Optical modulator-integrated light source and method for manufacturing same

Abstract

Provided are: an optical modulator-integrated light source in which effects on the characteristics of stress variation in insulating films around a high mesa waveguide can be reduced by removing the insulating films, and which has a structure in which the transmission characteristics of a high frequency signal are not impaired; and a method for manufacturing the same. Specifically, the optical modulator-integrated light source includes: a plurality of optical waveguides formed on a semiconductor substrate; an optical modulator formed in at least one optical waveguide among the plurality of optical waveguides; insulating films formed along both side surfaces of the at least one optical waveguide in which the optical modulator is formed; and high-frequency signal electrode wiring having a contact electrode, which is formed on the at least one optical waveguide in which the optical modulator is formed, and pad electrodes, which are formed on the insulating films and connected to the contact electrode. The at least one optical waveguide in which the optical modulator is formed has a high mesa waveguide shape, and some or all of the side surfaces of the insulating films are spaced apart from the side surface of the at least one optical waveguide having the high mesa waveguide shape in which the optical modulator is formed.

Description

Optical modulator integrated light source and its manufacturing method

[0001] The present disclosure relates to an optical modulator integrated light source and a manufacturing method thereof, and more particularly to an optical modulator integrated light source and a manufacturing method thereof that can prevent deterioration of element characteristics caused by stress fluctuations in an insulating film for high-frequency signal electrode wiring.

[0002] The spread of broadband services via the Internet has led to a rapid increase in the volume of communication traffic over networks. This has led to a surge in the trend toward larger network capacities. Furthermore, technologies for increasing system capacity are becoming increasingly important not only in traditional telecom networks but also in storage networks and datacom networks such as Ethernet. The throughput of these high-speed interface devices is limited not only by the speed per channel but also by the packaging density, which is determined by the module size and power consumption. This has made module miniaturization a key challenge.

[0003] The key technology for achieving miniaturization of optical modules is the integration of optical elements. For example, as in Non-Patent Document 1, a method for realizing a compact optical transceiver module has already been put into practical use, in which a distributed feedback (DFB) laser light source on the transmitting side is used, in which an optical modulator that combines an electro-absorption modulator (EAM) and a Mach-Zehnder interferometer is monolithically integrated. This configuration has advantages such as low-voltage operation and a high extinction ratio.

[0004] The optical modulator in the optical modulator integrated light source is an interferometer type, as mentioned above, and the ridge optical waveguide that constitutes the optical modulator is embedded in benzocyclobutene (BCB). BCB is an organic material with a low dielectric constant that can be deposited on a wafer using a simple coating process, and is therefore widely used as an insulating film for the high-frequency signal electrode wiring of optical modulators.

[0005] However, BCB is subject to stress fluctuations after the formation of the insulating film, which causes a change in the refractive index (Δn) of the waveguide. This change in refractive index (Δn) causes fluctuations in the electrical bias of the optical modulator and a shift in the absolute wavelength peak of the wavelength filter, affecting the interference characteristics within the waveguide (Non-Patent Document 2).

[0006] The optical modulator integrated light source described in Patent Document 1 has a structure in which a high mesa waveguide is buried in a semi-insulating semiconductor. The high mesa waveguide has the advantage of stronger optical confinement than a ridge optical waveguide.

[0007] International Publication No. WO2020 / 255183

[0008] Y. Ueda et al., “Low Driving Voltage Operation of MZI-Type EA Modulator Integrated With DFB Laser Using Optical Absorption and Interferometric Extinction,” IEEE J. Sel. Top. Quantum Electron., Vol. 21, No. 6, 2015.Y. Ueda et al., “Theoretical and experimental investigation of external-stress effect on quantum-well-based semiconductor interferometer performance,” Appl. Phys. Express, Vol. 14, No. 9, 091005, 2021.

[0009] An optical modulator integrated light source according to an embodiment of the present disclosure includes a plurality of optical waveguides formed on a semiconductor substrate, an optical modulator formed in at least one of the plurality of optical waveguides, an insulating film formed along both side surfaces of the at least one optical waveguide in which the optical modulator is formed, and high-frequency signal electrode wiring having a contact electrode formed on the at least one optical waveguide in which the optical modulator is formed, and a pad electrode formed on the insulating film and connected to the contact electrode, wherein the at least one optical waveguide in which the optical modulator is formed has a high-mesa waveguide shape, and some or all of the side surfaces of the insulating film are spaced apart from the side surfaces of the at least one optical waveguide in which the optical modulator is formed and having a high-mesa waveguide shape.

