JP2005055764A - Optical waveguide and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for stably preparing a butt joint with reduced optical coupling loss by reducing the swell of a semiconductor layer at the joining face of the butt joint, and also suppressing the variation of swell amounts. <P>SOLUTION: A 1st optical waveguide structured by stacking an InGaAsP active layer 152 and p-InP clad layer 154 on an InP substrate 150 is formed, and adjoining this, a 2nd optical waveguide with an InGaAsP core layer 160 and p-InP clad layer 162 stacked thereon is formed adjacent to the 1st optical waveguide. Both of the 1st and 2nd optical waveguides are formed to be extended in the direction <110>, and the joining face of the both is made a surface <100>. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical waveguide in which a plurality of waveguides are connected.

  Conventionally, when an optical system is composed of individual components such as a light emitting element, a lens, and a light receiving element, an optical axis alignment process is required. In this optical axis alignment step, since alignment is usually required in units of μm, there is a problem that it is difficult to reduce manufacturing time and cost. Further, this optical system has a problem that the optical axis is shifted due to thermal expansion and contraction of the material fixing the individual components due to fluctuations in environmental temperature.

  In order to solve such a problem, a technique for integrating a light emitting element, a light receiving element, a duplexer, a multiplexer, etc. on the same substrate has been proposed. In this way, the optical axis alignment process, which is the biggest problem of the optical system, is eliminated, so that the cost can be reduced in manufacturing the optical system. Further, since this optical system is integrated, it is possible to reduce the fluctuation of the optical axis deviation due to the fluctuation of the environmental temperature.

  In manufacturing such a system, it is an important technical problem to connect the element and the waveguide while suppressing optical loss. Conventionally, a joint structure called a butt joint (butt joint) has been employed at the joint between the light emitting element and the optical waveguide. The butt joint refers to a joint structure in which end faces of two or more optical waveguides having different refractive index distributions are brought into contact with each other in the optical axis direction.

Conventionally, several proposals have been made for a butt joint of an InGaAsP-based waveguide formed on a (001) InP substrate (Patent Documents 1 and 2). In such a butt joint, first, the first waveguide is formed by epitaxial growth of the semiconductor layer, and then the semiconductor layer is partially removed using a mask, and the second waveguide is epitaxially grown using the mask. Can be produced. In the InGaAsP-based waveguide, the joining surface of the butt joint is usually the (110) plane because the laser emission end face is the cleavage plane (110) plane.
On the other hand, in Patent Document 1, by setting the joint surface to a surface other than the (110) surface, the guided light reflected by the joint surface is radiated out of the waveguide and is incident on the waveguide again. It is described that it can be prevented from returning to the original direction and the inconvenience caused by reflected light can be eliminated. Further, the same document points out that when a low index surface such as the (110) surface is used as a bonding surface, abnormal growth of the semiconductor layer is likely to occur at the bonding surface. 110) It is described that it is effective to use a surface other than the surface.

On the other hand, Patent Document 2 describes that the abnormal growth of the semiconductor layer described above is caused by side etching of the end surface of the semiconductor layer by side etching when the first waveguide is etched. Has been. Further, this side etching amount becomes more conspicuous when the joint surface is provided obliquely with respect to the optical waveguide direction (when the joint surface is viewed from above) from the viewpoint of antireflection as described in Patent Document 1. It is described. In this document, it is described that the side etching of the first waveguide can be suppressed and the optical coupling loss can be reduced by using dry etching and wet etching together in order to solve such a problem.
Japanese Patent Laid-Open No. 9-197154 FIG. JP-A-11-87844 Paragraphs 0027 and 0044

  However, according to the study by the present inventor, it has been clarified that the bulge of the semiconductor layer on the bonding surface cannot be sufficiently eliminated only by providing the bonding surface obliquely with respect to the optical waveguide direction. In addition, it has been clarified that when the bonding surface is provided obliquely, the amount of swelling of the semiconductor layer varies greatly from element to element.

