Photoelectric conversion element and photoelectric conversion device

Abstract

To achieve a photoelectric conversion element and a photoelectric conversion device that can achieve a reduction in drive voltage.SOLUTION: A photoelectric conversion element has a first semiconductor region of a first conductivity type provided in contact with a first surface of a semiconductor layer, a second semiconductor region of a second conductivity type provided closer to a second surface of the semiconductor layer than the first semiconductor region, and a third semiconductor region provided closer to the second surface than the second semiconductor region. The first semiconductor region and the second semiconductor region constitute an avalanche photodiode, and the avalanche photodiode multiplies a signal charge generated in the third semiconductor region. In the second semiconductor region, a region with an effective impurity concentration of 1×1016 cm-3 or more has a width in a depth direction of 0.5 μm or less.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a photoelectric conversion element and a photoelectric conversion device. [Background technology]

[0002] Single photon avalanche diodes (SPADs) are known as detectors capable of detecting weak light at the single photon level. SPADs use the avalanche multiplication phenomenon that occurs due to a strong electric field induced in a PN junction of a semiconductor to amplify the signal charge excited by photons by several to several million times. The current generated by the avalanche multiplication phenomenon is converted into a pulse signal, and the number of pulse signals is counted, thereby making it possible to directly measure the number of incident photons. Patent Document 1 describes a photodetector and a photodetection system that use a SPAD. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-057650 Summary of the Invention [Problem to be solved by the invention]

[0004] SPADs are devices with extremely high current gain and operate at high voltages, requiring a large amount of energy per signal charge. Therefore, sensors using SPAD pixels require significantly more power than CMOS sensors and suffer from significant degradation of device characteristics due to heat generation. Furthermore, in the SPAD pixels described in Patent Document 1, reducing the pixel size strengthens the lateral electric field between the high-impurity-concentration N-type semiconductor region that constitutes the cathode and the high-impurity-concentration P-type semiconductor region to which the anode electrode is connected, resulting in an increase in dark current due to surface states. An object of the present invention is to provide a photoelectric conversion element and a photoelectric conversion device that can realize a lower driving voltage. [Means for solving the problem]

[0005] According to one disclosure of the present specification, there is provided a photoelectric conversion element provided in a semiconductor layer having a first surface and a second surface opposite to the first surface, the photoelectric conversion element including: a first semiconductor region of a first conductivity type provided in contact with the first surface; a second semiconductor region of a second conductivity type provided closer to the second surface than the first semiconductor region; and a third semiconductor region provided closer to the second surface than the second semiconductor region. a first impurity doped region doped with the first conductivity type impurity; a first electrode electrically connected to the first semiconductor region and a second electrode electrically connected to the second semiconductor region, the first semiconductor region and the second semiconductor region constituting an avalanche photodiode, the avalanche photodiode being configured to multiply signal charges generated in the third semiconductor region, and the second semiconductor region having an effective impurity density of 1×10 16 cm -3 The width of the region in the depth direction where the thickness is equal to or greater than 0.5 μm is 0.5 μm or less. The first impurity doped region overlaps with the second semiconductor region in a plan view and in a depth direction, the depth at which the density of the first conductivity type impurity constituting the first impurity doped region reaches a peak is deeper than the depth at which the density of the second conductivity type impurity constituting the second semiconductor region reaches a peak, and the impurity density per unit area of ​​the second conductivity type impurity constituting the second semiconductor region is 3×10 12 cm -2 and the impurity density per unit area of ​​the first conductivity type impurity constituting the first impurity doped region is 5×10 11 cm -2 or less than half the impurity density per unit area of ​​the second conductivity type impurity constituting the second semiconductor region. A photoelectric conversion element is provided. [Effects of the Invention]

[0006] According to the present invention, it is possible to reduce the driving voltage of a photoelectric conversion element and a photoelectric conversion device, which makes it possible to realize energy savings by reducing power consumption, alleviate deterioration of element characteristics by reducing heat generation, and reduce dark current. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a block diagram (part 1) showing a schematic configuration of a photoelectric conversion device according to a first embodiment of the present invention. [Figure 2]FIG. 2 is a block diagram (part 2) showing a schematic configuration of the photoelectric conversion device according to the first embodiment of the present invention. [Figure 3] 1 is a block diagram showing an example of the configuration of a pixel of a photoelectric conversion device according to a first embodiment of the present invention. [Figure 4] 1 is a perspective view showing an example of the configuration of a photoelectric conversion device according to a first embodiment of the present invention. [Figure 5] FIG. 2 is a diagram illustrating the basic operation of a photoelectric conversion unit of the photoelectric conversion device according to the first embodiment of the present invention. [Figure 6] 1 is a plan view showing the structure of a photoelectric conversion element of a photoelectric conversion device according to a first embodiment of the present invention. [Figure 7] 1 is a schematic cross-sectional view showing the structure of a photoelectric conversion element of a photoelectric conversion device according to a first embodiment of the present invention. [Figure 8] FIG. 3 is a diagram showing the depth profile of the impurity density in the photoelectric conversion element of the photoelectric conversion device according to the first embodiment of the present invention. [Figure 9] FIG. 2 is a diagram showing a potential distribution in a photoelectric conversion element of the photoelectric conversion device according to the first embodiment of the present invention. [Figure 10] FIG. 10 is a plan view showing the structure of a photoelectric conversion element of a photoelectric conversion device according to a second embodiment of the present invention. [Figure 11] FIG. 4 is a schematic cross-sectional view showing the structure of a photoelectric conversion element of a photoelectric conversion device according to a second embodiment of the present invention. [Figure 12] FIG. 10 is a schematic cross-sectional view showing the structure of a photoelectric conversion element of a photoelectric conversion device according to a third embodiment of the present invention. [Figure 13] FIG. 10 is a block diagram showing a schematic configuration of a light detection system according to a fourth embodiment of the present invention. [Figure 14] FIG. 10 is a block diagram showing a schematic configuration of a range image sensor according to a fifth embodiment of the present invention. [Figure 15] FIG. 10 is a schematic diagram showing an example of the configuration of an endoscopic surgery system according to a sixth embodiment of the present invention. [Figure 16] FIG. 13 is a schematic diagram showing an example of the configuration of a moving body according to a seventh embodiment of the present invention. [Figure 17]FIG. 13 is a block diagram showing a schematic configuration of a light detection system according to a seventh embodiment of the present invention. [Figure 18] FIG. 13 is a flowchart showing the operation of the light detection system according to the seventh embodiment of the present invention. [Figure 19] FIG. 13 is a schematic diagram showing a schematic configuration of a light detection system according to an eighth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0008] The embodiments shown below are intended to embody the technical concept of the present invention and are not intended to limit the present invention. The size and positional relationship of components shown in each drawing may be exaggerated for clarity. In the following description, the same components may be designated by the same reference numerals and their description may be omitted.

[0009] [First embodiment] The schematic configuration of a photoelectric conversion device according to a first embodiment of the present invention will be described with reference to Figs. 1 to 4. Figs. 1 and 2 are block diagrams showing the schematic configuration of a photoelectric conversion device according to this embodiment. Fig. 3 is a block diagram showing an example configuration of a pixel of a photoelectric conversion device according to this embodiment. Fig. 4 is a perspective view showing an example configuration of a photoelectric conversion device according to this embodiment.

[0010] As shown in FIG. 1, the photoelectric conversion device 100 according to this embodiment has a pixel region 10, a vertical scanning circuit section 40, a readout circuit section 50, a horizontal scanning circuit section 60, an output circuit section 70, and a control pulse generation section 80.

[0011] The pixel region 10 includes a plurality of pixels 12 arranged in an array of a plurality of rows and a plurality of columns. As described below, each pixel 12 may be composed of a photoelectric conversion unit including a photoelectric conversion element and a pixel signal processing unit that processes a signal output from the photoelectric conversion unit. The number of pixels 12 constituting the pixel region 10 is not particularly limited. For example, the pixel region 10 may be composed of a plurality of pixels 12 arranged in an array of several thousand rows and several thousand columns, as in a typical digital camera. Alternatively, the pixel region 10 may be composed of a plurality of pixels 12 arranged in a single row or a single column. Alternatively, the pixel region 10 may be composed of a single pixel 12.

[0012] A control line 14 is arranged in each row of the pixel array in the pixel region 10, extending in a first direction (the horizontal direction in FIG. 1 ). The control line 14 is connected to each of the pixels 12 aligned in the first direction and serves as a signal line common to these pixels 12. The first direction in which the control lines 14 extend may be referred to as the row direction or horizontal direction. Each of the control lines 14 may include multiple signal lines for supplying multiple types of control signals to the pixels 12. The control lines 14 in each row are connected to a vertical scanning circuit unit 40.

[0013] In addition, data lines 16 are arranged in each column of the pixel array in the pixel region 10, extending in a second direction (the vertical direction in FIG. 1 ) intersecting the first direction. The data lines 16 are connected to the pixels 12 aligned in the second direction, respectively, and serve as signal lines common to these pixels 12. The second direction in which the data lines 16 extend may be referred to as the column direction or vertical direction. Each of the data lines 16 may include multiple signal lines for transferring multi-bit digital signals output from the pixels 12 bit by bit.

[0014] The control lines 14 of each row are connected to a vertical scanning circuit unit 40. The vertical scanning circuit unit 40 is a control unit that receives control signals output from the control pulse generation unit 80, generates control signals for driving the pixels 12, and supplies the control signals to the pixels 12 via the control lines 14. The vertical scanning circuit unit 40 may include logic circuits such as a shift register and an address decoder. The vertical scanning circuit unit 40 sequentially scans the pixels 12 in the pixel region 10 row by row, and sequentially outputs pixel signals of each pixel 12 to the readout circuit unit 50 via the data lines 16.

[0015] The data lines 16 of each column are connected to a readout circuit unit 50. The readout circuit unit 50 includes a plurality of holding units (not shown) provided corresponding to each column of the pixel array of the pixel region 10, and has a function of holding pixel signals of the pixels 12 of each column, which are output row by row from the pixel region 10 via the data lines 16, in the holding unit of the corresponding column.

[0016] The horizontal scanning circuit unit 60 is a control unit that receives a control signal output from the control pulse generation unit 80, generates a control signal for reading out pixel signals from the holding units of each column of the readout circuit unit 50, and supplies the control signal to the readout circuit unit 50. The horizontal scanning circuit unit 60 may use logic circuits such as a shift register and an address decoder. The horizontal scanning circuit unit 60 sequentially scans the holding units of each column of the readout circuit unit 50, and sequentially outputs the pixel signals held in each to the output circuit unit 70.

[0017] The output circuit unit 70 has an external interface circuit and is a circuit unit for outputting the pixel signals output from the readout circuit unit 50 to the outside of the photoelectric conversion device 100. The external interface circuit included in the output circuit unit 70 is not particularly limited. For example, a SerDes (SERializer / DESerializer) transmission circuit such as an LVDS (Low Voltage Differential Signaling) circuit or an SLVS (Scalable Low Voltage Signaling) circuit can be used as the external interface circuit.

[0018] The control pulse generation unit 80 is a control circuit that generates control signals for controlling the operation and timing of the vertical scanning circuit unit 40, the readout circuit unit 50, and the horizontal scanning circuit unit 60, and supplies these to each functional block. Note that at least some of the control signals for controlling the operation and timing of the vertical scanning circuit unit 40, the readout circuit unit 50, and the horizontal scanning circuit unit 60 may be supplied from outside the photoelectric conversion device 100.

[0019] The connection of the functional blocks of the photoelectric conversion device 100 is not limited to the example configuration shown in FIG. 1, and may be configured as shown in FIG. 2, for example.

[0020] In the configuration example of FIG. 2, data lines 16 extending in a first direction are arranged in each row of the pixel array in the pixel region 10. The data lines 16 are connected to the pixels 12 aligned in the first direction, respectively, and serve as signal lines common to these pixels 12. Furthermore, control lines 18 extending in a second direction are arranged in each column of the pixel array in the pixel region 10. The control lines 18 are connected to the pixels 12 aligned in the second direction, respectively, and serve as signal lines common to these pixels 12.

