JP3811345B2 - Optical integrated circuit board - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical integrated circuit substrate in which an optical waveguide and a thin film type optical element are integrated on the same substrate, for example, a plurality of optical modules on a single substrate such as a WDM (Wavelength Division Multiplexing) optical module substrate. It is suitably used when mounting thin film type optical elements and other devices. The optical waveguide and the thin film type optical element are integrated on the same substrate to reduce the substrate size, improve productivity, and improve optical transmission and reception efficiency. The present invention relates to an optical integrated circuit substrate capable of realizing an increase.
[0002]
[Prior art]
In recent years, research and development of optical elements for improving the performance and productivity of optical transmission modules and research and development of optical element mounting technology with high density, high accuracy, and high optical connection efficiency have been promoted.
[0003]
For example, “Thin-Film Multimaterial Optoelectronic Integrated Circuits”, IEEE Transactions on Components, Packaging and Manufacturing Technology, part B, Vol. 19, No.1, February 1996. After that, a technique is described in which only the epitaxial layer is separated to produce a thin film type light receiving element and mounted on another mounting substrate. According to this technology, it is possible to mount a thin film type optical element made of a different material on a mounting substrate with high density and high accuracy.
[0004]
Further, as an example of the optical element mounting technique, an example of an optical integrated circuit substrate proposed in Japanese Patent Laid-Open No. 7-128531 is shown in a sectional view in FIG. In FIG. 2, 21 is a substrate, 24 is a lower cladding layer of the optical waveguide, 25 is a core layer of the optical waveguide, 26 is an upper cladding layer of the optical waveguide, and 27 is placed on the upper surface of the substrate 21 below the lower cladding layer 24. It is a surface type light receiving element which is a thin film type optical element. According to such a configuration, the light propagating around the core portion 25 spreads also to the lower clad layer 24 portion, so that it can be coupled to the surface light receiving element 27.
[0005]
[Problems to be solved by the invention]
On the other hand, when optical coupling is attempted between an optical waveguide formed on a substrate and a thin film type optical element embedded in the optical waveguide, the following problems occur.
[0006]
Since the thin film type optical element is composed of only an epitaxial layer, it has a thickness of several μm or less. Further, a general single mode optical waveguide has a relative refractive index difference of 0.2 to 1.5% between the clad part and the core part and a thickness of the core part of about 4 to 8 μm. In order to make the thickness sufficiently small, the thickness of the lower cladding portion needs to be about 1.5 times or more that of the core portion, and it is desirable that the lower cladding portion has a thickness of at least 6 to 12 μm. On the other hand, in order to increase the optical coupling efficiency between the optical waveguide and the thin film type optical element disposed below the optical waveguide, the lower clad portion of the optical waveguide is made as thin as possible so that the distance between the core and the thin film type optical element is reduced. There is a need.
[0007]
Conventionally, an optical waveguide is coated after a thin film type optical element is formed or placed on a substrate surface. Accordingly, in order to obtain an optical coupling after forming a thin film type optical element on a substrate and forming an optical waveguide thereon, as shown in FIG. 2, a curved portion or a bent portion is formed in the optical waveguide layer. Thus, it is necessary to make the lower cladding part thinner in the region above the thin film type optical element and to make the lower cladding part thicker in the region where the thin film type optical element is not present. In such a case, when the curvature of the curved portion is increased, there is a problem that the region where the interaction between the substrate and the propagation light occurs in the vicinity of the thin film type optical element is widened and the light propagation loss is increased. In addition, if the curvature of the curved part is reduced, the interaction area with the substrate in the vicinity of the thin film type optical element can be narrowed. However, the propagation light is radiated at the curved part and the light propagation loss increases, causing crosstalk. There is a problem that stray light is generated.