  When the swell of such a semiconductor layer occurs, the degree of light loss at the bonding surface increases. Further, if the degree of swell varies, the degree of optical coupling loss varies, causing a problem of variation in device performance.

  The present invention has been made in view of the above circumstances, and reduces the rise of the semiconductor layer on the joint surface of the butt joint and suppresses the variation in the amount of the rise, thereby stabilizing the butt joint with less optical coupling loss. The purpose is to provide the technology to create automatically.

According to the present invention, an optical waveguide in which a first waveguide and a second waveguide are butt-jointed, wherein the first and second waveguides are zinc-blende crystal structures on a substrate. The core layer and the clad layer made of the semiconductor are laminated in this order, and the bonding surface of the first and second waveguides is a surface equivalent to the (100) surface or a substrate with respect to these surfaces. An optical waveguide is provided that includes a surface that is inclined with respect to the normal of the surface and has an off angle of 7 degrees or less in the in-plane direction of the substrate.
According to the invention, a step of forming a waveguide structure by laminating a first core layer and a first cladding layer on a substrate, and removing the waveguide structure selectively to form a first waveguide. Forming a waveguide and laminating a second core layer and a second cladding layer on the substrate to form a second waveguide that is butt-jointed to the end face of the first waveguide. And the bonding surface of the first and second waveguides is a plane equivalent to the (100) plane, or is inclined with respect to the normal of the substrate plane with respect to these planes and is in the in-plane direction of the substrate An optical waveguide manufacturing method is provided, characterized in that the surface has an off angle of 7 degrees or less.

  The present invention employs the specific surface as described above as the waveguide bonding surface. As described in the section of the prior art, in order to avoid inconvenience due to light reflection or to suppress abnormal growth when the (110) plane perpendicular to the optical waveguide direction is used as the bonding surface, the bonding surface is inclined. It was known as conventional knowledge. On the other hand, the present invention not only makes the joint surface oblique but also selects the specific surface to remarkably suppress the swell of the semiconductor layer and reduce the variation of the swell and stabilize the swell. The present invention provides a butt joint that exhibits element performance. As described later in the embodiments and examples, the bonding surface can be stably formed into a good shape by using the surface as the bonding surface. Here, the plane equivalent to the (100) plane refers to the (100) plane, the (010) plane, the (-100) plane, and the (0-10) plane.

In this invention, it can be set as the structure by which the end surface of the clad layer of each waveguide contained in the said joint surface becomes a substantially perpendicular | vertical surface with respect to a board | substrate.
In this way, since the end surface of the cladding layer is a surface substantially perpendicular to the substrate, the degree of bulging of the semiconductor layer on the bonding surface can be made uniform, and variations between elements can be reduced.

  In this invention, it can be set as the structure which the end surface of the clad layer of the said waveguide receded rather than the said joint surface. For example, the end face of the cladding layer of the waveguide can be set back by 0.3 μm or more from the bonding surface.

  In this way, since the core layer is formed so as to recede from the cladding layer, a certain amount of semiconductor material is accommodated in the receding portion, and the rise of the semiconductor layer on the joint surface is further reduced. Can do.

In the manufacturing method of the present invention, the first waveguide layer may be formed by selectively removing the first core layer and the first cladding layer by dry etching. By doing so, it is possible to effectively reduce the variation in the rise of the semiconductor layer.
Alternatively, the first waveguide layer may be formed by selectively removing the first core layer and the first cladding layer by wet etching. Further, the first waveguide layer may be formed by selectively removing the first cladding layer by dry etching and selectively removing the first core layer by wet etching. By doing so, the amount of swelling of the semiconductor layer can be reduced.
Furthermore, in the manufacturing method of the present invention, the second core layer and the second cladding layer may be formed by epitaxial growth using a growth gas containing a halogen gas. By doing so, the amount of swelling of the semiconductor layer and its variation can be effectively reduced.

  ADVANTAGE OF THE INVENTION According to this invention, while raising the swell of the semiconductor layer in the joint surface of a butt joint, the dispersion | variation in the amount of the swell is suppressed, Thereby, a butt joint with few optical coupling losses can be provided stably.

