JPH11183735A - Production of three-dimensional semiconductor optical crystal element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for producing a three-dimensional semiconductor optical crystal element by constituting a three-dimensional semiconductor refractive index modulation structure having a size of about half the wavelength of light. SOLUTION: The three-dimensional semiconductor refractive index modulation structure as a whole is obtd. by combining a step of growing a multilayered semiconductor film 4 varying in compsn. on a semiconductor substrate, a step of opening periodic holes 6 in the multiplayered semiconductor film by lithography and a step of oxidizing only Al of the specific semiconductor layers constituting the multilayered film, thereby converting these layers to Al2 O3 layers 7 formed by forced oxidation. The multilayered semiconductor film 4 has a laminated structure alternately laminated with clad layers 2 consisting of a first semiconductor contg. Al and core layers 3 consisting of a second semiconductor which is a semiconductor not contg. Al or is smaller by 0.02 in the compsn. of Al than the first semiconductor even in the case of the semiconductor contg. Al.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a basic structure of various optical devices such as lasers, optical waveguides, and optical integrated circuits used for optical information processing and optical transmission.
The present invention relates to a method for manufacturing a two-dimensional semiconductor photonic crystal element.

[0002]

2. Description of the Related Art In a multi-dimensional periodic structure of a dielectric, a band gap is generated in an electronic state in a crystal.
Wavelength band that suppresses the wave of light (hereinafter referred to as “Photonic
"Band Gap". ) Occurs, and light can be confined two-dimensionally and three-dimensionally. Due to the similarity with an actual crystal, such a dielectric periodic structure is called a photonic crystal. Spontaneous emission light can be suppressed in this photonic crystal,
Further, by introducing an aperiodic portion into the photonic crystal, an element having functionality such as an optical resonator and an optical waveguide can be formed. The optical element thus configured can be reduced in size to about the wavelength of light, and such optical elements can be freely connected in a two-dimensional or three-dimensional space. Further, by controlling the spontaneous emission light, it is possible to dramatically improve the performance as a laser.

[0003] Against the background of such theoretical prediction, techniques for creating a two-dimensional or three-dimensional dielectric periodic structure (hereinafter referred to as "refractive index modulation structure") by various methods have been proposed. With the development of the semiconductor lithography technology, it has become sufficiently possible to create a two-dimensional refractive index modulation structure of about half a wavelength of light. On the other hand, as a method of creating a three-dimensional refractive index modulation structure, a method has been considered in which a two-dimensional refractive index modulation structure is created by lithography and another one-dimensional refractive index modulation structure is created by another method.
As one such method, Yablonovitc
proposed a method of forming a three-dimensional refractive index modulation structure in a semiconductor single crystal 30 by repeating etching three times in different directions using a two-dimensional periodic pattern 31 formed on a resist as shown in FIG. (Phy
s. Rev .. Lett. 67 (1991) p. 229
5).

[0004]

However, Yablon does not.
According to the method of Ovitch et al., it is very difficult to perform straight etching three times in an oblique direction, and there is no example of a structure in the wavelength region of light until now.

On the other hand, in order to realize a three-dimensional refractive index modulation structure, a semiconductor multilayer film is simply etched.
In a three-dimensional periodic structure, a sufficiently large modulation can be realized by a refractive index difference with air in the two-dimensional refractive index modulation. Since the modulation is limited by the rate difference, it is difficult to realize sufficiently large modulation.

In addition, Photonic B is three-dimensionally
In order to open the and gap, it is considered impossible unless the ratio of the refractive indexes of the constituent materials is 2 or more, so the conventional method is insufficient.

In order to obtain a large difference in refractive index from a normal semiconductor, an insulating crystal such as SiO ₂ is used. However, it is extremely difficult to grow a high-quality alternate multilayer film using an insulator and a semiconductor. Difficult and virtually impossible.

On the other hand, it is known that in an alternate multilayer film of AlGaAs and GaAs, it is possible to convert only the AlGaAs layer to Al ₂ O ₃ . However, although this method is applied to ordinary semiconductor devices, it is not yet applied to a photonic crystal having a fine structure of about half a wavelength of light.