[0021] The control line 18 of each column is connected to a horizontal scanning circuit unit 60. The horizontal scanning circuit unit 60 receives a control signal output from the control pulse generation unit 80, generates a control signal for reading out pixel signals from the pixels 12, and supplies the control signal to the pixels 12 via the control line 18. Specifically, the horizontal scanning circuit unit 60 sequentially scans the multiple pixels 12 in the pixel region 10 column by column, and outputs pixel signals of the pixels 12 in each row belonging to the selected column to the data line 16.

[0022] The data lines 16 of each row are connected to a readout circuit unit 50. The readout circuit unit 50 includes a plurality of holding units (not shown) provided corresponding to each row of the pixel array of the pixel region 10, and has a function of holding pixel signals of the pixels 12 of each row, which are output column by column from the pixel region 10 via the data lines 16, in the holding unit of the corresponding row.

[0023] The readout circuit section 50 receives a control signal output from the control pulse generation section 80, and sequentially outputs the pixel signals held in the holding section of each row to the output circuit section . Other components in the configuration example of FIG. 2 may be similar to those in the configuration example of FIG.

[0024] 3, each pixel 12 may be configured with a photoelectric conversion unit 20 and a pixel signal processing unit 30. The photoelectric conversion unit 20 may be configured with, for example, a photoelectric conversion element 22 and a quenching element 24. The pixel signal processing unit 30 may be configured with, for example, a waveform shaping unit 32, a counter circuit 34, and a selection circuit 36.

[0025] The photoelectric conversion element 22 may be an avalanche photodiode (hereinafter referred to as "APD"). The anode of the APD constituting the photoelectric conversion element 22 is connected to a node to which a voltage VL is supplied. The cathode of the APD constituting the photoelectric conversion element 22 is connected to one terminal of the quench element 24. The connection node between the photoelectric conversion element 22 and the quench element 24 is the output node of the photoelectric conversion unit 20. The other terminal of the quench element 24 is connected to a node to which a voltage VH higher than the voltage VL is supplied. The voltages VL and VH are set so that a reverse bias voltage sufficient for the APD to perform avalanche multiplication operation is applied. For example, a negative high voltage is applied as the voltage VL, and a positive voltage approximately equal to the power supply voltage is applied as the voltage VH. For example, the voltage VL may be −30 V and the voltage VH may be 3 V; however, from the viewpoints of improving element characteristics and suppressing degradation, it is desirable to lower the driving voltage of the APD.

[0026] As described above, the photoelectric conversion element 22 may be configured with an APD. When a reverse bias voltage sufficient for avalanche multiplication is applied to the APD, the charge generated by light incident on the APD undergoes avalanche multiplication, generating an avalanche current. When a reverse bias voltage is applied to the APD, the APD can operate in either Geiger mode or linear mode. In Geiger mode, a reverse bias voltage greater than the breakdown voltage of the APD is applied between the anode and cathode. In linear mode, a reverse bias voltage close to or less than the breakdown voltage of the APD is applied between the anode and cathode. An APD operating in Geiger mode is called a single photon avalanche diode (SPAD). The APD constituting the photoelectric conversion element 22 may operate in either linear mode or Geiger mode.

[0027] In this embodiment, the anode of the APD is set to a fixed potential, and a signal is extracted from the cathode side. That is, the first conductivity type semiconductor region, in which charges of the same polarity as the signal charges serve as majority carriers, is an N-type semiconductor region, and the second conductivity type semiconductor region, in which charges of the opposite polarity to the signal charges serve as majority carriers, is a P-type semiconductor region. The first conductivity type carriers are electrons, and the second conductivity type carriers are holes. The first conductivity type impurities are donor impurities, and the second conductivity type impurities are acceptor impurities. The following describes a case where one node of the APD is set to a fixed potential, but the potentials of both nodes may fluctuate.

[0028] Conversely to the above example, it is also possible to configure the APD so that the cathode is at a fixed potential and the signal is extracted from the anode side. In this case, the first conductivity type semiconductor region, whose majority carriers are charges of the same polarity as the signal charge, is a P-type semiconductor region, and the second conductivity type semiconductor region, whose majority carriers are charges of the opposite polarity to the signal charge, is an N-type semiconductor region. The first conductivity type carriers are holes, and the second conductivity type carriers are electrons. The first conductivity type impurities are acceptor impurities, and the second conductivity type impurities are donor impurities. In a configuration in which holes are detected as signal charges, the conductivity types of the semiconductor regions described below are opposite.

[0029] The quench element 24 has a function of converting a change in the avalanche current generated in the photoelectric conversion element 22 into a voltage signal. The quench element 24 also functions as a load circuit (quench circuit) during signal multiplication by avalanche multiplication, and has a function of reducing the voltage applied to the photoelectric conversion element 22 to suppress avalanche multiplication. The operation of the quench element 24 to suppress avalanche multiplication is called a quench operation. The quench element 24 also has a function of returning the voltage supplied to the photoelectric conversion element 22 to voltage VH by flowing a current equivalent to the voltage drop caused by the quench operation. The operation of the quench element 24 to return the voltage supplied to the photoelectric conversion element 22 to voltage VH is called a recharge operation. The quench element 24 can be configured using a resistor element, a MOS transistor, or the like.

[0030] The waveform shaping unit 32 has an input node to which the output signal of the photoelectric conversion unit 20 is input, and an output node. The waveform shaping unit 32 has a function of converting the analog signal output from the photoelectric conversion unit 20 into a pulse signal. The waveform shaping unit 32 can be configured using a NOT circuit (inverter circuit), for example, as shown in FIG. 3. While FIG. 3 shows an example in which the waveform shaping unit 32 is configured using a single inverter circuit, the waveform shaping unit 32 may also be configured using a circuit in which multiple inverter circuits are connected in series. Furthermore, the waveform shaping unit 32 can be configured not only using a NOT circuit, but also using other circuits that have a waveform shaping effect, such as logic circuits including NOR circuits and NAND circuits. The output node of the waveform shaping unit 32 is connected to a counter circuit 34.

[0031] The counter circuit 34 has an input node to which the output signal of the waveform shaping unit 32 is input, an input node connected to the control line 14, and an output node. The counter circuit 34 counts the pulses superimposed on the signal output from the waveform shaping unit 32 and holds a count value that is the counting result. Signals supplied to the counter circuit 34 from the vertical scanning circuit unit 40 via the control line 14 may include an enable signal for controlling the pulse count period (exposure period) and a reset signal for resetting the count value held by the counter circuit 34. The output node of the counter circuit 34 is connected to the data line 16 via the selection circuit 36.

[0032] The selection circuit 36 ​​has a function of switching the electrical connection state (connection or non-connection) between the counter circuit 34 and the data line 16. The selection circuit 36 ​​switches the connection state between the counter circuit 34 and the data line 16 in response to a control signal supplied from the vertical scanning circuit unit 40 via the control line 14 (in the configuration example of FIG. 2, a control signal supplied from the horizontal scanning circuit unit 60 via the control line 18). The selection circuit 36 ​​may include a buffer circuit for outputting a signal.

[0033] It should be noted that it is not necessary for one pixel signal processing unit 30 to be provided for each pixel 12, and one pixel signal processing unit 30 may be provided for multiple pixels 12. In this case, it is possible to configure the single pixel signal processing unit 30 to sequentially perform signal processing for multiple pixels 12. Furthermore, when the pixel signal processing unit 30 is made up of a waveform shaping unit 32, a counter circuit 34, and a selection circuit 36, it is not necessary for each pixel signal processing unit 30 to include all of the waveform shaping unit 32, the counter circuit 34, and the selection circuit 36.

[0034] The photoelectric conversion device 100 according to this embodiment may be formed on a single substrate, or may be configured as a stacked photoelectric conversion device in which multiple substrates are stacked. In the latter case, for example, as shown in FIG. 4, a stacked photoelectric conversion device can be configured in which a sensor substrate 110 and a circuit substrate 180 are stacked and electrically connected. At least the photoelectric conversion element 22, which is one of the components of the pixel 12, can be arranged on the sensor substrate 110. Furthermore, among the components of the pixel 12, the quench element 24 and the pixel signal processing unit 30 can be arranged on the circuit substrate 180. The photoelectric conversion element 22, the quench element 24, and the pixel signal processing unit 30 are electrically connected via connection wiring provided for each pixel 12. Furthermore, the circuit substrate 180 can further include a vertical scanning circuit unit 40, a readout circuit unit 50, a horizontal scanning circuit unit 60, an output circuit unit 70, a control pulse generation unit 80, and the like.

[0035] The photoelectric conversion element 22, quench element 24, and pixel signal processing unit 30 of each pixel 12 may be provided on the sensor substrate 110 and the circuit substrate 180 so as to overlap in a plan view. The vertical scanning circuit unit 40, readout circuit unit 50, horizontal scanning circuit unit 60, output circuit unit 70, and control pulse generation unit 80 may be arranged around a pixel region 10 made up of a plurality of pixels 12. Note that "plan view" here refers to a view from a direction perpendicular to the surface of the sensor substrate 110.

[0036] By configuring the stacked photoelectric conversion device 100, it is possible to increase the integration density of elements and achieve higher functionality. In particular, by arranging the photoelectric conversion elements 22, the quenching elements 24, and the pixel signal processing units 30 on separate substrates, it is possible to arrange the photoelectric conversion elements 22 at high density without sacrificing the light-receiving area of ​​the photoelectric conversion elements 22, thereby improving the photon detection efficiency.

[0037] The number of substrates constituting the photoelectric conversion device 100 is not limited to two, and the photoelectric conversion device 100 may be constituted by stacking three or more substrates.

[0038] 4, the sensor substrate 110 and the circuit substrate 180 are assumed to be diced chips, but the sensor substrate 110 and the circuit substrate 180 are not limited to chips. For example, the sensor substrate 110 and the circuit substrate 180 may each be a wafer. The sensor substrate 110 and the circuit substrate 180 may be stacked in the wafer state and then diced, or may be formed into chips and then stacked and bonded.

[0039] Next, the basic operation of the photoelectric conversion unit 20 in the photoelectric conversion device according to this embodiment will be described with reference to Fig. 5. Fig. 5 is a diagram illustrating the basic operation of the photoelectric conversion unit in the photoelectric conversion device according to this embodiment. Fig. 5(a) is a circuit diagram of the photoelectric conversion unit 20 and the waveform shaping unit 32, Fig. 5(b) shows the waveform of the signal at the input node (node ​​A) of the waveform shaping unit 32, and Fig. 5(c) shows the waveform of the signal at the output node (node ​​B) of the waveform shaping unit 32.

[0040] At time t0, a reverse bias voltage with a potential difference equivalent to (VH-VL) is applied to the photoelectric conversion element 22. A reverse bias voltage sufficient to cause avalanche multiplication is applied between the anode and cathode of the APD that constitutes the photoelectric conversion element 22, but in a state where no photons are incident on the photoelectric conversion element 22, no carriers exist to serve as seeds for avalanche multiplication. Therefore, avalanche multiplication does not occur in the photoelectric conversion element 22, and no current flows through the photoelectric conversion element 22.

[0041] At subsequent time t1, a photon is incident on the photoelectric conversion element 22. When the photon is incident on the photoelectric conversion element 22, electron-hole pairs are generated by photoelectric conversion, and avalanche multiplication occurs using these carriers as seeds, causing an avalanche multiplication current to flow through the photoelectric conversion element 22. This avalanche multiplication current flows through the quench element 24, causing a voltage drop across the quench element 24, and the voltage at node A begins to drop. The amount of voltage drop at node A increases, and when the avalanche multiplication operation stops at time t3, the voltage level at node A no longer drops.

[0042] When the avalanche multiplication operation in the photoelectric conversion element 22 stops, a current that compensates for the voltage drop flows from the node to which the voltage VL is supplied to the node A via the photoelectric conversion element 22, and the voltage at the node A gradually increases. After that, at time t5, the node A settles to its original voltage level.

