US-20260128570-A1 - OPTICAL INTEGRATED DEVICE AND METHOD FOR MANUFACTURING OPTICAL INTEGRATED DEVICE

US20260128570A1US 20260128570 A1US20260128570 A1US 20260128570A1US-20260128570-A1

Abstract

An optical integrated device that integrates an optical functional element and an optical circuit element according to the present disclosure includes: the optical functional element comprising a protruding-shaped high-mesa section that includes a part of the compound semiconductor substrate and comprises an active layer and a contact layer, and planar-shaped terrace portions positioned at a predetermined height with respect to the active layer, an optical circuit element comprising a lower cladding layer, a core layer and an upper cladding layer formed above the semiconductor substrate, a first recess and second recesses, wherein the optical functional element and the optical circuit element are flip-chip mounted.

Inventors

Keita MOCHIZUKI
Harunaka Yamaguchi
Kazumasa Kishimoto

Assignees

MITSUBISHI ELECTRIC CORPORATION

Dates

Publication Date: 20260507
Application Date: 20221109

Claims (16)

1 .- 15 . (canceled)
16 . An optical integrated device that integrates an optical functional element and an optical circuit element, the optical integrated device comprising: an optical functional element, the optical functional element including: a compound semiconductor substrate; a protruding-shaped high-mesa section that includes a part of the compound semiconductor substrate, the high-mesa section including at least an active layer and a contact layer from the side of the compound semiconductor substrate; and planar-shaped terrace portions provided along the high-mesa section, an optical circuit element, the optical circuit element including: a semiconductor substrate; a lower cladding layer, a core layer and an upper cladding layer formed above the semiconductor substrate; a first recess provided in the semiconductor substrate; second recesses that are provided along the side surfaces of the first recess and are separated from the side surfaces of the first recess; protrusion portions formed between the first recess and each second recesses; and an optical waveguide section including the lower cladding layer, the core layer and the upper cladding layer, the optical waveguide section being provided in contact with a side surface that is different from the side surface of the first recess and the side surface opposite the side surface of the first recess; wherein the surface height of each terrace portion is set at the interface between the compound semiconductor substrate and the active layer, and the height of the top of each protrusion portion is set at the surface of the core layer on the side of the upper cladding layer, and the surface of each terrace portion is contact with the top of each protrusion portion, and the active layer of the high-mesa section is optically coupled to the core layer of the optical waveguide section.
17 . An optical integrated device that integrates an optical functional element and an optical circuit element, the optical integrated device comprising: an optical functional element, the optical functional element including: a compound semiconductor substrate; a protruding-shaped high-mesa section that includes a part of the compound semiconductor substrate, the high-mesa section including at least an active layer and a contact layer from the side of the compound semiconductor substrate; and planar-shaped terrace portions provided along the high-mesa section, an optical circuit element, the optical circuit element including: a semiconductor substrate; a lower cladding layer, a core layer and an upper cladding layer formed above the semiconductor substrate; a first recess provided in the semiconductor substrate; second recesses that are provided along the side surfaces of the first recess and are separated from the side surfaces of the first recess; protrusion portions formed between the first recess and each second recesses; and an optical waveguide section including the lower cladding layer, the core layer and the upper cladding layer, the optical waveguide section being provided in contact with a side surface that is different from the side surface of the first recess and the side surface opposite the side surface of the first recess; wherein the surface height of each terrace portion is set at the interface between the active layer and the contact layer, and the height of the top of each protrusion portion is set at the surface of the core layer on the side of the lower cladding layer, and the surface of each terrace portion is contact with the top of each protrusion portion, and the active layer of the high-mesa section is optically coupled to the core layer of the optical waveguide section.
18 . An optical integrated device that integrates an optical functional element and an optical circuit element, the optical integrated device comprising: an optical functional element, the optical functional element including: a compound semiconductor substrate; a protruding-shaped high-mesa section that includes a part of the compound semiconductor substrate, the high-mesa section including at least an active layer, a contact layer, and an etching stop layer provided between the active layer and the contact layer from the side of the compound semiconductor substrate; and planar-shaped terrace portions provided along the high-mesa section, an optical circuit element, the optical circuit element including: a semiconductor substrate; a lower cladding layer, a core layer and an upper cladding layer formed above the semiconductor substrate; a first recess provided in the semiconductor substrate; second recesses that are provided along the side surfaces of the first recess and are separated from the side surfaces of the first recess; protrusion portions formed between the first recess and each second recesses; and an optical waveguide section including the lower cladding layer, the core layer and the upper cladding layer, the optical waveguide section being provided in contact with a side surface that is different from the side surface of the first recess and the side surface opposite the side surface of the first recess; wherein the surface height of each terrace portion is set at the interface between the contact layer and the etching stop layer, and the height of the top of each protrusion portion is set at the surface of the lower cladding layer on the side of the core layer, and the surface of each terrace portion is contact with the top of each protrusion portion, and the active layer of the high-mesa section is optically coupled to the core layer of the optical waveguide section.
