JP2643328B2 - Molecular beam crystal growth equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] Molecular beam crystal growth (MBE) that monitors the crystal growth rate by observing reflection high energy electron diffraction (RHEED) vibration
The equipment has a device to monitor the crystal growth rate by observing the RHEED oscillation with the aim of suppressing the attenuation of the RHEED oscillation, enabling the accurate measurement of the growth rate and contributing to the improvement of the MBE growth accuracy. The apparatus is configured such that the plane of incidence of the measuring electron beam incident on the substrate to be grown is substantially perpendicular to the plane of incidence of the molecular beam of the element that determines the growth rate.

[Industrial applications]

The present invention relates to a molecular beam crystal growth (MBE) apparatus for monitoring a crystal growth rate by observing reflection high energy electron diffraction (RHEED) vibration.

MBE devices are widely used for forming devices whose thickness is controlled in units of atomic layers, such as semiconductor devices using a superlattice. As a molecular beam source for generating a molecular beam, one or a plurality of elements are prepared according to a substance to be grown, and a desired material layer is grown by selectively using a necessary molecular beam source.

In such an MBE, the crystal growth rate is a very important factor. Conventionally, this growth rate was measured by growing a monitor epi and calculating it from its film thickness and growth time. However, the need for a monitor substrate and the monitor growth and film thickness Due to the time required for evaluation, in recent years, growth rate measurement by RHEED oscillation has been performed in order to accurately grow a predetermined number of atomic layers by forming a superlattice structure or the like.

[Conventional technology]

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

In the figure, 1 is the substrate to be grown, 2 is the incident electron beam for RHEED, 4
Is the molecular beam of the element that determines the growth rate, 5 is the molecular beam source (rutu with heating means), 6 is the shutter that shuts off the molecular beam, 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 epitaxial growth is performed on the substrate 1 using this apparatus, a crucible 5 storing a source for growing a desired semiconductor is heated to emit molecular beams. For example, Ga and As as sources
Can be used to grow a GaAs crystal, and Si can be used to grow a Si crystal.

RHEED applies the electron beam emitted from the electron gun 7 to the substrate surface
The intensity of the diffraction point of the RHEED pattern was measured during the growth by a method in which the light was incident on the substrate 1 at a shallow angle of 2 ° and the diffraction pattern by the reflected electron beam was projected on the fluorescent screen 8. Oscillations are seen, which can be used to monitor the growth rate.

RHEED oscillations occur when the crystal is growing in layers, and when the atoms are deposited flat on the surface, the RHEE
The intensity of D becomes maximal, and when atoms begin to accumulate on it, the intensity drops due to diffuse reflection. When the growth of one layer is over and the flat surface reappears, the intensity is again at its maximum. In this way, a strong vibration is obtained with a period corresponding to the growth of one atomic layer.

FIGS. 7 (1) to 7 (3) are diagrams for explaining conventional RHEED vibration.

As shown in FIG. 7 (1), the Ga molecular beam 4, which is an element determining the growth rate, was incident on the center of the substrate at an angle of 15 ° with the incident electron beam 2. At this time, as shown in FIG. 7 (2), the growth rate of GaAs is inclined by 1% per 1 mm in the direction of the incident electron beam 2 on the substrate, that is, the total length of the irradiation region 3 (see FIG. 1). (About 10mm) and had a 10% slope.

During the measurement, when the growth was performed at a growth rate of 0.6 μm / hour, the RHEED oscillation continued only about 10 times as shown in FIG. 7 (3).

[Problems to be solved by the invention]

When monitoring the growth rate by the RHEED vibration as in the conventional example, there is a disadvantage that the RHEED vibration is attenuated and accurate measurement cannot be performed.

There are several causes of RHEED vibration damping, but one of the major causes is as follows.

