JP6690457B2 - Method of manufacturing Mach-Zehnder modulator, Mach-Zehnder modulator - Google Patents

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 study by the inventor, the characteristics of the Mach-Zehnder modulator, specifically the high-frequency characteristics, vary from the product manufactured 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 prevent the surface of the semiconductor mesa from directly touching the resin, an inorganic insulating film, for example, a silicon oxide film is provided between the semiconductor mesa and the resin. The inorganic insulating film covers the upper surface and the side surface of the semiconductor mesa. The following steps are performed to form such a buried structure. The inorganic insulating film on the upper surface of the semiconductor mesa is exposed and the inorganic insulating film on the upper surface of the semiconductor mesa is removed by etching the resin. A metal body is formed on the upper surface of the resin body and the semiconductor mesa for embedding the semiconductor mesa for electrical connection onto 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, extends along the surface of the depression, and partially or entirely fills the depression.

  According to a further study, the depression is formed by the 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 dents in a product produced on one wafer in the manufacturing process varies within the wafer surface. The amount of depression depends on the etching time of the inorganic insulating film, and therefore can be reduced by shortening the etching time. The amount of processed inorganic insulating film also varies within the wafer surface. As a result, shortening the etching time increases the potential for film residue somewhere in the wafer plane, and the occurrence of inorganic insulating film residue leads to poor electrical connections.

  According to the study of the inventor, the occurrence of the depression due to the disappearance of the resin increases the capacitance related to the electrode, which leads to the reduction of the high frequency band in the Mach-Zehnder modulator.

  One aspect of the present invention is made in view of the above circumstances, and provides a method for manufacturing a Mach-Zehnder modulator, which forms a structure capable of avoiding deterioration of high-frequency characteristics of the Mach-Zehnder modulator. The purpose is to do. Another aspect of the present invention is to provide a Mach-Zehnder modulator having a structure capable of avoiding deterioration of 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 the waveguide mesa; and the waveguide mesa of the first substrate product. The step of etching the first resin body so as to expose the first insulating film on the upper surface of the first resin body, and the plasma of the etchant supplied to the plasma processing apparatus after the etching of the first resin body. Exposing the first resin body and the first insulating film to form an opening 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 A step of forming a second resin body on the upper surface, the first resin body, and the first insulating film to fill the upper surfaces of the first resin body and the waveguide mesa; and etching the second resin body. And a step of forming an opening on the upper surface of the waveguide mesa in the second resin body, and an ohmic contacting the upper surface of the waveguide mesa through the opening of the second resin body. And a step of 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, the lower semiconductor region and the waveguide mesa, and a position on an upper surface of the waveguide mesa. A first insulating film having an opening for opening, a first resin body provided on a side surface of the first insulating film so as to fill the waveguide mesa, and contacting the first resin body and the first insulating film. A second resin body having an opening located on the upper surface of the waveguide mesa, and the second resin body provided on the second resin body and 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 in the second insulating film And a metal electrode which is in contact with the ohmic electrode and extends on the second resin body, wherein the first resin body has a recess along a side surface of the waveguide mesa along the first insulating film. Then, 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 the 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 of manufacturing a Mach-Zehnder modulator that forms a structure capable of avoiding deterioration of the high frequency characteristics of the Mach-Zehnder modulator. Further, according to another aspect of the present invention, there is provided a Mach-Zehnder modulator having a structure capable of avoiding deterioration of high frequency characteristics of the Mach-Zehnder modulator.

FIG. 1 is a drawing schematically showing main steps in a method of 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 a method of manufacturing a 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 a method of manufacturing a Mach-Zehnder modulator according to the embodiment. FIG. 6 is a drawing schematically showing main steps in a method of manufacturing a Mach-Zehnder modulator according to the embodiment. FIG. 7 is a drawing schematically showing main steps in a method of manufacturing the Mach-Zehnder modulator according to the embodiment. FIG. 8 is a drawing schematically showing main steps in a method of manufacturing the Mach-Zehnder modulator according to the embodiment. FIG. 9 is a drawing schematically showing main steps in a 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 a method of manufacturing the Mach-Zehnder modulator according to the embodiment. FIG. 12 is a drawing schematically showing main steps in a method of manufacturing 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 a method of manufacturing the Mach-Zehnder modulator according to the embodiment. FIG. 15 is a drawing schematically showing main steps in a 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 drawing schematically showing the Mach-Zehnder modulator according to the embodiment.

