JP3831639B2 - Light receiving element and light receiving module - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light receiving element and a light receiving module including the light receiving element, and more particularly, to a light receiving element with enhanced filter function and electromagnetic shielding function and a light receiving module including the light receiving element.
[0002]
[Prior art]
A light receiving element mounted on a light receiving module or the like for a remote control is generally composed of a light receiving element for infrared light, and a light receiving portion made of a PIN photodiode is formed in the thickness direction of the substrate as shown in FIG. Alternatively, as shown in FIG. 9, the one formed in the same direction as the surface of the substrate is known.
[0003]
In the case of the structure shown in FIG. 8, carriers caused by an undesired long wavelength light component reaching the P + layer are diffused (indicated by Lp) and taken out as a photocurrent. In the case of the structure shown in FIG. 9, carriers generated outside the depletion layer (indicated by width W) due to the long wavelength light component also contribute to the photocurrent if within the diffusion length (Lp) range. Since the photocurrent due to the long wavelength light component is not the photocurrent due to the infrared light that is originally required, it should be removed.
[0004]
In many cases, these elements are covered with a visible light shielding resin to prevent malfunction due to visible light. In addition, the light receiving element is very weak against electromagnetic noise and may cause malfunction as a light receiving module. Therefore, a conductive film (metallized film) or the like is inserted into the light receiving module to prevent this. In addition, a mesh structure is arranged in the light receiving window of the module case. On the other hand, in a light receiving module in which resin sealing is performed instead of a metal case, a mesh-shaped metal conductor is formed on the surface of the internal light receiving element.
[0005]
[Problems to be solved by the invention]
In the light receiving element, light having a wavelength longer than the required wavelength may be received and malfunction may occur. Therefore, one of the problems is to prevent the malfunction.
[0006]
Further, in a lighting fixture using an infrared light receiving module, the influence of visible light is dealt with by using a light receiving module or a light receiving element covered with a visible light shielding resin. However, in practice, in a lighting fixture, a band-pass filter or the like is attached in order to suppress the influence of a large number of spectra (light) generated from a fluorescent lamp. In recent years, the number of fluorescent lamps has been increased and the output has been increased, and the malfunction of the light receiving module due to the spectrum of the fluorescent lamp (for example, 1013 nm light) has been highlighted. Against this background, an interference filter is placed on top of the light receiving element covered with visible light shielding resin to receive the signal that cuts off the unnecessary spectrum that is generated, and inside the visible light shielding resin A module in which an interference filter is embedded is used.
[0007]
However, in this case, as the light receiving module, the number of parts increases, the number of assembly steps increases, and the cost increases. In the case of embedding in the resin, there are problems in the mounting accuracy of the interference filter and the reliability such as the resin peeling between the resin and the interference filter. Therefore, the present invention has an object to solve such a problem.
[0008]
In other words, in the electromagnetic noise resistance characteristics of the light receiving module, one of the challenges is to reduce the number of parts by eliminating the conductive film (metallized film) that is installed inside the light receiving module as an electromagnetic shield and the mesh structure of the module case light receiving window. To do. In addition, in a light-receiving module sealed with resin instead of a metal case, the high-concentration impurity layer in the light-receiving part is equipotential with the ground, and the shield layer is used to provide a shielding effect to the element itself. One of the issues is to enable device manufacturing at low cost.
[0009]
In addition, in a light receiving module with resin sealing, a mesh-like metal conductor is formed on the inner light receiving surface. However, if a conductor is formed directly on the element surface, a parallel plate capacitor is equivalently formed on the element surface. This increases the capacity of the element, and when it is mounted on the light receiving module, the reach distance is shortened. Therefore, an object of the present invention is to prevent an increase in the element capacitance.
[0010]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a light receiving element having a pair of electrodes connected to the light receiving portion disposed on the surface thereof, wherein the first conductive type impurity layer and the second conductive layer are provided below the light receiving portion. A type impurity layer is formed. Thus, carriers generated due to light passing through the light receiving portion can be effectively absorbed and eliminated by the first conductivity type impurity layer and the second conductivity type impurity layer disposed below the light receiving portion. .
