light-receiving element

Abstract

This invention provides a photodetector and a method for manufacturing the same, which enable flip-chip mounting and achieve even faster operation. [Solution] The bonding substrate 1 has a first metal electrode layer 2 formed on its surface (top surface), a first semiconductor layer 3 having a semiconductor of a first conductivity type, a light absorption layer 4, a field relaxation layer 5, a second semiconductor layer 6 having a second conductivity type, and a second metal electrode layer 8, with each layer stacked in order, forming a three-stage mesa structure with a first mesa 10 having the second semiconductor layer 6, a second mesa 20 having the field relaxation layer 5, and a third mesa 30 having the first semiconductor layer 3 and the light absorption layer 4, and an opening 70 for injecting light 40 is provided in a part of the first metal electrode layer 2.

Description

Technical Field

[0001] The present disclosure relates to a light-receiving element, and specifically, to the structure of a metal-bonded light-receiving element with an aperture and a method for manufacturing the same.

Background Art

[0002] A conventional three-stage mesa-type photodiode with heterogeneous substrate bonding using metal has high-speed operability using electrons as conductive carriers, which is an advantage of the three-stage mesa-type photodiode, and low leakage current characteristics by suppressing the electric field on the side surface (see Non-Patent Document 1). Further, the three-stage mesa-type photodiode is widely adopted in the optical communication field where stable and high-speed operation is required as an optical element that can achieve broadband characteristics due to low resistance, which is an advantage of heterogeneous substrate bonding using metal.

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Figure 1 shows a cross-sectional view of a conventional photodetector using wire bonding. The photodetector 100 has a first metal electrode layer 2 formed on the surface (top surface) of the substrate 1, a first semiconductor layer 3 having a p-type semiconductor (referred to as the "p-contact layer"), a light absorption layer 4, a field relaxation layer 5, a second semiconductor layer 6 having an n-type semiconductor (referred to as the "n-contact layer"), and a second metal electrode layer 8, with each layer stacked in order. Light 40 is incident from the n-contact layer 6 side, and the second metal electrode layer 8 is provided with a low-reflection film 7 on the inside to prevent or reduce light reflection. The photodetector 100 is formed in a mesa structure, and an insulating film 9a such as an SiO2 film is attached to the side surface of the photodetector 100. This is to prevent current from flowing along the surface if the junction side surface is exposed. The second metal electrode layer 8 is connected to the wiring surface on the substrate 1 by wire bonding.

[0005] However, in the conventional three-stage mesa-type photodiode 100 using a metal and joined dissimilar substrates as shown in Figure 1, the p-contact layer 3 is completely covered by the metal electrode 2 due to the joining of dissimilar substrates, and the light incidence 40 always comes from the surface of the n-contact layer 6. Therefore, there is a problem that flip-chip mounting is not possible because the electrode 8 and the light incidence are on the same plane.

[0006] On the other hand, in order to achieve even more stable high-speed characteristics for photodetector modules using photodiode chips, flip-chip mounting without wire bonding is essential. [Means for solving the problem]

[0007] In view of the above-mentioned problems of the prior art, this disclosure provides a photodetector and a method for manufacturing the same, characterized by a structure in which an opening is provided in the electrode on the p-contact layer side in order to reverse the electrode surface and the light incident surface of the photodetector, thereby enabling flip-chip mounting on the electrode on the n-contact layer side.

[0008] A photodetector according to one embodiment of the present disclosure comprises a first metal electrode, a light-absorbing layer, a field relaxation layer, and a second semiconductor layer, all formed on a substrate. The contact surface area between the second semiconductor layer and the field relaxation layer is smaller for the second semiconductor layer. The contact surface area between the field relaxation layer and the light-absorbing layer is smaller for the field relaxation layer. The first metal electrode has an opening into which light is incident in part. [Effects of the Invention]

[0009] According to this disclosure, the photodetector can be mounted using a flip-chip design, enabling even faster operation. [Brief explanation of the drawing]

[0010] [Figure 1] This is a diagram showing a conventional semiconductor photodetector. [Figure 2] This is a cross-sectional view showing a semiconductor photodetector according to one embodiment of the present disclosure. [Figure 3] This is a process diagram showing a method for manufacturing a semiconductor photodetector according to one embodiment of the present disclosure. [Modes for carrying out the invention]

[0011] The semiconductor photodetector according to the embodiments of this disclosure will be described in detail below with reference to the figures. However, this disclosure is not limited to the embodiments described below, and may be described in this specification, etc. It will be obvious to those skilled in the art that the form and details can be modified in various ways without departing from the spirit of the invention. In the configuration of the invention described below, the same reference numerals are used for identical parts or parts having similar functions, and repeated descriptions may be omitted.