[0043] The waveform shaping unit 32 binarizes the signal input from node A in accordance with a predetermined decision threshold and outputs the binarized signal from node B. Specifically, when the voltage level of node A exceeds the decision threshold, the waveform shaping unit 32 outputs a low-level signal from node B, and when the voltage level of node A is equal to or lower than the decision threshold, the waveform shaping unit 32 outputs a high-level signal from node B. For example, as shown in FIG. 5(b), assume that the voltage of node A is equal to or lower than the decision threshold during the period from time t2 to time t4. In this case, as shown in FIG. 5(c), the signal level at node B is low during the period from time t0 to time t2 and the period from time t4 to time t5, and is high during the period from time t2 to time t4.

[0044] In this way, the analog signal input from node A is waveform-shaped into a digital signal by the waveform shaping unit 32. The pulse signal output from the waveform shaping unit 32 in response to the incidence of a photon on the photoelectric conversion element 22 is a photon detection pulse signal.

[0045] Next, the specific structure of the photoelectric conversion element 22 in the photoelectric conversion device 100 according to this embodiment will be described with reference to Figs. 6 to 8. Fig. 6 is a plan view showing the structure of the photoelectric conversion element of this embodiment. Fig. 7 is a schematic cross-sectional view showing the structure of the photoelectric conversion element of this embodiment. Fig. 8 is a diagram showing the depth profile of the impurity density in the photoelectric conversion element of this embodiment.

[0046] The photoelectric conversion elements 22 of the photoelectric conversion device 100 according to this embodiment may be provided in a semiconductor layer 120 included in the sensor substrate 110 in the configuration shown in FIG. 4, for example. FIG. 6 corresponds to a plan view from the first surface 122 side of the semiconductor layer 120. In the semiconductor layer 120, the photoelectric conversion elements 22 of the plurality of pixels 12 that constitute the pixel region 10 are arranged in a matrix, as shown in FIG. 6, for example. The two-dot chain line shown in FIG. 6 indicates the boundary between adjacent photoelectric conversion elements 22. In this specification, the term "plan view" refers to a view from the normal direction to the surface of the semiconductor layer 120 (the first surface 122 described below). Furthermore, the term "cross section" refers to a cross section parallel to the normal direction to the first surface 122 or the second surface 124 of the semiconductor layer 120.

[0047] Fig. 7 is a cross-sectional view taken along line VI-VI' in Fig. 6, and Fig. 8 shows the depth direction distribution of the impurity density (N) in the semiconductor layer 120 along line AB in Fig. 7. In this specification, the depth direction refers to the direction from the first surface 122 toward the second surface 124, and the depth refers to the distance from the first surface 122.

[0048] The semiconductor layer 120 may be a semiconductor layer obtained by thinning a low-impurity-density semiconductor substrate, for example, a low-impurity-density N-type silicon substrate. The semiconductor layer 120 includes N-type semiconductor regions 126 and 128, P-type semiconductor regions 130, 132, and 134, an N-type impurity-doped region 136, and a semiconductor region 138. Figure 7 shows the density distribution of donor impurities constituting the N-type semiconductor region 126 and the N-type impurity-doped region 136, and the density distribution of acceptor impurities constituting the P-type semiconductor regions 130 and 132. The N-type semiconductor region 128 and the semiconductor region 138 are not shown in the figure because their impurity densities are sufficiently lower than those of the N-type semiconductor region 126, the P-type semiconductor regions 130 and 132, and the N-type impurity-doped region 136, and their influence on these regions is small. A cathode electrode 144 electrically connected to the N-type semiconductor region 126 and an anode electrode 146 electrically connected to the P-type semiconductor region 134 are provided on the first surface 122 of the semiconductor layer 120.

[0049] The N-type semiconductor region 126 is provided from the first surface 122 to a depth D1 so that at least a portion thereof reaches the first surface 122. The N-type semiconductor region 128 is provided from the first surface 122 to a depth D2 deeper than the depth D1 so as to surround the N-type semiconductor region 126. The P-type semiconductor region 130 is provided from the depth D2 to a depth D4 deeper than the depth D2. The N-type impurity doped region 136 is provided from a depth D3 deeper than the depth D2 but shallower than the depth D4 to a depth D6 deeper than the depth D4. The semiconductor region 138 is provided from the depth D6 to a depth D8 deeper than the depth D6. The P-type semiconductor region 132 is provided from the depth D8 to the second surface 124. In plan view, the P-type semiconductor region 134 is arranged so as to surround the region in which the N-type semiconductor regions 126, 128, the P-type semiconductor region 130, the N-type impurity doped region 136, and the semiconductor region 138 are provided (see FIG. 6). The P-type semiconductor region 134 is arranged from the first surface 122 to a depth D8, and is electrically connected to the P-type semiconductor region 132. The region in the semiconductor layer 120 surrounded by the P-type semiconductor regions 132, 134 is the region in which one photoelectric conversion element 22 is arranged. Here, this region is referred to as a well region.

[0050] The N-type semiconductor region 126 is an N-type semiconductor region with a high impurity concentration that serves as the cathode of the APD constituting the photoelectric conversion element 22, and is disposed in the center of the well region in a planar view, as shown in FIG. 6 . A cathode electrode 144 is provided on the N-type semiconductor region 126. The cathode electrode 144 is ohmically connected to the N-type semiconductor region 126. The N-type semiconductor region 128 is an N-type semiconductor region with a lower impurity concentration than the N-type semiconductor region 126, and is disposed throughout the well region in a planar view. The P-type semiconductor region 130 is a P-type semiconductor region that serves as the anode of the APD constituting the photoelectric conversion element 22. The P-type semiconductor region 130 is disposed throughout the well region in a planar view, and is electrically connected to the P-type semiconductor region 134 at its periphery in a planar view. The N-type impurity-doped region 136 is disposed throughout the well region in a planar view so as to overlap with the bottom portion of the impurity density distribution of the P-type semiconductor region 130 on the second surface 124 side, as shown in FIG. 7 . In other words, the peak position of the impurity density of the donor impurity constituting the N-type impurity doped region 136 is located deeper than the peak position of the impurity density of the acceptor impurity constituting the P-type semiconductor region 130. The density of the donor impurity constituting the N-type impurity doped region 136 is lower than the density of the acceptor impurity constituting the P-type semiconductor region 130. The semiconductor region 138 is a low-impurity-density semiconductor region that serves as a photoelectric conversion region and may be either an N-type or a P-type semiconductor region. The P-type semiconductor region 132 serves to define the depth of the photoelectric conversion region. In addition, the P-type semiconductor region 132, in cooperation with the P-type semiconductor region 134, also serves as an isolation region that separates adjacent photoelectric conversion elements 22. The P-type semiconductor region 134 has a high-impurity-density P-type semiconductor region (not shown) at least in a portion that contacts the first surface 122 and is ohmically connected to the anode electrode 146.

[0051] The photoelectric conversion element 22 of the photoelectric conversion device 100 according to this embodiment can be manufactured using a general semiconductor device manufacturing method. For example, each semiconductor is formed from one surface (first surface 122) of a low-impurity-concentration N-type silicon substrate using photolithography and ion implantation. region and an N-type impurity doped region 136. Next, a wiring layer including a cathode electrode 144 and an anode electrode 146 is formed on the one surface of the N-type silicon substrate. Next, the N-type silicon substrate is thinned from the other surface side of the N-type silicon substrate to form the semiconductor layer 120. The new surface exposed by thinning the N-type silicon substrate becomes the second surface 124.

[0052] For example, the N-type semiconductor region 126 is formed by ion implantation of donor impurities so as to contact the first surface 122 of the semiconductor layer 120. The P-type semiconductor region 130 is formed by ion implantation of acceptor impurities deeper than the depth at which the N-type semiconductor region 126 is provided. The semiconductor region 138 may be formed by ion implantation of impurities deeper than the depth at which the P-type semiconductor region 130 is provided, or the N-type silicon substrate may be used as is. The N-type impurity doped region 136 is formed so as to overlap with the P-type semiconductor region 130 in the depth direction of the semiconductor layer 120. Furthermore, the N-type impurity doped region 136 is formed by ion implantation of donor impurities so that the depth at which the density of the donor impurities reaches its peak is deeper than the depth at which the density of the acceptor impurities constituting the P-type semiconductor region 130 reaches its peak.

[0053] When the second surface 124 of the semiconductor layer 120 is used as the light-receiving surface onto which light to be detected is incident, it is desirable to form the P-type semiconductor region 132 so as to be in contact with the second surface 124, as shown in FIG. 7. By configuring the P-type semiconductor region 132 in this manner, it is possible to prevent the generation of dark current in the second surface 124. Furthermore, a dielectric isolation structure using a deep trench may be used for the isolation region that separates adjacent photoelectric conversion elements 22. In this case, the P-type semiconductor region 134 may be arranged around the isolation dielectric.

[0054] In the photoelectric conversion element 22 of this embodiment, avalanche multiplication of signal charges occurs between the N-type semiconductor region 126 and the opposing P-type semiconductor region 130. Meanwhile, the distance between the N-type semiconductor region 126 and the P-type semiconductor region 134 is much longer than the distance between the N-type semiconductor region 126 and the P-type semiconductor region 130. Furthermore, the N-type semiconductor region 138 has a low impurity density. Therefore, electric field concentration does not occur in the lateral direction (direction parallel to the first surface 122) from the N-type semiconductor region 126 toward the P-type semiconductor region 134. In other words, the lateral electric field strength is not strong enough to cause avalanche multiplication, and avalanche multiplication does not occur due to the lateral electric field. Therefore, even if dark electrons are generated near the first surface 122, the lateral electric field will not cause avalanche multiplication, and the dark electrons will not be detected as noise.

[0055] 9 is a diagram showing the potential distribution in the semiconductor layer 120 along line AB in FIG. 7. The vertical axis represents the potential for electrons, which are signal carriers, with the potential decreasing upward on the vertical axis and increasing downward on the vertical axis. Note that line AB in FIG. 7 is a line that intersects the first surface 122 and the second surface 124 at right angles, passes through the center of the N-type semiconductor region 126, and overlaps with the main path along which signal charges (electrons) generated in the semiconductor region 138 flow toward the N-type semiconductor region 126.

[0056] The photoelectric conversion element 22 of this embodiment is basically divided into a high electric field region where avalanche multiplication occurs and a photoelectric conversion region where signal charges are generated. Specifically, along line AB in Figure 7, the high electric field region is from the N-type semiconductor region 126 to the P-type semiconductor region 130, and the photoelectric conversion region is from the P-type semiconductor region 130 to the P-type semiconductor region 132.

[0057] Signal charges generated in the photoelectric conversion region move along the potential gradient by drift or other means to the high electric field region, where they undergo avalanche multiplication and are collected via the cathode electrode 144, where they are detected as a signal. The P-type semiconductor region 130 is an intermediate region transitioning from the photoelectric conversion region to the high electric field region, and in order to obtain the potential distribution shown in Figure 9, at least the portion of the P-type semiconductor region 130 along line AB must be completely depleted. At least a large portion of the low impurity concentration semiconductor region 138 is also depleted. The structure described above is referred to here as a charge collection APD.

