JPH0312391A - Molecular-beam crystal growing device - Google Patents

Abstract

PURPOSE:To prevent molecules from being built-up on the surface of a shroud and to eliminate a factor of deterioration of quality of grown crystal by equipping the molecular-beam source cells, a growth base plate, a base plate supporting base and a liquid nitrogen shroud and detachably fitting a metallic foil to the specified face of the liquid nitrogen shroud incorporated in the device. CONSTITUTION:A molecular-beam crystal growing device is equipped with the molecular-beam source cells 11-13, a growth base plate 2, a heater 3, a base plate supporting base 4, a liquid nitrogen shroud 5, a vacuum wall 7 and a growth chamber 8. Graphite coating 51 is formed on the surface of the side for surrounding the supporting base 4 of the outer face of the shroud 5 incorporated in the device. A metallic foil 6 made of stainless steel is fitted thereon by a screw, etc. This metallic foil 6 may be considered as elongation of the shroud 5 and can be replaced when vacuum of the vacuum chamber 8 is broken. The metallic foil is replaced while excessive molecules are not built-up on the metallic foil 6. Thereby gas can be prevented from being redischarged from the surface of the metallic foil 6. Deterioration of quality of grown crystal can be prevented.

Description

[Detailed description of the invention] 〔overview] Regarding molecular beam crystal growth equipment.

The purpose of the present invention is to provide a molecular beam crystal growth apparatus that has a mechanism that prevents the quality of grown crystals from deteriorating.

a molecular beam source cell, a substrate support for supporting a growth substrate, a liquid nitrogen shroud disposed surrounding the substrate support, and a liquid nitrogen shroud attached to an outer surface of the liquid nitrogen shroud on a side surrounding the substrate support. It consists of a molecular beam crystal growth apparatus that includes a removable metal foil.

[Industrial application field]

The present invention relates to a molecular beam crystal growth (MBE) apparatus.

Crystal growth is a basic technology for producing semiconductor devices, and among these, molecular beam crystal growth (MBE) has come to be widely used for crystal growth of compound semiconductors.

The MBE method heats a metal source in an ultra-high vacuum to generate molecular beams, which are then irradiated onto the heated substrate.

This is a technology that grows crystals. Recently, a gas source MBE method using a compound gas instead of a metal source has also been developed.

The liquid nitrogen shroud of a molecular beam crystal growth (MBE) apparatus is extremely important as a component for maintaining ultra-high vacuum.

Of course, the liquid nitrogen shroud does not emit gas from itself, but it also releases gas from the vacuum wall.

This has the effect of taking in gas from the substrate support during crystal growth, and as a result, it is possible to maintain a high vacuum in the growth chamber.

By the way, during crystal growth, the surface of the liquid nitrogen shroud is also irradiated with molecular beams, so molecules adhere there as well. M.B.
In the E device, when the single molecule beam source is exhausted, the growth chamber is brought to atmospheric pressure and a new source charge is performed. At this time, the gas introduced into the growth chamber is nitrogen, but air is also mixed in.

As a result, molecules adhering to the surface of the liquid nitrogen shroud take in gases such as oxygen from the air.

This trapped gas is usually removed to some extent by baking when starting up the equipment, but as the amount of molecules attached to the surface of the liquid nitrogen shroud increases,
It becomes difficult to completely remove it.

The liquid nitrogen shroud was originally intended to capture gas on its surface, but when the surface of the liquid nitrogen shroud is heated by the heating of the growth substrate during crystal growth,
If the amount of molecules deposited there is large, the trapped gas is emitted and incorporated into the growing crystal as an impurity. This is one of the factors that reduces the quality of grown crystals.

Therefore, it is necessary to eliminate such factors.

[Conventional technology]

FIG. 3 shows a schematic cross-sectional view of a general conventional MBE device.

In FIG. 3, 11 to 13 are molecular beam source cells, 2 is a growth substrate, 3 is a heater, 4 is a substrate support, 5 is a liquid nitrogen shroud, 7 is a vacuum wall, and 8 is a growth chamber.

The vacuum wall 7 is made of stainless steel, and a liquid nitrogen shroud 5 surrounding the entire inner surface of the vacuum wall is arranged. The liquid nitrogen shroud 5 is generally made of stainless steel, and during crystal growth, liquid nitrogen flows therethrough and the temperature is about -200°C. The gas released from the vacuum wall 7 and the substrate support 4 is
Since the liquid nitrogen is adsorbed onto the surface of the liquid nitrogen shroud 5, the degree of vacuum in the growth chamber 8 is maintained at an ultra-high vacuum on the order of 10-'' Torr.

By the way, during crystal growth, the molecular beams from the molecular beam source cells 11 to 13 are not irradiated only to the growth substrate 2, but are irradiated to the liquid nitrogen shroud 5 surrounding the growth substrate 2 in a so-called cos 6 distribution. It is also irradiated onto the surface of and adsorbed there.

The amount of molecules adsorbed on the surface of the liquid nitrogen shroud 5 is accumulated each time the growth is repeated. If the amount of these deposited molecules is too large, when the temperature of the substrate support 4 is raised during crystal growth, the surface of the liquid nitrogen shroud 5 in the vicinity will be warmed, and the adsorbed gas will be re-released from there. Sometimes, especially.

Molecules with high vapor pressure, such as arsenic (As), are likely to be re-emitted. However, as long as the same source charge is used to perform the same growth every time, even if there is re-emission, the quality of the grown crystal will not deteriorate significantly.

