JP4971891B2 - Back-illuminated distance measuring sensor and distance measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a backside-illuminated distance measuring sensor and a distance measuring device capable of detecting distance at high precision. <P>SOLUTION: The backside-illuminated distance measuring sensor 1 includes a semiconductor board 1A having an image capturing region 1B which is composed of a plurality of two dimensionally arranged pixels P(m, n). Two electric charges (Q1, Q2) are output from the respective pixels P(m, n) as the signals d'(m, n) which have the above distance information. Respective pixels P(m, n) as micro distance measuring sensors output the signals d'(m, n) according to the distance to an object H so that, when the image of the reflected light from the object H is formed on the image capturing region 1B, the distance image of the object can be obtained as aggregates of the distance information to the respective points on the object H. It is preferable that unnecessary carriers disappear in the recombination region 1C of visible light exciting carriers and do not reach the region just below a photo-gate electrode PG. Furthermore, near-infrared light is absorbed in the region at the depth of 10 &mu;m or more and 100 &mu;m or less. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a back-illuminated distance measuring sensor and a distance measuring device.

  A conventional active optical distance measuring sensor irradiates light from a light source for light projection such as an LED (Light Emitting Diode), and detects reflected light from the object with a light detection element. It is known to output a signal corresponding to the distance up to. A PSD (Position Sensitive Detector) or the like is known as an optical triangulation type optical distance measuring sensor that can easily measure the distance to an object, but in recent years, in order to perform more precise distance measurement, Development of an optical distance measuring sensor of the TOF (Time-Of-Flight) type is expected.

  In addition, an image sensor that can simultaneously acquire distance information and image information with the same chip is required for in-vehicle use, factory automatic manufacturing system, and the like. If an image sensor is installed in front of the vehicle, it is expected to be used for detection / recognition of the vehicle ahead and detection / recognition of pedestrians. Apart from image information, an image sensor that acquires a distance image composed of a single distance information or a plurality of distance information is also expected. It is preferable to use the TOF method for such a distance measuring sensor.

  The TOF method emits pulsed light from a light source for projection toward an object, and detects the pulsed light reflected by the object with a light detection element, thereby making the time difference between the emission timing of the pulsed light and the detection timing. Is measuring. This time difference (Δt) is the time required for the pulsed light to fly at the speed of light (= c) twice as much as the distance d to the object (2 × d), so d = (c × Δt) / 2 is established. The time difference (Δt) can be rephrased as the phase difference between the emission pulse from the light source and the detection pulse. If this phase difference is detected, the distance d to the object can be obtained.

  In general, many light sources for emitting light that emit light in the near-infrared band are used. Since the wavelength in the near-infrared band is closer to the wavelength in the visible light band than the wavelength in the far-infrared band, it is possible to perform condensing and imaging using an optical system such as a lens. Moreover, since the energy density of the near-infrared light component contained in the spectrum of sunlight is less than the visible light component, by using a visible light cut filter, among the near-infrared light components detected by the light detection element, It becomes possible to detect with a high S / N by reducing the ratio of solar light.

  The charge distribution type image sensor has attracted attention as a light detection element for performing distance measurement by the TOF method. That is, in the charge distribution type image sensor, for example, the charge generated in the image sensor in response to the incident detection pulse is distributed in one potential well during the ON period of the emission pulse, and OFF. Distribute to the other potential well during the period. In this case, the ratio of the amount of charge distributed to the left and right is proportional to the phase difference between the detection pulse and the emission pulse, that is, the time required for the pulsed light to fly at the speed of light over twice the distance to the object. It will be. Various methods can be considered as the charge distribution method.

Patent Document 1 below discloses a distance measuring sensor that performs distance measurement by extracting a signal that depends on a delay time when repetitive pulsed light projected from a light source bounces back from a measurement object.
JP 2005-235893 A

  However, when measuring the distance to a moving object that moves at high speed, such as an in-vehicle ranging sensor or a military ranging sensor, it is necessary to increase the charge distribution speed so as to follow the movement of the moving object. Further, in the actual distance measurement, not only one charge distribution but also repeated charge distribution constitutes one frame by integrating charges, and when the charge distribution speed is low, There is a problem that the number of charge distributions constituting one frame must be reduced, sufficient S / N cannot be secured, and precise distance measurement cannot be performed.

  On the other hand, in the case of a TOF type charge distribution type distance measuring sensor using near infrared light as a light source for projection, carriers are generated in the deep part of the semiconductor in response to the incidence of light. For example, the thickness of silicon that absorbs half of light having a wavelength of 850 nm is about 20 μm. In this case, if the operation of attracting carriers into a plurality of potential wells is switched at high speed, most of the carriers cannot reach the potential well, and the amount of charge in the potential well regulates the distance measurement accuracy. The problem was that the charge amount could not be secured, but the normal charge distribution type distance measuring sensor could not detect with high accuracy. Since the measurement environment is basically visible light, visible light becomes noise for high-precision detection using near-infrared light, and it is also necessary to cut off visible light. is there. Although it is possible to provide a visible light cut filter as described above, it is common sense in the industrial use that it is desirable to omit extra parts.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a back-illuminated distance measuring sensor and a distance measuring device capable of performing highly accurate distance detection.

  In order to solve the above-mentioned problems, the inventors of the present invention have made extensive studies and found that carriers generated in the deep part of the semiconductor in response to the incidence of light for projection are carriers generated on the side opposite to the light incident surface. We have come to the knowledge that high-speed and accurate distance measurement can be achieved by drawing into a potential well provided in the vicinity.

That is, the back- illuminated distance measuring sensor according to the present invention includes a light incident surface that is incident after near-infrared light emitted from a light source is reflected by an object, and a semiconductor substrate having a surface opposite to the light incident surface. A photogate electrode provided on the surface, first and second gate electrodes provided adjacent to the photogate electrode on the surface, and immediately below the first and second gate electrodes from a region immediately below the photogate electrode First and second semiconductor regions for reading out carriers flowing into the region, respectively, and a visible light excited carrier recombination region comprising a P-type semiconductor layer or a defect layer is provided on the light incident surface side of the semiconductor substrate. .

