JP4349172B2 - Light receiving element array and manufacturing method of light receiving element array - Google Patents

Description

  The present invention relates to a light receiving element array, a method for manufacturing a light receiving element array, an optical module, and an optical transceiver.

  With the recent development of optical communication technology, communication using a high-capacity and high-speed optical fiber is possible. In communication using optical fibers, in order to further increase the transmission capacity, a wavelength division multiplexing system that transmits light of a plurality of wavelengths through a single optical fiber may be used.

  Therefore, there is a need for a device that can receive light of a plurality of wavelengths transmitted by such an optical fiber or the like.

  An object of the present invention is to provide a light receiving element array capable of efficiently receiving light of a plurality of wavelengths.

The light receiving element array according to the present invention is:
A substrate,
A plurality of light absorption layers formed in an array above the substrate;
An antireflection film formed above each of the light absorption layers;
Including
The antireflection film has mutually different wavelength regions of light to be transmitted.

  The light receiving element array according to the present invention can efficiently receive light of a plurality of wavelengths for each light receiving element.

  In the light-receiving element array according to the present invention, the antireflection films can have different wavelength regions of transmitted light by having different film thicknesses.

  In the light receiving element array according to the present invention, the thickness of each of the plurality of antireflection films is mλ / 4n (m is an odd number) where λ is a wavelength of transmitted light and n is a refractive index of the antireflection film. ).

  According to this aspect, the light receiving element array according to the present invention can further reduce the surface reflectance of the antireflection film.

In the light receiving element array according to the present invention,
The antireflection film is formed by discharging a droplet containing the material of the antireflection film toward the light receiving surface of the light absorption layer,
A damming portion for damming the discharged droplets may be further included around the antireflection film.

A method for manufacturing a light receiving element array according to the present invention is as follows.
Forming a plurality of light absorption layers in an array above the substrate;
Forming an antireflection film above each of the light absorption layers;
Including
Each of the antireflection films can be formed so that the wavelength regions of the transmitted light are different from each other by forming the antireflection films so as to have different film thicknesses.

  According to this aspect, an antireflection film having a desired film thickness can be formed for each light receiving element on the light receiving element array.

In the manufacturing method of the light receiving element array according to the present invention,
The antireflection film can be formed by discharging droplets containing the material of the antireflection film toward the light receiving surface that captures light in the light absorption layer.

  According to this aspect, it is possible to easily form antireflection films having different film thicknesses.

In the manufacturing method of the light receiving element array according to the present invention,
Prior to forming the antireflection film, the light receiving surface can be subjected to lyophilic treatment.

  According to such an aspect, the discharged droplets can be easily spread flat.

In the manufacturing method of the light receiving element array according to the present invention,
The method may further include a step of forming a damming portion for damping the discharged droplets above the substrate.

  According to this aspect, for example, by forming a damming portion having a shape corresponding to the desired film thickness of the antireflection film, the discharged droplets can be reliably damped.

An optical module according to the present invention includes:
A light receiving element array according to the present invention;
A transimpedance amplifier that converts the output current of the light receiving element array into a voltage;
including.

An optical transceiver according to the present invention includes:
An optical module according to the present invention;
A light emitting element;
A driver for driving the light emitting element;
And a limiting amplifier that sets the output voltage of the transimpedance amplifier to a constant level.

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

1. Light-Receiving Element Array FIG. 1 is a cross-sectional view schematically showing a light-receiving element array 100 according to this embodiment to which the present invention is applied. The light receiving element array 100 includes a semiconductor substrate 10 and a plurality of light receiving elements 90. Each light receiving element 90 is formed in an array on the semiconductor substrate 10 and includes a light absorption layer 20, a contact layer 30, a first electrode 40, and a second electrode 42. A first antireflection film 50, a second antireflection film 52, a third antireflection film 54, and a fourth antireflection film 56 are formed on each light receiving element 90. In the illustrated example, four light receiving elements 90 are formed on one array. However, the number of the light receiving elements 90 is not limited to this number. For example, according to the number of wavelength bands received by the light receiving element array, the light receiving elements 90 90 is formed.

  The first antireflection film 50, the second antireflection film 52, the third antireflection film 54, and the fourth antireflection film 56 have different film thicknesses. As a result, the first antireflection film 50, the second antireflection film 52, the third antireflection film 54, and the fourth antireflection film 56 are different in wavelength range of the transmitted light. Specifically, the film thicknesses of the first antireflection film 50, the second antireflection film 52, the third antireflection film 54, and the fourth antireflection film 56 are set so that the wavelength of light incident on the respective light receiving elements 90 is λ. When the refractive index of the film is n, mλ / 4n (m is an odd number). Thus, by setting the film thickness to mλ / 4n, the surface reflectance can be further reduced.