19 . An optical integrated device that integrates an optical functional element and an optical circuit element, the optical integrated device comprising: an optical functional element, the optical functional element including: a compound semiconductor substrate; a protruding-shaped high-mesa section that includes a part of the compound semiconductor substrate, the high-mesa section including at least an active layer, a first contact layer, an etching stop layer, and a second contact layer from the side of the compound semiconductor substrate; and planar-shaped terrace portions provided along the high-mesa section, an optical circuit element, the optical circuit element including: a semiconductor substrate; a lower cladding layer, a core layer and an upper cladding layer formed above the semiconductor substrate; a first recess provided in the semiconductor substrate; second recesses that are provided along the side surfaces of the first recess and are separated from the side surfaces of the first recess; protrusion portions formed between the first recess and each second recesses; and an optical waveguide section including the lower cladding layer, the core layer and the upper cladding layer, the optical waveguide section being provided in contact with a side surface that is different from the side surface of the first recess and the side surface opposite the side surface of the first recess; wherein the surface height of each terrace portion is set at the interface between the etching stop layer and the second contact layer, and the height of the top of each protrusion portion is set at the interface between the semiconductor substrate and the lower cladding layer, and the thickness of the etching stop layer and the thickness of the lower cladding layer is set to be equal, and the surface of each terrace portion is contact with the top of each protrusion portion, and the active layer of the high-mesa section is optically coupled to the core layer of the optical waveguide section.
20 . An optical integrated device that integrates an optical functional element and an optical circuit element, the optical integrated device comprising: an optical functional element, the optical functional element including: a compound semiconductor substrate; a protruding-shaped high-mesa section that includes a part of the compound semiconductor substrate, the high-mesa section including at least an active layer, a contact layer, and an etching stop layer provided between the active layer and the contact layer from the side of the compound semiconductor substrate; and planar-shaped terrace portions provided along the high-mesa section, an optical circuit element, the optical circuit element including: a semiconductor substrate; a lower cladding layer, a core layer and an upper cladding layer formed above the semiconductor substrate; a first recess provided in the semiconductor substrate; second recesses that are provided along the side surfaces of the first recess and are separated from the side surfaces of the first recess; protrusion portions formed between the first recess and each second recesses; and an optical waveguide section including the lower cladding layer, the core layer and the upper cladding layer, the optical waveguide section being provided in contact with a side surface that is different from the side surface of the first recess and the side surface opposite the side surface of the first recess; wherein the surface height of each terrace portion is set at the interface between the etching stop layer and the contact stop layer, and the height of the top of each protrusion portion is set at the interface between the semiconductor substrate and the lower cladding layer, and the thickness of the etching stop layer and the thickness of the lower cladding layer is set to be equal, and the surface of each terrace portion is contact with the top of each protrusion portion, and the active layer of the high-mesa section is optically coupled to the core layer of the optical waveguide section.
21 . An optical integrated device that integrates an optical functional element and an optical circuit element, the optical integrated device comprising: an optical functional element, the optical functional element including: a compound semiconductor substrate; a protruding-shaped high-mesa section that includes a part of the compound semiconductor substrate, the high-mesa section including at least an active layer, a first contact layer, a first etching stop layer, a second etching stop layer, and a second contact layer from the side of the compound semiconductor substrate; and planar-shaped terrace portions provided along the high-mesa section, an optical circuit element, the optical circuit element including: a semiconductor substrate; a lower cladding layer, a core layer and an upper cladding layer formed above the semiconductor substrate; a first recess provided in the semiconductor substrate; second recesses that are provided along the side surfaces of the first recess and are separated from the side surfaces of the first recess; protrusion portions formed between the first recess and each second recesses; and an optical waveguide section including the lower cladding layer, the core layer and the upper cladding layer, the optical waveguide section being provided in contact with a side surface that is different from the side surface of the first recess and the side surface opposite the side surface of the first recess; wherein the surface height of each terrace portion is set at the interface between the second etching stop layer and the second contact layer, and the height of the top of each protrusion portion is set at the interface between the semiconductor substrate and the lower cladding layer, and the surface of each terrace portion is contact with the top of each protrusion portion, and the first etching stop layer and the second etching stop layer are made of different compound semiconductor materials, and the refractive index of the first etching stop layer is higher than the refractive index of the second etching stop layer, and an etching selectivity of the second etching stop layer is higher than the etching selectivity of the first etching stop layer, and the active layer of the high-mesa section is optically coupled to the core layer of the optical waveguide section.