In particular, when the visible light absorption coefficient in the semiconductor substrate is α, the thickness of the semiconductor substrate is t1, and the thickness of the visible light excited carrier recombination region is t2, the following relational expression is preferably satisfied. For example, when the wavelength of visible light is set to 700 nm and the depth at which the power of light incident on the semiconductor substrate is 50% is considered as the characteristic amount, the following is obtained.
-(1 / α) × ln (0.5) μm ≦ t2,
・ 10μm ≦ t1 ≦ 100μm

  In this case, 50% of the visible light excited carrier recombination region disappears and does not reach the region immediately below the photogate electrode, and near infrared light is absorbed in a region having a depth of 10 μm or more and 100 μm or less. Therefore, carriers with excellent responsiveness can be collected with high sensitivity in the region immediately below the photogate electrode.

  In this case, the pulsed light from the object incident from the light incident surface (back surface) of the semiconductor substrate reaches a region directly below the photogate electrode provided on the front surface side of the semiconductor substrate. Carriers generated in the semiconductor substrate with the incidence of the pulsed light are distributed from the region directly under the photogate electrode to the region directly under the first and second gate electrodes adjacent thereto. That is, when the detection gate signal synchronized with the drive signal of the light source is alternately applied to the first and second gate electrodes, the carriers generated in the region immediately below the photogate electrode are the regions immediately below the first and second gate electrodes, respectively. And flows from these into the first and second semiconductor regions.

  The ratio of the charge amount of carriers accumulated in the first or second semiconductor region to the total charge amount is that the emitted pulse light emitted by applying a drive signal to the light source and the emitted pulse light reflected by the object are reflected. This corresponds to the phase difference of the detection pulse light that has returned. Even if the charge distribution speed is increased by increasing the frequency of the drive signal to the gate electrode, the generation region of carriers generated in response to the incidence of near-infrared light is opposite to the light incident surface of the semiconductor substrate. Since it is close to the surface on the side, many carriers flow into the first and second semiconductor regions from the region immediately below the photogate electrode, and can be read from these regions. In addition, since light with a wavelength shorter than near infrared tends to be removed in the region on the light incident surface side of the semiconductor substrate, detection for distance measurement is possible without providing a visible light cut filter on the light incident surface side. The detection accuracy of pulsed light can be improved.

  The above-mentioned photogate electrode may be one for each distance measuring sensor, but a plurality of micro distance measuring sensors including the photogate electrode are arranged in a one-dimensional or two-dimensional manner as pixels, and the one-dimensional or two-dimensional A distance measuring sensor capable of obtaining a distance image may be used.

That is, such back-illuminated distance measuring sensor comprises a semiconductor substrate having a light incident surface of the near-infrared light emitted from possess an imaging region including a plurality of pixels light source enters after being reflected by the object In the back-illuminated distance measuring sensor, each of the pixels is provided adjacent to the photogate electrode on the surface and the photogate electrode provided on the surface opposite to the light incident surface of the semiconductor substrate. First and second gate electrodes, and first and second semiconductor regions for reading out carriers flowing from the region immediately below the photogate electrode into the region immediately below the first and second gate electrodes, respectively. On the surface side, a visible light excited carrier recombination region made of a P-type semiconductor layer or a defect layer is provided.

  Since each pixel outputs a signal corresponding to the distance to the object as the above-mentioned minute distance measuring sensor, if the reflected light from the object is imaged in the imaging region, distance information to each point on the object It is possible to obtain a distance image of the object as a collection of

  A distance measuring device including the back-illuminated distance measuring sensor described above includes a back-illuminated distance measuring sensor, a light source that emits near-infrared light, a drive circuit that provides a pulse drive signal to the light source, A control circuit for providing a detection gate signal in synchronization with the pulse drive signal to the second gate electrode; and an arithmetic circuit for calculating a distance to the object from signals read from the first and second semiconductor regions. It is characterized by that.

  As described above, the signal read from the first and second semiconductor regions, that is, the ratio of the charge amount of carriers accumulated in the first or second semiconductor region to the total charge amount is the above-described phase difference, That is, it corresponds to the distance to the object. The arithmetic circuit calculates the distance to the object according to the phase difference. Assuming that the time difference corresponding to the phase difference is Δt, the distance d is preferably given by d = (c × Δt) / 2, but an appropriate correction operation may be added to this. For example, when the actual distance is different from the calculated distance d, a coefficient β for correcting the latter is obtained in advance, and the product obtained by multiplying the calculated distance d by the coefficient β is finally obtained in the product after shipment. It is good also as a general calculation distance d. In addition, when the outside air temperature is measured and the light speed c varies depending on the outside air temperature, the distance calculation can be performed after performing the calculation for correcting the light speed c. Further, the relationship between the signal input to the arithmetic circuit and the actual distance may be stored in advance in the memory, and the distance may be calculated by a lookup table method. The calculation method can be changed depending on the sensor structure, and a conventionally known calculation method can be used.

  In the distance measuring device according to the present invention, the surface of the back-illuminated distance measuring sensor is fixed on the mounting surface of the wiring board, and the photogate electrode, the first gate electrode, and the second gate electrode are It is characterized in that it is connected to the wiring on the wiring board via a bump. In this distance measuring device, when a back-illuminated distance measuring sensor is mounted on a wiring board, the signal can be given to each electrode via each wiring, and the device is miniaturized.

  According to the back-illuminated distance measuring sensor and distance measuring device of the present invention, highly accurate distance detection can be performed.

  Hereinafter, the back-illuminated distance measuring sensor and the distance measuring device according to the embodiment will be described. The same reference numerals are used for the same elements, and duplicate descriptions are omitted.

