JP5801833B2 - Integrated photo detector - Google Patents

Description

  The present invention relates to an integrated light receiving element, and in particular, includes a light wave circuit and a light receiving element such as a photodiode (also referred to as “PD” in this specification) used in the fields of optical communication and optical information processing. The present invention relates to an integrated light receiving element.

  In recent years, with the spread of optical fiber transmission, a technique for integrating a large number of optical functional elements at a high density is required. As one of such techniques, a quartz-based planar lightwave circuit (also referred to as “PLC” (Planar Lightwave Circuit) in this specification) is known. The PLC has excellent characteristics such as low loss, high reliability, and high design flexibility, and is promising as a platform for integrating multiple functions.

  Actually, the optical receiver at the transmission terminal station includes an optical module including a light receiving element such as a PD, a light emitting element such as a laser diode (also referred to as “LD” in this specification), a multiplexer / demultiplexer, a branching / combining unit. And a PLC on which functional elements such as an optical modulator and an optical modulator are formed are mounted by optical coupling.

  Further, for example, in a node device in the wavelength division multiplexing transmission system, a large number of PDs are integrated and mounted in order to monitor the light intensity of a plurality of optical waveguides in the PLC.

  As a structure that enables optical coupling between an optical waveguide and a light receiving (emitting) optical element, an element having a structure as shown in FIGS. 1 and 2 has been proposed. In this element, an oblique groove (also referred to as a “mirror groove” in this specification) is provided in an optical waveguide by anisotropic etching, and a metal or a multilayer film is deposited on a side surface of the oblique groove, and the substrate surface is formed. On the other hand, a mirror can be produced by using a reflecting surface that changes the optical path in the vertical direction.

  FIG. 1 is a perspective view of a conventional structure including a mirror that reflects light and couples it to a PD. 2A and 2B are diagrams illustrating the same structure, in which FIG. 2A is a top view, FIG. 2B is a front view, and FIG. 2C is a cross-sectional view taken along a cross-sectional line AA ′ in FIG. .

  The structure shown in FIGS. 1 and 2 includes a substrate 12, an optical waveguide 17 on the substrate 12 (the optical waveguide 17 is composed of a core 16 and a clad 14), and a mirror 18 provided at the end of the optical waveguide 17. The PD 22 is disposed on the optical waveguide 17 (the PD 22 includes the PD light receiving unit 20).

  In FIGS. 1 and 2, the direction in which the core 16 extends is the x-axis direction, the normal direction of the main surface of the substrate 12 on which the optical waveguide 17 is laminated is the z-axis direction, and the direction perpendicular to the x-axis and z-axis. The coordinate axes are set so that is in the y-axis direction. This coordinate axis is assumed to be set similarly in the following description.

  As the substrate 12, a Si substrate or the like can be used. The optical waveguide 17 includes a core 16 and a clad 14. The light propagating through the core 16 is reflected by the mirror 18 to change the optical path, and is coupled to the PD light receiving unit 20 of the corresponding PD 22.

  FIG. 3 shows an example of a method for manufacturing a structure (a structure shown in FIGS. 1 and 2) including a mirror that reflects light and couples to a PD according to the related art.

  First, a clad 14 and a core 16 are formed on a substrate 12 such as a Si substrate to produce an optical waveguide 17, and a PD 22 is produced on the produced optical waveguide 17 (FIG. 3A). reference).

  Next, a photoresist 24 is applied to the entire optical waveguide 17 (including the PD 22). After the exposure, development is performed to remove the photoresist in a portion where a mirror groove for forming a mirror is to be formed (see FIG. 3B). In this specification, the portion from which the photoresist has been removed to form the mirror groove is referred to as a mirror opening (the mirror opening is indicated by reference numeral 26 in FIG. 3B).

  After the photoresist 24 is formed in a region other than the mirror opening 26, an oblique mirror groove 28 is formed by anisotropic etching (see FIG. 3C). By forming the mirror groove 28, the end of the waveguide is exposed and a mirror surface 29 is formed. Although a resist mask is used here, a metal mask can also be used, and the present invention is not limited by the mask material.

  Next, metal is vapor-deposited on the mirror surface 29 to form the mirror 18 having a high reflectivity. Al, Au, or the like can be used as a metal to be deposited (see FIG. 3D). A reflective multilayer film may be deposited by sputtering or the like.