22 . The optical integrated device according to claim 18 , wherein the thickness of the etching stop layer is 0.1 μm or less.
23 . The optical integrated device according to claim 19 , wherein the thickness of the etching stop layer is 0.1 μm or less.
24 . The optical integrated device according to claim 21 , wherein the first etching stop layer is made of AlInAs, the second etching stop layer is made of AlInAs with a larger Al composition ratio than the first etching stop layer, and the second contact layer is made of InP.
25 . The optical integrated device according to claim 16 , wherein the compound semiconductor substrate is made of InP, and the active layer includes a multiple quantum well structure made of InGaAsP having a composition ratio corresponding to a photoluminescence peak wavelength of 1.2 μm or more, or AlGaInAs having a composition ratio corresponding to the photoluminescence peak wavelength of 1.2 μm or more, and the contact layer is made of InP.
26 . The optical integrated device according to claim 16 , wherein either one of the tip of the high-mesa section on the side of the optical waveguide section and the tip of the optical waveguide section on the side of the high-mesa section has a spot size converter structure.
27 . The optical integrated device according to claim 16 , wherein a first electrode formed on the top surface of the high-mesa section and a second electrode formed on the bottom of the first recess are mechanically and electrically bonded through a conductive bonding member.
28 . The optical integrated device according to claim 16 , wherein a distance between the active layer of the high-mesa section and the core layer of the optical waveguide section is 6 μm or less.
29 . A method for manufacturing an optical integrated device that integrates an optical functional element and an optical circuit element having a first recess and second recesses, the method for manufacturing an optical integrated device comprising: a step of manufacturing the optical functional element, the step of manufacturing the optical functional element including: a step of successively epitaxially growing an active layer and a contact layer above a compound semiconductor substrate; a step of forming, by etching, a protruding-shaped high-mesa section that includes a part of the compound semiconductor substrate, the high-mesa section including at least the active layer and the contact layer from the side of the compound semiconductor substrate; and a step of forming terrace portions by wet etching using a mixed solution of tartaric acid and hydrogen peroxide as an etchant, each terrace portion being exposed the outermost surface of the compound semiconductor substrate; a step of manufacturing the optical circuit element, a step of manufacturing the optical circuit element including: a step of forming a first recess and second recesses separated from the first recess in a semiconductor substrate with a lower cladding layer, a core layer, and an upper cladding layer; and a step of exposing the uppermost surface of the core layer by selectively removing the upper cladding layer at the top of the protrusion portions formed between the first recess and the second recesses; and a step of flip-chip mounting the optical functional element and the optical circuit element while making each terrace portion of the optical functional element and the top of each protrusion portion of the optical circuit element contact each other.
30 . A method for manufacturing an optical integrated device that integrates an optical functional element and an optical circuit element having a first recess and second recesses, the method for manufacturing an optical integrated device comprising: a step of manufacturing the optical functional element, the step of manufacturing the optical functional element including: a step of successively epitaxially growing an active layer, an etching stop layer, and a contact layer above a compound semiconductor substrate; a step of forming, by etching, a protruding-shaped high-mesa section that includes a part of the compound semiconductor substrate, the high-mesa section including at least the active layer, the etching stop layer, and the contact layer from the side of the compound semiconductor substrate; and a step of forming terrace portions by dry etching using methane gas as an etching gas, each terrace portion being exposed the outermost surface of the etching stop layer; a step of manufacturing the optical circuit element, a step of manufacturing the optical circuit element including: a step of forming a first recess and second recesses separated from the first recess in a semiconductor substrate with a lower cladding layer, a core layer, and an upper cladding layer; and a step of exposing the uppermost surface of the core layer by selectively removing the upper cladding layer at the top of the protrusion portions formed between the first recess and the second recesses; and a step of flip-chip mounting the optical functional element and the optical circuit element while making each terrace portion of the optical functional element and the top of each protrusion portion of the optical circuit element contact each other.