First Embodiment FIG. 1 shows a structure of a butt joint according to the present embodiment. In the figure, a first waveguide having a structure in which an InGaAsP active layer 152 (film thickness 0.4 μm) and a p-InP clad layer 154 (film thickness 1.5 μm) are stacked on an InP substrate 150 is formed. A second waveguide in which an InGaAsP core layer 160 (film thickness: 0.4 μm) and a p-InP cladding layer 162 (film thickness: 1.5 μm) are stacked is formed adjacent to this waveguide and the optical waveguide direction. . The first waveguide includes an InGaAsP active layer 152 having a gain and functions as an active element. On the other hand, the InGaAsP core layer 160 in the second waveguide is a layer having no gain.

  The first waveguide and the second waveguide extend in the <110> direction, and both are bonded by a bonding surface including a (010) plane. The InGaAsP active layer 152 and the InGaAsP core layer 160 are bonded to each other at a plane rotated about 45 degrees around the axis in the <100> direction with respect to the (010) plane. On the other hand, the p-InP cladding layer 154 and the p-InP cladding layer 162 are joined on a plane substantially equal to the (010) plane (within an off angle of 5 degrees).

  FIG. 2 is a view for explaining a method of forming the butt joint of FIG. First, as shown in FIG. 2A, an InGaAsP active layer 152 and a p-InP cladding layer 154 are stacked in this order on an InP substrate 150, and a mask 156 patterned into a predetermined shape is provided thereon. Next, as shown in FIG. 2B, the p-InP cladding layer 154 is selectively dry etched using the mask 156 as a mask. As the etching gas, a mixed gas containing one or both of methane and chlorine is preferably used. By using such an etching gas, the rising of the semiconductor layer on the bonding surface can be suppressed as described later. FIG. 2B shows a state in which only the p-InP cladding layer 154 is etched. At this time, a part of the InGaAsP active layer 152 may be dry etched at the same time.

  Next, the InGaAsP active layer 152 is selectively wet etched using an etching solution containing sulfuric acid using the mask 156 as a mask (FIG. 2C). As described above, the (010) plane and the core island whose end face is the plane inclined from this plane in the stacking direction of the semiconductor layer are formed.

  FIG. 3 is a diagram for explaining a method of forming a butt joint following FIG. From the state of FIG. 2C, using the mask 156, the InGaAsP core layer 160 and the p-InP clad layer 162 are selectively buried in this order around the obtained waveguide structure (FIG. 3A). As the growth method, MOVPE method or the like is used. Subsequently, as shown in FIG. 3B, a striped mask 164 extending in the <110> direction is formed on the surfaces of the mask 156 and the p-InP cladding layer 162. Next, as shown in FIG. 3C, the InGaAsP active layer 152, the p-InP clad layer 154, the InGaAsP core layer 160, and the p-InP clad layer 162 are selectively dry etched using the mask 164, as shown in FIG. 3C. A waveguide structure 166 is formed. As an etching gas, a mixed gas containing one or both of methane and chlorine can be used.

  The butt joint shown in FIG. 1 is formed by the above process. Since this butt joint uses the (010) plane or a plane inclined obliquely within a predetermined range from this plane, the rise of the semiconductor layer in the joint portion, which has been a problem in the past, is significantly reduced. Further, with respect to the degree of swelling of the semiconductor layer on the bonding surface, it is possible to reduce the variation between elements and stably form a waveguide with good performance. Furthermore, in this embodiment, since the InGaAsP active layer 152 is etched by wet etching and the p-InP cladding layer 154 is etched by dry etching in FIG. , It is possible to further reduce.

