JP2012189599A - Distance sensor and distance image sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a distance sensor and a distance image sensor in which moving speed of charges transferred from a charge generating region to a charge collecting region becomes high speed.SOLUTION: A distance image sensor comprises an imaging region which is constituted by a plurality of two-dimensionally arranged units (pixels P) and is provided on a semiconductor substrate. The distance image sensor obtains a distance image on the basis of charge quantities output from the units. One of the units comprises: a charge generating region (a region outside a transmission electrode 5) where charges are generated in accordance with incident light; semiconductor regions which are arranged spatially apart and collect charge from the charge generating region; the transmission electrodes 5 which are disposed at periphery of the semiconductor regions, are given with charge transmission signals, and surround the semiconductor regions; and a potential adjusting portion 6 which steeps a potential gradient from the charge generating region to the semiconductor regions.

Description

  The present invention relates to a distance sensor and a distance image sensor mounted on a product monitor or a vehicle in a production line of a factory.

  A conventional distance measuring device is described in Patent Document 1, for example. In this distance image sensor, four sides of the photosensitive region where light is incident are surrounded by four transfer gate electrodes, and transfer voltages having different phases are applied to these transfer gate electrodes and are positioned outside the transfer gate electrodes. The charges generated in the photosensitive region sequentially flow into the four charge storage regions. In this distance image sensor, the distance to the object is calculated based on the charge amount distributed in the accumulation region.

Special Table 2000-517427

  However, a distance image sensor having a conventional distance sensor has a configuration in which a small light incident area is surrounded by four triangular transfer gate electrodes, so that the aperture ratio is poor. Charges generated at positions away from the region cannot be collected, charge collection efficiency is poor, and charges that cannot be collected are likely to cause crosstalk. In addition, when the pixel is enlarged, it is necessary to lengthen the transfer gate electrode. Thus, the conventional distance image sensor cannot improve the charge collection efficiency and has a small signal amount, and therefore cannot obtain a distance image with a good S / N ratio.

  The present invention has been made in view of such problems, and is a distance sensor capable of obtaining a distance output having a good S / N ratio and a distance image capable of obtaining a distance image having a good S / N ratio. An object is to provide a sensor.

  In order to solve the above-described problem, a distance sensor according to the present invention is arranged at least spatially apart from a charge generation region in which charge is generated in response to incident light, and collects charge from the charge generation region. Two charge collection regions, and a transfer electrode provided around each of the charge collection regions, provided with charge transfer signals of different phases, and surrounding the charge collection region. The distance image sensor includes an imaging region composed of a plurality of units arranged two-dimensionally on a semiconductor substrate, and one unit is a distance image sensor that obtains a distance image based on the amount of charge output from the unit. And the distance sensor.

  When a plurality of units are arranged two-dimensionally, a plurality of transfer electrodes are positioned around the charge generation region, but conversely, a charge generation region is also positioned around the transfer electrode. Since the transfer electrode surrounds the charge collection region, it is possible to transfer charges from all directions to the charge collection region by giving a charge transfer signal to the transfer electrode. That is, substantially all the peripheral area of the transfer electrode can function as a charge generation area, and the aperture ratio is remarkably improved. Therefore, the signal amount can be increased and a distance image with a good S / N ratio can be obtained. Focusing on one distance sensor, since charges can be transferred from all directions outside the transfer electrode to the inside charge collection region, a large amount of charges can be collected, and when the distance is obtained based on such charges, S / A distance output with a good N ratio can be obtained.

  Further, at least two charge collection regions surrounded by transfer electrodes to which charge transfer signals having the same phase are applied may be electrically connected. In this case, the amount of charge output from these charge collection regions is averaged, and the characteristic difference for each charge collection region can be compensated.

  In addition, the distance image sensor of the present invention preferably further includes a potential adjusting unit that is provided in the charge generation region and makes the potential gradient from the charge generation region toward the charge collection region steep. When the potential gradient becomes steep by the potential adjusting means, the moving speed of the charge transferred from the charge generation region to the charge collection region becomes high. That is, high-speed imaging is possible.

  Such potential adjusting means can be composed of a semiconductor region having a conductivity type different from that of the charge collection region and having a higher impurity concentration than the surroundings. The potential gradient can be increased by different conductivity types.

