the anode and the cathode operates at a voltage difference near or below the breakdown voltage.

[0034] An APD operating in Geiger mode is called a SPAD. For example, the voltage VL (first voltage) is -30V and the voltage VH (second voltage) is 1V. The APD 201 may operate in linear mode or Geiger mode. In the case of a SPAD, since the potential difference is larger than that of a linear-mode APD and the effect of breakdown voltage is remarkable, it is preferably a SPAD.

[0035] The quenching element 202 is connected to the power supply that supplies the voltage VH and the APD 201. The quenching element 202 functions as a load circuit (quenching circuit) during signal multiplication by avalanche multiplication, and has the function of suppressing the voltage supplied to the APD 201 to suppress avalanche multiplication (quenching operation). Further, the quenching element 202 has the function of returning the voltage supplied to the APD 201 to the voltage VH by flowing a current corresponding to the voltage drop during the quenching operation (recharge operation).

[0036] The signal processing unit 103 includes a waveform shaping unit 210, a counter circuit 211, and a selection circuit 212. In this specification, the signal processing unit 103 may include any one of the waveform shaping unit 210, the counter circuit 211, and the selection circuit 212.

[0037] The waveform shaping unit 210 shapes the potential change of the cathode of the APD 201 obtained at the time of photon detection and outputs a pulse signal. As the waveform shaping unit 210, for example, an inverter circuit is used. In FIG. 4, an example in which one inverter is used as the waveform shaping unit 210 is shown, but a circuit in which a plurality of inverters are connected in series may be used, or any other circuit having a waveform shaping effect may be used.

[0038] The counter circuit 211 counts the pulse signal output from the waveform shaping unit 210 and holds the count value. Further, when the control pulse pRES is supplied via the drive line 213, the signal held in the counter circuit 211 is reset.

[0039] The selection circuit 212 is supplied with a control pulse pSEL from the vertical scanning circuit section 110 of FIG. 3 via a drive line 214 (not shown in FIG. 3) of FIG. 4, and switches the electrical connection and disconnection between the counter circuit 211 and the signal line 113. The selection circuit 212 includes, for example, a buffer circuit for outputting a signal.

[0040] A switch such as a transistor may be arranged between the quenching element 202 and the APD 201 or between the photoelectric conversion element 102 and the signal processing section 103 to switch the electrical connection. Similarly, the supply of the voltage VH or the voltage VL supplied to the photoelectric conversion element 102 may be electrically switched using a switch such as a transistor.

[0041] In this embodiment, a configuration using the counter circuit 211 is shown. However, instead of the counter circuit 211, a photoelectric conversion device 100 that acquires pulse detection timing using a time-to-digital conversion circuit (Time to Digital Converter: hereinafter, TDC) and a memory may be used. At this time, the generation timing of the pulse signal output from the waveform shaping section 210 is converted into a digital signal by the TDC. A control pulse pREF (reference signal) is supplied to the TDC from the vertical scanning circuit section 110 of FIG. 1 via a drive line for measuring the timing of the pulse signal. The TDC acquires, as a digital signal, a signal when the input timing of the signal output from each pixel via the waveform shaping section 210 is a relative time with reference to the control pulse pREF.

[0042] FIG. 5 is a diagram schematically showing the relationship between the operation of the APD and the output signal.

[0043] FIG. 5(a) is an extracted view of the APD 201, the quenching element 202, and the waveform shaping section 210 of FIG. 4. Here, the input side of the waveform shaping section 210 is designated as nodeA, and the output side is designated as nodeB. FIG. 5(b) shows the waveform change of nodeA in FIG. 5(a), and FIG. 5(c) shows the waveform change of nodeB in FIG. 5(a).

[0044] Between time t0 and time t1, a potential difference of VH - VL is applied to the APD 201 in FIG. 5(a). When a photon is incident on the APD 201 at time t1, avalanche multiplication occurs in the APD 201, an avalanche multiplication current flows through the quench element 202, and the voltage at node A drops. When the voltage drop amount becomes even larger and the potential difference applied to the APD 201 becomes smaller, the avalanche multiplication of the APD 201 stops as in time t2, and the voltage level at node A no longer drops below a certain value. Thereafter, between time t2 and time t3, a current that compensates for the voltage drop flows from the voltage VL to node A, and at time t3, node A settles to the original potential level. At this time, the portion of the output waveform at node A that exceeds a certain threshold is waveform-shaped by the waveform shaping unit 210 and output as a signal at node B.

[0045] Note that the arrangement of the signal line 113, the column circuit 112, and the output circuit 114 is not limited to FIG. 3. For example, the signal line 113 may be arranged to extend in the row direction, and the column circuit 112 may be arranged at the end where the signal line 113 extends.

[0046] Hereinafter, the photoelectric conversion device of each embodiment will be described.

[0047] (First Embodiment) The photoelectric conversion device according to the first embodiment will be described with reference to FIGS. 6 to 11.

[0048] FIG. 6 is a cross-sectional view in a direction perpendicular to the plane of the substrate of two pixels of the photoelectric conversion element 102 of the photoelectric conversion device according to the first embodiment.

[0049] The structure and function of the photoelectric conversion element 102 will be described. The photoelectric conversion element 102 has an N-type first semiconductor region 311, a fourth semiconductor region 314, a sixth semiconductor region 316, and a seventh semiconductor region 317. Further, it includes a P-type second semiconductor region 312, a third semiconductor region 313, and a fifth semiconductor region 315.

[0050] In this embodiment, in the cross-section shown in FIG. 6, an N-type first semiconductor region 311 is formed near the surface facing the light incident surface, and an N-type seventh semiconductor region 317 is formed around it. A P-type second semiconductor region 312 is formed at a position overlapping the first semiconductor region and the second semiconductor region in plan view. An N-type fourth semiconductor region 314 is further arranged at a position overlapping the second semiconductor region 312 in plan view, and an N-type sixth semiconductor region 316 is formed around it.

[0051] The first semiconductor region 311 has a higher N-type impurity concentration than the fourth semiconductor region 314 and the seventh semiconductor region 317. A PN junction is formed between the P-type second semiconductor region 312 and the N-type first semiconductor region 311. By making the impurity concentration of the second semiconductor region 312 lower than that of the first semiconductor region 311, all regions of the second semiconductor region 312 become depletion layer regions. Further, this depletion layer region extends to a part of the first semiconductor region 311, and a strong electric field is induced in the extended depletion layer region. Due to this strong electric field, avalanche multiplication occurs in the depletion layer region extending to a part of the first semiconductor region 311, and a current based on the amplified charge is output as a signal charge. When the light incident on the photoelectric conversion device 102 is photoelectrically converted and avalanche multiplication occurs in this depletion layer region (avalanche multiplication region), the generated charges of the first conductivity type are collected in the first semiconductor region 311.

[0052] In FIG. 6, the fourth semiconductor region 314 and the seventh semiconductor region 317 are formed to be of the same size, but the size of each semiconductor region is not limited to this. For example, the fourth semiconductor region 314 may be formed larger than the seventh semiconductor region 317, and charges may be collected in the first semiconductor region 311 from a wider range.

[0053] On the surface of the light incident surface side of the semiconductor layer, an uneven structure 325 is formed by trenches. The uneven structure 325 is surrounded by a P-type third semiconductor region 313 and scatters the light incident on the photoelectric conversion element 102. Since the incident light travels obliquely within the photoelectric conversion element, an optical path length equal to or greater than the thickness of the semiconductor layer 301 can be ensured, and it is possible to photoelectrically convert light with a longer wavelength compared to the case without the uneven structure 325. In addition, since the uneven structure 325 prevents reflection of the incident light within the substrate, an effect of improving the photoelectric conversion efficiency of the incident light can be obtained.