[0010] A method for manufacturing an optical modulator integrated light source in one embodiment of the present disclosure includes the steps of: forming a plurality of optical waveguides on a semiconductor substrate, some of the plurality of optical waveguides having a high-mesa waveguide shape; depositing an insulating film on a portion of a side surface of at least one of the plurality of optical waveguides; forming high-frequency signal electrode wiring, the steps including forming a contact electrode on the optical waveguide having the high-mesa waveguide shape, forming a pad electrode on the insulating film, and forming an extraction electrode between the contact electrode and the pad electrode; and removing a portion or all of the insulating film, wherein the insulating film from which a portion or all of the insulating film has been removed is separated from the optical waveguide having the high-mesa waveguide shape.

[0011] According to the present disclosure, by removing the insulating film around the high mesa waveguide, it is possible to reduce the influence of stress fluctuations on the characteristics of the insulating film, and to create a structure in which the transmission characteristics of high-frequency signals are not impaired. Furthermore, in a configuration in which the insulating film directly below the extraction electrode is removed to form an air bridge, the gas or vacuum directly below the extraction electrode has an even lower dielectric constant than the insulating film, which is advantageous for high-frequency signal wiring.

[0012] 1A is a schematic diagram showing an EA-MZ optical modulator integrated light source. FIG. 1B is a perspective view showing an optical modulator integrated light source according to an embodiment of the present disclosure. In (a), the BCB insulating film has been removed directly below the high-frequency signal electrode wiring, and in (b), the BCB insulating film remains. FIG. 1C is a diagram showing a first step according to an embodiment of the present disclosure. In (a), a top view of a device in which an MQW active layer is stacked on a semiconductor substrate, and in (b), a cross-sectional view. FIG. 1D is a diagram showing a second step according to an embodiment of the present disclosure. In (a), a top view of a device showing a region where an EA optical modulator layer is formed, and in (b), a cross-sectional view. FIG. 1E is a diagram showing a third step according to an embodiment of the present disclosure. In (a), a top view of a device showing a region where a passive optical waveguide layer is further formed, and in (b), a cross-sectional view. FIG. 1F is a diagram showing a fourth step according to an embodiment of the present disclosure. In (a), a top view of a device including an optical waveguide after etching, and in (b), a cross-sectional view. FIG. 1G is a diagram showing a fifth step according to an embodiment of the present disclosure. 1A is a top view of a device including a high mesa waveguide, (b) is a cross-sectional view of a region where an EA optical modulator layer is formed, and (c) is a cross-sectional view of a region where a passive optical waveguide layer is formed.

[0034] FIG. 1C is a diagram showing a sixth step in an embodiment of the present disclosure. (a) is a top view of a device where a first BCB insulating layer is formed, and (b) is a cross-sectional view.

[0035] FIG. 1D is a diagram showing a seventh step in an embodiment of the present disclosure. (a) is a top view of a device where a portion of the first BCB insulating layer has been removed, and (b) is a cross-sectional view.

[0036] FIG. 1E is a diagram showing an eighth step in an embodiment of the present disclosure. (a) is an enlarged top view of a device where a second BCB insulating film has been re-formed in the removed portion of the first BCB insulating layer, and (b) is a cross-sectional view.

[0037] FIG. 1F is a diagram showing a ninth step in an embodiment of the present disclosure. (a) is an enlarged top view of a device where high-frequency signal electrode wiring has been formed on a waveguide, and (b) is a cross-sectional view.

[0038] FIG. 1G is a diagram showing a tenth step in an embodiment of the present disclosure. 1A is an enlarged top view of a device in which one of the second BCB insulating layers has been removed, and FIG. 1B is a cross-sectional view. 11A is a diagram showing the eleventh step in an embodiment of the present disclosure. 11B is an enlarged top view of an optical modulator integrated light source in which an air bridge is formed, and FIG. 1B is a cross-sectional view. 12B is a diagram showing the structure of a device in another embodiment of the present disclosure.FIG. 1(a) is an enlarged top view of a device in which high-frequency signal electrode wiring is formed on a waveguide, and FIG. 1(b) is a cross-sectional view. FIG. 1(a) is an enlarged top view of an optical modulator integrated light source in another embodiment of the present disclosure, and FIG. 1(b) is a cross-sectional view. FIG. 1(a) is a flowchart showing a method for manufacturing an optical modulator integrated light source in an embodiment of the present disclosure. FIG. 1(b) is a flowchart showing a method for manufacturing an optical modulator integrated light source in another embodiment of the present disclosure.

