JP2018146669A - Optical semiconductor and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical semiconductor capable of allowing a structure such as a wiring to be formed above an optical waveguide while achieving a satisfactory light confinement effect, and a manufacturing method thereof.SOLUTION: An optical semiconductor 100 includes: a silicon substrate 101 formed with a cavity 118; a silicone oxide film 102 covering the cavity 118; an optical waveguide 107 formed on the silicone oxide film 102 and positioned in the cavity 118 in a plainer view; and clad films 114 and 117 which are formed on the silicone oxide film 102 to cover the optical waveguide 107 at the top and sides thereof including a space 116.SELECTED DRAWING: Figure 1A

Description

  The present invention relates to an optical semiconductor and a manufacturing method thereof.

  Silicon photonics is a technique for manufacturing an optical integrated circuit in which an optical circuit and an electronic circuit are integrated on a silicon substrate, and high functionality, low cost, and low power consumption can be expected. The optical circuit includes an optical waveguide made of silicon and having a small core diameter and a small bending radius, and can be miniaturized and integrated at a high density.

  Although optical waveguide loss occurs in the optical waveguide, an improvement in the optical confinement effect is effective for reducing the optical waveguide loss. The greater the difference in refractive index between the optical waveguide and the cladding film surrounding it, the greater the optical confinement effect. As the refractive index difference is larger, light is more easily reflected at the interface between the optical waveguide and the clad film, and light can be confined in the optical waveguide. Therefore, when silicon having a high refractive index of about 3.50 is used for the optical waveguide, an oxide film having a low refractive index of about 1.46 is mainly used for the cladding film. The oxide film also has an advantage of easy film formation and processing. In recent years, a structure in which air having a refractive index lower than that of an oxide film is provided around the optical waveguide has been proposed for the purpose of further improving the optical confinement effect.

  However, in the conventional structure in which air is provided around the optical waveguide, a structure such as wiring cannot be provided above the optical waveguide while obtaining a sufficient light confinement effect.

JP2015-191031A JP 2006-030733 A JP 2008-026641 A

  An object of the present invention is to provide an optical semiconductor capable of providing a structure such as wiring above an optical waveguide while obtaining a sufficient optical confinement effect, a method for manufacturing the same, and the like.

  In one aspect, the optical semiconductor includes a silicon substrate in which a cavity is formed, a silicon oxide film that covers the cavity, an optical waveguide that is formed on the silicon oxide film and is located inside the cavity in plan view, A clad film formed on the silicon oxide film and covering the optical waveguide from above and from the side through a space.

  In one aspect, an optical module includes the above optical semiconductor and an optical element connected to the optical semiconductor.

  In one aspect, an optical transceiver has the optical module described above.

  In one aspect, an optical semiconductor manufacturing method includes a step of forming an optical waveguide on a silicon oxide film on a silicon substrate, a step of forming a protective film covering the optical waveguide, and the optical waveguide upward and laterally. A step of forming a sacrificial film covering the protective film, a step of forming a first clad film covering the sacrificial film, a step of forming an opening in the first clad film, and the opening Removing the sacrificial film through the step of forming a space inside the first clad film, forming a second clad film on the first clad film, and forming a cavity in the silicon substrate, Forming the optical waveguide so as to be located inside the cavity in plan view.

  Since one side surface includes an appropriate space and a clad film, a structure such as a wiring can be provided above the optical waveguide while obtaining a sufficient light confinement effect.