[0008]
Japanese Patent Laid-Open No. 7-128531 discloses that in Example 3, the underlying semiconductor layer is secured to a height so that the active layer or light absorbing layer corresponding to the thin film type optical element is sufficiently separated from the substrate. A structure is shown in which the optical waveguide is formed on the optical waveguide. However, in this case, since the core portion of the optical waveguide is largely bent in the vicinity of the optical element, there is a problem that radiation loss at the bent portion and scattering loss at the optical element portion occur. In addition, when forming an optical waveguide covering, the processing accuracy of the core portion of the optical waveguide is deteriorated due to a step due to the optical element, or the shape of the covering portion or the bent portion near the optical element is controlled to a desired shape. However, it is difficult to obtain the designed performance.
[0009]
The present invention has been made in view of the above problems, and its object is to achieve a good optical coupling between a thin film type optical element disposed on a substrate and an optical waveguide coated thereon, and to achieve low optical coupling. An object of the present invention is to provide an optical integrated circuit substrate capable of lossy optical transmission.
[0010]
[Means for Solving the Problems]
An optical integrated circuit substrate of the present invention is formed in a substrate, a wiring conductor provided on the substrate, an optical waveguide formed on the substrate and having at least a lower cladding portion and a core portion, and the lower cladding portion. A metal installation part for optical element installation, a through conductor provided in the lower clad part and electrically connecting the wiring conductor and the metal installation part, and a light receiving surface or a light emitting part, A thin film type optical element which is installed in the lower clad part and on the metal installation part and embedded in the optical waveguide, wherein the light receiving surface is brought close to the core part or the light emitting part is placed in the core part And a thin film type optical element disposed so as to be positioned at the same position.
[0011]
According to the optical integrated circuit substrate of the present invention, an optical waveguide having at least a lower clad portion and a core portion is formed on the substrate, and the optical waveguide is electrically connected to a wiring conductor provided on the substrate. A metal installation portion for installing the optical element is formed in the lower clad portion, and on the metal installation portion, the thin film type optical element makes the light receiving surface close to the core portion in the lower clad portion, or the light emitting portion is the core portion. Since these are embedded in the optical waveguide, the distance between the thin film type optical element and the core part of the optical waveguide is reduced, or the thin film type optical element is positioned in the core part. As a result, it is possible to efficiently exchange optical signals between the optical element and the core part, and to ensure a sufficiently long distance between the core part of the optical waveguide and the substrate in a region where there is no thin film type optical element. In the optical waveguide It is possible to obtain good optical coupling between the buried thin-film optical element and the optical waveguide, it is possible to perform the low-loss optical transmission is no interaction between the propagating light and the substrate of the optical waveguide.
[0012]
In addition, the thin film type optical element has a light receiving surface in the lower clad part close to the core part or emits light to a metal installation part formed in the lower clad part and electrically connected to the wiring conductor provided on the substrate. This metal installation part is installed so that the part is located in the core part and embedded in the optical waveguide, so that signal output and input from the thin film type optical element, power supply and heat conduction and dissipation Can directly and efficiently perform on a thin film type optical device, so that input / output of high-frequency signals and input / output of high-power optical signals can be performed stably, with excellent high-frequency characteristics and stable operation. High-performance and high-reliability optical signal processing with excellent performance can be performed.
[0013]
Furthermore, the metal installation part and the thin film type optical element embedded in the optical waveguide can be formed by the same thin film formation process as the optical waveguide fabrication process, so that they can be formed with high processing accuracy and can be arranged at high density. And has the advantage of excellent productivity.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The optical integrated circuit substrate of the present invention will be described below with reference to the drawings.
[0015]
FIG. 1 is a sectional view showing an example of an embodiment of an optical integrated circuit substrate of the present invention. In FIG. 1, 1 is a substrate, 2 is a lower cladding portion of an optical waveguide formed on the substrate 1, 3 is a core portion of the optical waveguide, and 4 is an upper cladding portion of the optical waveguide. Reference numeral 5 denotes a thin film type optical element, 6 denotes a metal installation part for installing the thin film type optical element, 7 denotes a through conductor, 8 denotes a wiring conductor formed on the substrate 1, and the wiring conductor 8 to the through conductor 7 and the metal installation part An electrical signal is input to and output from the thin film type optical element 5 through 6.