  FIG. 1 is an explanatory diagram showing the configuration of the distance measuring apparatus.

The distance measuring device includes a back-illuminated distance measuring sensor 1, a light source 3 for emitting near-infrared light, a driving circuit 4 to the light source 3 providing a pulsed driving signal S _P, each of the back-illuminated distance measuring sensor 1 first and second gate electrode included in the pixel (TX1, TX2: see FIG. 5), the pulse drive signal _S gate signal detection is synchronous with the _{P S} L, a control circuit 2 to give _{S R,} measured back illuminated The distance from the signal d ′ (m, n) indicating the distance information read from the first and second semiconductor regions (FD1, FD2: see FIG. 5) of the distance sensor 1 to the object H such as a pedestrian. An arithmetic circuit 5 for calculating is provided. The distance in the horizontal direction D from the back-illuminated distance measuring sensor 1 to the object H is defined as d.

The control circuit 2 is input to the pulse drive signal S _P to the switch 4b of the driving circuit 4. A light projecting light source 3 comprising an LED or a laser diode is connected to a power source 4a via a switch 4b. Therefore, when the pulse drive signal S _P is input to the switch 4b, a drive current having the same waveform as the pulse drive signal S _P is supplied to the light source 3, the pulse light L _P as a probe light for distance measurement from the light source 3 Is output.

When the pulse light L _P is irradiated on the object H, the pulse light is reflected by the object H, the pulse light L _D, and enters the back-illuminated distance measuring sensor 1 outputs a pulse detection signal S _D .

  The back-illuminated distance measuring sensor 1 is fixed on the wiring board 10, and a signal d ′ (m, n) having distance information is output from each pixel via the wiring on the wiring board 10.

The waveform of the pulse drive signal S _P, a square wave of period T, the high level "1", when the low level is "0", the voltage V (t) is given by the following equation.
・ Pulse drive signal S _P :
・ V (t) = 1 (provided that 0 <t <(T / 2))
・ V (t) = 0 (provided that (T / 2) <t <T)
・ V (t + T) = V (t)

The waveforms of the detection gate signals S _L and S _R are square waves with a period T, and the voltage V (t) is given by the following equation.
・ Detection gate signal S _L :
・ V (t) = 1 (provided that 0 <t <(T / 2))
・ V (t) = 0 (provided that (T / 2) <t <T)
・ V (t + T) = V (t)
· Detection gate signal _S R (= _{S L} inversion):
・ V (t) = 0 (provided that 0 <t <(T / 2))
V (t) = 1 (provided that (T / 2) <t <T)
・ V (t + T) = V (t)

The pulse signal _{S P, S L, S R} , S D , it is assumed that has all pulse period 2 × _{T P.} Detection gate signal S _L and the pulse detection signal S _D are both the amount of charge generated in the back-illuminated distance measuring sensor within 1 when "1" Q1, the detection gate signal S _R and the pulse detection signal S _D are both The amount of charge generated in the back-illuminated distance measuring sensor 1 when “1” is defined as Q2.

The phase difference between one detection gate signal S _L and the pulse detection signal S _D in the back-illuminated distance measuring sensor 1, the overlap period when the gate signal for other detection S _R and the pulse detection signal S _D is "1" In FIG. 5, the charge quantity Q2 is proportional to the amount of charge Q2 generated in the back-illuminated distance measuring sensor 1. That is, the charge amount Q2 is the charge amount for the period logical product of the detection gate signal S _R and the pulse detection signal S _D is "1". The total charge quantity generated in one pixel is Q1 + Q2, when the pulse width of the half cycle of the drive signal _{S P} and _{T P, Δt = T P ×} Q2 / (Q1 + Q2) long enough, with respect to the drive signal _{S P} The pulse detection signal _SD is delayed. The flight time Δt of one pulsed light is given by Δt = 2d / c, where d is the distance to the object and c is the speed of light. Therefore, two charge amounts are used as a signal d having distance information from a specific pixel. When (Q1, Q2) are output, the arithmetic circuit 5, a charge amount Q1, Q2 input, based on the half cycle pulse width T _P that is known in advance, the distance to the object H d = ( c × Δt) / 2 = c × T _P × Q2 / (2 × (Q1 + Q2)) is calculated.

  As described above, if the charge amounts Q1 and Q2 are read out separately, the arithmetic circuit 5 can calculate the distance d. The above-described pulse is repeatedly emitted, and the integrated value can be output as the respective charge amounts Q1 and Q2.

  Further, the ratio of the charge amounts Q1 and Q2 to the total charge amount corresponds to the above-described phase difference, that is, the distance to the object H, and the arithmetic circuit 5 determines the distance to the object H according to the phase difference. The distance is calculated. As described above, when the time difference corresponding to the phase difference is Δt, the distance d is preferably given by d = (c × Δt) / 2, but an appropriate correction operation may be added to this. . For example, when the actual distance and the calculated distance d are different, a coefficient β for correcting the latter is obtained in advance, and the product after shipping is obtained by multiplying the calculated distance d by the coefficient β. The calculation distance d may be used. In addition, when the outside air temperature is measured and the light speed c varies depending on the outside air temperature, the distance calculation can be performed after performing the calculation for correcting the light speed c. Further, the relationship between the signal input to the arithmetic circuit and the actual distance may be stored in advance in the memory, and the distance may be calculated by a lookup table method. The calculation method can also be changed depending on the sensor structure, and a conventionally known calculation method can be used for this.

  FIG. 2 is a plan view of the distance measuring sensor.

  The back-illuminated distance measuring sensor 1 includes a semiconductor substrate 1A having an imaging region 1B made up of a plurality of pixels P (m, n) arranged two-dimensionally. From each pixel P (m, n), two charge amounts (Q1, Q2) are output as the signal d '(m, n) having the above-described distance information. Since each pixel P (m, n) outputs a signal d ′ (m, n) corresponding to the distance to the object H as a minute distance measuring sensor, the reflected light from the object H is coupled to the imaging region 1B. If an image is obtained, a distance image of the object as a collection of distance information to each point on the object H can be obtained.

