JP3808804B2 - Optical waveguide structure and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical waveguide structure and a manufacturing method thereof, and more particularly, to an optical waveguide structure and a manufacturing method thereof in an optical semiconductor device for transmission or reception in optical communication.
[0002]
[Prior art]
In response to a rapid increase in Internet demand, etc., there is an urgent need to expand communication capacity. As a method of expanding the communication capacity in optical communication, a time division multiplexing (TDM) system that multiplexes a plurality of signals by increasing the processing speed of each communication and a wavelength multiplexing that multiplexes signals using a plurality of different wavelengths. (WDM) schemes have been proposed. When the TDM system is adopted, it is inevitably necessary to increase the speed of the signal flowing in the fiber, but efforts are currently being made to increase from 10 Gbit / s to 40 Gbit / s. In the future, this communication speed will inevitably increase.
[0003]
Although it is technically difficult to input / output a 40 Gbit / s electric signal to / from a semiconductor integrated circuit (IC) contained in a package, it has been achieved at present. However, when the speed of the electric signal is about 60 Gbit / s or more, the loss increases and it becomes extremely difficult to input / output the signal to / from the package. In order to solve this problem, a high-speed signal of 60 Gbit / s or higher is input / output as an optical signal, and only a low-speed signal of 60 Gbit / s or lower is electrically input / output. R & D is underway.
[0004]
In situations where the communication speed has been increased and it is difficult for electrical signals to enter the package, high-speed signals are input / output with light, and only signals that have been speed-converted within the package are input / output with electricity to limit the mounting limit. It is possible to break down.
[0005]
In a semiconductor device that requires such an ultra-high-speed optical interface, it is not easy to align the optical element and the input / output terminal of the external optical signal. Therefore, the optical waveguide is also provided on the chip integrated on the semiconductor device. It has been proposed to form a structure. As one method for producing an optical waveguide in a semiconductor device, a V-shaped groove is formed by crystal facets of a semiconductor substrate material 1 as shown in FIGS. 1A and 1B, and cladding is formed in the V-shaped groove. A structure in which an optical waveguide structure composed of a layer 2 and a core layer 3 is embedded has been proposed (see, for example, Japanese Patent Application No. 2000-222988). 1A is a perspective view, FIG. 1B is a cross-sectional view, and reference numeral 4 in the drawing indicates a photodiode.
[0006]
[Problems to be solved by the invention]
In general, since the refractive index of a semiconductor material is large, in a structure in which a semiconductor substrate is engraved and an optical waveguide structure is embedded in the groove, it is necessary to increase the thickness of the lower cladding layer so that the influence of the substrate cannot be seen. is there. When the optical waveguide structure is embedded in the groove, an inorganic material film is usually used for the clad layer and an organic material is used for the core layer. Therefore, both are made of a material having a refractive index lower than that of the semiconductor substrate. .
[0007]
In order to reduce the propagation loss of the optical waveguide, it is necessary to completely confine the optical signal in the optical waveguide without leakage to the semiconductor substrate side. However, if the thickness of the cladding layer is not sufficient, leakage to the semiconductor substrate will occur. appear. In order to prevent signal light from leaking to the semiconductor substrate, a clad film having two to three times or more of the wavelength used is required. However, when using an optical signal in the 1.55 μm band, this thickness is 3 to 5 μm or more. Therefore, using an inorganic insulating film compost method such as sputtering generally used in a semiconductor process, only the inside of the groove is used. It was not easy to form a clad layer.
[0008]
When such a thick inorganic film is formed on the entire surface of the semiconductor substrate, an optical waveguide is formed as an optical interface on the ultrahigh-speed OEIC chip in order to induce warpage distortion in the semiconductor wafer due to the stress of the inorganic film. In this case, there is a concern that the characteristics of the electronic circuit and the like are deteriorated. For this reason, there is a limit to the thickness of the cladding layer that can be formed inside the groove. Therefore, in the structure in which the optical waveguide structure is embedded inside the semiconductor substrate, an organic material similar to the core material of the optical waveguide is used to form the surface of the substrate. There has been a problem that propagation loss is increased as compared with the formed organic rectangular optical waveguide or rib-type optical waveguide.
[0009]
The present invention has been made in view of such problems, and the object of the present invention is to reduce the leakage of light to the semiconductor substrate without increasing the thickness of the cladding layer and to reduce the propagation loss of the optical waveguide. It is an object of the present invention to provide an optical waveguide structure and a method for manufacturing the same.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, in the optical waveguide structure in which the optical waveguide is embedded in the semiconductor substrate, the optical waveguide is disposed in a peripheral portion along the longitudinal direction of the optical waveguide. A groove structure having a groove for providing a space between a beam portion for holding a waveguide and the semiconductor substrate and the optical waveguide is provided , and the groove has a refractive index smaller than that of the semiconductor substrate. Material or air is provided .
