KR19980050451A - Fabrication method of thinner waveguide using wet etching method - Google Patents

Abstract

In devices with many connection sites between optical waveguides and optical fibers at the input / output ends of devices, such as semiconductor lasers and semiconductor switches used in optical communication, it is very important to increase the optical coupling efficiency of the coupling portion.

The present invention relates to a method of making a tapered waveguide using a selective etching method. Particularly, the selective width and thickness of the waveguide can be made thinner by narrowing the width of the etch mask gradually and making the shape narrower than the actual mask width. Not only can it solve the problems in terms of reproducibility and economics.

Description

Fabrication method of thinner waveguide using wet etching method

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to semiconductor optical waveguide devices such as semiconductor lasers, and more particularly to a method for manufacturing a waveguide for improving optical coupling efficiency when packaged with an optical fiber.

In order to modularize semiconductor optical waveguide devices such as semiconductor lasers, packaging with optical fibers is one of the important process steps that determine the performance and price of a module. While the size of the beam emitted from the semiconductor optical waveguide device is small and the radiation angle is large, the waveguide beam of the optical fiber is large and the radiation angle is small. Due to the mismatch of the waveguide beams, the optical coupling efficiency is lowered when packaging with the optical fiber.

Therefore, in order to couple the light emitted from the semiconductor laser to the optical fiber as much as possible, a lens is generally inserted therebetween to adjust the shape of the beam to match each other to increase the coupling rate.

However, this method not only increases the manufacturing cost of the module but also lowers the reliability and yield. In particular, in the case of an optical switch and an array light source in which several input / output optical waveguides are narrowly formed, several optical fibers must be aligned and packaged at the same time, so it is impossible to insert a lens in principle.

As one method of solving this problem, a method of increasing the connection angle of an optical fiber by forming a lens with the optical fiber itself at the end of the optical fiber is used.

However, this method alone has a limitation in improving the coupling efficiency, and there is a difficulty in applying the array device. Therefore, in order to directly package a single mode optical fiber whose cross section is vertically cut, a method of modifying the waveguide shape of the optical waveguide device should be considered.

In other words, semiconductor light waveguide devices such as semiconductor lasers have a small beam size and a large radiation angle. InP and GaAs semiconductor waveguides have a large refractive index difference between the cladding layer and the core layer of 0.1 to 0.3, which satisfies the single mode. The width and thickness of the waveguide to be made are as small as 1 to 2 μm and 0.1 to 0.3 μm, respectively, and the size of the waveguide beam is also as small as 2-3 μm. Thus, there is a need for an area of the mode converter that allows the shape of the beam emitted within the semiconductor waveguide to be similar to the shape of the waveguide beam of the optical fiber. The most common structure of such a mode converter is that the core layer at the input / output end portion of the waveguide is made thinner or narrower in the direction perpendicular to the waveguide bonding direction or in the horizontal direction, thereby extending the shape of the waveguided beam to form a beam shape with the optical fiber. It is a method to increase the optical coupling efficiency by adjusting similarly to.

As such, the method proposed in the related art as a method of thinning the core layer of the waveguide has been proposed a multi-selective etching method, a selective growth method and a growth method using a shade mask.

In detail, first, the multiple etching method using selective etchant grows the core layer of the waveguide to include a plurality of intermediate layers capable of selective etching, and then gradually thins the thickness by several etching processes. The method is described in detail in FIGS. 1A-1F. As shown in FIG. 1A, an InGaAsP layer (waveguide core) 2 and a thin InP layer (etch stop thin film) 1a are alternately grown on the InP substrate 1, and then, as shown in FIG. After the photoresist shape 3a is formed, the top InGaAsP layer 2 is etched using a phosphoric acid and hydrogen peroxide solution that selectively etches only the exposed InGaAsP layer. Then, as shown in FIG. 1C, the InP layer is selectively etched using a phosphoric acid and hydrochloric acid solution, a new photoresist shape 3b is formed as shown in FIG. 1D, and the next InGaAsP layer 2 is selectively etched. 1E, the next InP layer 1a is selectively etched again. Subsequently, the etching process is repeated to finally form a waveguide structure as shown in FIG. 1F.

However, the conventional multi-selective etching method has manufacturing difficulties because it requires a plurality of intermediate layers in order to reduce light reflection and scattering loss in the etching cross section, and also requires many multi-step etching processes.

The selective area growth method shown in FIG. 2 forms a dielectric thin film, i.e., a SiNx or SiO ₂ thin film 22, on a portion of the semiconductor surface 21 where thin film growth takes place, The growth rate of the thin film 23 is increased compared to the region without the dielectric thin film (see A of FIG. 2). Therefore, in order to make the waveguide thinner and thinner, the main part of the waveguide needs to grow selectively, and the thinner area must grow in general.

