JP3228229B2 - Optical waveguide platform and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hybrid integrated waveguide type optical device used for optical communication and the like, and relates to an optical waveguide platform having electrode wirings for operating a hybrid integrated semiconductor optical device and a method of manufacturing the same.

[0002]

2. Description of the Related Art In recent years, as the capacity of an optical communication system has been increased and a multifunctional advanced system has been demanded, a demand for a cost reduction of an optical fiber network system has been increasing. Among them, miniaturization of optical devices,
High integration and low cost are essential items. Under these circumstances, an LD is placed on an optical waveguide platform in which a quartz-based optical waveguide is formed on a Si (silicon) substrate.
A technology that reduces the number of components and achieves miniaturization, multifunctionality, and cost reduction by mounting and integrating semiconductor optical elements such as (semiconductor laser), PD (photodiode), or SOA (semiconductor optical amplifier). Is considered to be promising, and research is being actively conducted. FIG. 3 is a perspective view showing a schematic configuration of this type of optical waveguide platform. An insulating film 102 is formed on a surface of a Si substrate 101, and a lower cladding layer 14 is formed on the surface of the insulating film 102.
1, an optical waveguide 104 including a core 142 and an upper cladding layer 143 is formed. Further, the optical waveguide 104
An electrode wiring 103 on which a metal film is patterned is extended on the surface of the Si substrate 101 on which no is formed.
Further, a part of the Si substrate 101 where the optical waveguide 104 is not formed is configured as an optical element mounting part 107,
An optical element 108 such as an LD or PD is mounted on the island portion 103 a provided on the electrode wiring 103. The optical element 108 is electrically connected to the electrode wiring 103, and an electric signal is transmitted to the optical element 108 through the electrode wiring 103.

However, the electrode wiring 103 formed on the platform electrically connected to such a hybrid integrated optical device is formed of a thin insulating film 102 of 1 μm or less such as a thermal oxide film formed on the Si substrate 101.
Since it is formed on the upper surface, the surface of the Si substrate 101 and the electrode wiring 103 are in a state where they are opposed to each other in a close state.
Dielectric loss due to the i-substrate 101 is large or Si
There is a problem that high-speed operation characteristics on the order of Gb / s are deteriorated due to a large parasitic capacitance between the substrate 101 and the electrode wiring 103. To solve this problem,
Proceedings of the 994 IEICE Autumn Conference C-195
FIG. 4 shows the configuration shown in FIG. This configuration is performed simultaneously with the formation of the lower cladding layer 141 of the optical waveguide 104.
The buffer layer 106 is formed on the surface of the Si substrate 101, and the electrode wiring 103 is formed on the buffer layer 106. Since the buffer layer 106 can be set to a thickness of about 30 μm, the Si substrate 101 as described above is used.
, The effect on the electrode wiring 103 can be sufficiently reduced, and good high-speed operation characteristics can be obtained.

[0004]

However, in the configuration of FIG. 4, in order to form the buffer
After the surface of the buffer layer forming region of the substrate 101 is etched in advance in a concave shape, the lower clad layer 141 is formed in the concave portion.
At the same time, a manufacturing process of depositing a quartz-based material and then mechanically polishing the surface of the quartz-based material to flatten the surface of the Si substrate 101 is required. There is a problem that becomes difficult. In addition, since the electrode wiring 103 is formed on the same surface as the optical element mounting portion 107 defined on the surface of the Si substrate 101, it is difficult to design a flexible wiring that crosses the optical waveguide 104, for example. Although not shown, electrode wiring was formed on the upper clad layer and formed on the semiconductor optical element mounting portion as shown in the 1996 IEICE General Conference Lecture Paper C-205. If electrode wiring is connected by wire bonding, the degree of freedom in wiring design will increase relatively.However, wire bonding requires more time and effort than patterning wiring, and the scale of hybrid integration will increase in the future. It cannot be said that the degree of design freedom is high for a wiring structure that is expanded and requires complicated and high density.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical waveguide platform and a method for manufacturing the same, which not only improve the high-speed operation characteristics of the electrode wiring, but also increase the degree of freedom in designing the electrode wiring and can easily manufacture the electrode waveguide. To provide.