  Next, 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, and 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 fill the waveguide mesa; and (b) the first substrate product. A step of etching the first resin body to expose the first insulating film on the upper surface of the waveguide mesa; and (c) supplying the plasma processing apparatus after the etching of the first resin body. Exposing the first resin body and the first insulating film to the plasma of the formed etchant to form an opening on the upper surface of the waveguide mesa in the first insulating film, and (d) the opening. Is formed 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 to embed 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 this method of 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 used as the first insulating film. Form. The plasma treatment is performed so as to surely expose the upper surface of the waveguide mesa. Observations made by the inventor reveal the following: The plasma of this etchant causes the first resin body exposed to the plasma, especially along the insulating film covering the side surface of the waveguide mesa, to move first. Unintentional etching of the resin body proceeds; the amount of resin disappeared due to unintentional etching varies in the wafer surface during the manufacturing process: the disappearance of the resin forms a recess along the side surface of the waveguide mesa. On the other hand, in the present manufacturing method, the second resin body that makes contact with the first resin body is formed, and the recess along the side surface of the waveguide mesa is filled with the second resin body. The resin application for the formation of the second resin body makes it possible to fill in recesses of various shapes, for example recesses that vary 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. The opening of the second resin body does not require etching of the first insulating film.

  A method of manufacturing a Mach-Zehnder modulator according to a specific example includes a step of forming a second insulating film that covers the ohmic electrode and the second resin body after forming the ohmic electrode, and etching the second insulating film. And forming an opening located on the ohmic electrode in the second insulating film, and 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 the 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, A method of manufacturing the Mach-Zehnder modulator includes a step of etching the first resin body to form an opening in the first resin body located on the second portion of the lower semiconductor region, And a step of forming another ohmic electrode in contact with the second portion through the opening of the first resin body, the step of burying the upper surfaces of the first resin body and the waveguide mesa. The 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 the opening in the first resin body on the second portion of the lower semiconductor region, and the metal electrode is formed on the first resin body. To form the opening.

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

  According to this 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 forming the second resin body and filling the upper surfaces 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 is (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, (c) a first resin body provided on a side surface of the first insulating film so as to fill the waveguide mesa, and (d) the first resin body and the first resin body. A second resin body which is in contact with the first insulating film and has an opening located on the upper surface of the waveguide mesa; and (e) the second resin body which is provided on the second resin body and has the opening of the first insulating film. 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 thereabove, (g) And a metal electrode which is in contact with the first ohmic electrode through the opening of the second insulating film and extends over the second resin body, wherein the first resin body is formed of the waveguide mesa. There is a recess along the first insulating film on the side surface, 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. Subsequently, a method of manufacturing a Mach-Zehnder modulator and an embodiment of the Mach-Zehnder modulator will be described with reference to the accompanying drawings. If possible, the same parts are designated by the same reference numerals.

  Main steps in a method of manufacturing a Mach-Zehnder modulator will be described with reference to FIGS. These figures show cross-sections along the line traversing the arm waveguide of the Mach-Zehnder modulator to be produced in the main steps of the production 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 clad layer, a second semiconductor layer 13b for the core layer, a third semiconductor layer 13c for the upper clad layer, and a fourth semiconductor layer for the contact layer. 13d is included. The preparation of the epitaxial substrate EP is to manufacture the epitaxial substrate EP in this embodiment. The substrate 11 is a growth substrate that enables epitaxial growth of semiconductor crystals on the main surface 11a, and the main surface 11a preferably includes a semi-insulating semiconductor. Specifically, the semiconductor stack 13 for the optical waveguide is grown on the substrate 11. The growth of the semiconductor stack 13 is performed by, for example, a metal organic chemical vapor deposition method or a molecular beam epitaxy method.
An example of the semiconductor stack 13.
Substrate 11: Semi-insulating InP.
First semiconductor layer 13a (lower clad 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 13a, the second semiconductor layer 13b, the third semiconductor layer 13c, and the fourth semiconductor layer 13d are sequentially arranged on the main surface 11a of the substrate 11.

