JPS61220321A - Selective vapor growth method - Google Patents

Abstract

PURPOSE:To enable selective crystal growth by opposing and contacting tightly a solid material on which a mask is patterned, a gaseous phase growth material, with a substrate to which selective crystal growth will be applied, and providing a temperature gradient between these two bodies in such a way that the substrate is on the low temperature side. CONSTITUTION:A mirror-finished surface of a GaAs single crystal raw material 11 is covered with a SiN laminar mask 12, on which striped windows 13 are formed. Subsequently a mirror-finished GaAs single crystal substrate 14, coated with a Ga0.65Al0.35As cladding layer 15, is opposed and tightly contacted with the material 11 on which the mask 12 is formed. Both bodies are held in a hydrogen atmosphere of 900 deg.C inside graphite holders 20, 21, where a temperature gradient is provided in the manner that the temperature of the substrate 14 is lower than that of the material 11. With this heat-treatment, part of the material 11 is consumed to selectively grow a GaAs light wave guide layer 16 on the substrate 14.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a vapor phase growth method, and particularly to a selective vapor phase growth method for selectively growing compound semiconductor crystals.

[Technical background of the invention and its problems]

BACKGROUND ART A technique for selectively performing epitaxial growth on a compound semiconductor substrate is an extremely important technique for manufacturing semiconductor optical devices such as semiconductor lasers and optical waveguides, and integrated optical devices that integrate these devices. In particular, a technique for selectively growing crystals in a vapor phase growth method that can realize homogeneous crystal growth on a large-area substrate is useful because it is excellent in mass productivity.

Traditionally, the selective crystal growth method in the vapor phase growth method is
First, as shown in FIG. 3(a), S is placed on the semiconductor substrate 31.
A dielectric film 132 such as iO2 or SiN is formed as a mask, and a window 33 is opened by selectively removing the dielectric film mask only in the area where crystal growth is to be performed. Thereafter, crystal growth is performed on the entire surface of the semiconductor substrate, and a semiconductor crystal 34 is grown as shown in FIG. M3 (b).

At this time, the semiconductor crystal layer 35 is also formed on the dielectric film mask 32.
grows. Next, a method has been used in which the crystal 35 grown on the dielectric film mask 32 and the yh electric mask 32 are removed by etching.

However, this type of method has the following problems. That is, as shown in FIG. 3(b), the semiconductor crystal 35 also grows on the dielectric film mask 32 during crystal growth. Since this portion is polycrystalline, it is selectively removed by utilizing the fact that the etching rate is higher than that of the single crystal portion 34 epitaxially grown on the semiconductor substrate 31 in the window portion of the dielectric film mask 32. However, at this time, there is a drawback that the single crystal portion 34 that should originally be left is also etched away.

Furthermore, so-called abnormal growth generally occurs at the boundary between the mask portion and the window portion. As shown in FIG. 3(b), this abnormally grown portion 36 usually appears in the form of a rise in the thickness direction and an overhang toward the mask portion.

If such an abnormally grown portion 36 exists, it becomes extremely difficult to perform a photolithography step after selective crystal growth or to form surface electrodes and wiring across this boundary portion, which greatly restricts the device fabrication process. receive. moreover·
The dielectric film used as a selective growth mask becomes densified due to the heat treatment effect in the upper part associated with crystal growth, or changes in film quality due to reaction with reactive gas that is a raw material for crystal growth. For this reason, etching removal after selective crystal growth may be difficult, which is also a drawback of the conventional method.

[Purpose of the invention]

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to enable selective crystal growth without forming a dielectric film mask on a semiconductor substrate on which crystal growth is to be performed; To provide a selective vapor phase growth method capable of realizing good selective crystal growth without any of the drawbacks of the conventional selective crystal growth method using a mask, such as crystal growth, abnormal growth at mask edges, and deterioration of the mask. It is in.

[Summary of the invention].

The gist of the present invention is to use a solid raw material obtained by patterning a mask as a vapor phase growth raw material, and to place this in close contact with and facing the substrate on which selective crystal growth is to be performed, so that the latter has a lower concentration. By providing a concentration gradient, selective crystal growth is made possible without forming a selective crystal growth mask on the substrate side.

In the vapor phase growth method for semiconductors, a solid source material with a flat surface is placed facing a substrate at a distance of several [#] diameters, and while a reactive gas serving as a carrier is flowing, the substrate side is kept at a low temperature. A method of growing crystals on a substrate by forming a concentration gradient is known as the proximity method. The present inventors have discovered that by mirror-polishing the surface of the solid raw material and the surface of the substrate, bringing them into close contact, and applying a concentration gradient so that the substrate side is at a lower temperature, the surface of the solid material can be polished onto the substrate without flowing a particularly reactive carrier gas. It was discovered that crystal growth occurs. Furthermore, when a mask such as a dielectric film is formed on the surface of the solid raw material, crystal growth does not occur on the substrate facing the masked portion, and crystal growth occurs selectively only on the substrate facing the unmasked portion. I found out what happens.

The present invention focuses on such points, and in a selective vapor phase growth method for selectively growing semiconductor crystals on a semiconductor substrate, selectively forming a mask such as a dielectric film on the surface of a solid raw material,
In this method, this is placed in close contact with the surface of a semiconductor substrate, and a concentration gradient is provided between the two so that the semiconductor substrate side is at a lower temperature, and heat treatment is performed.