  The potential adjusting means is an electrode to which a predetermined potential is applied. The potential gradient can be increased if a potential opposite to the potential caused by the donor or acceptor ionized in the charge collection region is applied to the electrode.

  The shape of the transfer electrode is preferably annular. As a result, it is possible to steadily collect the charge flowing from all directions to the charge collection region and to prevent the inflow thereof.

  According to the distance sensor of the present invention, a distance output with high charge collection efficiency and a good S / N ratio can be obtained. According to the distance image sensor using a plurality of distance sensors, the charge collection efficiency is high and S A distance image with a good / N ratio can be obtained.

It is a perspective view of the enlarged imaging region. It is II-II arrow sectional drawing of an imaging region. It is a figure which shows the potential distribution in an imaging region. It is a timing chart of various signals. It is a timing chart of various signals. It is sectional drawing of a part of imaging device which attached the imaging chip shown in FIG. 2 to the wiring board. It is sectional drawing of the whole imaging device. It is a figure which shows the whole structure of a distance image measuring device. It is a circuit diagram in a pixel. It is a perspective view of the imaging region of the distance image sensor which concerns on 2nd Embodiment. It is XI-XI arrow sectional drawing of the imaging region shown in FIG. It is a perspective view of the imaging region of the distance image sensor which concerns on 3rd Embodiment. It is XIII-XIII arrow sectional drawing of the imaging region shown in FIG. It is explanatory drawing for demonstrating pixel arrangement | positioning. It is a figure for demonstrating the connection of an electric charge collection area | region. It is explanatory drawing for demonstrating another structure of a transfer electrode.

  Hereinafter, a distance image sensor having a distance sensor according to an embodiment of the invention will be described. Note that the same reference numerals are used for the same elements, and redundant description is omitted.

  FIG. 1 is a perspective view of an imaging region of the distance image sensor according to the first embodiment, and FIG. 2 is a cross-sectional view of the imaging region along arrows II-II.

  A P-type epitaxial layer 2 having a lower concentration than the semiconductor substrate 1 is grown on the P-type semiconductor substrate 1, and a high-concentration N-type semiconductor region (charge collection region) is formed in the epitaxial layer 2. 3 are provided in a matrix. It is assumed that the substrate including the epitaxial layer 2 is also a semiconductor substrate. The surface of the epitaxial layer 2 is covered with an insulating layer 4, and the insulating layer 4 is provided with a contact hole for exposing the surface of the semiconductor region 3. A conductor 7 for connecting the semiconductor region 3 to the outside passes through the contact hole.

  An annular transfer electrode (gate) 5 is provided on the insulating layer 4 around the semiconductor region 3. A charge generation region extends in a region outside the transfer electrode 5, and a potential adjustment unit (potential adjustment means) 6 is provided at the center of the charge generation region in the pixel. The potential adjusting unit 6 of this example is an electrode disposed on the insulating layer 4. When the XYZ orthogonal coordinate system is set, one pixel P is formed in the XY plane, presents a quadrangle, and constitutes a distance sensor. The potential adjustment unit 6 is located on the center, corner, and midpoint of each side of the square pixel. In one pixel P, four transfer electrodes 5 are included, and a line connecting these centers can form a quadrangle, and one potential adjustment unit 6 is located on the center of the diagonal line. Yes.

  The semiconductor region 3 collects charges generated outside the transfer electrode 5 in response to the incidence of light. The transfer electrode 5 is denoted by A when the phase of the charge transfer signal applied thereto is 0 degree and B when it is 180 degrees. Different types of transfer electrodes 5 are alternately arranged along the X axis, and different types are alternately arranged along the Y axis direction. That is, when attention is paid to one transfer electrode A, The transfer electrode B is adjacent to the surrounding X-axis direction and Y-axis direction. Focusing on one transfer electrode B, the transfer electrode A is adjacent in the X-axis direction and Y-axis direction around the transfer electrode B. Note that the transfer electrodes A and B are described when attention is paid to the phase of the voltage applied to the transfer electrode, and the transfer electrode 5 when attention is paid to the transfer electrode regardless of the phase.