[0013] Hereinafter, embodiments of an optical modulator integrated light source according to the present disclosure will be described with reference to the drawings. Note that the drawings are schematic and are intended to conceptually explain functions or structures. Furthermore, the present invention is not limited to the embodiments shown below. In the drawings, the same reference numerals are used to refer to the same or similar components whenever possible.

[0014] To facilitate understanding of the embodiments of the present disclosure, an optical waveguide structure having a Mach-Zehnder interferometer electroabsorption modulator (hereinafter referred to as EA-MZ) using an asymmetric coupler used in the present disclosure will be described.

[0015] As shown in FIG. 1, the EA-MZ waveguide structure consists of two directional couplers (DC) and two arm waveguides. One waveguide includes an EAM, and the other waveguide includes an MQW phase shifter identical to the EAM arm. The DCs have an asymmetric configuration, and the coupling ratio is not 50%. The waveguides in the coupler sections (DC1 and DC2 in FIG. 1) are formed closer to each other (compared to other sections) to allow for mode coupling. In general, EA-MZs can be fabricated with lengths of several hundred micrometers, making them smaller than existing Mach-Zehnder modulators using the electro-optic effect. The waveguide structures described in the following embodiments should be understood based on the above-described waveguide configuration.

[0016] FIG. 2 is a perspective view showing the overall structure of an optical modulator integrated light source 300 according to an embodiment of the present disclosure. FIG. 2( a) is a diagram showing an optical modulator integrated light source 300A according to a first embodiment, characterized in that there is an open space below the high-frequency signal electrode wiring, particularly the extraction electrode 1103. FIG. 2( b) is a diagram showing an optical modulator integrated light source 300B according to a second embodiment, characterized in that there is a BCB insulating film below the extraction electrode 1103. As described above, the optical modulator integrated light source 300A and 300B according to the present disclosure are configured with two DCs and two optical waveguides. An EAM is formed in one optical waveguide (e.g., 601B), and a phase shifter is formed in the other optical waveguide (e.g., 601A). However, this disclosure does not mention the structure of the phase shifter or the light source portion, and mainly describes the structure around the EAM.

[0017] 2A includes a plurality of optical waveguides 601A and 601B formed on a semiconductor substrate 301. The optical waveguides 601A and 601B extend along the light-guiding direction (the X direction in FIG. 2 ) and have a structure in which the semiconductor substrate 301, which forms an undercladding layer, a core layer, and an overcladding layer 303 are stacked in the height direction (the Z direction in FIG. 2 ). The core layer also includes a plurality of portions having different functions along the X direction, namely, an active layer 302, an EA optical modulator layer 304, or passive optical waveguide layers 305 and 306.

[0018] The waveguides 601A and 601B having the active layer 302 are the light source portions and are formed in the shape of a ridge waveguide.

[0019] The optical waveguides 601A and 601B having the passive optical waveguide layers 305 and 306 are formed in a high mesa waveguide shape. Therefore, there is a step between the optical waveguides 601A and 601B having the active layer 302. However, in the DC portion, the optical waveguides 601A and 601B are formed relatively closer to each other than the optical waveguides 601A and 601B in other portions for the purpose of optical mode coupling, and a core layer is left in the region between the optical waveguides 601A and 601B. In one embodiment, the width (Y direction) of each optical waveguide 601A and 601B is desirably 1 μm to 3 μm, taking single-mode conditions into consideration.

[0020] The optical waveguides 601A and 601B having the EA optical modulator layer 304 are portions where the EA optical modulator layer and the phase shifter are formed, and are formed in a high mesa waveguide shape. One of the optical waveguides, optical waveguide 601A, is provided with a phase shifter, and the other, optical waveguide 601B, is provided with an EA optical modulator. In this disclosure, the phase shifter will be omitted and the explanation will focus on the EA optical modulator.