[0058] Here, the drive voltage applied to the charge collection APD (the voltage applied between the cathode electrode 144 and the anode electrode 146) is defined as drive voltage VDD. If the voltages applied to the high electric field region, intermediate region, and photoelectric conversion region along line AB are defined as voltage V1, voltage V2, and voltage V3, respectively, then drive voltage VDD can be expressed as follows: VDD=V1+V2+V3

[0059] More specifically, on line AB, the N-type semiconductor region 126 and the P-type semiconductor region 132 are a neutral region that is not depleted, and the entire region between them is depleted. Therefore, the drive voltage VDD applied to line AB is the potential difference between the N-type semiconductor region 126 and the P-type semiconductor region 132, and the potential distribution in the region between them is determined by the impurity distribution in the region between them. In other words, voltages V1, V2, and V3 are each determined by the impurity distribution in the region on line AB. Here, the high electric field region is from the N-type semiconductor region 126 to the P-type semiconductor region 130. The intermediate region is the P-type semiconductor region 130. Furthermore, the photoelectric conversion region is from the P-type semiconductor region 130 to the P-type semiconductor region 132. Referring to FIG. 8, due to the impurity density distribution, voltages V1 and V2 are higher than voltage V3. As described above, drive voltage VDD is the sum of these voltages. Due to the impurity density distribution shown in FIG. 8, the potential of the P-type semiconductor region 132 is higher than the potential of the P-type semiconductor region 130.

[0060] Voltage V1 is the voltage required for avalanche multiplication. If voltage V1 is equal to or greater than the voltage required for avalanche multiplication in the high electric field region, SPAD operation will occur. However, if voltages V2 and V3 are insufficient, quantum efficiency will decrease and signal response time will increase, ultimately resulting in degradation of signal performance. Therefore, voltages V2 and V3 must be carefully considered in charge collection APDs.

[0061] Of voltages V1, V2, and V3, voltage V3 is directly related to the time it takes for signal electrons generated in the photoelectric conversion region to reach the high electric field region, i.e., the signal response time, and is determined largely depending on the application. Therefore, in order to achieve low-voltage operation of the photoelectric conversion element 22, it is important to determine how to reduce voltages V1 and V2.

[0062] First, a method for reducing voltage V2 will be described. The voltage V2 is required to completely deplete the P-type semiconductor region 130 along the line AB, as well as to eliminate the potential barrier at the boundary between the intermediate region and the photoelectric conversion region along the line AB.

[0063] Because a high enough electric field must be formed between the N-type semiconductor region 126 and the P-type semiconductor region 130 to cause avalanche multiplication, the P-type semiconductor region 130 must have an effective impurity density equal to or greater than a certain value. Here, the effective impurity density refers to the net impurity density expressed as the difference between the acceptor impurity density and the donor impurity density when acceptor impurities and donor impurities are mixed. In this specification, to clarify the dominant impurity, the effective impurity density of a P-type semiconductor region containing donor impurities is sometimes referred to as the effective acceptor density. Furthermore, the effective impurity density of an N-type semiconductor region containing acceptor impurities is sometimes referred to as the effective donor density.

[0064] According to semiconductor theory, if the effective impurity density of a semiconductor layer is A, its width is W, and the impurity density per unit area (A x W) is a constant value, the voltage required to deplete this semiconductor layer is proportional to W. In other words, the depletion voltage decreases when the impurities are distributed over a narrower range. Therefore, to minimize voltage V2, it is desirable to narrow the depth direction width of the P-type semiconductor region 130 as much as possible.

[0065] Generally, boron is used as an acceptor impurity in forming a P-type semiconductor region. Ion implantation is often used to add impurities to semiconductors, as it allows for easy control of density and depth. When adding impurities to a semiconductor by ion implantation, a phenomenon known as channeling occurs, in which ions move along the crystal axis or crystal plane, resulting in a broad impurity distribution in the depth direction. Channeling is particularly likely to occur when using ions with a small atomic mass, such as boron. Therefore, when forming a P-type semiconductor region 130 that requires a narrow width in the depth direction, it is preferable to perform ion implantation in a direction that is somewhat inclined relative to the crystal axis, a so-called random direction.

[0066] Furthermore, by providing the N-type impurity doped region 136 so as to overlap with the bottom portion of the impurity density distribution of the P-type semiconductor region 130 on the side of the second surface 124, the effective width of the P-type semiconductor region 130 can be narrowed. When the N-type impurity doped region 136 is provided, part of the acceptor impurities in the P-type semiconductor region 130 is compensated for by the donor impurities in the N-type impurity doped region 136, and the effective impurity density of the P-type semiconductor region 130 decreases. Therefore, the amount of acceptor impurities introduced per unit area when forming the P-type semiconductor region 130 may be increased compared to a case where the N-type impurity doped region 136 is not formed, so that the P-type semiconductor region 130 has an effective impurity density equal to or greater than the above-mentioned certain value.

[0067] By configuring the photoelectric conversion element 22 in this way, the effective width of the P-type semiconductor region 130 can be narrowed, and the value of the voltage V2 can be reduced.

[0068] Next, a method for reducing the voltage V1 will be described. Whether avalanche multiplication occurs in a high electric field region depends on the amount of impact ionization caused by signal carriers traveling through the high electric field region. Here, if the electric field strength within the high electric field region is constant, the impact ionization rate, which is the number of impact ions generated per unit length, is α, and the width of the high electric field region in the depth direction is W1, the larger the value of α×W1, the higher the probability of avalanche multiplication. Therefore, to ensure a sufficient probability of avalanche multiplication, the value of α×W1 must be set to a certain value or higher. In practice, the value required for α×W1 is approximately 2.

[0069] Among the parameters that determine the probability of avalanche multiplication, the impact ionization rate α is highly dependent on the electric field strength in the high electric field region, i.e., V1 / W1. The electric field strength in the high electric field region of a typical SPAD is approximately 400 kV / cm to 600 kV / cm. On the other hand, if the width W1 of the high electric field region is changed from W1 to W1-ΔW, the impact ionization rate α increases exponentially as ΔW increases. In other words, the value of α×W1 increases as the value of W1 decreases. In other words, by reducing the width W1, the voltage V1 can be reduced while maintaining the value of α×W1.

[0070] For a more quantitative discussion, the width W1 of the N-type semiconductor region 126 is defined as follows: That is, the width W1 is defined as the width when the effective donor density of the N-type semiconductor region 126 is 1×10 16 cm -3 From the depth at which the effective acceptor density of the P-type semiconductor region 130 becomes 1×10 16 cm -3 The width is defined as the depth on the side of the first surface 122 (the bottom of the side of the first surface 122) at which the width is

[0071] Generally, when a reverse bias voltage is applied to a PN junction, the electric field strength peaks at the PN junction surface and decreases in the depleted regions on both sides of the PN junction surface. This is due to electrostatic shielding caused by the charge of impurity ions when the semiconductor region is depleted. However, when the density of impurity ions is 1×10 16 cm -3 Furthermore, in the region between the N-type semiconductor region 126 and the P-type semiconductor region 130, the acceptors and donors are particularly concentrated at 1×10 16 cm -3 Therefore, the effective donor density distribution and the effective acceptor density distribution are 1×10 16 cm -3 Below this level, the field intensity becomes very steep and the effect on the field intensity becomes even smaller. Therefore, the width W1 defined above can be regarded as a high field region that maintains a nearly constant field intensity.

[0072] Similarly, the width W2 in the depth direction of the P-type semiconductor region 130 is defined as follows: That is, the width W2 is the width when the effective acceptor density of the P-type semiconductor region 130 is 1×10 16 cm -3 From the depth on the first surface 122 side where the effective acceptor density of the P-type semiconductor region 130 is 1×10 16 cm -3 The width is defined as the width to the depth on the side of the second surface 124 where the

[0073] In the photoelectric conversion element 22 of this embodiment, as an example, the target driving voltage VDD is set to 25 V or less. Configuration examples of the width W1, the width W2, and the effective acceptor density NA of the P-type semiconductor region 130 for achieving this target are calculated below.

[0074] First, voltage V2, width W2 and BiP Let us consider the effective acceptor density NA of the type semiconductor region 130. The voltage V2 is expressed by the following equation (1), where Vb is the built-in voltage, q is the elementary charge, and ε is the dielectric constant of the semiconductor. V2 = qNA / (2ε) × (W22 )-Vb …(1)

[0075] The width W2 is 0.6 μm, and the effective acceptor density NA is 4 × 10 16 cm -3 Assuming that the built-in voltage Vb is 0.7V, the voltage V2 is calculated to be 10.3V from equation (1).

[0076] Without changing the value of W2 × NA, the width W2 is set to 0.4 μm and the effective acceptor density NA is set to 6 × 10 16 cm -3 , the voltage V2 is calculated to be 6.6 V from equation (1). In this way, by changing the relationship between the width W2 and the effective acceptor density NA from the former condition to the latter condition, the value of the voltage V2 is reduced by 3.7 V.

[0077] Note that the effective acceptor density NA actually has a distribution within the width W2, but for simplicity, it is taken as the average effective acceptor density within the width W2. Also, if the value of W2×NA is low, the value of voltage V2 will also be small, but if the value of W2×NA is too low, punch-through will occur in the P-type semiconductor region 130 when a high-field reverse bias voltage is applied to the APD, making it impossible to maintain a high electric field strength in the high-field region. Therefore, the value of W2×NA must be at least a certain value. In the above calculation example, the value of W2×NA is 2.4×10 12 cm -2 , which is the effective acceptor density partially offset by the donor impurities, and is 1×10 16 cm -3 Therefore, in order to form the P-type semiconductor region 130, the density of 3×10 12 cm -2 The above-mentioned introduction of acceptor impurities is necessary.

[0078] Next, we will consider the voltage V1 and width W1 required to generate avalanche multiplication. As mentioned above, the value of α×W1 must be approximately 2 or more. Therefore, if the width W1 is set to, for example, 0.4 μm, the impact ionization rate α is 5×10 4 / cm or more. If the signal carrier is an electron, the impact ionization rate α must be 5×10 4 The electric field strength at which the width W1 is 0.4 μm is 400 kV / cm. Therefore, if the width W1 is 0.4 μm, the voltage V1 must be 16 V.

[0079] From the above, the width W1 is set to 0.4 μm, the width W2 is set to 0.4 μm, and the effective acceptor density NA is set to 6×10 16 cm -3 In this case, voltage V1 is 16 V and voltage V2 is 6.6 V. Voltage V3 depends on the signal response speed requirements, but is usually around 1 to 5 V. Therefore, if voltage V3 is 2.4 V, the drive voltage VDD is V1 + V2 + V3 = 25 V.

[0080] From the above example, it can be seen that reducing the widths W1 and W2 is important to reduce the drive voltage VDD. Further investigation by the inventors into various other conditions revealed that it is important to set the value of (W1 + W2) to 0.8 μm or less. If the width W2 is set to 0.5 μm, the voltage V2 will increase, so in order to reduce the voltage V1, it is necessary to set the width W1 to 0.3 μm or less.

[0081] In order to reduce the width W2, it is important that the N-type impurity doped region 136 is provided so as to exactly cancel out the bottom portion of the acceptor impurity density distribution in the P-type semiconductor region 130. According to experiments by the inventors, the amount of donors per unit area required to form the N-type impurity doped region 136 may be about half or less of the amount of acceptors per unit area required to form the P-type semiconductor region 130, but should be at least 5×10 11 cm -2 Without the N-type impurity doped region 136 of this size, it is actually difficult to make the width W2 equal to or less than 0.5 μm, that is, to keep (W1+W2) equal to or less than 0.8 μm.

[0082] As described above, according to this embodiment, the drive voltage of the avalanche photodiode can be reduced, which makes it possible to achieve energy savings by reducing power consumption, alleviate deterioration of element characteristics by reducing heat generation, and reduce dark current.

[0083] [Second embodiment] A photoelectric conversion device according to a second embodiment of the present invention will be described with reference to Figs. 10 and 11. Components similar to those in the photoelectric conversion device according to the first embodiment are given the same reference numerals, and descriptions thereof will be omitted or simplified. Fig. 10 is a plan view showing the structure of a photoelectric conversion element in the photoelectric conversion device according to this embodiment. Fig. 11 is a schematic cross-sectional view showing the structure of a photoelectric conversion element in the photoelectric conversion device according to this embodiment.

[0084] The photoelectric conversion device according to this embodiment is similar to the photoelectric conversion device according to the first embodiment except for the configuration of the photoelectric conversion element 22. In this embodiment, the following description will focus on the differences between the photoelectric conversion element 22 of this embodiment and the photoelectric conversion element 22 of the first embodiment, and descriptions of the parts common to the photoelectric conversion element 22 of the first embodiment will be omitted as appropriate.