[0011]
When the short-circuited by the first conductivity type impurity layer and the second conductive type impurity layer electrodes disappearance of the carrier effectively performed it is possible. According to a second aspect of the present invention, the light receiving unit is composed of a PN type diode or a PIN type diode.
[0012]
According to a third aspect of the present invention, there is provided a light receiving element comprising: a first conductive type impurity layer and a second conductive type impurity layer as light receiving portions formed on a substrate having a low impurity concentration; In a light receiving element in which a type impurity layer is disposed in the same direction as the substrate surface, the first and second conductivity type impurity layers different from the first and second conductivity type impurity layers are short-circuited by a back electrode, and the back surface of the substrate It is characterized by being formed. As a result, carriers generated due to the light passing through the light receiving part are effectively absorbed by the first conductive type impurity layer and the second conductive type impurity layer arranged separately from the light receiving part and the electrodes that short-circuit them. Can be extinguished.
[0014]
According to a fourth aspect of the present invention, it is preferable to cover the first conductive type impurity layer constituting the light receiving part with an electrode connected to the second conductive type impurity layer constituting the light receiving part in order to enhance the shielding effect.
[0015]
As described in claim 5 , the light receiving module of the present invention may have a structure in which the light receiving element is fixed to a lead with an adhesive.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a first embodiment of a light receiving element of the present invention, and FIG. 2 is a plan view thereof. In the light receiving element 1, a light receiving portion 3 is formed on the surface of a semiconductor substrate 2 having a low impurity concentration, and a diode 4 for eliminating unnecessary carriers is formed on the back surface of the substrate 2. The diode 4 is formed separately from the diode forming the light receiving unit 3.
[0017]
The substrate 2 is a Si substrate having a low impurity concentration that can be regarded as substantially intrinsic. In this example, a first conductivity type (N-type) Si substrate having an impurity concentration of 4 × 10 13 cm ⁻³ or less and a thickness of about 300 μm is used. The substrate 2 has a high resistance and is set to a specific resistance of, for example, 500 Ωcm or more, and functions as a low concentration impurity layer (N−). The substrate 2 may be a second conductivity type (P-type) Si substrate having an impurity concentration of 4 × 10 13 cm ⁻³ or less and a thickness of about 300 μm. In this case, a low concentration impurity layer (P−) is used. Function as.
[0018]
The light receiving unit 3 includes a first conductivity type impurity layer 3a functioning as a high concentration N layer (N +) and a second conductivity type impurity layer 3b functioning as a high concentration P layer (P +). These layers are arranged in the same direction as the surface of the substrate 2. In order to function as the high-concentration first conductivity type impurity layer 3a, phosphorus (P) as an N-type impurity is diffused in a ring shape around the impurity layer 3b on the surface of the substrate 2. The N-type impurity layer 3a has a sheet resistance of about 20Ω / □ and a depth (thickness) of 1 to 2 μm.
[0019]
On the other hand, boron (B) as a P-type impurity is diffused in the center of the surface of the substrate 2 in order to function as a high-concentration second conductivity type impurity layer 3b. This P-type impurity layer 3b is formed with an impurity concentration of about 3 × 10 ¹⁹ cm ⁻³ and a depth (thickness) of about 3 μm.
[0020]
A film 5a that functions as a surface protective film and an antireflection film is formed on the surface of the substrate 2 by, for example, silicon oxide (SiO2). In order to make contact with the first and second conductivity type impurity layers 3a and 3b of the light receiving portion 3, a part of the film 5a is removed by photolithography. On the film 5a, a metal such as aluminum is vapor-deposited, and unnecessary portions are removed by photolithography, thereby making contact with the first and second conductivity type impurity layers 3a and 3b (hereinafter referred to as first electrodes). , N-side electrode) 6 and second electrode (hereinafter referred to as P-side electrode) 6.