[0021] The optical waveguide 601B having the EA optical modulator layer 304 is sandwiched between first BCB insulating films 802A and 802B and formed on the semiconductor substrate 301. In order to reduce the influence of stress fluctuations in the BCB insulating film on the optical modulator characteristics, empty spaces (grooves) are formed by an etching process between the side surfaces of the optical waveguides 601A and 601B and the first BCB insulating films 802A and 802B.

[0022] Furthermore, a contact electrode 1101 is formed in the optical waveguide 601B portion having the EA optical modulator layer 304, contacting the optical waveguide 601B from which the first and second dielectric films 801 and 901 (described later) have been removed. Furthermore, a pad electrode 1102 is formed on the upper surface of either the first BCB insulating film 802A or 802B, and an extraction electrode 1103 is formed between the contact electrode 1101 and the pad electrode 1102.

[0023] Furthermore, a back electrode 1303 is formed on the surface of the semiconductor substrate 301 on which no optical waveguide is formed, that is, on the back surface.

[0024] A first dielectric film 801 is formed on the entire upper surface of the semiconductor substrate 301, and a second dielectric film 901 is further formed in the optical waveguide 601B portion having the EA optical modulator layer 304. The second dielectric film 901 is not shown in FIG. 2, but will become clear from the specification and drawings described below.

[0025] 3 to 13 and 16, a method for manufacturing the optical modulator integrated light source 300A of the present disclosure will be described in detail below. In the following description, the optical modulator integrated light source 300A in the middle of the manufacturing process will be referred to as a "device."

[0026] 3A and 3B show the first step, in which Fig. 3A is a top view of the device and Fig. 3B is a cross-sectional view in the X direction. The optical waveguide direction in this structure is the X direction.

[0027] In the first step 1603, an active layer 302 constituting a 1.3 μm band laser is crystal-grown on a semiconductor substrate (e.g., n-InP) 301. In some embodiments, the active layer 302 has a multi-quantum well (MQW) structure. While the following description will refer to an MQW active layer 302, this is not intended to be limiting. A cap layer 303-A of i-InP is deposited on the active layer 302 to a thickness of several hundred nanometers. The cap layer 303-A is provided to protect the active layer 302 during the process and will be removed in a later step.

[0028] FIG. 4 shows the second step 1605, in which the layer structure of part of the MQW active layer 302 is replaced by a butt-joint process to form the EA optical modulator layer 304.

[0029] 5 shows the third step 1607, in which a butt-joint process is used to replace part of the layer structure of the MQW active layer 302, further fabricating a first passive optical waveguide layer 305 and a second passive optical waveguide layer 306. In one embodiment, the passive optical waveguide layers 305 and 306 are made of InGaAsP. The passive optical waveguide layers 305 and 306 are also structured to have a photoluminescence (PL) peak wavelength of 1.15 μm, for example. Furthermore, the i-InP cap layer 303-A is removed by etching, and then the overcladding layer (p-InP layer) 303 is regrown.

[0030] 6 shows the fourth step 1609, in which dry etching and / or wet etching using plasma is performed on the region of the MQW active layer 302 formed on the semiconductor substrate 301. As a result, as shown in FIG. 6, two optical waveguides (a first optical waveguide 601A and a second optical waveguide 601B) each having a ridge waveguide shape are formed on the semiconductor substrate 301 along the light guiding direction (X direction).

[0031] FIG. 7 shows the fifth step 1611, in which, after the above-mentioned fourth step, dry etching is further performed to form high mesa waveguides in the EA optical modulator layer 304 and passive optical waveguide layers 305 and 306 regions.

[0032] However, for mode coupling, the two optical waveguides 601A, 601B in the first passive optical waveguide layer 305 (not shown) and the second passive optical waveguide layer 306 (shown in FIG. 7(c)) are formed closer to each other than the optical waveguides formed in the MQW active layer 302 and EA optical modulator layer 304. Furthermore, a core layer is left in the region between the optical waveguides 601A, 601B. In one embodiment, the width (Y direction) of each of the optical waveguides 601A, 601B is desirably 1 μm to 3 μm, taking single-mode conditions into consideration.

