JPH01267510A - Production of directional coupler - Google Patents

Abstract

PURPOSE:To reduce the size of the directional coupler by reducing the width of the base of a sepn. zone, thereby forming two waveguides to the small distance therebetween. CONSTITUTION:A dielectric material is selectively grown by liquid epitaxy on a substrate 1 to form the sepn. zone 3 and thereafter, a 1st mask is removed and a 2nd mask 4 covering a 1st waveguide forming region 51 and the 2nd waveguide forming region 52 on the substrate on the sepn. zone and the substrate on both sides of the substrate are formed. A clad layer 6 is formed with the 2nd mask as a mask. The width and height of the base of the sepn. zone 3 can be controlled by changing the liquid phase epitaxial growth conditions. The spacing between the 1st waveguide forming region 51 and the 2nd waveguide forming region 52 on both sides of the sepn. zone can be thereby reduced and the spacing between the 1st waveguide 71 and the 2nd waveguide 72 is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a method of manufacturing a directional coupler, particularly a method of manufacturing a directional coupler using a semiconductor substrate.

The purpose of this is to reduce the distance between two waveguides, thereby reducing the size of the directional coupler.

(100) A step of forming a first mask 2 on the surface of the semiconductor substrate 1 to expose a long region in the (011) direction of the substrate, and using the first mask as a mask, applying a dielectric material onto the substrate. Phase epitaxial selective growth is performed to form a separation band 3, and then the first mask is removed. forming a second mask 4 that covers the second waveguide forming region S2, and performing selective liquid phase epitaxial growth of a dielectric material on the substrate using the second mask as a mask, forming a cladding layer 6; and then removing the second cough mask.

forming a core layer 7 including a first waveguide 71 and a second waveguide 72 by growing a material having a refractive index larger than the refractive index of the separation zone and the kraft layer on the entire surface of the substrate 2; A method for manufacturing a directional coupler includes the step of growing a material having a refractive index smaller than the refractive index of the core layer on the core layer to form the guide layer 8.

[Industrial application field]

The present invention relates to a method for manufacturing a directional coupler, and more particularly to a method for manufacturing a directional coupler using a semiconductor substrate.

In the field of optical communications, there is a demand for miniaturization of optical circuit elements. The directional coupler is also required to be made compact.
゛Figure 5 shows a conceptual diagram of a directional coupler. In FIG. 5, 71 and 72 represent a first waveguide and a second waveguide, respectively, and 6 represents a cladding layer. The first waveguide 71 and the second waveguide 72 run in parallel with a narrow interval between them, and a cladding layer 6 having a refractive index smaller than that of the waveguide is disposed around one periphery.

Light entering from one end of the first waveguide 71 gradually moves to the second waveguide 72 while propagating through the waveguide, and exits from one end of the second waveguide.

In order to completely transfer the light from the first waveguide 71 to the second waveguide 72, it is necessary that the optical coupling between the two be large, and an optical path of a certain length is also required. The greater the optical coupling, the more complete light can be transferred through a shorter optical path. Therefore, if the optical coupling can be increased, the length of the waveguide of the directional coupler can be shortened, and the directional coupler can be made smaller.

In order to increase the optical coupling, it is necessary to form a small interval between the first waveguide 71 and the second waveguide 72.

[Conventional technology]

FIGS. 6(a) to 6(C) are diagrams illustrating a conventional method for manufacturing a directional coupler. The conventional method will be explained with reference to those figures.

Referring to FIG. 6(a), a photoresist mask 9 exposing a first waveguide forming region 51 and a second waveguide forming region 52 is formed on a semiconductor substrate 1 made of non-doped InP.

Refer to FIG. 6(b). Using the mask as a mask, the first waveguide forming region and the second waveguide forming region are etched to form a groove in the substrate. The mask is then removed.

Referring to FIG. 6(c), non-doped InGaAsP is epitaxially grown on the entire surface to form a core layer 7 including a first waveguide 71 and a second waveguide 72.

Next, non-doped InP is epitaxially grown on the core layer to form an upper cladding layer 8.

In this way, a directional coupler having the cross-sectional shape shown in FIG. 6(C) is manufactured. However, in the conventional method, the first waveguide 71 and the The interval between the two waveguides 72 is set to 2.
It was difficult to reduce the thickness to less than μm.

[Problem to be solved by the invention]

Conventionally, the distance between the two waveguides in a directional coupler cannot be made small, so the optical coupling between the two waveguides cannot be made large, so the dimensions of the directional coupler in the light traveling direction are reduced. That was difficult.

In the present invention, the interval between two waveguides is formed small.

It is an object of the present invention to provide a manufacturing method for realizing a directional coupler with small dimensions.