[0085] The photoelectric conversion element 22 of this embodiment further includes a P-type semiconductor region 140 in addition to the N-type semiconductor regions 126 and 128, the P-type semiconductor regions 130, 132 and 134, the N-type impurity doped region 136 and the semiconductor region 138.

[0086] In the photoelectric conversion element 22 of the first embodiment, the P-type semiconductor region 130 and the N-type impurity doped region 136 are provided over the entire well region in a planar view. In contrast, in the photoelectric conversion element 22 of the present embodiment, the P-type semiconductor region 130 and the N-type impurity doped region 136 are arranged in the center of the well region in a planar view so as to overlap with the N-type semiconductor region 126 in a planar view, as shown in FIG. 11 . A P-type semiconductor region 140 is provided between the P-type semiconductor region 130 and the N-type impurity doped region 136 and the P-type semiconductor region 134 in a planar view. The P-type semiconductor region 130 is electrically connected to an anode electrode 146 via the P-type semiconductor region 140 and the P-type semiconductor region 134. The effective acceptor density per unit area of ​​the P-type semiconductor region 140 is higher than the effective acceptor density per unit area of ​​the P-type semiconductor region 130.

[0087] In the photoelectric conversion element 22 of the first embodiment, electrons generated in the semiconductor region 138, which is the photoelectric conversion region, may pass over the P-type semiconductor region 130 in the periphery of the well region in a planar view and reach the N-type semiconductor region 128. In this case, the electrons that reach the N-type semiconductor region 128 in the periphery of the well region do not undergo avalanche multiplication as described above and are not detected as a signal, resulting in a loss of sensitivity.

[0088] By further providing a P-type semiconductor region 140 on the periphery of the well region in plan view, the potential barrier between the semiconductor region 138 on the periphery of the well region in plan view and the N-type semiconductor region 128 becomes larger. As a result, electrons generated in the semiconductor region 138, which is the photoelectric conversion region, are more likely to reach the N-type semiconductor region 128 by passing over the central P-type semiconductor region 130 than by passing over the peripheral P-type semiconductor region 140 and reaching the N-type semiconductor region 128. If signal electrons follow such a path, avalanche multiplication occurs as they pass through the high electric field region, and this can be detected as a signal.

[0089] Therefore, compared to the photoelectric conversion element of the first embodiment, the photoelectric conversion element 22 of this embodiment can increase the proportion of signal electrons that reach the cathode through the center of the photoelectric conversion element 22, i.e., through the vicinity of line AB passing through the center of the cathode, thereby improving the light receiving sensitivity.

[0090] 11, the P-type semiconductor region 140 is provided from a depth deeper than depth D1 and shallower than depth D2 to a depth deeper than depth D6 and shallower than depth D8, but the depth at which the P-type semiconductor region 140 is provided is not limited to this. The P-type semiconductor region 140 should at least have an effective acceptor density per unit area higher than the effective acceptor density per unit area of ​​the P-type semiconductor region 130 and be electrically connected to the P-type semiconductor region 130 and the P-type semiconductor region 134.

[0091] The P-type semiconductor region 140 can be formed by various methods. For example, the P-type semiconductor region 140 can be formed by additionally introducing acceptor impurities into the peripheral portion of the well region in the structure of the first embodiment. Alternatively, in the structure of the first embodiment, the N-type impurity doped region 136 may be formed only in the central portion of the well region, and the P-type semiconductor region 130 in the peripheral portion of the well region that does not overlap with the N-type impurity doped region 136 may be substantially the P-type semiconductor region 140. Alternatively, in the structure of the first embodiment, the acceptor impurities in the P-type semiconductor region 130 in the central portion of the well region may be partially compensated for by donor impurities in the N-type semiconductor region 126 or an additionally formed N-type semiconductor region. In this case, the P-type semiconductor region 130 in the peripheral portion of the well region where the acceptor impurities are not partially compensated for by donor impurities will be substantially the P-type semiconductor region 140.

[0092] If the P-type semiconductor region 130 and the P-type semiconductor region 140 are considered to be one P-type semiconductor region, this P-type semiconductor region can be said to have a first region that overlaps with the N-type semiconductor region 126 in a planar view and a second region that does not overlap with the N-type semiconductor region 126 in a planar view. In this case, the effective impurity density per unit area of ​​the acceptor impurity that constitutes the second region is higher than the effective impurity density per unit area of ​​the acceptor impurity that constitutes the first region. The second region is typically a region that surrounds the first region.

[0093] As described above, according to this embodiment, in addition to the effects described in the first embodiment, it is possible to achieve the further effect of improving sensitivity.

[0094] [Third embodiment] A photoelectric conversion device according to a third embodiment of the present invention will be described with reference to Fig. 12. Components similar to those of the photoelectric conversion device according to the first or second embodiment are given the same reference numerals, and descriptions thereof will be omitted or simplified. Fig. 12 is a schematic cross-sectional view showing the structure of a photoelectric conversion element in the photoelectric conversion device according to this embodiment.

[0095] The photoelectric conversion device according to this embodiment is similar to the photoelectric conversion device according to the first embodiment except for the configuration of the photoelectric conversion element 22. In this embodiment, the following description will focus on the differences between the photoelectric conversion element 22 of this embodiment and the photoelectric conversion element 22 of the first embodiment, and descriptions of the parts common to the photoelectric conversion element 22 of the first embodiment will be omitted as appropriate.

[0096] The photoelectric conversion element 22 of this embodiment further includes a P-type impurity doped region 142 in addition to the N-type semiconductor regions 126 and 128, the P-type semiconductor regions 130, 132, and 134, the N-type impurity doped region 136, and the semiconductor region 138. The P-type impurity doped region 142 is provided from a depth D5 between the depths D4 and D6 to a depth D7 between the depths D6 and D8. More specifically, the P-type impurity doped region 142 is provided throughout the well region in plan view so as to overlap with the base portion of the impurity density distribution of the N-type impurity doped region 136 on the second surface 124 side. In other words, the peak position of the impurity density of the acceptor impurity that constitutes the P-type impurity doped region 142 is located deeper than the peak position of the impurity density of the donor impurity that constitutes the N-type impurity doped region 136. The P-type impurity doped region 142 is formed with an impurity concentration sufficient to compensate for the donor impurities in the skirt portion of the impurity concentration distribution of the N-type impurity doped region 136 on the side of the second surface 124. Typically, the impurity density of the P-type impurity doped region 142 is lower than the impurity density of the N-type impurity doped region 136.

[0097] The P-type impurity doped region 142 is formed so as to overlap with the N-type impurity doped region 136 in the depth direction of the semiconductor layer 120. The P-type impurity doped region 142 is formed by ion implanting acceptor impurities so that the depth at which the density of the acceptor impurity reaches its peak is located closer to the second surface 124 than the depth at which the density of the donor impurity constituting the N-type impurity doped region 136 reaches its peak.

[0098] By providing the N-type impurity doped region 136, the potential for electrons is lowered, making it easier for so-called potential pockets to form. Potential pockets make it easier for signal electrons to accumulate there, lengthening the time it takes for them to reach the high electric field region, ultimately resulting in a deterioration in signal response performance. By further providing the P-type impurity doped region 142, it is possible to prevent the formation of the above-mentioned potential pockets, thereby reducing the decrease in the movement speed of signal electrons caused by the provision of the N-type impurity doped region 136.

[0099] In addition to the above configuration of this embodiment, the P-type semiconductor region 140 described in the second embodiment may be further added.

[0100] As described above, according to this embodiment, in addition to the effects described in the first and second embodiments, it is possible to achieve the further effect of improving signal responsiveness.

[0101] [Fourth embodiment] A light detection system according to a fourth embodiment of the present invention will be described with reference to FIG. 13. FIG. 13 is a block diagram showing a schematic configuration of the light detection system according to this embodiment. In this embodiment, the first to third A light detection sensor to which the photoelectric conversion device 100 of the embodiment is applied will be described.

[0102] The photoelectric conversion device 100 described in the first to third embodiments can be applied to various photodetection systems. Examples of applicable photodetection systems include imaging systems such as digital still cameras, digital camcorders, surveillance cameras, copiers, fax machines, mobile phones, vehicle-mounted cameras, and observation satellites. Camera modules equipped with an optical system such as a lens and an imaging device are also included in the photodetection system. Fig. 13 illustrates a block diagram of a digital still camera as an example of such systems.

[0103] 13 includes a photoelectric conversion device 201, a lens 202 that forms an optical image of a subject on the photoelectric conversion device 201, an aperture 204 that adjusts the amount of light passing through the lens 202, and a barrier 206 that protects the lens 202. The lens 202 and the aperture 204 form an optical system that focuses light on the photoelectric conversion device 201. The photoelectric conversion device 201 is the photoelectric conversion device 100 described in any one of the first to third embodiments, and converts the optical image formed by the lens 202 into image data.

[0104] The light detection system 200 also has a signal processing unit 208 that processes the output signal output from the photoelectric conversion device 201. The signal processing unit 208 generates image data from the digital signal output from the photoelectric conversion device 201. The signal processing unit 208 also performs various corrections and compressions as necessary to output the image data. The photoelectric conversion device 201 may be provided with an AD conversion unit that generates a digital signal to be processed by the signal processing unit 208. The AD conversion unit converts the digital signal of the photoelectric conversion device 201 into an image data. photoelectric conversion element Alternatively, the photoelectric conversion device 201 may be formed on a semiconductor layer (semiconductor substrate) on which the photoelectric conversion element A semiconductor layer other than the semiconductor layer on which the layer The signal processing unit 208 may be formed on the same semiconductor as the photoelectric conversion device 201. layer The slit 20 may be formed as follows.

[0105] The light detection system 200 further includes a buffer memory unit 210 for temporarily storing image data, and an external interface unit (external I / F unit) 212 for communicating with an external computer or the like. The light detection system 200 also includes a recording medium 214 such as a semiconductor memory for recording or reading out imaging data, and a recording medium control interface unit (recording medium control I / F unit) 216 for recording or reading out imaging data from the recording medium 214. The recording medium 214 may be built into the light detection system 200 or may be removable. Communication between the recording medium control I / F unit 216 and the recording medium 214 and communication from the external I / F unit 212 may be performed wirelessly.

[0106] The photodetection system 200 further includes an overall control and calculation unit 218 that performs various calculations and controls the entire digital still camera, and a timing generation unit 220 that outputs various timing signals to the photoelectric conversion device 201 and the signal processing unit 208. Here, the timing signals and the like may be input from outside, and the photodetection system 200 only needs to include at least the photoelectric conversion device 201 and the signal processing unit 208 that processes the output signal output from the photoelectric conversion device 201. The timing generation unit 220 may be mounted on the photoelectric conversion device 201. The overall control and calculation unit 218 and the timing generation unit 220 may be configured to perform some or all of the control functions of the photoelectric conversion device 201.

[0107] The photoelectric conversion device 201 outputs an imaging signal to the signal processing unit 208. The signal processing unit 208 performs predetermined signal processing on the imaging signal output from the photoelectric conversion device 201 and outputs image data. The signal processing unit 208 generates an image using the imaging signal. The signal processing unit 208 may be configured to perform distance measurement calculations on the signal output from the photoelectric conversion device 201.

[0108] As described above, according to this embodiment, by configuring a light detection system using the photoelectric conversion devices of the first to third embodiments, it is possible to realize a light detection system capable of acquiring higher quality images.

[0109] [Fifth embodiment] A range image sensor according to a fifth embodiment of the present invention will be described with reference to Fig. 14. Fig. 14 is a block diagram showing a schematic configuration of the range image sensor according to this embodiment. In this embodiment, the range image sensor will be described as an example of a light detection system to which the photoelectric conversion device 100 described in the first to third embodiments is applied.