[0021]
With such a configuration, as in the structure shown in FIG. 9, a photodiode in which the photodiode is formed in the lateral direction, that is, in the same direction as the substrate surface, and the pair of electrodes 6 and 7 are formed on one surface is obtained. .
[0022]
Then, by diffusing phosphorus (P), for example, as an N-type impurity on the back surface of the substrate 2, the first conductivity type impurity layer 4a functioning as the N layer of the diode 4 has a depth (thickness) of about 150 μm. Form. In the first conductivity type impurity layer 4a, the carrier lifetime is abrupt when the impurity concentration is gradually increased in the characteristic diagram in which the horizontal axis indicates the impurity concentration and the vertical axis indicates the carrier lifetime at the impurity concentration. The impurity concentration is set to be higher than 1 × 10 ¹⁶ cm ^−3, which is an impurity concentration that starts to become shorter (in the case of a Si substrate), for example, about 3 × 10 ¹⁸ cm ⁻³ .
[0023]
Further, by diffusing, for example, boron (B) as a P-type impurity in the central portion of the first conductivity type impurity layer 4a on the back surface of the substrate 2, a second conductivity type impurity layer 4b functioning as a P layer of the diode 4 is formed. The depth (thickness) is about 80 μm. The second conductivity type impurity layer 4b is set to the same impurity concentration as the first conductivity type impurity layer 4a.
[0024]
A back electrode 8 is formed on the back surface of the substrate 2 via an insulating film 5b such as silicon oxide. The back electrode 8 is electrically connected to the first and second impurity layers 4a and 4b through contact holes formed in the insulating film 5b. Therefore, the diode formed by the first and second impurity layers 4 a and 4 b is short-circuited by the electrode 8. The contact hole formed in the insulating film 5b is formed away from the junction between the first conductivity type impurity layer 4a and the second conductivity type impurity layer 4b. In some cases, the back electrode 8 may be formed directly without using the insulating film 5b.
[0025]
The operation of this embodiment will be described focusing on the effect of long wavelength light cut. First, the quantum efficiency R at which light incident on the element 1 becomes a photocurrent with respect to the depth direction can be expressed by R = 1−exp (−αW) / (1 + αLp). Here, W is the width of the low-concentration impurity region (depletion layer width expanded by the voltage at the time of reverse bias), α is the light absorption coefficient for light of a certain wavelength, and Lp is the diffusion length of carriers in the high-concentration impurity layer on the back surface. is there. Accordingly, in order to increase the efficiency R, a sufficient width W of the low concentration impurity region may be provided. In other words, in order to extract only the current due to the desired light, it is only necessary to regulate the width of W with respect to unnecessary wavelength components. However, in the case of a normal light receiving element as shown in FIG. 8, even if the width of W is restricted, carriers (components of the diffusion length Lp) generated in the high-concentration impurity layer (P +) by long-wavelength light become photocurrents. The unnecessary output due to the long wavelength component cannot be sufficiently reduced. In addition, in the light receiving portion formed on the surface of the light receiving element shown in FIG. 9, the depletion layer, which is a region where light can be efficiently received, spreads in the depth direction of the depletion layer because an electric field is applied in parallel to the substrate surface. However, the carriers (diffusion length Lp component) generated outside the depletion layer contribute to the photocurrent, and the unnecessary output cannot be sufficiently reduced although it depends on the long wavelength component.
[0026]
However, in the first embodiment, as shown in FIGS. 1 and 2, the first and second conductivity type high-concentration high-concentration regions that regulate the width of the low-concentration impurity region 2 a to the width W calculated by the above equation. Since the impurity layers 4a and 4b are provided on the back surface, carriers generated by the light having a long wavelength reaching the impurity layers 4a and 4b are annihilated within the impurity layers 4a and 4b in a short time before contributing to the photocurrent. be able to.
