JP5297907B2 - Photodetector - Google Patents

Description

  The present invention relates to a photodetecting device including a photodiode array having a plurality of photodiodes operating in a Geiger mode.

  An avalanche photodiode (hereinafter referred to as APD) is limited to a multiplication factor of several hundreds as noise increases with increasing voltage. However, if a reverse bias voltage higher than the breakdown voltage of APD is applied, one photon is Even if it is incident, a discharge phenomenon occurs. This state is called “Geiger mode”, and the multiplication factor is about 1 million times. Therefore, even if there is one incident photon, it can be counted as a signal.

  However, in a normal APD, even if one photon enters one APD or multiple photons enter, it is counted as one signal, and the number of photons cannot be detected.

  On the other hand, in the photon counting optical semiconductor element “MPPC” (registered trademark), an APD is divided into small pixels, and these pixels are connected in parallel two-dimensionally to form a light detection surface. In MPPC, when a certain APD pixel detects a photon and performs Geiger discharge, a pulsed signal is obtained by the action of a quenching resistance of the pixel. Since each APD pixel counts photons, even when a plurality of photons are incident at the same timing, the number of incident photons is determined according to the output charge amount or signal intensity of the total output pulse.

  Such a photodiode array is described in, for example, Patent Document 1 described below, and exhibits excellent characteristics.

International Publication No. WO2008 / 004547 Pamphlet

  However, the output from the above APD pixel is expected to be further increased. Simply increasing the voltage applied to each APD pixel increases the output, but in this case the noise increases.

  The present invention has been made in view of such a problem, and an object thereof is to provide a photodetector that can increase the output from each photodiode without increasing the applied voltage.

According to the present invention, in order to measure a signal corresponding to the number of incident photons , in the photodetector having a photodiode array in which a plurality of photodiodes are formed on a semiconductor substrate, each photodiode operating in Geiger mode The semiconductor substrate of the first conductivity type, the first semiconductor region of the second conductivity type formed on one surface side of the semiconductor substrate, and formed in the first semiconductor region than the first semiconductor region. A second conductivity type second semiconductor region having a high impurity concentration; a first electrode electrically connected to the semiconductor substrate; a surface electrode formed on the second semiconductor region; end is connected, and a resistor layer connected in series with the photodiode, the light detection device is electrically connected to the other end of the resistive layer, wherein the semiconductor Provided on the plate, the signal read line for reading out a signal from the photodiode, provided at the periphery of each of the photodiodes on the semiconductor substrate, is disposed between the surface electrode and the signal read line, a first reflector made of a metal layer, a metal second reflector to re-reflecting the light reflected by said first reflector to said photodiode direction, Bei example and a first reflector, wherein There is a gap between the electrode and the surface electrode, and light can enter the first semiconductor region through the gap .

  According to this photodetection device, there is a first reflector on the surface of the semiconductor substrate, and in particular, since the first reflector can be provided in a dead space that does not have a photodetection function, it reflects incident light, This is reflected again by the second reflector and reenters each photodiode. Thereby, since the final incident light quantity to the photodiode can be increased, the output from each photodiode can be increased. Of course, since the signal readout wiring is also generally made of metal, it also functions as a reflector. However, in the present invention, in addition to such a negative reflector, a positive first reflector is provided on the substrate surface. It is provided.

  In addition, it is preferable that the photodetecting device includes a metal package that houses the photodiode array, and the second reflector is constituted by an inner surface of the package.

  In this case, since the second reflector can be constituted by the inner surface of the metal package, there is no need to separately provide another second reflector, and the number of parts can be reduced. Of course, another second reflector may be provided.

  Each of the photodiodes is formed in the first semiconductor region, the first conductivity type semiconductor substrate, a second conductivity type first semiconductor region formed on one surface side of the semiconductor substrate, and the first semiconductor region. A second conductivity type second semiconductor region having a higher impurity concentration than the first semiconductor region, a first electrode electrically connected to the semiconductor substrate, and a surface formed on the second semiconductor region An electrode, wherein the first reflector is electrically separated from the surface electrode.

  The semiconductor substrate and the first semiconductor region constitute a PN junction, and a photodiode is formed by providing a high-concentration second semiconductor region. The anode and cathode of the photodiode are provided with electrodes, respectively, and one surface electrode is electrically separated from the first reflector. Thereby, the 1st reflector is clearly distinguished from the surface electrode, and the freedom degree of the design for arrange | positioning this in the location suitable for reflection has increased.

