JPH0563305A - Manufacturing method of semiconductor quantum well case - Google Patents

Abstract

PURPOSE:To enable the etching step, etc., to be eliminated by a method wherein MOVPE process etc., is utilized for the initial crystal growing process on a substrate not to form a laminar single crystal film in the epitaxial growing step. CONSTITUTION:The title manufacturing method of quantum well case utilizing MOVPE process is described as follows. That is, when a III group material, e.g. trimethylgallium(TMG), etc., is fed to a heated substrate 10, the material is cracked on the substrate 10 to produce Ga atoms sucking at the substrate 10 if the substrate 10 temperature exceeds the cracking temperature of the organic metal. However, when the wettability of liquid Ga to the substrate 10 is inferior and the feed of Ga material to the substrate 10 runs short, Ga is formed into droplets (islands) on the substrate 10. Furthermore, when As material 11 is fed to the substrate 10 having such islands, the As atoms are diffused in the islands so as to be GaAs 11 crystallized. At this time, the total feed of organic gallium compound shall not exceed the feed by which the mean film thickness of the metallic film formed of the Ga material on the substrate 10 may be made to attain to 50mum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor quantum well box, and particularly to a large-scale optical control element using a nonlinear optical effect such as an ultrafast optical switch or optical logic element. The present invention relates to a material having a nonlinear optical constant.

[0002]

2. Description of the Related Art A semiconductor laminated structure (multiquantum well structure) in which two types of ultrathin films having different forbidden band widths are periodically stacked in a thickness range of several nm to several (+) nm Physical phenomena not found in compound semiconductors have occurred, and application to various devices has been attempted. For example, GaAs / AlGa
A semiconductor laser using an As multiple quantum well structure as an active layer is
It has been reported that it has various excellent characteristics such as a reduction in oscillation threshold, a reduction in spectral line width, and a higher output than those of the conventional double hetero semiconductor laser. The physical phenomenon that appears in such a multiple quantum well structure is due to the confinement of charged particles (quantum size effect) in the bottom (quantum well) of a potential that is periodic in the film thickness direction within the multiple quantum well structure. Is. On the other hand, not only in the film thickness direction, but also in the in-plane one direction, the potential changes periodically, and the quantum wire structure in which the confinement of charged particles is two-dimensional, or the potential periodically in two directions in the plane. In a quantum well box structure that achieves three-dimensional confinement including the film thickness direction, the confinement effect of charged particles becomes more remarkable than in the quantum well structure, and when applied to devices such as semiconductor lasers. , It is expected to greatly improve its characteristics.

The length of one side where the quantum size effect appears is a few
As a method of manufacturing a semiconductor quantum well box structure of several (+) nm from nm, a method using an ultrafine processing technology typified by an electron beam direct writing method has been tried. This is to fabricate a quantum well box by providing potential periodicity also in the in-plane direction by performing fine processing on the multiple quantum well structure.

That is, MOVPE (Metal Organic Vapor Phase Depositio) excellent in controlling the film thickness and the steepness of the interface.
n) method or MBE (Molecular Beam Epitaxy) method, etc., a barrier layer 41 made of AlGaAs and GaAs are formed on a GaAs substrate 40 as shown in FIG.
Epitaxially grow the quantum well 42 of. As shown in FIG. 4 (b), a grid pattern 43 of resist or the like is formed on the surface of this substrate by an electron beam exposure method or the like, and this is used as a mask for etching (FIG. 4C) (for example, M.A.
Reed et al., J, Vac. Sci. Technol., B4,358 (1986)),
Finally, when the grid pattern used as the etching mask is removed, a three-dimensional potential well in which the substrate direction is AlGaAs and the rest is surrounded by air, that is, a semiconductor quantum well box FIG. 4D is obtained.

[0005]

However, in the method of manufacturing a semiconductor quantum well box using the microfabrication technique, the following drawbacks occur in the electron beam exposure step and the etching step. That is, in the electron beam exposure process, there is no interference in the depth direction as in ordinary exposure using ultraviolet rays, but since the backscattering of electrons is large, the exposure line width becomes larger than the beam width of the electron beam, and the adjacent pattern A so-called proximity effect appears in which distortion occurs. For this reason, consideration must be given to increasing the accelerating voltage or reducing the resist film thickness for the purpose of suppressing the increase of the drawing line width due to scattering, and these effects must be incorporated into the drawing software. .. Furthermore, it took a long time for exposure.