[0006]

The present invention SUMMARY OF], the silicone which optical waveguide consisting of a core and cladding of an optical material on a silicon substrate is formed, and facing the optical waveguide end of the optical waveguide
An optical element is mounted on a substrate, and an electrode wiring for electrically connecting to the optical element is formed on the silicon substrate. In the optical waveguide platform, the electrode wiring is connected to the optical element. said part of the side you are
On the insulating film provided on the surface of the silicon substrate , formed below the optical waveguide, another part of the electrode wiring is formed above the optical waveguide, and each of the lower and upper electrode wirings Are electrically connected to each other by a conductive contact penetrating the optical waveguide in a thickness direction, and further, the conductive
The contact is located as far as possible from the core,
And at a position as close as possible to the place where the optical element is mounted.
The lower electrode wiring is formed at the mounting position of the optical element.
And between the positions of the conductive contacts.
Characterized in that that. The optical waveguide, a lower cladding layer, a core having a smaller width dimension than the lower cladding layer,
An upper clad layer formed on the lower clad layer to cover both side surfaces and an upper surface of the core is formed as a laminated structure, and the conductive contact includes the lower clad layer and the upper clad layer in a region where the core does not exist. penetrated in the thickness direction Ru formed.

According to the manufacturing method of the present invention, a step of forming an insulating film on a silicon substrate and forming a lower electrode wiring on the insulating film; a step of forming an optical waveguide on the lower electrode wiring; forming an optical element mounting portion having one end Ru is exposed part is removed the lower electrode wirings of the optical waveguide, the contact hole for conducting the other end of the lower electrode wiring to the optical waveguide a step of opening in the thickness direction, viewed including the step of forming the upper electrode wiring which is electrically connected through the conductive contact hole on the top surface of the optical waveguide to the other end of the lower electrode wirings, wherein The conductive contact hole is
It is formed at a position as close as possible to the element mounting portion . Here, a step of forming a metal film in the contact hole by a plating method and electrically connecting the upper electrode wiring to the lower electrode wiring via the metal film may be adopted.

According to the present invention, an electrical signal transmitted to the optical elements most part are formed on the top surface of the optical waveguide silico
Since the upper electrode wiring located at a position distant from the substrate is transmitted, the influence of the silicon substrate is reduced, and the high-frequency characteristics are improved. Further, since the upper electrode wiring is formed on the upper surface of the optical waveguide, the degree of freedom in design is increased, and the formation of the electrode wiring crossing the optical waveguide is facilitated. Furthermore, since a part of the lower electrode wiring exists below the optical waveguide, the degree of freedom in designing the lower electrode wiring increases even when the area of the optical element mounting portion is very small. In the production method according to the present invention, it is possible to produce an optical waveguide platform of the present invention by simply adding a few steps to the conventional light guide platform manufacturing process.

[0009]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a perspective explanatory view showing a first embodiment of the present invention. An optical waveguide 4 composed of a lower clad layer 41, a core 42 and an upper clad layer 43 formed by sequentially laminating dielectric materials on a substrate 1 made of Si having an insulating film 2 formed on the surface is formed. . The core 42 is formed narrower than the lower clad layer 41, and the upper clad layer 43 is formed so as to cover the side surface or the upper surface of the core 42. An upper electrode wiring 5 is formed on the upper surface of the upper clad layer 43. Further, an optical element mounting portion 7 is formed by partially removing the optical waveguide 4 on the substrate 1, and the optical element mounting portion 7 is formed on the surface of the insulating film 2. The lower electrode wiring 3 for driving the optical element is formed in a region including the lower electrode wiring. A part of the lower electrode wiring 3 is extended to below the cladding layer 41 constituting the optical waveguide 4, and the upper electrode wiring 5 formed on the upper surface of the upper cladding layer 43 is separated from the lower electrode wiring 3. Are electrically connected to each other through a contact hole 6 penetrating the cladding layers 41 and 43.
The contact hole 6 is provided at a position away from the core 42 and as close as possible to the optical element mounting portion 7 so as not to affect the guided light propagating through the core 42. A metal film 61 is formed in the contact hole 6, whereby the upper and lower electrode wirings 3, 5 are electrically connected to each other. Then, the island portion 3 formed by a part of the lower electrode wiring 3 of the optical element mounting portion 7
An optical element 8 such as an LD or PD is mounted on a.
It is electrically connected to the lower electrode wiring 3. Therefore, the optical element 8 is electrically connected to the upper electrode wiring 5 via the lower electrode wiring 3 and the contact hole 6 (metal film 61), and is supplied with power or outputs an electric signal through the upper electrode wiring 5. It is configured as follows.