  The problem of the rise of the semiconductor layer will be described below with reference to the drawings. FIG. 5 is a view showing the structure of a conventional butt joint. This butt joint uses a (110) plane perpendicular to the optical waveguide direction as a bonding surface. A first waveguide having a structure in which an InGaAsP active layer 152 and a p-InP cladding layer 154 are laminated on an InP substrate 150 is formed, and a mask 156 is provided thereon. The state in which the InGaAsP core layer 160 and the p-InP clad layer 162 are grown adjacent to this is illustrated. Since the bonding surface is the (110) plane, the lateral growth of the p-InP cladding layer 162 is fast, and the InGaAsP core layer 160 and the p-InP cladding layer 162 are raised as shown in the figure. The p-InP clad layer 162 is grown so as to cover the upper part of the mask 156. For this reason, there has been a problem that the degree of light loss at the joint surface increases. The joint according to the present embodiment can minimize the occurrence of such an abnormal shape, and can stably realize a joint structure with little optical loss.

Second Embodiment In the first embodiment, the clad layer constituting the waveguide is formed by dry etching and the core layer is formed by wet etching, but both may be formed by dry etching. Both may be formed by wet etching.
FIG. 4 is a diagram illustrating a layer structure of a semiconductor layer in the vicinity of the bonding surface. In the present embodiment, a plane perpendicular to the <010> direction, that is, a (010) plane or a plane obtained by side etching the plane is used as a bonding plane. By setting it as such a joint surface, the swelling of a semiconductor layer is suppressed.
On the right side in FIG. 4, an InGaAsP core layer 160 and a p-InP clad layer 162 are stacked. The light guiding direction is a direction from left to right in the drawing. As shown in the figure, the InGaAsP core layer 160 and the p-InP clad layer 162 have a shape that rises toward the top of the substrate. This is due to the instability of growth at the bonding surface 157 of these layers. When the bonding surface 157 is the (110) plane, the InGaAsP core layer 160 and the p-InP cladding layer 162 grow at a very high growth rate in the lateral direction, and as described in the prior art, as shown in FIG. Abnormal shape occurs.

  Each of the partial diagrams in FIG. 4 is obtained by changing the etching method of the InGaAsP active layer 152 and the p-InP cladding layer 154. FIG. 4A shows a structure obtained by processing both the InGaAsP active layer 152 and the p-InP cladding layer 154 by dry etching. When this method is adopted, variation in the amount of swelling can be remarkably suppressed, and good joint performance can be stably obtained.

  In FIG. 4B, the InGaAsP active layer 152 is processed by wet etching and the p-InP cladding layer 154 is processed by dry etching. This corresponds to the process of the above embodiment. According to this method, it is possible to effectively reduce the swell amount and its variation. In addition, since the bonding surface between the InGaAsP active layer 152 and the InGaAsP core layer 160 is formed below the p-InP clad layer 154 protruding in a bowl shape, a good optical coupling rate can be stably obtained. In FIG. 4B, the end face of the InGaAsP active layer 152 has a shape that is recessed by 0.3 μm or more from the end face of the p-InP cladding layer 154. That is, the upper end face of the InGaAsP active layer 152 is at a position that is recessed by 0.3 μm or more from the end face of the p-InP cladding layer 154. For this reason, the effect which stabilizes the said optical coupling factor is fully acquired.

  FIG. 4C shows an InGaAsP active layer 152 and a p-InP cladding layer 154 both formed by wet etching. When this method is adopted, a recess formed by wet etching is formed immediately below the mask 157. In the region 170 shown in FIG. 4C, the boundary between the InGaAsP core layer 160 and the p-InP cladding layer 162 becomes slightly unclear. On the other hand, at the time of growth of the semiconductor layer when forming the second waveguide, the semiconductor material is taken into the recess directly under the mask, and as a result, an advantage that the rising amount of the semiconductor layer is reduced is obtained.

As described above, the degree of swell of the semiconductor layer on the bonding surface varies greatly depending on the deviation from the (110) plane. In FIG. 4, when the maximum thickness of the InGaAsP core layer 160 is D and the thickness of the InGaAsP active layer 152 is d, the value of D / d is 1 or more and 1.6 or less, so that a good optical coupling ratio is exhibited. A butt joint can be obtained. In FIG. 4, D ₁ tends to have a larger value than D ₂ and D ₃ , but when growing, the value of D ₁ is reduced by adding a halogen gas such as chlorine to the growth gas. It is possible.