[0054] The fourth semiconductor region 314 and the uneven structure 325 are formed so as to overlap in plan view. The area where the fourth semiconductor region 314 and the uneven structure 325 overlap in plan view is larger than the area of the portion of the fourth semiconductor region 314 that does not overlap with the uneven structure 325. The charge generated at a position far from the avalanche multiplication region formed between the first semiconductor region 311 and the fourth semiconductor region 314 has a longer transit time until it reaches the avalanche multiplication region compared to the charge generated at a position closer to the avalanche multiplication region. Therefore, the timing jitter may deteriorate. By arranging the fourth semiconductor region 314 and the uneven structure 325 at positions that overlap in plan view, the electric field in the deep part of the photodiode can be enhanced, and the collection time of the charge generated at a position far from the avalanche multiplication region can be shortened, so that the reduction of the timing jitter is possible.

[0055] In addition, by the third semiconductor region 313 three-dimensionally covering the uneven structure, the generation of thermally excited charges at the interface portion of the uneven structure can be suppressed. Thereby, the DCR (Dark Count Rate) of the photoelectric conversion element is suppressed.

[0056] Pixels are separated from each other by a pixel isolation section 324 with a trench structure, and a P-type fifth semiconductor region 315 formed around it separates adjacent photoelectric conversion elements from each other by a potential barrier. Since the photoelectric conversion elements are also separated by the potential of the fifth semiconductor region 315, a trench structure such as the pixel isolation section 324 is not essential as a pixel isolation section. Also, when providing the pixel isolation section 324, its depth and position are not limited to the configuration of FIG. 6. The pixel isolation section 324 may be a DTI (deep trench isolation) that penetrates the semiconductor layer, or a DTI that does not penetrate the semiconductor layer. Metal may be embedded in the DTI to improve the light shielding performance. The pixel isolation section 324 may be configured to surround the entire periphery of the photoelectric conversion element in plan view, or may be configured only at the opposite sides of the photoelectric conversion element, for example.

[0057] The distance from the pixel isolation section to the pixel isolation section of an adjacent pixel or a pixel provided at the closest position can also be regarded as the size of one photoelectric conversion element 102. When the size of one photoelectric conversion element 102 is L, the distance d from the light incident surface to the avalanche multiplication region satisfies L√2 / 4 < d < L×√2. When the size and depth of the photoelectric conversion element satisfy this relational expression, the electric field strength in the depth direction and the electric field strength in the plane direction in the vicinity of the first semiconductor region 311 become approximately the same. Since the variation in the time required for charge collection can be suppressed, the generation of timing jitter can be reduced.

[0058] On the light incident surface side of the semiconductor layer, a pinning film 321, a planarization film 322, and a microlens 323 are further formed. A filter layer (not shown) or the like may be further arranged on the light incident surface side. Various optical filters such as a color filter, an infrared cut filter, and a monochrome filter can be used for the filter layer. For the color filter, an RGB color filter, an RGBW color filter, or the like can be used.

[0059] FIG. 7 is a potential diagram of the photoelectric conversion element 102 shown in FIG. 6.

[0060] The dotted line 70 in Fig. 7 shows the potential distribution of the line segment FF' in Fig. 6, and the solid line 71 in Fig. 7 shows the potential distribution of the line segment EE' in Fig. 6. In Fig. 7, the potential is shown as seen from the electrons which are the main carrier charges in the N-type semiconductor region. When the main carrier charges are holes, the relationship of the potential levels is reversed. Also, the depth A in Fig. 7 corresponds to the height A in Fig. 6. Similarly hereinafter, the depth B corresponds to the height B, the depth C corresponds to the height C, and the depth D corresponds to the height D respectively.

[0061] In Fig. 7, let the potential height of the solid line 71 at the depth A be A1, the potential height of the dotted line 70 be A2, the potential height of the solid line 71 at the depth B be B1, and the potential height of the dotted line 70 be B2. Also, let the potential height of the solid line 71 at the depth C be C1, the potential height of the dotted line 70 be C2, the potential height of the solid line 71 at the depth D be D1, and the potential height of the dotted line 70 be D2.

[0062] From Figs. 6 and 7, the potential height of the first semiconductor region 311 corresponds to A1, and the potential height near the center of the second semiconductor region 312 corresponds to B1. Also, the potential height of the seventh semiconductor region 317 corresponds to A2, and the potential height at the outer edge of the second semiconductor region 312 corresponds to B2.

[0063] Regarding the dotted line 70 in Fig. 7, the potential gradually decreases from the depth D towards the depth C. Then, the potential gradually increases from the depth C towards the depth B, and at the depth B, the potential becomes the B2 level. Further, the potential decreases from the depth B towards the depth A, and becomes the A2 level at the depth A.

[0064] On the other hand, regarding the solid line 71, the potential gradually decreases from the depth D to the depth C and from the depth C to the depth B, and becomes the B1 level at the depth B. Then, the potential sharply decreases from the depth B to the depth A, and the potential becomes the A1 level at the depth A. At the depth D, the potentials of the dotted line 70 and the solid line 71 are almost at the same height, and in the regions indicated by the line segments EE' and FF', there is a potential gradient that gently decreases toward the side of the second surface of the semiconductor layer 301. Therefore, the charges generated in the photodetection device move toward the second surface side due to the gentle potential gradient.

[0065] Here, in the avalanche diode of the present embodiment, the impurity concentration of the P-type second semiconductor region 312 is lower than that of the N-type first semiconductor region 311, and potentials that are reverse-biased to each other are supplied to the first semiconductor region 311 and the second semiconductor region 312. As a result, a depletion layer region is formed on the side of the second semiconductor region 312. With such a structure, the second semiconductor region 312 becomes a potential barrier for the charges photoelectrically converted in the fourth semiconductor region 314, resulting in a structure in which the charges are easily collected in the first semiconductor region 311.

[0066] Note that in FIG. 6, the second semiconductor region 312 is formed over the entire surface of the photoelectric conversion element. However, for example, the second semiconductor region 312 may not be provided in a portion that overlaps the first semiconductor region 311 in plan view, and a slit in which the fourth semiconductor region 314 extends may be formed. In that case, due to the potential difference between the second semiconductor region 312 and the slit portion, the potential decreases in the direction from the line segment FF' to the line segment EE' at the depth C in FIG. 6. As a result, in the process of the charges photoelectrically converted in the fourth semiconductor region 314 moving, the charges easily move in the direction of the first semiconductor region 311. On the other hand, when the second semiconductor region 312 is formed over the entire surface as shown in FIG. 6, compared with the case of forming a slit, the applied voltage for obtaining the strong electric field required for avalanche multiplication can be lowered, and noise due to the formation of a local strong electric field region can be suppressed.

[0067] The charges that have moved near the second semiconductor region 312 are multiplied by avalanche by being accelerated by the steep potential gradient from depth B to depth A of the solid line 71 in FIG. 7, that is, by a strong electric field.

[0068] On the other hand, between the seventh semiconductor region 317 and the P-type second semiconductor region 312 in FIG. 6, that is, from depth B to depth A of the dotted line 70 in FIG. 7, the potential distribution is such that avalanche multiplication does not occur. Therefore, without increasing the area of the strong electric field region (avalanche multiplication region) with respect to the size of the photodiode, the charges generated in the fourth semiconductor region 314 can be counted as signal charges. Note that although the conductivity type of the seventh semiconductor region 317 has been described as N-type up to this point, a P-type semiconductor region may also be used as long as the concentration satisfies the above-described potential relationship.

[0069] Also, the charges photoelectrically converted in the second semiconductor region 312 flow into the fourth semiconductor region 314 due to the potential gradient from depth B to depth C of the dotted line 70 in FIG. 7. The charges in the fourth semiconductor region 314 are structured to easily move to the second semiconductor region 312 for the reasons described above. For this reason, the charges photoelectrically converted in the second semiconductor region 312 move to the first semiconductor region 311 and are detected as signal charges by avalanche multiplication. Therefore, it has sensitivity to the charges photoelectrically converted in the second semiconductor region 312.