Generally, the electron beam has a shallow incidence angle (in this case, the angle of the incident beam with respect to the substrate) of 1 to 2 °, and is irradiated on the substrate in a range of several mm or more in the incidence direction. If there is a gradient in the growth rate in this range, the vibration will rapidly attenuate.

For example, suppose that the growth rates differ by 5% at both ends of the range where the electron beam is irradiated. (In a normal MBE, the substrate is rotated, so that a film thickness uniformity of about ± 1% can be obtained over the entire surface of the substrate. Since RHEED observation is performed with the substrate stopped,
This degree of growth rate gradient can occur), and when exactly 5 atomic layers are grown at one end (RHEED intensity maximum), 4.5 atomic layers are grown at the other end (RHEED intensity minimum), and the RHEED intensity is They will cancel each other out. Actually, the integral is obtained in the electron beam irradiation region, and the vibration causes undulation and rapidly attenuates. For this reason, it has been difficult to accurately measure the growth rate.

An object of the present invention is to suppress the attenuation of RHEED oscillation so that the growth rate can be measured accurately.

[Means for solving the problem]

The solution to the above problem is reflected high energy electron diffraction (RHEE).
The device has a device for monitoring the crystal growth by observing the vibration in D), and the incident surface (the surface including the normal line and the incident line set at the incident point) of the measurement electron beam of the device for incidence on the substrate to be grown is This is achieved by a molecular beam crystal growth apparatus configured to be perpendicular to the plane of incidence of the molecular beam of the element that determines the growth rate.

[Action]

 FIG. 1 is a plan view for explaining the principle of the present invention.

In the figure, an electron beam 2 is incident on a substrate 1 at the aforementioned shallow incidence angle. In this case, the irradiation area 3 on the substrate is an elongated area in the incident direction.

The present invention suppresses the attenuation of the RHEED oscillation by determining the direction of incidence of the molecular beam 4 of the element that determines the growth rate so that the growth rate is the most uniform in the irradiation region 3.

 To do so, the device is configured as follows.

(1) The emission direction of the molecular beam source (the direction of the molecular beam 4) and the emission direction of the RHEED electron gun (the direction of the incident electron beam 2) of the element that determines the growth rate are arranged toward the center of the substrate. Angle is approximately 90 °.

This is because the direction of 90 ° with respect to the molecular beam has the best uniformity of the film thickness on the substrate and the lowest uniformity in the direction along the molecular beam.

When there are a plurality of molecular beam sources of the element for monitoring the growth rate, the following (2) to (4) are performed.

(2) All molecular beam sources of the elements whose growth rates are to be monitored are arranged in a plane satisfying the condition (1).

(3) Provide a plurality of electron guns and fluorescent screens so as to satisfy the above condition (1).

(4) Deflection means for bending the electron beam in a desired direction in the MBE chamber is provided, and the electron beam is incident so as to satisfy the above condition (1).

According to the above (1) to (4), the growth rate becomes uniform in the electron beam irradiation region 3, so that the RHEED
Vibration damping is suppressed, III / V ratio (Group III element / Group V element)
The oscillation can be continued up to the limit determined by the growth conditions such as the temperature and the substrate temperature.

〔Example〕

In the following embodiment, the irradiation area 3 of the electron beam on the substrate is about 0.1 mm × 10 mm.

 The measurement of the example was performed as follows.

At least 20 periods of RHEED oscillation are measured for accurate measurement.

After opening the shutter, the growth rate stabilizes
Since it takes 2 minutes, the measurement of the above 20 cycles is at least 2
Perform after minutes.

Example 1 In the growth of GaAs, when the molecular beam source of Ga, the electron gun and the fluorescent screen were arranged at an angle of 90 ° between the molecular beam 4 of Ga and the incident electron beam 2 as shown in FIG. The variation in the growth rate in the electron beam irradiation area 3 was 0.5% or less, and the RHEED oscillation continued 100 times or more as shown in FIG.