[0012] The structure of the semiconductor photodetector according to this disclosure will be described in detail below with reference to Figure 2.

[0013] (Embodiment 1) Figure 2 shows a cross-sectional view of a photodetector according to an embodiment of the present disclosure. The photodetector 200 has a first metal electrode layer 2 formed on the surface (upper surface) of the bonding substrate 1, a first semiconductor layer 3 having a semiconductor of a first conductivity type, a light absorption layer 4, a field relaxation layer 5, a second semiconductor layer 6 having a second conductivity type, and a second metal electrode layer 8, with each layer stacked in order. An opening 70 for injecting light 40 is provided in a part of the first metal electrode layer 2. Generally, the first semiconductor layer 3 is a p-type semiconductor, and the second semiconductor layer 6 is an n-type semiconductor.

[0014] The photodetector 200 is a three-stage mesa type photodetector comprising a first mesa 10 having a second semiconductor layer 6, a second mesa 20 having an electric field relaxation layer 5, and a third mesa 30 having a first semiconductor layer 3 and a light absorption layer 4. The first mesa 10 has a smaller area in plan view than the second mesa 20 and is positioned inside the second mesa 20, with a first terrace 20a provided on the surface of the second mesa 20. Furthermore, the second mesa 20 has a smaller area in plan view than the third mesa 30 and is positioned inside the third mesa 30, with a second terrace 30a provided on the surface of the third mesa. In other words, as shown in Figure 2, the photodetector 200 has a stepped structure.

[0015] (substrate) The bonding substrate 1 is, for example, a semiconductor substrate such as Si or SiC, and by selecting a material that is transparent to the incident light 40, light can be propagated into the photodetector 200.

[0016] (First metal electrode layer and opening) A first metal electrode layer 2 is formed between the bonding substrate 1 and the first semiconductor layer 3. The first metal electrode layer 2 is formed from the bonding of dissimilar substrates, and the bonding process will be explained in detail in the manufacturing method described later. Generally, metallic materials such as copper (Cu), aluminum (Al), titanium (Ti), and gold (Au) can be used for the first metal electrode layer.

[0017] An opening 70 through which light 40 is incident is provided in a part of the first metal electrode layer 2 from the side of the bonding substrate 1. For example, the opening 70 is provided at a position in the first metal electrode layer 2 corresponding to the position of the region where the second semiconductor layer 6 and the electric field relaxation layer 5 are in contact. The shape of the opening 70 can be determined according to the shape of the incident light. As an example, it may be circular, elliptical, or rectangular. The area of the opening 70 only needs to be not larger than the area of the light absorption layer 4, and as a non-limiting example, it can be the same area as the second semiconductor layer 6.

[0018] Also, the thickness D of the opening 70 (in other words, the thickness of the first metal electrode layer 2 where the opening 70 is formed) is preferably λ / 2n. Here, λ is the wavelength of the incident light, and n is the refractive index of the opening 70. Reflection of the incident light due to the refractive index difference can occur at the interface between the bonding substrate 1 and the opening 70. The reflection at the above interface can be canceled by making the thickness D of the opening 70 near λ / 2n, and the loss due to multiple reflections can be reduced. Further, the opening 70 may be filled with a dielectric. Even when filled with a dielectric, the above thickness D condition is the same.

[0019] (First Semiconductor Layer) The first semiconductor layer 3 is formed on the surface (upper surface) of the first metal electrode layer 2 so as to cover the entire opening 70. The first semiconductor layer 3 is composed of, for example, a III-V compound semiconductor such as InP or InGaAsP, and is made p-type by introducing a high concentration of p-type impurities.

[0020] (Light Absorption Layer) The light absorption layer 4 is formed on the surface of the first semiconductor layer 3. As shown in FIG. 2, the light absorption layer 4 has the same area as the first semiconductor layer 3 and forms the third mesa 30. The light absorption layer 4 is a light absorption layer having a first conductivity type, a second conductivity type, or a non-doped semiconductor (for example, non-doped InGaAs).