The etching process includes wet etching and dry etching. In wet etching, GaA as shown in FIG. 5 (a) or 5 (b) is used.
Etching of a transzinc-type crystal 50 such as s or InP using a stripe-shaped mask 51 whose (100) plane is parallel to the <011> or <0-11> direction (10
The (111) planes or their equivalent planes having angles of 55 ° and 125 ° with respect to the (0) plane respectively appear, and
Only when etching is performed using a stripe mask in the <010> or <001> direction as in (C), <001> or <0> perpendicular to the (100) plane, respectively.
The 010> surface appears. That is, when a quantum well box is produced by wet etching of a single crystal using a lattice pattern, the pattern direction is limited. Further, in wet etching, even if a surface perpendicular to the substrate surface appears, the etching groove width becomes larger than the pattern width due to side etching as shown in FIG.

On the other hand, dry etching such as reactive ion etching and reactive ion beam etching can provide an etching surface that does not depend on the crystal plane. A vertical etching surface is obtained. Moreover, an etching width almost equal to the pattern width may be obtained. However, this has the drawback that etching is performed by ion bombardment, and there is a great possibility that damage will remain in the crystal.

[0008]

The present invention is a method of manufacturing a semiconductor quantum well box which does not require an electron beam exposure step or an etching step, and makes good use of the initial process of epitaxial growth. That is, the present invention comprises the steps of supplying the raw material to a substrate having poor wettability with a molten metal of Group 2 or Group 3 to form fine droplets of atoms of Group 2 or Group 3, and then forming Group 6 Or supplying a raw material containing atoms of group 5 to diffuse the atoms of group 6 or group 5 into the droplets of group 2 or group 3 to form semiconductor crystallites. The amount of tribal raw materials supplied is 50
A method for producing a semiconductor quantum well box of a 2-6 group compound or a 3-5 group compound, characterized in that the amount is not more than the amount required to form the metal film having an average film thickness of nm on the substrate.

GaA using the MOVPE method according to the present invention
A method of manufacturing an s semiconductor quantum well box will be described below.
When a Group 3 source material such as trimethylgallium (TMG) or triethylgallium (TEG) is supplied to the heated substrate, if the substrate is higher than the decomposition temperature of the organic metal, it decomposes on or near the substrate to cause Ga atoms. Are generated and adsorbed on the substrate. Ga is more stable when it forms a cluster than when it is energetically present as an atom. When the substrate has poor wettability with respect to the liquid Ga and the supply amount of Ga raw material is small, Ga forms droplets (islands) on the substrate. When the As raw material is supplied to the substrate having the Ga islands, As atoms diffuse into the Ga islands to generate GaAs crystals. A to GaAs crystal
Since the deposition rate of s is zero, the growth automatically stops when all Ga forms GaAs.

The formation of islands is qualitatively determined by the amount of decrease in potential energy associated with droplet formation, the increase in interface energy between the substrate and the droplet, and the increase in surface energy of the droplet. Therefore, in the present invention, a substrate made of a material having a large interface energy, that is, a substrate made of a material having poor wettability with a liquid metal, for example, a single crystal made of a dielectric substance such as quartz, alumina, silicon nitride, or glass,
A polycrystalline or amorphous substrate, or a semiconductor single crystal, polycrystalline, or amorphous substrate can also be used.

When the organic gallium compound is used as the raw material, the raw material can be supplied under the following conditions. The lower the substrate temperature at the time of supply, the shorter the diffusion distance of the adsorbed species. Therefore, the lower the substrate temperature, the more the G generated on the substrate.
a The droplet generation density is increased. Therefore, even if the amount of raw material supplied is the same, the size of each island becomes smaller when supplied at a low temperature. However, the temperature required for growing the metal island must be equal to or higher than the decomposition temperature of the supplied organogallium compound. For example, when trimethylgallium is used, the substrate temperature must be at least about 450 ° C. which is the decomposition temperature of trimethylgallium. On the other hand, when the substrate is heated to a high temperature, the generated liquid metal islands diffuse and bond with each other, so that the grain size of the finally obtained island increases, and finally As
Also, the GaAs crystal obtained by supplying From the above, the substrate temperature may be set to 1000 ° C. or lower.