[0016]
In the optical integrated circuit board according to the present invention, the metal installation portion 6 is formed in the optical waveguide, in this example, the lower cladding portion 2, and the thin film type optical element 5 is installed in the metal installation portion 6 to be the optical waveguide. Among these, in this example, they are also disposed in the lower clad part 2 and are both embedded in the optical waveguide. The thin film type optical element 5 includes a light receiving element and a light emitting element. In the case of the light receiving element, the light signal propagating through the core portion 3 is not scattered or attenuated as in this example. It is preferable to embed in the lower clad part 2 close to the core part 3. In the case of a light emitting element, the light emitting element is buried so as to be located in the core part 3 so that an optical signal can be efficiently output to the core part 3. It is preferable.
[0017]
In the optical integrated circuit substrate of the present invention, the substrate 1 is formed with an optoelectric circuit including an electric circuit and an optical waveguide, and functions as a support substrate for the thin film type optical element 5 embedded in the optical waveguide. In addition, various substrates used as optical signal processing substrates such as an optical integrated circuit substrate and an optoelectronic mixed substrate, for example, a silicon substrate, an alumina substrate, a glass ceramic substrate, a multilayer ceramic substrate, a plastic electric wiring substrate, and the like can be used.
[0018]
The optical waveguide formed on the substrate 1 and embedded with the thin film type optical element 5 has at least a lower clad part 2 and a core part 3, and preferably has an upper clad part 4 on the upper part thereof. It is a two-dimensional waveguide-shaped optical waveguide.
[0019]
As the material of the optical waveguide, an optical waveguide was laminated on the wiring conductor 8 formed on the substrate 1, the through conductor 7, the metal installation portion 6, and the thin film type optical element 5 installed on the metal installation portion 6. It can be formed at a low temperature so as not to cause damage, and the surface irregularity due to the wiring conductor 8, the through conductor 7, the metal installation portion 6, and the thin film type optical element 5 can be reduced. A material having excellent transparency and capable of propagating light with low loss is used. In particular, since the lower clad portion 2 functions also as a dielectric layer of electric wiring in the optical integrated circuit substrate, a material having a low dielectric loss and a low dielectric constant is preferable particularly when a high frequency electric signal is handled. For example, an optical material that can be applied on the substrate 1 in a solution state such as siloxane polymer, fluorinated polyimide, fluororesin, polymethyl methacrylate (PMMA), and polycarbonate (PC) is preferably used.
[0020]
As a method for manufacturing an optical integrated circuit substrate of the present invention, in the example shown in FIG. 1, first, a thin film type light is formed on a substrate 1 at the same time as a portion below a lower cladding portion 2 of an optical waveguide. A layer (a lower layer in which the lower clad portion 2 in FIG. 1 is separated by a dotted line) is formed to form the metal installation portion 6 for installing the element 5. Next, in this layer, the through conductor 7 connected to the wiring conductor 8 on the substrate 1 and the metal installation portion 6 for installing the thin film type optical element 5 are formed. Next, the thin film type optical element 5 is placed on the metal placement portion 6 or directly formed. Next, a layer that covers the metal installation portion 6 and the thin film type optical element 5 and is a part above the lower clad portion 2 (upper layer shown by dividing the lower clad portion 2 in FIG. 1 by a dotted line) is formed. Next, after forming a layer to be the core portion 3 on the lower clad portion 2, the core portion 3 is formed in a predetermined shape using a well-known thin film microfabrication technique such as photolithography or RIE (reactive ion etching). To do. And after forming the core part 3, the upper clad part 4 is coat | covered and a three-dimensional-shaped optical waveguide is formed. As a result, an optical waveguide in which the metal installation portion 6 and the thin film type optical element 5 are embedded in the lower cladding portion 2 is formed in the optical waveguide.
