JP2592133B2 - Crystal growth method - Google Patents

Description

The present invention is suitably implemented, for example, in the manufacture of a semiconductor device such as a semiconductor laser device having a superlattice structure, and is used for growing a crystal having a fine structure. The present invention relates to a crystal growth method.

[Conventional technology]

A superlattice element in which the crystal is controlled in units of atomic layers and several tens of different atomic layers are alternately stacked, for example, changes in the optical bandgap due to applied voltage, negative resistance, high mobility characteristics, etc. And has been applied to semiconductor laser devices, high mobility transistors, and the like.

Conventionally, MBE (Molecular Beam Epitaxy) has been used to grow semiconductor crystals for producing such a superlattice element, and crystal growth has been controlled for each atomic layer. The structure for this crystal growth is shown in FIG.

Substrate 2 held in a vacuum vessel 1 by a configuration not shown
A plurality of crucibles 3, 4, and 5 for melting and evaporating different substances are arranged opposite to. Shutter related to crucibles 3, 4, 5
Reference numerals 6, 7, and 8 are provided, and control of a substance deposited on the surface of the substrate 2 is performed by opening and closing each shutter.

An electron gun 9 is provided on the surface of the substrate 2 facing the crucibles 3, 4, and 5.
From the surface of the substrate 2, the diffracted electron beam 10a from the surface of the substrate 2 is incident on the fluorescent screen 11, and forms an image corresponding to the atoms on the surface of the substrate 2 on the fluorescent screen 11. This image is
So-called RHEED (Reflection High Energy Electron Dif
fraction: reflection high-energy electron beam diffraction) image.

In the RHEED image, the light at the brightest point near the center of the RHEED image is guided to the photomultiplier tube 13 via the optical fiber 12 and detected, and the output of the photomultiplier tube 13 (hereinafter referred to as “RHEED signal”)
That. ) Is supplied to the recorder 14 to record the change, and the RHEED signal is supplied to control means (not shown) to calculate the crystal growth rate. The opening / closing control of the shutters 6, 7, 8 corresponding to the growth rate is performed. Is performed.

The RHEED signal from the photomultiplier 13 corresponds to the intensity of the diffracted electron beam 10a, but the RHEED signal changes as shown in FIG. That is, the intensity of the diffracted electron beam 10a forming the brightest point near the center of the RHEED image is
Vibrates with the same synchronization as the formation of one atomic layer. This vibration is called RHEED vibration.

FIG. 5 is a simplified sectional view showing the state of formation of the atomic layer on the surface of the substrate 2 in a time series, and FIG. 6 is an explanatory view showing the recording mode in the recorder 14 in a time series. The recording states of the recorder 14 corresponding to the respective times in the states shown in FIGS. 5 (1) to (5) are shown in FIGS. 6 (1) to (5), respectively.

In the state shown in FIG. 5A before crystal growth is started, the surface of the substrate 2 is flat,
The electron beam 10 is reflected toward the center of the fluorescent screen 11. Therefore, the intensity of the diffracted electron beam 10a in this case is high, and the RHEED signal is relatively large.

When the growth of the crystal is started, the growth of the crystal 15 starts in an island shape on the flat surface of the substrate 2, and the electron beam 10 is scattered on the surface of the substrate 2. As a result, the phosphor screen
The intensity of the diffracted electron beam 10a toward the center of the substrate 11 decreases, and after passing through the state shown in FIG. 5 (2), the crystal 15a becomes 1/2 of the surface of the substrate 2 shown in FIG. 5 (3). Becomes minimum when grown.

As the growth of the crystal 15 progresses further from the state shown in FIG. 5 (3), the flatness of the surface of the substrate 2 reversely increases, so that the intensity of the diffracted electron beam 10a heading toward the center of the fluorescent plate 11 increases. Get higher. In this way, the RHEED signal increases during the period from the state shown in FIG. 5 (4) to the time when the growth of one atomic layer shown in FIG. It takes a maximum value when the growth of the atomic layer is completed.

Thus, one cycle of the RHEED oscillation corresponds to the cycle of one atomic layer. Therefore, by monitoring the recording of the recorder 14, it is possible to calculate the growth rate by counting the atomic layers, and by controlling the opening and closing of the shutters 6, 7, 8 corresponding to this growth rate, It is possible to obtain a semiconductor crystal having a structure.

[Problems to be solved by the invention]

However, in the configuration described above, the photomultiplier tube
Since various noises are included in the RHEED signal from 13, an error due to the noise becomes a problem when determining the growth rate, and as a result, it has been difficult to control the crystal growth in the atomic order.