  A first mask 15 defining a waveguide mesa is formed on the main surface 13e of the semiconductor stack 13 (main surface of the epitaxial substrate EP). This formation is performed, for example, by photolithography and etching. The first mask 15 includes a silicon-based inorganic insulating film (eg, 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. The etching can be, for example, dry etching, and the etchant includes, for example, a halogen-based gas. The end point of etching is determined so that the bottom of the waveguide mesa 17 is located in the first semiconductor layer 13a. By this etching, the waveguide mesa 17 for the two arm waveguides is formed. Each of the waveguide mesas 17 includes a lower clad layer 17a (for example, n-type InP), a core layer 17b (for example, AlGaInAs quantum well), an upper clad layer 17c (p-type InP) and a contact layer 17d (p-type InGaAs). . The waveguide mesa 17 extends over the conductive semiconductor layer 17g (eg, n-type InP) for the lower semiconductor region. The lower clad layer 17a, the core layer 17b, the upper clad 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 part (a) of FIG. 2, a second mask 19 defining an element isolation mesa is formed on the waveguide mesa 17 and the conductive semiconductor layer 17g. This formation is performed, for example, by photolithography and etching. The second mask 19 includes a silicon-based inorganic insulating film (for example, silicon nitride or 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 of the lower semiconductor region of the Mach-Zehnder modulator.

  As shown in part (b) of FIG. 2, the conductive semiconductor layer 17g is etched using the second mask 19. The etching can be, for example, dry etching, and the etchant includes, for example, a halogen-based gas. The end point of 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, the 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 has a pair of first portions 21b, a second portion 21c and a pair of third portions 21d, and the first portion 21b, the second portion 21c and the third portion 21d are the substrate 11. Are 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 such that the first portion 21b and the second portion 21c are provided between the third portion 21d. The waveguide mesa 17 is provided on each first portion 21b, and the second portion 21c connects these first portions. The lower semiconductor region 21a connects the lower ends of the waveguide mesas 17 for the two arm waveguides.

As shown in part (a) of FIG. 3, it 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 the 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 a chemical vapor deposition method. In this 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 a first resin body 25. The resin is applied so that the upper surface and the side surface of the waveguide mesa 17 and the element isolation mesa 21 are embedded. 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 part (b) of FIG. 3, in this embodiment, the entire surface of the first resin body 25 is etched without using a mask to remove the first insulating film 23 on the upper surface 17e of the waveguide mesa 17. Expose. Specifically, an opening for removing the insulating film on the upper surface 17e of the waveguide mesa 17 is formed in the first resin body 25. By this etching, in this embodiment, the first resin body 25a which is entirely etched is formed. This etching is performed by dry etching, and the etchant can be, for example, CF ₄ / O ₂ .

As shown in parts (a) and (b) of FIG. 4, a third mask 27 for forming an opening in the first resin body 25 a is provided on the first resin body 25 and the upper surface 17 e of the waveguide mesa 17. It is formed on the upper first insulating film 23. 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 21 a connected to the lower semiconductor of the waveguide mesa 17 for the two arm waveguides. The first opening 25b is formed in the first resin body 25a 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 part (b) of FIG. 4, the second opening 25c is formed by etching using the third mask 27 so that the resin body is not left under the pad electrode formed in a later step. The second opening 25c is provided in the peripheral area, for example, in an area where a pad electrode is to be formed. 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 parts (a) and (b) of FIG. 5, in the element area, the first insulating film 23 on the upper surface 17e of the waveguide mesa 17 is removed to expose the upper surface 17e of the waveguide mesa 17. 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 17e 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. By etching the first insulating film 23 using the first resin body 25a as a mask, the first insulating film 23 on the upper surface 17e of the waveguide mesa 17 can be removed. On the other hand, in the peripheral area, the first resin body 25a has already been removed in the desired area in the previous step, and the first insulating film 23 is exposed in the second opening 25c. A fourth mask 29 is formed in order to avoid removing the first insulating film 23 in the second opening 25c on the peripheral area. 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 exposed 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, the anisotropic plasma treatment removes the first insulating film 23 on the upper surface 17e of the waveguide mesa 17 to expose the upper surface 17e of the waveguide mesa 17 and the uppermost portion of the waveguide mesa 17. The side surface of the upper layer is also exposed. In addition to the desired removal of the first insulating film 23, unexpectedly, a part of the first resin body 25a disappears along the side surface of the waveguide mesa 17. Originally, the anisotropic plasma treatment does not substantially change the shape of the first resin body 25a by slightly etching the surface of the first resin body 25a. However, in the present embodiment, the first resin body 25a is formed with the concave portion 25e (for example, a wedge-shaped recess) and processed from the first resin body 25a to the first resin body 25d. In the upper surface 17e of the waveguide mesa 17, the lower part of the side surface of the uppermost layer (eg, contact layer) of the waveguide mesa 17 is covered with the first insulating film 23, and the first insulating film 23 is the upper surface of the contact layer. And an opening exposing the upper portion of the side surface.