[0021]
The metal installation part 6 and the through conductor 7 and the wiring conductor 8 for installing the thin film type optical element 5 are all made of a well-known thin film wiring conductor material such as Au, Ti, Pd, Pt, Al, Cu, W, and Cr. What is necessary is just to form using the method of a well-known thin film multilayer wiring. The size and shape of the metal installation portion 6 are the same as the size and shape of the electrode formed on the thin film type optical element 5. When the thin-film optical element 5 is a light receiving element, the core portion 3 and the light receiving surface are arranged so that the electromagnetic field distribution of propagating light reaches the light receiving surface. Set the position so that In the case of a general single mode optical waveguide, the distance between the core portion 3 and the light receiving surface needs to be at least 1.5 times the thickness of the core portion 3. Actually, simulations and experiments are conducted in consideration of the refractive index / transmittance / thickness of the thin film type optical element 5, the structure / refractive index / thickness of the optical waveguide, the sensitivity of the light receiving element, etc. What is necessary is just to determine so that it may be obtained. Further, when the thin film type optical element 5 is a light emitting element, the light emitting part is set at a position where the light emitting part is located in the core part 3 so that an optical signal can be efficiently output to the core part 3.
[0022]
Further, when the thin film type optical element 5 is installed on the outermost surface of the metal installation part 6 for installing the thin film type optical element, the thin film type optical element 5 is placed and joined to the metal installation part 6 If it is necessary for the case of performing a general connection, a solder layer such as AuSn / AuGe may be formed.
[0023]
FIG. 1 shows an example in which the metal installation portion 6 formed in the lower clad portion 2 is connected by the wiring conductor 8 and the through conductor 7 provided on the substrate 1, but the circuit formed on the optical integrated circuit substrate. The structure for electrically connecting the metal installation part 6 to the wiring may be a single-layer wiring, a multi-layered structure, a structure connected to the wiring formed on the optical waveguide, or the like. A wiring structure may be used.
[0024]
By forming such a metal installation portion 6 and installing the thin film type optical element 5, the step due to the installation of the thin film type optical element 5 is shown in Example 3 of the above-mentioned JP-A-7-128531. It can be made smaller than the above example, and can be about 2 to 3 μm or less. As described above, since the optical waveguide layer can be flattened to such an extent that no problem occurs when the optical waveguide layer is formed on the thin film type optical element 5, scattering loss and radiation loss in the vicinity of the optical element 5 can be sufficiently reduced. Furthermore, the processing accuracy of the core portion 3 of the optical waveguide is good, and the performance as designed can be easily realized.
[0025]
The thin film type optical element 5 installed on the metal installation unit 6 is a thin film type light receiving element or a thin film type light emitting element manufactured using a semiconductor material such as Si, Ge, InP, GaAs, InAs, InGaAsP, for example. Light-receiving elements such as pn photodiodes, pin photodiodes, phototransistors, MSM (Metal-Semiconductor-Metal) photodiodes, avalanche photodiodes, and light-emitting elements such as LEDs, vertical cavity surface emitting lasers, and edge emitting lasers are used. . In addition, the thin film type optical element referred to here is one whose thickness is thinner than the thickness of the lower clad part 2 or the core part 3 embedded therein.
[0026]
In order to obtain optical coupling with the optical waveguide, the thin film type optical element 5 has a light field propagating around the core portion 3 when the thin film type optical element 5 is, for example, a surface light receiving type light receiving element. It arrange | positions so that the light-receiving part of the optical element 5 may be covered. Further, in the case where the thin film type optical element 5 is an end surface light emitting type light emitting element, the light emitting part may be disposed in the core part 3. In the case where the thin film type optical element 5 is a waveguide type light receiving element, it may be arranged so that the field of light propagating around the core 3 covers the end face of the thin film type optical element 5. When the thin film type optical element 5 has a waveguide structure, optical coupling is achieved by arranging the core portion 3 and the optical waveguide portion in the thin film type optical element 5 in parallel to perform mode coupling. May be performed.
[0027]
The positional relationship between the thin-film optical element 5 embedded in the optical waveguide and the core portion 3 of the optical waveguide, the height / width / refractive index of the core portion 3, the thickness / refractive index of the lower cladding portion 2, and the upper cladding The thickness / refractive index of the portion 4 is determined by a well-known optical waveguide theory or the like so that a desired optical coupling efficiency can be obtained in consideration of the light receiving sensitivity, the propagation light intensity, the propagation light mode field, etc. It may be determined from simulations or experiments.