However, in the conventional selective growth method, it is difficult to obtain high-quality waveguide characteristics because the thin film is nonuniform and hard to achieve lattice matching, compared to the general thin film growth.

Finally, in the conventional shadow masked growth method (shadow masked growth) to form a mask shape using the InP (31a) after forming the InGaAs layer 32 on the semiconductor surface 31 to grow a thin film. After the growth of the waveguide layer. In this case, if the surface area of the actual growth region is relatively large compared to the region into which the growth source gas is introduced, and the non-planar shape is present, the movement of the source gas is restricted, and thus the growth rate of the semiconductor thin film inside the mask shape is increased. Is to use the principle that is reduced. 3A shows the shape B of the shade mask formed before growing the waveguide layer. 3B shows that the waveguide layer 31b thinner than the waveguide layer 31a grown on the mask is grown because the region B in which the waveguide layer is to be grown is wider than the area B 'where the shade mask is opened. .

However, in this case, in order to improve the properties of the thin film grown inside the mask shape, there is a disadvantage in that the thickness of the intermediate layer between the mask and the substrate is generally about 5 to 6 μm.

It is an object of the present invention to improve a waveguide structure of an input / output terminal of an optical waveguide device to increase optical coupling efficiency with an optical fiber, thereby improving the performance of the module and at the same time providing a method for manufacturing an inexpensive optical module.

1A to 1F are cross-sectional views illustrating a manufacturing process of a conventional waveguide structure gradually thinned by multiple selective etching;

2 is a cross-sectional view showing a conventional waveguide structure gradually thinned by a selective growth method;

3A and 3B are sectional views of a manufacturing process of a conventional waveguide structure gradually thinned by a growth method using a shaded mask;

4A to 4G are cross-sectional views of a manufacturing process of a waveguide structure in which width and thickness are thinned at the same time by wet etching and ionic etching.

* Explanation of symbols on the main parts of the drawings

41 InP layer 42 InGaAsP layer

43 InGaAs layer 44 SiN _X layer

The present invention is a manufacturing method that the etching occurs in the thickness direction in a relatively narrow area by using a certain amount of excessive etching by using an etching mask in which the width of the region to be etched gradually becomes narrow during selective etching, generally selective etching is This is possible when there is a large difference in etching rates for different materials. This occurs because of the difference in reactivity between the specific etchant and the material being etched. In the case of a semiconductor optical device, in particular, a semiconductor waveguide to be dealt with in the present invention, the waveguide core layer is composed of an InGaAsP layer, and the cladding layer surrounding the core of the waveguide is composed of InP. For these two materials, InGaAsP and InP, the following selective etching solutions exist. First, when only InGaAsP is to be etched, a solution obtained by mixing H ₃ PO ₄ and H ₂ O ₂ in a ratio of 5 to 1 is used. In order to etch only InP, a solution obtained by mixing H ₃ PO ₄ and HCl in a ratio of 5 to 1 is used. In this case, the material etched for each etching solution is etched at a relatively fast rate of about 500 kW / sec, but on the contrary, almost no etching occurs for each other. Therefore, since the above etching solution has very good etching selectivity, it is possible to realize a manufacturing method, such as the multiple selective etching method, which has been mentioned in the prior art. In contrast, the HBr-based solution has a slight difference in etch rate with respect to InP and InGaAsP, but has no characteristic of selective etching.

In actual shaping of waveguides of optical devices, wet etching using these two solutions has been appropriately used. In recent years, reactive ion etching has been used to shape waveguides because wet etching occurs not only in the vertical direction but also in the horizontal direction, so that an ideal rectangular waveguide structure cannot be realized.

Accordingly, the present invention relates to a method of simultaneously thinning the width and thickness of a waveguide by appropriately using the two types of wet etching solutions. In this case, in order to compensate for the disadvantage that the waveguide region does not become a rectangular shape, reactive ion etching is also performed in parallel.

According to the present invention, a method for manufacturing a semiconductor optical integrated circuit having a multilayer structure including a waveguide layer, the first etching mask consisting of a first pattern width and a second pattern tapered than the first pattern width on top of the multilayer structure Forming a lower portion of the waveguide layer by etching the multilayer structure below with a selective etching solution; And removing the first etch mask and forming a second etch mask on top of the multilayer structure formed by the etching process to etch the lower layer to form reactive waveguides, thereby forming a waveguide that becomes thinner and thinner. It includes.