[0033] 8A and 8B are diagrams showing the sixth step 1613 and the seventh step 1615, in which Fig. 8A is a top view of the device and Fig. 8B is a cross-sectional view of the EA optical modulator layer 304. In order to specifically illustrate the manufacturing process of the optical modulator integrated light source 300A, the cross-section shown in Fig. 8B shows only the second optical waveguide 601B.

[0034] In a sixth step 1613, a first dielectric passivation film 801 is deposited over the entire top surface of the device, followed by a seventh step 1615 in which a first BCB insulating film 802A, 802B is deposited around the second optical waveguide 601B in the EA optical modulator layer 304. Various insulating materials may be used according to some embodiments.

[0035] On the other hand, the first BCB insulating films 802A and 802B are not formed in the regions of the MQW active layer 302 and the passive optical waveguide layers 305 and 306. That is, the first BCB insulating films 802A and 802B are present only in the region of the EA optical modulator layer 304. In some embodiments, SiON or SiN is suitable for the passivation film 801, which can be easily formed by plasma-enhanced chemical vapor deposition (CVD).

[0036] 9A and 9B are diagrams showing the eighth step 1617 and the ninth step 1619, in which Fig. 9A is a top view of the device and Fig. 9B is a cross-sectional view of the EA optical modulator layer 304 region. As shown in Fig. 9B, parts of the first BCB insulating films 802A and 802B in contact with the side surfaces of the second optical waveguide 601B in the EA optical modulator layer 304 region are removed by dry etching using a resist mask.

[0037] Next, in a ninth step 1619, a second dielectric film 901 is formed over the entire upper surface of the device by sputtering or a spin-on-glass (SOG) method. As an example, the second dielectric film 901 is SiO2.

[0038] 10A and 10B are diagrams illustrating the tenth step 1621. FIG. 10A is an enlarged top view of the vicinity of the second optical waveguide 601B (see FIG. 9A) in the EA optical modulator layer 304 region, and FIG. 10B is a cross-sectional view thereof. In the tenth step, after the second dielectric film 901 is formed, second BCB insulating films 1001A and 1001B are formed. The second BCB insulating films 1001A and 1001B are provided for the purpose of providing a flat surface for forming the high-frequency signal electrode wiring (i.e., electrodes) described in the next step, but are ultimately removed.

[0039] 11 is a diagram showing the eleventh step 1623, in which the second dielectric film 901 and the passivation film 801 formed on the second optical waveguide 601B in the EA optical modulator layer 304 region are removed to form a window, and then a contact electrode 1101 is formed by evaporation and lift-off. The contact electrode 1101 is formed only in the EA optical modulator layer 304 region, and is electrically isolated from the MQW active layer 302 and the EA optical modulator layer 304.

[0040] Furthermore, when the contact electrode 1101 is vapor-deposited, a pad electrode 1102 is formed on either side of the contact electrode 1101 (on the upper or lower side of the contact electrode 1101 in the Y direction, as shown in FIG. 11(a)).

[0041] Furthermore, in an eleventh step 1623, an extraction electrode 1103 is formed to connect between the contact electrode 1101 and the pad electrode 1102. Therefore, the contact electrode 1101, the pad electrode 1102, and the extraction electrode 1103 constitute a high-frequency signal electrode wiring.

[0042] The width and length of the extraction electrode 1103 must be as small as possible without affecting the high-frequency transmission characteristics in order to reduce the area of ​​the portion 1301 to be processed to form an air bridge configuration, which will be described in the next step. This is because if the area of ​​the portion 1301 to be processed to form an air bridge configuration is large, the extraction electrode 1103 may be crushed by its own weight or external impact when the air bridge configuration is formed. In one embodiment, the width and length of the extraction electrode 1103 are both in the range of 5 to 20 μm. Note that, in FIG. 11, dotted lines are used to distinguish the regions between the contact electrode 1101 and the extraction electrode 1103, and between the pad electrode 1102 and the extraction electrode 1103, but this does not mean that the electrodes are electrically isolated.

[0043] FIG. 12 shows the twelfth step 1625, in which the second BCB insulating films 1001A and 1001B except for those directly below the extraction electrode 1103 are removed by dry etching.

[0044] 13 shows the thirteenth step 1627, in which the second BCB insulating film 1001B is removed by wet etching in a portion 1301 directly below the extraction electrode 1103. This step results in the extraction electrode 1103 forming an air bridge.