  The present invention has been described based on the embodiments. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications are possible and that such modifications are also within the scope of the present invention.

For example, in the above embodiment, the waveguide is configured using the InGaAsP-based semiconductor layer, but other III-V group compound semiconductors may be used. For example, a group III-V compound semiconductor in which a group III atom includes any of B, Al, Ga, In, and Tl and a group V includes any of N, P, As, Sb, and Bi can also be used. Specifically, InGaAsP, AlGaInAs, AlGaInAsP, AlGaInP, InGaAsSb, InGaPSb, InGaAsN, AlGaInN, TlGaInAs, TlGaInAsN, TlGaInPN, and the like can be exemplified.
The composition of the active layer can be designed as appropriate, for example, a 1.55-μm composition InGaAsP layer. Alternatively, the active layer may have a quantum well structure in which InGaAsP layers and InP layers are alternately stacked. The composition of the semiconductor layer is appropriately selected according to the purpose and application.
In the above-described embodiment, the (010) plane is used as the bonding surface. However, a plane equivalent to this or a plane having an inclination within a predetermined range can be used. FIG. 7 shows an example in which the (100) plane is adopted, and a waveguide structure having such a structure can also be used.

Example 1
A bad joint having the cross-sectional structure of FIG. 4B was manufactured by the method described in the first embodiment. In FIG. 4B, the upper end face of the InGaAsP active layer 152 is at a position retreated by about 0.3 μm from the end face of the p-InP cladding layer 154, and the inclination of the bonding face is about 20 degrees with respect to the <001> direction. The p-InP cladding layer 154 was processed by dry etching, and the InGaAsP active layer 152 was processed by wet etching.

  FIG. 6 is a top view of the waveguide structure evaluated in this example. The first waveguide 182 and the second waveguide 180 are connected in tandem in the waveguide direction. A plurality of butt joints were prepared by changing the value of θ in FIG. 6, and the appearance of the cross-sectional structure was observed with a scanning microscope. The results are shown in Table 1.

In the table, the maximum thickness of the InGaAsP core layer 160 in FIG. 4B is D, and the thickness of the InGaAsP active layer 152 is d.

  From the results of Table 1, when the angle of the bonding surface is perpendicular to the optical waveguide direction, that is, when the bonding surface is the (110) surface, the degree of abnormal growth (D / d) of the bonding surface is significant. It became clear that In addition, when θ is a value larger than 0 and the bonding surface is provided obliquely with respect to the optical waveguide direction, the degree of abnormal growth is reduced, but when θ is 15 degrees, 30 degrees, and 60 degrees, the reduction effect is It can be seen that D / d is remarkably reduced when the angle is not 45 degrees, that is, when the bonding surface is a (010) plane or a plane having an inclination within a predetermined range with respect to this plane.

  Further, it has been clarified that the variation in the value of D / d is remarkably smaller when the (010) plane or the like is used than when other planes are used. About this reason, it guesses as follows.

  FIG. 8 is an enlarged view of the joint surface between the first waveguide 182 and the second waveguide 180 in FIG. When θ in FIG. 6 is 45 degrees, the bonding surface is equivalent to the (100) plane, and the bonding surface is formed of one flat atomic surface (a surface extending horizontally from the left end to the right end in FIG. 8). . However, when θ is set to a value different from 45 degrees, the joint surface is composed of an uneven surface in which (100) equivalent surfaces are connected by steps (steps) that are an integral multiple of one atomic layer (step). Stepped surface in FIG. 8). Here, the step height and interval (terrace width) are not uniform within the joint surface. Although FIG. 8 shows variations in the size of steps and terraces in the substrate in-plane direction, this variation also occurs in the <001> direction. It is considered that the variation in the growth rate of the semiconductor layer in the vicinity of the bonding surface occurs due to the variation in the size of the step and the terrace, and the degree of swelling of the semiconductor layer varies.