  Moreover, it is preferable that there is a gap between the first reflector and the surface electrode, and light can enter the first semiconductor region through the gap. Thereby, the aperture ratio when light enters from the surface side can be increased, and the photon detection accuracy can be increased.

Further, the present invention is to measure the signal corresponding to the number of incident photons, the photodetector having a photodiode array comprising forming a plurality of photodiodes on a semiconductor substrate, each of said photo-operating in Geiger mode The diode is formed in the first semiconductor region, the first conductive type semiconductor substrate, a second conductive type first semiconductor region formed on one surface side of the semiconductor substrate, and the first semiconductor region. A second semiconductor region of a second conductivity type having a higher impurity concentration, a first electrode electrically connected to the semiconductor substrate, a surface electrode formed on the second semiconductor region, and the surface electrode on the other hand it is connected to an end to, and a resistor layer connected in series with the photodiode, the light detection device is electrically connected to the other end of the resistive layer, each A grid-like or mesh first reflector made of metal layer, wherein provided on said semiconductor substrate so as to surround the surface electrodes of the photodiode, the photodiode direction the light reflected by said first reflector A second reflector made of metal that re-reflects, and there is a gap between the first reflector and the surface electrode, and light enters the first semiconductor region through the gap. May be incident .

  According to this structure, since the reflected light can be effectively used by using the first and second reflectors, light detection can be performed with very high efficiency. Further, by using the first reflector as a signal line in common, the resistance value can be lowered, so that very high-speed signal reading can be performed.

  According to the photodetector of the present invention, the output from each photodiode can be increased.

It is a perspective view of a photodiode array. FIG. 2 is a cross-sectional view (a) taken along the line II-II of the photodiode array shown in FIG. It is a circuit diagram of the whole photodiode array. It is a perspective view of the photodiode array concerning another embodiment. FIG. 5 is a VV arrow cross-sectional view of the photodiode array shown in FIG. 4. It is a longitudinal cross-sectional view of the photodetector which accommodated the photodiode array in the package. It is a perspective view of the photodiode array concerning another embodiment.

  Hereinafter, a photodetecting device including the photodiode array according to the embodiment will be described. In the description, the same reference numerals are used for the same elements, and duplicate descriptions are omitted.

  FIG. 1 is a perspective view of a photodiode array, and FIG. 2 is a sectional view (a) taken along the line II-II of the photodiode array shown in FIG. 1 and a circuit diagram (b) thereof. FIG. 3 is an overall circuit diagram of the photodiode array.

  The photodiode array 10 is formed by forming a plurality of photodiodes D1 (see FIG. 3) on an N-type (first conductivity type) semiconductor substrate 1N.

  Each photodiode D1 is formed in a first semiconductor region 1PA of P type (second conductivity type) formed on one surface side of the semiconductor substrate 1N, and in the first semiconductor region 1PA. And a P-type (second conductivity type) second semiconductor region 1PB having a higher impurity concentration. Furthermore, the photodiode D1 has a first electrode E1 electrically connected to the semiconductor substrate 1N and a surface electrode E3 formed on the second semiconductor region 1PB. The planar shape of the first semiconductor region 1PA is a rectangle, the second semiconductor region 1PB is positioned inside the first semiconductor region, and the planar shape is a rectangle. Further, the depth of the first semiconductor region 1PA is deeper than that of the second semiconductor region 1PB. In addition, the semiconductor substrate 1 in FIG. 1 shows a substrate including both an N-type semiconductor substrate 1N and P-type semiconductor regions 1PA and 1PB.

  In addition, the photodiode array 10 includes a metal layer formed of an insulating layer L (see FIG. 2) on the semiconductor substrate 1N outside the first semiconductor region 1PA for each individual photodiode D1. One reflector E2 and a surface electrode E3 are provided with a resistance layer (quenching resistance) R1 which is continuous at one end and extends along the surface of the insulating layer L on the first semiconductor region 1PA. In FIG. 1, the insulating layer L shown in FIG. 2 is omitted for clarity of the structure.

  Further, the first reflector E2 of this example is made of a reflector E21 made of a metal layer having an L-shaped planar shape. The first reflector E21 (E2) located on the semiconductor substrate 1N and the annular surface electrode E3 having the first opening are electrically isolated. That is, the anode and the cathode of the photodiode D1 are provided with electrodes, respectively, but one surface electrode E3 is electrically separated from the first reflector E2. Thereby, the 1st reflector E2 is clearly distinguished from the surface electrode E3, and the freedom degree of the design for arrange | positioning this in the location suitable for reflection has increased. Note that the other end of the resistance layer R1 connected to each photodiode D1 is electrically connected to a common signal readout line TL via a wiring electrode continuous to the resistance layer R1 as necessary.