It is the top view and partially transparent perspective view which show the optical semiconductor which concerns on 1st Embodiment. It is sectional drawing which shows the optical semiconductor which concerns on 1st Embodiment. It is sectional drawing which shows the manufacturing method of the optical semiconductor which concerns on 1st Embodiment in order of a process. It is sectional drawing which shows the manufacturing method of the optical semiconductor which concerns on 1st Embodiment in order of a process following FIG. 2A. FIG. 2B is a cross-sectional view illustrating the optical semiconductor manufacturing method according to the first embodiment in the order of steps, following FIG. 2B. It is sectional drawing which shows the optical semiconductor which concerns on 2nd Embodiment. It is sectional drawing which shows the optical semiconductor which concerns on 3rd Embodiment. It is a top view which shows the spot size converter which concerns on 4th Embodiment. It is sectional drawing and a partially transparent perspective view which show the spot size converter which concerns on 4th Embodiment. It is a partially transparent perspective view and sectional drawing which show the optical semiconductor which concerns on 5th Embodiment. It is sectional drawing which shows the manufacturing method of the optical semiconductor which concerns on 5th Embodiment in process order. FIG. 7B is a cross-sectional view illustrating the optical semiconductor manufacturing method according to the fifth embodiment in the order of steps, following FIG. 7A. FIG. 7B is a cross-sectional view illustrating the optical semiconductor manufacturing method according to the fifth embodiment in the order of steps, following FIG. 7B. It is the top view and partially transparent perspective view which show the optical semiconductor which concerns on 6th Embodiment. It is sectional drawing which shows the optical semiconductor which concerns on 6th Embodiment. It is the top view and partially transparent perspective view which show the optical semiconductor which concerns on 7th Embodiment. It is a top view which shows the clad film in 1st Embodiment. It is a block diagram which shows the optical transceiver which concerns on 8th Embodiment. It is sectional drawing which shows the clad film of a laminated structure. It is sectional drawing which shows the example of the clad film of a single layer structure. It is a figure which shows the other example of the clad film of a single layer structure.

  Hereinafter, embodiments will be described in detail with reference to the accompanying drawings.

(First embodiment)
First, the first embodiment will be described. The first embodiment is an example of an optical semiconductor. 1A and 1B are diagrams illustrating an optical semiconductor according to the first embodiment. FIG. 1A (a) is a plan view, and FIG. 1A (b) is a partially transparent perspective view. 1B (c) is a cross-sectional view taken along line II in FIG. 1A (a), and FIG. 1B (d) is a cross-sectional view taken along line II-II in FIG. 1A (a).

  As shown in FIGS. 1A and 1B, the optical semiconductor 100 according to the first embodiment includes a silicon (Si) substrate 101 in which a cavity 118 is formed, a Si oxide film 102 covering the cavity 118, and a Si oxide film. The Si optical waveguide 107 formed on the Si layer 102 and located inside the cavity 118 in plan view, and the cladding film 114 formed on the Si oxide film 102 and covering the Si optical waveguide 107 from above and from the side through the space 116. And 117.

  The cladding film 114 includes a Si oxide film 112 and a Si nitride film 113. The space 116 is formed in a tunnel shape inside the cladding film 114 (on the Si optical waveguide 107 side). As shown in FIG. 1A (a), an opening 115 is formed in the cladding film 114 except for both ends in the longitudinal direction of the Si optical waveguide 107, and the cladding film 117 is also formed below the opening 115. Has been. The Si optical waveguide 107 is covered with a Si oxide film 106. The Si oxide film 106 is an example of a protective film.

  In the optical semiconductor 100, the Si optical waveguide 107 is surrounded by the Si oxide films 102 and 106, and the outside is a cavity 118 or a space 116. Therefore, an excellent optical confinement effect can be obtained, and the optical waveguide loss can be sufficiently reduced. Since the clad films 114 and 117 are included, a structure such as a wiring can be provided thereon. Since there is a space 116 between the cladding films 114 and 117 and the Si optical waveguide 107, the optical confinement effect is not reduced by the cladding films 114 and 117. The space 116 prevents impurities from entering the Si optical waveguide 107 from structures such as wiring. Since the cavity 118 is formed and no light leakage from the Si optical waveguide 107 to the Si substrate 101 occurs, the Si oxide film 102 may be thin.

  Next, a method for manufacturing the optical semiconductor 100 according to the first embodiment will be described. 2A to 2C are cross-sectional views illustrating the method of manufacturing the optical semiconductor 100 according to the first embodiment in the order of steps.