The pressure at the time of supplying the organic gallium compound may be any pressure from 1 Torr to normal pressure, but the average free path of the raw material becomes longer as the growth pressure becomes higher, so that the crystal formation density becomes higher. Since the total supply amount of the organic gallium compound mainly changes the particle size of the island to be formed, the particle size can be controlled. However, the total supply amount of the organic gallium compound needs to be smaller than the supply amount at which the average film thickness of the metal film formed from the (Ga) raw material on the substrate becomes 50 nm. Come into contact with each other to form a film. On the other hand, the supply amount of the organic gallium compound per unit time also has a great influence on the density of crystallite formation. Since the formation of nuclei in the initial stage of supply is caused by the collision between surface adsorbed species, increasing the supply amount of the raw material per unit time to increase the density of adsorbed species also increases the nucleation density. Since the purpose of the present invention is to finally supply As to Ga islands to generate GaAs microcrystals and to give the microcrystals a quantum size effect, increasing the supply amount of the raw material per unit time is as follows. The supply time must be extremely short. Therefore, considering the controllability of the supply of the organic Ga compound, it is desirable to supply the organic gallium compound over a time period of 1 second or more. Regarding the supply of As raw material per unit time,
At least an amount capable of suppressing As escape from GaAs is necessary. There is no problem if the substrate temperature at this time is changed from the temperature at which Ga islands are manufactured, but it suffices that the island growth based on the island coupling does not occur as described above.

The method of manufacturing a GaAs semiconductor quantum well box using the MOVPE method has been described above.
Various 3-5 group compound semiconductors including aAs, InP, InGaAsP, CdSe, CdSSe, ZnS
It is possible to manufacture a quantum well box made of a semiconductor such as a 2-6 group compound semiconductor such as e, ZnSSe, or CdTe. MOVPE has been described as the crystal growth method, but other growth methods such as MBE method and halide VPE method may be used. Further, a material having a band gap larger than the band gap of the microcrystal may be formed as a barrier layer on the substrate on which the compound semiconductor microcrystal is produced. Examples of this material include quartz, alumina, silicon carbide, silicon nitride, dielectric substances such as glass, and various semiconductors.

[0014]

According to the present invention, by using the initial process of the crystal growth by the MOVPE method or the like on the substrate on which the layered single crystal film cannot be formed by the epitaxial growth, it is necessary in the conventional manufacturing method of the semiconductor quantum well box. A semiconductor quantum well box can be manufactured without going through the existing electron beam exposure step and etching step. In this case, air or glassy amorphous surrounding the semiconductor quantum well box, or a material deposited on a substrate having compound semiconductor microcrystals acts as a barrier layer, and the semiconductor microcrystals have a potential well for confining carriers and excitons. Acts as.

[0015]

EXAMPLES Example 1 A quartz plate that had been optically polished was made hydrophilic by etching with hydrofluoric acid to clean the surface and used as a substrate. In this example, GaAs was grown using a MOVPE device. To grow GaAs, trimethylgallium and arsine (diluted with 10% hydrogen) were used as raw materials, and hydrogen was used as a carrier gas. The gas supply rates were trimethylgallium (-10 ° C) 8.6 cc / min, arsine 200 cc / min, and hydrogen 8000 cc / min.

First, the quartz substrate 10 was heated to 650 ° C. and trimethylgallium was supplied for 10 seconds. The surface of this sample is white, and it is considered that metal Ga was attached in the previous step. When it was observed with a transmission electron microscope (TEM), spherical particles adhered to the entire surface of the substrate 10 as shown in FIG. 1, and the particle size was about 5 nm. The particle size distribution was very small, and the density of crystallites per unit area was about 10 ⁸ cm ^-1 . In addition, it was confirmed from electron diffraction that it was in an amorphous state.

After depositing the metallic Ga droplets on the quartz substrate 10, arsine was supplied, and one minute after the start of the supply, the temperature of the substrate was lowered. The supply of arsine was continued until the substrate temperature fell below 350 ° C. When this sample was observed by TEM,
The particle size was about 8 nm, and it was found that each particle 11 had good crystallinity. Further, when the lattice constant was obtained from the electron beam diffraction pattern, it was almost the same as that of bulk GaAs, and it was confirmed that it was a GaAs microcrystal. FIG. 2 shows the photoluminescence measured using the 488 nm oscillation light of an Ar ion laser, and the emission having a peak near 830 nm was observed at room temperature. Bulk GaAs
Photoluminescence peak wavelength is 870 nm at room temperature
Since it is about the same, GaA on quartz produced by this method
It can be concluded that s crystals have a quantum size effect.