  Finally, the photoresist is washed with a resist removing solution to remove all the resist (not shown).

Japanese Patent No. 3834024

Kurata, Yu; Nasu, Yusuke; Tamura, Munehisa; Yokoyama, Haruki; Muramoto, Yoshifumi, “Heterogeneous Integration of High-Speed InP PDs on Silica-Based Planar Lightwave Circuit Platform”, Proc. ECOC2011, Th.12, LeSaleve.5 , (2011)

  In the integrated light receiving element shown in FIGS. 1 and 2, it is desirable to reduce the light receiving diameter of the PD light receiving portion in order to achieve miniaturization and high speed. However, if the light receiving diameter is small, the position of the beam incident on the PD is shifted, that is, the loss occurs due to the mirror being shifted from the optimum position.

  For example, as shown in FIG. 4, it is conceivable that the mirror surface is formed before the target location in the x-axis direction due to excessive etching (overetching). As shown in FIG. 4, when the mirror 18 is provided on the mirror surface formed in the x-axis direction before the initial schedule, a part of the light propagating through the core 16 is not coupled to the PD light receiving unit 20. . For this reason, a stricter manufacturing tolerance (allowable error) is set for mirror formation.

  In addition, parameters such as the angle and depth of the mirror surface are usually measured by cross-sectional observation, so that the sample is destroyed. Therefore, in order to form a mirror surface with higher accuracy, parameters such as position, angle, and depth can be determined without destroying the sample, and the mirror surface is not formed at a position suitable for optical coupling. In addition, there is a demand for a technique that can finely adjust the reflection position by trimming.

  The present invention has been made in view of the above problems, and its object is to provide information relating to etching during the manufacturing process (anisotropic etching process) (mirror formed by groove formation by anisotropic etching). It is an object of the present invention to provide an integrated light receiving element capable of accurately forming a mirror surface by having a structure capable of monitoring the angle and depth of the surface.

The present invention includes a substrate, an optical waveguide composed of a clad and a core on the substrate, a mirror provided at an end of the optical waveguide for reflecting light propagating through the core, and an optical waveguide. An integrated light receiving element composed of a photodiode for coupling the light reflected by the mirror, provided on the upper surface of the optical waveguide , and measuring the position of the core end in the core extension direction For measuring the position of the end of the core in the extension direction of the core , the surface scale is provided from above the optical waveguide. The core scale is arranged at an observable position .

  In the present invention, an integrated light receiving element is manufactured using an optical circuit having a surface scale and a core scale. In the present invention, the angle and depth of the mirror surface can be calculated and the state of etching can be grasped only by observing the upper surface during etching. Thereby, it is possible to easily determine whether or not the waveguide end portion needs to be trimmed.

  Therefore, it is possible to provide an integrated light receiving element in which the mirror surface is formed with high accuracy.

It is a perspective view explaining the structure provided with the mirror which reflects light and couple | bonds with PD based on a prior art. It is a figure explaining the structure provided with the mirror which reflects light and couple | bonds with PD based on a prior art, (a) is a top view, (b) is a front view, (c) is (a) Is a cross-sectional view taken along a cross-sectional line AA ′. It is a figure explaining the manufacturing method of the structure (structure shown in FIG. 1 and FIG. 2) provided with the mirror which reflects light and couple | bonds with PD based on a prior art. It is a figure explaining the subject of a prior art. It is a figure which shows the structure of the optical circuit based on this invention, (a) is a top view, (b) is sectional drawing in sectional line AA 'of (a), (c) is (a) It is sectional drawing in sectional line BB 'of (). It is a figure explaining the manufacturing process of the integrated light receiving element based on this invention. It is a figure explaining how the information regarding the progress of an etching is obtained when producing an integrated light receiving element using the optical circuit according to the present invention. It is a figure explaining the manufacture flow of the integrated light receiving element based on this invention. It is a figure explaining the manufacture flow of the integrated light receiving element based on this invention. It is a figure which shows the structure of the optical circuit based on one Embodiment of this invention.

  The optical circuit used for manufacturing the integrated light receiving element according to this embodiment has a structure shown in FIG. FIG. 5A is a top view of the optical circuit. FIG. 5B is a cross-sectional view taken along a cross-sectional line A-A ′ in FIG. FIG. 5C is a cross-sectional view taken along a cross-sectional line B-B ′ in FIG. Note that in FIG. 5B and FIG. 5C, those not having the same y-axis value as the cross-sectional line are also represented by a broken line or a one-dot chain line. Note that what is on the near side is represented by a one-dot chain line, and what is on the far side is represented by a broken line.