  First, as shown in FIG. 2A, an Si oxide film 105 is formed on the back surface of an SOI (Silicon on Insulator) substrate 101 including an Si substrate 101, an Si oxide film 102, and an Si layer 103. The Si oxide film 105 contributes to suppression of warpage of the SOI substrate 104.

  Next, as shown in FIG. 2A (b), the Si layer 103 is patterned to form the Si optical waveguide 107.

  Thereafter, as shown in FIG. 2A (c), a Si oxide film 106 covering the Si optical waveguide 107 is formed. The thickness of the Si oxide film 106 is about 5 nm to 20 nm, and preferably 10 nm or less. For example, the Si oxide film 106 can be formed by a thermal oxidation method.

  Subsequently, as shown in FIG. 2B (d), a Si film 111 is formed in a portion where the space 116 is to be formed. The thickness of the Si film 111 is about 500 nm to 1000 nm. The Si film 111 can be formed by, for example, forming a Si film by chemical vapor deposition (CVD) or sputtering, forming a mask by photolithography, and dry etching the Si film. The Si film 111 is, for example, a single crystal Si film, a polycrystalline Si film, or an amorphous Si film. The Si film 111 is an example of a sacrificial film.

  Next, as shown in FIG. 2B (e), a Si oxide film 112 and a Si nitride film 113 covering the Si film 111 are formed. The thickness of the clad film 114 is preferably 1000 nm or less. For example, the thickness of the Si oxide film 112 is about 100 nm to 200 nm, the thickness of the Si nitride film 113 is about 100 nm to 200 nm, and the thickness of the cladding film 114 including the Si oxide film 112 and the Si nitride film 113 is It is about 200 nm to 300 nm. For example, the Si oxide film 112 and the Si nitride film 113 can be formed by a CVD method or a sputtering method. The cladding film 114 includes a roof portion 114 a on the upper surface of the Si film 111 and a wall portion 114 b on the side surface of the Si film 111. Either the Si oxide film 112 or the Si nitride film 113 may be formed first.

  Thereafter, as shown in FIG. 2B (f), an opening 115 is formed in the cladding film 114. For example, the opening 115 is formed in the vicinity of the boundary between the cladding 114 and the wall 114 b of the roof 114 a except for both ends in the longitudinal direction of the Si optical waveguide 107. The opening 115 can be formed by, for example, forming a mask by photolithography and etching the cladding film 114.

  Subsequently, as shown in FIG. 2C (g), the Si film 111 is removed by dry etching. As a result, a space 116 is formed in a tunnel shape inside the cladding film 114. Since the Si optical waveguide 107 is covered with the Si oxide film 106, it is not etched. That is, the Si oxide film 106 functions as a protective film. As an etching gas, it is desirable to use a gas having a high etching selection ratio between the cladding film 114 and the Si film 111, such as xenon fluoride gas.

  Next, as shown in FIG. 2C (h), a clad film 117 is formed on the clad film 114. For example, the cladding film 117 is a Si oxide film. The thickness of the cladding film 117 is preferably larger than the height of the space 116. For example, the cladding film 117 can be formed by a CVD method.

  Thereafter, as shown in FIG. 2C (i), a cavity (cavity) 118 having a width larger than that of the Si optical waveguide 107 is formed in the Si oxide film 105 and the Si substrate 101. The cavity 118 can be formed by, for example, forming a mask by photolithography, and dry etching or wet etching. As the dry etching, for example, deep reactive ion etching (Deep RIE) is performed. In wet etching, for example, a potassium hydroxide (KOH) aqueous solution is used. If the Si optical waveguide 107 is inside the cavity 118 in plan view, the side surface of the cavity 118 may be perpendicular to the surface of the Si substrate 101 or may be inclined. That is, the cavity 118 may be formed in a tapered shape.

  In this way, the optical semiconductor 100 according to the first embodiment can be manufactured.

(Second Embodiment)
Next, a second embodiment will be described. The second embodiment is an example of an optical semiconductor. FIG. 3 is a cross-sectional view showing an optical semiconductor according to the second embodiment.