  In FIG. 1, a pair of photodiodes adjacent to each other in the column direction (regions immediately below the semiconductor region 1PA) are both connected to a signal readout line TL extending in the row direction via a resistance layer R1. A plurality of pairs of photodiodes are respectively connected to the signal readout line TL via a resistance layer R1. A plurality of signal lines TL extending in the row direction are aligned along the column direction, and a plurality of pairs of photodiodes are similarly connected to the individual signal lines TL via the resistance layer R1. Has been. Each signal line TL shown in FIG. 1 is finally all connected, and a circuit as shown in FIG. 3 is configured as one signal line TL in terms of circuit.

  The resistance layer R1 has a higher resistivity than the surface electrode E3 to which it is connected, and a higher resistivity than the first reflector E2. Specifically, the resistance layer R1 is made of polysilicon, and the remaining electrodes and reflectors are all made of a metal such as aluminum. When the semiconductor substrate 1 is made of Si, AuGe / Ni or the like is often used as the electrode material in addition to aluminum. Further, when Si is used, a Group 3 element such as B is used as the P-type impurity, and a Group 5 element such as N, P, or As is used as the N-type impurity. Note that the semiconductor conductivity type N-type and P-type can function even if they are replaced with each other to form an element. As a method for adding these impurities, a diffusion method or an ion implantation method can be used.

As a material of the insulating layer L, SiO ₂ or SiN can be used. As a method of forming the insulating layer L, when it is made of, for example, SiO ₂ , a thermal oxidation method or a sputtering method can be used.

  In the case of the above-described structure, a photodiode PN (FIG. 2B) is formed by forming a PN junction between the N-type semiconductor substrate 1N and the P-type first semiconductor region 1PA. . The semiconductor substrate 1N is electrically connected to the first electrode E1 formed on the back surface of the substrate, and the first semiconductor region 1PA is connected to the surface electrode E3 via the second semiconductor region 1PB. The resistance layer R1 is connected in series to the photodiode D1 (see FIG. 2B).

  In such a photodiode array, each photodiode is operated in a Geiger mode. In the Geiger mode, a reverse voltage larger than the breakdown voltage of the photodiode is applied between the anode and the cathode of the photodiode. That is, the (−) potential V1 is applied to the anode and the (+) potential V2 is applied to the cathode. Note that the polarities of these potentials are relative, and one of the potentials can be a ground potential.

  The anode is a P-type semiconductor region 1PA, and the cathode is an N-type semiconductor substrate 1N. This photodiode functions as an avalanche photodiode. When light (photon) is incident on the photodiode, photoelectric conversion is performed inside the substrate to generate photoelectrons, and the P-type semiconductor region 1PA shown in FIG. In the vicinity region AVC of the PN junction interface, avalanche multiplication is performed, and the amplified electron group flows toward the electrode E1.

  The first reflector E2 is provided on the surface of the semiconductor substrate 1N outside the first semiconductor region 1PA having a relatively low impurity concentration relative to the second semiconductor region 1PB. The area of the exposed surface of the semiconductor substrate 1N is a dead space that hardly contributes to detection with respect to light incidence, but in the present invention, since the first reflector E2 is provided, the light incident thereon Is reflected again by the second reflector (the inner surface of the metal package (see FIG. 6)), so that the re-reflected light can be effectively guided to the photodiode.

  In addition, in the case of this structure, the surface electrode E3 of the photodiode D1 and the first reflector E2 can be simultaneously formed by, for example, a sputtering method or a vapor deposition method, so that there is an advantage that the manufacturing method becomes easy. Of course, patterning may be performed by a lift-off method or an etching method. Note that the polysilicon resistance layer R1 continuous to the electrode may be patterned by a lift-off method or an etching method.

  Further, as described above, the other end of the resistance layer R1 connected to each photodiode D1 is electrically connected to the common signal readout line TL along the surface of the semiconductor substrate 1N. The plurality of photodiodes D1 operate in Geiger mode, and each photodiode D1 is connected to a common signal line TL. Therefore, when photons are incident on the plurality of photodiodes D1 simultaneously, the plurality of photodiodes D1. All the outputs of D1 are input to a common signal line TL, and are measured as a high-intensity signal according to the number of incident photons as a whole. A load resistor that causes a voltage drop for signal readout may be connected to the signal readout line TL.

