JPH0773097B2 - Molecular beam crystal growth method - Google Patents

Description

DETAILED DESCRIPTION [Outline] In order to supplement the detachment of an element having a high vapor pressure that constitutes the substrate due to temperature rise, the substrate temperature is raised while irradiating the substrate to be grown with a molecular beam of this element. Introducing crystal defects and impurities by pretreatment of the substrate by removing the oxide film on the substrate and irradiating a large area ion beam with low energy that does not damage the substrate to physically remove contaminants such as residual carbon. High quality crystal growth without any.

[Industrial application field]

The present invention relates to a pretreatment method for obtaining a high quality compound semiconductor epitaxial film on a substrate to be grown, especially a compound semiconductor substrate.

Since the molecular beam epitaxial growth (MBE) method can accurately form an extremely thin layer of several atomic layers, it has been widely used for forming a fine structure such as a superlattice structure.

Also in this case, the pretreatment of the substrate is an important issue for forming a film with good crystallinity as in other growth methods.

[Conventional technology]

The following method is used as a pretreatment method for a compound semiconductor substrate in the conventional MBE method.

A method of heating a substrate while irradiating the substrate with an element that is easily released in a vacuum (growth chamber).

For example, for gallium arsenide (GaAs) substrates, arsenic (A
The substrate is heated to 570 to 600 ° C. while irradiating with s).

This method can remove the oxide film, but cannot remove contaminants such as carbon (C).

A method of irradiating a beam of argon ions (Ar ⁺ ) in a vacuum.

In this method, contaminants such as C are repelled by the impact of Ar ⁺ , so that contaminants can be removed, but since a high acceleration voltage of about 0.5 to 1 KV is used, defects are introduced into the crystal.

After beam irradiation to remove this crystal defect, the substrate is
It was necessary to heat to 0-600 ° C and anneal for 10-20 minutes.

In the conventional method of irradiating with an ion beam and sputtering the substrate to perform pretreatment, the beam diameter is several 100 μm.
Since it is as thin as a few mm, it takes a long time to perform the whole surface treatment on a large-diameter substrate, and there is a problem that the once cleaned portion is contaminated again.

[Problems to be solved by the invention]

In the conventional pretreatment method for a substrate to be grown, there has been no complete method that can be performed in a short time, without introducing crystal defects, and capable of removing all contaminants on the surface.

[Means for solving problems]

To solve the above problems, in a vacuum before crystal growth,
While irradiating the growth substrate with a molecular beam of an element having a high vapor pressure that constitutes the growth substrate, the growth substrate is heated to a temperature at which the natural oxide film is decomposed and removed, and at the same time as the irradiation of the molecular beam. After the entire surface of the heated substrate to be grown is ion-irradiated with an ion beam having a beam area equal to or larger than the area of the substrate to be removed to remove contaminants on the surface of the substrate, This is achieved by the molecular beam crystal growth method according to the present invention, which has a step of growing a crystal on a substrate to be grown.

[Action]

The present invention is an improvement of the conventional substrate pretreatment by the ion sputtering method.

As described above, in the conventional substrate pretreatment method, in the case of the compound semiconductor substrate, the vapor pressure of the elements of group V and group VI that constitute the substrate is high, and therefore these elements are released when the substrate is heated. Then, surface roughness and crystal defects are introduced. In the conventional ion sputtering method, the substrate is heated while irradiating the substrate with the group V or VI element after the ion irradiation, and the crystal defects introduced by the ion irradiation are annealed.

According to the present invention, at the time of ion irradiation, the substrate temperature is already raised to an annealing temperature of 600 ° C. or higher, and at the same time, the group V or group VI element is irradiated and the surface contaminants are removed thermally. It is intended to promote.

Further, by irradiating the entire surface of the substrate with a low-acceleration beam having a large diameter of 100 eV or less, it is possible to perform processing in a short time and reduce the introduction of crystal defects. Large diameter beams are obtained using a Kaufman type ion beam source.

〔Example〕

FIG. 1 is a sectional view of an MBE device for explaining an embodiment of the present invention.

In the figure, a GaAs substrate [attached to a molybdenum (Mo) block with indium (In) solder] is used as the substrate 3 to be grown, and this is inserted from the substrate inlet / outlet 8 to the substrate exchange chamber 7
And evacuate to high vacuum.