  As shown in part (a) of FIG. 6, 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 the lift-off method, and the first lift-off mask 33 is formed for this lift-off. As shown in parts (a) and (b) of FIG. 6, 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 device area is covered. It has an opening 33a on the top. The first lift-off mask 33 can be, for example, a resist. After forming the first lift-off mask 33, the conductive film 31 for the ohmic electrode is deposited. The conductive film 31 includes, for example, AuGeNi / Au. The conductive film 31 includes an ohmic electrode 31a deposited on the opening 33a of the first lift-off mask 33 and an isolation portion 31b deposited on the first lift-off mask 33. After the deposition, the first lift-off mask 33 is peeled off to leave the ohmic electrode 31a on the lower semiconductor region 21a. The edge of the ohmic electrode 31a is separated from the first insulating film 23. Due to this separation, the ohmic electrode has poor adhesion to the insulating film, so if the electrodes and the insulating film are formed so as to be in contact with each other, the electrode and the insulating film are peeled off, which causes an undesired change in shape, but 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 resin body 25a is formed. A metal electrode is formed in the first opening 25b of the resin body 25d.

  As shown in parts (a) and (b) of FIG. 7, a metal thick film is formed on the ohmic electrode 31a in the device area, and a metal thick film for the pad electrode is formed in the first area in the peripheral area. It is formed on the insulating film 23. A first insulating mask is formed for applying the plating method. 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 the plating method. By energization in the electrolytic solution, the thick metal film 35 grows into the seed metal layer 39 connected to the conductor. In this embodiment, the thick metal film 35 can include, for example, gold (Au). The first insulating mask can be, for example, a resist. After forming the thick metal film 35, the first insulating mask is removed. Parts (a) and (b) of FIG. 7 are diagrams after the first insulating mask is removed. The metal thick film 35 is provided on the ohmic electrode 31a in the element area, and the metal thick 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 makes contact with the first insulating film 23. In the element area, the seed metal layer 39 makes contact with the ohmic electrode 31a.

  As shown in parts (a) and (b) of FIG. 8, a second resin body is formed on the element area and the peripheral area. An example of forming the second resin body is as follows. A resin is applied to the element area and the peripheral area by a spin coating method. 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 becomes 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 25e and covers the upper surface 17e 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, 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 17e 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 contacts the first resin body 25d.

  As shown in part (a) of FIG. 9, 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 45a on the upper surface 17e 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 recess formed along the first insulating film 23 on the side surface of the waveguide mesa 17 is filled with the embedded portion 43c of the second resin body 43a, and the surface of the embedded 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, the opening for electrical connection can be formed by etching the second resin body 43. In this embodiment, the second resin body 43a is formed by etching. In this 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 parts (a) and (b) of FIG. 10, 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 thick metal film 35) on the lower semiconductor region 21a in the element area, and the pad electrode in the peripheral area. Has a second opening 47b located on the metal stack (seed metal layer 39 and metal thick film 35) for the purpose. 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, by etching using the sixth mask 47, on the lower semiconductor region 21 a connecting the lower semiconductors of the waveguide mesas 17 for the two arm waveguides. 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 (the ohmic electrode 31a, the seed metal layer 39, and the metal thick film 35) appears in the second opening 43d1. Referring to part (b) of FIG. 10, 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 part (a) of FIG. 11, 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 the lift-off method, and the second lift-off mask 53 is formed for this lift-off. As shown in parts (a) and (b) of FIG. 11, 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 is covered. The upper surface 17e of 17 has an opening 53a. The second lift-off mask 53 can be, for example, a resist. After forming the second lift-off mask 53, the 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 51a deposited on the opening 53a of the second lift-off mask 53 and an isolation portion 51b 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 forming the second lift-off mask 53, the semiconductor surface of the waveguide mesa 17 may be etched by a wet etching etchant (for example, phosphoric acid / hydrogen peroxide solution / water mixture). Good.

