JP2017228569A - Avalanche photodiode and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an avalanche photodiode which suppresses a rise in element temperature so as to have improved optical input resistance even if a bonding area of a bonding portion is reduced for acceleration.SOLUTION: An avalanche photodiode is configured by an APD mesa in which a p-type contact layer, a light absorption layer, an avalanche layer, and an n-type contact layer are sequentially stacked on a first substrate made of InP. The avalanche photodiode comprises: a second substrate which is bonded, via a bonding layer, to a first surface of the first substrate where the APD mesa is formed; a bias electrode which is bonded to the n-type contact layer of the APD mesa by opening the second substrate and the bonding layer; and a signal electrode which is bonded to the p-type contact layer of the APD mesa through a via opened from the rear face of the first substrate.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an avalanche photodiode and a manufacturing method thereof, and more particularly to an avalanche photodiode applied to a light receiving element for optical fiber communication and a manufacturing method thereof.

  In recent years, with an increase in communication capacity in a data center or the like, an increase in transmission capacity of an optical fiber communication system has been demanded. Accordingly, a photodiode that is a photoelectric conversion element incorporated in a receiver of an optical fiber communication system is also required to be accelerated.

  A photodiode is an element that generates a current corresponding to the intensity of light when light is applied to a PN junction. The response speed of the photodiode is determined by the time constant of the load resistance and internal resistance and the junction capacitance of the junction. Therefore, it is conceivable to reduce the junction capacitance in order to increase the speed of the photodiode. The reduction of the junction capacity can be easily realized by reducing the junction area of the junction, but there is a demerit that the heat dissipation characteristics deteriorate if the junction area is reduced.

  On the other hand, an avalanche photodiode (APD) capable of increasing the light receiving sensitivity is known from the photodiode. APD can extend the communication distance by increasing sensitivity, and can constitute a receiver with low power consumption and compact light receiving parts.

  FIG. 1 shows the structure of a conventional inversion type APD. The inverted APD is an APD mesa in which a p-type contact layer (InAlGaAs) 102, an InGaAs light absorption layer 103, an InAlAs avalanche layer 104, an n-type contact layer (InP) 105, and an insulating film 106 are sequentially stacked on an InP substrate 101. (For example, refer to Patent Document 1). Further, a mesa for forming an electrode for connection to the outside is formed, the signal electrode 107 is connected to the p-type contact layer 102, and the bias electrode 108 is connected to the n-type contact layer 105. . A heat sink 109 is bonded to the back side of the InP substrate 101 via an adhesive layer. Light 111 is incident from the surface on which the APD mesa is formed.

  In a general APD, it is necessary to form a guard ring structure by selective doping in order to suppress edge breakdown. In the inverted APD, since the n-type electrode is arranged in the upper layer, the shape of the n-type electrode may be determined instead of the selective doping, so that edge breakdown can be suppressed without using selective doping. it can. Further, the inversion type APD can realize sufficient electric field confinement by a simple manufacturing method and has an advantage of high reliability (for example, see Non-Patent Document 1).

Japanese Patent No. 4728386

Nada et.al., “Triple-mesa Avalanche Photodiode with Inverted P-Down Structure for Reliability and Stability,” J. of Lightwave Tech., VOL. 32, NO. 8, APRIL 15, 2014, p1543-1548.

  As described above, in the inverted APD, the light absorption layer 103 is disposed closer to the InP substrate 101 than the avalanche layer 104. In the APD, since the current generated when light is input is multiplied by the avalanche layer 104, the amount of heat generated in the avalanche layer 104 is the largest.

  However, in the inverted APD, the InGaAs light absorption layer 103 disposed on the InP substrate 101 side has a lower thermal conductivity than other materials such as InP, InAlAs, Au, and the like. Therefore, even if the heat sink 109 is bonded to the InP substrate 101, heat in the avalanche layer 104 is not easily transmitted to the heat sink 109, and the element temperature is not easily lowered. For this reason, it has been a problem in improving the tolerance of optical input.

  An object of the present invention is to provide an avalanche photodiode that suppresses an increase in device temperature and has improved light input resistance even if the junction area of the junction is reduced for speeding up.

  In the present invention, in order to achieve such an object, in one embodiment, a p-type contact layer, a light absorption layer, an avalanche layer, and an n-type contact layer are sequentially laminated on a first substrate made of InP. An avalanche photodiode comprising an APD mesa, wherein the second substrate is bonded to the first surface of the first substrate on which the APD mesa is formed via an adhesive layer; A bias electrode bonded to the n-type contact layer of the APD mesa and a via opened from the back surface of the first substrate to the p-type contact layer of the APD mesa. The heat generation from the avalanche layer of the APD mesa is radiated through the bias electrode.

  According to the present invention, the heat generated in the avalanche layer is radiated through the n-type contact layer and the bias electrode, and can be efficiently radiated by joining the heat sink to the bias electrode. An inversion type APD with improved light input resistance can be realized by improving heat dissipation.

