JP2018018015A - Method for fabricating mach-zehnder modulator and mach-zehnder modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for fabricating a Mach-Zehnder modulator, for forming a structure capable of avoiding reduction in the high-frequency characteristics of a Mach-Zehnder modulator.SOLUTION: A Mach-Zehnder modulator includes: a first insulation film having an opening located above an upper face of a waveguide mesa; a first resin body disposed on a side face of the first insulation film so as to bury the waveguide mesa; a second resin body forming contact with the first resin body and the first insulation film and having an opening located above the upper face of the waveguide mesa; an ohmic electrode disposed on the second resin body and connected to the upper face of the waveguide mesa via the opening in the first insulation film and the opening in the second resin body; a second insulation film disposed on the second resin body and having an opening located on the ohmic electrode on the upper face of the waveguide mesa; and a metal electrode forming contact with the ohmic electrode via the opening in the second insulation film and extending on the second resin body. The first resin body has a recess along the side face of the waveguide mesa; and the second resin body fills the recess.SELECTED DRAWING: Figure 17

Description

  The present invention relates to a method of manufacturing a Mach-Zehnder modulator and a Mach-Zehnder modulator.

  Patent Document 1 discloses a Mach-Zehnder modulator.

JP 2009-206177 A

  According to the inventor's study, the characteristics of the Mach-Zehnder modulator, specifically the high-frequency characteristics, vary from the product produced on one wafer in the manufacturing process. The semiconductor mesa for the arm waveguide in these Mach-Zehnder modulators is embedded with resin. In order to avoid that the surface of the semiconductor mesa directly touches the resin, an inorganic insulating film such as a silicon oxide film is provided between the semiconductor mesa and the resin. The inorganic insulating film covers the upper surface and side surfaces of the semiconductor mesa. In order to form such a buried structure, the following steps are performed. The inorganic insulating film on the upper surface of the semiconductor mesa is exposed by etching of the resin, and the inorganic insulating film on the upper surface of the semiconductor mesa is removed. For electrical connection onto the semiconductor mesa, a metal body is formed on the resin body in which the semiconductor mesa is embedded and on the upper surface of the semiconductor mesa.

  According to the inventor's observation, in the Mach-Zehnder modulator that does not satisfy the desired high-frequency characteristics, the resin body disappears along the inorganic insulating film on the side surface of the semiconductor mesa to form, for example, a wedge-shaped depression. . The metal body formed on the resin body and the semiconductor mesa extends along the inorganic insulating film on the side surface of the semiconductor mesa, and extends along the surface of the recess to fill part or all of the recess.

  According to further studies, the recess is formed by unintentional etching of the resin when the inorganic insulating film is partially removed to expose the upper surface of the semiconductor mesa. The amount of resin depression in a product produced on one wafer in the manufacturing process varies in the wafer plane. The amount of depression depends on the etching time of the inorganic insulating film, and can be reduced by shortening the etching time. The amount of the inorganic insulating film to be processed also varies within the wafer surface. As a result, the shortening of the etching time increases the possibility of remaining film anywhere in the wafer surface, and the occurrence of remaining inorganic insulating film leads to poor electrical connection.

  According to the inventor's study, the occurrence of a dent due to the disappearance of the resin increases the capacitance associated with the electrode, which leads to a decrease in the high frequency band in the Mach-Zehnder modulator.

  One aspect of the present invention has been made in view of the above circumstances, and provides a method of manufacturing a Mach-Zehnder modulator that forms a structure that can avoid a decrease in high-frequency characteristics of the Mach-Zehnder modulator. The purpose is to do. Another object of the present invention is to provide a Mach-Zehnder modulator having a structure capable of avoiding a decrease in high-frequency characteristics of the Mach-Zehnder modulator.

  A method of manufacturing a Mach-Zehnder modulator according to one aspect of the present invention includes a waveguide mesa provided on a lower semiconductor region, a first insulating film provided on a side surface and an upper surface of the waveguide mesa, Preparing a first substrate product including a first resin body provided on a side surface and an upper surface of the first insulating film so as to embed a waveguide mesa; and the waveguide mesa of the first substrate product. Etching the first resin body so as to expose the first insulating film on the upper surface, and etching the plasma of the etchant supplied to the plasma processing apparatus after etching the first resin body. Exposing the first resin body and the first insulating film to form an opening located on the upper surface of the waveguide mesa in the first insulating film; and forming the opening in the first insulating film. After, before the waveguide mesa Forming a second resin body on the upper surface, the first resin body and the first insulating film, and embedding the upper surface of the first resin body and the waveguide mesa; and etching the second resin body And forming an opening located on the upper surface of the waveguide mesa in the second resin body, and an ohmic contact with the upper surface of the waveguide mesa through the opening of the second resin body Forming an electrode.

  A Mach-Zehnder modulator according to another aspect of the present invention includes a waveguide mesa provided on a lower semiconductor region, and provided on the lower semiconductor region and the waveguide mesa, and is located on an upper surface of the waveguide mesa. A first insulating film having an opening, a first resin body provided on a side surface of the first insulating film so as to embed the waveguide mesa, and in contact with the first resin body and the first insulating film A second resin body having an opening located on an upper surface of the waveguide mesa, and provided on the second resin body, through the opening of the first insulating film and the opening of the second resin body. An ohmic electrode connected to the upper surface of the waveguide mesa; a second insulating film provided on the second resin body and having an opening located on the ohmic electrode on the upper surface of the waveguide mesa; Through the opening of the second insulating film A metal electrode that contacts the ohmic electrode and extends on the second resin body, and the first resin body has a depression along the first insulating film on a side surface of the waveguide mesa. The second resin body fills the recess.

  The above and other objects, features, and advantages of the present invention will become more readily apparent from the following detailed description of preferred embodiments of the present invention, which proceeds with reference to the accompanying drawings.

  As described above, according to one aspect of the present invention, there is provided a method for manufacturing a Mach-Zehnder modulator that forms a structure that can avoid a decrease in high-frequency characteristics of the Mach-Zehnder modulator. According to another aspect of the present invention, there is provided a Mach-Zehnder modulator having a structure capable of avoiding a decrease in high-frequency characteristics of the Mach-Zehnder modulator.