  As shown in parts (a) and (b) of FIG. 12, after forming the ohmic electrode 51a, 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 this 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 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 (ohmic electrode 31a, seed metal layer 39, and metal thick film 35). It has an upper second opening 57b and a third opening 57c on the metal stack (seed metal layer 39 and metal thick film 35) for the pad metal in the peripheral area. Using the seventh mask 57, the second insulating film 55 is etched to form the first opening 55a, the second opening 55b, and the third opening 55c in the second insulating film 55. After forming these openings, the seventh mask 57 is removed. 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 in the first opening 55a, the second opening 55b, and the third opening 55c, respectively. And a thick metal film 35) is exposed. 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 thick metal film 35) and a metal stack (the seed metal layer 39, A contact is made with the peripheral portion of the upper surface of the thick metal 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 joint, and the second insulating film 55 is formed on the second resin body 43e. To be done. The metal layer is provided in the opening of the second insulating film 55 and can extend on the second insulating film 55.

  As shown in parts (a) and (b) of FIG. 13, the metal electrode 59 is formed by a plating method. 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 provided on the metal layer (in the peripheral area). 35, 39).

  Through these steps, the 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 plasma of the etchant in the plasma processing apparatus, and the opening located on the upper surface 17e of the waveguide mesa 17 is exposed. 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. Observations made by the inventor reveal the following matters: The plasma of this etchant is distributed along the first resin body 25 exposed to the plasma, particularly, along the insulating film covering the side surface of the waveguide mesa 17. The unintended etching of the first resin body 25 proceeds; the amount of resin disappeared due to the unintentional etching varies in the wafer surface during the manufacturing process: the disappearance of the resin forms the recess 25e along the side surface of the waveguide mesa 17. Therefore, the remaining of the recess 25e actually causes an increase in capacitance in the electrode formed in the subsequent step. On the other hand, in the present manufacturing method, the second resin body 43 that makes contact with the first resin body 25 is formed, and the recess 25 e along the side surface of the waveguide mesa 17 is filled with the second resin body 43. The resin application for forming the second resin body 43 makes it possible to fill in the recesses 25e having various shapes, for example, the recesses having variations 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 forming the second resin body 43. When forming the opening 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 FIG. 3B, 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 17e of the waveguide mesa 17. Instead of the step of etching the entire surface of the first resin body 25 without using a mask, another step can be performed. Part (a) of FIG. 14 is a drawing schematically showing main steps in a manufacturing method for 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 61a on the upper surface 17e 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 forming the first opening 25f in the first resin body 2 so as to remove the insulating film on the upper surface 17e of the waveguide mesa 17, as shown in part (b) of FIG. 14, the upper surface 17e of the waveguide mesa 17 is formed. The upper first insulating film 23 is removed to expose the upper surface 17e of the waveguide mesa 17. This process is performed in the same manner as the steps shown in 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. In the upper surface 17e of the waveguide mesa 17, the lower portion on the side surface of the uppermost layer (for example, the contact layer) in the waveguide mesa 17 is covered with the first insulating film 23, and the upper portions on the upper surface and the side surface of the contact layer are formed. Exposed. In addition to the removal of the first insulating film 23 on the upper surface 17e of the waveguide mesa 17, as described above, a part of the first resin body 25a disappears along the side surface of the waveguide mesa 17. Originally, the plasma treatment slightly etches the surface of the first resin body 25a, but the shape of the first resin body 25a does not substantially change. However, in this embodiment, the wedge-shaped recess 25e is formed in the first resin body 25a, and the first resin body 25a is processed into the first resin body 25d.

  Then, 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 steps performed with reference to parts (a) and (b) of FIG. The second resin body 43 is coated with 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 part (d) of FIG. 14, 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 17e 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, the second resin body 43g having the first opening 43f is formed. The recess formed along the first insulating film 23 on the side surface of the waveguide mesa 17 is filled with the embedded portion 43c of the second resin body 43g, and the surface of the embedded portion 43c is located at 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, the opening for electrical connection can be formed by etching the second resin body 43. In this 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, and is, for example, 1.5 micrometers. The first opening width MW1 is 5.0 to 15.0 micrometers, for example 10.0 micrometers. The second opening width MW2 is 3.0 to 13.0 micrometers, for example 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 processes from the steps already described (the steps shown in parts (a) and (b) of FIG. 10) are subsequently applied to this product.

  Part (a) of FIG. 15 is a plan view showing the area of the arm waveguide. Part (b) of FIG. 15 shows a cross section taken along line XVb-XVb shown in part (a) of FIG. 15. The ohmic electrode 51a makes contact with the lower semiconductor region 21a, and the first plated electrode (seed metal layer 39 and metal thick film 35) is provided on the ohmic electrode 51a. The edge of the first plated 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 the side surface of the peripheral edge of the first plated electrode (31a, 35, 39). By covering with BCB, peeling of the electrode can be suppressed. 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 manufactured as the second plating electrode makes contact with the underlying first plating electrode through the opening of the second insulating film 55. The second metal wiring layer 59b is provided around the edge of the second insulating film 55.