  The film thickness of the antireflection film is determined as follows based on the wavelength of light received by each light receiving element 90. FIG. 2 is a diagram showing the surface reflection characteristics of the antireflection film. The horizontal axis of the graph shown in FIG. 2 indicates the wavelength of light received by the light receiving element 90, and the vertical axis indicates the surface reflectance of the antireflection film. The four types of plots show the surface reflectance of antireflection films having different film thicknesses. As a sample of the antireflection film, an epoxy resin having a refractive index of 1.5 was used. The film thicknesses are 215 nm, 218.3 nm, 221.6 nm, and 225 nm.

  As shown in FIG. 2, it can be seen that the wavelength at which the surface reflectance of the antireflection film is minimized differs depending on the film thickness. That is, in order to prevent light reflection more efficiently, it is necessary to change the film thickness of the antireflection film depending on the wavelength of light received. Therefore, it is desirable to form an antireflection film in which a film thickness having a lower surface reflectance is selected at the wavelength of light received by each light receiving element 90.

  The materials of the first antireflection film 50, the second antireflection film 52, the third antireflection film 54, and the fourth antireflection film 56 are materials that transmit light. For example, inorganic materials such as silicon oxide and silicon nitride, or It may be made of resin. The materials used for the first antireflection film 50, the second antireflection film 52, the third antireflection film 54, and the fourth antireflection film 56 may be the same material or different materials. Also good. That is, each antireflection film can be formed by selecting a suitable material according to the wavelength of light received by the light receiving element 90. The antireflection film may be composed of a plurality of layers.

  The light receiving element 90 includes a pin photodiode in which a semiconductor substrate 10 made of an n-type GaAs layer, a light absorption layer 20 made of an undoped GaAs layer, and a contact layer 30 made of p-type GaAs are sequentially stacked. Configure.

  Furthermore, the light receiving element 90 includes a first electrode 40 and a second electrode 42, respectively. The second electrode 42 is used as a common electrode for the plurality of light receiving elements 90. The first electrode 40 and the second electrode 42 are used to drive the light receiving element 90 by applying a voltage. Specifically, the first electrode 40 is provided on the upper part of the contact layer 30, and the second electrode 42 is provided on the lower part of the semiconductor substrate 10. The second electrode 42 can be composed of a laminated film of, for example, an alloy of chromium, gold and germanium, nickel, and gold. The first electrode 40 can be made of, for example, a laminated film of platinum, titanium, platinum, and gold. In addition, it is preferable that the 1st electrode 40 is the height more than the height of each antireflection film. As a result, when the antireflection film is formed by the droplet discharge method, the first electrode 40 can block the liquid material.

  Next, the operation of the light receiving element array 100 according to the present embodiment will be described. An optical signal is input to the light receiving element 90. For example, the light passes through the first antireflection film 50 and enters the contact layer 30. The light incident on the contact layer 30 then enters the light absorption layer 20. As a result of a part of the incident light being absorbed by the light absorption layer 20, photoexcitation occurs in the light absorption layer 20, and electrons and holes are generated. Electrons move to the second electrode 42 and holes move to the first electrode 40 by an electric field applied from the outside of the element. As a result, in the light receiving element 90, a current (photocurrent) is generated in the direction from the second electrode 42 to the first electrode 40.

  As described above, light of different wavelengths enters each light receiving element 90. In this case, the film thickness of the antireflection film that minimizes the surface reflectance differs depending on the wavelength of each light. Therefore, by forming antireflection films having different thicknesses on one array, it is possible to efficiently receive light having a plurality of wavelengths.

2. Method for Manufacturing Light-Receiving Element Array Next, an example of a method for manufacturing the light-receiving element array 100 according to the present embodiment will be described with reference to FIGS. 3 to 6 are cross-sectional views schematically showing one manufacturing process of the light receiving element array 100 shown in FIG. 1, and each correspond to the cross-sectional view shown in FIG.

  (1) First, as shown in FIG. 3, the light absorption layer 20 and the contact layer 30 which are semiconductor layers are formed by epitaxial growth on the surface 10a of the semiconductor substrate 10 made of n-type GaAs. Here, the light absorption layer 20 is made of a GaAs layer not doped with impurities. The contact layer 30 is made of p-type GaAs.