  FIG. 3 is a cross-sectional view taken along the line III-III of the distance measuring sensor shown in FIG.

The back-illuminated distance measuring sensor 1, a pulse light L _D is made incident from the light incident surface 1BK. A surface 1FT opposite to the light incident surface 1BK of the back-illuminated distance measuring sensor 1 is connected to the wiring substrate 10 via an adhesive region AD. The adhesion region AD is a region including an adhesion element such as a bump, and has an insulating adhesive or filler as necessary. The semiconductor substrate 1A constituting the back-illuminated distance measuring sensor 1 has a reinforcing frame portion F and a thin plate portion TF thinner than the frame portion F, and these are integrated. The thickness of the thin plate portion TF is 10 μm or more and 100 μm or less. The thickness of the frame portion F in this example is 200 μm or more and 600 μm or less.

  FIG. 4 is a cross-sectional view of a distance measuring sensor according to a modification.

  This distance measuring sensor differs from that shown in FIG. 3 only in the shape of the semiconductor substrate 1A, and the other configurations are the same. The semiconductor substrate 1A further includes reinforcing portions AF formed in a stripe shape or a lattice shape, and a thin plate portion TF is formed between the reinforcing portions AF, and these are integrated. The thickness of the reinforcing portion AF in this example is the same as the thickness of the frame portion AF, and is 200 μm or more and 600 μm or less. Each pixel described above is formed in the thin plate portion TF. The thin plate portion TF is formed by wet etching using an alkaline etching solution such as KOH. The roughness of the exposed surface formed by etching is 1 μm or less.

  FIG. 5 is an enlarged view of the region V of the distance measuring sensor shown in FIG. 3 or FIG.

The back-illuminated distance measuring sensor 1 includes a light incident surface 1BK and a semiconductor substrate 1A having a surface 1FT opposite to the light incident surface 1BK, and a photogate electrode PG provided on the surface 1FT via an insulating layer 1E. The first and second gate electrodes TX1, TX2 provided adjacent to the photogate electrode PG via the insulating layer 1E on the surface 1FT, and the carriers flowing into the regions immediately below the first and second gate electrodes TX1, TX2 First and second semiconductor regions FD1 and FD2 for reading (electrons e) are provided. The semiconductor substrate 1A of the present embodiment is made of Si, the insulating layer 1E is made of SiO _2.

  The semiconductor substrate 1A is a low impurity concentration P-type semiconductor substrate, the first and second semiconductor regions FD1, FD2 are floating diffusion regions made of a high impurity concentration N-type semiconductor, and the first and second semiconductor regions FD1. , FD2 are formed in the P-type well regions W1, W2, respectively. The periphery of the first and second semiconductor regions FD1 and FD2 is surrounded by well regions W1 and W2 that are higher in concentration than the impurity concentration immediately below the substrate and the first and second gate electrodes. (2) The spread of the depletion layer from the semiconductor regions FD1 and FD2 can be suppressed, the leakage current can be reduced, and trapping of unnecessary carriers due to crosstalk and stray light can be reduced. In addition, the well regions W1 and W2 suppress the coupling between the depletion layer expanded by applying a voltage to the photogate electrode PG and the depletion layer expanded from the first and second semiconductor regions FD1 and FD2.

Part of the first and second semiconductor regions FD1, FD2 is in contact with a region immediately below the gate electrodes TX1, TX2 in the semiconductor substrate 1A. On the light incident surface 1BK side of the semiconductor substrate 1A, an antireflection film 1D is provided via a visible light excited carrier recombination region 1C. That is, a visible light excited carrier recombination region 1C made of a P-type semiconductor layer or a defect layer is provided on the light incident surface side of the semiconductor substrate 1A. The visible light excited carrier recombination region 1C made of a P-type semiconductor layer has a thickness of 0.1 μm to 5 μm, an impurity concentration of 10 ¹⁸ cm ⁻³ to 10 ²⁰ cm ⁻³ , and carriers generated by incidence of visible light are regenerated. Combine and disappear. Further, the thickness of the visible light excited carrier recombination region 1C made of a defect layer formed by gettering, ion implantation, or the like is 0.1 μm to 5 μm, and disappears by recombination of carriers generated by incidence of visible light. Let

When the absorption coefficient of visible light in the semiconductor substrate 1A is α, the thickness of the semiconductor substrate 1A (the total thickness of the thin plate portion including the recombination region 1C) is t1, and the thickness of the visible light excited carrier recombination region is t2, the following relationship It is preferable to satisfy the formula.
-(1 / α) × ln (0.5) μm ≦ t2,
・ 10μm ≦ t1 ≦ 100μm

  In this case, 50% of the visible light excited carrier recombination region 1C disappears and does not reach the region directly below the photogate electrode PG, and near infrared light is preferably in a region having a depth of 10 μm or more and 100 μm or less. Since it is absorbed, carriers with excellent responsiveness can be collected with high sensitivity in the region immediately below the photogate electrode PG.

  Further, the surface roughness of the exposed surface of the visible light excited carrier recombination region 1C, that is, the difference between the maximum value and the minimum value of the surface unevenness is 1 μm or less.

The material of the antireflection film 1D is SiO ₂ or SiN.