[0011]
According to a second aspect of the present invention, in the first aspect of the present invention, the plurality of beam portions and the plurality of grooves are formed so that the groove structure surrounds the optical waveguide embedded in the semiconductor substrate. It is formed.
[0012]
According to a third aspect of the invention, in the invention of the first or second aspect, the refractive index of the filling material provided in the groove is smaller than the refractive index of the clad layer constituting the optical waveguide. Features.
[0013]
Further, the invention according to claim 4, in the invention described in any one of claims 1 to 3, the refractive index of the filler material provided in the groove is smaller than the refractive index of the core layer of the optical waveguide, wherein A filling material is provided as an upper cladding layer of the optical waveguide .
[0014]
The invention according to claim 5 is the invention according to any one of claims 1 to 4 , wherein the filling material is an organic material .
[0015]
The invention according to claim 6 is the invention according to claim 5, wherein the optical waveguide has a spot size conversion structure whose width changes so as to expand toward the end. .
[0016]
The invention according to claim 7 is a method of manufacturing an optical waveguide structure , wherein the optical waveguide is embedded in the semiconductor substrate using an etching solution in the method of manufacturing an optical waveguide structure in which the optical waveguide is embedded in a semiconductor substrate. A step of forming a first groove for embedding, a step of forming the optical waveguide in the groove, and an etching solution for the semiconductor substrate on the periphery in the longitudinal direction of the optical waveguide. Forming a groove structure including a plurality of beam portions to be held and a plurality of second grooves for providing a space between the semiconductor substrate and the optical waveguide;
It is provided with.
[0017]
The invention according to claim 8 is the invention according to claim 7 , wherein a filling material having a refractive index smaller than the refraction of the semiconductor substrate is provided in the groove formed in the peripheral portion of the optical waveguide. A process is provided.
[0018]
The invention according to claim 9 is the invention according to claim 8, wherein the filling material is an organic material .
[0020]
As described above, according to the present invention, in the structure in which the optical waveguide is embedded in the semiconductor substrate, the peripheral semiconductor substrate is removed while leaving the beam portion holding the optical waveguide structure. Thereby, even if the thickness of the cladding layer is not sufficient, it is possible to effectively reduce the influence of the high refractive index of the semiconductor substrate, and it is possible to reduce the propagation loss. When the beam portion is periodically formed, the influence of interference and reflection can be excluded in particular by selecting the period length in consideration of the wavelength of light used.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[Example 1]
FIG. 2 is a perspective view for explaining the first embodiment of the optical waveguide structure of the present invention, and is a conceptual diagram of a portion for supplying an optical signal to a photodiode on the OEIC using the optical waveguide structure of the present invention. Is shown. In the figure, reference numeral 11 is a semiconductor substrate, 12 is a clad layer constituting an optical waveguide, 13 is a core layer constituting the optical waveguide, 14 is a photodiode for receiving signal light, 15 is a beam portion for holding the optical waveguide, Reference numeral 16 denotes a groove for effectively reducing the influence of the high refractive index of the semiconductor substrate 11.
[0022]
A groove structure embedded in the semiconductor substrate 11 and having a plurality of beam portions 15 and a plurality of grooves 16 sufficient to maintain the optical waveguide is provided in the peripheral portion along the longitudinal direction of the optical waveguide composed of the cladding layer 12 and the core layer 13. Is formed.
[0023]
3A and 3B are cross-sectional views perpendicular to the optical signal propagation direction of the optical waveguide along the lines AA ′ and BB ′ in FIG. Here, a structure is shown in which the formation position of the beam portion 15 for holding the optical waveguide is formed at the same position on the left and right of the optical waveguide. Of course, there is no problem even if the optical waveguide is held in any arrangement.
[0024]
Here, the core layer 13 and the clad layer 12 are formed only inside the V-shaped groove, but it goes without saying that the structure may be formed even above the V-shaped groove. Moreover, although a cross-sectional structure is V-shaped, a cup-type structure with a flat groove bottom may be used. Here, the cladding layer 12 is made of an inorganic insulating material, and the core layer 13 is made of an organic polymer material.
[0025]
Specifically, as an inorganic insulating material, a deposited film such as silicon dioxide formed by sputtering or chemical vapor deposition (CVD) is applied, and as an organic polymer material, spin coating is applied, and then heat or ultraviolet rays are applied. Resin cured (cured) by (UV). In the present invention, it goes without saying that these materials and formation methods are not particularly limited.
