JPH03200904A - Production of semiconductor optical waveguide - Google Patents

Abstract

PURPOSE:To decrease the radiation loss of a curved optical waveguide by etching the curved optical waveguide deeper than rectilinear optical waveguide to increase a rib height. CONSTITUTION:A 1st clad layer 2 of Al0.5 Ga0.5 As, a waveguide layer 3 consisting of GaAs and a 2nd clad layer 4 consisting of Al0.5Ga0.5As are grown on a GaAs substrate 1. After a crystal is grown, the semiconductor optical waveguide varying in the rib height of the rectilinear optical waveguide and the rib height of the curved optical waveguide is formed. Since the rib height of the curved optical waveguide 5 is allowed higher than the rib height of the rectilinear optical waveguide 6, the single mode condition of the curved optical waveguide 5 is easily realized. Further, the width of the rectilinear optical waveguide 6 and the width of the curved optical waveguide 5 are the same. The radiation loss can be effectively decreased even if the radius of curvature of the curved optical waveguide 5 is shortened to mm order or below. The radiation loss of the curved optical waveguide is thus decreased by the simple process.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for manufacturing a semiconductor optical waveguide used for connection between optical functional elements in semiconductor optical integrated circuits, etc. The present invention relates to a method for manufacturing an optical waveguide.

[Prior Art and its Issues] Along with the progress of optoelectronics, research and development on the integration of semiconductor optical devices has been actively promoted in recent years. In particular, semiconductor optical waveguides can be realized on semiconductor substrates by applying microfabrication technology cultivated in semiconductor electronic devices, and can be used for connections between each switch of a semiconductor optical matrix switch, and between semiconductor optical functional elements on the same substrate. (for example, connecting a light source to a switch or amplifier), and is considered to be one of the important components of semiconductor optical integrated circuits. As such a semiconductor optical waveguide, not only a straight leading waveguide but also a curved leading waveguide is required in order to connect each semiconductor optical device. Conventionally, it has been common practice to form this curved optical waveguide together with a straight optical waveguide using an ordinary one-shot photolithography method.

Incidentally, in order to downsize the integrated device, it is preferable to reduce the radius of curvature of the curved leading wavepath. However, since light inherently has the property of traveling in a straight line, if the radius of curvature of the curved leading waveguide is unnecessarily reduced, the conventional rib forming method has the problem of increasing radiation loss in the curved optical waveguide. Ta. Puri (R, J.

Electronics Letters No. 2 by DERI) et al.
Volume 3, page 845 (ELECTRONIC3LETTER3
Vol, 23 p, 845) 4;l: Reported. However, as the waveguide width increases, the guided light approaches the multi-mode condition, and at the same time, other integrated optical devices consisting of linear optical waveguides, such as directional coupler type optical switches, etc. adversely affect characteristics. Moreover, when the radius of curvature is made smaller than the order of magnitude, there is a problem in that even if the width of the waveguide is widened to strengthen the light confinement, the radiation loss is not reduced much.

Figure 3(a) is an example diagram showing the relationship between the radius of curvature and radiation loss when only the waveguide width of an S-curve optical waveguide is changed within single mode conditions. −
It can be seen that in the case of a radius of curvature of the order of magnitude, the radiation loss is reduced by widening the waveguide width, but in the case of a radius of curvature of the order of magnitude or less, the radiation loss is hardly reduced even if the waveguide width is widened.

As described above, the conventional methods have problems to be solved regarding reduction of radiation loss in the curved waveguide section.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a method for manufacturing a semiconductor optical waveguide, in which linear and curved rib-shaped optical waveguides are formed in succession, and a straight optical waveguide is formed. A method of manufacturing a semiconductor optical waveguide in which rib heights of a waveguide portion and a curved optical waveguide portion are different, the method comprising:
A step of laminating a cladding layer, a semiconductor waveguide layer, and a second semiconductor cladding layer in this order, and a step of laminating a portion other than a portion corresponding to a curved optical waveguide portion on the semiconductor substrate on which a semiconductor layer is laminated by this lamination step. Step 1 of covering with a mask,
forming a second mask in the shape of a waveguide in which the linear optical waveguide and the curved optical waveguide are continuous on the semiconductor substrate partially covered with the first mask by this masking step; etching the semiconductor substrate covered with the second mask until the first mask is removed in areas other than the areas covered with the second mask; and removing the second mask. It is characterized by including a process.