Next, the gate valve 9 is opened, the GaAs substrate 3 is put into the substrate pretreatment chamber 1 evacuated to a high vacuum, and the substrate heating holder 2 is attached, and the gate valve 9 is closed. The GaAs substrate 3 can be heated up to 800 ° C. by the substrate heater 4.

The substrate pretreatment chamber 1 is provided with a Kauffman ion source 5 having a beam diameter of 2 inches and an As molecular beam source 6.

The substrate temperature is raised to 600 ° C. while irradiating the GaAs substrate 3 with the As molecular beam at an intensity of about 1 × 10 ⁻⁵ Torr. While maintaining this temperature, the GaAs substrate 3 was irradiated with an argon ion (Ar ⁺ ) beam having an acceleration voltage of 50 eV for about 20 minutes.

After turning off the power to the substrate heater 4, when the substrate temperature drops to about 200 ° C, open the gate valve 10
The As substrate 3 is introduced into the crystal growth chamber 11 evacuated to a high vacuum,
It is attached to the substrate heating holder 12.

The As molecular beam source 14 and the As molecular beam source 14 are placed on the GaAs substrate 3 after this pretreatment.
A GaAs crystal was epitaxially grown using a Ga molecular beam source 15. At this time, from the Si molecular beam source 16, Si is the same as the substrate 1 × 10
^It was uniformly doped at about ¹⁷ cm ^-3 .

The growth temperature is 600 ° C., the growth rate is 1 μm / hour, and the growth film thickness is 1 μm. The substrate is heated by the substrate heater 13.

A carrier concentration profile in the vicinity of the substrate-epitaxial layer interface between a conventional crystal grown by performing only the thermal cleaning at 600 ° C. in the growth chamber and a crystal grown by performing the pretreatment of the present invention is CV. (Capacity-voltage) was measured.

FIG. 2 is a diagram showing the distribution of carrier concentration with respect to the depth of the crystal grown by the pretreatment of the present invention and the crystal grown by the conventional pretreatment of only substrate heating.

In the figure, in the conventional method (a), there is a carrier depletion region (b) which is considered to be due to carbon contamination.

According to Example (c) of the present invention, it was found that carrier depletion was almost eliminated.

That is, the contaminants on the substrate surface have been removed,
It was also found that no crystal defects were introduced.

In the examples, the substrate heating temperature during pretreatment was 600 ° C., and the Ar ⁺ beam irradiation was about 20 minutes. However, if the substrate heating temperature is higher than 600 ° C., the Ar ⁺ beam irradiation time Can be shortened.

In addition, although an Ar ⁺ beam was used in the examples, instead of this, neon ions (Ne ⁺ ) and helium ions (H
e ⁺ ), hydrogen ions (H ₂ ⁺ ), nitrogen ions (N ₂ ⁺ ), or an ion beam of a mixed gas thereof may be used.

〔The invention's effect〕

As described above in detail, in the pretreatment method for a substrate to be grown according to the present invention, the treatment can be performed in a short time, no crystal defects are introduced, and all contaminants on the surface can be removed.

Therefore, a high quality MBE growth film can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an MBE apparatus for explaining an embodiment of the present invention, and FIG. 2 is a crystal grown by the pretreatment of the present invention and a crystal grown by the conventional pretreatment of only substrate heating. It is a figure which shows the distribution of the carrier concentration with respect to depth. In the figure, 1 is a substrate pretreatment chamber, 2 is a substrate heating holder, 3 is a substrate to be grown, GaAs substrate, 4 is a substrate heating heater, 5 is a Kaufman type ion source, 6 is an As molecular beam source, and 7 is a substrate exchange chamber. , 8 is a substrate inlet / outlet, 9 and 10 are gate valves, 11 is a crystal growth chamber, 12 is a substrate heating holder, 13 is a substrate heating heater, 14 is an As molecular beam source, 15 is a Ga molecular beam source, and 16 is a Si molecular beam. Source.

Claims (1)

[Claims] 1. A natural oxide film is decomposed and removed from a growth substrate while irradiating the growth substrate with a molecular beam of an element having a high vapor pressure which constitutes the growth substrate in a vacuum before crystal growth. Simultaneously irradiating the entire surface of the heated substrate to be heated with a temperature equal to or higher than the temperature with an ion beam having a beam area equal to or larger than the area of the substrate to be grown. A molecular beam crystal growth method comprising a step of performing crystal growth on the substrate to be grown after removing contaminants on the surface portion of the substrate.