  A region immediately below the photogate electrode PG is a P-type having the same conductivity type as that of the semiconductor substrate 1A, and includes an electric field concentration region 1G having an impurity concentration higher than that of the semiconductor substrate 1A. Since the electric field concentration region 1G has an impurity concentration relatively higher than that of the semiconductor substrate 1A, the density of ionized impurities when depleted increases, so that the potential gradient, that is, the electric field can be increased. The electric field concentrates in the area. Since the impurity concentration of the semiconductor substrate 1A is relatively low, a depletion layer spreads over the semiconductor substrate 1A. Therefore, although the depletion layer spreads in the vertical direction from the electric field concentration region 1G immediately below the photogate electrode PG to the low concentration semiconductor substrate 1A, the spread in the horizontal direction is suppressed. As will be described in detail later, in this structure, in the semiconductor substrate 1A immediately below the electric field concentration region 1G, the depletion layer is prevented from spreading in the lateral direction to suppress carriers accumulated as signals, and the first and second Since the coupling with the depletion layer extending from the semiconductor regions FD1 and FD2 can be suppressed, carriers flowing directly into the first and second semiconductor regions FD1 and FD2 can be suppressed, and crosstalk can be reduced. .

  The electric field concentration region 1G is formed by diffusing or implanting an epitaxial layer or impurities in the silicon substrate. When the thickness of the electric field concentration region 1G is reduced to 0.2 μm to 3 μm, preferably 1 μm to 3 μm, an electric field is applied to the low concentration semiconductor substrate 1A, and a depletion layer spreads in the semiconductor substrate 1A.

  The conductivity types of the first and second semiconductor regions FD1, FD2 are different from the conductivity type of the semiconductor substrate 1A, and the first and second semiconductor regions FD1, FD2 are formed in the well regions W1, W2, The conductivity types of the regions W1 and W2 are the same conductivity type as that of the semiconductor substrate 1A, and have an impurity concentration higher than that of the electric field concentration region 1G.

  Since the conductivity types of the first and second semiconductor regions FD1 and FD2 are different from those of the semiconductor substrate 1A, they originally form a PN junction, and a depletion layer is formed from the interface toward the low-concentration semiconductor substrate. spread. On the other hand, in the configuration of the present embodiment, the first and second semiconductor regions FD1, FD2 are formed in the well regions W1, W2, and the impurity concentration of the well regions W1, W2 is sufficiently higher than that of the semiconductor substrate 1A. Since the thickness of the depletion layer extending from the interface between the first and second semiconductor regions FD1, FD2 and the well regions W1, W2 is suppressed, the depletion layer and the original depletion layer extending from directly below the photogate electrode PG are suppressed. Can be suppressed, and crosstalk can be suppressed as described above.

  The wiring substrate 10 includes a semiconductor substrate 10A made of Si, and readout wirings 11h and 15h formed on the semiconductor substrate 10A. These readout wirings 11h and 15h are respectively the first semiconductor region FD1 and the second semiconductor region FD1. It is electrically connected to the semiconductor region FD2.

  A contact electrode 11a, a pad electrode 11b, a bump 11c, a pad electrode 11d, a contact electrode 11e, an intermediate electrode 11f, and a contact electrode 11g are interposed between the first semiconductor region FD1 and the readout wiring 11h.

  A contact electrode 15a, a pad electrode 15b, a bump 15c, a pad electrode 15d, a contact electrode 15e, an intermediate electrode 15f, and a contact electrode 15g are interposed between the second semiconductor region FD2 and the read wiring 15h.

  A first gate line 12g, a second gate line 14g, and a photogate line 13g are provided on the semiconductor substrate 10A, and these are electrically connected to the first gate electrode TX1, the photogate electrode PG, and the second gate electrode TX2, respectively. Connected.

  A contact electrode 12a, a pad electrode 12b, a bump 12c, a pad electrode 12d, a contact electrode 12e, and an intermediate electrode 12f are interposed between the first gate electrode TX1 and the first gate wiring 12g.

  A contact electrode 13a, a pad electrode 13b, a bump 13c, a pad electrode 13d, a contact electrode 13e, and an intermediate electrode 13f are interposed between the photogate electrode PG and the photogate wiring 13g.

  A contact electrode 14a, a pad electrode 14b, a bump 14c, a pad electrode 14d, a contact electrode 14e, and an intermediate electrode 14f are interposed between the second gate electrode TX2 and the second gate wiring 14g.

  Each contact electrode is embedded in a contact hole provided in the insulating layers 1F, 10B, and 10C as shown in the figure.

  The adhesive region AD includes an adhesive layer AD1 made of resin, and bumps 11c, 12c, 13c, 14c, and 15c for connecting each electrode of the back-illuminated distance measuring sensor 1 to various wirings on the wiring board 10. .

  In this distance measuring device, the front surface 1FT of the back-illuminated distance measuring sensor 1 is fixed on the mount surface M of the wiring substrate 10, and the photogate electrode PG, the first gate electrode TX1, and the second gate electrode TX2 are wired. It is connected to wiring on the substrate 10 via bumps. In this distance measuring device, when the back-illuminated distance measuring sensor 1 is mounted on the wiring board 10, the signal can be given to each electrode via each wiring, and the device is miniaturized.

  A light absorption layer SH made of a black resin is formed on the mount surface M of the wiring board 10 to suppress the incidence of light transmitted through the back-illuminated distance measuring sensor 1 to the wiring board 10 and The light reflected by the wiring on the wiring board 10 is prevented from returning to the back-illuminated distance measuring sensor 1 and causing crosstalk. The various electrodes or wirings described above are made of aluminum or polysilicon. The thickness t1 of the semiconductor substrate made of Si in the back-illuminated distance measuring sensor 1 is 10 to 100 μm, preferably 15 to 50 μm, and 20 μm in this example.

  In this back-illuminated distance measuring sensor 1, carriers generated in the deep part of the semiconductor in response to the incidence of light for projection are drawn into a potential well provided in the vicinity of the carrier generation position on the side opposite to the light incident surface 1BK. Fast and accurate distance measurement is possible.