[Operation] Generally, light has the property of traveling in a straight line, so radiation loss occurs in the curved portion of a semiconductor optical waveguide.This radiation loss increases as the curvature of the curved optical waveguide is reduced. Conventionally, curved optical waveguides had to be fabricated with a curvature where radiation loss was negligible compared to waveguide loss, which was a major hindrance to shortening the overall length of the device. It is also possible to increase the width of the waveguide to strengthen the light confinement and reduce the radiation loss of a curved optical wavepath, but if the curvature is less than the order of magnitude, this method will not reduce the radiation loss much. Not only that, but
This approach is undesirable because it approaches a multi-mode condition, which adversely affects other optical devices on the same substrate.

In contrast, the present invention provides a manufacturing method for etching a curved optical waveguide deeper than a straight optical waveguide and making the rib height of the curved optical waveguide higher than that of the straight optical waveguide. By making the rib height of the waveguide higher than the rib height of the straight optical waveguide, it is possible to reduce the radiation loss of the curved optical waveguide when the radius of curvature is decreased, and it is also possible to easily realize single mode conditions, and it is possible to However, the present invention provides a manufacturing method that can effectively make the rib height of a curved waveguide higher than that of a straight waveguide. In the present invention, the ribs of the curved optical waveguide are formed by forming the first mask in a portion other than the portion corresponding to the curved optical waveguide portion, and then forming the second mask in the shape of the waveguide, which is the original mask. Since this is a method of making the height higher than the rib height of the straight optical waveguide section, it is possible to
Compared to the case where the etching process is performed multiple times, the number of etching steps required is only one. Furthermore, by appropriately selecting the material of the first mask, the height of the ribs in the straight and curved parts can be controlled with high precision, and strict alignment accuracy is required compared to the usual two-step photolithography process. The radiation loss of the curved optical waveguide section can be reduced through a simple process.

[Example] The present invention will be explained in more detail below with reference to the drawings.

FIG. 1 shows an example of the present invention, G a A s /A
1 is a perspective view showing an outline of a JGaAs semiconductor optical waveguide. FIG.

On the GaAs substrate 1, AN GaAs 0.
5 0.5 1 cladding layer 2 is grown, AJ GaO,50,
A GaAs waveguide N3 is grown on the 5 As first cladding layer 2. On the GaAs waveguide layer 3, an AJ GaAs second crystal having a rib portion is placed.
．． 5. A hard layer 4 is formed. The height of the rib portion is higher in the curved optical waveguide #r5 than in the straight optical waveguide portion 6.

First, a method for manufacturing the semiconductor optical waveguide shown in FIG. 1 will be described below. On the GaAs substrate 1, Aj Ga A
s First cladding layer 2.0.5 0.5 GaAs waveguide layer 3, A, Q GaAs second layer 0.50.5 Lat layer 4. The thickness of each layer is A, Go, sGa
o, s A s first cladding M2 has a thickness of about 1 to 2μ, GaAs waveguide layer 3 has a thickness of about 0.2μ, Ajo, sG
a o , s A s The second cladding layer 4 is approximately 1.2 μ square. After the crystal is grown as described above, a semiconductor optical waveguide is formed in which the rib height of the straight optical waveguide is different from the rib height of the curved optical waveguide.

The outline of the process of forming a semiconductor optical waveguide is shown in a perspective view in FIG. 2. First, as shown in FIG.
A portion 15 corresponding to the curved optical waveguide and its periphery is masked with a photoresist 11. Next, see Figure 2 (
As in b), Ti metal 9 is deposited over the entire surface to a thickness of about 15n1 by electron beam evaporation (EB method) or sputtering method. Since the photoresistor 11 can be easily removed using an organic solvent, only the portion 16 corresponding to the straight optical waveguide and its periphery is covered with Ti, as shown in FIG. 2(c).
It will be covered with metal 9. Using the usual photolithography method on this, as shown in Fig. 2(d),
A photoresist 41 is used to mask the shape of the waveguide to be formed.

Thereafter, when the portions other than those masked by the waveguide-shaped photoresist 41 are etched by the reactive beam etching method (RIBE method), the straight optical waveguide section 6 and the curved optical waveguide section are formed as shown in FIG. 2(e). 5 can be formed simultaneously. At this time, in the peripheral part of the straight optical waveguide section 6, T
Aj for the time required to completely remove the i metal layer 9
Since the etching time for the O, 5Ga, 5As second cladding layer 4 is reduced, the rib height of the curved optical waveguide section 5 can be made higher than the rib height of the straight optical waveguide section 6. After that, the photoresist 41 is made of GaAs/AjGaAs.
If it is removed with an organic solvent that does not react with the wafer and can only remove the photoresist, the rib height of the straight optical waveguide section 6 and the rib height of the curved optical waveguide section 5 will change as shown in Figure 2 (f>). Semiconductor optical waveguides with different values are formed.At this time,
The rib height of the straight optical waveguide section 6 is 0.9 μm, and the rib height of the curved optical waveguide section 5 is 1 μm.