  As shown in FIG. 3, the optical semiconductor 200 according to the second embodiment includes a filling film 201 filled in the cavity 118. The filling film 201 includes an organic material or an inorganic material that hardly absorbs light, such as benzocyclobutene (BCB), polyimide resin, and spin on glass (SOG). Other configurations are the same as those of the first embodiment.

  According to the second embodiment, the same effect as that of the first embodiment can be obtained. Further, since the filling film 201 is formed, mounting on a printed wiring board is easy.

(Third embodiment)
Next, a third embodiment will be described. The third embodiment is an example of an optical semiconductor. FIG. 4 is a cross-sectional view showing an optical semiconductor according to the third embodiment.

  As shown in FIG. 4, in the optical semiconductor 300 according to the third embodiment, the substrate 301 is bonded to the Si oxide film 105 via the Si oxide film 302 while maintaining the cavity 118. Other configurations are the same as those of the first embodiment.

  According to the third embodiment, the same effect as that of the first embodiment can be obtained. Moreover, since the board | substrate 301 is bonded together, the mounting to a printed wiring board is easy.

(Fourth embodiment)
Next, a fourth embodiment will be described. The fourth embodiment is an example of a spot size converter. 5A and 5B are diagrams showing a spot size converter according to the fourth embodiment. 5A (a) is a plan view, FIG. 5B (b) is a cross-sectional view taken along the line II in FIG. 5A (a), and FIG. 5B (c) is a partially transparent perspective view.

  As shown in FIGS. 5A and 5B, the spot size converter 400 according to the fourth embodiment includes a Si substrate 101 in which a cavity 118 is formed, a Si oxide film 102 covering the cavity 118, and a Si oxide film 102. An optical waveguide 403 formed on the inner side of the cavity 118 in plan view, and cladding films 114 and 117 formed on the Si oxide film 102 and covering the optical waveguide 403 from above and from the side through the space 116; , Is included. The optical waveguide 403 includes a Si optical waveguide 401 including a portion having a tapered planar shape, and a SiOC optical waveguide 402 covering the Si optical waveguide 401.

  According to the fourth embodiment, the same effect as that of the first embodiment can be obtained. Therefore, the optical coupling efficiency in connection with a semiconductor laser (laser diode) and an optical fiber can be improved.

(Fifth embodiment)
Next, a fifth embodiment will be described. The fifth embodiment is an example of a rib-type optical semiconductor. FIG. 6 is a diagram illustrating an optical semiconductor according to the fifth embodiment. 6A is a partially transparent perspective view, and FIG. 6B is a cross-sectional view.

  As shown in FIG. 6, in the optical semiconductor 500 according to the fifth embodiment, instead of the Si optical waveguide 107, a Si optical waveguide 501 and a silicon film 503 provided with a rib portion 502 thinner than the Si optical waveguide 501 are provided. included. The silicon film 503 is equivalent to a rib-type optical waveguide. A Si oxide film 504 is included instead of the Si oxide film 106, and the silicon film 503 is covered with the Si oxide film 504. Openings 511 reaching the ribs 502 are formed in the cladding film 117, the cladding film 114, and the Si oxide film 504, and wirings 512 that are electrically connected to the ribs 502 through the openings 511 are formed. A part of the wiring 512 is in the opening 511, and the other part is on the cladding film 117. Other configurations are the same as those of the first embodiment. The Si oxide film 504 is an example of a protective film.

  According to the fifth embodiment, the same effect as that of the first embodiment can be obtained. In addition, since current can be injected and voltage can be applied through the wiring 512, it can be applied to an optical device element such as a silicon modulator.

  Next, a method for manufacturing the optical semiconductor 500 according to the fifth embodiment will be described. 7A to 7C are cross-sectional views illustrating the method of manufacturing the optical semiconductor 500 according to the fifth embodiment in the order of steps.

  First, as shown in FIG. 7A (a), a Si oxide film 105 is formed on the back surface of an SOI substrate 104 including a Si substrate 101, a Si oxide film 102, and a Si layer 103, as in the first embodiment.

