JPH0226889A - Molecular beam crystal growing device - Google Patents

Abstract

PURPOSE:To improve the uniformity of film thickness and composition by suppressing damping of the vibration of the reflected high energy electron beam diffraction by such a method as to scan the electron beam made incident to the substrate while synchronizing with rotation of the substrate to enable accurate measurement of the growing rate. CONSTITUTION:The electron beams for measurement 2 which makes incident to the substrate 1 synchronizes with rotation of the substrate and scans it. The sensor 13 follows the scanning and detects the reflected electron beam. Then the growing rate of the crystal is monitered by the observation of the reflected high energy electron beam diffraction(RHEED) vibration.

Description

[Detailed Description of the Invention] [Summary] Molecular beam crystal growth (M
BE) The purpose is to suppress the attenuation of RHEED oscillations in the apparatus, enable accurate measurement of the growth rate, and prevent the growth layer from including a layer with non-uniform film thickness or composition.

It has a device that monitors the crystal growth rate by observing RIIEED vibrations, and scans a measurement electron beam of the device that is incident on the growth substrate in synchronization with the rotation of the substrate.

The reflected electron beam is detected following the scanning.

Moreover, the molecular beam source is configured to be asynchronous to the rotation of the substrate. Or, it has a device that monitors the crystal growth rate by observing RHEED vibration, and the device and the growth substrate are fixed.
The molecular beam source is configured to be rotatable about an axis perpendicular to the substrate.

[Industrial Application Field] The present invention relates to an MBE apparatus that monitors crystal growth rate by observing RHEED vibrations.

MBE apparatuses are widely used to form devices whose thickness is controlled on an atomic layer basis, such as semiconductor devices that utilize a superlattice. For the molecular beam source that generates molecular beams, one or more elements are prepared depending on the substance to be grown, and the desired molecular beam source is selectively used to grow a desired substance layer.

In such MBH, the crystal growth rate is a very important factor. Conventionally, this growth rate was measured by growing shrimp for monitoring and calculating from the film thickness and growth time, but this required a substrate for monitoring and evaluation of monitoring growth and film thickness. In recent years, growth rate measurement using RHEED vibration has been used to accurately grow a predetermined number of atomic layers in the formation of a superlattice structure.

[Conventional technology]

FIG. 6 is a schematic cross-sectional view of a conventional MBE apparatus.

In the figure, 1 is a substrate to be grown, 2 is an incident electron beam for RHEED, and 4 is a molecular beam that determines the growth rate (molecular beams that are not involved in the growth rate do not need to be measured).

5 is a molecular beam source (a crucible with heating means), 6 is a shutter that blocks the molecular beam, and 7 is an electron gun for RHEED.

8 is a fluorescent screen, 9 is an ultra-high vacuum chamber, 10 is a substrate holder, and 11 is a heater.

When performing growth on the substrate 1 using this apparatus, the crucible 5 containing a source for growing a desired semiconductor is heated to emit molecular beams. For example, Ga and A as sources
If s is used, a GaAs crystal can be grown, and if Si is used, a Si crystal can be grown.

The RHEED vibration observation method is a method in which an electron beam emitted from an electron gun 7 is incident on the substrate 1 at a shallow angle of 1 to 2 degrees with respect to the substrate surface, and a diffraction pattern due to the reflected electron beam is projected onto a fluorescent screen 8. When the intensity of the diffraction spots of the RHEED pattern is measured during this growth, oscillations corresponding to the growth rate are observed, and this can be used to monitor the growth rate.

1? HEED oscillations occur when a crystal grows in layers.2 When atoms are deposited flat on the surface, the RHEED intensity is at its maximum, and when atoms begin to deposit further on top of it, the intensity increases due to diffuse reflection. falls. When the growth of the first layer is finished and a flat surface appears again, the intensity of the second layer becomes maximum again. In this way, strong vibrations can be obtained with a period corresponding to the growth of one atomic layer.

FIG. 7 (11 to (3)) are diagrams illustrating RHEED vibration according to the conventional example.

As shown in Figure 7 (1), the Ga molecule v that determines the growth rate
A4 enters the substrate at an arbitrary angle 1, for example 15°, with the incident electron beam 2. At this time, as shown in FIG. 7(2), the growth rate of GaAs is at an inclination of 1% per 1 mm in the direction of the incident electron beam 2 on the substrate, that is, the irradiation area 3
(See Figure 1) The total length (about 10 mm) is l.

It had a slope of %.