Pulse light L _D from the object incident from the light incident surface (back surface) 1BK of the semiconductor substrate 1A leads to a region immediately under the photo gate electrode PG provided on the surface side of the semiconductor substrate 1A. The carriers generated in the semiconductor substrate 1A with the incidence of the pulsed light are distributed from the region immediately below the photogate electrode PG to the regions immediately below the first and second gate electrodes TX1 and TX2 adjacent thereto. That is, the first and second gate electrodes TX1, TX2 to the light source drive signal _S gate signal detection is synchronous with the _{P S} L, the _{S R,} via the wiring board 10, given alternating, immediately under the photo gate electrode PG The carriers generated in the first region flow into regions immediately below the first and second gate electrodes TX1 and TX2, respectively, and flow into the first and second semiconductor regions FD1 and FD2.

The ratio of the charge amounts Q1 and Q2 of the carriers accumulated in the first semiconductor region FD1 or the second semiconductor region FD2 to the total charge amount (Q1 + Q2) is the emitted pulse light emitted by applying the drive signal _SP to the light source. This corresponds to the phase difference of the detected pulse light that has returned by reflecting the emitted pulse light by the object H.

Even if the charge distribution speed is increased by increasing the frequency of the drive signals (detection gate signals S _L and S _R ) to the gate electrodes TX1 and TX2, it is generated in response to the incidence of near-infrared light. Since the carrier generation region is closer to the surface 1FT on the opposite side of the light incident surface 1BK of the semiconductor substrate 1A, many carriers flow into the first and second semiconductor regions FD1, FD2 from the region immediately below the photogate electrode PG. From these regions, the stored charges Q1 and Q2 can be read out via the wirings 11h and 15h of the wiring board 10. Further, since light having a wavelength shorter than near infrared tends to be removed in the region on the light incident surface 1BK side of the semiconductor substrate 1A, it is not necessary to provide a visible light cut filter on the light incident surface side. The detection accuracy of the detected pulse light can be improved.

  FIG. 6 is a plan view of a pixel of the distance measuring sensor.

In the back-illuminated distance measuring sensor 1 described above, an N-type well region W3 may be provided outside the P-type well region W2. The well region W3 can perform pixel separation and absorb unnecessary carriers generated due to stray light. The well regions W1, W2, and W3 have the same depth. The thickness / impurity concentration of each semiconductor region is as follows.
Semiconductor substrate 1A: thickness 10 to 100 μm / impurity concentration 1 × 10 ¹² to 10 ¹⁵ cm ⁻³
Well regions W1, W2: thickness 0.5 to 3 μm / impurity concentration 1 × 10 ¹⁶ to 10 ¹⁸ cm ⁻³
Semiconductor regions FD1, FD2: thickness 0.1 to 0.4 μm / impurity concentration 1 × 10 ¹⁸ to 10 ²⁰ cm ⁻³
Well region W3: thickness 0.5 to 3 μm / impurity concentration 1 × 10 ¹⁶ to 10 ¹⁸ cm ⁻³
Electric field concentration region 1G (FIG. 5): thickness 0.2 to 3 μm / impurity concentration 1 × 10 ¹³ to 10 ¹⁶ cm ⁻³

  In this example, by using a high resistance substrate (specific resistance 10 kΩ · cm in this example) as the semiconductor substrate 1A, a depletion layer starts from a region immediately below the photogate electrode PG when a bias voltage is applied to the photogate electrode PG. Can be spread radially, the light utilization efficiency (quantum efficiency) can be increased, and electric charges that directly enter the first and second semiconductor regions FD1 and FD2 can be captured to reduce crosstalk.

In addition, the thickness of the semiconductor substrate 1A of this example is 20 μm, the impurity concentration is 1 × 10 ¹² cm ⁻³ , the impurity concentrations of the well regions W1 and W2 are 1 × 10 ¹⁷ cm ⁻³ , and the impurity concentrations of the semiconductor regions FD1 and FD2 Is 1 × 10 ¹⁹ cm ⁻³ , the impurity concentration of the well region W3 is 1 × 10 ¹⁷ cm ⁻³ _{, and} the impurity concentration of the electric field concentration region 1G is 1 × 10 ¹⁵ cm ⁻³ .

  FIG. 7 is a cross-sectional view in the vicinity of the back gate. Note that the semiconductor substrate 1A having a low impurity concentration may be formed of an epitaxial layer.

  That is, in order to fix the potential of the semiconductor substrate 1A of the back-illuminated distance measuring sensor 1 to the reference potential, the P-type back gate semiconductor region containing a high concentration impurity in the P-type well region W1 (W2). BG is provided. A ground wiring 16h is provided on the semiconductor substrate 10A of the wiring substrate 10 provided with the signal readout circuit. A contact electrode 16a, a pad electrode 16b, a bump 16c, a pad electrode 16d, a contact electrode 16e, an intermediate electrode 16f, and a contact electrode 16g are interposed between the back gate semiconductor region BG and the ground wiring 16h. Electrically connected.

  FIG. 8 is a cross-sectional view of the vicinity of the through electrode.

  In order to fix the potential of the semiconductor substrate 1A of the back-illuminated distance measuring sensor 1 described above to the reference potential, it was electrically connected to the visible light excited carrier recombination region 1C made of a P-type semiconductor layer instead of the back gate electrode. It is good also as providing the penetration electrode 17x. A ground wiring 17 h is provided on the semiconductor substrate 10 </ b> A of the wiring substrate 10. A contact electrode 17a, a pad electrode 17b, a bump 17c, a pad electrode 17d, a contact electrode 17e, an intermediate electrode 17f, and a contact electrode 17g are interposed between the through electrode 17x and the ground wiring 17h. Connected to.

  FIG. 9 is a potential diagram for explaining the carrier accumulation operation.

At the time of light incidence, the potential φPG in the region immediately below the photogate electrode _PG is set slightly higher than the substrate potential. In this potential diagram, the downward direction is the positive direction of the potential. In the figure, the potential φ _TX1 in the region immediately below the gate electrode _TX1 , the potential φ _{TX2 in} the region immediately below the gate electrode TX2, and the potential φ _{FD1 in the} semiconductor region FD1 are shown. , potential phi _FD2 of the semiconductor area FD2 is shown.

