JPH07176523A - Forming method of semiconductor quantum structure - Google Patents

Abstract

PURPOSE:To form a semiconductor quantum structure of high quality on a grating substrate by a method wherein the grating substrate is cleaned taking advantage of thermal etching CONSTITUTION:An AlGaAs etching stop layer 2 and a GaAs protective layer 3 are made to grow on a GaAs substrate 1 through a molecular beam epitaxy method. Then, the substrate 1 is processed into the shape of a grating by selectively removing the AlGaAs etching stop layer 2 and the GaAs protective layer 3 front the grooves of the grating. Furthermore, the grating substrate 1 is subjected to thermal etching in a growth chamber, whereby only GaAs is selectively etched to obtain the clean surface of the grating substrate 1, and then AlAs trapping layers 4 and 6 and a fine GaAs layer 5 are made to grow. By this setup, GaAs buried quantum lines excellent in crystallinity can be formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming semiconductor quantum fine structures such as quantum wires and quantum boxes used in semiconductor devices such as semiconductor lasers and field effect transistors.

[0002]

2. Description of the Related Art Conventionally, as a method for forming a quantum wire on a semiconductor substrate processed into a grating shape, a journal,
Journal of of Growth (Journal of
(Crystal Growth), Volume 104, Volume 7
As described on pages 66 to 772, a submicron period grating is processed on a GaAs substrate by photolithography and wet etching, and an Al _t Ga _1-t As, GaAs layer is grown thereon by molecular beam epitaxial growth. It is known to grow by the method (MBE) to form a quantum wire structure in which a fine GaAs layer is provided in the grating groove portion.

[0003]

However, the above-mentioned conventional example has the following drawbacks. When a semiconductor quantum wire structure is formed on a grating substrate, a high quality product cannot be obtained by ordinary thermal cleaning because the surface of the grating substrate is not sufficiently cleaned. Therefore, for example, the emission efficiency of the semiconductor laser using the semiconductor quantum wire structure is not sufficient. In addition, since it is difficult to obtain a grating with a sharp grating and a shape with little fluctuation, it is easy for the fine semiconductor layer grown on this to grow because some of the neighboring semiconductors are connected to each other. It cannot be integrated in density.

Therefore, an object of the present invention is to provide a forming method capable of obtaining a high-quality semiconductor quantum fine structure by utilizing thermal etching in a growth chamber. Another object of the present invention is to provide a method for forming a semiconductor quantum fine structure that can be integrated at high density.

[0005]

According to a first method of forming a semiconductor quantum fine structure of the present invention, a surface of a semiconductor substrate made of a first compound semiconductor and capable of being thermally etched at a predetermined temperature is not thermally etched at the predetermined temperature. A step of sequentially epitaxially growing an etching stop layer and a protective layer made of a second compound semiconductor capable of being thermally etched at the predetermined temperature; a step of forming a recess reaching the semiconductor substrate by a lithography method; and a thermal etching at the predetermined temperature. And removing the protective layer, and epitaxially growing a first confinement layer made of a third compound semiconductor having a predetermined bandgap and having a recess corresponding to the recess to form a recess in the first confinement layer. A fourth compound having a band gap smaller than that of the first confinement layer Epitaxially growing a fine semiconductor layer made of a conductor, and epitaxially growing a second confinement layer made of a fifth compound semiconductor having a bandgap larger than that of the fine semiconductor layer, the first confinement layer and the fine semiconductor layer. And a quantum wire or quantum box composed of the second confinement layer.

The second method for forming a semiconductor quantum fine structure according to the present invention comprises a second compound semiconductor which has a predetermined band gap on the surface of a substrate made of the first compound semiconductor and which is not thermally etched at a predetermined temperature. A first etching stop layer, a semiconductor layer made of a third compound semiconductor having a band gap smaller than that of the second compound semiconductor and capable of being thermally etched at the predetermined temperature; a fourth layer having a band gap larger than that of the third compound semiconductor; A step of sequentially epitaxially growing a second etching stop layer made of a compound semiconductor and not thermally etched at the predetermined temperature and a protective layer made of a fifth compound semiconductor capable of being thermally etched at the predetermined temperature; and a step of forming the semiconductor layer by a lithography method. Surrounded by said groove by exposing and providing a groove A step of forming a raised portion and performing thermal etching at the predetermined temperature to remove the protective layer and expose the first etching stopper layer in the groove portion so that the upper surface is covered with the second etching stopper layer. The step of forming a protruding fine semiconductor layer; and the step of epitaxially growing a buried layer made of a sixth compound semiconductor having a band gap larger than that of the second compound semiconductor and filling the groove. And a confinement layer composed of the first etching stop layer, the buried layer, and the second etching stop layer, which are respectively joined at the bottom surface, the side surface, and the upper surface thereof, to form a quantum wire or quantum box.