During the measurement, when the growth rate was 0.6 μm/hour,
As shown in Figure 7 (3), the RHEED vibration lasted only about 10 times.

[Problem to be solved by the invention]

When monitoring the growth rate using RHEED oscillation as in the conventional example, I? There was a drawback that HEED vibration was attenuated and accurate measurement could not be performed.

R) There are many causes for the damping of IEED vibrations, but one of the major causes is as follows.

Generally, an electron beam has a shallow incident angle (in this case, the angle of the incident beam with respect to the substrate) of 1 to 2 degrees, so that the substrate is irradiated over a range of several mm or more in the direction of incidence. If there is a slope in the growth rate in this range, the vibration will be rapidly attenuated.

For example, suppose that the growth rate differs by 5% at both ends of the range irradiated with the electron beam (in normal MBE, the substrate is rotated, so a film thickness uniformity of about ±1% can be obtained over the entire surface of the substrate, but Because RHEED observation is performed with the substrate stopped, 1) a slope of growth rate of this degree can occur), and when exactly 5 atomic layers have grown at one end (RHEED intensity maximum), 4.5 atomic layers have grown at the other end. There is (RHE
ED strength is minimum), and the RHEED strength cancels each other out. In reality, it is an integral over the electron beam irradiation region, and the vibrations create undulations and are rapidly attenuated. For this reason, it has been difficult to accurately measure the growth rate.

In addition, since the observation of R1 (EED vibration) was carried out with the substrate stationary, it included a layer with non-uniform film thickness and composition (in the case of compound semiconductors), which was a problem (see Figure 1 (2)). ).

The purpose of the present invention is to suppress the attenuation of RHEED oscillations so that the growth rate can be measured accurately, and to prevent the growth layer from containing a layer with non-uniform film thickness or composition that is associated with observation of RHEED oscillations. .

[Means to solve the problem]

The solution to the above problem is to have a device that monitors the crystal growth rate by observing RHEED oscillations, scan the measuring electron beam of the device that is incident on the growth substrate in synchronization with the rotation of the substrate, and generate one reflected electron beam. R1 (EE
A molecular beam crystal that has a device for monitoring the crystal growth rate by observing D-vibration, and is configured such that the device and the growth substrate are fixed and the single molecule beam source can be rotated around an axis perpendicular to the substrate. Achieved by growth equipment.

[Effect]

FIGS. 1(1) to 1(3) are a plan view and a sectional view illustrating the present invention in detail.

In FIG. 1(1), an electron beam 2 is incident on a substrate 1 at the above-mentioned shallow incident angle. In this case, the irradiation area 3 on the substrate becomes an elongated area in the direction of incidence.

The present invention makes the growth rate uniform over the entire surface of the substrate and therefore within the irradiation area 3 by rotating the measurement electron beam together with the substrate or in an equivalent state during observation of RHEED oscillations, This suppresses the attenuation of RHEED vibration.

Figure 1 (21, (31 is a cross-sectional view of the board, 1^, IC
IB is the layer grown by rotation, IB is the layer where RHEED vibration was observed, and Figure 1 (2) shows the case when the substrate is stopped (conventional example).

FIG. 1(3) shows the case where the substrate is observed while being rotated (the present invention).

In the case of FIG. 1 (3), the growth is performed while rotating even during the observation of RHEED vibration, so the composition per film thickness is uniform throughout the entire layer.

To this end, the device is configured as follows.

(1> l? MBE the electron gun and detector for HEED
It is placed in a chamber and rotated together with the substrate.

(The electron gun and detector for 21RHE E D are fixed as before, and the turntable equipped with the bimolecular beam source is rotated.

(3) The incident electron beam of the RIIEED is scanned over the substrate in synchronization with the rotation of the substrate, and the detection system 5 is made to follow this.

A plurality of RHEED systems may be provided.

〔Example〕

In the following examples, the electron beam irradiation area 3 on the substrate is
is approximately 0.1 mm xio mm.

Measurements in Examples were carried out with the following points in mind.

■ For accurate measurements, a minimum of 2 RHEED vibrations is required.
Measure 0 cycles.

■ After opening the shutter, the growth rate stabilizes.
Since it takes ~2 minutes, the measurements of the above 20 cycles are performed after at least 2 minutes have elapsed after the start of growth.

Example 1: As shown in FIG. 3, an electron gun 7 and an electron beam intensity detector 13
is placed in the MBE chamber 9. First, after determining the incident direction of the electron beam and the position of the detector, the substrate 1, electron gun 7, and detector 13 are rotated at the same rotational speed.