[0021] (Electric Field Relaxation Layer) As shown in Figure 2, the electric field relaxation layer 5 is formed on the surface of the light absorption layer 4. The electric field relaxation layer 5 has a smaller area in plan view than the third mesa 30 which has the first semiconductor layer 3 and the light absorption layer 4, and is positioned inside the third mesa 30. Due to this mesa structure, a second terrace 30a is provided on the surface of the third mesa 30. Since there is no charge on the second terrace 30a, the region of the electric field induced in the photodetector 200 can be limited by the second mesa region which is the electric field relaxation layer 5. Therefore, the electric field relaxation layer 5 can alleviate electric field concentration and suppress malfunctions around the second semiconductor layer (e.g., n-contact layer) 6, which will be described later. In addition, by controlling the concentration of the electric field relaxation layer 5, the light absorption layer 4 is designed and manufactured so that a high electric field is not applied even when the device breaks down, and it also has the effect of suppressing the generation of tunnel current in the light absorption layer 4.

[0022] (Second semiconductor layer) The second semiconductor layer 6 is formed on the surface of the field relaxation layer 5. The second semiconductor layer 6 has a smaller area in plan view than the second mesa 20 having the field relaxation layer 5 and is positioned inside the second mesa 20. This mesa structure provides a first terrace 20a on the surface of the second mesa 20. Since there is no charge on the first terrace 20a, the region of the electric field induced in the photodetector 200 can be further limited. The second semiconductor layer 6 is composed of a III-V compound semiconductor such as InP or InGaAsP, and is made n-type by introducing a high concentration of n-type impurities.

[0023] (Second metal electrode layer) The second metal electrode layer 8 is formed on the surface of the second semiconductor layer 6. Generally, metallic materials such as titanium (Ti) and gold (Au) can be used for the second metal electrode layer.

[0024] Next to the photodetector 200, a plurality of supports 60a and 60b are formed to support the photodetector 200 when flip-mounted. The supports are formed to be taller than the total height of the photodetector 200 (for example, by the height h shown in Figure 2) to prevent the photodetector 200 from coming into contact with and being damaged by the circuit board on which it is mounted when flip-mounted. The height of the supports can be achieved by making the metal pads 60a and 60b on the supports thicker than the second metal electrode layer 8 on the photodetector 200.

[0025] The space between the light-receiving element 200 and the support 60 is filled with an insulating resin 9b (for example, benzocyclobeten (BCB)). Filling with an insulating resin ensures the electrical and structural stability and durability of the light-receiving element 200.

[0026] Finally, the first metal electrode layer 2 is configured to conduct electricity with the metal pad 60a on one of the multiple supports 50a. The second metal electrode layer 8 is configured to conduct electricity with the metal pad 60b on the other of the multiple supports 50b. This allows current to flow from the metal pads 60a and 60b of the supports connected to the circuit board after flip mounting to the first metal electrode layer 2 and the second metal electrode layer 8, applying a bias between the first metal electrode layer 2 and the second metal electrode layer 8, and enabling the photodetector 200 to operate.

[0027] The method for manufacturing a semiconductor photodetector according to this disclosure will be described in detail below with reference to Figure 3.

[0028] (Manufacturing method) In the first step, the bonding substrate 1 and the photodiode substrate are prepared. The bonding substrate 1 corresponds to the optical element substrate 1 shown in Figure 2, and the photodiode substrate is doped during growth, and a first semiconductor layer 3 having a first conductivity type semiconductor, a light absorption layer 4, a field relaxation layer 5, and a second semiconductor layer 6 having a second conductivity type semiconductor are stacked in order. However, in Figure 3, the doped layers are not shown for visibility.

[0029] Metal layers 2-1 and 2-2 for bonding the two substrates are formed on one surface of the bonding substrate and the photodiode substrate. At predetermined positions in each metal layer, light incidence apertures 70-1 and 70-2, alignment marks 80-1 and 80-2 for the photodiode process, and bonding alignment marks 90-1 and 90-2 are provided. The apertures 70-1 and 70-2 and the alignment marks may be formed by photolithography and lift-off techniques, or by etching after depositing the metal layer over the entire surface of one surface of both substrates.

[0030] In the second step, a metal layer 2-1 formed on one side of the target substrate and a metal layer 2-2 formed on one side of the photodiode substrate are joined using diffusion bonding (thermocompression bonding) or ultrasonic bonding. The joining position of the two substrates is determined by joining alignment marks 90-1 and 90-2 provided on each metal layer. Therefore, an aperture 70 is created in the metal layer between the target substrate and the photodiode substrate, allowing light to enter from the first semiconductor layer (P contact layer) even after flip mounting.