The above is an embodiment of the method for manufacturing a semiconductor optical waveguide according to the present invention, and in the semiconductor optical waveguide manufactured by the method described above, the radiation loss of the curved optical waveguide is improved compared to the conventional one, and single mode conditions can be easily realized. The principle will be explained below.

In this embodiment, as shown in FIG. 1, the rib height of the straight optical waveguide section 6 is the same as usual, whereas the rib height of the curved optical waveguide section 5 is slightly higher. Therefore, light is strongly confined in the curved optical waveguide s5, and radiation loss is reduced.

FIG. 3(a) shows an example of calculation of the relationship between the radius of curvature and the radiation loss when the waveguide width is changed within the single mode condition. The radiation loss is calculated as the total radiation loss per one S-shaped waveguide whose top view is shown in Fig. 4(a), and the cross-sectional structure of the S-shaped waveguide is shown in Fig. 4. Calculations were made for the layered structure shown in (b).

Here, the AJ GaAs first cladding layer 7
The layer thickness of 0.5 0.5 is 1.5 μm, the layer thickness of the waveguide layer 71 is 0.2 μm, Aj
Layer thickness of GaAs second cladding layer 72: 0.5
0.5 to 1.2 μm, etching depth t8 (74) to 0.9
) tri, the waveguide width W (73) is 2 μl, 2.5
The thickness was changed to 3 μm. From Figure 3 (a), when the radius of curvature is several ml+, the radiation loss can be reduced by widening the waveguide width, but when the radius of curvature is less than a few ml, the radiation loss does not change much even if the waveguide width is widened. It turns out that there isn't.

Figure 3(b) shows an example of the relationship between the radius of curvature and radiation loss when the rib height of the waveguide is changed within single mode conditions with the same structure as in Figure 3(a). As in (a), the calculation of radiation loss is as shown in Figure 4(a).
Figure 4(b) shows the cross-sectional structure of the S-shaped waveguide.
Calculations were made for the layered structure shown in , and here, AJ
Layer thickness o, s of GaAs first cladding layer 70
o, s are 1.5 μm, the layer thickness of the waveguide layer 71 is 0.2 μm, Aj
Layer thickness of GaAs second cladding layer 72: 0.5
0.5 to 1.2 μm and the waveguide width W (73) to 2 μm, the etching depth t. (74) to 0.9 μte, 0
．． The thickness was changed to 95 μm and 1 μm. From Figure 3(b),
It can be seen that when the rib height of the waveguide is increased, the radiation loss can be effectively reduced even if the radius of curvature is less than a quantity order.

In this embodiment, the height of the ribs is increased to strengthen the confinement of light. Therefore, even if the radius of curvature of the curved optical waveguide section 5 is shortened to less than the order of m, the width of the waveguide is increased and the confinement of light is increased. It is possible to effectively reduce radiation loss compared to the case where the

In addition, since the straight optical waveguide section 6 has the same rib height as before,
The single mode condition can be easily maintained in the straight optical waveguide section 6, and the single mode condition in the curved optical waveguide section 5 is acceptable even if the rib height is higher than that of the straight optical waveguide section 6. Single mode conditions can be achieved. Furthermore, the width of the straight optical waveguide section 6 and the curved optical waveguide section 5
Since the widths are the same, no particular problem arises regarding connection loss between the straight leading waveguide section 6 and the curved optical waveguide section 5.

Note that the present invention is not limited to the above embodiments. Although a GaAs-based material is used in the embodiment, the invention is not limited to this, and the present invention is applicable to other materials such as InP-based materials as long as they are materials for optical waveguides. Further, in this example, etching is performed by dry etching using the RIBE method, but other etching methods may be used as long as the rib portions are formed. For example, reactive ion etching (RIE method) may be used. In addition, in order to make the etching depth of the rib portion of the curved optical waveguide section 5 deeper than that of the straight optical waveguide section 6,
In this example, Ti metal 9 was deposited on the portion 16 corresponding to the straight optical waveguide section and its surroundings, but it is not limited to Ti metal, and any material that has excellent layer thickness controllability and etching rate controllability may be used. Other materials may be used.Furthermore, in this embodiment, the Ti metal layer 9 remains on the rib portion of the linear optical waveguide portion 6, but it is not necessary that the Ti metal layer 9 remains. There is nothing special about this, and it may be removed if necessary.