However, when the vacuum is broken to perform a new source charge, molecules adhering to the surface of the liquid nitrogen shroud 5 take in impurities such as oxygen, which poses a problem. The captured impurity gas is re-emitted from the surface of the liquid nitrogen shroud 5 during the next heating of the growth substrate, resulting in a decrease in the quality of the grown crystal.

Conventionally, attempts have been made to solve this problem by cleaning the surface of the liquid nitrogen shroud to remove deposits, but the process is difficult and impractical, requiring a long baking time when starting up the equipment. That was at best. However, it has been difficult to completely remove impurity gases trapped in deposits.

[Problem to be solved by the invention]

In order to solve the above problem, it would be very expensive and impractical to replace the liquid nitrogen shroud 5 every time a new source charge is performed.

Therefore, in the past, it was difficult to keep the surface of the liquid nitrogen shroud 5 always clean, and therefore it was difficult to prevent residual gas from entering the growing crystal.

An object of the present invention is to provide an MBE apparatus having a mechanism that prevents molecules from being deposited on the surface of the liquid nitrogen shroud 5 and eliminates the incorporation of residual gas, thereby eliminating the factors that degrade the quality of grown crystals. shall be.

[Means for solving the problem] The above problem is solved by the single molecule beam source cells 11 to 13 and the growth substrate 2.
a substrate support stand 4 supporting the substrate support stand 4; and a liquid nitrogen shroud 5 disposed surrounding the substrate support stand 4.

The present invention is solved by a molecular beam crystal growth apparatus including a removable metal foil 6 attached to the outer surface of the liquid nitrogen shroud 5 on the side surrounding the substrate support 4.

[Function] In the present invention, a removable metal foil 6 is attached to the surface of the liquid nitrogen shroud 5 placed surrounding the growth substrate 2. This metal foil 6 should be regarded as an extension of the liquid nitrogen shroud 5, so to speak.

It can be replaced when the vacuum in the growth chamber 8 is broken.

If this metal foil 6 is replaced before excessive molecules are deposited on it, re-emission of gas from the surface of the metal foil 6 can be prevented.

In this way, deterioration in the quality of the grown crystal can be prevented.

Ideally, the metal foil 6 should have the same temperature as the surface of the liquid nitrogen shroud 5 during crystal growth, and therefore it is desirable that heat exchange with the surface of the liquid nitrogen shroud 5 be good. Metal foil has a high thermal conductivity and can be in good contact with the surface of the liquid nitrogen shroud 5, so it is suitable for the above purpose.

〔Example〕

FIG. 1 is a schematic cross-sectional view of the MBE apparatus of the present invention. 1st
In the figure, 11 to 13 are molecular beam source cells.

2 is a growth substrate 53, a heater, 4 is a substrate support, 5 is a liquid nitrogen shroud, and 51 is a graphite coating.

6 represents a metal foil, 7 represents a vacuum wall, and 8 represents a growth chamber.

A graphite coating 51 with a thickness of 50 μm is formed on the outer surface of the liquid nitrogen shroud 5 on the side surrounding the substrate support stand 4 . Further, on the graphite coating 51, a thickness of 50
Attach a μm stainless steel metal foil 6. metal foil 6
It is not necessary to attach it to the entire surface of the graphite coating 51, and a great effect can be obtained just by attaching it to the surface near the substrate support 4 where the influence is greatest.

FIG. 2 is a diagram for explaining the attachment of the metal foil 6.

The metal foil 6 does not need to be a single sheet (although it is possible to use multiple sheets to attach the screw 6 to the liquid nitrogen shroud 5 with the graphite coating 51 in between.
It is fixed at 1.

The graphite coating 51 is formed to increase the efficiency of heat exchange between the metal foil 6 and the liquid nitrogen shroud 5.

The surface of the metal foil 6 on the substrate support stand 4 side is made smooth to prevent heat reflection and to avoid temperature rise as much as possible. The surface of the metal foil 6 that is in contact with the graphite coating 51 is a finely uneven surface that allows the graphite coating 5 to be formed by conduction and radiation.
1 to increase the efficiency of heat exchange with 1.

Using the MBE apparatus having such a structure, a GaAs layer was grown 100 times to a thickness of 1 μm on the GaAs substrate 2.

The 100th grown crystal was evaluated and it was confirmed that the quality of the crystal had not deteriorated. This shows that the stainless steel metal foil 6 sufficiently functions as an extension of the liquid nitrogen shroud 5. When we measured the temperature of the metal foil 6 during crystal growth, it was 10°C to 30°C higher than the temperature of the liquid nitrogen shroud 5 without it.
Although it was somewhat high, it was not to the extent that it degraded the quality of the grown crystal.

Thereafter, the vacuum was broken for a new source charge, the stainless steel metal foil 6 was replaced, a normal start-up was performed, and the growth test was performed again. At this time, no deterioration in quality of the grown crystal was observed.

(Effects of the Invention) As explained above, according to the present invention, the surface of the liquid nitrogen shroud 5 can be kept clean at all times.

Since the conditions of the crystal growth apparatus can always be kept constant, high-quality grown crystals can be stably obtained.

represents.

Claims (1)

[Claims] Molecular beam source cells (11 to 13), a substrate support (4) that supports a growth substrate (2), and a liquid nitrogen shroud (4) disposed surrounding the substrate support (4). 5) and the substrate support (4) on the outer surface of the liquid nitrogen shroud (5).
) A removable metal foil (6) attached to a surface surrounding the molecular beam crystal growth apparatus.