〔Effect of the invention〕

According to the present invention, selective crystal growth is possible without forming a mask such as a dielectric film on a semiconductor substrate on which crystal growth is to be performed. There are no problems such as deterioration of quality. Therefore, the device fabrication process including selective crystal growth becomes easy and simple, and the yield of the process is improved. As a result, it is effective in reducing the cost of semiconductor devices that require selective crystal growth. In addition, since abnormal growth does not occur at the mask edge, it is possible to wire electrodes across this area, which increases the degree of freedom in device design and is extremely effective in improving device characteristics. .

[Embodiments of the invention]

Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

FIGS. 1(a) to 1(d) are cross-sectional views showing an optical waveguide manufacturing process for explaining a selective vapor growth method according to an embodiment of the present invention. First, as shown in FIG. 1(a), SiN! A mask 12 consisting of
After forming 800 [μTrL] striped windows 1 by photolithography method, striped windows 1 with a width of 10 [μTrL] were formed.
form 3.

Next, as shown in FIG. 1(b), mirror-polished GaA
Gao, a6A on s single crystal substrate (semiconductor substrate) 14
j2o, ss A S cladding layer 15 to 3 [μ77
L] is formed and placed in close contact with and facing the single crystal raw material 11 on which the mask 12 is formed. Note that the cladding layer 15
The formation of the metal-organic vapor phase epitaxy method (
It is desirable to use the MOCVD method (MOCVD method) or the molecular beam epitaxy method (MBE method).

Next, as described above, GaAS are placed in close contact with each other.
The raw material 11 and the GaAS substrate 14 are held in a graphite holder 20, 21 as shown in FIG.
"C" is held in a hydrogen atmosphere for 2 hours. At this time, G
A concentration gradient is realized such that the concentration of the aAs substrate 14 is lower than the concentration of the GaAs raw material 11. Here, 2[℃
/α]. Note that the crystal growth rate can be controlled by the retention concentration of the substrate 14, the retention time, and the magnitude of the concentration gradient.

Through the above heat treatment, a part of the single crystal raw material 11 is consumed as shown in FIG.
An S optical waveguide layer 16 was selectively grown. That is, GaA
Corresponding to the pattern of the SiN mask 12 formed on the surface of the S single-crystal raw material 11, a striped G layer with a layer width of 5 [μm] and a height of 3 [μm] is formed on the GaAnAS cladding layer 15.
An aAS optical waveguide 16 was formed. On both sides of this striped optical waveguide 16, there was no abnormal growth as seen in conventional selective crystal growth methods, and the striped optical waveguide 16 had a favorable shape as an optical waveguide.

Thus, according to the method of this embodiment, the GaAS optical waveguide 1116 can be formed without forming a 1111 mask or the like on the GaAS substrate 14 (actually, the GaAβAs cladding layer 15).
can be grown selectively. Therefore, good crystal growth can be performed without causing problems such as crystal growth on the mask, abnormal growth at the mask edge, and deterioration of the mask. In addition, since the dielectric film mask is not on the substrate 14, there is no need for a process to remove any deterioration of the mask that occurs after selective crystal growth, which simplifies the process of manufacturing the guided waveguide and improves yield. It can be measured.

Note that the present invention is not limited to the method of the embodiment described above. For example, various conditions during crystal growth high temperature heat treatment are as follows:
It can be changed as appropriate depending on the semiconductor layer to be grown and other specifications. The atmosphere at this time may be a gas other than hydrogen or a vacuum. In addition, the material used is Ga
It is not limited to the As/GaAnAs system (, InP/In
GaAsp type ■-v group compound semiconductor, zns, zns
It is also possible to apply to ■-■ group compound semiconductors such as e, and other materials. Furthermore, by forming the crystal growth raw material into a multilayer structure with different compositions, selective crystal growth of a multilayer structure can be performed.

Furthermore, the mask formed on the surface of the solid raw material is not limited to SiN, but is SiO2゜Affi20:+
A dielectric material such as the following can be used. Furthermore, it is not limited to dielectric materials, and any material can be used as long as it has a sufficiently low vapor pressure and does not contaminate the semiconductor substrate or solid raw material. In addition, various modifications can be made without departing from the gist of the present invention.

[Brief explanation of drawings]

FIGS. 1(a) to (C) are cross-sectional views showing the optical waveguide manufacturing process for explaining a selective vapor deposition method according to an embodiment of the present invention, and FIG. Cross-sectional view showing the two sides of the graphite holder used, Figure 3 (a>(
b) is a cross-sectional view for explaining a conventional selective vapor growth method. 11...GaAS single crystal raw material (solid raw material), 12...
・SiN film mask, 13... selective crystal growth window, 14.
G a A S board, 15 ・” G ao, as A
Qo, ss A S cladding layer, 16-G a A
s optical waveguide, 20. 21... graphite holder, 31... substrate, 32... dielectric film mask, 33.
...Selective crystal growth window, 34...Selective crystal growth layer, 35
...Polycrystalline layer, 36...Abnormal growth part. Applicant's representative Patent attorney Takehiko Suzue! A410

Claims (4)

[Claims] (1) selectively forming a mask on the surface of the solid raw material;
The method includes the steps of arranging the solid raw material so that its surface closely faces the surface of the semiconductor substrate, and heat-treating the semiconductor substrate by providing a concentration gradient so that the temperature is lower than that of the solid raw material. Choose a vapor phase growth method. (2) The selective vapor phase growth method according to claim 1, wherein the solid raw material has a multilayer structure. (3) The selective vapor phase growth method according to claim 1, wherein the solid source material is a III-V group compound semiconductor. (4) The selective vapor phase growth method according to claim 1, wherein the opposing surfaces of the solid raw material and the semiconductor substrate are each mirror-polished.