As described above, it is difficult to three-dimensionally form a refractive index modulation structure on the order of the wavelength of light even with advanced lithography technology, and it can be a substrate for an optical integrated circuit at a practical level. Things have not been found yet. In view of the above, the present invention has been made to solve the problems of the conventional technology, to provide a three-dimensional refractive index modulation structure having a size about the wavelength of light, and to provide a method of manufacturing a three-dimensional semiconductor photonic crystal element. It was made for the purpose.

[0010]

SUMMARY OF THE INVENTION The present inventor has studied various methods for overcoming the above problems and producing a three-dimensional refractive index modulation structure in a semiconductor multilayer film to manufacture a three-dimensional semiconductor photonic crystal element. As a result, the specific type of semiconductor layer containing Al as a constituent element has a very high degree of oxidation sensitivity to the Al composition, and if a slight difference is made in the Al composition, a large amount of Al can be obtained by selecting conditions. It is possible to selectively oxidize only Al in the semiconductor layer, and Al ₂ O ₃ oxidized in this way is an insulator and has a low refractive index, so that it is used as a cladding layer for optical confinement. Focusing on what can be done, the present invention has been completed.

That is, the present invention relates to a method for manufacturing a three-dimensional semiconductor photonic crystal element in which a plurality of optical confinement cladding layers and a plurality of optical transmission core layers are alternately stacked, On the cladding layer made of the first semiconductor containing Al, even if the semiconductor does not contain Al or the semiconductor contains Al, the composition of Al is 0.02 or more smaller than that of the first semiconductor. The core layer made of the second semiconductor is grown alternately in a laminated structure, and then a plurality of holes having a two-dimensional periodic array are formed by etching perpendicular to the multilayer film formed by the laminated structure. After the formation, finally, the Al in the cladding layer is selectively oxidized to partially or entirely change the Al into an oxide.

Further, the present invention relates to a method for manufacturing a three-dimensional semiconductor photonic crystal element comprising a plurality of optical confinement cladding layers and a plurality of optical transmission core layers alternately laminated on a semiconductor substrate. First, on the semiconductor substrate, the cladding layer made of the first semiconductor containing Al, and even if the semiconductor does not contain Al or the semiconductor contains Al, the composition of Al is higher than that of the first semiconductor. The core layer made of the second semiconductor smaller than 0.02 is grown alternately in a laminated structure.
Is selectively oxidized to convert a part or the whole thereof into an oxide, and finally, a plurality of holes having a two-dimensional periodic array is formed by etching perpendicular to the multilayer film having the laminated structure. It is characterized by the following.

The present invention also relates to a method for manufacturing a three-dimensional semiconductor photonic crystal element comprising a plurality of light-trapping cladding layers and a plurality of light-transmitting core layers alternately stacked on a semiconductor substrate. First, on the semiconductor substrate, the cladding layer made of the first semiconductor containing Al, and even if the semiconductor does not contain Al or the semiconductor contains Al, the composition of Al is higher than that of the first semiconductor. The core layer made of the second semiconductor smaller than 0.02 or more grows a laminated structure alternately laminated, and then a two-dimensional periodic array is formed by etching perpendicular to the multilayer film having the laminated structure. A plurality of columnar structures are formed, and finally, the Al in the cladding layer is selectively oxidized to change a part or all of the Al into an oxide.

Further, the present invention relates to a method for manufacturing a three-dimensional semiconductor photonic crystal element comprising a plurality of optical confinement cladding layers and a plurality of optical transmission core layers alternately laminated on a semiconductor substrate. First, on the semiconductor substrate, the cladding layer made of the first semiconductor containing Al, and even if the semiconductor does not contain Al or the semiconductor contains Al, the composition of Al is higher than that of the first semiconductor. By growing a structure in which the core layer made of the second semiconductor smaller than 0.02 or more is alternately stacked, and then selectively oxidizing Al of the cladding layer, a part or the whole thereof is partially removed. The oxide is changed to an oxide, and finally, a plurality of columnar structures having a two-dimensional periodic arrangement are formed by etching perpendicular to the multilayer film having the stacked structure.

Further, according to the present invention, the semiconductor substrate is GaAs and the first semiconductor is AlGaAs, or the semiconductor substrate is InP and the first semiconductor is InAlGaAs.
s or AlAsSb.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the drawings.

As shown in FIG. 1D, the three-dimensional semiconductor photonic crystal element obtained by the manufacturing method of the present invention has an Al ₂ O ₃ layer 7, a GaAs semiconductor layer 3, and a GaAs substrate 1 formed by forced oxidation. And a hole 6 formed in the laminated structure 8 by etching.

In order to create this structure, first, an AlGaAs semiconductor layer 2 as a first semiconductor containing Al and an AlGaAs semiconductor layer 2 as a first semiconductor are formed on a GaAs substrate 1 as a semiconductor substrate.
A semiconductor multilayer film 4 composed of a GaAs semiconductor layer 3 as a second semiconductor whose Al composition is 0.02 or more smaller than that of the first semiconductor even if the semiconductor does not contain Al or a semiconductor containing Al It is created (FIG. 1A).
As a method for growing each semiconductor layer, a semiconductor epitaxial growth method, for example, a molecular beam epitaxial growth method (M
BE) and metal organic chemical vapor deposition. The thickness of each semiconductor layer is about half the wavelength of light, but the value differs depending on the wavelength of light to be used. The thickness of each semiconductor layer is acceptable even if there is some variation. The number of the semiconductor layers is preferably large, but may be about three. The AlGaAs semiconductor layer has a composition represented by Al _x Ga _(1-x) As. Here, Al is the G of the GaAs crystal.
It is added in a form that replaces a. The composition x of Al is not limited to a specific value as long as it contains 0.02 or more Al than the second semiconductor layer serving as a core. The upper part is x = 0.
Three or more are considered appropriate. The resulting semiconductor multilayer film 4 is of extremely high quality because it is a growth of the same kind of semiconductor with lattice matching. The film thickness of the AlGaAs semiconductor layer can be made thicker by incorporating the size change in the subsequent oxidation step.

Next, a two-dimensional refractive index modulation structure is created in the semiconductor multilayer film 4 by lithography technology. First, an arbitrary mask pattern 5 having a two-dimensional periodic structure is created on the surface of the semiconductor multilayer film by electron beam lithography ( FIG.
(b)). The creation of the mask pattern is not limited to the electron beam, but may be lithography using an X-ray or an ion beam. The etching is performed vertically based on the mask pattern to form periodic vertical holes 6 in the semiconductor multilayer film.
(c)). Etching methods include plasma etching and reactive ion etching. With respect to the refractive index modulation in the two-dimensional direction by this process, the refractive index of the hole 6 (refractive index of air = 1) and the semiconductor portion 3
(Refractive index of GaAs = 3.4) can realize sufficiently large modulation. In addition,
The diameter of the hole may be about the same as the film pressure of the GaAs semiconductor layer serving as the core, and the shape and diameter of the hole are not particularly limited.

Finally, only the AlGaAs semiconductor layer 2 is selected.
Oxidation selectively. As a method of oxidation, use steam
Or another method. At this time, oxidation
Proceed from the end 6 and the hole 6 formed by etching.
You. Al is much more easily oxidized than Ga or As
Therefore, oxidation proceeds only for Al, and
Al formed only by oxidation of the conductor layer 2 and forced oxidation
_TwoO_Three Replace with layer 7. As a result, as shown in FIG.
In the multi-layer stacking direction, the
Al formed_TwoO_Three Layer and core GaAs semiconductor layer
Are alternately stacked to realize a stacked structure 8. here,
Al_TwoO_Three Has a low refractive index (refractive index = 1.5) and is a multilayer film
Strong one-dimensional refractive index modulation was also obtained in the stacking direction.
It is compatible with the two-dimensional refractive index modulation structure by the above etching
As a result, an effective three-dimensional refractive index modulation structure can be realized.
And the whole Photonic Band Gap
Three-dimensional photonic crystal with a refractive index ratio of 2 or more required for formation
Becomes In this oxidation step, the clad Al
Al of the GaAs semiconductor layer is Al _TwoO_Three Make a crystal of
Ga and As fall off from the crystal lattice and disappear.
Become. Therefore, in this oxidation step, AlGaAs half
Al with conductor layer formed by forced oxidation_TwoO_Three Converted into layers
This causes a slight size change, but this size
In consideration of the change in size, the AlGaAs semiconductor layer is
It is better to make it thicker. The change in size is
O atoms enter instead of the dropped Ga and As atoms,
Al bonds with Al atom_TwoO_Three Just to form a crystal
There is no practical problem. The number created by this
The layer film becomes a lattice-matched, extremely high-quality semiconductor layer of the same type.
As a result, the GaAs semiconductor layer
3 and Al formed by forced oxidation_TwoO_Three Layered structure of layer 7
The structure 8 is also formed of a sufficiently high quality. What
The speed at which Al is oxidized depends on the Al composition x.
If the value of x is large, it is fast, and if it is small, it is slow. Obedience
Therefore, the larger the value of the composition x of Al, the higher the work efficiency.
You.

In the above case, the oxidation treatment is performed after the etching.
A configuration in which only the s-semiconductor layer 2 is selectively oxidized and finally etched may be employed. Even in this case, A
Only 1 is selectively oxidized, and the GaAs semiconductor layer 3 is not oxidized, and a three-dimensional refractive index modulation structure is obtained.
In addition, the semiconductor multilayer film 4 is not a concave type in which a hole is formed, and FIG.
As described above, the same purpose as that of the concave type can be achieved even with the convex type structure in which the semiconductor multilayer film is left in a columnar shape. As in the case of the concave type, the pillars of the multilayer film 13 etched into the pillar shape also have the GaAs semiconductor layer 11 serving as a core and Al ₂ O ₃ formed by forced oxidation serving as a clad.
And a layer 12.

Here, Al ₂ formed by forced oxidation is used.
The O ₃ layers 7 and 12 electrically insulate the GaAs substrates 1 and 10 from the GaAs semiconductor layers 3 and 11, which are core portions. The unoxidized AlGaAs region 22 can be left, and with such a configuration, it is possible to make electrical contact in the vertical direction of the multilayer film. In FIG. 3B, reference numeral 21 is an enlarged view of one period portion of the multilayer film 20 which has been etched into a columnar shape. A central portion 22 is an unoxidized AlGaAs region, and a portion 23 is formed by forced oxidation. Al ₂ O ₃
Area. In this case, if electrodes are formed above and below the multilayer film, a current can flow in the vertical direction, and it can be used for a current injection type laser or the like. This configuration can be realized irrespective of a concave type or a convex type. In addition,
In the oxidation step, the uppermost layer is oxidized not only from the periphery of the multilayer film but also from above, so that the uppermost layer ends with a semiconductor layer having a small Al composition x or a protective layer for preventing oxidation. It is necessary to attach. In addition, when a part of the multilayer film is oxidized in the oxidation step and then etched, only the peripheral part of the multilayer film is oxidized, and an unoxidized region is formed in the central part. Can be used not only as a photonic crystal but also as a conductive region, so there is no problem.

Further, a three-dimensional refractive index modulation structure can be obtained by forming a semiconductor multilayer film of two or more AlGaAs semiconductor layers having different compositions and selectively oxidizing a layer having the largest Al composition x. it can. Further, InP is used as the semiconductor substrate, and InAlGa is used as the configuration of the semiconductor multilayer film.
An As semiconductor layer or an AlAsSb semiconductor layer may be used. Similarly, a material system in which a mixed crystal material containing Al is grown on a semiconductor substrate may be used. In the case where Al is oxidized in a semiconductor multilayer film having a different Al composition x, if there is a difference of 0.02 or more in the Al composition x, only the Al in the semiconductor layer having a large x value is selectively oxidized. , X is not oxidized. Therefore, the composition x of Al
Can be selectively converted to an Al ₂ O ₃ layer formed by forced oxidation,
It is possible to easily create a three-dimensional refractive index modulation structure. Also in the oxidation step in this case, as in the case of the semiconductor multilayer film including the AlGaAs semiconductor layer and the GaAs semiconductor layer, the smaller the composition x of Al in the semiconductor layer, the longer the time required to oxidize Al becomes longer. Tend to be. Further, in the oxidation step, as the difference in the composition x of Al in the semiconductor layer is larger, only the Al in the semiconductor layer in which the value of x is larger is easily oxidized selectively, and the difference in the composition x of Al has the same value. In this case, as the absolute value of x increases, only Al in a semiconductor layer having a large value of x tends to be selectively oxidized.

[0024]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

First, an Al _x Ga layer having a thickness of 0.12 μm is formed on a GaAs substrate 1 by a molecular beam epitaxial growth method.
_1-x As (x = 0.95) semiconductor layer 2 and 0.12 μm thick G
aAs semiconductor layers 3 are alternately grown in ten layers to form a semiconductor multilayer film 4.
(Fig. 1 (a)). A mask pattern 5 having a two-dimensional periodic structure is formed on the multilayer film by electron beam lithography (FIG. 1B). Using this as a mask, etching is performed vertically to form periodic vertical holes 6 having a diameter of 0.12 μm in the multilayer film (FIG. 1C).

Next, this is heat-treated in a 425 ° C. high-temperature steam atmosphere for 30 minutes to oxidize the AlGaAs semiconductor layer. Thereby, the AlGaAs semiconductor layer 2 is replaced with the Al ₂ O ₃ layer 7 formed by forced oxidation. As a result,
As a structure, as shown in FIG. 1D, a laminated structure 8 in which an Al ₂ O ₃ layer and a GaAs semiconductor layer formed by forced oxidation are alternately laminated in a multilayer film laminating direction is realized.

[0027]

According to the method of the present invention, only a specific film composed of a specific material is oxidized and converted into a material having a low refractive index by a process after the formation of the multilayer film. , A strong refractive index modulation can be obtained.
Therefore, it is possible to easily create a three-dimensional refractive index modulation structure on the order of the wavelength of light, which has been difficult only by lithography technology.

Further, since the first multilayer film is a growth of the same kind of semiconductor with lattice matching, it is possible to form a very high quality semiconductor multilayer film. As a result, the AlGaAs semiconductor layer film is forcibly combined with the oxidized GaAs semiconductor layer. A sufficiently high-quality laminated structure of Al ₂ O ₃ layers formed by oxidation can be formed. In this oxidation process, a semiconductor containing Al as a constituent element has a very high degree of oxidation sensitivity to the Al composition x, and if a slight difference is made in the Al composition, one of the materials can be selected by selecting conditions. Can be selectively oxidized, and a three-dimensional semiconductor photonic crystal element can be manufactured using a wide range of materials.

Further, Al ₂ formed by forced oxidation
The O ₃ layer is an insulating layer and electrically insulates the substrate and the core. However, if the unoxidized AlGaAs region 22 is partially left as shown in FIG. A current can also flow in the direction perpendicular to the film, and it can be used for a current injection type laser or the like.

In addition to the case where GaAs is used as the substrate and the AlGaAs semiconductor layer and the GaAs semiconductor layer are used as the structure of the semiconductor multilayer film, the semiconductor multilayer film may be formed of two or more kinds of AlGaAs semiconductor layers having different compositions. InP is used as the substrate, and InAl is used as the configuration of the multilayer film.
Even if a GaAs semiconductor layer or an AlAsSb semiconductor layer is used, a three-dimensional refractive index modulation structure can be formed even if a mixed material containing Al is grown on a semiconductor substrate. A three-dimensional semiconductor photonic crystal device can be manufactured.

[Brief description of the drawings]

FIG. 1 is a diagram showing a method for manufacturing a three-dimensional semiconductor photonic crystal device according to the present invention. (a) is a perspective view of an epitaxially grown semiconductor multilayer film, (b) is a perspective view of a two-dimensional periodic mask pattern formed on the semiconductor multilayer film, (c)
3 is a perspective view (partially transparent view) of the semiconductor multilayer film after etching, and (d) is a perspective view (partially transparent view) of the multilayer film after oxidation treatment.

FIG. 2 is a diagram showing a three-dimensional optical semiconductor photonic crystal device manufactured according to another embodiment of the present invention.

FIG. 3 is a view showing a structure in which an unoxidized region is left in an AlGaAs semiconductor layer by controlling an oxidation time in the present invention to secure a channel through which a current flows. (A)
Is a multi-layered pillar 1 etched into a pillar shape in FIG.
FIG. 2B is a perspective view showing the book, and FIG. 2B is a perspective view (partially see-through view) of an enlarged one-period portion of the column.