In this configuration, a part of the electrode wiring electrically connected to the optical element 8 mounted on the Si substrate 1 is made of Si.
The lower electrode wiring 3 is formed along the surface of the substrate 1, but the other part is formed by the upper electrode wiring 5 on the optical waveguide 4 connected via the contact hole 6. . Therefore, most of the electric signals are transmitted on the thick quartz film of 20 μm or more on the surface of the Si substrate 1, and the high frequency characteristics are excellent in which the influence of the parasitic capacitance with the Si substrate 1 is reduced. An electrode wiring structure can be obtained. Further, since the upper electrode wiring 5 is formed on the upper surface of the upper cladding layer 43, the degree of freedom in design is large, and for example, an electrode wiring pattern crossing over the core 42 can be easily formed. Further, even when the area of the optical element mounting part 7 is very small, the area of the optical element mounting part 7 is restricted because the lower electrode wiring 3 is partially formed below the optical waveguide 4. Therefore, the degree of freedom in design is increased and the setting is easy.

Here, the material of the optical waveguide 4 can be, for example, a quartz-based material. Examples of the film-forming technique using the quartz-based material include a flame deposition (FHD) method, a chemical vapor deposition (CVD) method, and the like. There are sputtering method, vapor deposition method, SOG coating, and the like, but the method involving high temperature treatment of 1000 ° C. or more for forming the optical waveguide such as FHD causes a large damage to the electrode wiring 7 formed thereunder. A method that can form an optical waveguide at a low temperature is desirable. For example, if the CVD method is used, the optical waveguide 4 can be formed at 900 ° C. or less even if annealing treatment or the like is included. When the optical waveguide 4 is configured as a quartz-based single mode waveguide, the lower clad layer 41 and the upper clad layer 43 usually have a thickness of 10 μm or more. Therefore, as described above, most of the electric signals that are conducted to the optical element 8 and flow through the electrode wiring are 20 μm.
The electrode wiring 5 propagates on the quartz film having a thickness of not less than m, and an electrode wiring structure excellent in high-frequency characteristics in which the influence of the Si substrate 1 is reduced can be obtained.

On the other hand, the material of the lower electrode wiring 3 is, for example, WSi (tungsten silicide) or Ti having excellent heat resistance.
A high melting point metal silicide such as Si (titanium silicide) or a high melting point metal such as Ti (titanium) or CR (chromium) can be used. If the optical waveguide 4 can be formed at a lower temperature, for example, at 400 ° C. or lower, a metal such as Al (aluminum) can be used. The materials of these metals can thus be variously selected based on the process temperature. Note that it is better to design the length of the lower electrode wiring 3 as short as possible. This reduces the influence of the dielectric loss of the Si substrate 1 as much as possible, and the resistance after the optical waveguide forming process of the high melting point metal or the silicide mentioned as the material of the lower electrode wiring 3 is several tens μΩcm or more. This is because it is larger than a low resistance metal such as (Au) by two digits or more. On the other hand, the upper electrode wiring 5 formed on the upper clad layer 43 has a low resistance material such as Au (gold), Ag (silver), Cu
Common low-resistance wiring materials such as (copper) and Al (aluminum) can be used. The same applies to the metal film 61 in the contact hole 6. However, the metal film 61 needs to be a material that can be formed by plating.