[0028]
As a method of installing the thin film type optical element 5 in the metal installation part 6, for example, “Thin-Film Multimaterial Optoelectronic Integrated Circuits”, IEEE Transactions on Components, Packaging and Manufacturing Technology, part B, Vol. 19, No. 1 , February 1996. A well-known thin film type device mounting method may be used.
[0029]
【Example】
Next, specific examples of the optical integrated circuit substrate of the present invention will be described.
[0030]
First, electrical wiring by a wiring conductor made of Ti / Pt / Au (thickness: 0.1 μm / 0.2 μm / 0.8 μm) on the silicon substrate by using photolithography, electron beam evaporation method, and lift-off method, and the outside The connection pad was formed.
[0031]
Next, an organic solvent solution of siloxane polymer is applied onto the substrate by spin coating, and heat treatment is performed at 85 ° C./30 minutes and 270 ° C./30 minutes, and a part of the lower cladding part having a thickness of 8 μm (refractive (Rate 1.4405, λ = 1.3 μm). Subsequently, RIE processing was performed using the opening pattern of the Al thin film as a mask to form a through hole. After removing the Al thin film mask, a Ti / Pt / Au thin film (thickness: 0.1 μm / 0.2 μm / 0.5 μm) is deposited by electron beam evaporation, photolithography and dry etching are performed, and the conductor in the through hole Thus, a thin-film light receiving element installation pad as a metal installation portion, which is electrically connected to an external connection pad, was formed.
[0032]
Next, an MSM type thin film light receiving element composed of a GaAs-based material having a thickness of 1 μm and an Au electrode having a thickness of 0.2 μm was mounted and installed on a thin film light receiving element installation pad.
[0033]
Next, on this substrate, an organic solvent solution of a siloxane polymer of the same material as that of a part of the lower clad part is applied by spin coating, and heat treatment is performed at 85 ° C./30 minutes and 270 ° C./30 minutes, A 10 μm thick layer (refractive index 1.4405, λ = 1.3 μm) was formed. Thereafter, the entire surface was etched by RIE using CF ₄ gas and O ₂ gas, so that the thickness of the clad layer covering the thin film light receiving element became 1 μm. At this time, the step formed on the surface of the lower clad portion between the thin film light receiving element portion and the other portions was 0.3 μm or less, and there was no problem. The thickness of the lower clad formed in this way was about 11 μm without the thin film light receiving element.
[0034]
Next, a mixed solution of siloxane polymer and tetra-n-butoxytitanium is applied onto the clad layer by spin coating, heat treatment is performed at 85 ° C./30 minutes and 150 ° C./30 minutes, and a core layer having a thickness of 7 μm (Refractive index 1.4450, λ = 1.3 μm) was formed.
[0035]
Subsequently, an Al film having a thickness of 0.5 μm was formed on the core layer by a sputtering method, and a photoresist pattern to be a pattern of the core portion was formed by a photolithography technique. Next, the Al film was etched with a mixed solution of phosphoric acid, acetic acid and nitric acid to form an Al pattern to which the resist pattern was transferred.
[0036]
Next, after removing the resist, the core portion was etched by RIE using CF ₄ gas and O ₂ gas to form a core portion having a width of 7 μm and a height of 7 μm and a substantially rectangular cross section. The core portion is positioned above the light receiving portion of the thin film light receiving element.
[0037]
Thereafter, the Al pattern is removed, and a cladding layer (refractive index: 1.4405, λ = 1.3 μm) is formed in the same manner as described above to embed the core portion, the cladding portion is made of a siloxane polymer, and the core portion is a titanium-containing siloxane system. A step index optical waveguide made of polymer was formed.
[0038]
Next, ablation processing by excimer laser was performed to expose a part of the external connection pad formed on the silicon substrate surface. Further, at the same time that the substrate was cut into chips, a connection end face for entering light from the outside of the optical waveguide was formed by dicing.