  Light incident on the center of one pixel P is converted into electric charge in the semiconductor substrate, and the electric charge generated in this way is directed to one of the transfer electrodes 5 in accordance with the potential gradient formed by the potential adjusting unit 6. Drive to.

  When a positive potential is applied to the transfer electrode 5, the gate of the transfer electrode 5 is opened, and negative charges (electrons) are drawn in the direction of the transfer electrode 5 and enter the potential well formed by the N-type semiconductor region 3. Accumulated. N-type semiconductors contain positively ionized donors, have a positive potential, and attract electrons.

  When a potential (ground potential) lower than the positive potential is applied to the transfer electrode 5, the gate by the transfer electrode 5 is closed, and the charge generated in the semiconductor region 3 is not drawn into the semiconductor region 3.

The semiconductor is made of Si, the insulating layer 4 is made of SiO ₂ , and the transfer electrode 5 and the potential adjusting unit 6 are made of polysilicon, but these may be made of other materials.

  FIG. 3 is a diagram illustrating a potential distribution in the imaging region.

  3A is a potential diagram along the horizontal direction of the cross section of FIG. 2 when the phase of the transfer electrode A is 0 degree, and FIG. 3B is a diagram when the phase of the transfer electrode A is 180 degrees. FIG. 3 is a potential diagram along the horizontal direction of the cross section of FIG. 2. FIG. 3C is a potential diagram in the horizontal direction in the cross section taken along the line C-C ′ of FIG. 1 in the state of FIG. In the figure, the downward direction is the positive direction of the potential.

  As shown in FIG. 3A, when the phase of the transfer electrode A is 0 degree, a positive potential is applied to the transfer electrode A, and a reverse phase potential, that is, the phase is 180 degrees. A potential (ground potential) is applied. In this case, the negative charge e generated in the charge generation portion located between the transfer electrodes A and B is reduced in the semiconductor region inside the transfer electrode A by lowering the potential barrier of the semiconductor immediately below the transfer electrode A. Flows in. On the other hand, the potential barrier of the semiconductor immediately below the transfer electrode B does not go down, and no charge flows into the semiconductor region 3 inside the transfer electrode B.

  Further, as shown in FIG. 3B, when the phase of the transfer electrode B is 0 degree, a positive potential is applied to the transfer electrode B, and a reverse-phase potential, that is, a phase of 180 is applied to the transfer electrode A. Degree potential (ground potential). In this case, the negative charge e generated in the charge generation unit located between the transfer electrodes A and B is lowered in the semiconductor region inside the transfer electrode B by lowering the potential barrier of the semiconductor immediately below the transfer electrode B. Flows in. On the other hand, the potential barrier of the semiconductor immediately below the transfer electrode A does not go down, and no charge flows into the semiconductor region 3 inside the transfer electrode A.

  In addition, as shown in FIG. 3C, the potential adjustment unit 6 is not originally located between the transfer electrode A and the transfer electrode B, and in a cross section that does not pass through the potential adjustment unit 6, At the midpoint between the transfer electrode A and the transfer electrode B, the potential barrier seen in FIGS. 3A and 3B is not observed. On the other hand, since the cross sections in FIGS. 3A and 3B pass through the potential adjusting unit 6, the energy at the midpoint between the transfer electrodes A and B is high, and the potential gradient is steep. High-speed charge transfer is realized. Note that charges generated between the transfer electrodes A and B in FIG. 3C also flow into the semiconductor region 3.

  FIG. 4 is a timing chart of various signals.

The light source drive signal S _D described later, the reflected light intensity signal L _P when the light source hits the object and returns to the imaging region, the charge transfer signal S _L applied to the transfer electrode A, and the transfer electrode B are applied. charge transfer signal S _R are shown. Since the charge transfer signal S _L is synchronized with the drive signal S _D , the phase of the reflected light intensity signal L _P with respect to the charge transfer signal S _L is the time of flight of light, which is from the sensor to the object. Shows the distance. Here, each of the charge transfer signal S _L, upon application of S _R, the amount of charge collected in the semiconductor region 3 Q _L, by using the ratio of Q _R, and calculates the distance d. That is, when one pulse width of the drive signal is T _P , the distance is given by d = (c / 2) × (T _P × Q _R / (Q _L + Q _R )). C is the speed of light.