  Next, as shown in FIG. 7A (b), the Si layer 103 is patterned to form a silicon film 503 having Si optical waveguides 501 and rib portions 502.

  Thereafter, as shown in FIG. 7A (c), a Si oxide film 504 covering the Si optical waveguide 501 is formed. The thickness of the Si oxide film 504 is about 5 nm to 20 nm, and preferably 10 nm or less. For example, the Si oxide film 504 can be formed by a thermal oxidation method.

  Subsequently, as shown in FIG. 7B (d), processing up to the formation of the cladding film 117 is performed in the same manner as in the first embodiment.

  Next, as shown in FIG. 7B (e), openings 511 reaching the ribs 502 are formed in the cladding film 117, the cladding film 114, and the Si oxide film 504. The opening 511 can be formed by, for example, forming a mask by photolithography and etching the cladding film 117 and the like.

  Subsequently, as shown in FIG. 7C (f), a wiring 512 electrically connected to the rib portion 502 through the opening 511 is formed. A part of the wiring 512 is formed in the opening 511, and the other part is formed on the cladding film 117. The wiring 512 can be formed by, for example, forming a metal film such as a Cu film, an Al film, or an Al alloy film, forming a mask by photolithography, and dry etching the metal film.

  Next, as shown in FIG. 7C (g), cavities 118 are formed in the Si oxide film 105 and the Si substrate 101 in the same manner as in the first embodiment.

  In this way, the optical semiconductor 500 according to the fifth embodiment can be manufactured.

(Sixth embodiment)
Next, a sixth embodiment will be described. The sixth embodiment is an example of a side lattice type optical semiconductor. 8A and 8B are diagrams showing an optical semiconductor according to the sixth embodiment. FIG. 8A (a) is a plan view showing an optical waveguide, and FIG. 8A (b) is a partially transparent perspective view. 8B (c) is a cross-sectional view taken along line II in FIG. 8A (a), and FIG. 8B (d) is a cross-sectional view taken along line II-II in FIG. 8A (a).

  As shown in FIGS. 8A and 8B, the optical semiconductor 600 according to the sixth embodiment includes a silicon film 604 provided with a Si optical waveguide 601, a lattice waveguide 602, and a connection portion 603 instead of the Si optical waveguide 107. Is included. The silicon film 604 is equivalent to a side grating type optical waveguide. A Si oxide film 606 is included instead of the Si oxide film 106, and the silicon film 604 is covered with the Si oxide film 606. An opening 611 that reaches the connection portion 603 is formed in the cladding film 117, the cladding film 114, and the Si oxide film 606, and a wiring 612 that is electrically connected to the connection portion 603 through the opening 611 is formed. A part of the wiring 612 is in the opening 611, and the other part is on the cladding film 117. A lattice waveguide 602 connects the Si optical waveguide 601 and the connection portion 603. Other configurations are the same as those of the first embodiment. The Si oxide film 606 is an example of a protective film.

  According to the sixth embodiment, the same effect as that of the first embodiment can be obtained. In addition, since current can be injected and voltage can be applied through the wiring 612, it can be applied to an optical device element such as a silicon modulator.

(Seventh embodiment)
Next, a seventh embodiment will be described. The seventh embodiment is an example of an optical semiconductor. FIG. 9 is a diagram illustrating an optical semiconductor according to the seventh embodiment. FIG. 9A is a plan view showing a clad film, and FIG. 9B is a partially transparent perspective view. FIG. 10 is a plan view showing the clad film 114 in the first embodiment.

  In the first embodiment, as shown in FIG. 10, the opening 115 is formed in the cladding film 114 except for both ends in the longitudinal direction of the Si optical waveguide 107. In contrast, in the optical semiconductor 700 according to the seventh embodiment, as shown in FIG. 9, a plurality of openings 715 are formed in the cladding film 114, and the openings adjacent to each other in the longitudinal direction of the Si optical waveguide 107. Between 715 there are beams 716. Other configurations are the same as those of the first embodiment.

