JPH0485503A - Manufacture of semiconductor optical input and output circuit - Google Patents

Abstract

PURPOSE:To accurately guide part of propagated light in an optical waveguide out at a desired light guide-out rate by controlling the size along the optical axis of the core layer at the opening part of a mask and controlling the depth size of a groove. CONSTITUTION:A specific crystal surface which has positional relation of 54.7 deg. to the optical axis line 2a, i.e. a crystal face 10 where a (111) face 10 is exposed is used as an optical reflecting surface by chemical etching so as to guide the propagated light in the semiconductor optical waveguide at the specific rate to, for example, a substrate side where the optical waveguide is formed. The light intensity distribution of the propagated light in the optical waveguide is determined unequivocally by determining the refractive indexes and film thicknesses of a core layer 2 and clad layers 3 and 4 which constitute the optical waveguide. Therefore, the depth size D of the groove needs to be determined according to the light intensity distribution and further the width L of the opening part 14 of a mask pattern 13 needs to be determined according to a relational equation D=0.707L so as to obtain a desired value as the rate of the light which can be guided out of the crystal face 10 as the optical reflecting surface to all the propagated light, so that the crystal face 10 can be formed to desired depth.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1] The present invention relates to a method for manufacturing an optical input/output circuit in a semiconductor optical waveguide device, and in particular, a method for extracting a part of light propagating in an optical waveguide to the outside of the optical waveguide. The present invention also relates to a method of manufacturing an optical input/output circuit that can take in external light as propagation light of an optical waveguide.

[Prior Art 1] Conventionally, such semiconductor optical input/output circuits have been known, for example, structures shown in FIGS. 7A and 8.

First, the optical input/output circuit 1 shown in FIG. 7A includes a core layer 2 mainly forming an optical waveguide on a semiconductor substrate (not shown),
Upper and lower cladding layers 3.4 sandwich this core layer 2, and a groove having an optical reflective surface 5a formed by dry etching from the upper cladding layer 3 to the core layer 2 so as to form an angle of 45 degrees with the optical axis 2a of the optical waveguide. It is roughly composed of 5. In this circuit 1, a part of the light propagating in the optical waveguide is reflected by the above-mentioned optical reflection surface 5a in a direction perpendicular to the optical axis 2a of the optical waveguide, in this example, in the direction indicated by arrow 6 in FIG. 78. It is possible to output light to

Further, the optical input/output circuit 7 shown in FIG. 8 is formed at a period of 0.25 μm within the core layer 2, the upper and lower cladding layers 3.4 sandwiching the core layer 2, and the optical waveguide below the core layer 2. It is generally composed of a secondary grating 8. In this circuit 7, a part of the light propagating in the optical waveguide is transferred to the grating 8.
It is possible to diffract the light and output light in the direction shown by arrow 6 in FIG.

[Problem to be Solved by the Invention 1] However, in the conventional optical input/output circuit described above, in order to extract a part of the light propagating in the optical waveguide at a predetermined ratio, the following manufacturing technology is used. There was an issue.

That is, in the optical input/output circuit 1 shown in FIG. 7A, the desired light extraction is performed in the distribution area of propagating light distributed in the core layer 2 and the portions of the upper and lower cladding layers 3.4 that are close to the core layer 2. It is necessary to provide an optical reflective surface 5a with a cross-sectional area corresponding to the proportion.

However, as shown in FIG. 7B, the above-mentioned light distribution area has a dimension of approximately 0.3 μm along the cross-sectional direction of the substrate, that is, the same direction as the arrow 6, and is extremely narrow in area. Even with extremely high-precision dry etching technology, it is difficult to form the optical reflective surface 5a within such a narrow optical plane region so as to have a cross-sectional area corresponding to the desired light extraction ratio. .

Furthermore, in the optical input/output circuit 7 shown in FIG. 8, the shape and length of the grating 8 must be strictly defined in order to control the extraction rate from the light propagating in the optical waveguide. Therefore, it is necessary to use a high-precision photolithography technique such as an electron beam to form the grating 8. Furthermore, it is necessary to use advanced recrystallization growth technology to embed the grating 8 in the optical waveguide, and
Due to the deformation of the grating 8 during this regrowth,
Since the ratio of light intensity of light extracted as diffracted light changes, it is still difficult to extract propagating light in the optical waveguide at a desired light extraction ratio.