[0045] In the final fourteenth step 1629, the rear surface of the semiconductor substrate 301 is polished, and then the rear electrode 1303 (FIG. 2A) is formed. Then, the substrate is cleaved into individual chips to complete the optical modulator integrated light source 300A.

[0046] In the present disclosure, removing a portion of the BCB insulating films 802A, 802B around the second optical waveguide 601B in the EA optical modulator layer 304 region makes it possible to reduce the influence of stress fluctuations in the BCB insulating films 802A, 802B. Furthermore, since the air, inert gas such as nitrogen, or vacuum directly below the electrodes in an air bridge generally has an even lower dielectric constant than the BCB insulating film, an optical modulator integrated light source 300A can be provided that is more advantageous for high-frequency signal wiring.

[0047] 2B is a modification of the optical modulator integrated light source 300A shown in the first embodiment, and is almost entirely the same as the optical modulator integrated light source 300A except for a portion of the structure of the optical modulator integrated light source 300A. Therefore, the following description will focus on the portion of the structure that is different.

[0048] The optical modulator integrated light source 300B in the second embodiment further includes a first BCB insulating film 802B directly below the extraction electrode 1103. Compared to the optical modulator integrated light source 300A, which has a space (groove) directly below the extraction electrode 1103, the extraction electrode 1103 can be prevented from being crushed by its own weight or external impact, and steps 8 to 10 for forming the extraction electrode 1103 can be omitted. In other words, in the second embodiment, the steps of partially removing the first dielectric film, forming the second dielectric film 901 and the second BCB insulating films 1001A and 1001B, opening windows for removing these films, and removing the second dielectric film 901, which were performed to form the space (groove) directly below the extraction electrode 1103 in the first embodiment, can be omitted. This process will be described in detail below.

[0049] Hereinafter, a method for manufacturing an optical modulator integrated light source 300B having a partially different structure will be described based on the above-described first embodiment, with further reference to Figures 14, 15, and 17. Since the first step 1603 to the seventh step 1615 in the first embodiment are the same, in this embodiment, the seventh step and subsequent steps will be mainly described.

[0050] After the deposition of the first BCB insulating films 802A and 802B in the seventh step 1615, in the eighth step 1723, a window is formed to remove the first dielectric film 801 deposited on the second optical waveguide 601B in the EA optical modulator layer 304 region, and then a contact electrode 1101 is formed by evaporation and lift-off, as shown in Fig. 14. The contact electrode 1101 is formed only in the EA optical modulator layer 304 region, and is electrically isolated from the MQW active layer 302 and the EA optical modulator layer 304.

[0051] When the contact electrode 1101 is vapor-deposited, a pad electrode 1102 is formed on either side of the contact electrode 1101 (on the upper or lower side of the contact electrode 1101 in the Y direction, as shown in FIG. 14A).

[0052] Furthermore, in an eighth step 1723, an extraction electrode 1103 is formed to connect the contact electrode 1101 and the pad electrode 1102. The contact electrode 1101, pad electrode 1102, and extraction electrode 1103 constitute a high-frequency signal electrode wiring. Unlike the first embodiment, in this embodiment, the portion 1301 directly below the extraction electrode 1103 is not processed (because the extraction electrode 1103 does not form an air bridge), so the restrictions on the width and length of the extraction electrode 1103 are not as severe as in the first embodiment. Note that, in FIG. 14, dotted lines are used to distinguish the regions between the contact electrode 1101 and the extraction electrode 1103, and between the pad electrode 1102 and the extraction electrode 1103, but this does not mean that the electrodes are electrically isolated.

[0053] 15, in a ninth step 1725, portions of the first BCB insulating films 802A and 802B that contact the side surfaces of the second optical waveguide 601B in the EA optical modulator layer 304 region are removed by dry etching using a resist mask. However, the portion of the first BCB insulating film 802B that exists directly below the extraction electrode 1103 is not removed, and supports the extraction electrode 1103. Therefore, there is no portion 1301 in which gas or vacuum is the insulator, as in the air bridge configuration of the first embodiment.

[0054] Finally, in a ninth step 1629, the rear surface of the wafer is polished, and then the rear electrode 1303 (FIG. 2B) is formed. Then, the wafer is cleaved into individual chips to complete the optical modulator integrated light source 300B.