  According to the seventh embodiment, the same effect as that of the first embodiment can be obtained. Further, since the beam 716 supports the roof portion 114a of the cladding film 114, the mechanical strength of the cladding film 114 is improved, and deformations such as warpage, bending, and breakage of the roof portion 114a can be more reliably suppressed. The deformation of the roof portion 114a may occur, for example, when the Si film 111 is removed and the space 116 is formed, or when the cladding film 117 is formed.

  The beam 716 can be formed by changing the mask pattern used when forming the opening 115 in the first embodiment. The greater the number of beams 716 and the larger the area of the beams 716, the higher the mechanical strength.

  In the second to sixth embodiments, a beam may be provided on the clad film 114 as in the seventh embodiment.

(Eighth embodiment)
Next, an eighth embodiment will be described. The eighth embodiment is an example of an optical transceiver. FIG. 11 is a block diagram showing an optical transceiver according to the eighth embodiment.

  As shown in FIG. 11, the optical transceiver 800 according to the eighth embodiment includes a control circuit 801, a light receiving module 802, and a light emitting module 803. The light receiving module 802 includes an input port and a photodiode (Photo Diode: PD), and the optical semiconductor according to any one of the first to seventh embodiments is provided between the input port and the PD. The light emitting module 803 includes an output port and a laser diode (LD), and the optical semiconductor according to any one of the first to seventh embodiments is provided between the output port and the LD. The light receiving module 802 and the light emitting module 803 are controlled by the control circuit 801.

  Since the light receiving module 802 and the light emitting module 803 include the optical semiconductor of any of the first to seventh embodiments, a structure such as a wiring is provided above the Si optical waveguide while sufficiently reducing the optical waveguide loss. be able to.

  One of the Si oxide film 112 and the Si nitride film 113 may be omitted, but it is preferable to form both of them as in the first to seventh embodiments. This is because internal stress acting in opposite directions acts on the Si oxide film 112 and the Si nitride film 113, and the internal stress acting on the cladding film 114 can be offset. For example, as shown in FIG. 12A, when the Si oxide film 112 and the Si nitride film 113 are formed, compressive stress acts on the Si oxide film 112, and tensile stress acts on the Si nitride film 113. Thereafter, as shown in FIG. 12B, even if the Si film 111 is removed and the space 116 is formed, the compressive stress and the tensile stress cancel each other, and the deformation of the cladding film 114 due to the internal stress hardly occurs. Therefore, as shown in FIG. 12C, the shape of the clad film 114 can be easily maintained.

  As shown in FIG. 13A, when the formation of the Si oxide film 112 is omitted, as shown in FIG. 13B, when the space 116 is formed by removing the Si film 111, the Si nitride film 113 is formed. The tensile stress acts strongly on the roof portion 114a, and the roof portion 114a is easily bent downward as shown in FIG. Therefore, as shown in FIG. 13D, when the wall 114b is low, the roof 114a may come into contact with the Si oxide film 106.

  As shown in FIG. 14A, when the formation of the Si nitride film 113 is omitted, as shown in FIG. 14B, when the space 116 is formed by removing the Si film 111, the Si oxide film 112 is formed. The compressive stress acts strongly on the roof portion 114a, and the roof portion 114a tends to warp upward as shown in FIG. Therefore, as shown in FIG. 14D, excessive stress may act on the connecting portion between the roof portion 114a and the wall portion 114b to cause damage.

  Therefore, the cladding film 114 preferably includes the Si oxide film 112 and the Si nitride film 113. When one of the Si oxide film 112 and the Si nitride film 113 is omitted, it is preferable to provide a beam as in the seventh embodiment in order to ensure mechanical strength.

  Hereinafter, various aspects of the present invention will be collectively described as supplementary notes.

(Appendix 1)
A silicon substrate in which a cavity is formed;
A silicon oxide film covering the cavity;
An optical waveguide formed on the silicon oxide film and positioned inside the cavity in plan view;
A cladding film formed on the silicon oxide film and covering the optical waveguide from above and from the side through a space;
An optical semiconductor comprising:

(Appendix 2)
2. The optical semiconductor according to appendix 1, wherein the optical semiconductor has a filling film provided in the cavity and having a refractive index lower than that of silicon.