SUMMARY OF THE INVENTION In order to solve the above-mentioned technical problems, an object of the present invention is to provide a method for easily manufacturing an optical input/output circuit that can accurately extract a part of the light propagating in an optical waveguide at a desired light extraction ratio. shall be.

[Means for Solving the Problems 1] The first invention of the present application includes a step of laminating a core layer and cladding layers sandwiching the core layer on a semiconductor substrate to form a semiconductor optical waveguide element; A step of disposing a mask on the surface of the cladding layer on the side opposite to the semiconductor substrate, and chemical etching is performed through the opening of the mask to reach the core layer from the cladding layer and remove the etching from the core layer. forming a groove formed by a crystal plane tilted with respect to the optical axis of the core layer, and in the groove forming step, by controlling the dimension of the opening of the mask along the optical axis of the core layer. , characterized in that the depth dimension of the groove is controlled.

Moreover, the second invention in the present application provides, on the semiconductor substrate,
forming a semiconductor optical waveguide device by laminating a core layer and a cladding layer sandwiching the core layer and made of a material having chemical properties different from that of the constituent material of the core layer; The steps include a step of disposing a mask on the cladding surface opposite to the semiconductor substrate, and selectively etching only the cladding layer through the opening of the mask to form a crystal plane having an inclination with respect to the optical axis of the core layer. It is characterized by comprising the step of forming.

[Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

First, the first invention will be explained.

In order to extract the light propagating in a semiconductor optical waveguide at a predetermined ratio, for example, to the substrate side on which the optical waveguide is formed, it is necessary to reproducibly create an optical reflecting surface that is tilted relative to the optical axis of the propagating light. In general, in a substrate whose surface is the (001) plane on which an optical waveguide is formed, when the optical waveguide is arranged so that its optical axis is in the <011> direction, As shown in FIGS. 20 to 2E, chemical etching is applied to the optical axis 2a by
．． A specific crystal plane having a positional relationship tilted at 7 degrees, that is, the (111) plane 10 is exposed. 10 such crystal planes
In the first invention, it is used as an optical reflection surface for extracting propagating light in an optical waveguide.

To form this crystal plane IO in the optical waveguide, as shown in FIG. 2A, first, a mask pattern 13 having an opening with a width dimension is formed on the surface of the cladogram layer of the optical waveguide, and then the entire substrate is covered. This is done by contacting with a chemical etching solution. At this time, as shown in FIG. 2C, the chemical etching progresses from the surface of the cladding layer exposed through the opening of the mask pattern 13 to the deep layer, and as the contact time elapses, the depth of the groove formed increases. is increasing. The above-mentioned crystal plane 10 is exposed inside this groove. The etching rate for this crystal plane 10 is (001) as the bottom surface of the groove.
Compared to the etching rate for the surface 11, the etching rate is so low that it can be virtually ignored in terms of crystal orientation. Therefore, with continued contact with the etchant, Figures 2D and 2
As shown in Figure E, the etching progresses until the (111) planes 10 on both inner surfaces of the groove intersect with each other at the bottom of the groove, and at that stage it stops naturally, forming a groove 14 having a V-shaped cross section. The depth dimension of the groove 14 obtained in this way is determined from the crystal orientation relationship on the substrate surface (in this example, (001
) plane) and the above-mentioned crystal plane 10 ((111) plane) is θ, it is expressed as D=1/2tanθ−L. In this example, θ is 54.7 degrees, so
D can be expressed by the relational expression D=0.707L.

Further, the light intensity distribution of the propagating light in the optical waveguide is uniquely determined by determining the refractive index and film thickness of each layer of the core layer and cladding layer that constitute the optical waveguide. Therefore, in order to set the proportion of the light extracted by the crystal plane 10 as an optical reflecting surface to the total propagated light to a desired value, the depth of the groove 5 is determined based on the light intensity distribution, and the above-mentioned D= Mask pattern 13 from the relational expression of 0.707L
It is necessary to determine the width of the opening 14, and this can be achieved by forming the crystal plane 10 to a desired depth.

Next, the second invention will be explained.