FIG. 1 is a drawing schematically showing main steps in a method for manufacturing a Mach-Zehnder modulator according to an embodiment. FIG. 2 is a drawing schematically showing main steps in the method of manufacturing the Mach-Zehnder modulator according to the embodiment. FIG. 3 is a drawing schematically showing main steps in the method of manufacturing the Mach-Zehnder modulator according to the embodiment. FIG. 4 is a drawing schematically showing main steps in the method of manufacturing the Mach-Zehnder modulator according to the embodiment. FIG. 5 is a drawing schematically showing main steps in the method of manufacturing the Mach-Zehnder modulator according to the embodiment. FIG. 6 is a drawing schematically showing main steps in the method of manufacturing the Mach-Zehnder modulator according to the embodiment. FIG. 7 is a drawing schematically showing main steps in the method of manufacturing the Mach-Zehnder modulator according to the embodiment. FIG. 8 is a drawing schematically showing main steps in the method of manufacturing the Mach-Zehnder modulator according to the embodiment. FIG. 9 is a drawing schematically showing main steps in the method of manufacturing the Mach-Zehnder modulator according to the embodiment. FIG. 10 is a drawing schematically showing main steps in the method of manufacturing the Mach-Zehnder modulator according to the embodiment. FIG. 11 is a drawing schematically showing main steps in the method of manufacturing the Mach-Zehnder modulator according to the embodiment. FIG. 12 is a drawing schematically showing main steps in a method for producing a Mach-Zehnder modulator according to another embodiment. FIG. 13 is a drawing schematically showing main steps in a method of manufacturing a Mach-Zehnder modulator according to another embodiment. FIG. 14 is a drawing schematically showing main steps in the method of manufacturing the Mach-Zehnder modulator according to the embodiment. FIG. 15 is a drawing schematically showing main steps in the method of manufacturing the Mach-Zehnder modulator according to the embodiment. FIG. 16 is a plan view schematically showing the Mach-Zehnder modulator according to the embodiment. FIG. 17 is a diagram schematically illustrating a Mach-Zehnder modulator according to an embodiment.

  Some specific examples will be described.

  A method of manufacturing a Mach-Zehnder modulator according to a specific example includes: (a) a waveguide mesa provided on a lower semiconductor region; a first insulating film provided on a side surface and an upper surface of the waveguide mesa; Preparing a first substrate product including a first resin body provided on a side surface and an upper surface of the first insulating film so as to embed a waveguide mesa; and (b) the first substrate product. Etching the first resin body so as to expose the first insulating film on the upper surface of the waveguide mesa; and (c) supplying the plasma processing apparatus after etching the first resin body. Exposing the first resin body and the first insulating film to the plasma of the etched etchant to form an opening on the upper surface of the waveguide mesa in the first insulating film; and (d) the opening. After forming the first insulating film on the first insulating film, Forming a second resin body on the upper surface of the waveguide mesa, the first resin body and the first insulating film, and embedding the upper surface of the first resin body and the waveguide mesa; and (e) Etching the second resin body to form an opening on the upper surface of the waveguide mesa in the second resin body; and (f) the opening through the opening of the second resin body. Forming an ohmic electrode in contact with the upper surface of the waveguide mesa.

  According to the method for manufacturing the Mach-Zehnder modulator, the first resin body and the first insulating film are exposed to the plasma of the etchant in the plasma processing apparatus, and the opening located on the upper surface of the waveguide mesa is formed in the first insulating film. Form. The plasma treatment is performed so as to surely expose the upper surface of the waveguide mesa. According to the inventor's observation, the following matters are clarified: The plasma of this etchant is a first resin body that is exposed to the plasma, in particular, along the insulating film covering the side surface of the waveguide mesa. Unintentional etching of the resin body proceeds; the amount of resin lost due to unintentional etching varies within the wafer surface during the manufacturing process: the disappearance of the resin forms a recess along the side of the waveguide mesa. On the other hand, this manufacturing method forms the 2nd resin body which makes contact on the 1st resin body, and fills the dent along the side of a waveguide mesa with the 2nd resin body. Resin application for forming the second resin body makes it possible to bury recesses of various shapes, for example, recesses varying in depth and width. The second resin body covers the upper surface of the waveguide mesa, and the first insulating film does not cover the upper surface of the waveguide mesa when forming the second resin body. In the opening formed in the second resin body, it is not necessary to etch the first insulating film.

  A method of manufacturing a Mach-Zehnder modulator according to a specific example includes: forming a second insulating film covering the ohmic electrode and the second resin body after forming the ohmic electrode; and etching the second insulating film. A step of forming an opening located on the ohmic electrode in the second insulating film, and a step of forming a metal layer on the opening of the second insulating film and the second insulating film, The metal layer is connected to the ohmic electrode through the opening of the second insulating film.

  According to the method of manufacturing the Mach-Zehnder modulator, the first resin body and the second resin body are in direct contact with each other to form an interface between the resins, and the second insulating film is formed on the second resin body. . The metal layer is provided in the opening of the second insulating film and can extend over the second insulating film.

  In a method of manufacturing a Mach-Zehnder modulator according to a specific example, the lower semiconductor region includes a first portion and a second portion, and the waveguide mesa is provided on the first portion of the lower semiconductor region, The method of manufacturing the Mach-Zehnder modulator includes a step of etching the first resin body to form an opening located on the second portion of the lower semiconductor region in the first resin body, Forming another ohmic electrode in contact with the second portion through the opening of one resin body, and embedding the upper surface of the first resin body and the waveguide mesa. Two resin bodies cover the second portion of the lower semiconductor region and the separate ohmic electrode.

  According to the method of manufacturing the Mach-Zehnder modulator, the first resin body is etched to form an opening in the first resin body on the second portion of the lower semiconductor region, and the metal electrode is attached to the first resin body. Formed in the opening.

  In the method of manufacturing the Mach-Zehnder modulator according to the specific example, the second resin body is etched by etching the second resin body after the opening is formed in the second resin body and before the ohmic electrode is formed. The method further includes the step of forming an opening in the second resin body on the ohmic electrode.

