JP2535560B2 - Molecular beam crystal growth method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] The present invention relates to a molecular beam crystal growth method, and more particularly to an epitaxial growth method of a compound semiconductor crystal of a Group III element and a Group V element, in which constituent elements having different vapor pressures are alternately opened and closed. When irradiating on a heated substrate, the purpose is to remove the constituent elements with high vapor pressure remaining on or near the surface of the substrate after closing the shutter. First, open the shutter of the group III element source. , After the substrate is irradiated for a predetermined time, the shutter is closed, and then the V-th
The shutter of the source of the group element is opened, the shutter is closed after irradiating the substrate for a predetermined time, and the shutter of the source of the group V element is closed when the above steps are repeated.
Hydrogen gas is blown onto the substrate surface and exhausted at the same time until the shutter of the source of group elements is opened.

[Industrial applications]

The present invention relates to a molecular beam crystal growth method for growing an ultrathin crystal of a compound semiconductor with good controllability.

[Conventional technology]

In recent years, compound semiconductor devices have tended to be manufactured using ultra-thin epitaxial single crystal layers.

As a technique for growing a very thin single crystal layer of several A to several tens A in multiple layers, a monoatomic layer epitaxial growth method (At
omic Layer Epitaxy; ALE) and Migration Enhanced Epit
axy (MEE) is given. The characteristics of these growth technologies are:
A flat surface on the order of atomic layers is obtained in the lateral direction of the substrate surface, and the film pressure control on the order of atomic layers is easy.

MEE has also been performed using conventional molecular beam crystal growth (MBE) equipment. Taking the MEE of GaAs as an example, a method has been used in which Ga beams and As beams are irradiated alternately onto a properly heated substrate by opening and closing the respective shutters. That is, by irradiating the Ga beam on the substrate with the As beam cut off, and then irradiating the As beam on the substrate with the Ga beam cut off, the migration of Ga atoms or As atoms on the substrate is increased. Then, we tried to obtain a flat surface of the atomic layer order in the lateral direction within the substrate surface.

[Problems to be solved by the invention]

 However, this method had the following problems.

In the case of a group III-V compound semiconductor such as GaAs, the vapor pressure of the group V element is high and excessive supply is required, which causes re-evaporation of the group V element from the heated substrate surface or the outside of the substrate. Heating part of the substrate, for example, the Vth from the substrate heating holder part
There was re-evaporation of group elements, and vapor of As element could not be completely removed from the substrate surface only by closing the shutter of As molecular beam source. Therefore, it was difficult to grow a flat surface. The present invention provides a method of removing excess Group V element on or near the surface of the substrate to continuously grow a flat surface.

[Means for solving problems]

In order to solve the above-mentioned problem, the remaining excess V-th
The point of the present invention is to forcibly exhaust the group element.

FIG. 1 illustrates the principle of the present invention, and shows the growth process of a compound semiconductor ultrathin film crystal composed of a Group III element A and a Group V element B.

In the state where the A beam shutter is closed and the B shutter is opened as shown in FIG. 1 (a), the group V element B is excessively supplied, so that it is more than necessary to form a monoatomic layer on the compound semiconductor substrate. B atom will remain. As shown in FIG. 1 (b), B is removed as the next process in order to remove the excess B atoms.
After closing the beam shutter, before opening the A beam shutter and supplying the A beam, hydrogen (H ₂ ) gas is blown onto the substrate surface in an amount close to a viscous flow. By exhausting this hydrogen gas flow, surplus B atoms near the substrate surface can be forcibly eliminated at the same time.

[Action]

By forcibly excluding B atoms together with hydrogen gas, the surface layer on which A atoms are to be stacked next can be flattened to form an A atom monoatomic layer.

Thus, flat atomic layers can be stacked one after another.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to examples. Second
The figure shows an example of an MBE device embodying the invention. High purity (99.
(999%) hydrogen (H ₂ ) gas is introduced from the inlet 1, and is led to the hydrogen introduction nozzle 4 protruding into the MBE growth chamber 14 via the flow meter 2 and the opening / closing valve 3. The nozzle 4 is oriented so that hydrogen is ejected onto the surface of the GaAs substrate 6. The growth of GaAs was performed by the following procedure. In order to remove the natural oxide film on the GaAs substrate under As beam irradiation, the growth temperature is lowered to 400 ° C after heating it once to 600 ° C or more. To grow, close the shutter 1 of As molecular beam source 8 and shutter 11 of Ga molecular beam source 9.
Opened and started. After irradiating the Ga molecular beam for one atomic layer, the shutter 11 was closed, and then the shutter 10 of the As molecular beam source 8 was opened to irradiate the As molecular beam. Then, the shutter 10 for As molecular beam is closed, and then H ₂ gas is supplied from the nozzle 4 to the substrate 6.
Sprayed on. The vacuum degree in the temporary growth chamber at this time is 10
^-4 Torr range. The introduced H ₂ gas was exhausted using a turbo molecular pump 13. After blowing H ₂ gas for about 10 seconds, the on-off valve 3 was closed. Next, Ga molecular beam shutter
After opening 11, the substrate 6 was irradiated again with Ga atoms for the atomic layer. Next, open the As molecular beam shutter 10 again to supply As atoms,
It closed in about 2 seconds. In this way, the supply of Ga, As, and hydrogen was repeated in this order to continue the growth of GaAs.

In order to confirm that the growth of the monoatomic layer continued, the substrate surface was observed by RHEED oscillation during the growth. The RHEED vibration is less attenuated when the substrate surface is flat and the crystallinity is better, and the attenuation increases as the surface becomes rough. Although the crystal growth progresses and the attenuation increases as the film thickness increases, in the case of the present invention, compared with the case where the conventional growth is performed only by switching the shutter of the Ga molecular beam and the As molecular beam.
It was found that the attenuation of RHEED vibration was suppressed to less than half.

〔The invention's effect〕

According to the present invention, the growth of each monoatomic layer can be sustained over the film thickness twice or more as compared with the conventional MEE technique. Moreover, the present invention has made it possible to grow an ultrathin film crystal with good controllability.

INDUSTRIAL APPLICABILITY The method of the present invention can be applied not only to the epitaxial growth of compound semiconductor crystals of group III elements and group V elements, but also to the compound semiconductor crystals of group VI elements and group II elements containing group VI elements with high vapor pressure. It can also be applied to epitaxial growth.

[Brief description of drawings]

 FIG. 1 is an explanatory view of the principle of the present invention, and FIG. 2 shows an example of an apparatus for carrying out the present invention. In the figure, 1 is a hydrogen gas inlet, 2 is a flow meter, 3 is an opening / closing valve, 4 is a hydrogen introducing nozzle, 5 is a liquid nitrogen shroud, 6 is a GaAs substrate, 7 is a heater, 8 is an As molecular beam source, 9 Is a Ga molecular beam source, 10 is an As molecular beam shutter, 11 is a Ga molecular beam shutter, 12 is an oil rotary pump, 13 is a turbo molecular pump, and 14 is an MBE growth chamber.

Claims (1)

(57) [Claims] 1. In the epitaxial growth process of a compound semiconductor crystal of a group III element and a group V element by a molecular beam crystal growth method, first, a shutter of a source of the group III element is opened and the substrate is irradiated for a predetermined time. Close the shutter,
Next, the shutter of the source of the group V element is opened, the shutter is closed after irradiating the substrate for a predetermined time, and when the above steps are repeated, the shutter of the source of the group V element is closed and the group III element is closed. The molecular beam crystal growth method characterized in that hydrogen gas is blown onto the substrate surface and exhausted at the same time until the shutter of the radiation source is opened.