[0027]
Furthermore, since the impurity layers 4a and 4b are connected to each other by the electrode 8 and the diode constituted by the adjacent impurity layers 4a and 4b is held in a short-circuited state, carriers generated in each of the impurity layers 4a and 4b are retained. Can be exchanged with each other using the electrode 8 as a path, and carriers can be annihilated by recombination. Here, the back surface impurity layers 4a and 4b and the back surface electrode 8 are in a state of being substantially electrically insulated independently of the front surface electrodes (N side electrode 6 and P side electrode 7).
[0028]
Thereby, the high-concentration impurity layer 4a (4b) regulates the width of the low-concentration impurity region 2a (N−) (depletion layer) to the optimum width W, and the unnecessary impurity reaches the impurity layer 4a (4b). The lifetime of the carriers generated due to the light component is shortened (Lp is shortened), the effect of preventing diffusion is brought about, and unnecessary components (long wavelength light components) can be sufficiently cut.
[0029]
In this embodiment, the width (W) of the low-concentration impurity layer 2a is 90 μm for the purpose of removing a signal by incident light having a wavelength of 1000 nm or more. Here, the diffusion length of carriers in the high-concentration impurity layer 4a on the back surface is 1 μm, and the absorption coefficient of incident wavelength light of 1000 nm is 7 × 10 ¹ cm ⁻¹ . 4 shows the spectral sensitivity characteristic A of the light receiving element shown in FIG. 1 and the spectral sensitivity characteristic B of the light receiving element shown in FIG. The light receiving sensitivity of incident wavelength light of 1000 nm is reduced to about 1/6 compared with the conventional case.
[0030]
FIG. 3 is a principal plan view showing an embodiment of a light receiving module including the light receiving element 1. This module has a structure in which the light receiving element 1 is mounted on a metal lead frame 9 and is integrally molded with an insulating resin 10 containing a visible light shielding component. Here, the light receiving element 1 is mounted on the central lead 12 with a conductive or insulating adhesive 11, but the mounted lead 12 is separated from the other leads 13 and 14 and is electrically floating. . Then, by wire-bonding gold wires 15 and 15 between the other two leads 13 and 14 located at both ends and the N-side electrode 6 and the P-side electrode 7, the detection signal of the light receiving element 1 is transferred to the upper surface. The electrodes 6 and 7 are taken out through the gold wires 15 and 15 and the leads 13 and 14. Usually, a reverse bias voltage is applied to the light receiving element 1.
[0031]
In the above embodiment, the conductivity type of the impurity layer constituting the light emitting unit 3 can be changed to the opposite conductivity type, that is, 3a can be changed to P type, and 3b can be changed to N type. Further, the conductivity type of the impurity layer constituting the diode 4 can be changed to the opposite conductivity type, that is, 4a can be changed to P type, and 4b can be changed to N type.
[0032]
5 and 6 show still another embodiment of the light receiving element 1 and show a configuration example in which an electromagnetic shield is provided on the light receiving surface. 5 is a cross-sectional view taken along the line AA in FIG. The light receiving element 1 has the same configuration as the light receiving element shown in FIG. 1, but differs in that a shield electrode 16 is formed on the surface of the substrate 2. Therefore, the description of the configuration equivalent to the previous embodiment is omitted, and the present embodiment will be described focusing on the differences.
[0033]
The P-side electrode 7 formed on the insulating layer 5a is formed wider than the impurity layer 3a so as to cover most of the impurity layer 3a. The P-side electrode 7 is formed in an annular shape so as to cover the impurity layer 3a except for the region where the N-side electrode 6 is formed, and constitutes the shielding electrode 16. That is, the shape of the P-side electrode 7 is changed to integrally form the shield electrode 16. The electrode 16 can block light to the impurity layer 3a located therebelow.
[0034]
FIG. 7 shows an embodiment of a light receiving module on which the light receiving element 1 shown in FIGS. This light receiving module has a single mold configuration in which the light receiving element 1 serving as a light detection unit and an IC 17 for driving the light receiving element 1 are arranged on a common frame 9 and molded with a resin 10. The resin 10 uses an insulating resin containing a visible light shielding material, but can be molded with other resins.