  The temperature at which the epitaxial growth is performed is appropriately determined depending on the growth method and raw material, the type of the semiconductor substrate 10, the types of the light absorption layer 20 and the contact layer 30 to be formed, the thickness, the carrier density, and the like. It is preferable that it is a C-800 degreeC. Further, the time required for performing the epitaxial growth is also appropriately determined in the same manner as the temperature. As a method for epitaxial growth, a metal-organic vapor phase epitaxy (MOVPE) method, an MBE method (Molecular Beam Epitaxy) method, or an LPE method (Liquid Phase Epitaxy) can be used.

  (2) Next, the light absorption layer 20 and the contact layer 30 (see FIG. 3) are patterned into a predetermined shape to form the light absorption layer 20 and the contact layer 30 (see FIG. 4). Specifically, a resist layer having a predetermined pattern is formed by first applying a resist on at least the contact layer 30 and then patterning the resist using a lithography method.

  Next, the light absorption layer 20 and the contact layer 30 are etched by, for example, a dry etching method or a wet etching method using the resist layer as a mask. Through the above steps, the contact layer 30 and the light absorption layer 20 are formed as shown in FIG. Thereafter, the resist layer is removed.

  (3) Next, as shown in FIG. 5, the first electrode 40 is formed on the contact layer 30. Specifically, for example, a laminated film (not shown) of platinum, titanium, platinum, and gold is formed by, for example, a vacuum deposition method, a sputtering method, or a plating method. Next, the first electrode 40 is formed by removing the laminated film other than the predetermined region by, for example, a lift-off method or a dry etching method. Here, the first electrode 40 is formed in a shape whose outer peripheral portion is closed. Thereby, the droplet discharged from the inkjet 110 can be stopped as will be described later.

  In addition, the material for forming the 1st electrode 40 is not necessarily limited to what was mentioned above.

  (4) Next, as shown in FIG. 5, the second electrode 42 is formed on the lower surface of the semiconductor substrate 10. Specifically, a laminated film of, for example, chromium, an alloy of gold and germanium, nickel, and gold is formed by, for example, a vacuum deposition method, a sputtering method, or a plating method. Next, the second electrode 42 is formed by removing the laminated film other than the predetermined region by, for example, a lift-off method or a dry etching method. Next, an annealing process is performed. The annealing temperature depends on the electrode material. In the case of the electrode material used in the present embodiment, it is usually performed at around 400 ° C.

  (5) Next, a method for forming an antireflection film will be described with reference to FIG. FIG. 6 is a diagram in which the second antireflection film 52 is formed. The antireflection film is formed by a droplet discharge method. In FIG. 6, an inkjet method is used as an example of a droplet discharge method.

  The ink jet 110 ejects liquid material droplets 114 toward the light receiving surface 60. As a discharge method of the inkjet 110, for example, (I) a method in which pressure is generated by changing the size of bubbles in the liquid by heat, and the liquid is discharged, and (II) liquid is discharged by the pressure generated by the piezoelectric element. There is a method to make it. From the viewpoint of controllability of pressure, the method (II) is desirable.

  Alignment between the position of the nozzle 114 of the inkjet head 112 and the discharge position of the droplet is performed using a known image recognition technique used in an exposure process and an inspection process in a general semiconductor integrated circuit manufacturing process. For example, as shown in FIG. 6, alignment between the position of the nozzle 114 of the inkjet head 112 and the position of the light receiving surface 60 is performed. After the alignment, the voltage applied to the inkjet head 112 is controlled to discharge the liquid material droplet 114. The discharged droplet 114 spreads on the light receiving element 90 and is blocked by the first electrode 40. Then, the coating film is dried and the second antireflection film 52 is formed by removing the solvent and the like.

  The inkjet 110 sequentially moves on the light receiving element array 100 and forms, for example, a fourth antireflection film 56, a third antireflection film 54, a second antireflection film 52, and a first antireflection film 50 in this order.

  The film thickness of the antireflection film is controlled by changing the ejection amount of the droplets of the inkjet 110. The liquid for forming each antireflection film is preferably a material having a low viscosity in order to form the antireflection film flat. Specifically, the viscosity of the material of the antireflection film can be lowered by adjusting the amount of the solvent.

  Moreover, it is preferable that the light receiving surface 60 on which droplets are ejected by the ink jet 110 is subjected to lyophilic treatment such as oxygen plasma treatment before the droplets are ejected. Thereby, the droplet discharged from the inkjet 110 can be easily spread on the light receiving surface 60, and the antireflection film can be formed more flatly.