  According to the method of manufacturing the Mach-Zehnder modulator, the metal electrode on the second portion of the lower semiconductor region is formed in the second resin body in the step of embedding the upper surface of the first resin body and the waveguide mesa. Covered by resin body. An opening is formed in the second resin body by etching the second resin body alone.

  A Mach-Zehnder modulator according to a specific example includes: (a) a waveguide mesa provided on a lower semiconductor region; and (b) provided on the lower semiconductor region and the waveguide mesa and on an upper surface of the waveguide mesa. A first insulating film having an opening located at (3), (c) a first resin body provided on a side surface of the first insulating film so as to embed the waveguide mesa, and (d) the first resin body and the first resin body. A second resin body in contact with one insulating film and having an opening located on an upper surface of the waveguide mesa; and (e) provided on the second resin body, the opening of the first insulating film and An ohmic electrode connected to the upper surface of the waveguide mesa through the opening of the second resin body; and (f) the ohmic electrode provided on the second resin body and on the upper surface of the waveguide mesa. A second insulating film having an opening located thereon; (g) A metal electrode that contacts the first ohmic electrode through the opening of the second insulating film and extends on the second resin body, wherein the first resin body is formed of the waveguide mesa. A side surface has a recess along the first insulating film, and the second resin body fills the recess.

  According to this Mach-Zehnder modulator, the first resin body has a recess along the side surface of the waveguide mesa, while the recess is filled with the second resin body.

  The knowledge of the present invention can be easily understood by considering the following detailed description with reference to the accompanying drawings shown as examples. Next, a method for manufacturing a Mach-Zehnder modulator and an embodiment related to the Mach-Zehnder modulator will be described with reference to the accompanying drawings. Where possible, the same parts are denoted by the same reference numerals.

  With reference to FIGS. 1 to 15, main steps in the method of manufacturing the Mach-Zehnder modulator will be described. These drawings show a cross-section along a line crossing the arm waveguide of the Mach-Zehnder modulator to be manufactured in the main steps of the manufacturing method.

As shown in part (a) of FIG. 1, an epitaxial substrate EP including a semiconductor stack 13 for an optical waveguide provided on the substrate 11 is prepared. The semiconductor stack 13 includes a first semiconductor layer 13a for the lower cladding layer, a second semiconductor layer 13b for the core layer, a third semiconductor layer 13c for the upper cladding layer, and a fourth semiconductor layer for the contact layer. 13d is included. The preparation of the epitaxial substrate EP is to produce the epitaxial substrate EP in this embodiment. The substrate 11 is a growth substrate that enables epitaxial growth of a semiconductor crystal on the main surface 11a, and the main surface 11a preferably includes a semi-insulating semiconductor. Specifically, a semiconductor stack 13 for an optical waveguide is grown on the substrate 11. The semiconductor stacked layer 13 is grown by, for example, metal organic vapor phase epitaxy or molecular beam epitaxy.
An example of the semiconductor stack 13.
Substrate 11: Semi-insulating InP.
First semiconductor layer 13a (lower cladding layer): n-type InP.
Second semiconductor layer 13b (core layer): AlGaInAs quantum well.
Third semiconductor layer 13c (upper clad layer): p-type InP.
Fourth semiconductor layer 13d (contact layer): p-type InGaAs.
The first semiconductor layer 13 a, the second semiconductor layer 13 b, the third semiconductor layer 13 c, and the fourth semiconductor layer 13 d are arranged in order on the main surface 11 a of the substrate 11.

  A first mask 15 that defines a waveguide mesa is formed on the main surface 13e of the semiconductor multilayer 13 (the main surface of the epitaxial substrate EP). This formation is performed by, for example, photolithography and etching. The first mask 15 includes a silicon-based inorganic insulating film (for example, silicon nitride, silicon oxide). In this embodiment, the first mask 15 is a 300 nm thick SiN film. The first mask 15 has a pattern for the waveguide of the Mach-Zehnder modulator.

  As shown in part (b) of FIG. 1, the semiconductor stack 13 is etched using the first mask 15. This etching can be, for example, dry etching, and the etchant includes, for example, a halogen-based gas. The end point of the etching is determined so that the bottom of the waveguide mesa 17 is located in the first semiconductor layer 13a. By this etching, a waveguide mesa 17 for the two arm waveguides is formed. Each of the waveguide mesas 17 includes a lower cladding layer 17a (for example, n-type InP), a core layer 17b (for example, AlGaInAs quantum well), an upper cladding layer 17c (p-type InP), and a contact layer 17d (p-type InGaAs). . The waveguide mesa 17 extends on the conductive semiconductor layer 17g (for example, n-type InP) for the lower semiconductor region. The lower cladding layer 17a, the core layer 17b, the upper cladding layer 17c, and the contact layer 17d are sequentially arranged in the direction of the normal line NX of the main surface 17h of the conductive semiconductor layer 17g. After the etching, the first mask 15 is removed.

  As shown in FIG. 2A, a second mask 19 that defines an element isolation mesa is formed on the waveguide mesa 17 and the conductive semiconductor layer 17g. This formation is performed by, for example, photolithography and etching. The second mask 19 includes a silicon-based inorganic insulating film (for example, silicon nitride, silicon oxide). In this embodiment, the second mask 19 is a 300 nm thick SiN film. The second mask 19 has a pattern for element isolation in the lower semiconductor region of the Mach-Zehnder modulator.

  As shown in part (b) of FIG. 2, the conductive semiconductor layer 17 g is etched using the second mask 19. This etching can be, for example, dry etching, and the etchant includes, for example, a halogen-based gas. The end point of the etching is determined so that the bottom of the element isolation mesa is located in the semi-insulating semiconductor region (for example, the substrate 11 including the semi-insulating semiconductor). By this etching, an element isolation mesa 21 is formed. After the etching, the second mask 19 is removed. The lower semiconductor region 21a of the element isolation mesa 21 includes a pair of first portions 21b, a second portion 21c, and a pair of third portions 21d. The first portion 21b, the second portion 21c, and the third portion 21d are the substrate 11. It is arranged along the main surface 11a. The first portion 21b and the second portion 21c are arranged so that the second portion 21c is provided between the first portions 21b. The first portion 21b, the second portion 21c, and the third portion 21d are arranged so that the first portion 21b and the second portion 21c are provided between the third portions 21d. The waveguide mesa 17 is provided on each first portion 21b, and the second portion 21c connects the first portions. The lower semiconductor region 21a connects the lower ends of the waveguide mesas 17 for the two arm waveguides.