[0070] Also, the dotted line 70 in FIG. 7 indicates the cross-sectional potential of the line segment FF' in FIG. 3. At the dotted line 70, let the point where the height A in FIG. 6 intersects the line segment FF' be A2, the point where the height B intersects the line segment FF' be B2, the point where the height C intersects the line segment FF' be C2, and the point where the height D intersects the line segment FF' be D2. The electrons photoelectrically converted in the fourth semiconductor region 314 of FIG. 6 move along the potential from D2 to C2 in FIG. 7. However, from C2 to B2, it becomes a potential barrier for the electrons and they cannot overcome it. Therefore, the electrons move to the vicinity of the center indicated by the line segment EE' in the fourth semiconductor region 314 of FIG. 6. The moved electrons move along the potential gradient from C1 to B1 in FIG. 7, are avalanche multiplied by the steep potential gradient from B1 to A1, and after passing through the first semiconductor region 311, are detected as signal charges.

[0071] Also, the charges generated near the boundary between the third semiconductor region 313 and the sixth semiconductor region 316 in FIG. 6 move along the potential gradient from the potential B2 to C2 in FIG. 7. Then, as described above, they move to the vicinity of the center indicated by the line segment EE' in the fourth semiconductor region 314 of FIG. 6. And they are avalanche multiplied by the steep potential gradient from B1 to A1. The avalanche multiplied charges are detected as signal charges after passing through the first semiconductor region 311.

[0072] FIG. 8 is an enlarged cross-sectional view of two of the trenches forming the concavo-convex structure 325 of the photoelectric conversion device according to the first embodiment.

[0073] The trench structure is formed of a material different from that of the third semiconductor region 313. For example, when the third semiconductor region 313 is silicon, the main members constituting the trench structure are a silicon oxide film and a silicon nitride film, but metals and organic materials may also be included. The trench is formed, for example, at a depth of 0.1 to 0.6 μm from the surface of the semiconductor layer. In order to sufficiently enhance the diffraction of incident light, it is desirable that the depth of the trench be greater than the width of the trench. Here, the width of the trench is the width from the interface between the pinning film 321 and the third semiconductor region 313 to the interface between the pinning film 321 and the third semiconductor region 313 in a plane passing through the centroid of the trench cross-section, and the depth of the trench is the depth from the light incident surface to the bottom of the trench.

[0074] Also, the period p indicated by the arrow in FIG. 8 represents one period of the uneven structure 325 formed by a plurality of trenches. The distance from the centroid of one trench, which is one of the uneven structures, to the centroid of another trench adjacent to the trench in the cross-sectional view is defined as the period of the uneven structure 325, and the average of the uneven periods of the entire uneven structure 325 is defined as the effective period.

[0075] The trench formation process will be described. First, a groove is formed by etching in the third semiconductor region 313 of the semiconductor layer. Then, a pinning film 321 is formed on the surface of the third semiconductor region 313 and inside the trench by a method such as chemical vapor deposition. The inside of the trench covered with the pinning film 321 is filled with a filling member 332. The trenches forming the uneven structure 325 can be filled by the same process as the trenches constituting the pixel isolation portion. In this case, the side wall portions of the trenches forming the uneven structure 325 and the side wall portions of the trenches constituting the pixel isolation portion will have the same impurity concentration.

[0076] The filling member 332 may have a void 331 inside. Since the refractive index of the void 331 is lower than that of the filling member 332, an optical path difference occurs between the light passing through the void and the light passing through other parts. Compared with the case where no void is provided in the filling member, the refractive index difference of the entire concavo-convex structure 325 becomes larger, and the phase difference generated in the light transmitted through the concavo-convex structure 325 also becomes larger. Therefore, the diffraction of the incident light is likely to be enhanced. That is, by providing a void in the filling member, the intensity of the incident light increases at a specific phase, and the effect of improving the sensitivity can be obtained.

[0077] FIG. 9 is a pixel plan view of two pixels of the photoelectric conversion device according to the first embodiment. FIG. 9(a) is a plan view seen from the surface opposite to the light incident surface, and FIG. 9(b) is a plan view seen from the light incident surface side.

[0078] In FIG. 9(a), the first semiconductor region 311, the fourth semiconductor region 314, and the seventh semiconductor region 317 are circular and arranged concentrically. By adopting such a structure, the effect of suppressing local electric field concentration at the end of the strong electric field region between the first semiconductor region 311 and the second semiconductor region 312 and reducing DCR can be obtained. The shape of each semiconductor region is not limited to a circle, and for example, a polygon with aligned centroid positions may also be used.

[0079] In FIG. 9(b), the concavo-convex structure 325 is formed in a lattice shape in plan view. The concavo-convex structure 325 is formed to overlap with the first semiconductor region 311 and the fourth semiconductor region 314, and the centroid position of the concavo-convex structure 325 is included in the avalanche multiplication region in plan view. In the lattice trench structure shown in FIG. 9(b), the trench depth at the intersection of the trenches is deeper than the trench depth at the portion where the trench extends alone. However, the bottom of the trench at the intersection of the trenches is located closer to the light incident surface side than half of the thickness of the semiconductor layer. Here, the trench depth is the depth from the second surface to the bottom, and it can also be referred to as the depth of the concave portion of the concavo-convex structure 325.

[0080] FIG. 10 is a comparative example of the photoelectric conversion device 102 according to the first embodiment. In FIG. 10, the photoelectric conversion device 102 is shown in a simplified manner. The photoelectric conversion device 102 is a photoelectric conversion device having an avalanche multiplication region 501, a wiring layer 502, and a concavo-convex structure 325.

[0081] When light is incident on such a photoelectric conversion element, avalanche emission may occur in the avalanche multiplication region 501. Avalanche emission is a phenomenon in which a large number of electrons or holes generated by avalanche multiplication recombine with charges of different polarities to generate photons. The photons generated by avalanche emission leak into adjacent pixels, resulting in a false signal and a deterioration in image quality.

[0082] In the photoelectric conversion element shown in FIG. 10, the effective period of the concavo-convex structure 325 formed on the light incident surface side of the semiconductor layer is larger than the avalanche emission wavelength. Here, although the spectrum of the avalanche emission light has a certain spread from a short wavelength to a long wavelength, the component with a short wavelength has a short absorption length in the substrate and is photoelectrically converted at a position close to the emission region, so the probability of reaching adjacent pixels and generating a false signal is low. On the other hand, the component with a long wavelength has a long absorption length in the substrate and a high probability of generating a false signal at a position farther from the emission region, so it becomes the dominant factor in the above-mentioned image quality deterioration. Therefore, among the spectra of the avalanche emission light, the component with the maximum wavelength can be approximately regarded as a typical factor in the above-mentioned image quality deterioration. The maximum value of the wavelength of the avalanche emission is determined by the bandgap of the substrate material, hc / eE a (h: Planck's constant, c: speed of light, e: elementary charge, Ea: bandgap of the substrate) shall be obtained by. For example, when the sensor substrate is silicon, the maximum value of the wavelength of the avalanche emission light is about 1.1 μm.

[0083] When the effective period of the concavo-convex structure is larger than the avalanche emission wavelength, the avalanche emission light behaves particle-like with respect to the concavo-convex structure. Since the change in the effective refractive index with respect to the substrate depth becomes steep, the avalanche emission light is reflected at the bottom of the concavo-convex structure, and the reflected light becomes stray light within the pixel.

[0084] FIG. 11 shows an example of a photoelectric conversion device according to the first embodiment. Also in FIG. 11, the photoelectric conversion device 102 is shown in a simplified manner as in FIG. 10.

