JPH0794411A - Manufacture of semiconductor thin film - Google Patents

Abstract

PURPOSE:To grow a thin film having excellent electrical and optical characteristics by using molecular beam epitaxy by providing a process for confirming a group III stabilized surface formed by performing thermal cleaning on the surface of a mixed crystal of compound semiconductors exposed on the surface of a substrate. CONSTITUTION:An oxide on the surface of a substrate is completely removed by thermal cleaning. In order to accomplish the above-mentioned purpose, the temperature of the substrate must meet such two requirements that all kinds of oxides existing on the surface of the substrate can be sublimated and the surface of a crystal must be stabilized. When the substrate is composed of InGaAs, InGaP, GaAsP, or InGaAsP, the temperature of the thermal cleaning is set at about 60 deg.C. In case the substrate is composed of InAsP, the temperature is set at about 540 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a semiconductor thin film by a molecular beam epitaxy method, and particularly to a substrate material II
The present invention relates to a thin film manufacturing method using a group IV compound semiconductor mixed crystal.

[0002]

2. Description of the Related Art In order to grow a good thin film by the molecular beam epitaxy method, it is necessary to completely remove the oxide on the surface of the substrate before the growth. If growth is performed without satisfying this condition, many dislocations occur at the interface between the substrate and the growth layer, and a thin film having good electrical and optical characteristics cannot be obtained.

Conventionally, with respect to main binary compound semiconductor substrates, it has been possible to completely remove oxides on the surface of the substrate by a thermal cleaning process in which the outermost surface of the substrate is a group V or group III stabilizing surface. Here, thermal cleaning is a method of sublimating oxides by heating a substrate while irradiating a group V beam for preventing group V desorption in ultrahigh vacuum. This method has an advantage over other methods in that damage to the substrate is less.

Regarding the thermal cleaning of the III-V group binary compound semiconductor substrate of this type, see, for example, Institute of Electronics, Information and Communication Engineers, OQE 91-182, p. 85
(1992).

[0005]

However, a good thin film has heretofore been obtained only when the outermost surface of the substrate is a binary compound semiconductor. Therefore, when the ternary or higher group III-V compound semiconductor mixed crystal is exposed on the outermost surface of the substrate, the oxide on the surface of the substrate cannot be completely removed, and dislocations occur at the interface between the mixed crystal substrate and the growth layer. There is a problem that a large number of them occur and a thin film having good electrical and optical characteristics cannot be obtained.

An object of the present invention is InGaAs, InGa.
It is an object of the present invention to provide a method which makes it possible to grow a thin film having good electrical and optical characteristics on a compound semiconductor mixed crystal such as P, InAsP, GaAsP, or InGaAsP by using a molecular beam epitaxy method.

Another object of the present invention is to provide a part of the substrate surface,
When at least two kinds of binary or more compound semiconductors whose constituent elements are In, Ga, As, or P are exposed, both of the two kinds of compound semiconductors are electrically exposed by a molecular beam epitaxy method, It is an object of the present invention to provide a method that makes it possible to grow a thin film having good optical characteristics.

[0008]

To achieve the above object, the present invention comprises a thermal cleaning step in which the crystal surface of the compound semiconductor mixed crystal exposed on the substrate surface is a group III stabilizing surface. A method of manufacturing a semiconductor thin film is provided. That is, as shown in FIG. 1, after the normal process of bringing the substrate into the growth chamber and heating the substrate under the irradiation of the group V molecular beam to raise the substrate temperature, in the present invention, the group III stabilization is performed. Provide a process to confirm the surface. After this step, the substrate temperature is set to the growth temperature and the growth is started, which is a normal step.

In order to achieve the above-mentioned other objects, the present invention includes the above-mentioned thermal cleaning step after the step of substituting the oxide of the compound semiconductor mixed crystal surface exposed on the substrate surface with another compound. The present invention provides a method for manufacturing a semiconductor thin film. That is, in the present invention, a step of substituting the oxide with another compound (step in parentheses in FIG. 1) is provided before the step of loading into the growth chamber.

In the method of confirming the III-group stabilized surface in the present invention, a method of observing a change in a reflection high-energy electron diffraction image, a substrate temperature at which a change in the reflection high-energy electron diffraction image occurs is examined, and the substrate temperature is obtained. As described above, there are a method of monitoring the substrate temperature and a method of attaching the substrate and a flat plate substrate for stabilizing surface identification to a plate-shaped substance.

Further, as a step of substituting the oxide with another compound in the present invention, there is a method of substituting it with a sulfide by immersing it in an ammonium polysulfide solution or a phosphorus pentasulfide / ammonium polysulfide mixed solution.