  The optical circuit according to the present embodiment is composed of the clad 14 laminated on the substrate 12 and the core 16 because the optical circuit used in the conventional integrated light receiving element (see FIGS. 1 and 2). It is the same.

  However, the optical circuit according to the present embodiment includes the surface scale 30 on the optical waveguide 17 (on the clad 14), and the same height in the clad 14 and the core 16 (that is, a place where the z-axis values are equal). Is provided with a core scale 32, which is different from the conventional optical circuit in this point.

  The surface scale 30 is a scale for measuring the distance in the x-axis direction provided at predetermined intervals (such as 1 μm). The surface scale 30 is provided so that the x-axis value of the end portion of the photoresist to be applied is a reference (origin, start point) (this will be described later with reference to FIG. 6). The surface scale 30 has a distance along the x-axis direction between the x-axis origin and the end of the mirror surface of the surface of the optical waveguide 17 formed by the anisotropic etching (this specification). (This is also referred to as “etching shift”) and the like (this will be described later with reference to FIG. 7).

  The surface scale 30 can be obtained by (1) forming the clad 14 and the core 16 on the substrate 12 to form the optical waveguide 17 and then processing the metal into a scale shape by photolithography, or (2) When forming the optical waveguide 17 by forming the clad 14 and the core 16 on the substrate 12, it can be produced by processing the surface of the clad 14 to provide irregularities.

  The core scale 32 is a scale for measuring the distance in the x-axis direction provided at the same height as the core 16 and at predetermined intervals (such as 1 μm). The core scale 32 has a distance along the x-axis direction between the end of the mirror surface on the surface of the optical waveguide 17 formed by the anisotropic etching and the end of the core 16 during the anisotropic etching. In the specification, it is also produced to measure “core shift”. Although the core scale 32 is manufactured inside the optical waveguide 17, it can be observed from the upper surface of the optical waveguide 17. Therefore, the progress of etching can be estimated by observing the upper surface (see FIG. 7 for this). Will be described later).

  The core scale 32 is used when the optical waveguide 17 is formed by forming the clad 14 and the core 16 on the substrate 12, and more specifically, when the optical waveguide having the height of the core 16 is formed. The clad 14 having the same height as 16 can be manufactured by putting a scale shape as shown in FIG.

  With reference to FIG. 6, how the mirror surface is formed using the optical circuit shown in FIG. 5 will be described.

  First, a clad part 14 and a core part 16 are formed on a substrate 12 to produce an optical waveguide 17 having a refractive index difference between the core and the clad of 1.5%, and the optical waveguide shown in FIG. Is made. A PD 22 having a light receiving diameter of 19 μm is produced on the produced optical waveguide 17. The thickness of the core portion is 4.5 μm, the thickness of the cladding portion under the core is 20 μm, and the thickness of the cladding portion on the core is 15.5 μm. The PD 22 is made by bonding an optical semiconductor material substrate such as InP formed with an epitaxial layer to the optical waveguide 17 with polyimide, removing the InP substrate by polishing and wet etching, and processing the remaining epitaxial layer by a photo process, It is produced (see FIG. 6A, see Non-Patent Document 1).

  Next, a photoresist 24 is applied to the entire optical waveguide 17 (including the PD 22). After the exposure, development is performed, and the photoresist 24 is partially removed to form a mirror opening 26 (see FIG. 6B).

  Next, after forming the oblique mirror groove 28 and the mirror surface 29 by anisotropic etching, the photoresist 24 is washed with a resist removing solution to remove all the resist (see FIG. 6C). In this state, observation (from the upper surface), information on the progress of etching (angle, depth, etc. of the mirror surface) is calculated.

  With reference to FIG. 7, how to calculate information on the progress of etching (angle and depth of the mirror surface formed by etching) will be described.

  FIG. 7 is a diagram for explaining how to obtain information on the progress of etching, FIG. 7A is a top view, and FIG. 7B is a cross-sectional line of FIG. It is sectional drawing in AA '. Note that for the sake of illustration, FIGS. 7A and 7B are shown with the PD omitted.