FIG. 4 is a view showing a method for manufacturing a three-dimensional semiconductor photonic crystal element in a conventional method.

[Explanation of symbols]

1; GaAs substrate 2; AlGaAs semiconductor layer 3; GaAs semiconductor layer 4; semiconductor multilayer film 5; mask pattern 6; hole 7; Al ₂ O ₃ layer 8 formed by forced oxidation; stacked structure 10; GaAs substrate 11; GaAs Semiconductor layer 12; Al ₂ O ₃ layer 13 formed by forced oxidation 13; multilayer film 20 etched in a columnar shape 20; one pillar of multilayer film 21; one-period portion 22; unoxidized AlGaAs region 23; Formed Al ₂ O ₃ region 24; GaAs semiconductor layer 30; semiconductor single crystal 31; two-dimensional periodic pattern 32 formed on resist; beam for etching

Claims (5)

[Claims] 1. A method for manufacturing a three-dimensional semiconductor photonic crystal element comprising a plurality of light-trapping cladding layers and a plurality of light-transmitting core layers alternately stacked on a semiconductor substrate. On the substrate, the cladding layer made of the first semiconductor containing Al, and even if the semiconductor does not contain Al or the semiconductor contains Al, the composition of Al is 0.02 or more than that of the first semiconductor. A step of growing a stacked structure in which the core layer made of the small second semiconductor is alternately stacked; and a plurality of two-dimensional periodic arrays formed by etching perpendicular to the multilayer film having the stacked structure. Forming a hole, and finally, selectively oxidizing Al of the cladding layer to change a part or all of the hole to an oxide. Method for producing a conductive optical crystal element. 2. A method for manufacturing a three-dimensional semiconductor photonic crystal element comprising a plurality of light-trapping cladding layers and a plurality of light-transmitting core layers alternately stacked on a semiconductor substrate. On the substrate, the cladding layer made of the first semiconductor containing Al, and even if the semiconductor does not contain Al or the semiconductor contains Al, the composition of Al is 0.02 or more than that of the first semiconductor. A step of growing a laminated structure in which the core layer made of a small second semiconductor is alternately laminated; and then, by selectively oxidizing Al of the cladding layer, a part or the whole thereof is oxidized. A step of forming a plurality of holes having a two-dimensional periodic array by etching perpendicularly to the multilayer film having the laminated structure. Method for producing a conductive optical crystal element. 3. A method for manufacturing a three-dimensional semiconductor photonic crystal element comprising a plurality of light-trapping cladding layers and a plurality of light-transmitting core layers alternately stacked on a semiconductor substrate. On the substrate, the cladding layer made of the first semiconductor containing Al, and even if the semiconductor does not contain Al or the semiconductor contains Al, the composition of Al is 0.02 or more than that of the first semiconductor. A step of growing a stacked structure in which the core layer made of the small second semiconductor is alternately stacked; and a plurality of two-dimensional periodic arrays formed by etching perpendicular to the multilayer film having the stacked structure. Forming a columnar structure, and finally, selectively oxidizing Al of the cladding layer to change a part or all of the cladding layer to an oxide. Method of manufacturing dimensional semiconductor optical crystal element. 4. A method for manufacturing a three-dimensional semiconductor photonic crystal element comprising a plurality of light-trapping cladding layers and a plurality of light-transmitting core layers alternately laminated on a semiconductor substrate. On the substrate, the cladding layer made of the first semiconductor containing Al, and even if the semiconductor does not contain Al or the semiconductor contains Al, the composition of Al is 0.02 or more than that of the first semiconductor. A step of growing a laminated structure in which the core layer made of a small second semiconductor is alternately laminated; and then, by selectively oxidizing Al of the cladding layer, a part or the whole thereof is oxidized. And a step of forming a plurality of columnar structures having a two-dimensional periodic array by etching perpendicularly to the multilayer film having the laminated structure. Method of manufacturing dimensional semiconductor optical crystal element. 5. The semiconductor device according to claim 1, wherein the semiconductor substrate is GaAs and the first semiconductor is AlGaAs, or the semiconductor substrate is InP and the first semiconductor is InAlGaAs or AlAsSb. A method for manufacturing a three-dimensional semiconductor photonic crystal device according to claim 1.