[Means for Solving the Problems] (100) A step of forming a first mask 2 on the surface of a semiconductor substrate 1 to expose a long region in the (Oll) direction of the substrate, and using the first mask as a mask. forming a separation zone 3 by selective liquid phase epitaxial growth of a dielectric material on the substrate, and then removing the first mask; (1) forming a second mask 4 covering the first waveguide forming region 51 and the second waveguide forming region 52; and (2) selective liquid phase epitaxial growth of a dielectric material on the substrate using the second mask as a mask. forming a cladding layer 6, and then removing the second mask.

forming a core layer 7 including a first waveguide 71 and a second waveguide 72 by growing a material having a refractive index larger than the refractive index of the substrate, the separator, and the craft layer on the entire surface; The above problem is solved by a method for manufacturing a directional coupler, which includes the step of forming a guide layer 8 by growing a material having a refractive index smaller than the refractive index of the core layer on the core layer.

[Effect]

FIG. 1 is a perspective view of a directional coupler according to the method of the invention. In FIG. 1, 1 is a (100) semiconductor substrate, 3 is a separation band, 6 is a cladding layer, 8 is a core layer, 71 is a first waveguide, and 72 is a second waveguide.

8 represents the upper cladding layer.

In the directional coupler according to the method of the present invention, the distance between the first waveguide 71 and the second waveguide 72 is determined by the width of the bottom surface of the separation zone 3; The width can be made small.

In liquid phase epitaxial selective growth, it is known that a specific plane near the boundary between the mask-present and mask-free regions appears preferentially.
0) It is based on the new knowledge that within a mask groove extending in the (011) direction of a semiconductor substrate, growth of two planes having intersecting lines in the (011) direction progresses.

FIG. 2 shows the orientation relationship of the separation band 3 that grows in a long region in the (Oll) direction on the surface of the (100) semiconductor substrate 1. Second
As shown in the figure, the outer surface of the separation zone consists of two planes that intersect in the [011) direction, and one of the two planes is (I
One is the IT aspect, and the other is the (ITI) aspect. What is noteworthy is that a separation band with a width much narrower than the width of the patterning of the first mask 2 is obtained. The width and height of the bottom surface of the separation zone can be controlled by changing the liquid phase epitaxial growth conditions.

Thus, the first waveguide forming regions 51 on both sides of the separation zone
The interval between the first waveguide 71 and the second waveguide 72 can be decreased, and the interval between the first waveguide 71 and the second waveguide 72 can be decreased. By doing so, the optical coupling between the two becomes tight, and the directional coupler can be made smaller.

[Embodiment] FIG. 3 is an embodiment of the present invention, and is a diagram illustrating the manufacturing process of a directional coupler. FIG. 4 is a diagram showing the formation of separation zones in the manufacturing process. Hereinafter, embodiments will be described in detail with reference to FIGS. 3 and 4.

Refer to FIG. 3 <a> As the semiconductor substrate 1, a (100) n-InP substrate is used. Chemical vapor deposition (CVD) is applied to the entire surface of the substrate.
After forming a Si02 film with a thickness of 0.3 μm using +1 cal Vapor Deposition,
A first mask 2 is formed by patterning the 02 film.

The patterning has a long width of 2μ in the (011) direction of the substrate.
A trench of m length is dug in the SiO2 film, and the substrate is exposed within the trench.

The substrate is both a semiconductor material and a dielectric material.

Referring to FIG. 3(b), using the first mask 2 as a mask, n-1nP having the same composition as the substrate is selectively grown in the trench on the substrate by liquid phase epitaxial growth. Growth conditions were 585'C.

3 minutes, and under these conditions, at the center of the substrate surface in the groove, there are two planes that intersect in the (011) direction, that is, the (IIT) plane and the (ITI) plane, and the width of the bottom plane is approximately 1. A crm separation zone 3 is formed.

See FIG. 4 FIG. 4 is a diagram showing the formation of a separation zone by liquid phase epitaxial selective growth. 4I6(a) shows the state during liquid phase epitaxial selective growth, and FIG. 4(b) shows the state after liquid phase epitaxial selective growth.

31 represents a substrate holder, 32 represents a boat, and 33 represents a melt. The substrate l on which the first mask 2 is formed is held in the substrate holder 31
installed inside. A boat 32 having a hole for accommodating a melt 33 of a material to be selectively grown in a liquid phase epitaxial manner slides on the holder and carries the melt onto the substrate for selective growth (FIG. 4(a)).

After growing at a predetermined temperature and time, the vaginal boat is slid to release the melt from the substrate. In this way, the separation zone 3 is formed (FIG. 4(b)).