  By observing the surface scale 30 and the core scale 32 from the upper surface, the distance along the x-axis direction between the end of the mirror surface 29 on the surface of the optical waveguide 17 formed by etching and the end of the core 16 (this In the specification, it can also be measured as “core shift”. Let the value of this core shift be a.

  The distance along the z-axis direction between the surface of the optical waveguide 17 and the core 16 (also referred to as “core depth” in this specification) is based on information obtained when the optical waveguide 17 is formed on the substrate 12. Known. When the value of the core depth is b and the angle between the substrate 12 and the mirror surface 29 (also referred to as “angle of the mirror surface” in this specification) is θ, the following (Expression 1) is satisfied.

Therefore, the angle θ of the mirror surface 29 can be calculated.

  Next, by observing the surface scale 30 and the core scale 32 from the upper surface, between the end portion of the mirror surface 29 on the surface of the optical waveguide 17 and the end portion of the mirror surface 29 on the bottom surface of the optical waveguide 17 formed by etching. A distance along the x-axis direction (also referred to as “mirror shift” in this specification) can be measured.

  Assuming that the value of this mirror shift is c, from the following (Equation 2), along the z-axis direction between the end of the mirror surface 29 on the surface of the optical waveguide and the end of the mirror surface 29 on the bottom of the optical waveguide. Distance (also referred to as “depth of mirror surface” in the present specification) can be calculated. Here, if the depth value of the mirror surface is d,

It becomes.

  Therefore, it is possible to obtain information on the progress of etching (angle and depth of the mirror surface formed by etching) just by observing from the upper surface without destroying the optical circuit. It can be judged whether it can be formed at an appropriate position at an appropriate angle.

  FIG. 8 is a flowchart of a method for manufacturing an integrated light receiving element according to this embodiment.

  In step 800, the optical waveguide shown in FIG. 5 is prepared, and an etching mask is formed on the optical waveguide by applying a photoresist.

  In step 802, oblique mirror grooves are formed by anisotropic etching. The waveguide end face exposed by forming the mirror groove is the mirror surface.

  In step 804, the etching mask is removed and the optical waveguide is observed from above. Information on the progress of etching (angle and depth of the mirror surface formed by etching) is derived by observing the upper surface. The method for calculating the angle and depth of the mirror surface formed by etching is as described above (see FIG. 7).

  In step 806, it is determined whether or not trimming of the end face is necessary based on the obtained information on the progress of etching (angle and depth of the mirror surface).

If it is excessively etched (overetched), in step 808, a SiO ₂ film is deposited on the end face of the optical waveguide to form a mirror surface at the optimum position (see FIG. 9A).

  If the etching is insufficient, in step 810, additional etching is performed, the optical waveguide is further cut, and the mirror surface is formed at the optimum position (see FIG. 9C).

  After the mirror surface is formed at the optimum position, in step 812, a reflective film such as Au is deposited on the mirror surface to form a mirror.

  In the above description, an integrated light receiving element is manufactured using a surface scale provided on the surface of the optical waveguide and an optical waveguide provided with a core scale provided at the same height as the core. As described above, an integrated light receiving element may be fabricated using an optical waveguide further provided with a substrate surface scale 34 on the substrate 12.

  In such a case, the surface scale, core scale, and substrate surface scale are observed from the top during etching, and the same calculation as described above is performed to derive information on the progress of etching (mirror surface angle and mirror surface depth). Therefore, more accurate values for the angle and depth of the mirror surface can be calculated as compared with the case where only the surface scale and the core scale are observed from the upper surface.

12 substrate 14 clad 16 core 17 optical waveguide 18 mirror 20 PD light receiving part 22 PD
24 Photoresist 26 Mirror opening 28 Mirror groove 29 Mirror surface 30 Surface scale 32 Core scale 34 Substrate surface scale

Claims (1)

A substrate,
An optical waveguide composed of a cladding and a core on the substrate;
A mirror provided at the end of the optical waveguide to reflect light propagating through the core;
An integrated light-receiving element provided on the optical waveguide and configured by a photodiode for coupling light reflected by the mirror;
A surface scale provided on the upper surface of the optical waveguide for measuring the position of the end of the core in the extending direction of the core ;
A core scale provided on the clad having the same height as the core for measuring the position of the end of the core in the extension direction of the core, and the surface scale from above the optical waveguide. An integrated light receiving element, wherein the scale is disposed at a position where the scale can be observed .

Images