Embodiment 2: When there are a plurality of elements that determine the growth rate such as AlGaAs and InAlGaAs, the molecular beam sources 5-1 to 5-4, the electron gun and the fluorescent screen are arranged as shown in FIG.

The figure shows a cross-sectional view of the apparatus on a plane passing through the center of the substrate and perpendicular to the substrate and the incident surface of the electron beam. Each of the devices is arranged such that the outgoing molecular beams 3-1 to 3-4 exist in this plane. Molecular beam source 5-
If 1 to 5-4 are arranged, the growth rate of each molecular beam in the irradiation area 3 becomes uniform.

The electron gun and the fluorescent screen are not shown in the drawing because they are arranged in a direction substantially perpendicular to the paper surface.

Embodiment 3 Another embodiment when there are a plurality of elements for determining the growth rate is as follows.

As shown in FIG. 4, electron guns 7-1 to 7 for RHEED
-3 and a plurality of fluorescent screens 8-1 to 8-3 are provided. The electron gun 7 and the fluorescent screen are so arranged that the growth rate in the irradiation area 3 is the most uniform for any of the molecular beam sources 5-1 to 5-6. A set of light screens 8 is selected.

 That is, the following is selected.

For the molecular beam sources 5-1 and 5-4, a set of an electron gun 7-1 and a fluorescent screen 8-1 is selected.

For the molecular beam sources 5-2 and 5-5, a combination of an electron gun 7-2 and a fluorescent screen 8-2 is selected.

For the molecular beam sources 5-3 and 5-6, a combination of an electron gun 7-3 and a fluorescent screen 8-3 is selected.

Embodiment 4: Another embodiment in which there are a plurality of elements for monitoring the growth rate is as follows.

As shown in FIG. 5, although only one set of the electron gun 7 for RHEED and the fluorescent screen 8 are provided, the electron guns are provided by electron beam deflection coils 12-1 to 12-6 provided in the chamber. Change the incident direction of the beam so that it is perpendicular to the molecular beam to be monitored.

For example, when monitoring the molecular beam emitted from the molecular beam source 5-1, the electron beam emitted from the electron gun 7 is reflected by the deflection coil 12-.
The light is deflected by the light beams 12-1 and 12-2 so as to be incident on the substrate and perpendicularly to the molecular beam.

In any of the above embodiments, the molecular beam to be measured and the incident electron beam are configured to be perpendicular to each other, and the growth rate during the measurement in the irradiation region becomes uniform.

〔The invention's effect〕

As described above, according to the present invention, it is possible to suppress the attenuation of the RHEED oscillation and accurately measure the growth rate, thereby contributing to the improvement of the MBE growth accuracy.

[Brief description of the drawings]

FIG. 1 is a plan view for explaining the principle of the present invention, FIG. 2 is a diagram showing RHEED vibration of the embodiment, FIG. 3 is a cross-sectional view of an apparatus for explaining the embodiment 2, and FIG. FIG. 5 is a plan view of an apparatus for explaining Embodiment 4, FIG. 6 is a schematic cross-sectional view of a conventional MBE apparatus, and FIGS. 7 (1) to (3) are RHEEDs of a conventional example. It is a figure explaining a vibration. In the figure, 1 is a substrate to be grown, 2 is an incident electron beam for RHEED, 3 is an electron beam irradiation area, 4 is a molecular beam of an element which determines the growth rate, 5 is a molecular beam source, 6 is a shutter, and 7 is a RHEED. An electron gun, 8 is a fluorescent screen, 9 is an ultra-high vacuum chamber, 10 is a substrate holder, and 11 is a heater.

Claims (1)

(57) [Claims] An apparatus for monitoring crystal growth by observing reflected high energy electron beam diffraction (RHEED) vibration, and having an incident surface of an electron beam for measurement of the apparatus to be incident on a substrate to be grown An apparatus for growing a molecular beam crystal, wherein a plane including a normal line and an incident line is perpendicular to an incident surface of a molecular beam of an element for determining a growth rate.