[0026]
The length and width of the beam portion for holding the optical waveguide structure and the interval to be formed are not particularly limited, but it is desirable that the structure length does not cross the utilized optical signal wavelength. Similarly, the length and width of the groove for effectively reducing the influence of the high refractive index of the semiconductor substrate is not particularly limited, but the structure length of the groove does not interact with the utilized optical signal wavelength. Needless to say, it is desirable. Moreover, although the anisotropic etching shape is illustrated as the cross-sectional structure of the groove, the cross-sectional shape is not particularly limited as long as a space is provided between the cross-section of the optical waveguide and the semiconductor substrate.
[0027]
[Example 2]
FIG. 4 is a cross-sectional view for explaining a second embodiment of the optical waveguide structure of the present invention. In the figure, reference numeral 17 denotes an organic material. Grooves formed in the periphery of the optical waveguide are filled with an organic material 17 or the like. The filling material needs to have a refractive index smaller than that of the semiconductor substrate on which the optical waveguide structure is fabricated. Further, it is more desirable if the refractive index of the filling material is smaller than the refractive index of the cladding material constituting the optical waveguide, but there is no particular limitation.
[0028]
When the refractive index of the filling material is smaller than the refractive index of the core material of the optical waveguide, it can be used as the upper cladding layer 18 of the optical waveguide as shown in FIG.
[0029]
[Example 3]
6A to 6H are process diagrams for explaining the method of manufacturing the optical waveguide structure according to the present invention. FIGS. 6A to 6D are cross-sectional views, and FIGS. It is a perspective view corresponding to sectional drawing. Here, the semiconductor substrate to be used is described as a (100) plane InP substrate.
[0030]
First, after forming a resist pattern for a groove for forming an optical waveguide structure on a semiconductor substrate by a normal semiconductor process, anisotropic wet etching is performed with an acid or a mixture thereof (FIGS. 6A and 6B). e)). When the groove structure is formed using wet etching, when performing anisotropic etching, the surface index of the substrate and the crystal facet formed by the etching solution are different.
[0031]
When a (100) plane InP substrate is used as the semiconductor substrate and an etching solution containing about several percent bromine in methanol is used, the groove perpendicular to the (01-1) plane is formed in the depth direction. A forward mesa surface (specifically, a (111) plane and a (1-1-1) plane) is formed such that the width is reduced. Further, with respect to the direction perpendicular to the (0-1-1) plane, the reverse mesa plane (specifically, the (-11-1) plane and (-1-11) whose groove width increases in the depth direction). Surface) is formed.
[0032]
Therefore, in order to obtain the structure as shown in FIG. 3, a desired mesa surface can be formed by making the longitudinal direction of the optical waveguide perpendicular to the (01-1) plane. In addition to the above, other etchants that give such a shape are known, such as odorous acid (HBr) stock solution or a mixture of odorous acid and hydrogen peroxide, but are not particularly limited here. After removing the resist mask, a clad layer of an inorganic insulating film is formed in the previously formed etching groove. Here, the inorganic insulating film can be formed by sputtering, chemical vapor deposition (CVD), or the like.
[0033]
The film formed other than the groove may be removed by a lift-off method, a reactive ion beam etching (RIE) method or the like, and the inorganic insulating film deposition method can be any method that can form a clad layer. However, it goes without saying that it is also possible (FIGS. 6B and 6F).
[0034]
Subsequently, a core layer made of an organic polymer material is formed by spin coating or the like (FIGS. 6C and 6G). Here, the organic polymer material is an organic polymer resin such as polyimide, BCB (benzocyclobutene), organosilicon polymer, and epoxy resin, which are usually used as a planar flat material in the field of electronic devices. After the organic material film is formed, the core material is cured (cured) with heat or ultraviolet light (UV). It is also possible to remove an unnecessary portion of the organic polymer material in the same manner as the cladding layer, and this removing step may be performed simultaneously with that of the lower cladding layer.
[0035]
Thereafter, a resist pattern for forming a groove structure is formed in the periphery of the optical waveguide, and then wet etching is performed again (FIGS. 6D and 6H). The etching here may be anisotropic or isotropic, but it is necessary that the etching solution does not erode the cladding layer.
[0036]
As for the optical waveguide, as shown in FIGS. 7A to 7H, a part of the spot size conversion structure 19, that is, a portion where the width of the optical waveguide changes so as to expand toward the end. Needless to say, it can be produced in the same manner even if it exists. 7A to 7D are perspective views, and FIGS. 7E to 7H are top views corresponding to the perspective views.