High potential of the detection gate signal S _L is inputted to the gate electrode TX1, the carriers generated immediately under the photo gate electrode PG (electrons e), according to the potential gradient, through a region immediately below the gate electrode PX1 Thus, the charge is accumulated in the potential well of the first semiconductor region FD1, and the charge amount Q1 is accumulated in the potential well.

  FIG. 10 is a potential diagram for explaining the carrier accumulation operation.

At the time of light incidence, the potential φPG in the region immediately below the photogate electrode _PG is set slightly higher than the substrate potential.

Following detection gate signal S _L, the high potential of the detection gate signal S _R is inputted to the gate electrode TX2, carriers generated immediately under the photo gate electrode PG (electrons e), according to potential gradient Then, it accumulates in the potential well of the second semiconductor region FD2 through the region immediately below the gate electrode PX2, and the charge amount Q2 is accumulated in this potential well.

  As described above, the charges Q1 and Q2 accumulated in each potential well are read out to the outside through the read wirings 11h and 15h (see FIG. 5) provided on the wiring board 10.

  FIG. 11 is a graph showing the relationship between the wavelength (nm) of incident light and the absorption coefficient α.

For light absorption, I (light intensity at a certain depth), I _o (light intensity near the semiconductor substrate surface), x (depth from the semiconductor substrate surface), α (light absorption coefficient) are used. , I = I _o × exp (−α × x). From this equation, the depth of the Si semiconductor substrate that absorbs half of the light of wavelength = 700 nm is about 3 μm. The thickness t1 of the thin plate portion of the semiconductor substrate 1A in this embodiment is 10 μm to 100 μm, light in the visible band shorter than the near infrared band is absorbed, and a visible light cut filter is not provided on the light incident surface side. High-precision ranging is possible. In other words, the thickness of the light sensitive area t = t1 - is - (1 / α) × ln (I / I O) ().

Also, the light absorption coefficient α = 1.0 × 10 ³ (cm ⁻¹ ) when the wavelength is 800 nm, and the light absorption coefficient α = 2.0 × 10 ² (cm ⁻¹ ) when the wavelength is 900 nm. The depth at which 63% of the incident light is absorbed (when I / I _o = 1 / e) is 10 μm at a wavelength of 800 nm and 50 μm at a wavelength of 900 nm. Thereby, if the thickness of the semiconductor substrate is 10 to 50 μm, light in the near-infrared band can be sufficiently absorbed.

  FIG. 12 is a graph showing a spectrum (solid line) indicating the energy density of sunlight and a spectrum (dotted line) indicating the relative light intensity of the near-infrared light emitting LED.

  The spectrum of sunlight has a peak in the visible band (about 500 nm), while the spectrum of a near infrared light emitting LED has a peak at, for example, 870 nm. Therefore, by removing the visible band light with an appropriate visible band cut filter, the pulsed light from the light source 3 is selectively separated from the sunlight, and further, carriers are formed on the side opposite to the light incident surface of the semiconductor substrate. Since it is configured to generate, carriers generated with high near-infrared sensitivity can be collected in response to a high sorting speed, and highly accurate ranging can be performed. Further, since light in the visible band shorter than the near-infrared band is absorbed on the light incident surface of the semiconductor substrate of the back-illuminated distance measuring sensor, high-precision can be achieved without providing a visible light cut filter on the light incident surface side. Ranging is possible.

  FIG. 13 is a graph showing the relationship between the depth (μm) from the light incident surface and the light intensity (au).

  The thickness of the thin plate portion of the semiconductor substrate of the back-illuminated distance measuring sensor is 15 μm. The light intensity (au) corresponds to the number of electrons generated at that position.

  In the front-illuminated distance measuring sensor, if the depletion layer expands to a depth of 10 μm and carriers can be captured, a carrier signal component corresponding to the dotted hatched region R1 is obtained.

  On the other hand, in the case of a back-illuminated distance measuring sensor, assuming that carriers are captured in a range of 10 μm, the solid line hatched region R2 is a carrier signal component. If the number of carriers (sensitivity) is simply compared, the back-illuminated distance measuring sensor seems to be inferior to the front-illuminated distance measuring sensor in terms of sensitivity. However, the necessary signal is near-infrared wavelength, and if the substrate concentration, applied voltage, etc. are adjusted and the depletion layer just below the photogate electrode is expanded to the thickness of the substrate, it is higher than the surface incidence type distance measuring sensor Sensitivity is obtained. Furthermore, by expanding the depletion layer, crosstalk with respect to oblique incidence can be reduced.

  Also, if the gate electrodes PG, TX1, TX2 are made of metal, or if a metal film is formed on the light incident surface side as polysilicon, the light once transmitted through the semiconductor substrate is reflected by this metal. Light utilization efficiency can be increased. By utilizing reflection, carriers generated in the hatched region R3 can also be captured, so that sensitivity can be improved.

  Further, a visible band cut filter may be deposited on the light incident surface side of the semiconductor substrate. The distance measuring sensor described above can be modularized including a light source.

  Further, as a result of examining the relationship between the frequency of the drive signal and the measurement distance range, it was found that when the measurement range is a little less than 1 m to 200 m, the operation frequency of the drive signal is appropriately 0.375 MHz to 100 MHz.

  Since carrier mobility is a unique value, there is no operating frequency dependency. Further, by changing parameters such as the voltage applied to the gate electrode, the substrate concentration, and the gate oxide film thickness, the charge distribution efficiency (transfer rate) changes. For example, when a high voltage is applied to the gate voltage and the gate oxide film thickness is increased appropriately on a low-concentration (high-resistance) substrate, the effect of a fringing electric field is added in addition to the movement of carriers due to diffusion, and charges are transferred at high speed. It becomes possible to do. By increasing the thickness of the insulating layer 1E, a fringing electric field can be formed. A preferable thickness of the insulating layer 1E for forming a fringing electric field is 50 to 1000 nm.