[0055] In the air bridge configuration of the second embodiment, the structure lacks the portion 1301 that uses gas or vacuum as an insulator, so there is no risk of the portion 1301 collapsing and damaging the extraction electrode 1103, as occurs in the air bridge configuration. Although a portion of the BCB insulating film 802B equivalent to the area of ​​the extraction electrode 1103 remains on the side surface of the second optical waveguide 601B, the length of the remaining BCB insulating film 802B is small compared to the overall length of the interferometer, and therefore the effect on the interference characteristics is not significant.

[0056] Additional Considerations The foregoing description of embodiments of the present invention has been presented for purposes of illustration and is not intended to be exhaustive or to be limited to the precise form disclosed. Those skilled in the art will recognize that many modifications and variations are possible in light of the above disclosure.

[0057] Finally, the language used herein has been selected primarily for readability and instructional purposes, and may not have been selected to delineate or limit the subject matter of the invention. Accordingly, it is intended that the scope of the invention be limited not by this detailed description, but rather by the appended claims. Accordingly, the disclosure of embodiments of the invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the claims.

[0058] The present disclosure provides a structure in which the influence of stress fluctuations on the characteristics of the BCB can be reduced by removing the BCB around the high mesa waveguide, and the transmission characteristics of high-frequency signals are not impaired. Furthermore, in a configuration in which the insulating film directly below the extraction electrode is removed to form an air bridge, the gas or vacuum directly below the extraction electrode has an even lower dielectric constant than the BCB, which is advantageous for high-frequency signal wiring.

[0059] 300A, 300B Optical modulator integrated light source 301 Semiconductor substrate 302 Active layer 303 Overcladding layer 303-A Cap layer 304 EA optical modulator layer 305 First passive optical waveguide layer 306 Second passive optical waveguide layer 601A First optical waveguide 601B Second optical waveguide 801 Passivation film (first dielectric film) 802A, 802B First BCB insulating film 901 Second dielectric film 1001A, 1001B Second BCB insulating film 1101 Contact electrode 1102 Pad electrode 1103 Extraction electrode 1301 Portion directly below the extraction electrode

Claims

1. An optical modulator integrated light source comprising: a plurality of optical waveguides formed on a semiconductor substrate; an optical modulator formed in at least one of the plurality of optical waveguides; an insulating film formed along both side surfaces of the at least one optical waveguide in which the optical modulator is formed; and radio frequency signal electrode wiring having: a contact electrode formed on the at least one optical waveguide in which the optical modulator is formed; and a pad electrode formed on the insulating film and connected to the contact electrode, wherein the at least one optical waveguide in which the optical modulator is formed has a high mesa waveguide shape, and a part or all of the side surfaces of the insulating film are spaced apart from the side surfaces of the at least one optical waveguide having the high mesa waveguide shape in which the optical modulator is formed.

2. The optical modulator integrated light source according to claim 1, wherein the high-frequency signal electrode wiring further has an extraction electrode connecting the contact electrode and the pad electrode, and the part of the side of the insulating film having the high-mesa waveguide shape in which the optical modulator is formed and spaced apart from the side of the at least one optical waveguide is a portion excluding the insulating film directly below the extraction electrode.

3. The optical modulator integrated light source according to claim 1, wherein the high frequency signal electrode wiring further comprises an extraction electrode, the width and length of which are both in the range of 5 to 20 μm.

4. A method for manufacturing an optical modulator integrated light source, comprising: a step of forming a plurality of optical waveguides on a semiconductor substrate, some of the plurality of optical waveguides having a high mesa waveguide shape; a step of forming an insulating film on a portion of a side surface of at least one of the plurality of optical waveguides; a step of forming high-frequency signal electrode wiring, the step of forming a contact electrode on the optical waveguide having the high mesa waveguide shape, a step of forming a pad electrode on the insulating film, and a step of forming an extraction electrode between the contact electrode and the pad electrode; and a step of removing a part or all of the insulating film, the insulating film from which the part or all has been removed being separated from the optical waveguide having the high mesa waveguide shape.

5. The manufacturing method according to claim 4, wherein the portion removed from the insulating film does not include the insulating film directly below the extraction electrode.

Images