JPS63180910A - Flush type light guide - Google Patents

Abstract

PURPOSE:To form a low-loss light guide by using the light guide which has a refractive index difference between a core and clad as a distribution type and is decreased in the refractive index difference at the boundary face thereof as the light guide on a semiconductor substrate. CONSTITUTION:After a transparent material layer to serve as a 1st clad layer 2 is formed on the substrate 1, a core layer 3 consisting of multi-component glass is formed thereon and is made into a core part 3A having a high refractive index by channeling. Said core part is then embedded by the 2nd clad layer consisting of multi-component glass. The refractive indices of the distribution type are thereafter formed to the core part 3A and the 2nd clad layer 4 by the ion exchange of the ion A to increase the refractive index and the ion B to lower the refractive index between the core part 3A and the 2nd clad layer 4. A method of preparing the core part by a sputtering method using the same glass layer as the clad layer 4 as a target, then bringing said part into contact with a fused salt contg. the ion A and increasing at least part of the refractive index in the core part by the ion exchange with the ion B in the core part is used as the method for forming the core part 3B. The flush type light guide of a small propagation loss is thereby realized on the semiconductor substrate.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an optical waveguide device used for optical fiber communication, optical fiber sensors, etc., and in particular to a composite integrated device that can be integrated with electric elements including light emitting and receiving elements. Embedded optical waveguide device.

[Conventional technology]

For example, the method shown in FIG. 2 is known as a method for integrating various waveguides, light receiving and emitting elements, and electric elements used for optical 7-eye communication, optical fiber sensors, and the like. This is Applied Physics Lett
ers (1973, Volume 2, page ≠63),
B. 0STROWSKY et al. reported that a SiO2 cladding layer (22) and a glass core layer (23) are formed on a silicon substrate (21), and a diffraction grating coupler (2) is formed on the silicon substrate (21).
4) is an optical-electrical composite integrated optical waveguide device that guides the incident light to the P+ region (25)K and receives the light. Second
In the figure, (26) represents an electrode, and (27) represents a bias voltage power source. In this device, an optical waveguide (28
) and the light-receiving element (two) at its end, as a substrate to create an electric element! Since it uses a silicon substrate that is easy to add, it has the advantage of being able to be integrated into multiple structures. Although this optical waveguide is not a buried type, a method shown in FIG. 3, for example, is known as a method of forming a buried waveguide suitable for complex integration. This was reported peacefully at the 1988 IEICE General Conference (Proceedings AqO/), and it is based on a silicon substrate (31) with Sio2 g (32) as the cladding layer and 5iTi as the core part.
In this method, after forming the 02 layer (33), the 5iTi02 layer is made into a channel and embedded with the 8102 layer (34) of the embedding cladding. Si○2N (32), (34) and 5
For the formation of iTi○2N (33), 5iCJ4-Ti (
A flame deposition method using J4-based material is used, and the relative refractive index difference Δ of one layer can be set to an appropriate value.

[Problem that the invention seeks to solve]

However, in the conventional method for fabricating waveguides on silicon substrates, a complicated and expensive flame deposition device is essential, and the refractive index distribution of the formed waveguide is step-shaped. There were serious problems such as scattering loss tending to increase due to fluctuations in the interface between the 5iTi○2 layer (33) and the SiO2 layer (34), making it difficult to obtain a low-loss waveguide. Therefore, there has been a need for a simple method for forming a low-loss waveguide on a silicon substrate that allows for multiple integration.

[Means for solving problems]

In order to solve the above conventional problems, the present invention provides a waveguide on a semiconductor substrate in which the refractive index difference between the core and the cladding is distributed, and the refractive index difference at the interface is reduced. was used.

That is, the present invention includes a first cladding layer made of a low refractive index dielectric material created on a substrate, a core part made of a high refractive index dielectric material created on a part of the first cladding layer,
In an optical waveguide consisting of the first cladding layer and a second cladding layer made of a low refractive index dielectric formed on the core part, refraction occurs at least between the core part and the second cladding layer. This causes the exchange of ions, which are holes contributing to the refractive index, and ions, which make a small contribution to the refractive index, and makes the change in refractive index between the core portion and the second cladding layer smooth.

Semiconductor substrates that can be used in the present invention include silicon substrates, GaAS substrates, and InP substrates.

To fabricate the waveguide of the present invention, first, a transparent material layer serving as a first cladding layer is formed on a substrate, and then a core layer of multi-component glass is formed to form a core portion with a high refractive index by channeling. Next, a second cladding layer of multi-component glass is embedded, and the core and the second cladding layer are bonded by ion exchange between A ions, which increase the refractive index, and B ions, which decrease the refractive index, at least between the core and the second cladding layer. A distributed refractive index is formed in the second cladding layer.

The core part can be formed by sputtering using glass with a high refractive index as a target, or by sputtering using the same glass layer as the cladding layer as a target and then forming the core by sputtering.
A method can be used in which the refractive index of the core portion is at least partially increased by contacting with a molten salt containing ions and ion exchange with B ions in the core portion.

[For production]

According to the present invention, since the buried waveguide on the semiconductor substrate is of a gradient index type, even if there is fluctuation at the interface between the core part and the cladding part, the effects of scattering loss and mode conversion can be suppressed to a small level. , this buried waveguide functions as a low-loss waveguide on the semiconductor substrate. Further, by using the method shown in the explanation of the embodiment, this waveguide can be manufactured with a simple device.