Description

TECHNICAL FIELD This disclosure relates to an optical integrated device and a method for manufacturing an optical integrated device. BACKGROUND ART In recent years, silicon photonics technology, which integrates optical functional elements on silicon (Si) substrates, has attracted attention in the field of optical devices such as communications. Silicon photonics technology allows the mature silicon substrate processing technology developed in the manufacture of electronic circuits to be diverted to manufacturing. In addition, since silicon has a refractive index higher than that of glass, which is generally used as an optical element, it is possible to confine light in a small area, and thus, it is expected to achieve large-scale optical integrated devices that are inexpensive and miniaturized. In optical semiconductor devices made of various materials such as indium phosphide (InP), gallium arsenide (GaAs), gallium nitride (GaN), lithium niobate (LiNbO3), and compound semiconductors including these materials, the optical waveguide is the most basic component that can locally confine light to a specific region by increasing the refractive index higher than that of the surrounding area, and propagate light to a desired region by forming such specific region in a linear shape, that is, a striped shape. In optical integrated devices made of semiconductors including silicon optical circuit elements, a large-scale optical integrated device with various functions can be achieved by interconnecting functional blocks such as semiconductor lasers, optical receivers, modulators, and optical filters with the above-mentioned optical waveguides. Unfortunately, there is a significant problem with using silicon optical circuit elements as optical semiconductor devices. That is, since silicon is an indirect transition semiconductor, the interaction between electrons and light is limited, and thus, it is difficult to achieve active functions such as semiconductor lasers and optical amplifiers by silicon alone. Consequently, direct transition semiconductors, such as InP and other compound semiconductors, are essential as the constituent materials for achieving active functions. Accordingly, in silicon photonics technology, integration technology to achieve passive functions and active functions using different materials is widely studied. Monolithic integration of silicon and compound semiconductor materials on the same substrate using epitaxial crystal growth is difficult due to the difference of lattice constants between silicon and compound semiconductor materials. Consequently, currently, so-called hybrid integrated structures in which active functional elements (Hereinafter referred to as optical functional element) made of compound semiconductor materials are mounted and integrated on silicon optical circuit elements are widely applied. In the following description, silicon optical circuit elements and optical functional elements may be collectively referred to simply as optical elements. Various types of hybrid integrated structures between silicon optical circuit elements and optical functional elements have been proposed. As an example of the hybrid integrated structures, for example, there is a butt coupling method in which the silicon optical circuit elements and optical functional elements, each of which has the above-described optical waveguides extending to the optical end faces, are arranged in close proximity so that the cross sections of the respective optical waveguides on the end faces of the respective optical elements face each other, so that light propagating in one optical element is introduced into the other optical element through a free space. As another example of the hybrid integrated structures, there is a grating coupler method in which light propagating in the optical waveguides formed on the silicon optical circuit elements or optical functional elements is reflected in the vertical direction of the optical element by a grating, and then, the light is introduced into the optical waveguide of the other optical element through a grating formed on the other optical element arranged opposite to the optical element. Furthermore, there is a bonding method in which the silicon optical circuit elements and optical functional elements are physically bonded in such a way that the optical waveguides of both run very close to each other, and light propagating in one optical element is introduced into the other optical element by evanescent waves. Unfortunately, in the butt coupling method, the cross-sectional size of a typical optical waveguide in the silicon optical circuit element and the optical functional element is small, from sub-micron to several microns at most. Consequently, in the case where the mounting positions of the silicon optical circuit element and the optical functional element are slightly misaligned, the light emitted from one optical element cannot be successfully introduced into th