The rotation speed may be as long as the time required for one rotation is about the same as the time required to grow one atomic layer or faster.

In this example, the period of RHEED oscillation was made to match the rotation period for observation.

As a result of rotating the substrate, the growth rate becomes uniform on the substrate, and the variation is less than 1% over the entire surface of the substrate.
The ED vibration continued for more than 100 times as shown in Figure 2.

Furthermore, since the substrate is rotated even during the observation of RHEED vibration, the grown layer does not include a layer with a non-uniform thickness and composition.

Embodiment 2: As shown in FIG. 4, the electron gun 7 and the fluorescent screen 8 are fixedly attached to the MBE chamber 9 in the same way as in the conventional case, and the turntable 14 to which a plurality of molecular beams a5 are attached is rotated. The same effect as the first embodiment shown in FIG. 3 can be obtained.

Embodiment 3: As shown in FIG. 5 (1), one set of an electron gun 7 and a fluorescent screen 8 for RHEED was provided, and a deflection coil 12-1 attached to the electron gun 7 and a set of a fluorescent screen 8 were installed in the chamber 9. Using the deflection coil 12-2, the electron beam 2 is made to enter the rotating substrate from a constant direction (for example, always parallel to the facets of the substrate).

In this case, the incident electron beam 2 is scanned in synchronization with the rotation of the substrate as shown by the arrow over a section of approximately 306 from the center of the substrate from the solid line position to the dotted line position in the figure using the two deflection coils. Make it.

By increasing the number of RHBED systems, this 30° section can be seen twice during one rotation of the board.

This number can also be increased.

As a detection system, a detector 13 was moved over a fluorescent screen 8.

In the example, two periods, the rotation period of the substrate and the RIIEED vibration, were made to lose once, and the vibration of the same phase portion was taken every time.

FIG. 5(2) shows the obtained vibration waveform, and the two-dot line portion in FIG. 9 is the waveform that would be obtained if the RIIEED vibration was observed continuously as in Example 1.2.

The solid line portion is the actually obtained waveform.

In this case as well, since the substrate is rotating even during observation of RHEED vibrations, the same effects as in the previous embodiments can be obtained.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to suppress the attenuation of RHEED oscillations, to accurately measure the growth rate, and to eliminate layers with non-uniform film thickness and composition within the growth layer due to RHEED oscillation observation. It is no longer included.

This can contribute to improving the precision of MBE growth.

[Brief explanation of the drawing]

FIGS. 1 (1) to (3) are a plan view and a sectional view illustrating the present invention in detail. FIG. 2 shows the R)IEED vibration of Example 1, and FIG. 3 is a cross-sectional view of the device for explaining Example 1. FIG. 4 is a plan view of the apparatus for explaining the second embodiment. 5(1), (2+ is a plan view of the device for explaining Example 3, and FIG. 6 is a schematic sectional view of the conventional MBE device showing RII IE E D vibration. 3) is R 11 E E according to the conventional example.
It is a figure explaining D vibration. In fig. 1 is a growth substrate. 2 is the incident electron beam for RHEεD. 3 is the electron beam irradiation area. 4 is a molecular beam 5 is a molecular beam source. 6 is the shutter. 7 is R1 (electron gun for scanning. 8 is a fluorescent screen. 9 is an ultra-high vacuum chamber. 10 is a substrate holder 11 is a heater. 12-1, 12-2 is a deflection coil. 13 is a detector for electron beam intensity. 14 is turntable 2, practice B gate h?, Kuri E] 1st (l12] (Z) '!? (W "J36"f'DIDhgHEEE) Dingshinju 17th 52nd Minoru & (FIJ j (7) R [T] Q Fig. 3 A symbol of the molecular edge Shao crystal hemp length of the poor end

Claims (2)

[Claims] (1) Reflected high-energy electron diffraction (RHEED) It has a device that monitors the crystal growth rate by observing oscillations, and scans the measurement electron beam of the device that is incident on the growth substrate in synchronization with the rotation of the substrate. A molecular beam crystal growth apparatus characterized in that the apparatus is configured to detect a reflected electron beam following the scanning, and the molecular beam source is configured to be asynchronous with the rotation of the substrate. (2) It has a device that monitors the crystal growth rate by observing reflected high-energy electron diffraction (RHEED) oscillations, the device and the growth substrate are fixed, and the molecular beam source is rotated around an axis perpendicular to the substrate. A molecular beam crystal growth apparatus characterized in that it is configured to be rotatable.