Semiconductor optical waveguides are constructed by laminating crystal layers such as core layers and cladding layers with different material compositions, that is, different chemical properties, in order to control the refractive index distribution to confine light. The light propagating in such an optical waveguide has its light intensity center in the core layer, and is also slightly distributed in a part of the cladding layers that sandwich the core layer. That is, in the second invention, based on the fact that the light intensity distribution of propagating light is distributed over a plurality of crystal layers having different chemical properties, the cladding layer forming a part of the optical waveguide has a cladding layer that is a part of the optical waveguide. A selective, non-etching etchant is applied to expose specific crystal planes within the cladding layer, which crystal planes are used as optically reflective surfaces.

Here, the first invention and the second invention involve chemically etching a plurality of crystal layers constituting an optical waveguide as an optical reflecting surface that is useful for extracting propagating light in the optical waveguide. In this method, a crystal plane having a specific inclination with respect to the optical axis of an optical waveguide is formed. In the first invention, the depth of the groove formed by the crystal plane is controlled by adjusting the width of the opening of the mask. Further, in the second invention, the formation of crystal planes and the adjustment of groove depth are performed by selective etching included in chemical etching.

[Example 11] The present invention will be described in detail below when applied to a semiconductor ridge type laser.

First, on an n-type InP wafer having a (001) plane orientation as the lower cladding layer 4, a core layer 3 with a thickness of 0.05 cm is placed.
A double heterostructure consisting of a 1 μm active layer made of InGaA and sP crystals, a 1.5 μm thick p-type InP cladding layer as the upper cladding layer 2, and a 3 μm thick p-type InGaAs P character layer 12 stacked one after another. A structural board was prepared. On this substrate, as shown in Figure 1, < 01.1
．． A semiconductor laser was constructed by forming a ridge-type optical waveguide with a width of 4 μm extending in the > direction.

The light intensity distribution in the optical waveguide of the semiconductor laser configured in this way is calculated based on the refractive index of each crystal layer and the film thickness of each crystal layer constituting the optical waveguide.
Shown in the figure. In addition, based on this light intensity distribution, the depth dimension of the groove to be formed and the ratio of the light intensity of the light extracted by the optical reflection surface of this groove to the propagation light intensity in the optical waveguide are shown in Figure 4. Indicated. From these FIGS. 3 and 4, the width dimension of the opening of the mask used to form the groove that will become the optical input/output circuit is 2.5 to 4.5 mm in this example.
It can be seen that it can be changed within a range of 3 μm.

Next, a resist pattern 13 having an opening 14 with a width dimension was formed on the top of the ridge of the ridge-type optical waveguide of the semiconductor laser described above (see FIG. 2A).

Next, using this resist pattern 13 as a mask, the InGaAsP cap layer 12 is coated with H,SO through the opening 14.
This was removed by etching with an etchant having a composition of 2.H2O,:H20=1:1:10 (see FIG. 2B).

Next, the upper cladding layer 3 exposed by removing the cap layer 12 described above is treated with HCl:H3PO.

An etchant having a composition of =1=1 was contacted. Through such chemical etching, the (111) plane 10, which has the lowest etching rate, is exposed as the crystal plane of the upper cladding layer 3 due to the above-mentioned crystal orientation relationship. The bottom surface 11 of the groove etched between these crystal planes 10 is etched at a relatively faster rate than the above-mentioned crystal planes 10 (see FIG. 2C). Here, if the width of the opening is set so that the light extraction ratio is, for example, 10%, the two crystal planes 10 exposed inside the groove formed by etching will be inside the upper cladding layer 3. They intersect with each other to form a 7-figure 14.

At this point, etching stops naturally (see Figure 2D). Further, when the width of the opening is set so that the light extraction ratio is, for example, 90%, the two crystal planes 10 need to intersect with each other in the core layer 2 and the lower cladding layer 4. In this case, at the stage when the surface of the core layer 2 is exposed by etching, H2SO,: H,O□
The core layer 2 is etched with an etchant having a composition of :HzO=1.1:10, and further HCl:H,PO
.

= Lower cladding layer 4 with an etchant having a composition of 1:1.
A portion near the core layer is etched to finally form a figure-7 groove 14 having a structure as shown in FIG. 2E.

A current is injected into a plurality of semiconductor lasers (see FIG. 2D or FIG. 2E) equipped with optical input/output circuits having openings of different sizes formed in this way to cause laser oscillation.
When we measured the intensity of light 9 by placing a photodetector on the underside of the substrate (not shown), we found that under a constant injection current, as the aperture size increases from 2.5 μm, the intensity of extracted light tends to increase. was observed, and the operation of the semiconductor optical input/output circuit obtained by the present invention could be confirmed.