[0031] In the third step, the photodiode substrate above the alignment mark 80 for the photodiode process is removed by wet etching or the like to expose the alignment mark 80 for the photodiode process.

[0032] In the fourth step, the photodiode substrate is etched above the opening 70 to form a three-tiered mesa structure, using the exposed alignment mark 80 for the photodiode process as a reference. The lengths of the terraces 20a and 30a formed on the upper surface of the mesa structure closest to the metal layer 2-2 and the upper surface of the second closest mesa structure, respectively, range from a few micrometers to several hundred micrometers. In this disclosure, the photodetector 200 is formed using the alignment mark 80 for the photodiode process as a reference, but in some cases, the bonding alignment mark 90 may be used as a reference, either as a substitute for or in addition to the alignment mark 80 for the photodiode process. If the bonding alignment mark 90 is used as a substitute for the alignment mark 80 for the photodiode process, the bonding alignment mark 90 is not required.

[0033] Furthermore, although not shown in the figures, a second metal electrode layer 8 is formed on the upper surface of the second semiconductor layer 6, and the first metal electrode layer 2 and the second metal electrode layer 8 are connected to their respective corresponding metal pads. In addition, the aforementioned insulating resin 9b is filled into the gap of the photodetector and / or the aperture 70 is filled with dielectric material. The photodiode manufacturing method in this disclosure is the same as the commonly used prior art.

[0034] (Additional considerations) The foregoing description of embodiments of this disclosure is provided for illustrative purposes only and is not intended to be exhaustive or to limit the disclosure to the exact forms. Those skilled in the art will understand that many modifications and changes are possible in light of the above disclosure.

[0035] Finally, the language used herein has been selected primarily for readability and explanatory purposes, and may not be selected to describe or limit the subject matter of the invention. Therefore, the scope of the invention is intended to be limited by the appended claims, not by this detailed description. Accordingly, the disclosure of embodiments of this disclosure is intended to illustrate, not limit, the scope of the disclosure as set forth in the claims. [Industrial applicability]

[0036] According to the embodiments of this disclosure, the photodetector can be mounted using a flip-chip design, enabling even faster operation. [Explanation of Symbols]

[0037] 1. Bonding substrate 2 First metal electrode layer 3. First semiconductor layer (P-contact layer) 4. Light-absorbing layer 5. Electric field relaxation layer 6. Second semiconductor layer (n-contact layer) 7 Low reflective coating 8 Second metal electrode layer 9a Insulating film 9b Insulating resin 10. Mesa 1 20. Mesa No. 2 20a Terrace 1 30. Third Mesa 30a Second Terrace 40 light incidence 50a, 50b support 60a, 60b electrode pads 70, 70-1, 70-2 opening Alignment marks for 80, 80-1, and 80-2 photodiode processes. 90, 90-1, 90-2 Alignment marks for joining 100, 200 photodetectors

Claims

1. Formed on the substrate, First metal electrode and Light-absorbing layer, The electric field relaxation layer, The second semiconductor layer, In a light-receiving element equipped with, The size of the contact surface between the second semiconductor layer and the field relaxation layer is such that the second semiconductor layer is smaller. The size of the contact surface between the electric field relaxation layer and the light absorption layer is such that the electric field relaxation layer is small. The first metal electrode has an opening into which light enters in part, A light-receiving element characterized by the following features.

2. The thickness of the first metal electrode having the opening is λ / (2n), The photodetector according to claim 1, wherein n is the refractive index of the opening and λ is the wavelength of light incident on the light absorption layer through the opening.

3. The photodetector according to claim 1 or 2, wherein the aperture is filled with a dielectric.

4. The light-receiving element according to claim 1 or 2, wherein the light-receiving element comprises a plurality of supports, the height of which is greater than the height of the light-receiving element.

5. A step of forming a metal layer on each of a bonding substrate and a photodiode substrate, the step of forming a metal layer, the step of forming a light incident aperture and at least one alignment mark at a predetermined position in the metal layer, The steps include joining the metal layer formed on the target substrate and the metal layer formed on the photodiode substrate based on the at least one alignment mark, The steps include removing the photodiode substrate to expose the at least one alignment mark, The steps include processing the photodiode substrate into a mesa structure based on the at least one exposed alignment mark, A method that includes this.

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