As shown in FIG. 3A, the substrate 11 grows so as to cover the main surface 11a of the substrate 11, the surface of the lower semiconductor region 21a, and the upper surface 17e and side surface 17f of the waveguide mesa 17. The first insulating film 23 can include a silicon-based inorganic insulating film (for example, silicon oxide or silicon nitride), and the silicon-based inorganic insulating film is formed by chemical vapor deposition. In the present embodiment, the first insulating film 23 is a 300 nm thick SiO ₂ film. After forming the first insulating film 23, a resin is applied on the first insulating film 23 and cured by heat treatment to form the first resin body 25. The resin is applied so as to embed the upper surface and side surfaces of the waveguide mesa 17 and the element isolation mesa 21. The first resin body 25 includes, for example, a benzocyclobutene resin. The first resin body 25 covers the waveguide mesa 17 and the element isolation mesa 21 on the first insulating film 23.

As shown in FIG. 3B, in this embodiment, the entire surface of the first resin body 25 is etched without using a mask, and the first insulating film 23 on the upper surface 17e of the waveguide mesa 17 is formed. Expose. Specifically, an opening is formed in the first resin body 25 so as to remove the insulating film on the upper surface 17 e of the waveguide mesa 17. By this etching, the first resin body 25a etched on the entire surface is formed in this embodiment. This etching is performed by dry etching, and the etchant can be, for example, CF ₄ / O ₂ .

4A and 4B, a third mask 27 for forming an opening in the first resin body 25a is used as the first resin body 25 and the upper surface 17e of the waveguide mesa 17. It is formed on the first insulating film 23 located above. The third mask 27 has a first opening 27b in the element area and a second opening 27c in the peripheral area. The first resin body 25a is etched using the third mask 27 to form an opening in the first resin body 25a. This etching is performed by dry etching, and the etchant can be, for example, CF ₄ / O ₂ . Specifically, referring to part (a) of FIG. 4, in order to form an electrical connection to the lower semiconductor region 21a connected to the lower semiconductor of the waveguide mesa 17 for the two arm waveguides. The first opening 25 b is formed in the first resin body 25 a by etching using the third mask 27. The first opening 25b is provided on the second portion 21c located between the first portions 21b. The first insulating film 23 appears in the first opening 25b. Referring to FIG. 4B, the second opening 25c is formed by etching using the third mask 27 so as not to leave a resin body under the pad electrode formed in a later step. The second opening 25c is provided, for example, in an area where a pad electrode is to be formed in the peripheral area. The first insulating film 23 appears in the second opening 25c. After the etching is completed, the third mask 27 is removed.

As shown in FIGS. 5A and 5B, in the element area, the first insulating film 23 on the upper surface 17e of the waveguide mesa 17 is removed, and the upper surface 17e of the waveguide mesa 17 is exposed. Let The height of the tip of the first insulating film 23 left on the side surface of the waveguide mesa 17 is lower than the upper surface 17 e of the waveguide mesa 17. By this processing (processing of the first resin body 25a), the first insulating film 23 on the upper surface 17e of the waveguide mesa 17 is not covered with the first resin body 25a. The first insulating film 23 on the upper surface 17e of the waveguide mesa 17 can be removed by etching the first insulating film 23 using the first resin body 25a as a mask. On the other hand, in the peripheral area, the first resin body 25a is already removed in a desired area in the previous step, and the first insulating film 23 is exposed in the second opening 25c. In order to avoid the removal of the first insulating film 23 in the second opening 25c on the peripheral area, a fourth mask 29 is formed. The fourth mask 29 generally has an opening in the element area and covers the peripheral area. In the element area, the first insulating film 23 appearing in the opening of the fourth mask 29 is removed by dry etching using an etchant capable of removing the first insulating film 23. This etching is performed by, for example, CF ₄ reactive ion etching. In the embodiment, by this anisotropic plasma treatment, the first insulating film 23 on the upper surface 17e of the waveguide mesa 17 is removed, the upper surface 17e of the waveguide mesa 17 is exposed, and the top of the waveguide mesa 17 is exposed. The upper side surface is also exposed. In addition to the desired removal of the first insulating film 23, unexpectedly, a part of the first resin body 25 a disappears along the side surface of the waveguide mesa 17. In the anisotropic plasma treatment, the surface of the first resin body 25a is slightly etched, and the shape of the first resin body 25a is not substantially changed. However, in the present embodiment, a concave portion 25e (for example, a wedge-shaped depression) is formed in the first resin body 25a, and the first resin body 25a is processed into the first resin body 25d. On the upper surface 17e of the waveguide mesa 17, the lower portion of the side surface of the uppermost layer (for example, contact layer) of the waveguide mesa 17 is covered with the first insulating film 23, and the first insulating film 23 is the contact layer. And an opening exposing an upper portion of the side surface.

  As shown in FIG. 6A, the ohmic electrode 31a is formed in the first opening 25b of the first resin body 25d in the element area. In this embodiment, the ohmic electrode 31a is formed by a lift-off method, and the first lift-off mask 33 is formed for this lift-off. As shown in FIGS. 6A and 6B, since the ohmic electrode 31a is not formed in the peripheral area, the first lift-off mask 33 covers the peripheral area, while the lower semiconductor region 21a in the element area. An opening 33a is provided on the top. The first lift-off mask 33 can be a resist, for example. After forming the first lift-off mask 33, a conductive film 31 for ohmic electrodes is deposited. The conductive film 31 includes, for example, AuGeNi / Au. The conductive film 31 includes an ohmic electrode 31 a deposited in the opening 33 a of the first lift-off mask 33 and an isolation portion 31 b deposited on the first lift-off mask 33. After the deposition, the first lift-off mask 33 is peeled off and the ohmic electrode 31a is left on the lower semiconductor region 21a. The edge of the ohmic electrode 31 a is separated from the first insulating film 23. Due to this separation, the ohmic electrode has poor adhesion to the insulating film.If the ohmic electrode is formed so as to be in contact with each other, the electrode and the insulating film are peeled off, resulting in an undesirable shape change.However, the separation can prevent film peeling. The shape as formed can be maintained.

