JPH05229894A - Method for growing crystal - Google Patents

Abstract

PURPOSE:To improve the distribution and reproducibility of the film thickness by irradiating a substrate with prescribed molecular beams after the initial step for crystal growth and removing an excessively grown part in alternately growing plural crystal layers composed of different elements on the substrate. CONSTITUTION:The top surface of a substrate 11 is irradiated with molecular beams of a group V raw material to grow a group V crystal layer 12. The top surface of the crystal layer 12 is then irradiated with molecular beams 13 of a group III raw material to grow a group III crystal layer13'. In the process, an excessively grown part 14 growing over one atomic layer on the crystal layer 13' is irradiated with accelerated molecular beams 15 to remove the excessively grown part 14. The accelerated molecular beams 15 are composed of elements different from the group III element and have larger bond energy than that between the group III crystal layer 13' and the excessively grown part 14 and smaller kinetic energy than the bond energy of the group V crystal layer 12 to the group TV crystal layer 13'. The top surface of the one atomic layer 13' composed of the group III element in the absenpe of the excessively grown part 14 is subsequently irradiated with group V molecular beams to perform the atomic layer epitaxy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crystal growth method for compound semiconductors, and more particularly to improvement of film thickness controllability.

[0002]

2. Description of the Related Art At present, a molecular beam epitaxy method (MBE method) and a metal organic chemical vapor deposition method (MOCVD method) are mainly used for producing a compound semiconductor crystal.

In these methods, the control of the film thickness (distribution and reproducibility) is performed by controlling the molecular beam intensity in the case of the MBE method,
In the case of the MONBE method, it was performed by controlling the gas flow. However, since there is a technical limit to these controls, a method for controlling the growth of one atomic layer, that is, an atomic layer epitaxy method (ALE method) has been proposed in principle.

MOCV is a method for realizing ALE.
There are reports that basically use D and MBE. First, MO
As an example using CVD, Applied, Physics Letter, Vol. 53, pp. 1509-1511 (1988)
As reported in the above, by alternately supplying trimethylgallium and arsine, it is possible to grow almost one atomic layer unit. On the other hand, in the example using the MBE method, as shown in Japanese of Applied Physics, Vol. A method of performing pseudo-atomic layer epitaxy by a method of re-evaporation by heat has been proposed.

[0005]

However, the MOC
In the ALE method using VD, there are problems that extremely highly toxic arsine is used and that it is difficult to obtain a high-purity crystal because carbon is incorporated into the crystal from an organic metal.

Further, in the ALE method using MBE, since the substrate temperature is as high as 700 ° C., there are problems such as diffusion of impurities in the underlying layer and formation of group V vacancies, which makes practical use difficult.

An object of the present invention is to eliminate the problems of MOCVD by basically relying on the MBE method and to realize ALE at low temperature.

[0008]

According to the present invention, in a crystal growth method for alternately growing crystals of at least two crystal layers made of different elements on a substrate, after the crystal growth step of one of the crystal layers, A crystal growth method, comprising: a removal step of irradiating a molecular beam made of an element different from the element to an overgrown portion grown over one atomic layer of the crystal layer to remove the overgrown portion. Is obtained.

According to the present invention, further, a group V crystal growth step of crystal-growing a group V crystal layer by irradiating a substrate with a molecular beam of a group V raw material composed of a group V element, and a group V crystal layer on the substrate. , II
A group III crystal growth step of irradiating a molecular beam of a group III raw material composed of a group I element to grow a group III crystal layer;
In the overgrowth part grown over one atomic layer of the group crystal layer,
A molecular beam composed of an element different from the group III element and having a kinetic energy larger than the bond energy between the group III crystal layer and the overgrown portion and smaller than the bond energy between the group V crystal layer and the group III crystal layer. And a removing step of removing the excessively grown portion by irradiating the crystal growth method.

That is, according to the present invention, a group III molecular beam and a V
In the crystal growth method for producing group III-V compound crystals by alternately supplying group molecular beams, after supplying group III molecular beams of one atomic layer or more, the constituent elements before irradiation with group V molecular beams are By irradiating different kinds of accelerated molecular beams, crystal growth in which the growth of each atomic layer occurs can be obtained.

[0011]

[Function] Alternate supply of group III and group V molecular beams II
In the method for growing a group IV compound crystal, the group III atoms irradiated on the group V surface in excess of one atomic layer cover the group V surface with the one atomic layer and form the group III surface. II
Group I atoms form droplets on the Group III surface.
At this time, the energy required for the vaporization of the group III atom is smaller in the group III atom forming the droplet than in the surface group III atom bonded to the group V atom. Next, the surface is irradiated with a molecular beam having a kinetic energy of about the evaporation energy of group III atoms forming droplets. In this process, the droplets evaporate, but III
Since the group III atom forming the group surface is bonded to the group V atom, it does not evaporate. As a result, the crystal surface becomes a group III monoatomic layer surface without droplets. Then, atomic layer epitaxy is performed by irradiating the group V molecular beam.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIGS. 1 (a) to 1 (d) are views showing a process flow of a crystal growth method according to this embodiment. Also, FIG.
Is a molecular beam epitaxy apparatus used in this example, that is,
It is a schematic sectional drawing of a crystal growth apparatus.

In this embodiment, GaAs is formed on the GaAs substrate.
The case of growing a crystal will be described. The growth process will be described below with reference to FIG.