  Note that the above-described photogate electrode PG may be one for each distance measuring sensor, and a plurality of micro distance measuring sensors including a photogate electrode are arranged in a one-dimensional or two-dimensional manner as pixels. A distance measuring sensor capable of obtaining a distance image may be used. It is also possible to provide a light-shielding film opened only above the photogate electrode on the light incident surface side of the back-illuminated distance measuring sensor 1, thereby reducing crosstalk due to oblique incidence on the semiconductor regions FD1 and FD2. You can also

  The potential distribution in the distance measuring sensor was simulated.

  FIG. 14 is a diagram showing the potential distribution in the semiconductor substrate, and FIG. 15 shows the potential immediately below the photogate electrode PG, the two gate electrodes TX1, TX2, and the semiconductor regions FD1, FD2. The horizontal axis in FIG. 15 corresponds to the horizontal axis in FIG.

  2V was applied to the gate electrode TX1, 1V was applied to the photogate electrode PG, and 0V was applied to the gate electrode TX2. The potential immediately below the gate electrodes TX1 and TX2 rises from the region immediately below the photogate electrode PG. By the incidence of near-infrared light to these regions, carriers are efficiently acquired and the potential is significantly higher than the surroundings. Can be transferred into the semiconductor regions FD1 and FD2. The semiconductor regions FD1 and FD2 are N-type semiconductors having a high impurity concentration, and there are positively ionized donors inside, and the potential is high.

It is explanatory drawing which shows the structure of a distance measuring device. It is a top view of a ranging sensor. FIG. 3 is a sectional view of the distance measuring sensor shown in FIG. 2 along arrows III-III. It is sectional drawing of the distance measuring sensor which concerns on a modification. FIG. 5 is an enlarged view of a region V of the distance measuring sensor shown in FIG. 3 or FIG. 4. It is a top view of the pixel of a ranging sensor. It is sectional drawing of the back gate vicinity. It is sectional drawing of the penetration electrode vicinity. It is a potential diagram for explaining carrier accumulation operation. It is a potential diagram for explaining carrier accumulation operation. It is a graph which shows the relationship between the wavelength (nm) of incident light, and the absorption coefficient (alpha). It is a graph which shows the spectrum (solid line) of sunlight, and the spectrum (dotted line) of a light source. It is a graph which shows the relationship between the depth (micrometer) from a light-incidence surface, and light intensity (au). It is a figure which shows potential distribution in a semiconductor substrate. It is a graph which shows the potential right under photogate electrode PG, 2 gate electrode TX1, TX2, and semiconductor region FD1, FD2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Back-illuminated type distance measuring sensor, 1A ... Semiconductor substrate, 1B ... Imaging area, 1C ... Visible light excitation carrier recombination area, 1D ... Antireflection film, 1E ... Insulation Layer, 1BK ... light incident surface, 1FT ... surface, 2 ... control circuit, 3 ... light source, 4 ... drive circuit, 5 ... arithmetic circuit, 10 ... wiring board, 17x ... through electrode, AD1 ... adhesive layer, AD ... adhesive region, AF ... reinforcing part, BG ... back gate semiconductor region, F ... frame part, FD1, FD2 ... Semiconductor region, H ... object, M ... mount surface, P ... pixel, PG ... photogate electrode, PX1 ... gate electrode, PX2 ... gate electrode, SH ... light Absorbing layer, TF ... thin plate, W1, W2, W3 ... each well region, 1G ... electric field concentration Pass.

Claims (5)

A semiconductor substrate having a light incident surface incident after the near infrared light emitted from the light source is reflected by the object and a surface opposite to the light incident surface;
A photogate electrode provided on the surface;
First and second gate electrodes provided adjacent to the photogate electrode on the surface;
First and second semiconductor regions for reading out carriers flowing from the region immediately below the photogate electrode into the regions immediately below the first and second gate electrodes, respectively;
With
The light incident surface side of the semiconductor substrate is provided with a visible light excited carrier recombination region composed of a P-type semiconductor layer or a defect layer,
A back-illuminated distance measuring sensor. In the back-illuminated distance measuring sensor having a semiconductor substrate having a light incident surface of the near-infrared light emitted from possess an imaging region including a plurality of pixels light source enters after being reflected by the object,
Each of the pixels
A photo gate electrode provided on a surface of the opposite side to the light incident surface of the semiconductor substrate,
First and second gate electrodes provided adjacent to the photogate electrode on the surface;
First and second semiconductor regions for reading out carriers flowing from the region immediately below the photogate electrode into the regions immediately below the first and second gate electrodes, respectively;
With
The light incident surface side of the semiconductor substrate is provided with a visible light excited carrier recombination region composed of a P-type semiconductor layer or a defect layer,
A back-illuminated distance measuring sensor. When the absorption coefficient of visible light in the semiconductor substrate is α, the thickness of the semiconductor substrate is t1, and the thickness of the visible light excited carrier recombination region is t2, the following relationship:
− (1 / α) × ln (0.5) μm ≦ t2,
10 μm ≦ t1 ≦ 100 μm
The back-illuminated distance measuring sensor according to claim 1 or 2, wherein: The back-illuminated distance measuring sensor according to any one of claims 1 to 3,
A light source for emitting near-infrared light,
A drive circuit for applying a pulse drive signal to the light source;
A control circuit for providing a detection gate signal in synchronization with the pulse drive signal to the first and second gate electrodes;
From the read signal from said first and second semiconductor regions, and the arithmetic circuit for calculating a distance to the object,
A distance measuring device comprising:   4. The surface of the back-illuminated distance measuring sensor according to claim 1 is fixed on a mounting surface of a wiring board, and the photogate electrode, the first gate electrode, and the second gate electrode are fixed. Is connected to the wiring on the wiring board via a bump.

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