JPH03208886A - Molecular beam crystal growing device - Google Patents

Abstract

PURPOSE:To form a semiconductor thin film which has less surface defects, a uniform film thickness and good boundary steepness by providing a mechanism to rotate a crucible in the molecular beam crystal growing device equipped with an ultra-high vacuum chamber, a molecular beam source and a substrate holder. CONSTITUTION:The crucible 4 contg. raw materials 3 for crystal growth is put into a cell 5 and is supported by a hollow supporting bar 7. A magnet 8 is mounted to this supporting bar 7. The crucible 4 is heated by a heater 2 separated from the cell 5. The temp. of the crucible 4 is measured by a thermocouple 6 adapted in contact with the bottom of the crucible. A lead wire is connected to a thermocouple 11 for temp. control through the hollow part of the supporting bar 7. The crucible is rotated at an arbitrary rotating speed by the magnetic force of the magnets 8. The raw materials in the crucible are uniformly heated on rotating of the crucible, by which the space temp. distribution of the raw materials is eventually stabilized and uniformized. The defects of the epitaxially grown layer are thereby decreased and further, the control of the growth rate and the compsn. of the mixed crystal layer are improved. The steepness of the boundary is improved and the good-quality boundary having the steepness of <=1-atom layer is obtd.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a molecular beam crystal growth apparatus.

[Conventional technology]

In the molecular beam crystal growth method, a semiconductor substrate is placed in an ultra-high vacuum chamber of IQ-16 to 10-'' Torr, and a molecular beam is emitted from a molecular beam source to grow crystals on the substrate.

Molecular beam sources are generally pyrolytic boron nitride (PBN).
) and a heater to heat it. The heater is attached to the outer periphery of the crucible, and heats the raw material in the crucible by heating the heater with electricity. The heated raw material evaporates into molecular beams that are adsorbed onto the substrate. There is a thermocouple at the bottom of the crucible that measures the temperature of the crucible and controls the temperature. Using this molecular beam crystal growth method, field effect transistors (
Electronic devices and light emitting devices such as FETs) and high electron mobility transistors (HEMTs) can be manufactured.

[Problem to be solved by the invention]

However, semiconductor thin films fabricated using equipment used in conventional molecular beam crystallization methods have surface defects ranging from several thousand to tens of thousands/cj, making devices fabricated using such thin films unreliable. There is a problem of lack of sexuality.

In other words, with conventional molecular beam crystal growth equipment, stable and uniform molecular beam intensity cannot be obtained, a uniform composition cannot be obtained during epitaxial growth on the substrate, and the uniformity of film thickness within the substrate surface is poor, resulting in high quality epitaxial growth. A film cannot be obtained.

Naturally, it is also inferior in terms of the steepness of the interface, making it difficult to fabricate devices such as superlattice devices and quantum effect devices.

[Means to solve the problem]

There are various possible causes for such problems, but in the case of molecular beam sources, bumping occurs in the raw material inside the molecular beam source,
This is thought to occur because liquid raw material fine particles fly out from the raw material liquid surface and adhere to the substrate as a liquid.

This is because conventional molecular beam sources perform heating with the crucible in a fixed state, so the spatial distribution of temperature in the molten state of the raw material contained in the crucible is uneven, and intense convection occurs. it is conceivable that. In other words, when the temperature at the bottom becomes higher than at the surface and evaporation occurs near the bottom, bubbles are generated at the bottom and rise to the top, causing bumping when they reach the surface.

The present invention was obtained as a result of intensive studies to develop a molecular crystal growth apparatus that stabilizes and makes the molecular beam intensity uniform, thereby reducing defects in epitaxially grown films, and further improving controllability and obtaining steep interfaces. It is. That is, the present invention provides a molecular beam crystal growth apparatus comprising a vacuum chamber maintained at an ultra-high vacuum, a plurality of molecular beam sources constituted by a crucible and a heater set in the vacuum chamber, and a substrate holding device. This is a molecular beam crystal growth apparatus characterized by being equipped with a rotating mechanism.

[Effect]

Next, an example of the molecular beam source of the molecular beam crystallization apparatus of the present invention will be explained with reference to the drawings. Figure 1 shows a cross-sectional view of the molecular beam source. In the figure, 1 is the outer wall of the vacuum chamber, 2 is the heater, 3 is the raw material, and 4 is the
Crucible, 5 is cell, ε is thermocouple, 7 is support rod, 8, 9
1 is a magnet, 10 is a heater terminal, and 11 is a thermocouple terminal.

A crucible 4 containing raw material 3 for crystal growth is placed in a cell 5 and supported by a hollow support rod 7, and a magnet 8 is attached to this support rod 7. The crucible 4 is heated by a heater 2 that is separate from the cell 5, and the temperature of the crucible 4 is measured by a thermocouple 6 that is in contact with the bottom of the crucible. Also support rod 7
A lead wire to the temperature control thermocouple 11 is connected through the hollow part of the thermocouple.

The crucible is rotated at an arbitrary rotational speed by the magnetic force of the magnet 8.9.

As the crucible rotates, the raw material in the crucible is heated uniformly, and the spatial temperature distribution of the raw material is stabilized and made uniform. This reduces defects in the epitaxially grown film and further improves the controllability of the growth rate and composition of the mixed crystal layer. gets better. In addition, the steepness of the interface is improved, and a high-quality interface with a steepness of less than 1 atomic layer can be obtained.

〔Example〕

A GaAs WIM was formed on a GaAs substrate using the apparatus of the present invention. Table 1 shows a comparison between when the crucible was rotated at 30 r, p, and when it was not rotated.

Table 1 In addition, quantum and superlattice structures were fabricated from GaAs thin films obtained by rotating the crucible, and the interface steepness was determined by photoluminescence measurements, X-ray diffraction, and transmission electron microscopy (TEM) measurements. As a result of investigation, a steepness of one atomic layer or less was obtained.

From the above results, it is clear that the thin film obtained by molecular beam crystal growth using the apparatus of the present invention has few surface defects (the thin film has a uniform thickness and has good interface steepness).

〔Effect of the invention〕

As described above, according to the present invention, a semiconductor thin film having a uniform thickness and good interface steepness with few surface defects can be obtained, and it has a significant industrial effect.

[Brief explanation of drawings]

FIG. 1 is a sectional view of the molecular beam source of the present invention. 3... Raw material, 4... Crucible, 7... Support rod,
8.9...Magnet.

Claims (1)

[Claims] In a molecular beam crystal growth apparatus consisting of a vacuum chamber maintained at an ultra-high vacuum, a plurality of molecular beam sources and a substrate holding device consisting of a crucible and a heater installed in the vacuum chamber, a mechanism for rotating the crucible is used. A molecular beam crystal growth apparatus characterized by: