JPH01301584A - Process for growing crystal and apparatus therefor - Google Patents

Abstract

PURPOSE:To form a flat interface free from defect and impurity and form an excellent epitaxial layer on the interface, by thermally dissociating hydrogen at a high temperature and supplying the dissociated hydrogen to the surface of a compound semiconductor substrate in high vacuum. CONSTITUTION:For example, for the preparation of a re-grown surface of GaAs, a molecular beam epitaxial growth chamber 3 is charged with Ga, As and Si as an n-type dopant and an Si-doped GaAs epitaxial layer is grown on the Si-doped GaAs substrate. The substrate is taken out of a substrate- exchange chamber 9, exposed to air, introduced again into the chamber 9, evacuated and returned to the growth chamber 3. The substrate temperature is raised, the substrate is irradiated with hydrogen heated at 800-1,000 deg.C in As atmosphere and an Si-doped GaAs is epitaxially grown on the substrate by a molecular beam epitaxial process. An excellent re-grown thin film having flat and clean interface free from defect can be formed by this process.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a crystal growth method and a crystal growth apparatus, and more particularly to cleaning of a compound semiconductor substrate before crystal growth thereon.

(Prior Art) In recent years, the development of high-speed devices, optical devices, and optical integrated circuits (OEICs) using compound semiconductors has progressed rapidly, and the associated device manufacturing processes have also become more sophisticated.

As a characteristic of compound semiconductor crystals, GaA, which is the representative
Taking s as an example, the electron mobility is 5 to 6 times faster than that of Si, and if mixed crystals such as AlGaAs and InGaP are used,
It is possible to artificially change the lattice constant and forbidden band width,
A new device structure can be created using this. However, the surface of compound semiconductors is generally active and easily incorporates impurities, and the interfaces with metals, insulators, and semiconductors are unstable. However, in order to achieve high performance and high integration of devices, it is necessary to clean and flatten such interfaces, which can be done using ordinary molecular beam epitaxial method (MBE).
Reactive ion beam etching (RIB)
Etching techniques such as E) alone are no longer sufficient.

It is known that when regrowth is performed on a substrate that has undergone crystal processing, carbon-based contaminants and oxides are generated at the interface, forming deep levels.
Have difficulty.

In the ordinary molecular beam epitaxial method (MBE method), Japan, Journal of Applied Physics (
Japan Journal of Applied
Physics), Vol. 25, p. 1216 (1986), impurities at the interface are removed by heating the substrate to 700° C. or higher to evaporate the crystals on the surface.

In addition, in reactive ion beam etching (RIBE method), the substrate surface is etched using radicalized reactive gas or hydrogen using an ECR ion source under high vacuum, as reported by Asakawa et al.
Of Vacuum Science Technology-A (J
internal of vacuum 5science
Technology A) Volume 4, page 677 (198
It was reported in 2006).

In addition, J. P. Contour et al. used a method in which hydrochloric acid (MCI) was introduced into the MBE preparation chamber, adsorbed onto the substrate surface, and then heated in the MBE chamber to clean the substrate surface. . Journal of Vacuum Science and Technology-B
Vacuum Science Technology
B) Volume 5, page 730 (1987).

All of these methods have the advantage that there is no contamination from the atmosphere because they are performed under high vacuum.

(Problems to be Solved by the Invention) However, these methods described above have the following problems.

First, in the MBE method, which uses heat to evaporate the crystal surface at high temperatures (thermal etching method), the flatness of the surface is impaired, and the high temperature causes redistribution of impurity concentrations, which causes deterioration of device characteristics. It becomes. Furthermore, this method cannot completely remove carbon-based impurities.

Next, radical etching using the RIBE method is effective in removing carbon-based impurities, but molecules with high energy damage the substrate surface and cause defects. Furthermore, the inner walls of the growth apparatus are sputtered by ions and radicals, causing contamination with impurities (mainly heavy metals), making it difficult to obtain a clean interface.

Further, a method of etching the surface by introducing a reactive gas causes no damage and does not impair flatness, but is not very effective in removing carbon-based impurities.

An object of the present invention is to form a flat interface free of defects and impurities, and to grow a good epitaxial layer thereon.

(Means for Solving the Problems) In the present invention, in a crystal growth method in which the surface of a compound semiconductor substrate is cleaned and crystals are grown thereon, the surface of the compound semiconductor substrate is heated to a high temperature under a high vacuum. A crystal growth method characterized in that a step of supplying thermally dissociated hydrogen by cleaning a surface and a step of growing a crystal on the substrate are successively performed, and a vacuum container. a substrate holder provided in the vacuum container to hold and heat the substrate; a gas introduction tube to introduce hydrogen into the vacuum container; a heating device capable of heating hydrogen; and a molecular beam capable of epitaxial growth of semiconductor crystals. A crystal growth apparatus is provided, characterized in that it is equipped with a crystal growth source.

(Function) Hydrogen gas is known to be effective in removing oxide films and carbon-based impurities on the surface of compound semiconductors, but no reaction occurs at room temperature, and it is necessary to give high energy to hydrogen to dissociate it. be. In the present invention, hydrogen is heated to a high temperature, thermally dissociated, and supplied to the substrate surface, so there is no need to raise the substrate temperature that high, and there is no need to convert hydrogen into ions or radicals. Therefore, no redistribution of impurities or damage occurs. In addition, when hydrogen heated at 800° C. was measured using a mass spectrometer, it was found that 1% of hydrogen was dissociated. More preferably 1O-3
When carried out under a high vacuum of torr or less, the gas flow becomes almost a molecular flow, and the dissociated hydrogen is effectively supplied to the substrate surface.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing the configuration of a semiconductor crystal growth apparatus according to the second invention of the present application.

The apparatus of this embodiment is a conventional molecular beam epitaxial (
MBE) A growth chamber 3, a mass flow controller 1 for introducing hydrogen gas, a gas introduction pipe 4, a heating device 5 for heating hydrogen gas, and a group III raw material cell 6 for supplying molecular beams.
, a group V raw material cell, a dopant raw material cell 8, a substrate exchange chamber 9, and a gate valve 10. The gas introduction tube 4 on the growth chamber 3 side is made of stainless steel, and a quartz tube is connected to this stainless steel portion, leading to a mass controller 11. The heating device 5 has a structure in which a heater is wound around the quartz portion of the gas introduction pipe 4. Note that the heating device 5 is not limited to this structure, and may be of a type in which a heater is enclosed within a quartz tube, for example.

In an example of the first invention of the present application, a GaAs regrowth interface was produced using the present apparatus in the following procedure. First, in the MBE growth chamber, metal Ga as a group III raw material and As as a group V raw material were introduced into the MBE growth chamber.
, Si is introduced as an n-type dopant, and Si-doped 3
A Si-doped 3×10 16 cm −3 GaAs epitaxial layer was grown to a thickness of 1.5 pm on a GaAs substrate of 1.018 cm ” at a growth temperature of 6000 C.

This board is taken out from the board exchange chamber 9 to the atmosphere, exposed to the atmosphere, then put back into the board exchange chamber 9 and evacuated, and then
Returned to BE growth room 3. Next, the substrate temperature was raised to 500° C., and the substrate was irradiated with hydrogen heated to various temperatures of 800° C. to 1000° C. for 10 minutes in an As atmosphere.

The partial pressure of hydrogen is 5 x 10-' Torr.

After that, Si-doped 3×1 was deposited on the substrate by MBE.
0110l6 GaAs was epitaxially grown to a thickness of 0.511 m. The substrate temperature was 600°C.

As an evaluation of the regrowth interface, the carrier concentration distribution in the depth direction from the substrate surface was determined by C-■ measurement. Figure 2 shows the results. For comparison, FIG. 2 shows the regrown interface treated with the conventional thermal etching method. In the conventional method, a decrease in carrier concentration was observed at the interface, but in the method of this example, Since there is no impurity or damage at the interface, no decrease in carrier concentration is observed at all. Also, the heating temperature of hydrogen is 800°C to 1000°C.
The effects of the invention were observed at each temperature.

Furthermore, when the etched surface before regrowth was observed by RHEED, the substrate etched in this example showed a streak superstructure pattern, confirming the formation of a good interface without damage.

The substrate used in this example was GaAs, but other materials such as I
Similar effects were obtained with other III-V group compounds such as nP and AlGaAs, or their mixed crystals.

Further, the material grown on the IILV group compound semiconductor substrate may be other semiconductors such as Si, electrode metals, or may be polycrystalline or amorphous.

(Effects of the Invention) As described above, according to the present invention, a good regrown thin film having a flat, defect-free and clean interface can be obtained, which has the effect of improving device characteristics.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the apparatus of the present invention. FIG. 2 is a diagram showing the depth distribution of the carrier concentration of the GaAs growth layer from the surface toward the substrate. 1. Exhaust device, 2. substrate holder, 3. MBE growth room,
4° gas introduction pipe, 5. Heating device, 6. Group III raw material cell, 7° Group V raw material cell, 8. Dopant raw material cell, 9. Board exchange room, 10. Gate valve, 11. mass flow controller.

Claims (2)

[Claims] (1) A step of supplying hydrogen, which has been thermally dissociated at least in part by heating it to a high temperature, to the surface of a compound semiconductor substrate under high vacuum to clean the surface; A crystal growth method characterized in that the steps of growing crystals are performed continuously. (2) In a crystal growth apparatus equipped with a vacuum vessel, a substrate holder provided in the vacuum vessel to hold and heat a semiconductor substrate, and a molecular beam source for growing a crystal, hydrogen is introduced into the vacuum vessel. A crystal growth apparatus characterized by comprising a gas introduction pipe for introducing hydrogen and a heating device for heating hydrogen.