[0039]
With respect to the optical integrated circuit substrate of the present invention thus fabricated, a laser beam having a wavelength of 1.3 μm is incident on the end face for connecting the optical waveguide through the single mode optical waveguide, and the optical propagation characteristics and light reception of the optical integrated circuit substrate are measured. Characteristics were evaluated.
[0040]
As a result, it was confirmed that the optical waveguide without the thin film light-receiving element had a thickness of the lower cladding portion of 11 μm, and the interaction with the underlying silicon substrate was sufficiently small, and good light propagation could be achieved with low loss. On the other hand, it was confirmed that the light-receiving efficiency of the thin-film light-receiving element was as excellent as about 10%.
[0041]
Note that the above are merely examples of the embodiments of the present invention, and the present invention is not limited to these embodiments, and various modifications and improvements may be added without departing from the scope of the present invention. . For example, the core part may be formed directly on the surface of the thin film light receiving element without interposing the clad part between the thin film light receiving element and the core part. A function such as wavelength demultiplexing may be added by forming a grating in the cladding part between the thin film light receiving element and the core part.
[0042]
【The invention's effect】
As described above, according to the optical integrated circuit substrate of the present invention, the optical waveguide having at least the lower clad portion and the core portion is formed on the substrate, and the wiring conductor provided on the substrate is electrically connected to the optical waveguide. The metal installation part connected to the optical element and the thin film type optical element installed on the metal installation part are formed in the lower cladding part, and the thin film type optical element is in the lower cladding part. Since the light receiving surface is placed close to the core portion or the light emitting portion is positioned in the core portion and embedded, light is efficiently transmitted between the thin film type optical element and the core portion of the optical waveguide. Signals can be exchanged and good optical coupling can be obtained, and in the region where there is no thin film type optical element, the distance between the core portion of the optical waveguide and the substrate can be secured sufficiently long. Wave propagation light and substrate It can interact without performing low-loss optical transmission.
[0043]
In addition, the thin film type optical element has a light receiving surface in the lower clad part close to the core part or emits light to a metal installation part formed in the lower clad part and electrically connected to the wiring conductor provided on the substrate. Is placed in the core and embedded in the optical waveguide, the thin film type optical element can be used to input and output signals, supply power, and conduct and dissipate heat. Type optical elements can be directly and efficiently performed, so that high-frequency signal input / output and high-output optical signal input / output can be performed stably, with excellent high-frequency characteristics and operational stability. Can perform high-performance and high-reliability optical signal processing.
[0044]
Furthermore, the metal installation part and the thin film type optical element embedded in the optical waveguide can be formed by the same thin film formation process as the optical waveguide fabrication process, so that they can be formed with high processing accuracy and can be arranged at high density. And has the advantage of excellent productivity.
[0045]
As described above, according to the present invention, an optical integrated circuit capable of obtaining a good optical coupling between a thin film type optical element arranged on a substrate and an optical waveguide coated thereon and capable of low-loss optical transmission. A substrate could be provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an example of an embodiment of an optical integrated circuit substrate of the present invention.
FIG. 2 is a cross-sectional view showing an example of a conventional optical integrated circuit substrate.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Board | substrate 2 ... Lower clad part 3 of optical waveguide ... Core part 4 of optical waveguide ... Upper clad part 5 of optical waveguide ... Thin film type Optical element 6 ... Metal installation part

Claims (1)

A substrate,
A wiring conductor provided on the substrate;
An optical waveguide formed on the substrate and having at least a lower cladding part and a core part;
A metal installation portion for optical element installation formed in the lower clad portion;
A through conductor provided in the lower clad part and electrically connecting the wiring conductor and the metal installation part;
A thin film type optical element having a light receiving surface or a light emitting portion , installed in the lower clad portion and on the metal setting portion and embedded in the optical waveguide, wherein the light receiving surface is brought close to the core portion Or a thin film type optical element disposed so that the light emitting part is positioned in the core part.

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