[0085] The period of the concavo-convex structure formed on the light incident surface side of the semiconductor layer of the photoelectric conversion element shown in FIG. 11 is smaller than the avalanche emission wavelength. When the sensor substrate is silicon, the concavo-convex structure is formed with a period of 1.1 μm to 0.2 μm. When avalanche emission occurs in such a photoelectric conversion element, the avalanche emission light behaves in a wavy manner. Since the change in the effective refractive index with respect to the semiconductor layer depth becomes gentle, the reflection of the avalanche emission light at the bottom of the concavo-convex structure becomes small, and the avalanche emission light incident on the concavo-convex structure travels toward the outside of the substrate, so that stray light in the pixel is suppressed. At this time, by arranging the concavo-convex structure at the center of the photoelectric conversion element where the light intensity of the avalanche emission light on the light incident surface of the semiconductor layer is high, an effect of more efficiently suppressing stray light can be obtained.

[0086] Note that the trench forming the concavo-convex structure illustrated in FIG. 11 is tapered and does not have a uniform width. In such a concavo-convex structure, the effect of the present application can be obtained as long as the condition that the period is smaller than the avalanche emission wavelength is satisfied at the average width in the cross-sectional structure (the width at half the depth of the trench depth in FIG. 11). In other words, the trench width satisfies hc / 2eE a (h: Planck's constant, c: speed of light, e: elementary charge of electricity, Ea: band gap of the substrate), and for example, when the sensor substrate is silicon, the trench width is 0.55 μm or less. It can also be said that the effective period is smaller than the wavelength at which the optical absorption length of the semiconductor substrate is equal to the distance from the light incident surface to the interface between the first semiconductor region and the second semiconductor region.

[0087] Further, the wiring layer 502 includes an AL wiring or the like and functions as a reflecting member that reflects the light transmitted through the semiconductor layer 301 inside the pixel.

[0088] In this way, crosstalk can be reduced by making the period of the concavo-convex structure formed on the light incident surface side of the semiconductor layer smaller than the avalanche emission light.

[0089] (Second Embodiment) The photoelectric conversion device according to the second embodiment will be described with reference to FIG. 12.

[0090] Parts common to the description of the first embodiment will be omitted, and mainly differences from the first embodiment will be described. In this embodiment, the concavo-convex structure is formed so as to have a point where it overlaps in a T shape in plan view.

[0091] FIG. 12 is a pixel plan view of two pixels of the photoelectric conversion device according to the second embodiment.

[0092] In a plan view from the light incident surface side, the trenches forming the concavo-convex structure 325 are arranged so as to form a shape in which a plurality of rectangles are connected by repeating a T-shaped configuration. It can also be said that the structure of the concavo-convex structure 325 is a lattice structure in which the lattice-shaped trench structure shown in FIG. 9 is shifted by a half pitch for each row.

[0093] In such a configuration, compared with the case where the concavo-convex structure 325 forms a lattice intersecting vertically and horizontally, the number of portions where the trenches overlap and are over-etched in the etching process for forming the trenches is small. Therefore, damage such as lattice defects is less likely to occur in the semiconductor layer due to etching, and the possibility of deterioration of DCR due to being a cause of dark current can be reduced.

[0094] (Modification of the Second Embodiment) FIG. 13 shows a pixel plan view of two pixels of the photoelectric conversion device according to a modification of the second embodiment.

[0095] In a plan view from the light incident surface side, the trenches forming the concavo-convex structure 325 are arranged so as to form a shape in which a plurality of rectangles having different areas are connected by repeating a T-shaped configuration.

[0096] Even with such a configuration, compared to the case where the concavo-convex structure 325 forms a lattice where the concavities and convexities overlap vertically and horizontally, the number of portions where the trenches overlap and are over-etched is reduced. Therefore, it is possible to reduce the possibility that damage such as lattice defects is caused in the semiconductor layer by etching and the DCR deteriorates due to the resulting dark current.

[0097] (Third Embodiment) The photoelectric conversion device according to the third embodiment will be described with reference to FIGS. 14 to 17.

[0098] Parts that are common to the descriptions of the first embodiment and the second embodiment will be omitted, and mainly parts different from the first embodiment will be described.

[0099] FIG. 14 is a pixel plan view as viewed from the plane of the surface facing the light incident surface of four pixels of the photoelectric conversion device according to the third embodiment. The point that an N-type eighth semiconductor region 318 is provided around the seventh semiconductor region 317 is different from the photoelectric conversion devices according to the first and second embodiments. The N-type impurity concentration of the eighth semiconductor region 318 formed on the surface facing the light incident surface is lower than the N-type impurity concentration of the first semiconductor region 311.

[0100] FIG. 15 is a pixel plan view as viewed from the plane of the light incident surface side of four pixels of the photoelectric conversion device according to the third embodiment.

[0101] In a plan view from the light incident surface side, the concavo-convex structure 325 has an aperiodic structure formed by randomly arranged trenches. Also in this case, the effective period of the concavo-convex structure 325 is configured to be shorter than the wavelength of the avalanche emission light.

[0102] By randomizing the distribution of the concavo-convex structure 325, the angular distribution of the diffracted light when the incident light is diffracted by the concavo-convex structure 325 can be made uniform, and it is possible to enhance the sensitivity improvement effect. The arrangement of the concavo-convex structure 325 is not limited to this, and for example, a plurality of independent island-like structures may be formed in the plane.

[0103] FIG. 16 is a cross-sectional view of a pixel of a photoelectric conversion device according to the third embodiment, taken along the line A-A' in FIG. 15, and FIG. 17 is a cross-sectional view of a pixel of the photoelectric conversion device according to the third embodiment, taken along the line B-B' in FIG. 15.

[0104] The pixel according to the present embodiment does not have the fifth semiconductor region 315 that extends to the surface facing the light incident surface side in the cross section in the A-A' direction (the opposite side direction of the pixel). The fifth semiconductor region 315 and the eighth semiconductor region 318 have a separated structure. On the other hand, in the cross section in the B-B' direction (the diagonal direction of the pixel), the fifth semiconductor region 315 extends from the light incident surface side to the surface facing the light incident surface.

[0105] By providing the eighth semiconductor region 318 without providing the fifth semiconductor region 315 at the corner of the pixel, the electric field in the planar direction is relaxed. When dark charges are generated at the corner of the pixel, the dark charges are collected in the first semiconductor region 311 by the lateral electric field and are easily discharged without passing through the strong electric field region that induces avalanche multiplication. This reduces the deterioration of DCR. Also, by not providing the fifth semiconductor region 315 at the corner of the pixel, the lateral electric field concentration between the fifth semiconductor region 315 and the first semiconductor region 311 can be suppressed, so that the miniaturization of the pixel can be facilitated.

[0106] (Fourth Embodiment) The photoelectric conversion device according to the fourth embodiment will be described with reference to FIGS. 18 to 20.

[0107] Parts that are common to the descriptions of the first to third embodiments will be omitted, and mainly parts different from the first embodiment will be described.

[0108] FIG. 18 is a cross-sectional view of two pixels of the photoelectric conversion device 102 according to the fourth embodiment, and FIG. 19 is a plan view of two pixels of the photoelectric conversion device 102 according to the fourth embodiment. FIG. 19(a) is a plan view in a plan view from the surface facing the light incident surface, and FIG. 19(b) is a plan view in a plan view from the light incident surface side.

[0109] As shown in FIGS. 18 and 19, in the photoelectric conversion device according to the present embodiment, an antireflection film 326 is provided between the semiconductor layer 301 and the interlayer film 322. Further, it is different from the first to third embodiments in that a light-shielding portion 327 is provided between pixels and the uneven structure 325 is formed so as to have a density distribution within the pixel.