In addition, in the above-mentioned example, a case was shown in which a substrate having a (001) plane orientation was used, but when a substrate having another plane orientation is used, the crystal plane I
The inclination angle of O becomes different. For example, when a substrate with a (011) plane orientation is used, the crystal plane 10 has an angle of 35.3 degrees with the substrate plane, and when a substrate with a (111) plane orientation is used, the crystal plane 10 is the board surface and 70.5
having an angle of degrees. Therefore, the relationship between the opening dimension and the groove depth dimension is such that when a substrate with a (011,) plane orientation is used, the angle θ between the substrate plane and the crystal plane 10 is 35.3 degrees. Therefore, D=0.354L, and when a substrate with a (111) plane orientation is used, the above angle θ becomes 70.
Since it is 5 degrees, D=1. ．． It becomes 412L. By considering the relationship between D and L, it becomes clear that the desired optical input/output circuit can be manufactured as in the case of the above-described embodiment using a substrate having a (001) plane orientation.

[Example 2] Below, the present invention will be described in detail when applied to a semiconductor orbiting laser.

First, on an n-type InP wafer having a (001) plane orientation as the lower cladding layer 4, a core layer 3 with a thickness of 0.05 cm is placed.
A double heterostructure in which an active layer made of 1 tLm InGaAsP crystal, a 1.5 μm thick p-type InP cladding layer as the upper cladding layer 2, and a 0.3 μm thick p-type InGaAsP cap layer 12 are sequentially laminated. A board was prepared. As shown in FIG. 5, <011> is placed on this substrate.
Circular optical waveguide 20 including direction and <011> direction
A circular laser was constructed by forming the following.

Next, among the optical waveguides of the orbiting laser having such a configuration, an opening 1 is formed in the upper part of the optical waveguide 20 along the <011> direction.
A resist pattern 13 having a pattern of 4 was formed (see FIG. 6A).

Next, using this resist pattern 13 as a mask, the I'nGaAsP cap layer 12 is formed through the opening 14 as H2SO4:H202:H,O=1:l:
This was removed by etching with an etchant having a composition of 1O (see Figure 6B).

Next, the upper cladding layer 3 exposed by removing the cap layer 12 was brought into contact with a selective etchant having a composition of HCI:HsPO,=1:1. This selective etchant etches only the upper cladding layer 3, but does not etch the core layer 2 or the cap layer 12. Through such selective etching, the (111) plane 21, which has the slowest etching rate, is exposed as the crystal plane of the upper cladding layer 3, but as shown in FIG. 6C, the crystal plane 21 is completely exposed. Stop. This crystal face 21
was a plane that always had an inclination of 54.7 degrees with respect to the optical axis 2a of the optical waveguide 20 due to the crystal orientation.

A current was injected into the orbiting laser having the crystal plane 21 thus formed to cause the laser to oscillate, and a photodetector was placed above the substrate (not shown) to measure the intensity of the light 9. As a result, the current - We confirmed the existence of a threshold value observed in ordinary lasers in the light intensity characteristics, and found that a part of the laser light 22 propagating in the optical waveguide is extracted by the crystal surface (optical reflection surface) 21, and this reflection surface 21 We confirmed that it works as an optical output circuit to an optical waveguide.

It should be noted that even if the thickness of the cladding layer and the selective etching time are set to conditions different from those of this example, the selective etching described above can provide a crystal surface as an optical reflection surface with a structure as shown in FIG. 6C. We were able to manufacture an optical input/output circuit.

[Example 3] The composition of the 0.1 μm thick InGaAsP crystal forming the core layer was selected so that the laser oscillation wavelength was 1.55 μm, and 1nP cladding layers were laminated above and below this core layer. A semiconductor orbiting laser in which a reflective surface was formed was manufactured in the same manner as in Example 2 described above. Approximately 50% of the laser light within this orbiting laser could be extracted through its reflective surface.

In addition, in the above-mentioned Examples 2 and 3, (001)
Although the case where a substrate with a plane orientation is used is shown, when a substrate with another plane orientation is used, the tilt angle of the crystal plane lO will be different reflecting the crystallographic plane orientation relationship, but the above-mentioned light It is clear that input/output circuits can be constructed.