[0110] 14, the range image sensor 300 according to this embodiment may include an optical system 302, a photoelectric conversion device 304, an image processing circuit 306, a monitor 308, and a memory 310. This range image sensor 300 receives light (modulated light or pulsed light) emitted from a light source device 320 toward a subject 330 and reflected by the surface of the subject 330, and obtains a range image according to the distance to the subject 330.

[0111] The optical system 302 is composed of one or more lenses, and serves to focus image light (incident light) from the subject 330 onto the light receiving surface (sensor section) of the photoelectric conversion device 304.

[0112] The photoelectric conversion device 304 is the photoelectric conversion device 100 described in any of the first to third embodiments, and has the function of generating a distance signal indicating the distance to the subject 330 based on image light from the subject 330, and supplying the generated distance signal to the image processing circuit 306.

[0113] The image processing circuit 306 has a function of performing image processing to construct a distance image based on the distance signal supplied from the photoelectric conversion device 304 .

[0114] The monitor 308 has a function of displaying the distance image (image data) obtained by the image processing in the image processing circuit 306. The memory 310 has a function of storing (recording) the distance image (image data) obtained by the image processing in the image processing circuit 306.

[0115] Thus, according to this embodiment, by constructing a distance image sensor using the photoelectric conversion devices of the first to third embodiments, it is possible to realize a distance image sensor that can acquire distance images containing more accurate distance information, in combination with improved characteristics of pixel 12.

[0116] [Sixth embodiment] An endoscopic surgery system according to a sixth embodiment of the present invention will be described with reference to Fig. 15. Fig. 15 is a schematic diagram showing an example of the configuration of the endoscopic surgery system according to this embodiment. In this embodiment, the endoscopic surgery system will be described as an example of a light detection system to which the photoelectric conversion device 100 described in the first to third embodiments is applied.

[0117] FIG. 15 shows a state in which an operator (doctor) 460 is performing surgery on a patient 472 on a patient bed 470 using an endoscopic surgery system 400.

[0118] 15, an endoscopic surgery system 400 of this embodiment may include an endoscope 410, a surgical tool 420, and a cart 430 on which various devices for endoscopic surgery are mounted. The cart 430 may be mounted with a CCU (camera control unit) 432, a light source device 434, an input device 436, a treatment tool control device 438, a display device 440, and the like.

[0119] The endoscope 410 includes a lens barrel 412, a region of a predetermined length from the tip of which is inserted into a body cavity of a patient 472, and a camera head 414 connected to the base end of the lens barrel 412. Although Fig. 15 illustrates the endoscope 410 configured as a so-called rigid lens barrel having a rigid lens barrel 412, the endoscope 410 may also be configured as a so-called flexible lens barrel having a flexible lens barrel. The endoscope 410 is held in a movable state by an arm 416.

[0120] An opening into which an objective lens is fitted is provided at the tip of the lens barrel 412. A light source device 434 is connected to the endoscope 410, and light generated by the light source device 434 is guided to the tip of the lens barrel by a light guide extending inside the lens barrel 412, and is irradiated via the objective lens towards an observation target inside the body cavity of the patient 472. The endoscope 410 may be a direct-viewing endoscope, an oblique-viewing endoscope, or a side-viewing endoscope.

[0121] An optical system and a photoelectric conversion device (not shown) are provided inside the camera head 414, and light reflected from the observation object (observation light) is collected by the optical system onto the photoelectric conversion device. The photoelectric conversion device photoelectrically converts the observation light to generate an electrical signal corresponding to the observation light, i.e., an image signal corresponding to the observation image. The photoelectric conversion device may be the photoelectric conversion device 100 described in any of the first to third embodiments. The image signal is transmitted to the CCU 432 as RAW data.

[0122] The CCU 432 is configured with a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), etc., and comprehensively controls the operations of the endoscope 410 and the display device 440. Furthermore, the CCU 432 receives an image signal from the camera head 414, and performs various image processing on the image signal, such as development processing (demosaic processing), to display an image based on the image signal.

[0123] The display device 440 , under the control of the CCU 432 , displays an image based on the image signal that has been subjected to image processing by the CCU 432 .

[0124] The light source device 434 is configured from a light source such as an LED (Light Emitting Diode), and supplies the endoscope 410 with irradiation light when photographing an operation site or the like.

[0125] The input device 436 is an input interface for the endoscopic surgery system 400. A user can input various information and instructions to the endoscopic surgery system 400 via the input device 436.

[0126] The treatment tool control device 438 controls the driving of an energy treatment tool 450 for cauterizing tissue, incising, sealing blood vessels, or the like.

[0127] The light source device 434, which supplies illumination light to the endoscope 410 when photographing the surgical site, can be configured from a white light source configured from, for example, an LED, a laser light source, or a combination of these. When the white light source is configured from a combination of RGB laser light sources, the output intensity and output timing of each color (each wavelength) can be controlled with high precision, making it possible to adjust the white balance of the captured image in the light source device 434. In this case, it is also possible to capture images corresponding to each RGB color in a time-division manner by irradiating the object of observation with laser light from each RGB laser light source in a time-division manner and controlling the drive of the image sensor of the camera head 414 in synchronization with the irradiation timing. According to this method, a color image can be obtained without providing a color filter to the image sensor.

[0128] Furthermore, the light source device 434 may be controlled to change the intensity of light it outputs at predetermined time intervals. By controlling the driving of the image sensor of the camera head 414 in synchronization with the timing of the change in the light intensity to acquire images in a time-division manner and combining the images, it is possible to generate an image with a high dynamic range that is free of so-called blocked-up shadows and blown-out highlights.

[0129] The light source device 434 may also be configured to supply light in a predetermined wavelength band corresponding to special light observation. Special light observation utilizes, for example, the wavelength dependency of light absorption in body tissue. Specifically, by irradiating light with a narrower band than the light (i.e., white light) used in normal observation, a predetermined tissue, such as blood vessels on the surface of the mucosa, can be photographed with high contrast. Alternatively, special light observation may involve fluorescence observation, in which an image is obtained using fluorescence generated by irradiating excitation light. Fluorescence observation can involve irradiating excitation light onto a body tissue and observing the fluorescence from the body tissue, or locally injecting a reagent such as indocyanine green (ICG) into the body tissue and irradiating the body tissue with excitation light corresponding to the fluorescent wavelength of the reagent to obtain a fluorescent image. The light source device 434 may be configured to supply narrow band light and / or excitation light corresponding to such special light observation.

[0130] Thus, according to this embodiment, by configuring an endoscopic surgery system using the photoelectric conversion devices of the first to third embodiments, it is possible to realize an endoscopic surgery system that can acquire higher quality images.

[0131] [Seventh embodiment] A light detection system and a moving body according to a seventh embodiment of the present invention will be described with reference to Figs. 16 to 18. Fig. 16 is a schematic diagram showing an example of the configuration of a moving body according to this embodiment. Fig. 17 is a block diagram showing a schematic configuration of a light detection system according to this embodiment. Fig. 18 is a flow diagram showing the operation of the light detection system according to this embodiment. In this embodiment, an example of application to an in-vehicle camera is shown as a light detection system to which the photoelectric conversion device 100 described in the first to third embodiments is applied.

[0132] FIG. 16 is a schematic diagram showing an example of the configuration of a moving body (vehicle system) according to this embodiment. FIG. 16 shows the configuration of a vehicle 500 (automobile) as an example of a vehicle system incorporating a light detection system to which the photoelectric conversion device described in any of the first to third embodiments is applied. FIG. 16(a) is a schematic front view of the vehicle 500, FIG. 16(b) is a schematic plan view of the vehicle 500, and FIG. 16(c) is a schematic rear view of the vehicle 500. The vehicle 500 is provided with a pair of photoelectric conversion devices 502 on the front side. Here, the photoelectric conversion devices 502 are the photoelectric conversion devices 100 described in any of the first to third embodiments. The vehicle 500 also includes an integrated circuit 503, an alarm device 512, and a main control unit 513.

[0133] FIG. 17 is a block diagram showing an example configuration of a photodetection system 501 mounted on a vehicle 500. The photodetection system 501 includes a photoelectric conversion device 502, an image preprocessing unit 515, an integrated circuit 503, and an optical system 514. The photoelectric conversion device 502 is the photoelectric conversion device 100 described in the first embodiment. The optical system 514 forms an optical image of a subject on the photoelectric conversion device 502. The photoelectric conversion device 502 converts the optical image of the subject formed by the optical system 514 into an electrical signal. The image preprocessing unit 515 performs predetermined signal processing on the signal output from the photoelectric conversion device 502. The function of the image preprocessing unit 515 may be incorporated into the photoelectric conversion device 502. The photodetection system 501 includes at least two sets of the optical system 514, the photoelectric conversion device 502, and the image preprocessing unit 515, and the output from each set of the image preprocessing unit 515 is input to the integrated circuit 503.

[0134] The integrated circuit 503 is an integrated circuit for use in an imaging system, and includes an image processing unit 504, an optical distance measuring unit 506, a parallax calculation unit 507, an object recognition unit 508, and an abnormality detection unit 509. The image processing unit 504 processes an image signal output from an image pre-processing unit 515. For example, the image processing unit 504 performs image processing such as development processing and defect correction on the output signal of the image pre-processing unit 515. The image processing unit 504 includes a memory 505 that temporarily stores the image signal. For example, the positions of known defective pixels in the photoelectric conversion device 502 can be stored in the memory 505.

[0135] The optical distance measurement unit 506 performs focusing and distance measurement of the subject. The parallax calculation unit 507 calculates distance information (distance information) from multiple image data (parallax images) acquired by the multiple photoelectric conversion devices 502. Each of the photoelectric conversion devices 502 may be configured to be able to acquire various information such as distance information. The object recognition unit 508 recognizes subjects such as cars, roads, signs, and people. When the abnormality detection unit 509 detects an abnormality in the photoelectric conversion device 502, it notifies the main control unit 513 of the abnormality.

[0136] The integrated circuit 503 may be realized by dedicated hardware, a software module, or a combination thereof. It may also be realized by an FPGA (Field Programmable Gate Array), an ASIC (Application Specific Integrated Circuit), or the like, or a combination thereof.

[0137] The main control unit 513 supervises and controls the operations of the light detection system 501, the vehicle sensor 510, the control unit 520, etc. Note that the vehicle 500 does not necessarily have to include the main control unit 513. In this case, the photoelectric conversion device 502, the vehicle sensor 510, and the control unit 520 transmit and receive control signals via a communication network. For example, the CAN standard may be applied to the transmission and reception of these control signals.

[0138] The integrated circuit 503 has a function of receiving a control signal from the main control unit 513 or transmitting a control signal or a set value to the photoelectric conversion device 502 by its own control unit.

[0139] The optical detection system 501 is connected to a vehicle sensor 510 and can detect the vehicle's driving conditions, such as vehicle speed, yaw rate, and steering angle, as well as the conditions of the environment outside the vehicle and other vehicles and obstacles. The vehicle sensor 510 also serves as a distance information acquisition means for acquiring distance information to an object. The optical detection system 501 is also connected to a driving assistance control unit 511 that performs various driving assistance functions, such as automatic steering, automatic cruising, and collision prevention functions. In particular, the collision determination function determines whether or not a collision with another vehicle or obstacle has occurred based on the detection results of the optical detection system 501 and the vehicle sensor 510. This allows for avoidance control when a collision is estimated, and activation of safety devices in the event of a collision.

[0140] The optical detection system 501 is also connected to an alarm device 512 that issues an alarm to the driver based on the determination result of the collision determination unit. For example, if the collision determination unit determines that there is a high possibility of a collision, the main control unit 513 performs vehicle control to avoid the collision and mitigate damage by applying the brakes, releasing the accelerator, suppressing engine output, etc. The alarm device 512 warns the user by sounding an alarm or the like, displaying alarm information on a display screen of a car navigation system or meter panel, vibrating the seat belt or steering wheel, etc.

[0141] In this embodiment, the surroundings of the vehicle, for example, the front or rear, are photographed by the light detection system 501. Fig. 16(b) shows an example of the arrangement of the light detection system 501 when the light detection system 501 photographs the area in front of the vehicle.