[0110] The effects of the fourth embodiment will be described using FIG. 20, which is a comparison diagram of two pixels of the photoelectric conversion device 102 according to the fourth embodiment. In FIG. 20, the photoelectric conversion device 102 is shown in a simplified manner. The photoelectric conversion device 102 is a photoelectric conversion device having an avalanche multiplication region 501, a wiring layer 502, an uneven structure 325, an antireflection film 326, and a light-shielding portion 327.

[0111] The refractive index of the antireflection film 326 is higher than the effective refractive index of the uneven structure 325. Here, the effective refractive index is the substantial refractive index of the entire uneven structure 325 formed by combining the substrate on which the trenches are formed and the members filling the trenches. For example, when the semiconductor layer 301 is Si with a refractive index of 4 and the interlayer film 322 is SiO with a refractive index of 1.5, the effective refractive index of the uneven structure 325 is 2.8 to 3.8. By providing the antireflection film 326 between the semiconductor layer 301 and the interlayer film 322, the change in the refractive index from the semiconductor layer 301 to the interlayer film 322 can be made gentle. Thereby, reflection of the avalanche emission light on the back surface of the semiconductor layer can be prevented, and crosstalk due to the avalanche emission light can be reduced.

[0112] Further, by providing the light-shielding portion 327 between pixels, crosstalk caused by the avalanche emission light generated in each pixel entering an adjacent pixel when the avalanche emission light exits the pixel can be reduced.

[0113] As shown in Fig. 19(a), the concavo-convex structure 325 in this embodiment is formed such that a density distribution occurs within the pixel. Specifically, in each pixel, the trench density at the pixel periphery where the intensity distribution of the avalanche emission light is low is reduced. Thereby, the area occupancy rate of the trenches with respect to the entire pixel can be decreased. Since the locations where trenches are formed can be sources of dark current due to damage to the semiconductor layer caused by etching or the like, by decreasing the area occupancy rate of the trenches, it is possible to reduce DCR while suppressing crosstalk.

[0114] (Fifth Embodiment) The photoelectric conversion device according to the fifth embodiment will be described with reference to Fig. 21.

[0115] Parts that are common to the description of the first to fourth embodiments will be omitted, and mainly parts different from the first embodiment will be described.

[0116] Fig. 21 is a cross-sectional view of a pixel of the photoelectric conversion device according to the fifth embodiment.

[0117] In the photoelectric conversion device according to the fifth embodiment, the depths of the trenches forming the concavo-convex structure 325 are not uniform. In the pixel shown in Fig. 21, the trenches are formed to a depth of, for example, 0.1 to 0.6 μm in the portion near the pixel center where the intensity of the avalanche emission light is high, and are formed relatively shallow in the portion near the outer edge of the pixel where the intensity of the avalanche emission light is low.

[0118] By forming the concavo-convex structure 325 including a plurality of trenches with different depths in this way, the reflection of the emission light in the vicinity of the pixel center where the avalanche emission light strongly gathers can be particularly suppressed, and crosstalk can be reduced. Also, since the total volume of the concavo-convex structure 325 can be suppressed, the generation of dark current is suppressed, and the deterioration of DCR can be reduced.

[0119] (Sixth Embodiment) The photoelectric conversion device according to the sixth embodiment will be described with reference to Fig. 22.

[0120] The parts that are common to the descriptions from the first embodiment to the fifth embodiment are omitted, and the parts that are mainly different from the first embodiment will be described.

[0121] The cross-section of the trench forming the concavo-convex structure 325 is not limited to the shape shown in FIG. 8. For example, it may have an inverted taper shape where the light incident surface side is narrow and the side closer to the surface facing the light incident surface is wide, as shown in FIG. 22(a). By forming the trench forming the concavo-convex structure 325 in such a shape, the diffraction effect can be enhanced and the sensitivity can be improved.

[0122] Also, the trench forming the concavo-convex structure 325 may be hemispherical as shown in FIG. 22(b). By suppressing a sharp change in the refractive index and obtaining an antireflection effect, the sensitivity can be improved. FIG. 22(b) shows a hemisphere with a semicircular shape having a central angle of 180° in the cross-section, but the same effect can be obtained if the cross-section has an arc shape.

[0123] Similarly, a stepped trench as shown in FIG. 22(c) can suppress a sudden change in the refractive index and improve the sensitivity due to the antireflection effect. FIG. 22(c) shows a stepped trench having two planes parallel to the light incident surface, but the number of parallel planes (the number of steps of the staircase) is not limited to this.

[0124] (Seventh Embodiment) The photoelectric conversion device according to the seventh embodiment will be described with reference to FIGS. 23 and 24.

[0125] The parts that are common to the descriptions from the first embodiment to the sixth embodiment are omitted, and the parts that are mainly different from the first embodiment will be described.

[0126] FIG. 23 is a cross-sectional view in a direction perpendicular to the plane direction of the semiconductor layer of the photoelectric conversion element 102 of the photoelectric conversion device according to the seventh embodiment. In the photoelectric conversion device according to the present embodiment, compared with the photoelectric conversion device according to the first embodiment, the ratio of the N-type first semiconductor region 311 occupying the light receiving surface of the pixel is large, and the seventh semiconductor region 317 is disposed between the first semiconductor region 311 and the second semiconductor region 312.

[0127] Further, the concavo-convex structure 325 has a quadrangular pyramid shape such that its cross section is triangular with the light incident surface as the bottom surface.

[0128] FIG. 24 is a pixel plan view of two pixels of a photoelectric conversion device according to the seventh embodiment. FIG. 24(a) is a plan view in a plan view from the surface facing the light incident surface, and FIG. 24(b) is a plan view in a plan view from the light incident surface side.

[0129] In a plan view from the light incident surface side, a third semiconductor region 313 is disposed between the first semiconductor region 311 and the second semiconductor region 312. The incident light is avalanche multiplied between the first semiconductor region 311 and the second semiconductor region 312. Therefore, when the pixel opening is designed such that the first semiconductor region 311 and the second semiconductor region 312 are exposed, the aperture ratio of the photoelectric conversion device according to the present embodiment is smaller than that of the photoelectric conversion devices according to the first to fifth embodiments. By reducing the aperture ratio, the volume of the photoelectric conversion region where signals can be detected can be suppressed, so that crosstalk can be reduced.

[0130] (Eighth Embodiment) The photoelectric conversion system according to the present embodiment will be described with reference to FIG. 25. FIG. 25 is a block diagram showing a schematic configuration of the photoelectric conversion system according to the present embodiment.

[0131] The photoelectric conversion devices described in the first to sixth embodiments can be applied to various photoelectric conversion systems. Examples of applicable photoelectric conversion systems include digital still cameras, digital camcorders, surveillance cameras, copiers, fax machines, mobile phones, in-vehicle cameras, observation satellites, and the like. In addition, a camera module including an optical system such as a lens and an imaging device is also included in the photoelectric conversion system. FIG. 25 illustrates a block diagram of a digital still camera as an example of these.

[0132] The photoelectric conversion system illustrated in FIG. 25 includes an imaging device 1004 which is an example of a photoelectric conversion device, and a lens 1002 that forms an optical image of a subject on the imaging device 1004. Further, it has a diaphragm 1003 for varying the amount of light passing through the lens 1002, and a barrier 1001 for protecting the lens 1002. The lens 1002 and the diaphragm 1003 are an optical system that condenses light on the imaging device 1004. The imaging device 1004 is a photoelectric conversion device according to any of the above embodiments, and converts the optical image formed by the lens 1002 into an electrical signal.

[0133] The photoelectric conversion system also has a signal processing unit 1007 which is an image generation unit that generates an image by processing the output signal output from the imaging device 1004. The signal processing unit 1007 performs operations such as various corrections and compressions as necessary to output image data. The signal processing unit 1007 may be formed on the semiconductor substrate on which the imaging device 1004 is provided, or may be formed on a semiconductor substrate different from the imaging device 1004.