Next, a method of manufacturing the optical waveguide platform of the present invention shown in FIG. 1 will be described with reference to the manufacturing process side view of FIG. First, as shown in FIG.
The surface of a substrate 1 made of is thermally oxidized to form an insulating film 2 made of a silicon thermal oxide film on the surface. Here, the insulating film 2 may be, for example, a silicon nitride film in addition to the silicon thermal oxide film. Next, WSi is applied to the surface of the insulating film 2.
(Tungsten silicide) film and the WS
The lower electrode wiring 3 for driving the optical element is formed by selectively etching the i film by photolithography.
Here, the material of the lower electrode wiring 3 is, for example, TiS
Any material that can withstand the subsequent optical waveguide forming process, such as i, Ti, and Cr, may be used.

Next, as shown in FIG. 2B, a lower clad layer 41 and a core layer of a quartz optical waveguide are deposited on the surface of the insulating film 2 by the CVD method, and then a photolithography method is formed on the surface. Then, a core pattern is formed, and the core layer is selectively etched by RIE (reactive ion etching) using the core pattern as a mask to form a core 42. Next, an upper clad layer 43 is deposited thereon to form the optical waveguide 4. The thickness of each layer is such that the lower clad layer 41 and the upper
The thickness is about 0 μm to 20 μm, and the core 42 is about 7 μm or less. The deposition of the quartz-based film may be performed by a low-temperature film formation method of about 900 ° C. or less, such as a sputtering method or a vapor deposition method, in addition to the CVD method. The optical waveguide material may be an organic polymer or the like in addition to the quartz-based material.

Next, as shown in FIG. 2C, a pattern mask is formed leaving a part on the surface of the optical waveguide 4, and a part of the optical waveguide 4 is formed by RIE using the pattern mask. Over the entire thickness, that is, the upper clad layer 43, the core 42, and the lower clad layer 41 are selectively etched, respectively, to form the insulating film 2 on the surface of the substrate 1 and the lower film formed on the surface of the insulating film 2. The optical element mounting portion 7 exposing the side electrode wiring 3 is formed. At this time, the optical waveguide 4 is etched so that a part of the lower electrode wiring 3 exists below the lower clad layer 41. At the same time as the selective etching of the optical waveguide 4,
A contact hole 6 is opened in a part of the optical waveguide 4 by using the pattern mask and the RIE method. The contact hole 6 is opened so as to communicate with the lower electrode wiring 3 existing below the lower clad layer 41 of the optical waveguide 4. The diameter of the contact hole 6 is about several μm to 20 μm.

Subsequently, as shown in FIG. 2D, a metal film is deposited on the upper cladding layer 43, and the metal film is selectively etched by photolithography to pattern the upper electrode wiring 5. Form. At this time, by forming a part of the metal film in the contact hole 6, the upper electrode wiring 5 is electrically connected to the lower electrode wiring 3 through the contact hole 6.
The metal film 61 in the contact hole 6 may be formed by electroplating. In this case, the current is supplied to the electrode wiring 3 exposed in the contact hole 6. Here, the steps of patterning the upper electrode wiring 5 and forming the metal film 61 by plating may be reversed. Further, in order to improve adhesion of the metal film by plating, a thin film of the same material as the metal film 61 may be formed in advance on the lower electrode wiring 3 at the bottom of the contact hole 6 by vapor deposition or sputtering. Upper electrode wiring 5 and metal film 61
Various low-resistance metals such as gold, silver, copper, and aluminum can be used as the material.

Then, an optical element 8 such as an LD or PD is mounted on the island portion 3a of the electrode wiring 3 of the optical element mounting section 7.
To electrically connect the optical element 8 to the lower electrode wiring 3, and furthermore, to contact the upper electrode wiring 5 through the contact hole 6.
Make an electrical connection.