[0142] As described above, the photoelectric conversion device 502 is disposed in front of the vehicle 500. Specifically, if the center line of the vehicle 500's heading or outer shape (for example, vehicle width) is regarded as an axis of symmetry, and the two photoelectric conversion devices 502 are disposed symmetrically about the axis of symmetry, this is preferable for obtaining distance information between the vehicle 500 and an object to be photographed and determining the possibility of a collision. Furthermore, the photoelectric conversion device 502 is preferably disposed so as not to obstruct the driver's field of vision when the driver visually checks the situation outside the vehicle 500 from the driver's seat. The warning device 512 is preferably disposed so as to be easily within the driver's field of vision.

[0143] Next, a fault detection operation of the photoelectric conversion device 502 in the light detection system 501 will be described with reference to Fig. 18. The fault detection operation of the photoelectric conversion device 502 can be performed according to steps S110 to S180 shown in Fig. 18.

[0144] Step S110 is a step for performing startup settings for the photoelectric conversion device 502. That is, settings for the operation of the photoelectric conversion device 502 are transmitted from outside the photodetection system 501 (for example, from the main control unit 513) or from inside the photodetection system 501, and the image capturing operation and fault detection operation of the photoelectric conversion device 502 are started.

[0145] Next, in step S120, pixel signals are acquired from valid pixels. Furthermore, in step S130, output values ​​are acquired from failure detection pixels provided for failure detection. These failure detection pixels, like valid pixels, have photoelectric conversion elements. A predetermined voltage is written to these photoelectric conversion elements. The failure detection pixels output signals corresponding to the voltage written to these photoelectric conversion elements. Note that steps S120 and S130 may be reversed.

[0146] Next, in step S140, a correspondence between the expected output value of the fault detection pixel and the actual output value from the fault detection pixel is determined. If the result of the correspondence determination in step S140 indicates that the expected output value and the actual output value match, the process proceeds to step S150, where it is determined that the imaging operation is normal, and the process proceeds to step S160. In step S160, the pixel signals of the scanning row are sent to memory 505 and temporarily stored. Thereafter, the process returns to step S120, where the fault detection operation continues. On the other hand, if the result of the correspondence determination in step S140 indicates that the expected output value and the actual output value do not match, the process proceeds to step S170. In step S170, it is determined that an abnormality exists in the imaging operation, and an alarm is issued to the main control unit 513 or the alarm device 512. The alarm device 512 displays the detection of the abnormality on the display unit. Thereafter, in step S180, the photoelectric conversion device 502 is stopped, and the operation of the light detection system 501 is terminated.

[0147] In this embodiment, the flowchart is looped for each line, but the flowchart may be looped for each set of lines, or the fault detection operation may be performed for each frame. The issuance of the alarm in step S170 may be notified to the outside of the vehicle via a wireless network.

[0148] Furthermore, although the present embodiment has been described as a control for preventing collisions with other vehicles, the present invention is also applicable to control for automatic driving by following other vehicles, control for automatic driving so as not to deviate from a lane, and the like. Furthermore, the light detection system 501 is not limited to vehicles such as the subject vehicle, but can be applied to moving bodies (moving devices) such as ships, aircraft, and industrial robots. In addition, the present invention is not limited to moving bodies, but can be applied to a wide range of devices that use object recognition, such as intelligent transport systems (ITS).

[0149] [Eighth embodiment] An optical detection system according to an eighth embodiment of the present invention will be described with reference to Fig. 19. Fig. 19 is a schematic diagram showing an example of the configuration of the optical detection system according to this embodiment. In this embodiment, an example of application to eyeglasses (smart glasses) will be described as an optical detection system to which the photoelectric conversion device 100 described in the first to third embodiments is applied.

[0150] 19(a) shows glasses 600 (smart glasses) according to one application example. The glasses 600 include lenses 601, a photoelectric conversion device 602, and a control device 603.

[0151] The photoelectric conversion device 602 is the photoelectric conversion device 100 described in any one of the first to third embodiments, and is provided on the lens 601. There may be one or more photoelectric conversion devices 602. When multiple photoelectric conversion devices 602 are used, multiple types of photoelectric conversion devices 602 may be combined. The arrangement position of the photoelectric conversion device 602 is not limited to that shown in FIG. 19( a). A display device (not shown) including a light-emitting device such as an OLED or LED may be provided on the back side of the lens 601.

[0152] The control device 603 functions as a power source that supplies power to the photoelectric conversion device 602 and the display device. The control device 603 also has a function of controlling the operations of the photoelectric conversion device 602 and the display device. The lens 601 is provided with an optical system for condensing light onto the photoelectric conversion device 602.

[0153] 19(b) shows glasses 610 (smart glasses) according to another application example. The glasses 610 include lenses 611 and a control device 612. The control device 612 may be equipped with a photoelectric conversion device (not shown) corresponding to the photoelectric conversion device 602 and a display device.

[0154] The lens 611 is provided with a photoelectric conversion device in the control device 612 and an optical system for projecting light from the display device, and an image is projected. The control device 612 functions as a power source that supplies power to the photoelectric conversion device and the display device, and also has a function of controlling the operations of the photoelectric conversion device and the display device.

[0155] The control device 612 may further include a gaze detection unit that detects the gaze of the wearer. In this case, an infrared light emitting unit may be provided in the control device 612, and the infrared light emitted from the infrared light emitting unit may be used to detect the gaze. Specifically, the infrared light emitting unit emits infrared light toward the eyeball of the user gazing at the displayed image. An imaging unit having a light receiving element detects the reflected light of the emitted infrared light from the eyeball, thereby obtaining an image of the eyeball. By providing a reduction unit that reduces the light from the infrared light emitting unit to the display unit in a planar view, it is possible to reduce degradation of image quality.

[0156] The user's line of sight with respect to the displayed image can be detected from an image of the eyeball obtained by capturing infrared light. Any known method can be applied to gaze detection using an image of the eyeball. As an example, a gaze detection method based on a Purkinje image formed by reflection of irradiated light on the cornea can be used. More specifically, a gaze detection process based on the pupil-corneal reflex method is performed. Using the pupil-corneal reflex method, a gaze vector representing the direction (rotation angle) of the eyeball is calculated based on the image of the pupil and the Purkinje image included in the image of the eyeball, thereby detecting the user's gaze.

[0157] The display device of this embodiment may include a photoelectric conversion device having a light receiving element, and may be configured to control a display image based on user line-of-sight information from the photoelectric conversion device. Specifically, the display device determines a first field of view area where the user gazes and a second field of view area other than the first field of view area based on the line-of-sight information. The first field of view area and the second field of view area may be determined by a control device of the display device or by an external control device. If determined by an external control device, they are communicated to the display device via communication. In the display area of ​​the display device, the display resolution of the first field of view area may be controlled to be higher than the display resolution of the second field of view area. In other words, the resolution of the second field of view area may be lower than the resolution of the first field of view area.

[0158] The display area may also be configured to have a first display area and a second display area different from the first display area, and to determine a high-priority area from the first display area and the second display area based on line-of-sight information. The first display area and the second display area may be determined by a control device of the display device or by an external control device. If determined by an external control device, the determination is communicated to the display device via communication. The resolution of the high-priority area may be controlled to be higher than the resolution of areas other than the high-priority area. In other words, the resolution of an area with a relatively low priority may be lowered.

[0159] Note that AI may be used to determine the first field of view area and areas with high priority. The AI ​​may be a model configured to estimate the angle of gaze and the distance to an object in the line of sight from an image of the eyeball, using as training data an image of the eyeball and the actual direction in which the eyeball in the image was looking. The AI ​​program may be included in the display device, the photoelectric conversion device, or an external device. If included in an external device, it is transmitted to the display device via communication.

[0160] When display control is performed based on visual recognition detection, the present invention is preferably applied to smart glasses that further include a photoelectric conversion device for capturing images of the outside world. The smart glasses can display captured external information in real time.

[0161] [Modified embodiment] The present invention is not limited to the above-described embodiment, and various modifications are possible.

[0162] For example, an example in which part of the configuration of any one of the embodiments is added to another embodiment, or an example in which part of the configuration of another embodiment is substituted therefor, is also an embodiment of the present invention.

[0163] The circuit configuration of the pixel 12 is not limited to that of the above embodiment. For example, a switch such as a transistor may be provided between the photoelectric conversion element 22 and the quench element 24 or between the photoelectric conversion unit 20 and the pixel signal processing unit 30 (waveform shaping unit 32) to control the electrical connection state therebetween. Furthermore, a switch such as a transistor may be provided between the node to which the voltage VH is supplied and the quench element 24 and / or between the node to which the voltage VL is supplied and the photoelectric conversion element 22 to control the electrical connection state therebetween.

[0164] Furthermore, in the above embodiment, a configuration using the counter circuit 34 as the pixel signal processing unit 30 has been described, but a TDC (Time to Digital Converter) and a memory may be used instead of the counter circuit 34. In this case, the generation timing of the pulse signal output from the waveform shaping unit 32 is converted into a digital signal by the TDC. When measuring the timing of the pulse signal, a control pulse pREF (reference signal) is supplied to the TDC from the vertical scanning circuit unit 40 via the control line 14. The TDC acquires, as a digital signal, a signal obtained when the input timing of the signal output from each pixel 12 is converted into a relative time based on the control pulse pREF.

[0165] Furthermore, in the above embodiment, a configuration has been shown in which one pixel 12 has one photoelectric conversion element 22, but one pixel 12 may have multiple photoelectric conversion elements 22. Furthermore, in the above embodiment, one photoelectric conversion element 22 is arranged in one well region surrounded by the P-type semiconductor regions 132, 134, but multiple photoelectric conversion elements 22 may be arranged in one well region.

[0166] It should be noted that the above-described embodiments are merely examples of specific embodiments for carrying out the present invention, and the technical scope of the present invention should not be construed as being limited by these embodiments. In other words, the present invention can be carried out in various forms without departing from its technical concept or main features.