[0007]

By providing the protective layer on the surface of the etching stopper layer, it is possible to prevent the surface of the etching stopper layer from being oxidized at the time of forming the recess or the protrusion. Then, by thermal etching, a confinement layer and the like are grown after exposing a clean surface free of oxides and carbides, so that good crystallinity can be obtained.

Further, during the thermal etching, since the semiconductor substrate of the concave portion or the semiconductor layer of the protruding portion is etched, when a plurality of gratings are formed adjacent to the concave portion or the protruding portion, a sharp grating profile including an undercut is obtained. To be

[0009]

Embodiments of the present invention will now be described with reference to the drawings.

1A to 1D are sectional views in order of steps for explaining a first embodiment of the present invention.

First, as shown in FIG.
On the (100) surface of the substrate 1, Al _x Ga _1-x As (0.1
≦ x ≦ 1, for example x = 0.3), the etching stopper layer 2 (thickness 10 nm) and the GaAs protective layer 3 (thickness 10 n).
m) are sequentially epitaxially grown. Next, the sample was taken out from the growth chamber and subjected to electron beam lithography and wet etching, as shown in FIG. 1B, to a grating with a pitch of 100 nm (stripe direction [0-1
1]) is formed. At this time, the GaAs crystal under the etching stopper layer 2 is etched only in the grating groove portion. This grating sample is again introduced into the growth chamber, and thermal etching is performed at 750 ° C. while irradiating As. The degree of vacuum before As irradiation is an ultra-high vacuum state of about 1.3 × 10 ⁻⁸ Pa, and the degree of vacuum is 1.3 × 10 ⁻³ depending on As.
Set to about Pa. At this temperature, Al _0.3 Ga _0.7 As is not etched but only GaAs is etched. Therefore, the protective layer 3 of the grating mountain portion and the Ga of the groove portion are
As crystals are etched, and a clean Al _0.3 Ga _0.7 As surface free of oxides and carbides is obtained at the peaks and a similarly clean GaAs surface is obtained at the valleys. Since the etching rate at 750 ° C. is 6 nm / min, the protective layer 3 having a thickness of 10 nm can be sufficiently removed if the etching time is 2 minutes. Since there is the etching stop layer 2 in the grating peak portion and this is not etched, as shown in FIG. 1C, the groove portion becomes deep and a grating having a sharper profile can be obtained. Then, the second epitaxial growth for forming the quantum wire structure is immediately started. As shown in FIG. 1D, an AlAs layer (thickness 30 nm) as a first confinement layer 4, a fine GaAs layer 5 (thickness 10 nm, width 2).
0 nm), an AlAs layer (thickness 30 nm) as the second confinement layer 6, and an Al _0.2 Ga _0.8 As cap layer 7 (thickness 100 nm). Since AlAs preserves the grating shape and GaAs grows so as to accumulate at the bottom of the groove, the fine GaAs layer 5 is AlA in the groove of the grating.
There is a structure embedded in s. Since these layers grow on a clean grating substrate after thermal etching, a high-quality semiconductor quantum wire structure with good crystallinity can be obtained. For example, when a semiconductor laser array is formed, high luminous efficiency can be obtained. Further, since a sharp grating profile is obtained by thermal etching, the shape of the plurality of quantum thin wire structures grown on it has no fluctuation.