  FIG. 5 is a timing chart of actual various signals.

Focusing on one pixel within a period _{TF of} one frame, a drive signal _SD having a plurality of pulses is applied to the light source, and in synchronization with this, the charge transfer signals S _L and S _R are in opposite phases to each other. Applied to the transfer electrodes A and B. Prior to the distance measurement, a reset signal reset is applied to the semiconductor region 3, and the charge accumulated inside is discharged to the outside. In this example, after the reset signal reset is turned ON for a moment and then turned OFF, a plurality of drive vibration pulses are sequentially applied, and further, charge transfer is sequentially performed in synchronization with this, and charge is transferred into the semiconductor region 3. Are accumulated and accumulated. Thereafter, the charge accumulated in the semiconductor region 3 is read out before the next reset signal reset is turned ON.

  FIG. 6 is a cross-sectional view of a part of an imaging device in which the imaging chip shown in FIG. 2 is attached to a wiring board.

  This imaging device is obtained by inverting the imaging chip CP shown in FIG. 2 and attaching the imaging chip CP to the wiring board WB via the multilayer wiring board M1 and the adhesive FL. Inside the multilayer wiring board M1, there are provided through electrodes 7, 5E, 6E electrically connected to the semiconductor regions 3, the transfer electrodes 5, and the potential adjusting unit 6, respectively. The through electrode 7 is connected to the through electrode 8 of the wiring board WB via a bump electrode BP interposed between the wiring board WB and the multilayer wiring board M1, and the through electrode 8 is exposed on the back surface of the wiring board WB. is doing. The through electrode 5E connected to each transfer electrode 5 is connected to the internal wiring 50E of the wiring board WB through a wiring (not shown). A light shielding layer 40 is formed on the surface of the insulating substrate M2 constituting the wiring board WB on the interface side with the adhesive FL, and the incidence of light transmitted through the imaging chip CP to the wiring board WB is suppressed. .

  FIG. 7 is a cross-sectional view of the entire imaging device.

  This imaging device is a back-illuminated distance image measuring device. An enlarged view of a region surrounded by a dotted line G in FIG. 7 corresponds to FIG. In the imaging chip CP, the central portion CR is thinner than the peripheral portion PR, and the thinned region becomes the imaging region, and the reflected light IM from the object enters. In this apparatus, since there is no electrode on the light incident side of the charge generation unit, a distance output and a distance image with a high S / N ratio can be obtained.

  FIG. 8 is a diagram illustrating an overall configuration of the distance image measurement device.

The distance d to the object OJ is measured by a distance image measuring device. As described above, the light source 100 such as LED, the drive signal S _D is applied, the intensity signal L _P of the reflected light image reflected by the object OJ is incident on the imaging area IA of the imaging chip CP. From the imaging chip CP, the charge transfer signal S _L. Charge amounts Q _L and Q _R collected in synchronization with S _R are output, and are input to the arithmetic circuit ART in synchronization with the drive signal _SD . In the arithmetic circuit ART, the distance d is calculated for each pixel as described above, and the calculation result is transferred to the control unit CONT. Control unit CONT controls the driving circuit DRV for driving the light source 100, the charge transfer signal _S L, outputs _{S R,} and displays on the display DSP of the operation result inputted from the arithmetic circuit ART.

  FIG. 9 is a circuit diagram in the pixel.

  When the potential adjusting unit 6 is used as a charge generation region, the charges generated in this region are distributed to the left and right semiconductor regions 3 by alternately applying a voltage to the transfer electrodes A and B. The transfer electrodes A and B each constitute a gate electrode of a field effect transistor.

As described above, the above-described distance image sensor includes an imaging region including a plurality of units (pixels P) arranged two-dimensionally on a semiconductor substrate, and charge amounts Q _L and Q output from the units. _{In the} distance image sensor that obtains a distance image based on _R , one unit is arranged spatially separated from a charge generation region (a region outside the transfer electrode 5) where charge is generated according to incident light. And at least two semiconductor regions (charge collection regions) 3 that collect charges from the charge generation region, and are provided around each of the semiconductor regions 3 and are supplied with charge transfer signals of different phases, and transfer surrounding the semiconductor region 3 And an electrode 5.