  According to the method of manufacturing the Mach-Zehnder modulator, the first resin body 25a is etched to form the first opening 25b of the first resin body 25d on the second portion of the lower semiconductor region, and the first A metal electrode is formed in the first opening 25b of the resin body 25d.

  As shown in FIGS. 7A and 7B, a thick metal film is formed on the ohmic electrode 31a in the element area, and a thick metal film for the pad electrode is first formed in the peripheral area. It is formed on the insulating film 23. For application of the plating method, a first insulating mask is formed. The first insulating mask has a first opening on the ohmic electrode 31a and a second opening in the peripheral area. After forming the first insulating mask, the seed metal layer 39 is formed, and after forming the seed metal layer 39, the metal thick film 35 is formed by a plating method. By energization in the electrolytic solution, the thick metal film 35 grows on the seed metal layer 39 connected to the conductor. In the present embodiment, the metal thick film 35 can include, for example, gold (Au). The first insulating mask can be a resist, for example. After forming the thick metal film 35, the first insulating mask is removed. FIGS. 7A and 7B are views after the first insulating mask is removed. A thick metal film 35 is provided on the ohmic electrode 31a in the element area, and a thick metal film 35 is provided on the first insulating film 23 for the pad electrode in the peripheral area. In the peripheral area, the seed metal layer 39 is in contact with the first insulating film 23. In the element area, the seed metal layer 39 is in contact with the ohmic electrode 31a.

  As shown in FIGS. 8A and 8B, a second resin body is formed on the element area and the peripheral area. An example of the formation of the second resin body is as follows. Resin is applied onto the element area and the peripheral area by spin coating. The applied resin fills the first opening 25b and the second opening 25c of the first resin body 25d and the recess 25e of the first resin body 25d. The applied resin is cured by heat treatment to form the second resin body 43. This heat treatment is applied not only to the resin for the second resin body 43 but also to the first resin body 25d. The second resin body 43 reaches the seed metal layer 39 and the metal thick film 35 on the ohmic electrode 31a through the first opening 25b, and reaches the seed metal layer 39 and the metal thick film 35 for the pad electrode in the second opening 25c. To reach. The second resin body 43 completely fills the recess 25 e and covers the upper surface 17 e of the waveguide mesa 17 and the first insulating film 23 on the side surface of the waveguide mesa 17. In the present embodiment, the second resin body 43 can be, for example, a BCB resin. The first resin body 25d and the second resin body 43 can be made of the same type of resin. The thickness of the second resin body 43 can be, for example, about 1 to 4 μm on the upper surface 17 e of the waveguide mesa 17. The thickness of the second resin body 43 can be about 3 to 8 μm in the ohmic electrode 31a. In most of the element area, most of the second resin body 43 is in contact with the first resin body 25d.

  As shown in FIG. 9A, a fifth mask 45 for forming an opening in the second resin body 43 is formed on the second resin body 43. The fifth mask 45 has an opening 45 a on the upper surface 17 e of the waveguide mesa 17. The width W1 of the opening 45a is larger than the width WMS of the upper surface 17e of the waveguide mesa 17. The fifth mask 45 can be, for example, a resist mask. As shown in part (b) of FIG. 9, the fifth mask 45 covers the peripheral area. As shown in part (a) of FIG. 9, the second resin body 43 is etched using the fifth mask 45 to form an opening in the second resin body 43 that reaches the upper surface 17 e of the waveguide mesa 17. . By this etching, the second resin body 43a having the first opening 43b is formed. The depression formed along the first insulating film 23 on the side surface of the waveguide mesa 17 is filled with the buried portion 43c of the second resin body 43a, and the surface of the buried portion 43c is located at the first opening 43b. To do. Since the first insulating film 23 on the upper surface 17e of the waveguide mesa 17 has been removed in the previous step, an opening for electrical connection can be formed by etching the second resin body 43. In the present embodiment, the second resin body 43a is formed by etching. In the present embodiment, the first resin body 25d is not etched. The etching has not reached the interface between the second resin body 43a and the first resin body 25d.

As shown in FIGS. 10A and 10B, a sixth mask 47 for forming an opening in the second resin body 43a is formed on the second resin body 43a. This mask can be, for example, a resist mask. The sixth mask 47 has a first opening 47a located on the metal stack (the ohmic electrode 31a, the seed metal layer 39 and the metal thick film 35) on the lower semiconductor region 21a in the element area, and the pad electrode in the peripheral area. And a second opening 47b located on the metal stack (the seed metal layer 39 and the metal thick film 35). The second resin body 43a is etched using the sixth mask 47 to form the second opening 43d1 and the third opening 43d2 in the second resin body 43a. By this etching, the second resin body 43e is formed. This etching is performed by dry etching, and the etchant can be, for example, CF ₄ / O ₂ . Specifically, referring to part (a) of FIG. 10, on the lower semiconductor region 21 a connecting the lower semiconductor of the waveguide mesa 17 for the two arm waveguides by etching using the sixth mask 47. A second opening 43d1 is formed in the second resin body 43a in order to form an electrical connection to the laminated electrode. The second opening 43d1 is provided on the first portion 21b located between the second portions 21c. A metal stack (ohmic electrode 31a, seed metal layer 39, and metal thick film 35) appears in the second opening 43d1. Referring to FIG. 10B, the third opening 43d2 is formed on the metal stack (the seed metal layer 39 and the metal thick film 35) for the pad electrode by etching using the sixth mask 47. A metal stack for the pad electrode appears in the third opening 43d2.