The quantum wire structure can be formed by molecular beam epitaxial growth (MBE) on a grating substrate.
This is because the growth morphology differs between As and Al _q Ga _1-q As. When a GaAs layer is grown on a substrate having a groove shape, G
Since the migration of a atoms is large, the GaAs layer is formed so as to accumulate at the bottom of the groove. On the other hand, Al _q Ga
_Since Al atom migration is small when _1-q As is grown, the Al _q Ga _1-q As layer preserves the shape of the groove. Therefore, the GaAs layer on the grating should be Al.
_When grown so as to be sandwiched between _q Ga _1-q As layers, fine GaA
A structure in which the s layer is filled with Al _q Ga _{1 -q} As (AlAs in this embodiment) is formed.

In this embodiment, a grating substrate in which a plurality of stripe-shaped grooves are arranged in parallel at a predetermined pitch is used for forming a quantum wire structure, but a single stripe-shaped groove may be provided, or a quantum box structure can be formed. For this purpose, MB is formed on a dot-shaped pattern substrate in which one recess or a plurality of recesses are arranged.
E You may grow up. In this case, Ga under the same growth conditions
A structure in which As is three-dimensionally surrounded by Al _q Ga _1-q As is formed.

The material system is In _p instead of GaAs.
Other compound semiconductors such as Ga _1-p As may be used.

FIGS. 2A to 2D are sectional views in order of steps for explaining the second embodiment of the present invention.

First, as shown in FIG. 2A, GaAs
The first etching stop layer 4A is formed on the (100) surface of the substrate 1.
An AlAs layer (thickness 3) is used as the first confinement layer.
0 nm), GaAs layer 8 (thickness 10 nm), AlA as the second etching stop layer 9 (which becomes the second confinement layer).
An s layer (thickness 30 nm) and a GaAs layer (thickness 10 nm) are sequentially grown as the protective layer 10. This sample was taken out of the growth chamber and subjected to electron beam lithography and wet etching to obtain a pitch of 100 nm as shown in FIG. 2 (b).
Processed into a grating shape. At this time, the protective layer 10 and the second etching stop layer 9 are removed only in the grating groove portion. Moreover, the width of the grating crest portion is set to 30 nm. Next, this grating substrate is reintroduced into the growth chamber, and thermal etching is performed at 750 ° C. Since only GaAs is etched in this thermal etching, as shown in FIG. 2C, the protective layer 10 in the grating mountain portion and the GaAs layer 8 in the groove portion are removed by etching.
A clean AlAs layer (9) surface beneath appears. Further, the GaAs layer 8 in the grating mountain portion (projection portion) is thermally etched, so that the etching proceeds from the side surface together with the etching in the groove portion. By this undercut etching, the GaAs layer 8 becomes a fine protruding fine GaAs layer 11 having a width of about 20 nm. This protruding fine G
Since the side surface of the aAs layer 11 is obtained by thermal etching, it also has a clean surface. Then, the second epitaxial growth is performed. As shown in FIG. 2D, an AlAs burying layer 12 (thickness: 30 nm, which serves as a third confinement layer), an Al _0.2 Ga _0.8 As cap layer 7
A (thickness 100 nm) is sequentially grown. The AlAs burying layer 12 fills the side surface of the protruding fine GaAs layer 11. Thus, the buried layer 12 grown on the grating cleaned by thermal etching and its interface have good crystallinity, and non-radiative recombination on the side surface of the protruding fine GaAs layer cannot be performed. Thus, a high-quality quantum wire structure in which the protruding fine GaAs layer is surrounded by the AlAs layer (confinement layer) is obtained.

In the present embodiment, a plurality of protruding fine GaAs layers can be reliably formed by lithography and thermal etching, and a buried layer is deposited on a clean surface, so that a good quantum wire structure can be reliably realized.

Similar to the first embodiment, a single stripe-shaped protruding fine GaAs layer may be formed, or a single or a plurality of doft-shaped quantum boxes may be formed. Further, other compound semiconductor such as In _p Ga _1-p As may be used instead of GaAs.

[0019]

According to the present invention, after performing patterning by a lithography method, cleaning is performed by using thermal etching, and epitaxial growth is continuously performed in the same growth chamber to obtain a semiconductor quantum fine structure of high quality. Can be formed into Thereby, for example, a high-performance semiconductor laser or laser array using the quantum wire structure for the active layer can be easily manufactured.