(Appendix 3)
3. The optical semiconductor according to appendix 1 or 2, wherein the optical semiconductor has a substrate attached to the back surface of the silicon substrate.

(Appendix 4)
The optical semiconductor according to any one of appendices 1 to 3, wherein the optical waveguide has a portion whose size narrows toward one end thereof.

(Appendix 5)
Having a silicon film including the optical waveguide;
5. The optical semiconductor according to any one of appendices 1 to 4, further comprising a wiring connected to the silicon film.

(Appendix 6)
The optical semiconductor according to appendix 5, wherein the silicon film is thinner than the optical waveguide and includes a rib portion connected to the wiring.

(Appendix 7)
The silicon film is
A connecting portion connected to the wiring;
A grating waveguide connecting the optical waveguide and the connecting portion;
The optical semiconductor according to appendix 5, characterized by comprising:

(Appendix 8)
The cladding film is
A first film on which internal stress in a first direction acts;
A second film laminated on the first film and subjected to internal stress in a second direction opposite to the first direction;
8. The optical semiconductor according to any one of appendices 1 to 7, wherein:

(Appendix 9)
The optical semiconductor according to any one of appendices 1 to 8,
An optical element connected to the optical semiconductor;
An optical module comprising:

(Appendix 10)
An optical transceiver comprising the optical module according to appendix 9.

(Appendix 11)
Forming an optical waveguide on a silicon oxide film on a silicon substrate;
Forming a protective film covering the optical waveguide;
Forming a sacrificial film covering the optical waveguide from above and from the side around the protective film;
Forming a first clad film covering the sacrificial film;
Forming an opening in the first cladding film;
Removing the sacrificial film through the opening to form a space inside the first cladding film;
Forming a second cladding film on the first cladding film;
Forming a cavity in the silicon substrate such that the optical waveguide is located inside the cavity in plan view;
A method for producing an optical semiconductor, comprising:

100, 200, 300, 500, 600, 700: Optical semiconductor 400: Spot size converter 101: Si substrate 102: Si oxide film 106: Si oxide film 107, 501, 601: Optical waveguide 114, 117: Clad film 115: Opening 116: Space 118: Cavity

Claims (9)

A silicon substrate in which a cavity is formed;
A silicon oxide film covering the cavity;
An optical waveguide formed on the silicon oxide film and positioned inside the cavity in plan view;
A cladding film formed on the silicon oxide film and covering the optical waveguide from above and from the side through a space;
An optical semiconductor comprising:   The optical semiconductor according to claim 1, further comprising a filling film provided in the cavity and having a refractive index lower than that of silicon.   The optical semiconductor according to claim 1, further comprising a substrate attached to a back surface of the silicon substrate.   4. The optical semiconductor according to claim 1, wherein the optical waveguide has a portion whose size narrows toward one end thereof. 5. Having a silicon film including the optical waveguide;
The optical semiconductor according to claim 1, further comprising a wiring connected to the silicon film. The cladding film is
A first film on which internal stress in a first direction acts;
A second film laminated on the first film and subjected to internal stress in a second direction opposite to the first direction;
The optical semiconductor according to claim 1, comprising: The optical semiconductor according to any one of claims 1 to 6,
An optical element connected to the optical semiconductor;
An optical module comprising:   An optical transceiver comprising the optical module according to claim 7. Forming an optical waveguide on a silicon oxide film on a silicon substrate;
Forming a protective film covering the optical waveguide;
Forming a sacrificial film covering the optical waveguide from above and from the side around the protective film;
Forming a first clad film covering the sacrificial film;
Forming an opening in the first cladding film;
Removing the sacrificial film through the opening to form a space inside the first cladding film;
Forming a second cladding film on the first cladding film;
Forming a cavity in the silicon substrate such that the optical waveguide is located inside the cavity in plan view;
A method for producing an optical semiconductor, comprising:

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