Example 2 FIG. 3 shows a schematic view of a non-linear waveguide manufactured by using the method of the present invention. In this, a SiO ₂ film with GeO ₂ added was formed to a thickness of 35 μm 31 on a quartz plate 30 by a high frequency sputtering method, and a GaAs microcrystal 33 was grown on this substrate 32 by the same method as in Example 1. Next, similarly, a GeO ₂ -added SiO ₂ film 34 having a thickness of 3.5 μm and a SiO ₂ film 35 having a thickness of 5 μm were formed by sputtering.

As described above, a slab waveguide having the highest refractive index in the layers 31, 33 and 34 containing GaAs microcrystals and the lowest in the quartz plate 30 and the SiO ₂ film 35 can be formed.
Further, in order to confine the guided light also in the lateral direction, a ridge structure having a width of 6 μm was formed by photolithography and reactive ion etching using CF ₄ . This optical non-linearity is caused by dye laser (styry 19, wavelength 790 to 890 nm)
The absorption coefficient α was about 25 cm ⁻¹ at about 820 nm, and the nonlinear susceptibility χ ⁽³⁾ was about 1 ×.
A value of 10 ⁻¹⁰ esu was obtained.

[0020]

According to the present invention, since it is a method of manufacturing a semiconductor quantum well box without going through an electron beam exposure step and an etching step as in the prior art, no special operation for the exposure line width is required, In addition, it is possible to manufacture a semiconductor quantum well box having an excellent quantum size effect that does not depend on the crystal plane in the etching process and does not damage the crystal. Further, the semiconductor quantum well box manufactured according to the present invention can be manufactured, for example, on a glass waveguide,
It can be applied as a substrate for a waveguide type optical control device using a nonlinear optical effect.

[Brief description of drawings]

FIG. 1 is a schematic perspective view of a GaAs quantum well box manufactured on a quartz substrate according to the present invention.

FIG. 2 is a diagram showing a photoluminescence spectrum of the GaAs quantum well box shown in FIG.

3A to 3D are perspective explanatory views showing a manufacturing process of a nonlinear waveguide using the GaAs quantum well box of the present invention.

4A to 4D are explanatory views showing a manufacturing process of a conventional semiconductor quantum well box.

FIG. 5 shows a cross-sectional shape obtained by wet-etching a trans-zinc ore crystal having a crystal plane orientation (100) on the surface, in which (a) shows a stripe mask <0-11. > Direction, (b) shows the <011> direction, and (c) shows the case parallel to <010> or <0-10>.

[Explanation of symbols]

10, 30 Quartz plate 11, 33 GaAs microcrystal 31, 34 GeO ₂ added SiO ₂ film 35 SiO ₂ film

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[Procedure amendment]

[Submission date] May 10, 1991

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

First, the quartz substrate 10 was heated to 650 ° C. and trimethylgallium was supplied for 10 seconds. The surface of this sample is white, and it is considered that metal Ga was attached in the previous step. When it was observed with a transmission electron microscope (TEM), spherical particles adhered to the entire surface of the substrate 10 as shown in FIG. 1, and the particle size was about 5 nm. The particle size distribution was very small, and the density of crystallites per unit area was about 10 ⁸ cm ^-2 . In addition, it was confirmed from electron diffraction that it was in an amorphous state.

Claims (1)

[Claims] 1. A step of supplying a raw material to a substrate having poor wettability with a molten metal of group 2 or group 3 to form fine droplets of atoms of group 2 or group 3, and then group 6 Or supplying a raw material containing atoms of group 5 to diffuse the atoms of group 6 or group 5 into the droplets of group 2 or group 3 to form semiconductor crystallites. The supply amount of the group I raw material is less than or equal to the amount required to form the metal film having an average film thickness of 50 nm on the substrate 2.
A method for manufacturing a semiconductor quantum well box of a -6 group compound or a 3-5 group compound.