[0134] The photoelectric conversion system further has a memory unit 1010 for temporarily storing image data, and an external interface unit (external I / F unit) 1013 for communicating with an external computer or the like. Further, the photoelectric conversion system has a recording medium 1012 such as a semiconductor memory for recording or reading imaging data, and a recording medium control interface unit (recording medium control I / F unit) 1011 for recording or reading from the recording medium 1012. Note that the recording medium 1012 may be built into the photoelectric conversion system, or may be detachable.

[0135] Furthermore, the photoelectric conversion system has an overall control and arithmetic unit 1009 that performs various operations and controls the entire digital still camera, and a timing generation unit 1008 that outputs various timing signals to the imaging device 1004 and the signal processing unit 1007. Here, the timing signal or the like may be input from the outside, and the photoelectric conversion system may have at least the imaging device 1004 and the signal processing unit 1007 that processes the output signal output from the imaging device 1004.

[0136] The imaging device 1004 outputs an imaging signal to the signal processing unit 1007. The signal processing unit 1007 performs predetermined signal processing on the imaging signal output from the imaging device 1004 and outputs image data. The signal processing unit 1007 generates an image using the imaging signal.

[0137] As described above, according to the present embodiment, a photoelectric conversion system to which the photoelectric conversion device (imaging device) of any of the above embodiments is applied can be realized.

[0138] (The Ninth Embodiment) The photoelectric conversion system and the moving body of the present embodiment will be described with reference to FIG. 26. FIG. 26 is a diagram showing the configuration of the photoelectric conversion system and the moving body of the present embodiment.

[0139] FIG. 26(a) shows an example of a photoelectric conversion system related to an in-vehicle camera. The photoelectric conversion system 1300 includes an imaging device 1310. The imaging device 1310 is a photoelectric conversion device described in any of the above embodiments. The photoelectric conversion system 1300 has an image processing unit 1312 that performs image processing on a plurality of image data acquired by the imaging device 1310, and a parallax acquisition unit 1314 that calculates parallax (phase difference of a parallax image) from the plurality of image data acquired by the photoelectric conversion system 1300. Further, the photoelectric conversion system 1300 has a distance acquisition unit 1316 that calculates the distance to an object based on the calculated parallax, and a collision determination unit 1318 that determines whether there is a possibility of collision based on the calculated distance. Here, the parallax acquisition unit 1314 and the distance acquisition unit 1316 are examples of distance information acquisition means for acquiring distance information to an object. That is, the distance information is information related to parallax, defocus amount, distance to an object, and the like. The collision determination unit 1318 may determine the possibility of collision using any of these distance information. The distance information acquisition means may be realized by dedicatedly designed hardware, or may be realized by a software module. Further, it may be realized by an FPGA (Field Programmable Gate Array), an ASIC (Application Specific Integrated Circuit), or the like, or may be realized by a combination of these.

[0140] The photoelectric conversion system 1300 is connected to a vehicle information acquisition device 1320 and can acquire vehicle information such as vehicle speed, yaw rate, and steering angle. Further, the photoelectric conversion system 1300 is connected to a control ECU 1330, which is a control unit that outputs a control signal for generating a braking force for the vehicle based on the determination result of the collision determination unit 1318. Further, the photoelectric conversion system 1300 is also connected to an alarm device 1340 that issues an alarm to the driver based on the determination result of the collision determination unit 1318. For example, when the determination result of the collision determination unit 1318 indicates a high possibility of collision, the control ECU 1330 performs vehicle control to avoid collision and reduce damage, such as applying brakes, returning the accelerator, and suppressing engine output. The alarm device 1340 warns the user by sounding an alarm such as a sound, displaying alarm information on a screen of a car navigation system, or applying vibration to a seat belt or steering wheel.

[0141] In the present embodiment, the photoelectric conversion system 1300 images the surroundings of the vehicle, for example, the front or the rear. FIG. 26(b) shows the photoelectric conversion system when imaging the front of the vehicle (imaging range 1350). The vehicle information acquisition device 1320 sends an instruction to the photoelectric conversion system 1300 or the imaging device 1310. With such a configuration, the ranging accuracy can be further improved.

[0142] In the above, an example of controlling so as not to collide with other vehicles has been described, but it is also applicable to control for automatically driving following other vehicles and control for automatically driving so as not to deviate from the lane. Further, the photoelectric conversion system is not limited to vehicles such as the host vehicle, and can be applied to moving bodies (moving devices) such as ships, aircraft, or industrial robots. In addition, it can be applied not only to moving bodies but also to devices that widely utilize object recognition, such as an advanced road traffic system (ITS).

[0143] (Tenth Embodiment) The photoelectric conversion system of the present embodiment will be described with reference to FIG. 27. FIG. 27 is a block diagram showing a configuration example of a distance image sensor that is the photoelectric conversion system of the present embodiment.

[0144] As shown in FIG. 27, the distance image sensor 401 includes an optical system 407, a photoelectric conversion device 408, an image processing circuit 404, a monitor 405, and a memory 406. The distance image sensor 401 can obtain a distance image corresponding to the distance to the subject by projecting light from the light source device 409 toward the subject and receiving the light (modulated light or pulsed light) reflected by the surface of the subject.

[0145] The optical system 407 is configured to have one or more lenses, guide image light (incident light) from the subject to the photoelectric conversion device 408, and form an image on the light receiving surface (sensor unit) of the photoelectric conversion device 408.

[0146] As the photoelectric conversion device 408, the photoelectric conversion devices of the above-described embodiments are applied, and a distance signal indicating the distance obtained from the light reception signal output from the photoelectric conversion device 408 is supplied to the image processing circuit 404.

[0147] The image processing circuit 404 performs image processing for constructing a distance image based on the distance signal supplied from the photoelectric conversion device 408. Then, the distance image (image data) obtained by the image processing is supplied to the monitor 405 for display or supplied to the memory 406 for storage (recording).

[0148] In the distance image sensor 401 configured as described above, by applying the above-described photoelectric conversion device, for example, a more accurate distance image can be obtained as the characteristics of the pixels are improved.

[0149] (Embodiment 11) The photoelectric conversion system of this embodiment will be described with reference to FIG. 28. FIG. 28 is a diagram showing an example of a schematic configuration of an endoscope surgical system which is the photoelectric conversion system of this embodiment.

[0150] In FIG. 28, an operator (doctor) 1131 is shown performing a surgery on a patient 1132 on a patient bed 1133 using an endoscopic surgery system 1150. As shown, the endoscopic surgery system 1150 includes an endoscope 1100, a surgical instrument 1110, and a cart 1134 equipped with various devices for endoscopic surgery.

[0151] The endoscope 1100 includes a lens barrel 1101 whose tip region of a predetermined length is inserted into the body cavity of the patient 1132, and a camera head 1102 connected to the proximal end of the lens barrel 1101. In the illustrated example, an endoscope 1100 configured as a so-called rigid endoscope having a rigid lens barrel 1101 is shown, but the endoscope 1100 may be configured as a so-called flexible endoscope having a flexible lens barrel.

[0152] An opening in which an objective lens is fitted is provided at the tip of the lens barrel 1101. A light source device 1203 is connected to the endoscope 1100, and the light generated by the light source device 1203 is guided to the tip of the lens barrel by a light guide extending inside the lens barrel 1101 and irradiated toward the observation target in the body cavity of the patient 1132 through the objective lens. Note that the endoscope 1100 may be a direct vision endoscope, a forward oblique endoscope, or a side vision endoscope.