[0035]
In general, a monolithic type in which the photodetection unit and drive IC unit are configured with a single chip, this module is a light-receiving element with excellent high speed and high sensitivity because the photosensitivity of the photodetection unit is insufficient. 2 and a driving IC 17 are combined. That is, the light receiving element 1 is fixedly disposed on the frame 9 with the adhesive 18, and the IC 17 is fixedly disposed with the conductive adhesive 19. And the connection between both is only wiring the N side electrode 6 of the light receiving element 1 and the amplifier circuit part of the IC 17 with the gold wire 20 or the like. The P-side electrode 7 of the light-emitting element 1 is wired to the frame 9 with a gold wire 21 or the like and connected to the ground potential.
[0036]
As described above, the light receiving element 1 is bonded to the common frame 9 with the insulating or conductive adhesive 18, and the electrode 7 on the surface of the light receiving element 1 is wired to the frame 9. The structure is such that the upper and lower sides of the light receiving element 1 are sandwiched at the same potential, so that an effective electromagnetic shield is formed. Further, the upper portion of the high gain impurity layer 3 a can be shielded by the shielding electrode 16.
[0037]
The light receiving module shown in FIG. 7 has a structure for covering the side surface of the light receiving element 1 with the same potential as the frame 9 in order to further improve the electromagnetic shielding property. That is, a wall 22 having the same height as that of the side surface of the light receiving element 1 is integrally formed on the frame 9 and electromagnetic shielding is performed using this wall 22, but a part of the frame 9 is dropped to form a dent. The light receiving element 1 may be mounted therein. The wall 22 covering the side surface of the element 1 may be a single surface, but it is preferable to arrange a plurality of surfaces so as to cover the four surfaces of the element. The wall 22 is not necessarily required for the structure, but is useful for enhancing the shielding effect.
[0038]
In the above description, the PIN photodiode type light receiving element 1 is taken as an example. However, the present invention is not limited to these, and the PN type general photodiode and the driving IC are formed on the same substrate. The present invention can also be applied to a built-in light receiving element in the formed IC.
[0039]
Also, in the above-described embodiment shown in FIGS. 5 to 7, the conductivity type of the impurity layer can be a PN reverse pole, as in the previous embodiment. The conductivity type of the substrate 2 can be changed to the opposite conductivity type, that is, 3a can be changed to P type, and 3b can be changed to N type. Further, the conductivity type of the impurity layer constituting the light emitting unit 3 can be changed to the opposite conductivity type, that is, can be changed to the P type. Further, the conductivity type of the impurity layer constituting the diode 4 can be changed to the opposite conductivity type, that is, 4a can be changed to P type, and 4b can be changed to N type.
[0040]
Further, when the impurity layers 4a and 4b are short-circuited by the electrode 8, they can be recombined via the electrode 8 even if the lifetime of carriers generated in the impurity layers 4a and 4b is long. The impurity concentration of the impurity layers 4a and 4b need not be as high as described above, and can be set to an impurity concentration lower than 1 × 10 ¹⁶ cm ⁻³ , for example.
[0041]
According to the above embodiment, the following effects can be obtained.
[0042]
First, (1) the light receiving element itself can have a cut filter function for reducing the sensitivity to long-wavelength light. Conventionally, in a lighting fixture, a bandpass is used to suppress the influence of a large number of spectra (light) generated from a fluorescent lamp. In recent years, the number of fluorescent lamps has been increased and the output has been increased, and the malfunction of the light receiving module due to the spectrum of the fluorescent lamp (for example, 1013 nm light) has been highlighted more than ever. An interference filter is arranged above the light receiving element covered with the light shielding resin, and a module that receives the signal with the generated spectrum cut off or a module in which the interference filter is embedded inside the visible light shielding resin is used. In this case, however, the light receiving module increases the number of parts, increases the number of assembly steps, and increases the cost. It is also limited, thereby enabling inexpensive micro modules can solve this problem.