  As described above, when the plurality of pixels P are two-dimensionally arranged, the plurality of transfer electrodes 5 are located around the charge generation region. Conversely, the charge generation region is also located around the transfer electrode 5. Will be. Since the transfer electrode 5 surrounds the semiconductor region 3, it is possible to transfer charges from all directions to the semiconductor region 3 by giving a charge transfer signal to the transfer electrode 5. That is, substantially all the peripheral region of the transfer electrode 5 can function as a charge generation region, and the aperture ratio is remarkably improved. Accordingly, the signal amount can be increased, and a distance output with a good S / N ratio and a distance image as its collective information can be obtained.

  In addition, the distance image sensor of the first embodiment further includes a potential adjustment unit 6 provided in the charge generation region and steepening the potential gradient from the charge generation region toward the semiconductor region 3. When the potential gradient becomes steep by the potential adjusting unit 6, the moving speed of the charge transferred from the charge generation region to the semiconductor region 3 becomes high. That is, high-speed imaging is possible. In addition, the potential adjustment unit 6 of the first embodiment is an electrode to which a predetermined potential is applied. Preferably, in this example, a potential lower than the lowest value of the potential applied to the transfer electrode is applied to this electrode. The potential gradient can be increased by applying to the electrode a potential opposite to that caused by an ionized donor (all conductivity types are reversed or acceptor) in the charge collection region.

  Further, the shape of the transfer electrode 5 is an annular shape, so that it is possible to steadily collect charges flowing from all directions into the charge collection region and to prevent the inflow thereof. The shape of the transfer electrode 5 is an annular shape, but it may be a rectangular shape, or may be composed of a group of microelectrodes arranged apart from each other as shown in FIG. In the transfer electrode 5 shown in FIG. 16, a plurality of partial transfer electrodes 51, 52, 53, 54, 55, 56, 57, 58, 59 are arranged at equal intervals. Each of the partial transfer electrodes 51 to 59 has an arc shape, and the inner side surface is along a circle indicated by a dotted line. As described above, the transfer electrode 5 forms an annular shape having a gap. However, in this case, it is assumed that the microelectrodes are electrically connected so that potentials are simultaneously applied to all the electrodes.

  In the above description, the region including the four transfer electrodes is one pixel. However, this may be a region including two transfer electrodes to which charge transfer signals having different phases are applied.

  FIG. 10 is a perspective view of the imaging region of the distance image sensor according to the second embodiment, and FIG. 11 is a cross-sectional view taken along the line XI-XI of the imaging region shown in FIG.

  In the first embodiment, an electrode is used as the potential adjustment unit 6, but the potential adjustment unit 6 of this example is in the same in-plane position as the potential adjustment unit 6 of the first embodiment, and the insulating layer 4. Is a P-type semiconductor region formed under. In this case, the potential adjustment unit 6 functions to increase the potential gradient as in the case of the first embodiment.

  The potential adjusting unit 6 according to the present embodiment has a conductivity type different from that of the semiconductor region 3 and is composed of a semiconductor region having a higher impurity concentration than the surroundings. Thus, the potential gradient can be increased by the conductivity type of the potential adjusting unit 6 being different from that of the semiconductor region 3.

  FIG. 12 is a perspective view of the imaging region of the distance image sensor according to the third embodiment, and FIG. 13 is a cross-sectional view taken along the arrow XIII-XIII of the imaging region shown in FIG.

  In this example, the transfer electrode 5 includes an annular portion 5X and a radiating portion 5Y extending radially outward from the annular portion 5X, and does not include a potential adjusting portion. The radiating portion 5Y extends toward a location where the potential adjusting portion is located in the above-described embodiment, and charges generated in the vicinity of this location are also transferred into the semiconductor region 3 through the radiating portion 5Y. Can do.

  FIG. 14 is an explanatory diagram for describing pixel arrangement.

  In the first to third embodiments, the transfer electrodes A and B are arranged as shown in FIG. 14A, and a square area including four transfer electrodes is described as one pixel P. As shown in FIG. 14B, a group including eight transfer electrodes A and B surrounded by a one-dot chain line may be used as one pixel P. In FIG. 14B, two transfer electrodes A and B adjacent at the center are composed of a set of five transfer electrodes A and B surrounded by a dotted line and five transfer electrodes A and B surrounded by a two-dot chain line. It belongs to both sides of the set. In this case, as shown in FIG. 14A, the charge is collected from the charge generation region having an area nearly twice as large as that in the case where the square region including the four transfer electrodes is one pixel. There is an effect that can be improved.