[0153] An optical system and a photoelectric conversion device are provided inside the camera head 1102, and the reflected light (observation light) from the observation target is condensed on the photoelectric conversion device by the optical system. The observation light is photoelectrically converted by the photoelectric conversion device, and an electrical signal corresponding to the observation light, that is, an image signal corresponding to the observation image, is generated. As the photoelectric conversion device, the photoelectric conversion devices described in the above embodiments can be used. The image signal is transmitted as RAW data to a camera control unit (CCU) 1135.

[0154] The CCU 1135 is composed of a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), etc., and comprehensively controls the operations of the endoscope 1100 and the display device 1136. Further, the CCU 1135 receives an image signal from the camera head 1102, and performs various image processes for displaying an image based on the image signal, such as development processing (demosaicing processing), on the image signal.

[0155] The display device 1136 displays an image based on the image signal that has been subjected to image processing by the CCU 1135 under the control of the CCU 1135.

[0156] The light source device 1203 is composed of a light source such as an LED (Light Emitting Diode), and supplies irradiation light for photographing the surgical site, etc. to the endoscope 1100.

[0157] The input device 1137 is an input interface for the endoscope surgical system 1150. The user can input various information and give instructions to the endoscope surgical system 1150 via the input device 1137.

[0158] The treatment instrument control device 1138 controls the driving of the energy treatment instrument 1112 for tissue cauterization, incision, or blood vessel sealing, etc.

[0159] The light source device 1203 that supplies irradiation light for photographing the surgical site with the endoscope 1100 can be configured from, for example, an LED, a laser light source, or a white light source composed of a combination thereof. When a white light source is configured by a combination of RGB laser light sources, since the output intensity and output timing of each color (each wavelength) can be controlled with high precision, the white balance of the captured image can be adjusted in the light source device 1203. Further, in this case, the laser light from each of the RGB laser light sources is irradiated to the observation target in a time-division manner, and by controlling the driving of the imaging element of the camera head 1102 in synchronization with the irradiation timing, it is also possible to capture images corresponding to each of RGB in a time-division manner. According to this method, a color image can be obtained without providing a color filter on the imaging element.

[0160] Further, the driving of the light source device 1203 may be controlled so as to change the intensity of the output light at predetermined time intervals. By controlling the driving of the imaging element of the camera head 1102 in synchronization with the timing of the change in the intensity of the light and acquiring images in a time-division manner and synthesizing the images, it is possible to generate a high-dynamic-range image without so-called black crush and white clip.

[0161] Further, the light source device 1203 may be configured to be able to supply light in a predetermined wavelength band corresponding to special light observation. In special light observation, for example, the wavelength dependence of light absorption in body tissue is utilized. Specifically, by irradiating light with a narrower band than the irradiation light (that is, white light) during normal observation, a predetermined tissue such as blood vessels in the mucosal surface layer can be photographed with high contrast. Alternatively, in special light observation, fluorescence observation may be performed to obtain an image by fluorescence generated by irradiating excitation light. In fluorescence observation, it is possible to irradiate body tissue with excitation light and observe the fluorescence from the body tissue, or to locally inject a reagent such as indocyanine green (ICG) into the body tissue and irradiate the body tissue with excitation light corresponding to the fluorescence wavelength of the reagent to obtain a fluorescence image. The light source device 1203 can be configured to be able to supply such narrow-band light and / or excitation light corresponding to special light observation.

[0162] (Embodiment 12) The photoelectric conversion system of this embodiment will be described with reference to FIGS. 29(a) and (b). FIG. 29(a) illustrates glasses 1600 (smart glasses), which are the photoelectric conversion system of this embodiment. The glasses 1600 include a photoelectric conversion device 1602. The photoelectric conversion device 1602 is the photoelectric conversion device described in each of the above embodiments. Also, a display device including a light-emitting device such as an OLED or an LED may be provided on the back side of the lens 1601. There may be one or more photoelectric conversion devices 1602, or a plurality of them may be used. Also, a combination of multiple types of photoelectric conversion devices may be used. The arrangement position of the photoelectric conversion device 1602 is not limited to FIG. 29(a).

[0163] The glasses 1600 further include a control device 1603. The control device 1603 functions as a power supply that supplies power to the photoelectric conversion device 1602 and the above display device. Also, the control device 1603 controls the operations of the photoelectric conversion device 1602 and the display device. An optical system for condensing light onto the photoelectric conversion device 1602 is formed in the lens 1601.

[0164] FIG. 29(b) illustrates glasses 1610 (smart glasses) according to one application example. The glasses 1610 have a control device 1612, and a photoelectric conversion device corresponding to the photoelectric conversion device 1602 and a display device are mounted on the control device 1612. An optical system for the photoelectric conversion device within the control device 1612 and for projecting light emitted from the display device is formed in the lens 1611, and an image is projected onto the lens 1611. The control device 1612 functions as a power supply that supplies power to the photoelectric conversion device and the display device, and controls the operations of the photoelectric conversion device and the display device. The control device may have a gaze detection unit that detects the wearer's gaze. Infrared rays may be used for gaze detection. An infrared light emitting unit emits infrared light to the eyeball of the user who is gazing at the display image. An imaging unit having a light receiving element detects the reflected light of the emitted infrared light from the eyeball, thereby obtaining an imaging image of the eyeball. By having a reduction means for reducing the light from the infrared light emitting unit to the display unit in a frontal view, a reduction in image quality is reduced.

[0165] The user's line of sight with respect to the display image is detected from the captured image of the eyeball obtained by infrared imaging. Any known method can be applied to the line-of-sight detection using the captured image of the eyeball. As an example, a line-of-sight detection method based on the Purkinje image by the reflection of the irradiation light on the cornea can be used.

[0166] More specifically, a line-of-sight detection process based on the pupillary corneal reflex method is performed. Using the pupillary corneal reflex method, a line-of-sight vector representing the orientation (rotation angle) of the eyeball is calculated based on the image of the pupil and the Purkinje image included in the captured image of the eyeball, thereby detecting the user's line of sight.

[0167] The display device of the present embodiment may include a photoelectric conversion device having a light receiving element, and control the display image of the display device based on the user's line-of-sight information from the photoelectric conversion device.

[0168] Specifically, the display device determines a first visual field region that the user is gazing at and a second visual field region other than the first visual field region based on the line-of-sight information. The first visual field region and the second visual field region may be determined by the control device of the display device, or may receive those determined by an external control device. In the display area of the display device, the display resolution of the first visual field region may be controlled to be higher than that of the second visual field region. That is, the resolution of the second visual field region may be made lower than that of the first visual field region.

[0169] Further, the display area has a first display area and a second display area different from the first display area, and based on the line-of-sight information, a region with a higher priority may be determined from the first display area and the second display area. The first visual field region and the second visual field region may be determined by the control device of the display device, or may receive those determined by an external control device. The resolution of the region with a higher priority may be controlled to be higher than that of the region other than the region with a higher priority. That is, the resolution of the region with a relatively lower priority may be made lower.

[0170] Note that AI may be used to determine the first visual field area or the area with high priority. The AI may be a model configured to estimate the angle of the line of sight and the distance to the object at the tip of the line of sight from the eye image, using the eye image and the direction in which the eye in the image is actually looking as teacher data. The AI program may be provided in the display device, the photoelectric conversion device, or an external device. When provided in an external device, it is transmitted to the display device via communication.

[0171] When performing display control based on visual recognition detection, it is preferably applicable to smart glasses further having a photoelectric conversion device that images the outside. The smart glasses can display the captured external information in real time.

[0172] [Modified Embodiment] The present invention is not limited to the above embodiments, and various modifications are possible.

[0173] For example, embodiments of the present invention also include examples in which a part of the configuration of one embodiment is added to another embodiment, or examples in which a part of the configuration of another embodiment is replaced.