GaAs single crystal substrate (thickness 500 μm)
After removing the surface layer by 11 to H ₂ SO ₄ etchant, the gate valve 1 from the load lock chamber (not shown)
It is introduced into the vacuum chamber 16 via 7 and fixed to the holder 20.

The shutter 23 provided in front of the molecular beam cell 22 is opened, and the surface of the substrate 11 is irradiated with As ₄ molecular beam from the molecular beam cell 22, while the heater 19 is used to irradiate the substrate 11.
Is heated to remove the oxide film on the substrate surface. The substrate temperature at this time was 600 ° C.

The substrate temperature is set to 580 ° C. and the vacuum chamber 1
The substrate 11 is irradiated with an electron beam from the electron gun 27 provided in FIG. 6 and the diffraction pattern appearing on the fluorescent screen 28 is a (2 × 4) surface rearrangement structure that is an As stabilization surface (As1).
2) and then As ₄
The supply of the molecular beam is stopped, the shutter of the Ga cell (not shown) is opened, and the growth is started.

Although any of Ga, trimethylgallium, and triethylgallium may be used as a Ga raw material, in this embodiment, the case of using Ga will be described. The molecular beam intensity of Ga is determined by reflection high-speed electron diffraction (RHE
ED) vibration was converted into a GaAs crystal growth rate of 0.
It was 4 atomic layers / second (ML / sec).

A description will be given below with reference to FIG.

In FIG. 1A, the Ga cell shutter is opened for 3 seconds, and Ga13 is irradiated onto the substrate for 1.2 ML. At this time, 0.5 ML of excess Ga aggregates to form droplets 14, which are overgrown portions.

In FIG. 1B, the Ga shutter is closed and the valve 25 is opened to introduce H ₂ gas. Other gas species may be He, Ne and Ar. The H ₂ gas is discharged by the plasma cell 24 and is cracked to 2.5-
Accelerated to 4.5 eV. In addition, as the plasma cell 24, a method using electron cyclotron resonance plasma,
A method of discharging with a CW-CO ₂ laser and irradiating through a nozzle was used, but in any case, it is important to put the energy of the molecular beam 15 in the range of 2.5 to 4.5 eV.

By the molecular beam 15 of the above-mentioned energy, the Ga atom in the droplet 14 having the activation energy of evaporation of 3 eV or less is vaporized, but the Ga atom bound to the underlying As12 is Ga.
The evaporation of 13 'requires more than 5 eV of energy, so it does not evaporate. In this way, only the droplet 14 disappears, and the surface is completely covered with one atomic layer of Ga atoms as shown in FIG. 1 (c).

In FIG. 1 (d), after closing the valve 25, the As ₄ molecular beam 12 is radiated to expose the As 13 on the Ga 13 ′ surface.
Twelve sides are formed.

When the process shown in FIG. 1 is repeated, Ga
Planes and As planes were formed alternately, and so-called atomic layer epitaxy (ALE) was realized.

In the compound semiconductor crystal grown as described above, the in-plane (2 inch diameter) film thickness distribution was ± 3% when grown by the conventional MBE.
It was ± 1% or less. In addition, the reproducibility of the film thickness is
What was ± 5% in BE became ± 1% or less.
Further, the substrate temperature was about 580 ° C. when it was about 700 ° C. by ALE by MBE using a conventional solid raw material.
I was able to lower the temperature.

[0026]

According to the crystal growth method of the present invention, after the crystal growth step of one of the crystal layers, a molecule composed of an element different from the above element is present in the overgrown portion grown over one atomic layer of the crystal layer. Since the method has a step of irradiating a line to remove the excessively grown portion, a high-purity crystal having a favorable film thickness distribution and film thickness reproducibility can be obtained.

Further, since the substrate temperature can be made relatively low, it is possible to prevent the diffusion of impurities in the base and the formation of V group vacancies.

[Brief description of drawings]

FIG. 1 is a diagram showing a process flow of a crystal growth method according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view showing a crystal growth apparatus used in the crystal growth method shown in FIG.

[Explanation of symbols]

 11 Substrate 12 As 13, 13 'Ga 14 Droplet 15 Accelerating Molecular Beam 16 Vacuum Chamber 17 Gate Valve 18 Substrate Manipulator 19 Heater 20 Holder 22 Molecular Beam Cell 23 Shutter 24 Plasma Cell 25 Valve 26 Liquid Nitrogen Shroud 27 Electron Gun 28 Fluorescent Screen

Claims (2)

[Claims] 1. A crystal growth method in which at least two crystal layers made of different elements are alternately grown on a substrate, and after the crystal growth step of one crystal layer, one atomic layer of the crystal layer is exceeded. A crystal growth method comprising a removal step of irradiating the grown overgrown portion with a molecular beam made of an element different from the above element to remove the overgrown portion. 2. A group V crystal growth step of crystal-growing a group V crystal layer by irradiating a substrate with a molecular beam of a group V raw material composed of a group V element, and a group III element from the group III element on the group V crystal layer. Composed III
The Group III crystal growth process of irradiating the group III crystal layer with the molecular beam of the Group III raw material and the overgrowth portion of the Group III crystal layer grown over one atomic layer are different from the Group III element. An element, which is larger than the binding energy between the group III crystal layer and the overgrown portion and is larger than the group V crystal layer and the group III crystal layer.
A removal step of irradiating a molecular beam having a kinetic energy smaller than the binding energy between the group crystal layers to remove the excessively grown portion.