[Brief description of drawings]

FIG. 1A is a view for explaining a first embodiment of the present invention.
It is a process order sectional view divided and shown in (d).

FIG. 2 is a view for explaining a second embodiment of the present invention (a).
It is a process order sectional view divided and shown in (d).

[Explanation of symbols]

1 GaAs Substrate 2 Etch Stop Layer 3 Protective Layer 4 First Confinement Layer 5 Fine GaAs Layer 6 Second Confinement Layer 7,7A Al _0.2 Ga _0.8 As Cap Layer 4A First Etch Stop Layer 8 GaAs Layer 9 Second Etching stop layer 10 Protective layer 11 Fine protrusion GaAs layer 12 Buried layer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location H01L 29/68

Claims (6)

[Claims] 1. A surface of a semiconductor substrate which is made of a first compound semiconductor and is capable of being thermally etched at a predetermined temperature, and an etching stopper layer which is not thermally etched at the predetermined temperature, and a second compound semiconductor which is capable of being thermally etched at the predetermined temperature. A step of sequentially epitaxially growing a protective layer, a step of forming a recess reaching the semiconductor substrate by a lithography method, a step of performing thermal etching at the predetermined temperature to remove the protective layer, and a third step of forming a predetermined band gap. Of the fourth compound semiconductor having a smaller bandgap than that of the first confinement layer is epitaxially grown on the first confinement layer having a recess corresponding to the recess. Epitaxially grow the semiconductor layer and Epitaxially growing a second confinement layer made of a fifth compound semiconductor having a band gap larger than that of the body layer, the first confinement layer,
A method for forming a semiconductor quantum fine structure, comprising forming a quantum wire or quantum box comprising a fine semiconductor layer and a second confinement layer. 2. The first compound semiconductor, the second compound semiconductor, and the fourth compound semiconductor are GaAs, and the third compound semiconductor is Al _x Ga _{1 -x} As (0 <x ≦ 1), and the fourth compound semiconductor is Of the compound semiconductor of Al _y Ga _1-y As (0 <y ≦ 1)
The method for forming a semiconductor quantum fine structure according to claim 1, wherein 3. The etch stop layer is Al _z Ga _{1 -z} As.
The method for forming a semiconductor quantum fine structure according to claim 2, wherein (0 <z ≦ 1). 4. A first etching stop layer made of a second compound semiconductor which has a predetermined band gap on the surface of a substrate made of the first compound semiconductor and is not thermally etched at a predetermined temperature. A semiconductor layer made of a third compound semiconductor having a small band gap and capable of thermal etching at the predetermined temperature, and a second semiconductor layer made of a fourth compound semiconductor having a band gap larger than that of the third compound semiconductor, and not thermally etched at the predetermined temperature. A step of sequentially epitaxially growing an etching stopper layer and a protective layer made of a fifth compound semiconductor capable of being thermally etched at the predetermined temperature, and exposing the semiconductor layer by a lithography method to form a groove The step of forming the protrusion and the thermal etching at the predetermined temperature are performed. Etching to remove the protective layer and expose the first etching stop layer in the groove to form a projecting fine semiconductor layer having an upper surface covered with the second etching stop layer; Two
And a step of epitaxially growing a buried layer made of a sixth compound semiconductor having a band gap larger than that of the compound semiconductor and filling the groove, and the projecting fine semiconductor layer is bonded to the bottom surface, the side surface, and the top surface, respectively. 1. A method for forming a semiconductor quantum fine structure, comprising forming a quantum wire or a quantum box having a confinement layer composed of an etching stop layer No. 1, a buried layer and a second etching stop layer. 5. The first compound semiconductor, the third compound semiconductor, and the fifth compound semiconductor are GaAs, and the second compound semiconductor is Al _u Ga _1-u As (0 <u ≦ 1), and the fourth compound semiconductor is the fourth compound semiconductor. Compound semiconductor of Al _v Ga _1-v As (0 <v ≦
1), the sixth compound semiconductor is Al _w Ga _1-w As (0 <
The method for forming a semiconductor quantum fine structure according to claim 4, wherein w ≦ 1). 6. The method for forming a semiconductor quantum fine structure according to claim 5, wherein u = v = w = 1.