[0037]
[Example 4]
Hereinafter, the second manufacturing method of the optical waveguide structure of the present invention will be described. After the groove 16 is formed outside the optical waveguide according to the manufacturing method described in the third embodiment, an organic material having a refractive index smaller than that of the semiconductor substrate is applied to fill the groove 16. Here, ideally, it is desirable that the inside of the groove is completely filled. However, even if the filling is not complete and bubbles remain inside, there is no particular problem as long as large irregularities do not occur on the surface portion.
[0038]
Then, it is completed by curing (curing) with heat or ultraviolet rays (UV). If the refractive index of the filling material is smaller than that of the core material, it may be formed not only inside the groove but also on the upper surface of the optical waveguide forming portion.
[0039]
【The invention's effect】
As described above, according to the present invention, in the optical waveguide structure in which the optical waveguide is embedded in the semiconductor substrate, the groove structure including the beam portion and the groove is provided in the peripheral portion along the longitudinal direction of the optical waveguide. In an optical waveguide embedded in a semiconductor substrate with a large refractive index, it is possible to reduce light leakage to the semiconductor substrate and reduce the propagation loss of the optical waveguide without increasing the thickness of the cladding layer. is there. In particular, when an optical waveguide is formed as an optical interface in a part of an ultra-high speed OEIC, it is possible to realize a low-loss optical waveguide without greatly affecting an electronic circuit or the like.
[Brief description of the drawings]
1A and 1B are diagrams showing a conventional structure in which an optical waveguide is embedded in a semiconductor substrate, where FIG. 1A is a perspective view and FIG. 1B is a cross-sectional view.
FIG. 2 is a perspective view for explaining a first embodiment of the optical waveguide structure of the present invention.
3A and 3B are cross-sectional views perpendicular to the optical signal propagation direction of the optical waveguide along the lines AA ′ and BB ′ in FIG.
FIG. 4 is a cross-sectional view for explaining a second embodiment of the optical waveguide structure of the present invention.
FIG. 5 is a cross-sectional view when an upper clad layer is formed as a second embodiment of the present invention.
FIGS. 6A to 6H are process diagrams illustrating a method for manufacturing an optical waveguide structure according to the present invention.
FIGS. 7A to 7H are process diagrams for explaining a method of manufacturing an optical waveguide structure according to the present invention when the width of the optical waveguide is partially changed.
[Explanation of symbols]
1 Semiconductor substrate material 2 Clad layer 3 Core layer 3
4 Photodiode 11 Semiconductor substrate 12 Clad layer 13 Core layer 14 Photodiode 15 Beam portion 16 Grooves 17 and 18 Organic material 19 Spot size conversion structure

Claims (9)

In an optical waveguide structure in which an optical waveguide is embedded in a semiconductor substrate, a space is provided between a beam portion holding the optical waveguide and a semiconductor substrate and the optical waveguide in a peripheral portion along the longitudinal direction of the optical waveguide . An optical waveguide structure , wherein a groove structure having a groove is provided , and a filling material or air having a refractive index smaller than that of the semiconductor substrate is provided in the groove .   The optical waveguide structure according to claim 1, wherein the groove structure is formed by a plurality of the beam portions and the plurality of grooves so as to surround the optical waveguide embedded in the semiconductor substrate. The optical waveguide structure according to claim 1 or 2 , wherein a refractive index of a filling material provided in the groove is smaller than a refractive index of a clad layer constituting the optical waveguide. Any refractive index of the filler material provided in the groove is smaller than the refractive index of the core layer of the optical waveguide, according to claim 1 to 3, characterized in that a said filling material as the upper cladding layer of the optical waveguide the optical waveguide structure according to any. The optical waveguide structure according to any one of claims 1 to 4, wherein the filler material is an organic material. 6. The optical waveguide structure according to claim 5, wherein the optical waveguide has a spot size conversion structure whose width changes so as to expand toward an end . In a manufacturing method of an optical waveguide structure in which an optical waveguide is embedded in a semiconductor substrate,
Forming a first groove for embedding the optical waveguide in the semiconductor substrate using an etching solution;
Forming the optical waveguide in the groove;
A plurality of beam portions for holding a space between the semiconductor substrate and the optical waveguide at a peripheral portion in the longitudinal direction of the optical waveguide and a plurality of beam portions for holding the optical waveguide using an etching solution on the semiconductor substrate. Forming a groove structure with two grooves;
Method of manufacturing an optical waveguide structure comprising the. 8. The manufacturing of an optical waveguide structure according to claim 7, further comprising a step of providing a filling material having a refractive index smaller than that of refraction of the semiconductor substrate in the groove formed in a peripheral portion of the optical waveguide. Method. 9. The method of manufacturing an optical waveguide structure according to claim 8, wherein the filling material is an organic material .

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