Refer to FIG. 3(c), the first mask 2 is removed. Next, a 0.3 μm thick SiO2 film was formed on the entire surface by chemical vapor deposition.
The S i O□ film is patterned to form a second mask 4.
form. The patterning is performed on the first waveguide forming region 51 (3) on the substrate on the separation band 3 and on both sides of the separation band
3 μm width) and the second waveguide formation region 52 (3 μm width), and leave the SiO2 film on the second waveguide formation region 52 (3 μm width), and
The O□ film is removed to expose the substrate.

Referring to FIG. 3(d), on the substrate outside the waveguide forming region, a material having the same composition as the substrate is selectively grown in liquid phase epitaxially to form a cladding layer 6 having a thickness of 0.2 μm. Growth conditions are 59
7° C., 2.5 seconds.

See Figure 3(e) The second mask 4 is removed by etching.

Refer to FIG. 3(f).
Ganic Vapor Phase Epitaxy
), the film thickness is 0.2. crm non-doped in
A core layer 7 of GaAsP (7 μm equivalent to 1.3 μm) is grown. The growth conditions are 650°C and 2 minutes.

The core layer 7 has a first waveguide 71 on the first waveguide formation region 51 and a second waveguide 7 on the second waveguide formation region 52.
2, and a portion connected to the waveguide.

Furthermore, an upper cladding layer 8 of non-doped InP having a thickness of 3 μm is grown on the core layer 7 by metal organic chemical vapor deposition. The growth conditions were 650°C and 60 minutes.

Thereafter, the lower surface of the semiconductor substrate 1 is polished to a total thickness of 150 μm.

The refractive index of each layer for light with a wavelength of 1.55 μm is as follows.

1, (100) semiconductor substrate 3.16933,
Separation zone 3.16936, cladding layer 3.16937, core layer
3.17098, upper cladding layer
3.1693 In this example, the compositions of the isolation zone 3 and the cladding layer 6 were made the same as the composition of the (100) semiconductor substrate 1.

This is not necessarily necessary, and other compositions may be used as long as the refractive index is smaller than the refractive index of the cladding layer 6.

In this embodiment, wavelength 1. This is a directional coupler for light with a diameter of about 10 μm, and the length of this directional coupler in the direction of light propagation is 0.8 m.
It is m.

When the width of the 5-separation zone 3 is formed to be 2 μm by the conventional method, the length of the directional coupler is 2 mm.

According to the method of the present invention, if the growth conditions for forming the 1-separation zone 3 are selected, it is possible to form a separation zone with a narrower width than in this embodiment, and therefore the length of the directional coupler can be reduced. It is possible to make it even shorter than this example.

〔Effect of the invention〕

As explained above, according to the present invention, the interval between the two waveguides in a directional coupler can be formed small, and therefore a directional coupler with small dimensions can be realized, which is useful in the field of optical communication. There is a lot to contribute.

[Brief explanation of the drawing]

FIG. 1 shows a directional coupler according to the present invention. Figure 2 shows the azimuth relationship of the separation zone, - Figure 3 shows an example. Figure 4 shows the formation of separation zones. FIG. 5 is a conceptual diagram of a directional coupler. Figure 6 shows the conventional method De6・Figure 4:,t;l,゛r・　. ■ indicates (100) semiconductor substrate≠semiconductor substrate. 2 is the first mask. 3 is the separation zone. 31 is a board holder. 32 is a boat. 33 is Melt. 4 is the second mask. 51 is a first waveguide forming region. 52 is a second waveguide forming region. 6 is the craft layer. 7 is the core layer. 71 is a first waveguide. 72 is a second waveguide. 8 is the upper craft layer; 9 is a photoresist mask How to say the 59th month of the month (IIT) side Ii＼Drunk TeIcy＞　Priif LF! 51 spears. Cow 2 ■ CQ> Cb) (C> ((i) 芙　稗】 Figure 3 Yα 1) (e) Banquet coloring Graduation 3rd figure (Y2) 33 Melt The custom of having a separate bath Cow 4 diagram A L-meshi committee where people can eat together? [Z Half 5th

Claims (1)

[Claims] (100) [011] of the semiconductor substrate (1) on the surface of the substrate
forming a first mask (2) that exposes a long region in the direction; and using the first mask as a mask, selective liquid phase epitaxial growth of a dielectric material is performed on the substrate to form a separation band (3). forming a first waveguide forming region (51) and a second waveguide forming region (52) on the separation band and the substrate on both sides of the separation band; ), forming a second mask (4) covering the cladding layer (6), and performing selective liquid phase epitaxial growth of a dielectric material on the substrate using the second mask as a mask.
forming a first waveguide ( forming a core layer (7) including a guide layer (71) and a second waveguide (72), and growing a material having a refractive index smaller than that of the core layer on the core layer to form a guide layer (71); 8) A method for manufacturing a directional coupler, comprising the step of forming.