[0174] Also, the photoelectric conversion systems shown in the above seventh and eighth embodiments are examples of photoelectric conversion systems to which a photoelectric conversion device can be applied, and the photoelectric conversion systems applicable to the photoelectric conversion device of the present invention are not limited to the configurations shown in FIGS. 25 to 26. The same applies to the ToF system shown in the tenth embodiment, the endoscope shown in the eleventh embodiment, and the smart glasses shown in the twelfth embodiment.

[0175] Note that the above embodiments are merely specific examples for implementing the present invention, and the technical scope of the present invention should not be construed in a limited manner by these. That is, the present invention can be implemented in various forms without departing from its technical idea or its main features.

Explanation of Reference Numerals

[0176] 100 Photoelectric conversion device 101 pixels 311 First semiconductor region 312 Second semiconductor region 325 Concavo-convex structure

Claims

1. A photoelectric conversion device having a plurality of avalanche diodes arranged in a semiconductor layer having a first surface and a second surface opposite to the first surface, Each of the plurality of avalanche diodes includes a first semiconductor region of a first conductivity type disposed at a first depth, and a second semiconductor region of a second conductivity type disposed at a second depth that is deeper than the first depth relative to the second surface; the semiconductor layer has a relief structure provided on the first surface, a first period of the concave-convex structure being smaller than hc / eEa (h: Planck's constant, c: speed of light, e: elementary charge, Ea: band gap of the semiconductor layer);

2. the uneven structure is formed by a trench structure, The width of the trench structure is hc / 2eE ａ (h: Planck constant, c: speed of light, e: elementary charge, E ａ 2. The photoelectric conversion device according to claim 1, wherein the band gap of the semiconductor layer is smaller than the band gap of the semiconductor layer.

3. A photoelectric conversion device having a plurality of avalanche diodes arranged in a semiconductor layer having a first surface and a second surface opposite to the first surface, Each of the plurality of avalanche diodes includes a first semiconductor region of a first conductivity type disposed at a first depth, and a second semiconductor region of a second conductivity type disposed at a second depth that is deeper than the first depth relative to the second surface; the semiconductor layer has a relief structure provided on the first surface, A photoelectric conversion device, wherein the effective period of the uneven structure is smaller than 1.1 μm.

4. the uneven structure is formed by a trench structure, 4. The photoelectric conversion device according to claim 3, wherein the width of the trench structure is less than 0.55 [mu]m.

5. 5. The photoelectric conversion device according to claim 1, further comprising a third semiconductor region of the second conductivity type arranged at a third depth that is deeper than the second depth relative to the second surface.

6. a fourth semiconductor region of the first conductivity type is provided between the second semiconductor region and the third semiconductor region; 6. The photoelectric conversion device according to claim 5, wherein a concentration of the first conductive type impurity in the fourth semiconductor region is lower than a concentration of the first conductive type impurity in the first semiconductor region.

7. In a plan view from a direction perpendicular to the first surface, 7. The photoelectric conversion device according to claim 6, wherein an area of ​​the uneven structure overlapping the fourth semiconductor region is larger than an area of ​​the uneven structure not overlapping the fourth semiconductor region.

8. a fifth semiconductor region is provided, the fifth semiconductor region being disposed at the first depth and surrounding the first semiconductor region in a plan view from the first surface; 8. The photoelectric conversion device according to claim 1, wherein an impurity concentration in the fifth semiconductor region is lower than an impurity concentration in the first semiconductor region.

9. 9. The photoelectric conversion device according to claim 8, wherein a potential difference between the first semiconductor region and the second semiconductor region is larger than a potential difference between the second semiconductor region and the fifth semiconductor region.

10. In a plan view from a direction perpendicular to the first surface, 10. The photoelectric conversion device according to claim 1, wherein a multiplication region formed between the first semiconductor region and the second semiconductor region is included in the uneven structure.

11. In a plan view in a direction perpendicular to the first surface, The photoelectric conversion device according to claim 10 , wherein the center of gravity of the concave-convex structure is included in the multiplication region.

12. the plurality of avalanche diodes include a first avalanche diode and a second avalanche diode adjacent to the first avalanche diode; 12. The photoelectric conversion device according to claim 10, further comprising a pixel separating section between the first avalanche diode and the second avalanche diode.

13. the plurality of avalanche diodes includes a third avalanche diode adjacent to the second avalanche diode; a first pixel isolation portion between the first avalanche diode and the second avalanche diode; a second pixel isolation portion between the second avalanche diode and the third avalanche diode; 13. The photoelectric conversion device according to claim 12, wherein the second semiconductor region in the second avalanche diode extends from the first pixel isolation portion to the second pixel isolation portion in a cross section perpendicular to the first surface.

14. In each of the plurality of avalanche diodes, when a distance from the pixel isolation unit to a closest pixel isolation unit is L, 14. The photoelectric conversion device according to claim 13, wherein a distance d from the first surface to the multiplication region satisfies L√2 / 4<d<L×√2.

15. an anti-reflection film laminated on the second surface side of the concave-convex structure; 15. The photoelectric conversion device according to claim 10, wherein the refractive index of the anti-reflection film is higher than the effective refractive index of a region that overlaps with the multiplication region in a planar view in a direction perpendicular to the first surface and is sandwiched between the surface of the uneven structure on the second surface side and the first surface.

16. In a plan view from a direction perpendicular to the first surface, 16. The photoelectric conversion device according to claim 1, wherein the uneven structure includes a T-shaped trench structure.

17. In a plan view from a direction perpendicular to the first surface, 17. The photoelectric conversion device according to claim 1, wherein the concave-convex structure includes a non-periodically configured trench structure.

18. 18. The photoelectric conversion device according to claim 1, wherein the density distribution of the uneven structure is not uniform within the first surface.

19. 19. The photoelectric conversion device according to claim 18, wherein the density of the uneven structure in the central portion of the avalanche diode is higher than the density of the uneven structure in the outer edge portion of the avalanche diode.

20. The photoelectric conversion device according to any one of claims 1 to 19, characterized in that the uneven structure has a first uneven structure and a second uneven structure, and the depth from the first surface to the bottom of the first uneven structure is different from the depth from the first surface to the bottom of the second uneven structure.

21. The photoelectric conversion device according to claim 20, characterized in that the depth from the first surface to the bottom of the first uneven structure arranged in the center of the avalanche diode is deeper than the depth from the first surface to the bottom of the second uneven structure arranged in the outer edge of the avalanche diode.

22. The photoelectric conversion device described in claim 20 or 21, characterized in that the depth from the first surface to the bottom at a portion of the uneven structure where a recess extending in a first direction intersects with a recess extending in a second direction is deeper than the depth from the first surface to the bottom of a recess extending in the second direction that does not intersect with a recess extending in the first direction.

23. The bottom at the intersection is 23. The photoelectric conversion device according to claim 22, wherein the second surface is closer to the first surface than half the distance between the first surface and the second surface.

24. 24. The photoelectric conversion device according to claim 1, wherein the uneven structure is made up of a plurality of independent regions in a plan view in a direction perpendicular to the first surface.

25. 25. The photoelectric conversion device according to claim 1, wherein the uneven structure has voids.

26. 26. The photoelectric conversion device according to claim 1, wherein the uneven structure has a pinning film.

27. 27. The photoelectric conversion device according to claim 1, wherein the effective period of the uneven structure is smaller than a wavelength at which the optical absorption length of the semiconductor layer is equal to the distance from the first surface to between the first semiconductor region and the second semiconductor region.

28. The photoelectric conversion device according to any one of claims 1 to 27, a signal processing unit that generates an image using a signal output from the photoelectric conversion device.

29. A moving object comprising the photoelectric conversion device according to any one of claims 1 to 27, A control unit that controls the movement of the moving body using a signal output from the photoelectric conversion device. A moving object characterized by:

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