  The shape of the surface electrode E3 shown in FIG. 1 is annular, and a first opening is formed inside thereof. A gap (second opening) is formed between the first reflector E21 separated from the surface electrode E3 and the surface electrode E3. The shape of the first reflector E21 is L-shaped, and the L-shaped first reflector E21 is arranged with a substantially L-shaped gap so as to face two sides of the rectangular annular surface electrode E3. It is. Light can enter the first semiconductor region 1PA through the first opening and the second opening, respectively. Thereby, the aperture ratio when light enters from the surface side can be increased, and the photon detection accuracy can be increased.

  The above-described structure is a structure of a front-illuminated photodiode array, in which the thickness of the semiconductor substrate is reduced and the backside electrode E1 is used as a transparent electrode, or another position of the semiconductor substrate 1N (for example, the substrate surface) If it is arranged on the side), it can function as a back-illuminated photodiode array. Of course, such a modification can also be applied to other embodiments.

  FIG. 4 is a perspective view of a photodiode array according to another embodiment. FIG. 5 is a cross-sectional view of the photodiode array shown in FIG.

  The photodiode array according to this embodiment is different from the photodiode array shown in FIG. 1 only in the formation region of the first reflector E2, and the other configuration is the same as that shown in FIG. . In the figure, the insulating layer L on the surface is omitted for clarity of explanation, but actually, the insulating layer L exists as shown in FIG.

  The first reflector E2 in the present embodiment includes the reflector E21 shown in FIG. 1 and the extended reflector E21e. The reflector E21 as the main body is a portion located via the insulating layer L directly above the high impurity concentration semiconductor substrate 1N shown in FIG. The extended reflector E21e is continuous with the two inner sides of the L-shaped reflector E21 and is interposed between the surface electrode E3 and the surface electrode E3. Even in such a structure, since the extended reflector E21e reflects light in addition to the normal reflector E21, the second reflector re-reflects the light so that the light is reflected by the photodiode. Can be made incident.

  FIG. 6 is a longitudinal sectional view of a photodetecting device in which a photodiode array is housed in a package.

  In this photodetection device, the lower end portion of the metal cylinder is bent outward so that it has an L-shaped cross section, so that the stem 16 constituting the lip portion and the side tube with the inner surface fixed to the outer surface of the stem 16 As a metal cap body 15. The cap body 15 has a hat shape in which one end of a cylindrical shape having a tube axis AX is closed, and a glass incident window 20 is attached to the top of the cap body 15. A hermetic seal 17 made of glass is interposed between the stem 16 and the leads (pins) 12 and 14, and the inside of the container (package) made of these is sealed. The lead pin 12 is electrically connected to the signal readout line TL (see FIG. 1) of the photodiode array 10 through the bonding wire 18, and the lead pin 14 is connected through the metal support 11 as an attachment member. Are electrically connected to the first electrode E1 (see FIG. 2A), and a reverse bias voltage is applied between them.

  A photodiode array 10 is fixed on the support base 11. The lead pin 13 is electrically connected to the stem 16 and the cap body 15.

  The support base 11, the lead pins 12, 13, and 14, the stem 16, and the cap body 15 are made of Kovar.

  When light (photon) 21 enters through the entrance window 20, it enters into the opening of any pixel (photodiode D1) of the photodiode array 10, is multiplied, and is taken out from the lead 12 as a signal. It is.

  The cap body 15 constituting the package is made of metal, and the inner surface thereof constitutes a second reflector. Therefore, as shown in the figure, even when incident light is reflected by the first reflector formed on the surface of the photodiode array 10, it is reflected by the mirror surface inside the cap body 15, and is reflected by the photodiode array 10. Can re-enter. Thereby, since the final incident light quantity to each photodiode can be increased, the output from each photodiode can be increased.

  In this case, since the second reflector can be constituted by the inner surface of the metal package, there is no need to separately provide another second reflector, and the number of parts can be reduced. Of course, another second reflector may be provided at an appropriate position.

  The signal readout wiring TL shown in FIG. 1 is also made of a metal and thus functions as a reflector. However, in the present invention, in addition to such a negative reflector, positive first reflection is performed. The body is provided on the substrate surface.