It is a figure which shows the structure of the conventional inversion type APD. It is a figure which shows the structure of the inversion-type APD concerning one Embodiment of this invention. It is a figure which shows the manufacturing process of the inversion type APD of this embodiment. It is a figure which shows the manufacturing process of the inversion type APD of this embodiment. It is a figure which shows the manufacturing process of the inversion type APD of this embodiment. It is a figure which shows the manufacturing process of the inversion type APD of this embodiment. It is a figure which shows the manufacturing process of the inversion type APD of this embodiment. It is a figure which shows the manufacturing process of the inversion type APD of this embodiment. It is a figure which shows the manufacturing process of the inversion type APD of this embodiment. It is a figure which shows the manufacturing process of the inversion type APD of this embodiment. It is a figure which shows the manufacturing process of the inversion type APD of this embodiment. It is a figure which shows the manufacturing process of the inversion type APD of this embodiment. It is a figure which shows the manufacturing process of the inversion type APD of this embodiment. It is a figure which shows the manufacturing process of the inversion type APD of this embodiment. It is a figure which shows the manufacturing process of the inversion type APD of this embodiment. It is a figure which shows the manufacturing process of the inversion type APD of this embodiment. It is a figure which shows the relationship between the magnitude | size of the mesa of APD, and a temperature rise.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 2 shows the structure of an inversion APD according to an embodiment of the present invention. For the inverted APD formed on the InP substrate (first substrate) 201, a BCB (Benzocyclobutene) film 211 is used as an adhesive layer on the surface (first surface) on which the APD mesa 210 is formed. A silicon substrate (second substrate) 212 is bonded. Vias are opened from the surface (second surface) facing the first surface of the InP substrate 201 to connect the signal electrode 207. Vias are also opened in the bonded silicon substrate 212, and the bias electrode 208 and the heat sink 209 are bonded to the silicon substrate 212 in order.

  With such a configuration, heat generated in the avalanche layer 204 is transmitted to the heat sink 209 via the n-type contact layer 205 and the bias electrode 208, so that heat can be efficiently radiated. An inversion type APD with improved light input resistance can be realized by improving heat dissipation.

  With reference to FIGS. 3 to 15, a manufacturing method of the inversion type APD of this embodiment will be described. A p-type InAlGaAs contact layer 202 and an InGaAs light absorption layer are formed on the first surface of an InP substrate 201 made of high-resistance InP doped with Fe or the like by using an epitaxial growth method such as metal organic chemical vapor deposition (MOVPE). 203, an InAlAs avalanche layer 204 and an n-type InP contact layer 205 are sequentially formed (FIG. 3).

  Next, the p-type contact layer 202, the light absorption layer 203, the avalanche layer 204, and the n-type contact layer 205 are processed into a mesa shape by a known photolithography and etching technique (FIG. 4). At this time, an APD mesa 210 for forming the APD and an electrode mesa 220 for forming the signal electrode 207 are formed. Electrodes 214, 215, and 221 that are in ohmic contact are formed on the p-type contact layer 202, the APD mesa 210, and the n-type contact layer 205 of the electrode mesa 220, respectively (FIG. 5).

  The surface on which the mesa is formed is coated with a BCB film 211 and planarized to form an adhesive layer. A SiN film 216 is formed on the surface of the BCB film 211 in order to protect the semiconductor surface from moisture and the like (FIG. 6).

  By dry etching, the SiN film 216 and the BCB film 211 are opened so that the electrode 214 of the p-type contact layer 202 and the electrode 221 of the electrode mesa 220 are exposed (FIG. 7). A wiring electrode 217 made of Au is formed by photolithography, lift-off technology, vacuum deposition technology, or plating technology, and the electrode 214 of the p-type contact layer 202 and the electrode 221 of the electrode mesa 220 are connected (FIG. 8).

  Next, a silicon substrate 212 coated with a BCB film 218 as an adhesive layer is prepared, and the SiN film 216 on the first surface on which the APD mesa 210 of the InP substrate 201 is formed and the BCB film 218 of the silicon substrate 212 are bonded together. (FIGS. 9, 10). After the second surface of the InP substrate 201 is polished using a known technique such as a grinder, an antireflection film (for improving the transmittance with respect to laser light having a communication wavelength in the 1.3 μm band) AR film) 213 is formed (FIG. 11).

  The AR film 213, the InP substrate 201, and the mesa 220 are opened so that the electrode 221 of the electrode mesa 220 is exposed by a known photolithography and dry etching method (FIG. 12). A via such as Au is formed by a known plating method to form a signal electrode 207 on the AR film 213 (FIG. 13).

  Using known photolithography and dry etching, the silicon substrate 212, the BCB films 218, 211, and the SiN film 216 are opened so that the electrode 215 bonded to the n-type contact layer 205 of the mesa 210 is exposed ( FIG. 14). Vias such as Au are formed by a known plating method, and a bias electrode 208 connected to the n-type contact layer 205 is formed (FIG. 15).

  Finally, the chip is formed by dicing, and the bias electrode 208 of the APD chip is joined to the heat sink 209 to complete the inverted APD of this embodiment (FIG. 16).