[0167] The disclosure of the above embodiment includes the following configurations and methods. (Configuration 1) A photoelectric conversion element provided in a semiconductor layer having a first surface and a second surface opposite to the first surface, a first semiconductor region of a first conductivity type provided in contact with the first surface; a second semiconductor region of a second conductivity type provided closer to the second surface than the first semiconductor region; a third semiconductor region provided closer to the second surface than the second semiconductor region; a first electrode electrically connected to the first semiconductor region; a second electrode electrically connected to the second semiconductor region; the first semiconductor region and the second semiconductor region form an avalanche photodiode, and the avalanche photodiode is configured to multiply signal charges generated in the third semiconductor region; The second semiconductor region has an effective impurity density of 1×10 16 cm -3 The width of the region in the depth direction where the thickness is equal to or greater than 0.5 μm is 0.5 μm or less. A photoelectric conversion element characterized by: (Configuration 2) The effective impurity density of the first semiconductor region is 1×10 16 cm -3 the effective impurity density of the second semiconductor region is 1×10 on the second surface side from the depth at which the density of the second conductivity type impurity constituting the second semiconductor region reaches a peak. 16 cm -3 The distance to the depth where 2. The photoelectric conversion element according to configuration 1, (Configuration 3) a first impurity doped region doped with the first conductivity type impurity, the first impurity doped region overlaps with the second semiconductor region in a plan view and in a depth direction; a depth at which the density of the first conductivity type impurity constituting the first impurity doped region reaches a peak is deeper than a depth at which the density of the second conductivity type impurity constituting the second semiconductor region reaches a peak; The impurity density per unit area of ​​the second conductivity type impurity constituting the second semiconductor region is 3×10 12 cm -2 That's all, The impurity density per unit area of ​​the first conductivity type impurity constituting the first impurity doped region is 5×10 11 cm -2 or less than half the impurity density per unit area of ​​the second conductivity type impurity constituting the second semiconductor region. 3. The photoelectric conversion element according to configuration 1 or 2. (Configuration 4) The first impurity doped region is provided on the second surface side of a depth at which a density of the second conductivity type impurity constituting the second semiconductor region reaches a peak, so as to compensate for the second conductivity type impurity. 4. The photoelectric conversion element according to configuration 3. (Configuration 5) a second impurity doped region doped with the second conductivity type impurity, the second impurity doped region overlaps with the first impurity doped region in a plan view and in a depth direction, a depth at which the density of the second conductivity type impurity constituting the second impurity doped region reaches a peak is deeper than a depth at which the density of the first conductivity type impurity constituting the first impurity doped region reaches a peak; The impurity density of the second conductivity type impurity constituting the second impurity doped region is lower than the impurity density of the first conductivity type impurity constituting the first impurity doped region. 5. The photoelectric conversion element according to configuration 3 or 4. (Configuration 6) The second impurity doped region is provided on the second surface side of a depth at which the density of the first conductivity type impurity constituting the first impurity doped region reaches a peak, so as to compensate for the first conductivity type impurity. 6. The photoelectric conversion element according to configuration 5, (Configuration 7) the second semiconductor region has a first region that overlaps with the first semiconductor region in a planar view and a second region that does not overlap with the first region in a planar view; The effective impurity density per unit area of ​​the second conductivity type impurity constituting the second semiconductor region is higher in the second region than in the first region. 7. The photoelectric conversion element according to any one of configurations 1 to 6, wherein: (Configuration 8) The second region is disposed so as to surround the first region. 9. The photoelectric conversion element according to configuration 8, (Configuration 9) a fourth semiconductor region of the first conductivity type provided on the first surface side of the second semiconductor region so as to surround the first semiconductor region; The impurity density of the fourth semiconductor region is lower than the impurity density of the first semiconductor region. 9. The photoelectric conversion element according to any one of configurations 1 to 8, wherein: (Configuration 10) a fifth semiconductor region of the second conductivity type provided closer to the second surface than the third semiconductor region; a sixth semiconductor region of the second conductivity type that is arranged so as to surround a region in which the first semiconductor region, the second semiconductor region, and the third semiconductor region are arranged in a plan view and is electrically connected to the second semiconductor region and the fifth semiconductor region. 10. The photoelectric conversion element according to any one of configurations 1 to 9, wherein: (Configuration 11) The sixth semiconductor region is in contact with the second surface. 11. The photoelectric conversion element according to configuration 10. (Configuration 12) The signal charge is a carrier of the first conductivity type. 12. The photoelectric conversion element according to any one of configurations 1 to 11, wherein: (Configuration 13) A photoelectric conversion device having a plurality of pixels arranged in a plurality of rows and a plurality of columns, Each of the plurality of pixels includes a photoelectric conversion element according to any one of claims 1 to 12 and a signal processing unit that processes a signal output from the photoelectric conversion element. A photoelectric conversion device characterized by: (Configuration 14) a first substrate including the semiconductor layer on which the photoelectric conversion elements of the plurality of pixels are provided; a second substrate on which the signal processing unit of each of the plurality of pixels is provided; and 14. The photoelectric conversion device according to claim 13, comprising: (Configuration 15) The photoelectric conversion device according to configuration 13 or 14, a signal processing device that processes a signal output from the photoelectric conversion device; An optical detection system comprising: (Configuration 16) The signal processing device generates a distance image representing distance information to an object based on the signal. 16. The optical detection system of claim 15. (Configuration 17) A mobile object, The photoelectric conversion device according to configuration 13 or 14, a distance information acquisition means for acquiring distance information to an object from a parallax image based on a signal output from the photoelectric conversion device; a control means for controlling the moving object based on the distance information; A moving object characterized by having: (Method 1) A method for manufacturing a photoelectric conversion element having a first semiconductor region of a first conductivity type, a second semiconductor region of a second conductivity type, and a third semiconductor region, wherein the first semiconductor region and the second semiconductor region form an avalanche photodiode that multiplies signal charges generated in the third semiconductor region, forming the first semiconductor region so as to contact a first surface of a semiconductor layer; forming the second semiconductor region in the semiconductor layer at a depth greater than the depth at which the first semiconductor region is provided; doping the semiconductor layer with impurities of the first conductivity type to form a first impurity doped region that overlaps with the second semiconductor region in a depth direction of the semiconductor layer and has a depth at which the density of the first conductivity type impurities reaches a peak that is deeper than a depth at which the density of the second conductivity type impurities constituting the second semiconductor region reaches a peak; A method for producing a photoelectric conversion element, comprising: (Method 2) The method further includes a step of doping the semiconductor layer with impurities of the second conductivity type, and forming a second impurity doped region that overlaps with the first impurity doped region in the depth direction of the semiconductor layer and has a depth at which the density of the second conductivity type impurity peaks that is deeper than a depth at which the density of the first conductivity type impurity constituting the first impurity doped region peaks. 3. The method for producing a photoelectric conversion element according to method 2, (Method 3) The width of the second semiconductor region in the depth direction is controlled by the first impurity doped region. 3. The method for producing a photoelectric conversion device according to Method 1 or 2, [Explanation of symbols]

[0168] 12...pixels 20...Photoelectric conversion unit 30...Pixel signal processing unit 120...Semiconductor layer 126, 128...N-type semiconductor region 130, 132, 134, 140...P-type semiconductor region 136...N-type impurity doped region 138...Semiconductor field 142...P-type impurity doped region

Claims

1. A photoelectric conversion element provided in a semiconductor layer having a first surface and a second surface opposite to the first surface, a first semiconductor region of a first conductivity type provided in contact with the first surface; a second semiconductor region of a second conductivity type provided closer to the second surface than the first semiconductor region; a third semiconductor region provided closer to the second surface than the second semiconductor region; a first impurity doped region doped with the first conductivity type impurity; a first electrode electrically connected to the first semiconductor region; a second electrode electrically connected to the second semiconductor region; the first semiconductor region and the second semiconductor region form an avalanche photodiode, and the avalanche photodiode is configured to multiply signal charges generated in the third semiconductor region; The second semiconductor region has an effective impurity density of 1×10 １６ cm －３ the width in the depth direction of the region where the width is equal to or greater than 0.5 μm is 0.5 μm or less, the first impurity doped region overlaps with the second semiconductor region in a plan view and in a depth direction, a depth at which the density of the first conductivity type impurity constituting the first impurity doped region reaches a peak is deeper than a depth at which the density of the second conductivity type impurity constituting the second semiconductor region reaches a peak; the impurity density per unit area of ​​the second conductivity type impurity constituting the second semiconductor region is 3×10 12 cm −2 or more; The impurity density per unit area of ​​the first conductivity type impurity constituting the first impurity doped region is 5×10 11 cm −2 or more, and is ½ or less of the impurity density per unit area of ​​the second conductivity type impurity constituting the second semiconductor region. A photoelectric conversion element characterized by:

2. The effective impurity density of the first semiconductor region is 1×10 １６ cm －３ the effective impurity density of the second semiconductor region is 1×10 on the second surface side from the depth at which the density of the second conductivity type impurity constituting the second semiconductor region reaches a peak. １６ cm －３ The distance to the depth at which 2. The photoelectric conversion element according to claim 1.

3. The first impurity doped region is provided on the second surface side of a depth at which the density of the second conductivity type impurity constituting the second semiconductor region reaches a peak, so as to compensate for the second conductivity type impurity.

2. The photoelectric conversion element according to claim 1.

4. a second impurity doped region doped with the second conductivity type impurity, the second impurity doped region overlaps with the first impurity doped region in a plan view and in a depth direction, a depth at which the density of the second conductivity type impurity constituting the second impurity doped region reaches a peak is deeper than a depth at which the density of the first conductivity type impurity constituting the first impurity doped region reaches a peak; The impurity density of the second conductivity type impurity constituting the second impurity doped region is lower than the impurity density of the first conductivity type impurity constituting the first impurity doped region.

2. The photoelectric conversion element according to claim 1.

5. The second impurity doped region is provided on the second surface side of a depth at which the density of the first conductivity type impurity constituting the first impurity doped region reaches a peak, so as to compensate for the first conductivity type impurity.

5. The photoelectric conversion element according to claim 4.

6. the second semiconductor region has a first region that overlaps with the first semiconductor region in a planar view and a second region that does not overlap with the first region in a planar view; The effective impurity density per unit area of ​​the second conductivity type impurity constituting the second semiconductor region is higher in the second region than in the first region.

6. The photoelectric conversion element according to claim 1, wherein the first and second electrodes are electrically connected to each other.

7. The second region is disposed so as to surround the first region.

7. The photoelectric conversion element according to claim 6.

8. a fourth semiconductor region of the first conductivity type provided on the first surface side of the second semiconductor region so as to surround the first semiconductor region, The impurity density of the fourth semiconductor region is lower than the impurity density of the first semiconductor region.

6. The photoelectric conversion element according to claim 1, wherein the first and second electrodes are electrically connected to each other.

9. a fifth semiconductor region of the second conductivity type provided closer to the second surface than the third semiconductor region; a sixth semiconductor region of the second conductivity type that is arranged so as to surround a region in which the first semiconductor region, the second semiconductor region, and the third semiconductor region are arranged in a plan view and is electrically connected to the second semiconductor region and the fifth semiconductor region.

6. The photoelectric conversion element according to claim 1, wherein the first and second electrodes are electrically connected to each other.

10. The sixth semiconductor region is in contact with the second surface.

10. The photoelectric conversion element according to claim 9.

11. The signal charge is a carrier of the first conductivity type.

6. The photoelectric conversion element according to claim 1, wherein the first and second electrodes are electrically connected to each other.

12. A photoelectric conversion device having a plurality of pixels arranged in a plurality of rows and a plurality of columns, Each of the plurality of pixels includes a photoelectric conversion element according to claim 1 and a signal processing unit that processes a signal output from the photoelectric conversion element. A photoelectric conversion device characterized by:

13. a first substrate including the semiconductor layer on which the photoelectric conversion elements of the plurality of pixels are provided; a second substrate on which the signal processing unit of each of the plurality of pixels is provided; 13. The photoelectric conversion device according to claim 12, further comprising:

14. The photoelectric conversion device according to claim 12; a signal processing device that processes a signal output from the photoelectric conversion device; An optical detection system comprising:

15. The signal processing device generates a distance image representing distance information to an object based on the signal.

15. The optical detection system of claim 14.

16. A mobile object, The photoelectric conversion device according to claim 12; a distance information acquisition means for acquiring distance information to an object from a parallax image based on a signal output from the photoelectric conversion device; a control means for controlling the moving object based on the distance information; A moving object characterized by having:

17. A method for manufacturing a photoelectric conversion element having a first semiconductor region of a first conductivity type, a second semiconductor region of a second conductivity type, and a third semiconductor region, wherein the first semiconductor region and the second semiconductor region form an avalanche photodiode that multiplies signal charges generated in the third semiconductor region, forming the first semiconductor region so as to contact a first surface of a semiconductor layer; forming the second semiconductor region in the semiconductor layer at a depth greater than the depth at which the first semiconductor region is provided; a step of doping the semiconductor layer with the impurity of the first conductivity type to form a first impurity doped region that overlaps with the second semiconductor region in a depth direction of the semiconductor layer and has a depth at which the density of the impurity of the first conductivity type reaches a peak that is deeper than a depth at which the density of the impurity of the second conductivity type that constitutes the second semiconductor region reaches a peak; doping the semiconductor layer with impurities of the second conductivity type to form a second impurity doped region that overlaps with the first impurity doped region in a depth direction of the semiconductor layer and has a depth at which the density of the impurity of the second conductivity type reaches a peak that is deeper than a depth at which the density of the impurity of the first conductivity type that constitutes the first impurity doped region reaches a peak; A method for producing a photoelectric conversion element, comprising:

18. The width of the second semiconductor region in the depth direction is controlled by the first impurity doped region.

18. The method for manufacturing a photoelectric conversion device according to claim 17.

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