  As shown in FIG. 11A, the ohmic electrode 51a is formed in the first opening 43b of the second resin body 43e in the element area. In this embodiment, the ohmic electrode 51a is formed by a lift-off method, and a second lift-off mask 53 is formed for the lift-off. As shown in FIGS. 11A and 11B, since the ohmic electrode 51a is not formed in the peripheral area, the second lift-off mask 53 covers the peripheral area while the waveguide mesa in the element area. 17 has an opening 53a on the upper surface 17e. The second lift-off mask 53 can be a resist, for example. After forming the second lift-off mask 53, a conductive film 51 for the ohmic electrode is deposited. The conductive film 51 includes, for example, TiPtAu. The conductive film 51 includes an ohmic electrode 51 a deposited in the opening 53 a of the second lift-off mask 53 and an isolation portion 51 b deposited on the second lift-off mask 53. After the deposition, the second lift-off mask 53 is peeled off and the ohmic electrode 51a is left on the upper surface 17e of the waveguide mesa 17. If necessary, after the second lift-off mask 53 is formed, the semiconductor surface of the waveguide mesa 17 may be etched with a wet etching etchant (for example, a mixture of phosphoric acid / hydrogen peroxide solution / water). Good.

  As shown in FIGS. 12A and 12B, after the ohmic electrode 51a is formed, the second insulating film 55 is formed on the ohmic electrode 51a and the second resin body 43e. The second insulating film 55 can include, for example, a silicon-based inorganic insulating film, and specifically includes silicon oxide, silicon nitride, and silicon oxynitride. In the present embodiment, the second insulating film 55 is a silicon oxide film. The second insulating film 55 covers the surface of the ohmic electrode 51a and the surface of the second resin body 43e.

  Next, an opening is formed in the second insulating film 55 in order to enable electrical connection to the ohmic electrode 31a and the ohmic electrode 51a in the element area and the metal stack (metal stack for the pad electrode) in the peripheral area. A seventh mask 57 is formed on the second insulating film 55. The seventh mask 57 can be, for example, a resist mask. The seventh mask 57 includes a first opening 57a on the ohmic electrode 51a on the upper surface 17e of the waveguide mesa 17, and a metal stack on the lower semiconductor region 21a (the ohmic electrode 31a, the seed metal layer 39, and the metal thick film 35). The upper second opening 57b and the third opening 57c on the metal stack (the seed metal layer 39 and the metal thick film 35) for the pad metal in the peripheral area are provided. Using the seventh mask 57, the second insulating film 55 is etched to form a first opening 55a, a second opening 55b, and a third opening 55c in the second insulating film 55. After these openings are formed, the seventh mask 57 is removed. In the first opening 55a, the second opening 55b, and the third opening 55c, the ohmic electrode 51a, the metal stack (the ohmic electrode 31a, the seed metal layer 39, and the metal thick film 35), and the metal stack (the seed metal layer 39, respectively) are provided. And a thick metal film 35) appears. The second insulating film 55 includes a peripheral portion on the upper surface of the ohmic electrode 51a, a peripheral portion on the upper surface of the metal stack (the ohmic electrode 31a, the seed metal layer 39, and the metal thick film 35), and a metal stack (the seed metal layer 39, and Contact is made with the peripheral edge of the upper surface of the metal thick film 35).

  According to the method of manufacturing the Mach-Zehnder modulator, the first resin body 25d and the second resin body 43e are in direct contact with each other to form a strong bond, and the second insulating film 55 is formed on the second resin body 43e. Is done. The metal layer is provided in the opening of the second insulating film 55 and can extend over the second insulating film 55.

  As shown in FIGS. 13A and 13B, the metal electrode 59 is formed by plating. The metal electrode 59 includes a first metal wiring layer 59a, a second metal wiring layer 59b, and a third metal wiring layer 59c. The first metal wiring layer 59a is provided on the ohmic electrode 51a, the second metal wiring layer 59b is provided on the metal stack (31a, 35, 39), and the third metal wiring layer 59c is formed on the metal stack (in the peripheral area). 35, 39).

  Through these steps, a Mach-Zehnder modulator is manufactured. According to the method of manufacturing the Mach-Zehnder modulator, the first resin body 25 and the first insulating film 23 are exposed to the etchant plasma in the plasma processing apparatus, and the opening located on the upper surface 17e of the waveguide mesa 17 is formed. 1 formed on the insulating film 23; The plasma treatment is performed so as to surely expose the upper surface 17e of the waveguide mesa 17. According to the inventor's observation, the following matters are clarified: The plasma of this etchant is along the insulating film covering the first resin body 25 exposed to the plasma, in particular, the side surface of the waveguide mesa 17. Unintentional etching of the first resin body 25 proceeds; the amount of resin disappearance due to unintentional etching varies within the wafer surface in the manufacturing process: The disappearance of the resin forms a recess 25e along the side surface of the waveguide mesa 17. Thus, the remaining recess 25e actually causes an increase in capacitance of the electrode formed in the subsequent process. On the other hand, this manufacturing method forms the 2nd resin body 43 which contacts on the 1st resin body 25, and fills the recessed part 25e along the side surface of the waveguide mesa 17 with the 2nd resin body 43. FIG. Resin application for forming the second resin body 43 makes it possible to bury recesses 25e having various shapes, for example, recesses varying in depth and width. The second resin body 43 covers the upper surface 17e of the waveguide mesa 17, and the first insulating film 23 does not cover the upper surface 17e of the waveguide mesa 17 when the second resin body 43 is formed. When the opening is formed in the second resin body 43, the etching of the first insulating film 23 is unnecessary.

  The structure of the Mach-Zehnder modulator according to the present embodiment is not limited to the device obtained by the above manufacturing method.

In the specific example shown in part (b) of FIG. 3, the entire surface of the first resin body 25 is etched without using a mask to expose the first insulating film 23 on the upper surface 17 e of the waveguide mesa 17. Another step can be performed instead of the step of etching the entire surface of the first resin body 25 without using a mask. Part (a) of FIG. 14 is a drawing schematically showing main steps in the manufacturing method of exposing the first insulating film 23 on the upper surface 17e of the waveguide mesa 17 using a mask. As shown in part (a) of FIG. 14, a mask 61 is formed on the first resin body 25. The mask 61 has an opening 61 a on the upper surface 17 e of the waveguide mesa 17. The opening 61a is provided to define a contact hole in the upper surface 17e of the waveguide mesa 17. The first opening width MW1 of the opening 61a is larger than the first opening width MW1 of the upper surface 17e of the waveguide mesa 17. The mask 61 can be, for example, a resist mask. The first resin body 25 is etched using the mask 61 to form a first opening 25f in the first resin body 25a that reaches the first insulating film 23 on the upper surface 17e of the waveguide mesa 17. The etched first resin body 25a has a first opening 25f. This etching is performed by dry etching, and the etchant can be, for example, CF ₄ / O ₂ .