[0043]
(2) In the case of embedding in the resin, there arises a problem in the mounting accuracy of the interference filter and the reliability such as the resin peeling between the resin and the interference filter, but such instability can be eliminated. Since carriers generated at the junction (other than the depletion layer) can be prevented, the diffusion component can be suppressed and only the drift component can be obtained, and high-speed response can be obtained.
[0044]
(3) Since the light receiving element itself has an electromagnetic shielding function on the element surface and the element side surface, when a metal conductor is used as an electromagnetic shield, incident light is reflected by the metal conductor and an effective light receiving area is reduced ( (Incident light loss) can be eliminated. When a metal conductor is used as an electromagnetic shield, the effective light receiving area is reduced. Therefore, the metal conductor cannot be arranged on the surface of the light receiving element in a wide area, so that it is insufficient as an effective electromagnetic shield. In the above embodiment, the surface of the light receiving element itself becomes a shield layer, so that a sufficient electromagnetic shielding effect can be obtained. In a light receiving module that is sealed with resin, a mesh-like metal conductor is formed on the surface of the internal light receiving element, but in order to form a conductor directly on the surface of the element, a parallel plate capacitor is equivalently formed on the element surface. As a result, the capacitance of the element increases and the reachable distance is shortened when mounted on the light receiving module. However, according to the above embodiment, an increase in element capacitance can be prevented, and the reach distance when the light receiving module is mounted is not impaired. Since the light receiving element itself has an electromagnetic shielding function, conventionally, a conductive film (metallized film) mounted inside the light receiving module and a mesh structure of the module case light receiving window are not required as electromagnetic noise resistance. As described above, since the electromagnetic shielding component can be eliminated, an ultra-small light receiving module is possible.
[0045]
【The invention's effect】
As described above, according to the present invention, it is difficult to be affected by noise and the occurrence of malfunction can be prevented. The number of parts and assembly man-hours can be reduced. An increase in element capacitance can be prevented and high-speed response can be achieved. Miniaturization can be achieved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment of a light receiving element of the present invention.
FIG. 2 is a plan view of the same embodiment.
FIG. 3 is a plan view showing an embodiment of a light receiving module of the present invention.
FIG. 4 is a diagram showing spectral sensitivity characteristics.
FIG. 5 is a cross-sectional view showing another embodiment of the light receiving element of the present invention.
FIG. 6 is a plan view of the same embodiment.
FIG. 7 is a schematic cross-sectional view showing another embodiment of the light receiving module of the present invention.
FIG. 8 is a schematic cross-sectional view showing a conventional example.
FIG. 9 is a schematic cross-sectional view showing another conventional example.
[Explanation of symbols]
1 Light-receiving element 2 Substrate 3 Light-receiving part 4 Diode

Claims (5)

In the light receiving element disposed a pair of electrodes connected to the light receiving portion to the surface, the a light receiving element formed of a first conductivity type impurity layer and the second conductive type impurity layer below the light receiving portion, the first conductive And a second conductivity type impurity layer short-circuited by an electrode .   The light receiving element according to claim 1, wherein the light receiving unit is configured by a PN type diode or a PIN type diode.   In a light receiving element in which a first conductivity type impurity layer and a second conductivity type impurity layer as light receiving portions are formed on a substrate having a low impurity concentration, and the first and second conductivity type impurity layers are arranged in the same direction as the substrate surface. 1. A light receiving element, wherein first and second conductivity type impurity layers different from the first and second conductivity type impurity layers are formed on a back surface of the substrate in a state of being short-circuited by a back electrode. Photodetector according to claim 3, characterized in that covered by the electrode connected to the second conductivity type impurity layer constituting the light receiving portion of the first conductive type impurity layer constituting the light receiving portion. Optical receiver module characterized by being fixed by the adhesive receiving element according to lead to any one of claims 1-4.

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