  Through the above steps, the light receiving element array 100 is obtained (see FIG. 1). By using the droplet discharge method in this way, antireflection films having different film thicknesses can be easily manufactured. Further, since the antireflection film can be formed only on the light receiving surface 60 of the light receiving element 90, the material of the antireflection film can be saved as compared with the case where the antireflection film is collectively formed on the substrate by sputtering, for example. be able to.

3. Modified Example A modified example of the light receiving element array 100 according to the present embodiment will be described with reference to FIG. FIG. 7 is a cross-sectional view schematically showing a light receiving element array 150 according to a modification. The light receiving element array 150 further includes a blocking portion 80 for blocking the droplets 116 (see FIG. 6) discharged from the inkjet 110 around the light receiving element 90 on the semiconductor substrate 10. Different from the element array 100.

  The damming portion 80 is formed in a shape that embeds between the light receiving elements 90. The damming portion 80 has a shape inclined so that the opening becomes larger upward, and is formed higher than the height of the contact layer 30. The first electrode 40 is provided on the contact layer 30 and the damming portion 80. The damming portion 80 is made of polyimide, for example. A first electrode 40 is formed on the damming portion 80.

  Thereby, for example, even when a droplet discharged from the inkjet 110 falls on the first electrode 40, the first electrode 40 is formed in a shape inclined toward the light receiving element 90. Flows into the contact layer 30 from the first electrode 40. Therefore, the antireflection film can be formed more easily.

  Further, by forming the damming portion 80, even an antireflection film thicker than the thickness of the first electrode 40, such as the first antireflection film 58, can be easily formed.

4). FIG. 8 is a cross-sectional view schematically showing an optical transceiver 700 having a light receiving element array according to the present invention. In FIG. 8, the light receiving element array 100 shown in FIG. 1 is applied. The optical transceiver 700 includes a receiving unit 200, a transmitting unit 300, and an electronic circuit unit 600. The electronic circuit unit 600 includes an amplifier circuit unit 400 and a drive circuit unit 500. The receiving unit 200 includes the semiconductor substrate 10 on the submount substrate 220, and includes the light receiving element 90 and the transimpedance amplifier 120 thereon. The transmission unit 300 includes a semiconductor substrate 330 on the submount substrate 340, and includes a light emitting element 310 and a light amount monitor photodiode 320 on the semiconductor substrate 330.

  The casing 202 is made of a resin material and is formed integrally with a sleeve 204 described later. Similarly, the housing portion 302 is formed of a resin material and is formed integrally with a sleeve 304 described later. As the resin material, a material that can transmit light is selected. For example, polymethyl methacrylate (PMMA), epoxy resin, phenol resin, diallyl phthalate, phenyl methacrylate, fluorine polymer, etc. used for plastic optical fiber (POF) Can be adopted.

  The sleeve 204 is formed so that a light guide member (not shown) such as an optical fiber can be fitted from the outside, and constitutes a part of the peripheral wall of the accommodation space 208. In the receiving unit 200, the sleeve 204 has a lens unit 206 for condensing and sending out an optical signal from the light guide member on the accommodation space 208 side. Thereby, the loss of light from the light guide member can be reduced, and the light coupling efficiency between the light receiving element 90 and the light guide member can be improved.

  In the transmitting unit 300, an oblique glass unit 306 that reflects and transmits light from the light emitting element 310 is provided on the accommodation space 308 side of the sleeve 304. The light quantity monitor photodiode 320 receives the reflected light. The drive circuit unit 500 adjusts the amount of light emitted by the light emitting element 310 according to the amount of light received by the monitor photodiode 320. The light transmitted through the oblique glass portion 306 is sent out to a light guide member fitted into the sleeve 304 of the transmission portion 300.

  The light emitting element 310 converts an electrical signal input from the outside into an optical signal, and outputs it to the outside via an optical fiber (not shown). The light receiving element 90 receives an optical signal via an optical fiber, converts it into a current, and sends the converted current to the transimpedance amplifier 120. The transimpedance amplifier 120 converts the received current into a voltage output, amplifies it, and sends it to the electronic circuit unit 600. The amplifier circuit unit 400 controls the voltage output so as not to exceed a certain level, and outputs the voltage output to the outside. In addition, description of external terminals, such as an electrical signal output terminal and an input terminal, is abbreviate | omitted.