  After the first opening 25f is formed in the first resin body 2 so as to remove the insulating film on the upper surface 17e of the waveguide mesa 17, the upper surface 17e of the waveguide mesa 17 is shown in FIG. 14B. The upper first insulating film 23 is removed, and the upper surface 17e of the waveguide mesa 17 is exposed. This process is performed in the same manner as the steps shown in the parts (a) and (b) of FIG. The exposed first insulating film 23 is removed by an etchant capable of removing the first insulating film 23. By the plasma treatment, the first insulating film 23 on the upper surface 17e of the waveguide mesa 17 is removed, and the upper surface 17e of the waveguide mesa 17 is exposed. On the upper surface 17e of the waveguide mesa 17, the lower portion of the side surface of the uppermost layer (for example, contact layer) in the waveguide mesa 17 is covered with the first insulating film 23, and the upper portion of the upper surface and side surface of the contact layer). Exposed. In addition to the removal of the first insulating film 23 on the upper surface 17e of the waveguide mesa 17, a part of the first resin body 25a disappears along the side surface of the waveguide mesa 17, as already described. Although the plasma treatment originally etches the surface of the first resin body 25a slightly, the shape of the first resin body 25a does not substantially change. However, in this embodiment, a wedge-shaped recess 25e is formed in the first resin body 25a, and the first resin body 25a is processed to become the first resin body 25d.

  Thereafter, the second resin body 43 is formed on the first resin body 25d. The formation of the second resin body 43 can be performed in the same manner as the process performed with reference to the parts (a) and (b) of FIG. The second resin body 43 is applied with a resin by a spin coating method. As shown in part (c) of FIG. 14, the applied resin fills the first opening 25b of the first resin body 25g and the recess 25e (and the second opening 25c) of the first resin body 25g. The applied resin is cured by heat treatment to form the second resin body 43. This heat treatment is applied not only to the resin for the second resin body 43 but also to the first resin body 25d.

  As shown in FIG. 14D, the second resin body 43 is etched using the fifth mask 45 to form an opening in the second resin body 43 that reaches the upper surface 17 e of the waveguide mesa 17. . This etching is performed in the same manner as the process performed with reference to part (a) of FIG. By this etching, a second resin body 43g having a first opening 43f is formed. The depression formed along the first insulating film 23 on the side surface of the waveguide mesa 17 is filled with the buried portion 43c of the second resin body 43g, and the surface of the buried portion 43c is located in the first opening 43f. . Since the first insulating film 23 on the upper surface 17e of the waveguide mesa 17 has been removed in the previous step, an opening for electrical connection can be formed by etching the second resin body 43. In the present embodiment, the second resin body 43g is formed by etching, and the first resin body 25d is not etched. The etching has not reached the interface between the second resin body 43g and the first resin body 25g. The second opening width MW2 of the first opening 43f of the second resin body 43g is smaller than the first opening width MW1 of the first opening 25f of the first resin body 25d and larger than the mesa width MS1 of the upper surface 17e of the waveguide mesa 17. . The mesa width MS1 is, for example, 1.2 to 2.2 micrometers, for example, 1.5 micrometers. The first opening width MW1 is 5.0 to 15.0 micrometers, for example 10.0 micrometers. 2nd opening width MW2 is 3.0-13.0 micrometers, for example, is 8.0 micrometers. The upper surface 17e of the waveguide mesa 17 appears in the first opening 43b of the second resin body 43g. The processing from the steps already described (steps shown in the (a) part and (b) part of FIG. 10) is continuously applied to this product.

  FIG. 15A is a plan view showing an area of the arm waveguide. (B) part of FIG. 15 shows the cross section taken along the XVb-XVb line | wire shown by the (a) part of FIG. The ohmic electrode 51a is in contact with the lower semiconductor region 21a, and the first plating electrode (the seed metal layer 39 and the metal thick film 35) is provided on the ohmic electrode 51a. The edge of the first plating electrode is separated from the first insulating film 23 and the first resin body 25d. The second resin body 43e covers the upper surface and side surfaces of the peripheral edge of the first plating electrode (31a, 35, 39). The electrode peeling can be suppressed by covering with BCB. The surface of the second resin body 43e and the upper surface of the first plating electrode are covered with the second insulating film 55. The second metal wiring layer 59b produced as the second plating electrode is in contact with the underlying first plating electrode through the opening of the second insulating film 55. The second metal wiring layer 59 b is provided around the edge of the second insulating film 55.

  FIG. 16 is a plan view schematically showing an example of a Mach-Zehnder modulator device manufactured by the above manufacturing method. The Mach-Zehnder modulator device 63 includes an element area DEV and a peripheral area PF. The Mach-Zehnder modulator device 63 includes Mach-Zehnder modulators MZ1, MZ2, MZ3, and MZ4 provided in the element area DEV. In the present embodiment, the Mach-Zehnder modulators MZ1, MZ2, MZ3, and MZ4 have substantially the same structure. The Mach-Zehnder modulator device 63 includes pad electrodes that are electrically connected to the Mach-Zehnder modulators MZ1, MZ2, MZ3, and MZ4 provided in the peripheral area PF. The inputs of the Mach-Zehnder modulators MZ1, MZ2, MZ3, and MZ4 are optically connected to the optical input IN, and receive laser light from the optical input IN through the branching device. The outputs of the Mach-Zehnder modulators MZ1 and MZ2 reach the first optical output OUT_X through the multiplexer. Further, the outputs of the Mach-Zehnder modulators MZ3 and MZ4 reach the first optical output OUT_Y through the multiplexer. Each of the Mach-Zehnder modulators MZ1, MZ2, MZ3, and MZ4 includes a modulation electrode MDLE located on the waveguide mesa and a phase electrode PHLE located on the waveguide mesa.