  FIG. 15 is a diagram for explaining the connection of the charge collection regions.

  In this configuration, in one pixel, at least two semiconductor regions 3 surrounded by a transfer electrode A to which a charge transfer signal having the same phase is applied are electrically connected. In this configuration, at least two semiconductor regions 3 surrounded by transfer electrodes B to which charge transfer signals having the same phase are applied are electrically connected in one pixel.

  In order to connect the semiconductor regions 3 surrounded by the transfer electrode A, metal wirings W1A, W1B, and W1C are used. The metal wiring W1A connected to one semiconductor region 3 surrounded by the transfer electrode A is connected to the metal wiring W1B through the contact hole, and the metal wiring W1B is further connected to the metal wiring W1C through the contact hole. The metal wiring W1C is connected to the other semiconductor region 3.

  Similarly, the metal wiring W2A connected to one semiconductor region 3 surrounded by the transfer electrode B is connected to the metal wiring W2B through a contact hole, and the metal wiring W2B is further connected to the metal wiring W2C through the contact hole. The metal wiring W2C is connected to the other semiconductor region 3 surrounded by the transfer electrode B.

  In this case, the charge amount output from the semiconductor region 3 of each group is averaged, and the characteristic difference for each semiconductor region 3 can be compensated.

  Further, a high-concentration N-type semiconductor region 3 is formed as a charge collection region in a P-type epitaxial layer 2 having a lower concentration than the P-type semiconductor substrate 1 grown on the P-type semiconductor substrate 1. However, if a P-type layer having a higher concentration than the concentration of the P-type epitaxial layer 2 is provided at the bottom of the high-concentration N-type semiconductor region 3 (interface with the P-type epitaxial layer 2), a high concentration is obtained. This is preferable because the influence of an electric field caused by applying a voltage to the N-type semiconductor region 3 can be suppressed. This is because when a voltage is applied to the high-concentration N-type semiconductor region 3, the depletion layer spreads between the P-type epitaxial layer 2 and the electric charge generated by light is transferred to the potential of the transfer electrode by the electric field inside the depletion layer. However, a P-type layer having a concentration higher than that of the P-type epitaxial layer 2 may be provided under the high-concentration N-type semiconductor region 3. This is because the depletion layer can be prevented from spreading so much in the P type epitaxial layer 2 by doing so. Note that the above-described conductivity types can be reversed at once.

  3... Semiconductor region (charge collection region), 5, A, B... Transfer electrode, 6.

Claims (7)

A charge generation region in which charge is generated in response to incident light;
A charge collection region for collecting charges from the charge generation region;
A transfer electrode provided around the charge collection region and provided with a charge transfer signal, and surrounding the charge collection region;
A potential adjusting means for steepening a potential gradient from the charge generation region to the charge collection region;
A distance sensor comprising:   2. The distance sensor according to claim 1, wherein the potential adjusting unit includes a semiconductor region having a conductivity type different from that of the charge collection region and having a higher impurity concentration than the surroundings.   The distance sensor according to claim 1, wherein the potential adjusting unit is an electrode to which a predetermined potential is applied. A plurality of the potential adjusting means;
The plurality of potential adjusting means are arranged at square corners having diagonal lines orthogonal to each other and at which the charge collection regions are located at intersections of the diagonal lines. The distance sensor according to one item. A plurality of the charge collection regions,
2. The potential adjusting means positioned between the plurality of charge collection regions as viewed in a direction connecting the plurality of charge collection regions is shared by the plurality of charge collection regions. The distance sensor as described in any one of -4.   The distance sensor according to claim 1, wherein the transfer electrode has an annular shape. In a distance image sensor that has an imaging region consisting of a plurality of units arranged two-dimensionally on a semiconductor substrate, and obtains a distance image based on the amount of charge output from the unit,
One said unit is the distance sensor as described in any one of Claims 1-6, The distance image sensor characterized by the above-mentioned.

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