[0012]

First, the object of the present invention, InGaAs, In
GaP, InAsP, GaAsP, or InGaAs
The action of the present invention for making it possible to grow a thin film having good electrical and optical characteristics on a compound semiconductor mixed crystal such as P by the molecular beam epitaxy method will be described.

In order to completely remove the oxide on the substrate surface by thermal cleaning, the substrate temperature is such that all kinds of oxides existing on the substrate surface sublime, and the substrate temperature is such that the crystal surface is a stabilizing surface. It is necessary to satisfy the following two conditions:

InGaAs, InGaP, InAsP,
Indium, Ga, As, and P oxides are present on the surface of a compound semiconductor mixed crystal such as GaAsP or InGaAsP. Among these oxides, the sublimation temperature is as follows: Ga oxide (about 600 ° C.)> As oxide (about 54
0 ° C.)> In oxide> P oxide. Therefore In
GaAs, InGaP, GaAsP, and InGaA
In case of sP, the thermal cleaning temperature is about 600 ℃
And the thermal cleaning temperature is set to about 540 ° C. in the case of InAsP, all kinds of oxides existing on the substrate surface can be sublimated. Less than,
Of the sublimation temperatures of the oxides present on the substrate surface, the highest temperature is abbreviated as To.

InGaAs, InGaP, GaAs
When the compound semiconductor mixed crystal such as P and InGaAsP is heated on the substrate under the irradiation of the group V molecular beam, the mixed crystal crystal surface becomes a group V stabilizing surface at a substrate temperature lower than about 600 ° C.
It changes to the group III stabilization surface and is stable even at about 600 ° C. In the case of InAsP, at a substrate temperature lower than about 500 ° C., the group V stabilization surface changes to the group III stabilization surface, and
It is stable even at ℃. That is, the thermal cleaning temperature is a temperature at which the mixed crystal crystal surface becomes a stabilizing surface. Hereinafter, the temperature at which the mixed crystal surface changes from the group V stabilized surface to the group III stabilized surface by heating the substrate under irradiation of the group V molecular beam is abbreviated as Ts.

Therefore, by setting the thermal cleaning temperature of the above-mentioned material system to the substrate temperature at which the clean crystal surface shows the group III stabilizing surface in the group V molecular beam intensity for performing thermal cleaning, the above compound semiconductor mixed crystal is formed. It is possible to grow a thin film having excellent electrical and optical characteristics.

Next, another object of the present invention, where at least two kinds of binary or more compound semiconductors whose constituent elements are In, Ga, As, or P are exposed on a part of the substrate surface. The action of the present invention for growing a thin film having good electrical and optical characteristics on both of the two types of compound semiconductors by using the molecular beam epitaxy method will be described.

By providing a step of immersing in an ammonium polysulfide solution or a phosphorus pentasulfide / ammonium polysulfide mixed solution during the pretreatment step, oxides existing on the III-V group compound semiconductor mixed crystal surface are sulfided. Can be replaced with This has the following two effects. One effect is that To can be lowered from the sublimation temperature of Ga oxide (about 600 ° C.) to the sublimation temperature of Ga sulfide (about 550 ° C.). Therefore, thermal cleaning at a lower temperature can suppress thermal diffusion of the substrate structure. Another effect is that the sublimation temperature of both Ga sulfide and As sulfide is about 550 ° C., and the difference in sublimation temperature can be eliminated. Therefore, To is Ga
A material system (GaA) that has an oxide sublimation temperature (about 600 ° C.)
s, InGaAs, InGaP, GaAsP, and I
nGaAsP, etc.) and a material system (InAsP, etc.) in which To is the sublimation temperature of As oxide (about 540 ° C.) (InAsP, etc.), the thermal cleaning temperature is set to Ga By setting the sublimation temperature of sulfides and As sulfides (about 550 ° C.), the deposits existing on the substrate surface are sublimated, and the substrate temperature is a temperature at which the crystal surface becomes a stabilizing surface. A thin film having good electrical and optical characteristics can be grown simultaneously on two types of compound semiconductors.

To further elaborate on the operation of the present invention to achieve another object, InP and InGaAs
Take the case where good growth is simultaneously performed on the above.

It is well known that the surface oxide of InP contains As oxide when it is irradiated with As molecular beam in order to prevent excessive desorption of group V from the mixed crystal surface during thermal cleaning. . That is, at this time, InP and In
Simultaneous good growth on GaAs is achieved by InAs
This is equivalent to the simultaneous good growth on P and InGaAs. For InAsP, To is the sublimation temperature of As oxide (about 540 ° C.), and for InGaAs, G is G.
It is the sublimation temperature (about 600 ° C.) of the oxide a. By providing a step of immersing in an ammonium polysulfide solution or a phosphorus pentasulfide / ammonium polysulfide mixed solution, these Ga
Oxides and As oxides with a sublimation temperature of about 550 ° C
It can be replaced with a sulfide or As sulfide. Also I
The Ts of nAsP and InGaAs are both 550 ° C. or less, which is a group III stabilizing surface at about 550 ° C. Therefore, the temperature of the clean crystal is determined by the temperature of the group V molecular beam for performing the thermal cleaning.
By setting the substrate temperature showing the III-stabilized surface,
A thin film having good electrical and optical characteristics can be grown on InAsP and InGaAs at the same time.

[0021]

EXAMPLES Example 1 (1-1) Single Quantum Well Structure and Manufacturing Method Thereof The molecular beam epitaxy method was used for crystal growth of single quantum wells. FIG. 2 shows a single quantum well structure made of a III-V group compound semiconductor to which the present invention is applied. The formed semiconductor crystals are all non-doped,
The carrier concentration is <1 × 10 ¹⁵ / cm ³ .

In FIG. 2, the crystals from 2 to 10 are
Both are mixed crystals lattice-matched to the semi-insulating InP substrate 1 (layer thickness 450 μm, carrier concentration <1 × 10 ¹⁵ / cm ³ ). First, the InAlAs buffer layer 2 (layer thickness 0.5
InGaAs single quantum well 6 (layer thickness 19.
2 nm), 7 (layer thickness 9.6 nm) and 8 (layer thickness 4.8)
nm). Here, the InAlAs barrier layer 3 (layer thickness 30.0 nm) was used as the barrier layer of the single quantum well.

Next, the sample was taken out into the atmosphere and immersed in pure running water to form an InGaAs surface oxide. After the organic washing, the sample was dried and again loaded into the growth chamber.

The present invention was used to remove InGaAs surface oxide. That is, the substrate temperature is raised while irradiating the As molecular beam of 8 μTorr, and thermal cleaning is performed at a temperature (620 ° C., 5 minutes) at which the reflected high-energy electron diffraction image becomes a (4 × 2) pattern representing the group III stabilization surface. went. After that, the hatched portion in FIG. 2 was formed.

The observation of the reflected high-energy electron beam diffraction image is not necessarily required to be performed next time. By monitoring that the substrate temperature is 620 ° C,
The same effect can be obtained.

The structure of the hatched portion in FIG. 2 is as follows. InGaAs single quantum well 9 (layer thickness 2.4 nm)
And 10 (layer thickness 1.2 nm). The InAlAs barrier layer 4 (layer thickness 30.0 nm) was used as the barrier layer of the single quantum well, and finally the InAlAs cap layer (layer thickness 0.1 μm).
Was formed.

As a comparative example, a sample in which the same structure as in FIG. 2 was grown normally without the above growth interruption was also prepared.

(1-2) Results of optical characteristic evaluation of a single quantum well in the hatched portion in FIG. 2 FIG. 3 shows an Ar ion laser (wavelength 51) as an excitation light source.
(4.5 nm) is a photoluminescence spectrum from a single quantum well. 11 is regrowth InG
spectrum from aAs well layer 6, 12 is regrown InG
spectrum from aAs well layer 7, 13 is InGaAs
The spectrum from the well layer 9 and the spectrum 14 from the InGaAs well layer 10. Note that carriers were depleted at the regrowth interface due to non-radiative centers such as dislocations.
The spectrum from the nGaAs well layer 7 is not obtained.

The full width at half maximum of the spectrum from the InGaAs well layer 9 is 26.0 meV (Comparative Example 23.0 meV),
The full width at half maximum of the spectrum from the InGaAs well layer 10 was 31.0 meV (Comparative Example 32.9 meV), and a crystal having the same optical characteristics as the Comparative Example could be grown. This is due to thermal cleaning for 5 minutes at 620 ° C., which is a Group III stabilizing surface before formation of the hatched portion in FIG.
It is considered that the InGaAs surface oxide could be completely removed. That is, when a ternary or higher group III-V compound semiconductor mixed crystal substrate is used as the substrate material, the surface oxide cannot be completely removed, and many dislocations occur at the interface between the mixed crystal substrate and the growth layer. However, the effect of the present invention was confirmed with respect to the problem that a thin film having good electrical and optical characteristics could not be obtained.

Example 2 (2-1) Device Structure and Manufacturing Method Thereof In this example, a semiconductor crystal was used as a passivation film of an absorption layer multiplication layer separated type mesa type back illuminated superlattice APD (avalanche photodiode). Is used. Figure 4
[FIG. 3] is an element cross-sectional structure of an APD made of a III-V group compound semiconductor. The molecular beam epitaxy method was used for all crystal growth of this device.

First, the n-InP substrate 21 (layer thickness 150 μm
m, electron concentration n = 2 × 10 ¹⁸ / cm ³ ) and a mixed crystal of 15 to 20 lattice-matched was grown. 15 is p
-InGaAs contact layer (layer thickness 0.2 μm, hole concentration p = 2 × 10 ¹⁹ / cm ³ ), 16 is p-InAlA
s buffer layer (layer thickness 1.0 μm, hole concentration p = 2 × 1
0 ¹⁸ / cm ³ ), 17 is a p-InGaAs light absorption layer (layer thickness 0.6 μm, hole concentration p = 2 × 10 ¹⁵ / cm ³ ) 1.
8 is a p-InAlAs electrolytic relaxation layer (layer thickness 0.1 μm, hole concentration p = 2 × 10 ¹⁷ / cm ³ ), 19 is a superlattice multiplication layer, InGaAs (well layer width is 5 nm) and I
A laminated structure in which nAlAs (barrier layer width 15 nm) is repeated 17 times (total layer thickness 0.35 μm, n <1 × 10 ¹⁵ / c)
m ³ ), and 20 are n-InAlAs buffer layers (layer thickness 0.1 μm, hole concentration p = 2 × 10 ¹⁸ / cm ³ ).

Next, a mesa shape was formed by wet etching using a well-known Br type solution. The junction diameter of the element is 50 μm.

In growing the passivation crystal 24, especially the p-InGaAs absorption layer 17 and the n-InP are grown.
The present invention was applied to grow an InAlAs passivation crystal with good properties on the substrate 21. In order to completely sublime the surface oxides of InGaAs and InP exposed on the side surface of the mesa, Sample 26 was immersed in a commercially available ammonium polysulfide solution for 10 seconds, washed with pure running water, and then spinner dried. Also, for observation of the reflected high-speed electron beam diffraction image,
Similarly, an InGaAs flat substrate 25 was immersed in a commercially available ammonium sulfide solution for 10 seconds, washed with pure running water, and spinner dried.
Was prepared and attached to the Si plate 27 with In as shown in FIG.

Although the InGaAs flat plate substrate 25 for observation of the reflection high-energy electron diffraction image is attached here, when the relation between the substrate temperature and the stabilizing surface is obvious, the substrate for reflection high-energy electron diffraction image observation is performed. A flat substrate is not always necessary.

This sample was again loaded into the growth chamber, and 8 μTo
The substrate temperature was raised while irradiating the As molecular beam of rr, and thermal cleaning was performed at a temperature (580 ° C., 5 minutes) at which the reflected high-energy electron diffraction image became a (4 × 2) pattern representing the III-group stabilized surface. . Thereafter, non-doped InAlAs24 was grown as a passivation crystal to a film thickness of 0.2 μm. At this film thickness, the resistance of the entire passivation crystal has a small cross-sectional area, and the resistivity also increases due to surface depletion, so that the resistance is sufficiently high (500 Mohm or more) to function as an APD.

Finally, the p-type electrode 2 is formed by the vacuum evaporation method.
2. The n-type electrode 23 was formed using Au / Pt / Ti.

For comparison, the same structure was also prepared under the other conditions without the ammonium sulfide solution immersion.

(2-2) Evaluation of element characteristics The characteristics of these elements are shown below. The dark current at a multiplication factor of 10 was 0.05 μA (comparative example 0.2 μA), and low dark current characteristics were obtained. This is InGaAs and In
It is considered that a good passivation crystal could be grown on P, the interface state density of the APD mesa side crystal surface was reduced, and the surface leak current was smaller than that in the comparative example. That is, among the III-V group compound semiconductor mixed crystals,
The effects of the present invention have been confirmed regarding a method of sublimating at least two kinds of surface oxides at the same time.

[0039]

As described above in detail, according to the present invention, the intended purpose can be achieved. That is, InGaA
s, InGaP, InAsP, GaAsP, or In
There is an effect that it is possible to provide a method that makes it possible to grow a thin film having excellent electrical and optical characteristics on a compound semiconductor mixed crystal such as GaAsP by using a molecular beam epitaxy method. Further, the constituent element I is formed on a part of the substrate surface.
When at least two kinds of binary or more compound semiconductors of n, Ga, As, or P are exposed, both the compound semiconductors of the two kinds are exposed to electric and optical characteristics by using a molecular beam epitaxy method. There is an effect that it is possible to provide a method that makes it possible to grow a good thin film.

[Brief description of drawings]

FIG. 1 is a flowchart of the present invention.

FIG. 2 is a cross-sectional view of a single quantum well structure formed by applying the present invention.

FIG. 3 is a photoluminescence characteristic of a single quantum well structure formed by applying the present invention.

FIG. 4 is a sectional view of a device structure formed by applying the present invention.

FIG. 5 is a state in which a Si plate is pasted to form by applying the present invention.

[Explanation of symbols]

1 ... Semi-insulating InP substrate, 2 ... InAlAs buffer layer, 3 ... InAlAs barrier layer, 4 ... Regrowth InAlAs
Barrier layer, 5 ... Regrown InAlAs cap layer, 6 ... In
GaAs well layer (layer thickness 19.2 nm), 7 ... InGaA
s well layer (layer thickness 9.6 nm), 8 ... InGaAs layer (layer thickness 4.8 nm), 9 ... regrown InGaAs well layer (layer thickness 2.4 nm), 10 ... regrown InGaAs well layer (layer thickness 1. 2 nm), 11 ... InGaAs well layer (layer thickness 19.
Photoluminescence from 2 nm), 12 ... InGa
Photoluminescence from As well layer (layer thickness 9.6 nm), 13 ... Regrown InGaAs well layer (layer thickness 2.4 n)
photoluminescence from m), 14 ... Regrown InG
Photoluminescence from aAs well layer (layer thickness 1.2 nm), 15 ... p-InGaAs contact layer, 16 ...
p-InAlAs buffer layer, 17 ... p-InGaAs
Light absorption layer, 18 ... p-InAlAs electric field relaxation layer, 19 ...
InAlAs / InGaAs superlattice multiplication layer, 20 ... n-
InAlAs buffer layer, 21 ... n-InP substrate, 22
... p electrode, 23 ... n electrode, 24 ... InAlAs passivation layer, 25 ... flat plate In for observing reflection high-energy electron diffraction images
GaAs, 26 ... Sample to be grown, 27 ... Si plate.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroaki Inoue 1-280, Higashi Koikekubo, Kokubunji, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd.

Claims (8)

[Claims] 1. A method for producing a semiconductor thin film by a molecular beam epitaxy method, wherein the entire substrate surface is made of InGaAs or InGa.
A method for producing a semiconductor thin film, which comprises a thermal cleaning step in which the outermost surface of the substrate is a Group III stabilizing surface when any one of P, InAsP, GaAsP, and InGaAsP is used. 2. A method of manufacturing a semiconductor thin film by a molecular beam epitaxy method, wherein the entire substrate surface is made of InGaAs or InGa.
When any one of P, InAsP, GaAsP, and InGaAsP is used, it includes a step of substituting the oxide with another compound, and a thermal cleaning step in which the entire substrate surface becomes a group III stabilizing surface. A method for manufacturing a semiconductor thin film. 3. A method for producing a semiconductor thin film by a molecular beam epitaxy method, wherein InGaAs and InG are formed on a part of the substrate surface.
aP, InAsP, GaAsP, or InGaAsP
If at least one of the
A method of manufacturing a semiconductor thin film, which comprises a thermal cleaning step for stabilizing a group I surface. 4. A method for producing a semiconductor thin film by a molecular beam epitaxy method, wherein the constituent elements are In and G on a part of the substrate surface.
When at least two kinds of binary semiconductor compounds of a, As, or P which are a or As are exposed, a step of substituting the oxide with another compound, and a thermal cleaning step in which the exposed part is a group III stabilizing surface A method of manufacturing a semiconductor thin film, comprising: 5. The method for producing a semiconductor thin film according to claim 1, wherein a method of observing a change in a reflection high-energy electron diffraction image is used as a method of confirming the group III stabilizing surface. 6. The method for confirming the group III stabilization surface is characterized by using a method of examining a substrate temperature at which a reflection high-energy electron diffraction image change occurs and monitoring the substrate temperature so as to be the substrate temperature. The method for producing a semiconductor thin film according to claim 1, wherein 7. A method for confirming the Group III stabilizing surface, comprising a step of sticking the substrate and a flat plate substrate for identifying the stabilizing surface to a plate-like substance, the flat plate for identifying the stabilizing surface. InGaAs, InGaP, InAsP, GaA on the outermost surface of the substrate
5. The method of manufacturing a semiconductor thin film according to claim 1, wherein either one of sP and InGaAsP is exposed. 8. The method of immersing in an ammonium polysulfide solution or a phosphorus pentasulfide / ammonium polysulfide mixed solution is used as a step of substituting the oxide with another compound. Method for manufacturing semiconductor thin film.