  17A shows a cross section taken along the line XVIIa-XVIIa shown in FIG. 16, and FIG. 17B shows the part taken along the line XVIIb-XVIIb shown in FIG. The cross section taken is shown. The Mach-Zehnder modulator MZ1 includes the waveguide mesa 17, the first insulating film 23, the first resin body 25d, the second resin body 43e, the ohmic electrode 51a, the second insulating film 55, and the metal electrode 59. Is provided. The waveguide mesa 17 is provided on the lower semiconductor region 21a. The first insulating film 23 is provided on the lower semiconductor region 21 a and the waveguide mesa 17 and has an opening 23 a located on the upper surface 17 e of the waveguide mesa 17. The first resin body 25 d is provided on the first insulating film 23 so as to embed the waveguide mesa 17. The second resin body 43e is in contact with the first resin body 25d and the first insulating film 23 and has a first opening 43b located on the upper surface 17e of the waveguide mesa 17. The ohmic electrode 51a is provided on the second resin body 43e, and is connected to the upper surface 17e of the waveguide mesa 17 through the opening 23a of the first insulating film 23 and the first opening 43b of the second resin body 43e. The second insulating film 55 is provided on the second resin body 43 e and has a first opening 55 a located on the ohmic electrode 51 a on the upper surface 17 e of the waveguide mesa 17. The metal electrode 59 is in contact with the ohmic electrode 51a through the first opening 55a of the second insulating film 55 and extends on the second resin body 43e. The first resin body 25d has a recess 25e along the side surface of the waveguide mesa 17, and the second resin body 43e fills the recess 25e. According to the Mach-Zehnder modulator MZ1, the first resin body 25d has the recess 25e along the side surface of the waveguide mesa 17, while the recess 25e is filled with the second resin body 43e.

  While the principles of the invention have been illustrated and described in the preferred embodiments, it will be appreciated by those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. The present invention is not limited to the specific configuration disclosed in the present embodiment. We therefore claim all modifications and changes that come within the scope and spirit of the following claims.

  As described above, according to the present embodiment, there is provided a method for manufacturing a Mach-Zehnder modulator that forms a structure capable of avoiding the deterioration of the high-frequency characteristics of the Mach-Zehnder modulator. There is provided a Mach-Zehnder modulator having a structure capable of avoiding deterioration of characteristics.

63 ... Mach-Zehnder modulator device, DEV ... Element area, PF ... Peripheral area, MZ1, MZ2, MZ3, MZ4 ... Mach-Zehnder modulator, 11 ... Substrate, 17 ... Waveguide mesa, 21a ... Lower semiconductor region, 23 ... First DESCRIPTION OF SYMBOLS 1 insulating film, 25d ... 1st resin body, 25e ... recessed part, 43e ... 2nd resin body, 31a, 51a ... ohmic electrode, 55 ... 2nd insulating film, 59 ... metal electrode.

Claims (5)

A method of fabricating a Mach-Zehnder modulator,
A waveguide mesa provided on the lower semiconductor region, a first insulating film provided on the side and upper surfaces of the waveguide mesa, and on the side and upper surfaces of the first insulating film so as to embed the waveguide mesa Preparing a first substrate product including a first resin body provided in
Etching the first resin body to expose the first insulating film on the top surface of the waveguide mesa of the first substrate product;
Exposing the first resin body and the first insulating film to an etchant plasma supplied to a plasma processing apparatus to form an opening located on the upper surface of the waveguide mesa in the first insulating film;
After the opening is formed in the first insulating film, a second resin body is formed on the upper surface of the waveguide mesa, the first resin body, and the first insulating film, and the first resin body and the Embedding the upper surface of the waveguide mesa;
Etching the second resin body to form an opening located on the upper surface of the waveguide mesa in the second resin body;
Forming an ohmic electrode in contact with the upper surface of the waveguide mesa through the opening of the second resin body;
A method for fabricating a Mach-Zehnder modulator. Forming a second insulating film covering the ohmic electrode and the second resin body after forming the ohmic electrode;
Etching the second insulating film to form an opening located on the ohmic electrode in the second insulating film;
Forming a metal layer on the opening of the second insulating film and the second insulating film;
With
The method for producing a Mach-Zehnder modulator according to claim 1, wherein the metal layer is connected to the ohmic electrode through the opening of the second insulating film. The lower semiconductor region includes a first portion and a second portion,
The waveguide mesa is provided on the first portion of the lower semiconductor region;
A method of manufacturing the Mach-Zehnder modulator is as follows:
Before forming the first resin body, etching the first resin body to form an opening located on the second portion of the lower semiconductor region in the first resin body;
Forming another ohmic electrode in contact with the second portion through the opening of the first resin body;
Further comprising
2. The step of embedding the first resin body and the top surface of the waveguide mesa, wherein the second resin body covers the second portion of the lower semiconductor region and the another ohmic electrode. A method for producing the Mach-Zehnder modulator described in 2.   After forming the opening in the second resin body and before forming the ohmic electrode, an opening is formed in the second resin body by etching the second resin body. The method of making a Mach-Zehnder modulator according to claim 3, further comprising a step. A Mach-Zehnder modulator,
A waveguide mesa provided on the lower semiconductor region;
A first insulating film provided on the lower semiconductor region and the waveguide mesa and having an opening located on an upper surface of the waveguide mesa;
A first resin body provided on a side surface of the first insulating film so as to embed the waveguide mesa;
A second resin body that is in contact with the first resin body and the first insulating film and has an opening located on an upper surface of the waveguide mesa;
An ohmic electrode provided on the second resin body and connected to the upper surface of the waveguide mesa through the opening of the first insulating film and the opening of the second resin body;
A second insulating film provided on the second resin body and having an opening located on the ohmic electrode on the upper surface of the waveguide mesa;
A metal electrode which contacts the ohmic electrode through the opening of the second insulating film and extends on the second resin body;
With
The Mach-Zehnder modulator, wherein the first resin body has a recess along the first insulating film on a side surface of the waveguide mesa, and the second resin body fills the recess.

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