  FIG. 7 is a perspective view of a photodiode array according to another embodiment. In this photodiode array, the shape of the first reflector made of the metal layer in FIG. 1 is a lattice shape, and the signal line TL is integrated with the first reflector E2. The other structures and functions are as follows. It is the same as that shown in FIG. The photodetecting device provided with this photodiode array is arranged in the package shown in FIG. 6 as described above. The signal extracted from the signal line TL in FIG. 1 is extracted from the electrode pad PAD electrically connected to the first reflector E2. More specifically, in FIG. 1, the L-shaped reflector E21 is originally enlarged and integrated with the signal line TL and the adjacent reflector E21, thereby forming a lattice-like reflector E2. The shape of the reflector E2 is a lattice shape or a mesh shape, and has a plurality of openings, and the quenching resistor R1 and the surface electrode 15 are located in each opening.

  According to this structure, it is possible to expect sufficient light reflection and accompanying light re-incidence by enlarging the reflection region of the reflector E2. Further, the resistor R1 and the surface electrode E3 are continuously surrounded by the reflector E2 in the plane in which the resistor R1 and the surface electrode E3 are provided. Becomes higher. In addition, since the very wide reflector E2 is used as the signal transmission member, the resistance value is low, and very high-speed signal reading can be performed.

  As described above, the photodetector of this embodiment is a photodetector including a photodiode array in which a plurality of photodiodes are formed on a semiconductor substrate, and the semiconductor substrate surrounds each photodiode. A grid-like or mesh-like first reflector E2 made of a metal layer provided above, and a metal second reflector that re-reflects the light reflected by the first reflector E2 toward the photodiode (FIG. 6). A package inner surface). According to this structure, as described above, reflected light can be used effectively, so that light detection can be performed with very high efficiency, and the resistance value of the reflector E2 is low. Can be read out.

  The present invention can be used in a light detection device including a photodiode array that detects weak light.

  1N ... Semiconductor substrate, E2 ... First reflector, L ... Insulating layer, 1PA ... First semiconductor region, D1 ... Photodiode, E1 ... First electrode, 1PB ... -2nd semiconductor region, E3 ... surface electrode, 15 ... 2nd reflector (package).

Claims (5)

In order to measure a signal according to the number of incident photons, in a photodetecting device including a photodiode array in which a plurality of photodiodes are formed on a semiconductor substrate,
The individual photodiodes operating in Geiger mode are:
The semiconductor substrate of the first conductivity type;
A first semiconductor region of a second conductivity type formed on one surface side of the semiconductor substrate;
A second conductivity type second semiconductor region formed in the first semiconductor region and having an impurity concentration higher than that of the first semiconductor region;
A first electrode electrically connected to the semiconductor substrate;
A surface electrode formed on the second semiconductor region;
A resistance layer connected at one end to the surface electrode and connected in series to the photodiode;
With
This photodetector is
Wherein is electrically connected to the other end of the resistor layer provided on said semiconductor substrate, and a signal read line for reading out a signal from the photodiode,
A first reflector provided on the semiconductor substrate around each of the photodiodes , disposed between the signal readout line and the surface electrode, and made of a metal layer;
A second reflector made of metal that re-reflects the light reflected by the first reflector toward the photodiode;
Bei to give a,
There is a gap between the first reflector and the surface electrode, and light can enter the first semiconductor region through the gap.
An optical detection device characterized by that. A metal package for housing the photodiode array;
The second reflector is constituted by an inner surface of the package.
The photodetection device according to claim 1. The photodetecting device according to claim 1, wherein the first reflector is electrically separated from the surface electrode. In order to measure a signal according to the number of incident photons, in a photodetecting device including a photodiode array in which a plurality of photodiodes are formed on a semiconductor substrate,
The individual photodiodes operating in Geiger mode are:
The semiconductor substrate of the first conductivity type;
A first semiconductor region of a second conductivity type formed on one surface side of the semiconductor substrate;
A second conductivity type second semiconductor region formed in the first semiconductor region and having an impurity concentration higher than that of the first semiconductor region;
A first electrode electrically connected to the semiconductor substrate;
A surface electrode formed on the second semiconductor region;
A resistance layer connected at one end to the surface electrode and connected in series to the photodiode;
With
This photodetector is
A grid-like or mesh-like first reflector made of a metal layer electrically connected to the other end of the resistance layer and formed on the semiconductor substrate so as to surround the surface electrode of each photodiode.
A second reflector made of metal that re-reflects the light reflected by the first reflector toward the photodiode;
Equipped with a,
There is a gap between the first reflector and the surface electrode, and light can enter the first semiconductor region through the gap.
An optical detection device characterized by that.   A metal package for housing the photodiode array;
  The second reflector is constituted by an inner surface of the package.
The photodetection device according to claim 4.

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