In addition, in the above-mentioned Examples 2 and 3, the optical input/output circuit was manufactured with a configuration in which the propagating light is extracted to the upper side of the substrate in each drawing, but when the propagating light is extracted to the lower side of the substrate, the above-mentioned An optical reflecting surface may be formed on the optical waveguides arranged in a direction perpendicular to the crystal orientation of the optical waveguides in Examples 2 and 3 by the same method as in Examples 2 and 3 described above.

In addition, in Examples 1 to 3 described above, only the optical output operation of the manufactured optical input/output circuit was confirmed, but based on the reciprocity of light, it can also operate as an optical input circuit to an optical waveguide. is clear.

Furthermore, in Examples 1 to 3 above, an InP-based laser was used as an example, but the desired light can be obtained by etching other semiconductor optical waveguides, such as GaAs-based, with an appropriate etchant. It is possible to manufacture input/output circuits.

[Effect of the Invention 1] As explained above, according to the present invention, it is possible to easily form a crystal plane as an optical reflection surface for extracting propagating light in an optical waveguide by chemical etching, and Since the depth of the groove formed by the plane can be controlled based on the relationship with the crystal orientation, it is possible to manufacture a light input/output circuit that can accurately extract light at a desired light extraction ratio. Further, according to the present invention, it is possible to accurately control the depth of the above-mentioned grooves even by using selective etching.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing a ridge type semiconductor laser to which the present invention can be applied, and FIGS. 2A to 2E are diagrams illustrating a first aspect of the present invention using the semiconductor laser shown in FIG. FIG. 3 is a schematic cross-sectional view for explaining the steps of manufacturing the optical input/output circuit in order of process; FIG. 3 is a schematic diagram showing the light intensity distribution of light propagating in the optical waveguide of the semiconductor laser shown in FIG. 1; FIG. 4 shows the ratio of the light intensity to the propagating light of the light that can be reflected and extracted by the crystal plane as an optical input/output circuit manufactured according to the present invention, and the size of the opening of the mask and the above-mentioned crystal plane. A graph showing the relationship between the depth and dimension of the configured grooves,
FIG. 5 is a schematic configuration diagram showing a circular semiconductor laser to which the present invention can be applied, and FIGS. 68 to 6C show a second invention of the present invention using the semiconductor laser shown in FIG. FIG. 7A is a schematic cross-sectional view showing a conventional optical input/output circuit equipped with an optical reflective surface; Figure 7A is a graph showing the light intensity distribution of the optical input/output circuit, and Figure 8 is a schematic cross-sectional view showing a conventional optical input/output circuit equipped with a grating for diffracting propagating light in an optical waveguide. be. DESCRIPTION OF SYMBOLS 1... Optical input/output circuit, 2... Core layer, 2a... Optical axis of core layer, 3... Upper cladding layer, 4... Lower cladding layer, 5... Groove, 5a. ... Optical reflective surface, 6... Light output direction, 7... Optical input/output circuit, 8... Grating, 9... Light (output light), 10... Optical reflective surface, 12 ... Cap layer, 13... Mask (resist pattern), 14... Groove, 20... Circulating optical waveguide, 1... Optical reflective surface, 22-... Laser light.

Claims (1)

[Claims] 1) forming a semiconductor optical waveguide element by laminating a core layer and cladding layers sandwiching the core layer on a semiconductor substrate; arranging a mask on the surface of the cladding layer on the opposite side, and performing chemical etching through the opening of the mask so as to reach the core layer from the cladding layer and have an inclination with respect to the optical axis of the core layer. forming a groove formed by a crystal plane, and in the groove forming step, the depth dimension of the groove is controlled by controlling the dimension of the opening of the mask along the optical axis of the core layer. A method for manufacturing a semiconductor optical input/output circuit, characterized by: 2) Forming a semiconductor optical waveguide element by laminating a core layer and a cladding layer made of a material having chemical properties different from the constituent material of the core layer and sandwiching the core layer on the semiconductor substrate. and a step of disposing a mask on the surface of the cladding layer on the side opposite to the semiconductor substrate, and selectively etching only the cladding layer through the opening of the mask so that the optical axis of the core layer is etched. 1. A method of manufacturing a semiconductor optical input/output circuit, comprising the step of forming a crystal plane having an inclination.