〔Example〕

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 7 is a diagram showing the fabrication process and final structure of a buried optical waveguide according to the present invention.

In Figure 1 (al), / is a silicon substrate with a polished surface, ko is the first cladding layer of silicon dioxide obtained by thermally oxidizing the silicon substrate /, and 3 is a silicon substrate formed by sputtering. This is a glass layer for the core of multi-component glass.The above thermal oxidation process is achieved by placing the silicon substrate l in a high m'rIt furnace containing air containing water vapor and exposing it to high temperature. The first cladding layer is required to prevent the guided light from reaching the silicon substrate, and it is desirable to have a thickness of at least 'f&ioμm.The core glass N3 is as follows. In the process described, it is necessary to increase the refractive index by an ion exchange method, so it is necessary to contain a small amount of at least one kind of alkali metal ion (for example, Li, +Na ion, etc.).As an example, SiO2゜B2O3 ,AJ20
3. 20. Aluminoborosilicate glass made of Na2O, divalent (7) flukaline earth oxide, etc. is effective. The thickness of the core glass layer 3 is preferably about several to 10 μm.

FIG. 3(b) shows ions of A ions in an ion exchange medium such as molten salt and B ions in the core glass layer 3 after the core glass layer 3 is made into channels by photolithography and etching. For the above ion exchange process, for example, a molten salt in which the A ion is a Tl ion, that is, Tl2SO4
:ni2SO4:Zn5O4-io : tts : I
A mixed salt proportioned to Ir can be used. The ion exchange method for increasing the refractive index is described, for example, in ``New Glass and its Physical Properties'' published by Management System Research Institute. It is desirable that the refractive index distribution of the intermediate stage core portion 3A is a step-type distribution after complete ion exchange, and the refractive index of the core portion 3A after ion exchange is determined according to the design of the intended optical waveguide. It is desirable that the value is appropriate.

Figure 3 (C) shows the core part 3A after the process of Figure 3 (bl).
A second cladding layer l of multi-component glass is formed on the first cladding layer λ, and then the core 53 and the second cladding layer are formed by ion exchange between the core portion 3A and the second cladding layer λ. This shows a state in which a distributed refractive index distribution is formed near the boundary between the layer 1 and the layer 1. The above ion exchange step is easily realized by heating the silicon substrate l on which the first cladding layer is formed to a certain temperature or higher. As a result of this ion exchange, the core part 3A becomes a final core part 3B with a distributed type in which the refractive index is at least partially lowered, and at the same time, the region in contact with the core part 3BVCm in the first clad carving becomes a distributed type with an increased refractive index. A cladding portion 4 (/) is formed.

Through this step, the refractive index difference at the boundary between the core portion 3B and the cladding portion tIl can be made smaller than before ion exchange.

As the multi-component glass used for the second cladding layer ψ, the same glass as the core glass layer 3 can be used, but A
Other multi-component glasses can also be used as long as they contain monovalent ions that can be exchanged with ions to increase the refractive index. In particular, if the second cladding layer and the core glass layer 3 are made the same and the ion exchange conditions are appropriately determined, the difference in refractive index between them can be made substantially zero.

〔Effect of the invention〕

According to the present invention, a buried waveguide with a continuous refractive index distribution and low propagation loss, which was previously impossible, can be realized on a semiconductor substrate.

By using the waveguide of the present invention, it is possible to couple between the light receiving and light emitting elements on the semiconductor substrate and the outside with low loss, and it is effective for constructing a composite integrated waveguide device.

Note that when the semiconductor substrate is other than a silicon substrate, a SiO2 layer formed by sputtering or the like may be used as the first cladding layer.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the internal structure and manufacturing process of an embodiment of the present invention, FIG. 2 is a conventional optical waveguide-light receiving element composite integrated device, and FIG. 3 is a conventional optical waveguide embedded on a semiconductor substrate. be. l... Silicon substrate 2... First cladding layer 3... Core glass Ff/j3A...
...Intermediate stage core part 3B...tg core part Da-
...Second cladding layer L/...Refractive index distribution cladding part Fig. 1 Fig. 2 Fig. 3 Procedure Correction Book Showa Ω Year Month 10th

Claims (3)

[Claims] (1) A first layer made of a low refractive index dielectric material created on a substrate.
a cladding layer, a core portion made of a high refractive index dielectric material formed on a portion of the first cladding layer, and a low refractive index dielectric material formed on the first cladding layer and the core portion. In an optical waveguide consisting of a second cladding layer consisting of,
refraction between the core portion and the second cladding layer, causing exchange of ions having a large contribution to the refractive index and ions having a small contribution to the refractive index between the core portion and the second cladding layer; A buried optical waveguide characterized by a smooth distribution type of rate change. (2) Claim 1, wherein the core portion is a glass containing one or more types of ions selected from the ion group consisting of alkali monovalent metals and thallium ions, and the cladding layer is a multicomponent glass. Embedded optical waveguide described. (3) The buried optical waveguide according to claim 1, wherein the substrate is a single-crystal silicon substrate, and the first cladding layer is a SiO_2 layer obtained by thermal oxidation of the silicon substrate.