JPH0139205B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a molecular beam source for obtaining a stable and uniform molecular beam with good reproducibility in molecular crystal growth.

A semiconductor substrate is placed in an epitaxial growth chamber kept in an ultra-high vacuum, and a small chamber connected to the epitaxial growth chamber contains carbon or pyrolitic boron containing a material that will become the source of a thin film to be formed on the substrate.・Night Ride (PBN)
An oven cell consisting of the following is disposed, and by heating the semiconductor substrate and the oven cell, the substrate is irradiated with a molecular beam in which the source material has been evaporated. A molecular beam epitaxial growth method for forming a thin film having a desired composition on a substrate is already well known.

In a molecular beam epitaxial growth apparatus for carrying out such a molecular beam epitaxial method,
A conventional structure of a molecular beam source comprising a molecular beam source cell filled with the molecular beam forming material and a heater for heating the molecular beam source cell is shown in cross-sectional view in FIG.

As shown in the figure, the conventional molecular beam source consists of a molecular beam source cell 2 having a small chamber 1 formed by hollowing out a cylindrical carbon or PBN jig, and a heater 3 made of tungsten or tantalum. After filling a metal 4, such as gallium (Ga), which is a material for the wire, the molecular beam source cell is placed in a small room connected to an epitaxial growth chamber in which a semiconductor substrate to be epitaxially grown is installed. After the growth chamber and the small room in which the molecular beam source cell was installed were evacuated to an ultra-high vacuum, the semiconductor substrate and the heater 3 around the molecular beam source cell were heated to cause evaporation from the ejection hole 5 of the molecular beam source cell. A Ca molecular beam was irradiated onto the substrate.

However, in the molecular beam source cell having the above-mentioned shape, Ca melted within the cell becomes a large number of molecular particles due to bumping, etc., which fly out from the ejection hole 5 and fly to the substrate, where they adhere to the substrate. When such grains adhere to a substrate, crystals grow abnormally only in the adhered portions, resulting in problems such as a decrease in yield when ICs and the like are manufactured from a crystal substrate having many such abnormally grown portions.

The present invention eliminates the above-mentioned drawbacks, prevents the molecular beam ejected from the molecular beam source cell from ejecting as multiple molecular particles due to phenomena such as bumping, and stabilizes the molecular beam as a uniform single molecule. The purpose is to provide a molecular beam source that can be extracted.

In order to achieve such an object, the present invention includes a partition wall provided with a small hole through which the molecular beam evaporated from the molecular beam forming material passes, a plurality of small chambers partitioned by the partition wall, and a separate partition for each small chamber. A molecular beam source for molecular beam crystal growth includes a heater provided for heating the small chambers, and by adjusting the heating temperature of the heater, each of the plurality of small chambers is heated to a different temperature. This method is characterized in that the molecular size of the molecules is made uniform and the molecular beams are emitted into a molecular beam epitaxial growth chamber.

That is, in the molecular beam source cell of the present invention, the interior of the conventional molecular beam source cell is divided into a number of small chambers, and the molecular beam source material is melted in the first chamber to form a gaseous molecular beam source. The molecular beam is reheated in a second chamber connected to the chamber, and then the molecular beam is sequentially moved to adjacent chambers and reheated, changing the intensity of the molecular beam in each chamber to form a molecular beam. The size of the molecules is made uniform.

An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a sectional view of a molecular beam source according to the present invention. As shown in the figure, a molecular beam source cell 11 constituting the molecular beam source is made of high-purity graphite. It is divided into a second small chamber 13 and a third small chamber 14, respectively. Each chamber is divided by carbon partition walls 15 and 16, and the partition walls have small holes 17 and 18 for connecting adjacent chambers and ejecting the formed molecular beam.
is provided. Further, an ejection hole 19 is provided for irradiating the substrate with a molecular beam from the third small chamber 14. Also, heater groups 20, 21, 2 made of tantalum for heating each of the small chambers separately.
2 are provided respectively. The molecular beam source material is introduced into the first chamber 12 of such a molecular beam source cell.
After filling with Ga23, the molecular beam source cell is installed in a small chamber connected to the epitaxial growth chamber, and then the epitaxial growth chamber and the small chamber are evacuated to ultra-high vacuum. After that, the temperature of the heater 20 that heats the first small chamber is set to 1500 to 1600°C, the temperature of the heater 21 that heats the second small chamber is set to 1600°C, and the temperature of the heater 21 that heats the second small chamber is set to 1600°C.
The temperatures of the heaters 22 that heat the small chambers are adjusted to 1000° C. to raise the temperature of the heaters.

In this way, the Ga heated in the first chamber with a volume of about 20 c.c. becomes steam with a vapor pressure of 5 to 6 Torr, and this steam connects the first chamber and the second chamber. The liquid is then injected into the second chamber 13 through a small hole 17 having a much smaller cross-sectional area than the first chamber. The steam transferred to this second chamber is reheated to about 1600° C. by the heater 21 that heats the second chamber, and becomes Ga vapor at 10 ⁻¹ Torr. This Ga vapor further passes through the small hole 18 connecting the second small chamber 13 and the third small chamber 14 to the third small chamber 14.
It is further heated to about 1000°C by the heater 22 and heated to 5 to 6×10 ^-3 to 5 to 6×
It becomes Ga vapor at 10 ^-2 Torr. and spout 19
The molecular beams are projected onto the substrate as molecular beams.

In this way, the molecular beam directly ejected from the molten Ga in the first small chamber collides with the wall surface of the molecular beam source cell in the second and subsequent small chambers and is heated again. At this time, a large number of molecules are disintegrated by the thermal energy from the wall surface and become a single molecule, which is then extracted as a uniform molecular beam of uniform size from the ejection port 19 at the final stage.

In this way, Ga
A uniform thin film can be formed on the substrate with good reproducibility without abnormal crystal growth caused by a large number of molecules gathering and bumping and adhering to the substrate as clusters of Ga molecule particles. Become.

In addition, in the above embodiment, three molecular beam source cells are used.
Although it is divided into two small chambers, the more the number of chambers is divided, the more uniform the molecular beam can be obtained.

Further, in the above embodiments, Ga was used as the molecular beam forming material, but any other material for molecular beam crystal growth such as Al, In, etc. can be used.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the structure of a conventional molecular beam source cell, and FIG. 2 is a sectional view showing the structure of an embodiment of the molecular beam source cell of the present invention. In the figure, 1 is a small chamber, 2 is a molecular beam source cell, and 3 is a small chamber.
1 is a heater, 4 is a Ga metal, 5 is an ejection hole, 11 is a molecular beam source cell, 12 is a first small chamber, 13 is a second small chamber, 14 is a third small chamber, 15 and 16 are partition walls, 1
7, 18 are small holes, 19 is an ejection hole, 20, 21, 2
2 is a heater group, 23 is a Ga metal.

Claims (1)

[Scope of Claims] 1. A partition wall provided with small holes through which molecular beams evaporated from a molecular beam forming material pass, a plurality of small chambers partitioned by the partition walls, and A molecular beam source for molecular beam crystal growth has a heater for heating the small chambers, and by adjusting the heating temperature of the heater, each of the plurality of small chambers is heated to a different temperature, and the molecules in the molecular beam are heated. A molecular beam epitaxial growth method characterized by emitting the molecular beam into a molecular beam epitaxial growth chamber with a uniform size.