SUMMARY OF THE INVENTION An object of the present invention is to provide a crystal growth method which solves the above-mentioned technical problem and enables crystal growth of a fine structure to be performed extremely well.

[Means for solving the problem]

According to the crystal growth method of the present invention, the detection signal of the intensity of the diffracted electron beam from the substrate surface is Fourier-transformed, the crystal growth rate is obtained from the Fourier-transformed signal, and the irradiation of the molecular beam is performed in accordance with the growth rate. The control is performed.

[Action]

According to the configuration of the present invention, the detection signal of the intensity of the diffracted electron beam that oscillates with the same period as the growth of the atomic layer is converted to a frequency by Fourier transform, so that the frequency of the oscillation of the intensity of the diffracted electron beam is changed. Can be obtained without the influence of noise. That is, the crystal growth rate can be accurately obtained from the Fourier-transformed signal. Therefore, if the irradiation of the molecular beam is controlled in accordance with the growth rate, the crystal growth can be controlled in the atomic order. Becomes possible.

〔Example〕

FIG. 1 is a conceptual diagram showing a basic configuration for implementing a crystal growth method according to one embodiment of the present invention.

In FIG. 1, parts corresponding to the respective parts shown in FIG. 3 are given the same reference numerals. In this embodiment, the RHEED signal from the photomultiplier tube 13 is input to a signal processing computer 16, where it is subjected to Fourier transform. Photomultiplier tube 13
The RHEED signal changes from the RHEED signal as shown in FIG. 4 described above. By subjecting this RHEED signal to Fourier transform, it can be converted into a signal having a peak P as shown in FIG. .

Frequency f _o at the peak P is the frequency of oscillation of the RHEED signal, as is clear from the Figure 2, the noise component is clearly separated. Therefore, by obtaining the growth rate of the crystal based on the frequency f _o at the peak P, as compared with the conventional methods, it is possible to determine the order of magnitude exact growth rate.

In FIG. 1, reference numeral 17 denotes a display device such as a CRT (cathode ray tube), and reference numeral 18 denotes a printing device. For example, the display device 17 displays Fourier-transformed signals shown in FIG.
The printing device 18 may output the waveform of the RHEED signal from the photomultiplier 13 or the like.

As described above, by determining the crystal growth rate based on the frequency fo at the peak P of the signal obtained by Fourier-transforming the RHEED signal, an accurate growth rate can be determined.Based on the crystal growth rate thus determined,
By controlling the opening and closing of the shutters 6, 7, 8 to control the irradiation of each molecular beam from the crucibles 3, 4, and 5, a superlattice structure with precise control of the atomic order on the surface of the substrate 2 And the like can be formed.

〔The invention's effect〕

As described above, according to the crystal growth method of the present invention, the detection signal of the intensity of the diffracted electron beam that oscillates with the same period as the growth of the atomic layer is Fourier-transformed and converted into a frequency. The frequency of the vibration of the line intensity can be obtained without the influence of noise. That is, the crystal growth rate can be accurately obtained from the Fourier-transformed signal. Therefore, if the irradiation of the molecular beam is controlled in accordance with the growth rate, the crystal growth can be controlled in the atomic order. Becomes possible. As a result, it becomes possible to favorably grow a crystal having a fine structure, and to obtain good characteristics in, for example, a semiconductor crystal having a superlattice structure.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a basic structure for implementing a crystal growth method according to one embodiment of the present invention, and FIG. 2 is a photomultiplier tube.
Diagram showing a signal obtained by Fourier transforming the RHEED signal from 13;
FIG. 3 is a conceptual diagram showing a basic configuration of the prior art, FIG. 4 is a diagram showing an RHEED signal from the photomultiplier tube 13, and FIG. 5 is a simplified cross section showing a state of crystal growth on the surface of the substrate 2. FIG. 6 is an explanatory diagram showing the recording mode of the recorder 14 in a simplified manner. 2 ... Substrate, 9 ... Electron gun, 10 ... Electron beam, 10a ... Diffraction electron beam, 11 ... Fluorescent plate, 13 ... Photomultiplier tube, 16 ...
Computer for signal processing

Claims (1)

(57) [Claims] 1. A method for irradiating a molecular beam on a substrate surface to grow a crystal, irradiating an electron beam on the substrate surface, detecting a vibration of a diffracted electron beam intensity from the substrate surface, In the crystal growth method of controlling the irradiation of the molecular beam based on the Fourier transform of the detection signal of the intensity of the diffracted electron beam, the crystal growth rate is obtained from the Fourier transformed signal,
A crystal growth method, wherein the irradiation of the molecular beam is controlled according to the growth rate.