  As described above, the light receiving element array 100 is used in the optical transceiver 700 in a state having a plurality of light receiving elements 90 having different wavelength bands. As a result, laser beams having a plurality of wavelengths can be simultaneously received efficiently. Further, since the plurality of light receiving elements 90 formed in one array are integrated, the manufacturing process of the optical transceiver 700 can be simplified as compared with the case where the plurality of light receiving elements 90 formed in different chips are integrated. it can.

  FIG. 9A is a cross-sectional view schematically showing an optical transceiver 750 according to a modification. FIG. 9B is a cross-sectional view taken along the line A-A ′ of FIG.

  In the optical transceiver 700 described above, the light receiving element 90 and the transimpedance amplifier 120 are formed on the same semiconductor substrate 10. However, in the optical transceiver 750, the transimpedance amplifier 120 is not formed on the semiconductor substrate 10. The optical transceiver 700 is different in that it is mounted on the mount substrate 220. Also in the transmission unit 300, the above-described optical transceiver 700 has the light emitting element 310 and the light amount monitor photodiode 320 formed on the same semiconductor substrate 330, but both are formed on different substrates. This is different from the optical transceiver 700 in that respect.

  Specifically, the light receiving element 90 is formed on the semiconductor substrate 10, and the transimpedance amplifier 120 is mounted on the submount 220. The light emitting element 310 is formed on the semiconductor substrate 330, and the light amount monitor photodiode 320 is formed on the semiconductor substrate 332. The sleeve 204 and the sleeve 304 are formed so that four light guide members (not shown) that transmit light having different wavelengths can be fitted through the connectors.

  By adopting the structure as shown in FIGS. 9A and 9B, the optical transceiver can be further downsized as compared with the structure as shown in FIG.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to these embodiments and can take various forms.

Sectional drawing of the light receiving element array which concerns on this Embodiment. The figure which shows the surface reflection characteristic of an antireflection film. Sectional drawing which shows the manufacturing method of the light receiving element array which concerns on this Embodiment. Sectional drawing which shows the manufacturing method of the light receiving element array which concerns on this Embodiment. Sectional drawing which shows the manufacturing method of the light receiving element array which concerns on this Embodiment. Sectional drawing which shows the manufacturing method of the light receiving element array which concerns on this Embodiment. Sectional drawing which shows typically the light receiving element array 150 which concerns on a modification. Sectional drawing which shows typically the optical transceiver 700 which concerns on this Embodiment. (A) Sectional drawing which shows typically the optical transceiver 750 which concerns on a modification. (B) A-A 'sectional view of Drawing 9 (a).

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Semiconductor substrate, 20 Light absorption layer, 30 Contact layer, 40 1st electrode, 42 2nd electrode, 50 1st antireflection film, 52 2nd antireflection film, 54 3rd antireflection film, 56 4th antireflection film , 80 Damping section, 90 light receiving element, 100 light receiving element array, 110 inkjet, 120 transimpedance amplifier, 700 optical transceiver

Claims (3)

A substrate,
A plurality of light absorption layers formed in an array above the substrate;
An antireflection film formed above each of the plurality of light absorption layers;
An electrode surrounding each of the plurality of antireflection films;
Including
The height of the electrode is not less than the height of the antireflection film,
A plurality of the antireflection film by the film thickness are different from each other, unlike the wavelength region of the transmitted light from each other,
The film thickness of each of the plurality of antireflection films is mλ / 4n (m is an odd number) where λ is the wavelength of transmitted light and n is the refractive index of the antireflection film.
The light receiving element array , wherein the antireflection film is formed by a droplet discharge method using droplets containing a material of the antireflection film . In claim 1,
Around the antireflection film further comprises a ruse-out preventing portion dammed droplets,
The light-receiving element array , wherein the damming portion is inclined so that an opening becomes larger upward . Forming a plurality of light absorption layers in an array above the substrate;
Forming an electrode above each of the plurality of light absorption layers so as to surround an antireflection film forming region;
Forming an antireflection film in a region surrounded by the electrodes ;
Including
The electrode is formed such that the height of the electrode is equal to or higher than the height of the antireflection film,
Before SL plurality of antireflection film by the film thickness are different from each other, unlike the wavelength region of the transmitted light from each other, each of the thickness of said plurality of anti-reflection film, a wavelength of the transmitted light as lambda, the When the refractive index of the antireflection film is n, droplets containing the material of the antireflection film are discharged toward the light receiving surface that takes in light in the light absorption layer so that mλ / 4n (m is an odd number). method for manufacturing a photodiode array, characterized in that it is made form by to.

Images