[Effects of the Invention] As described above, the present invention provides a semiconductor optical waveguide in which the radiation loss is improved compared to the conventional one even in a curved optical waveguide portion with a curvature of the order of a circle or less, and it is easy to realize a single mode condition. A manufacturing method is provided. Therefore, by adopting the manufacturing method of the present invention, it is possible to shorten the length occupied by the curved optical waveguide of the semiconductor optical waveguide in an optical device such as an optical switch, making it possible to shorten the device and reduce the device length. As the optical path length becomes shorter due to miniaturization, it is also possible to reduce waveguide loss, and furthermore, it is possible to manufacture a semiconductor optical waveguide that does not adversely affect other optical devices on the same substrate. Moreover, in the present invention, the curved optical waveguide is formed by forming the first mask in a portion other than the portion corresponding to the curved waveguide portion, and then forming the second mask in the waveguide shape, which is the original mask. Since we have adopted a clever method of making the rib height of the straight optical waveguide section higher than the rib height of the straight optical waveguide section, the conventional method of creating a difference in rib height requires two etching steps. The method of the present invention requires only one etching step, and furthermore, the method of the present invention allows the heights of the ribs in the straight and curved portions to be controlled with high precision by appropriately selecting the material for the first mask. Furthermore, compared to the usual two-step photolithography process, strict alignment accuracy is not required, and the radiation loss of the curved optical waveguide can be reduced through a simple process.

[Brief explanation of drawings]

FIG. 1 shows GaAs/AjGaA, which is an embodiment of the present invention.
FIG. 2 is a perspective view showing an outline of an s-semiconductor optical waveguide. FIG. 2 is a perspective view showing an outline of the process of forming a semiconductor optical waveguide according to an embodiment of the present invention. It is a perspective view showing an outline of a state in which the corresponding portion 15 is masked with photoresist 11, and FIG. 2(b) is F, B.
FIG. 2(c) is a perspective view schematically showing a state in which Ti metal 9 is deposited on the entire surface by a method, and FIG. 2(c) is a perspective view schematically showing a state in which the photoresist 11 shown in FIG. 2(b) has been removed. 2(d) is a perspective view schematically showing a state in which a GaAs/AJGaAs wafer is masked in the shape of a waveguide to be formed with a photoresist 41, and FIG. 2(e) is a
FIG. 2(f) is a perspective view schematically showing a state in which the waveguide is etched into the shape of the waveguide to be formed by the IBE method, and FIG.
FIG. 3 is a schematic perspective view after removing the photoresist 41 shown in FIG. Figure 3 is a diagram showing the relationship between radiation loss and radius of curvature R of a curved optical waveguide.
) is a diagram showing the relationship between radiation loss and R when changing the waveguide width within single mode conditions, and Figure 3 (b) shows the same structure as Figure 3 (a) but with rib height changed under single mode conditions. FIG. 3 is a diagram showing the relationship between radiation loss and R when the height is changed. Figure 4 is a diagram that supplements the calculation of radiation loss in Figure 3.
FIG. 4(b) is a sectional view showing a model of the waveguide structure of the curved optical waveguide used for calculation of radiation loss. 1 ・-Ga As substrate, 2-AJ Ga
AsO, 50, 5 first cladding layer, 3...GaAs waveguide layer, 4...A
(GaAs second cladding layer, 5... curved light guide 0
．． 5 0.5 Wave path section, 6... Straight leading wave path section, 9... Ti metal layer, 10.-GaAs wafer GaAs wafer, 11゜4
DESCRIPTION OF SYMBOLS 1... Photoresist, 15... Portion corresponding to a curved optical waveguide and its surroundings, 16... Portion corresponding to a straight optical waveguide and its surroundings, 70... Aj Ga0.
5 o, sAs first cladding layer, 71-GaAs waveguide layer, 72...AJo, sGao
, sA s second cladding layer, 73... waveguide width W,
74...Etching depth t.

Claims (1)

[Claims] In a method for manufacturing a semiconductor optical waveguide, in which straight and curved rib-type optical waveguides are successively formed and the rib heights of the straight optical waveguide section and the curved optical waveguide section are different, at least a semiconductor waveguide is formed on a semiconductor substrate. A step of laminating a first cladding layer, a semiconductor waveguide layer, and a second semiconductor cladding layer in this order, and a step of laminating a portion of the semiconductor substrate other than a portion corresponding to a curved optical waveguide portion on which a semiconductor layer is laminated by this lamination step. a step of covering with a first mask, and a step of covering the straight optical waveguide and the curved optical waveguide on the semiconductor substrate partially covered with the first mask by this masking step, and forming a second waveguide shape in which the straight optical waveguide and the curved optical waveguide are connected. a step of forming a mask; and a step of etching the semiconductor substrate covered with the second mask until the first mask is removed in a portion other than the portion covered with the second mask; A method for manufacturing a semiconductor optical waveguide, comprising the step of removing the second mask.