  A bias voltage is applied between the bias electrode 208 and the signal electrode 207, and light 231 is incident from the second surface of the InP substrate 201 and the surface opposite to the surface on which the APD mesa is formed. For example, according to Non-Patent Document 1, when the multiplication factor is 10, the bias voltage is about 22V. The incident light 231 is absorbed by the light absorption layer 203 and a photocurrent is generated. The photocurrent is composed of electrons and holes. When electrons reach the avalanche layer 204, avalanche multiplication occurs, and new electrons and holes are generated.

  At this time, Joule heat is generated in proportion to the voltage applied to the APD and the photocurrent generated by light incidence, but the electric field is mainly confined in the avalanche layer. Fever is the main. The generated heat is conducted to the heat sink 209 through the n-type contact layer 205 and the bias electrode 208. Accordingly, the heat dissipation characteristics are improved as compared with the conventional inverted APD.

  FIG. 17 shows the relationship between the APD mesa size and the temperature rise. The horizontal axis represents the diameter of the mesa of the inverted APD, and the vertical axis represents the amount of temperature rise at the junction of the APD. As described above, the conventional inversion type APD shown in FIG. 1 has the InGaAs light absorption layer 103 between the avalanche layer 104 and the heat sink 109, so that heat is not easily transmitted to the heat sink 109. In the conventional inversion type APD, when the junction area is reduced in order to reduce the junction capacitance, that is, when the diameter of the mesa is reduced, the temperature increase amount increases rapidly.

  On the other hand, since the inverted APD of this embodiment does not have an InGaAs layer with low thermal conductivity between the avalanche layer 204 and the heat sink 209, the heat dissipation characteristics are improved. As shown in FIG. 17, even if the mesa diameter is reduced, the temperature rise is small, and the temperature rise is suppressed to about 1/3 to 1/5 as compared with the conventional inversion type APD. Therefore, according to the present embodiment, even if the junction area of the junction is reduced for speeding up, the increase in element temperature can be suppressed and the light input resistance can be improved.

  In this embodiment, the silicon substrate 212 is used as the substrate to be bonded to the surface on which the APD mesa 210 is formed. However, the same effect can be obtained by using a substrate of another material, for example, an InP substrate. It is self-evident.

  Further, regarding the material of each layer, the p-type contact layer 202 has been described as InAlGaAs, the avalanche layer 204 as InAlAs, and the n-type contact layer 205 as InP. However, other materials may be used. For example, the p-type and n-type contact layers may be InGaAsP, and the avalanche layer may be InP.

101, 201 InP substrate 102, 202 p-type contact layer 103, 203 light absorption layer 104, 204 avalanche layer 105, 205 n-type contact layer 106 insulating film 107, 207 signal electrode 108, 208 bias electrode 109, 209 heat sink 210, 220 Mesa 211,218 BCB film 212 Silicon substrate 213 AR film 214,215,221 electrode 216 SiN film 217 wiring electrode 111,231 light

Claims (4)

An avalanche photodiode including an APD mesa in which a p-type contact layer, a light absorption layer, an avalanche layer, and an n-type contact layer are sequentially stacked on a first substrate made of InP,
A second substrate bonded via an adhesive layer to the first surface on which the APD mesa is formed on the first substrate;
A bias electrode that opens the second substrate and the adhesive layer and is bonded to the n-type contact layer of the APD mesa;
A signal electrode joined to the p-type contact layer of the APD mesa through a via opened from a second surface facing the first surface of the first substrate;
The avalanche photodiode is characterized in that heat generated from the avalanche layer of the APD mesa is radiated through the bias electrode.   The avalanche photodiode according to claim 1, wherein the p-type contact layer is made of InAlGaAs, the light absorption layer is made of InGaAs, the avalanche layer is made of InAlAs, and the n-type contact layer is made of InP. . An avalanche photodiode manufacturing method comprising an APD mesa in which a p-type contact layer, a light absorption layer, an avalanche layer, and an n-type contact layer are sequentially stacked on a first substrate made of InP,
Forming the APD mesa and an electrode mesa for forming a signal electrode on the first substrate, forming a first adhesive layer, and planarizing the first step;
Opening the first adhesive layer so that the first electrode formed in the p-type contact layer of the APD mesa and the second electrode formed in the n-type contact layer of the electrode mesa are exposed; A second step of connecting the first and second electrodes by wiring electrodes;
A second substrate on which a second adhesive layer is formed is bonded to the first surface on which the APD mesa is formed on the first substrate via the first and second adhesive layers. A third step;
Via a via that opens the electrode mesa from a second surface facing the first surface of the first substrate so that the second electrode formed in the n-type contact layer of the electrode mesa is exposed. Forming a signal electrode joined to the p-type contact layer of the APD mesa;
And a fifth step of forming a bias electrode by opening the second substrate and the adhesive layer so that the third electrode formed in the n-type contact layer of the APD mesa is exposed. A method of manufacturing an avalanche photodiode.   4. The avalanche photodiode according to claim 3, wherein the p-type contact layer is made of InAlGaAs, the light absorption layer is made of InGaAs, the avalanche layer is made of InAlAs, and the n-type contact layer is made of InP. Manufacturing method.

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