Hereinafter, with reference to the accompanying drawings will be described in detail the present invention.

First, referring to FIG. 4A, an InGaAsP waveguide layer 42, an InP layer 41a, and an InGaAs layer 43 are grown on an InP substrate 41. After the SiNx layer 44 is grown thereon, patterning is performed so that its width gradually narrows from 4 m to 1 m. The etching process is performed by first using a solution of H ₃ PO ₄ and H ₂ O ₂ in a ratio of 5 to 1, until the InGaAs almost disappears from the 1 μm wide region as shown in FIG. 4B. do. Next, as shown in FIG. 4C, the InP layer 41a is etched by using reactive ion etching or a solution in which H ₃ PO ₄ and HCl are mixed at a ratio of 5 to 1. In FIG. 4D, etching is performed using HBr solution without selective etching characteristics. At this time, the InGaAs layer 43, which has a relatively high etching rate with respect to the HBr solution, is removed first, and the surface of the InP layer 41a enters from the region where the width is extremely narrow, and the thickness of the InP layer gradually becomes thinner by etching. . When observing under a microscope, when the shape of the InP layer 41a at the end of the waveguide is formed to some extent, the etching is stopped and the SiNx mask layer 44 is removed (FIG. 4E). As shown in FIG. 4F, the region where the InGaAs layer 43 is removed and covered with the thinned InP layer by the reactive ion etching without the mask becomes gradually thinner as the waveguide core InGaAsP layer is exposed. As shown in FIG. 4G, the SiNx mask layer 44a is grown again to form an actual waveguide shape, and then, a reactive waveguide is etched to form a waveguide shape, and then an InP waveguide clad layer is grown to manufacture a waveguide.

The waveguide manufactured so as to become thinner and narrower in this manner, the growth of the waveguide layer on the flat substrate through a single growth process under the same conditions, so that the characteristics of the waveguide layer becomes thinner and the region is not exactly the same . In addition, the thinning structure can be obtained by only one exposure process, and the waveguide structure can be realized by two relatively simple exposure processes.

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and it is common in the art that various substitutions, modifications, and changes can be made without departing from the technical spirit of the present invention. It will be evident to those who have knowledge of.

As described above, the present invention provides a method of improving the waveguide structure of the input / output terminal of the optical waveguide device to obtain a high optical coupling efficiency, improving the performance of the module, and manufacturing the optical module at low cost. This is expected to contribute to the development of the semiconductor optical integrated circuit field.

Claims (9)

A method for manufacturing a semiconductor optical integrated circuit having a multilayer structure including a waveguide layer, the method comprising: forming a first etching mask having a first pattern width and a second pattern tapered and tapered than the first pattern width on an upper portion of the multilayer structure; Etching the multilayer structure with a selective etching solution to form a thickness of the waveguide layer gradually; And removing the first etch mask and forming a second etch mask on top of the multilayer structure formed by the etching process to etch the lower layer to form reactive waveguides, thereby forming a waveguide that becomes thinner and thinner. Waveguide manufacturing method comprising a. The method of claim 1, further comprising: forming a waveguide layer; Forming a lower waveguide cladding layer on the waveguide layer; Forming a layer for controlling an etching rate on the lower waveguide cladding layer; Forming the first mask having a width of an etch mask pattern on the layer for controlling the etch rate; A first etching step of etching a portion of the layer for controlling the etching rate by the selective wet etching method; A second etching step of etching a portion of the waveguide cladding layer under the layer for controlling the etching rate by the selective wet etching method; A third etching step of etching the layer for adjusting the etching rate and the lower waveguide cladding layer by the selective wet etching method so as to expose the lower waveguide layer; A fourth etching step of removing the etching mask and removing the layer for controlling the etching rate by removing the etching mask, and simultaneously etching the lower waveguide cladding layer and the waveguide layer to become thinner; And forming a second etching mask after the etching to etch the lower layer, thereby forming a waveguide that becomes thinner as the thickness of the waveguide layer becomes thinner. The method of claim 2, wherein the etching mask is SiN _X. The method of claim 2, wherein the waveguide layer is an InGaAsP layer. The method of claim 2, wherein the waveguide cladding layer is an InP layer. The method of claim 2, wherein the layer for controlling the etching rate is an InGaAs layer. The method of claim 2, wherein the selective etching solution in the first etching step is a mixture solution of phosphoric acid and hydrogen peroxide. The method of claim 2, wherein the selective etching solution in the second etching step is a mixed solution of phosphoric acid and hydrochloric acid. The method of claim 2, wherein the selective etching solution in the third etching step is an HBr solution.