  Further, as θ is away from 45 degrees, the height or density of the step becomes higher and the terrace width becomes narrower. Specifically, assuming that the bonding surface is (010), the width of the terrace per molecular layer step becomes narrower as θ increases. When θ is 5 degrees, the terrace width is 11.4 times the step height, 8.1 times when 7 degrees, 5.7 times when 10 degrees, and 3.73 times when 15 degrees. For this reason, it is considered that the growth rate is likely to vary, and the degree of protrusion on the mask will vary greatly.

It is a figure which shows the structure of the butt joint which concerns on embodiment. It is a figure explaining the formation method of the butt joint of FIG. It is a figure explaining the formation method of the butt joint following FIG. It is a figure which shows the layer structure of the semiconductor layer of a joint surface vicinity. It is a figure which shows the structure of the conventional butt joint. It is the figure which looked at the structure of the waveguide evaluated in the Example from the upper surface. It is a figure which shows the structure of the butt joint which concerns on embodiment. It is a figure explaining the dispersion | variation in the semiconductor layer growth rate in a junction surface.

Explanation of symbols

150 substrate 152 active layer 154 clad layer 156 mask 157 joint surface 160 core layer 162 clad layer 164 mask 166 waveguide structure 170 region 180 second waveguide 182 first waveguide

Claims (12)

An optical waveguide in which the first waveguide and the second waveguide are butt-jointed,
The first and second waveguides have a layer structure in which a core layer and a clad layer made of a zincblende-type crystal structure semiconductor are laminated in this order on a substrate,
The joint surface of the first and second waveguides is a plane equivalent to the (100) plane, or is inclined with respect to the normal of the substrate surface with respect to these surfaces, and is off within 7 degrees in the in-plane direction of the substrate. An optical waveguide comprising a surface having a corner.   2. The optical waveguide according to claim 1, wherein an end surface of the cladding layer of the first waveguide is a surface substantially perpendicular to the substrate at the bonding surface.   3. The optical waveguide according to claim 1, wherein an end surface of the core layer of the first waveguide is a surface substantially perpendicular to the substrate at the bonding surface.   3. The optical waveguide according to claim 1, wherein an end surface of a core layer of the first waveguide is recessed from an end surface of a cladding layer of the first waveguide at the joint surface. .   The optical waveguide according to claim 1, wherein the core layer of the first waveguide includes a light emitting layer. The core layers of the first and second waveguides are
In _x Ga _1-x As _y P _1-y (where x and y are 0 or more and 1 or less)
The optical waveguide according to claim 1, comprising: Forming a waveguide structure by laminating a first core layer and a first cladding layer on a substrate;
Selectively removing the waveguide structure to form a first waveguide;
Laminating a second core layer and a second cladding layer on the substrate to form a second waveguide that is butt-joined to the end face of the first waveguide;
Including
The joint surface of the first and second waveguides is a plane equivalent to the (100) plane, or is inclined with respect to the normal of the substrate surface with respect to these surfaces and is off within 7 degrees in the in-plane direction of the substrate. A method for manufacturing an optical waveguide, characterized in that the surface has a corner.   8. The method of manufacturing an optical waveguide according to claim 7, wherein the first waveguide layer is formed by selectively removing the first core layer and the first cladding layer by dry etching.   8. The method of manufacturing an optical waveguide according to claim 7, wherein the first waveguide layer is formed by selectively removing the first core layer and the first cladding layer by wet etching.   8. The first waveguide is formed by selectively removing the first cladding layer by dry etching and selectively removing the first core layer by wet etching. Manufacturing method of the optical waveguide.   The method for manufacturing an optical waveguide according to claim 7, wherein the second core layer and the second cladding layer are formed by epitaxial growth using a growth gas containing a halogen gas. The first and second core layers are
In _x Ga _1-x As _y P _1-y (where x and y are 0 or more and 1 or less)
The method for manufacturing an optical waveguide according to claim 7, comprising:

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