[0018]

As described above, according to the present invention, the lower electrode wiring provided on the lower side of the optical waveguide and partially having an optical element mounted thereon, and the upper wiring provided on the upper side of the optical waveguide, Since it is configured to be electrically connected to each other via through holes provided in the optical waveguide, most of the electric signals transmitted to the optical element propagate on the upper surface of the optical waveguide made of a thick quartz film, and silicon The influence of the substrate is reduced, and an optical waveguide platform having excellent high-frequency characteristics can be obtained. Further, since the upper electrode wiring is formed on the upper surface of the optical waveguide, the degree of freedom in design is increased, and, for example, an electrode wiring pattern that crosses over the core of the optical waveguide can be easily formed.
Further, since a part of the lower electrode wiring is formed below the optical waveguide, even when the area of the optical element mounting portion is small, the degree of freedom in design is increased and the design is facilitated.
On the other hand, according to the manufacturing method of the present invention, the optical waveguide platform of the present invention can be easily manufactured by adding a few manufacturing steps to a normal optical waveguide platform.

[Brief description of the drawings]

FIG. 1 is a perspective view of a main part of an embodiment of an optical waveguide platform of the present invention.

FIG. 2 is a cross-sectional view illustrating a method of manufacturing the optical waveguide platform of FIG. 1 in the order of steps.

FIG. 3 is a perspective view showing an example of a conventional optical waveguide platform.

FIG. 4 is a cross-sectional view illustrating an improved example of a conventional optical waveguide platform.

[Explanation of symbols]

 Reference Signs List 1 Si substrate 2 Insulating film 3 Lower electrode wiring 4 Optical waveguide 41 Lower cladding layer 42 Core 43 Upper cladding layer 5 Upper electrode wiring 6 Through hole 7 Optical element mounting part 8 Optical element

Claims (5)

(57) [Claims] 1. A light waveguide consisting of a core and cladding of an optical material on a silicon substrate is formed, and an optical element is mounted on the silicon substrate facing the optical waveguide end of the optical waveguide, and to the optical element In an optical waveguide platform in which electrode wiring for making electrical connection is formed on the silicon substrate, the electrode wiring is connected to the optical element.
Part of the side being continued is provided on the surface of the silicon substrate
On the insulating film formed, the lower part of the optical waveguide is formed, the other part of the electrode wiring is formed above the optical waveguide, and each of the lower and upper electrode wirings has a thickness of the optical waveguide. Are electrically connected to each other by a conductive contact penetrating in the vertical direction, and the conductive contact is larger than the core.
As far away as possible and where the optical element is mounted
Formed as close as possible to the lower electrode wiring,
From the mounting position of the optical element to the position of the conductive contact.
An optical waveguide platform formed therebetween . 2. The optical waveguide, comprising: a lower cladding layer; a core having a smaller width dimension than the lower cladding layer; and an upper cladding formed on the lower cladding layer so as to cover both side surfaces and an upper surface of the core. 2. The optical waveguide platform according to claim 1, wherein the conductive contact is formed as a layered structure, and the conductive contact is formed to penetrate the lower clad layer and the upper clad layer in a thickness direction in a region where the core does not exist. Wherein said optical waveguide is composed of silica-based material,
The optical waveguide platform according to claim 1, wherein at least the lower electrode wiring of the electrode wiring is made of a high melting point metal or a high melting point metal silicide. 4. A step of forming an insulating film on a silicon substrate, forming a lower electrode wiring on the insulating film, forming an optical waveguide on the lower electrode wiring, and forming one of the optical waveguides. forming a <br/> optical element mounting portion to which one end portion of the lower electrode wirings Ru is exposed by removing the part, a contact hole electrically connected to the other end portion of the lower electrode wirings to the optical waveguide a step of opening in the thickness direction, viewed including the step of forming the upper electrode wiring which is electrically connected through the conductive contact hole on the top surface of the optical waveguide to the other end of the lower electrode wirings,
The conductive contact hole is as large as possible in the optical element mounting part
A method for manufacturing an optical waveguide platform, wherein the optical waveguide platform is formed at a position close to the optical waveguide. 5. The optical waveguide platform according to claim 4 , wherein a metal film is formed in the contact hole by a plating method, and the upper electrode wiring is electrically connected to the lower electrode wiring via the metal film. Manufacturing method.