  FIG. 16 is a plan view schematically showing an example 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, MZ4 provided in the element area DEV. In this embodiment, the Mach-Zehnder modulators MZ1, MZ2, MZ3 and MZ4 have substantially the same structure. The Mach-Zehnder modulator device 63 includes pad electrodes electrically connected to the Mach-Zehnder modulators MZ1, MZ2, MZ3, 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 the laser light from the optical input IN via the branching device. The outputs of the Mach-Zehnder modulators MZ1 and MZ2 reach the first optical output OUT_X via the multiplexer. The outputs of the Mach-Zehnder modulators MZ3 and MZ4 reach the first optical output OUT_Y via 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.

  Part (a) of FIG. 17 shows a cross section taken along line XVIIa-XVIIa shown in FIG. 16, and part (b) of FIG. 17 is taken along line XVIIb-XVIIb shown in FIG. The cross section taken is shown. The Mach-Zehnder modulator MZ1 includes a waveguide mesa 17, a first insulating film 23, a first resin body 25d, a second resin body 43e, an ohmic electrode 51a, a second insulating film 55, and a metal electrode 59. Equipped with. 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 25d is provided on the first insulating film 23 so as to fill 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 43e and has a first opening 55a located on the ohmic electrode 51a on the upper surface 17e of the waveguide mesa 17. The metal electrode 59 makes 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 this 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 embodiment, those skilled in the art will recognize 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 this embodiment. We therefore claim all modifications and variations coming within the scope and spirit of the claims.

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

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 ... 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 making a Mach-Zehnder modulator,
A waveguide mesa provided on the lower semiconductor region, a first insulating film provided on a side surface and an upper surface of the waveguide mesa, and a side surface and an upper surface of the first insulating film so as to fill the waveguide mesa. A step of 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 upper surface of the waveguide mesa of the first substrate product;
Exposing the first resin body and the first insulating film to plasma of an etchant supplied to a plasma processing apparatus to form an opening on the upper surface of the waveguide mesa in the first insulating film;
After forming the opening 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 to form the first resin body and the second resin body. Embedding the upper surface of the waveguide mesa,
Etching the second resin body to form an opening in the second resin body located on the upper surface of the waveguide mesa;
Forming an ohmic electrode in contact with the upper surface of the waveguide mesa through the opening of the second resin body;
Equipped with
After forming the opening in the first insulating film, the first resin body has a recess along the first insulating film on the side surface of the waveguide mesa,
A method of manufacturing a Mach-Zehnder modulator , wherein in the step of filling the upper surfaces of the first resin body and the waveguide mesa, the second resin body fills the recess . 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 on the ohmic electrode in the second insulating film;
Forming a metal layer on the opening of the second insulating film and on the second insulating film;
Equipped with
The method of manufacturing 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,
The method of manufacturing the Mach-Zehnder modulator is
Etching the first resin body to form an opening on the second portion of the lower semiconductor region in the first resin body before forming the opening in the first insulating film ; ,
Forming a separate ohmic electrode in contact with the second portion through the opening of the first resin body;
Further equipped with,
The method of embedding the first resin body and the upper surface of the waveguide mesa, wherein the second resin body covers the second portion of the lower semiconductor region and the separate ohmic electrode. A method for manufacturing 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 on the separate ohmic electrode by etching the second resin body. The method of making a Mach-Zehnder modulator of claim 3, further comprising the steps of: A Mach-Zehnder modulator,
A waveguide mesa provided on the lower semiconductor region,
A first insulating film provided on the side surfaces of the lower semiconductor region and the waveguide mesa , and having an opening located on the 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;
Together form a contact with the first resin member and the first insulating film, a second resin body having an opening located on said top surface of said 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;
Provided on the second resin member, a second insulating film having an opening positioned on the ohmic electrode on the upper surface of the semiconductor mesa,
A metal electrode that makes contact with the ohmic electrode through the opening of the second insulating film and extends over the second resin body;
Equipped with
The first resin body has a first recess along the insulating film on the side surface of the semiconductor mesa, wherein the second resin body filling the recesses, the Mach-Zehnder modulator.

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