JPS5895695A - Crystal growing apparatus with molecular beam - Google Patents

Abstract

PURPOSE:To expel impurities in a molecular beam source in a short time and form a semiconductor single crystal of high purity efficiently, by means of separate introducing and evacuating means for an atmospheric gas in molecular beam source oven chambers and dividing the molecular beam source oven chambers from a crystal growing chamber with gate valves. CONSTITUTION:Molecular beam source oven chambers 7, 8, 9 and 10, containing a material for a molecular beam source, and connecting to a crystal growing chamber 1 are respectively divided by gate valves 13, 14, 15 and 16 (through shutters 12), and gas introductory pipes (2a), (2b), (2c) and (2d) are separately connected to the respective oven chambers 7, 8, 9 and 10 through valves (3a), (3b), (3c) and (3d). In growing a single crystal with the above-mentioned apparatus, hydrogen is fed to the oven chamver 7 filled with Ga to reduce impurities, e.g. gallium oxide, contained therein. The reduced impurities are then discharged by an ion pump 17, and high-purity Ga is fed to the single crystal growing step. If the material for the molecular beam source is Al, NH4 is introduced thereinto as an introductory gas. The above-mentioned operations are similarly conducted in the oven chambers 8, 9 and 10.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a molecular beam crystal growth apparatus, and more particularly to a molecular beam crystal growth apparatus capable of obtaining highly pure semiconductor crystals with good surface morphology.

(2) Background of the Technology Various growth apparatuses have been proposed as epitaxial growth apparatuses for semiconductor thin films.

Liquid-phase epitaxial growth equipment and vapor-phase epitaxial growth equipment are generally known, but in these epitaxial growth equipment, control during crystal growth is determined mainly by temperature, and many parameters are required. Semiconductor crystals obtained by a molecular beam crystal growth apparatus (MBE) that allows substrate control are expected to have high purity.

The above MBE apparatus is a high-grade vacuum evaporation apparatus that can precisely control various parameters, and its structure is such that component elements evaporated from one or more cell-type crucibles are irradiated onto the substrate in the form of a beam. Molecules that are not captured by the substrate are carried away in a vacuum system, and the substrate surface is constantly irradiated with a fresh molecular beam that has been evaporated from the crucible of the molecular beam source oven. The number of molecules of each element that reaches the substrate is uniquely determined by the geometry of the deposition system and the temperature of the deposition source, so it is possible to accurately control the crystal growth rate, concentration of added impurities, etc. The growth rate of regular t# crystals is several A to several μ/hr.

In the above-mentioned MBE apparatus, the inside of the crystal growth chamber is kept in an ultra-high vacuum and the molecular beam source material is heated to emit a molecular beam. However, when the molecular beam source material is inserted into the open molecular beam source, it is exposed to the atmosphere. The surface becomes oxidized due to exposure. In order to remove this oxide, it was necessary to heat the molecular beam source material for a long time and to exhaust the gas in an ultra-high vacuum. However, in this gas exhaust method, the oxide of the molecular beam source material is extremely stable, so it takes a long time to exhaust gas components such as oxygen, and it is not possible to completely exhaust gas components such as oxygen.

Furthermore, much of the molecular beam source material is used for gas evacuation and cannot be used effectively for crystal growth, and there is a need for a molecular beam crystal growth apparatus that can exhaust the oxides of the molecular beam source material in a short period of time. .

(3) Problems with the prior art Figure 1 shows a schematic configuration of a conventional MBE @ system. The molecular beam source oven 7°8.9.10 has a heater 11 wound around it, and these molecular beam source ovens contain molecular beam source materials such as arsenic (As), aluminum (AI), and gallium. (G
a) 0 molecular beam source oven filled with silicon (St) etc. as a dopant? , 8.9.10, a shutter 12 is disposed on the front side, a substrate 5 is placed on the substrate holder 4, and a heater 6 is placed on the back side of the substrate holder 4.
and is heated.

In the above configuration, the crystal growth chamber 1 is set to an ultra-high vacuum of, for example, 10"-' Torr or less, and the molecular beam source oven is heated with the shutter closed. For example, the molecular beam source material In the case of Ga, the surface of Ga is an oxide of Gay Os, and in the case of AI, the surface is a monide of AI 2.0.

These oxides are very stable, and when heated at a high temperature of 1200° C. in vacuum, the following reaction occurs.

Ga 2 0 m + 4 G tosa 3 Ga 20, that is, GazO, turns into vapor and flies out from Gas 02 together with the molecular beam of Ga. In this case, the above Ga20s
Since Ga and AlzO are extremely stable, Ga
Gas components such as yO mix into the molecular beam of Ga and impair the purity during crystal growth. Therefore, these gases such as Ga2O must be exhausted for a long time, but not only can they not be completely removed, but also the molecular beam of Ga etc. Since the source materials are consumed, these materials are in short supply during actual MBE.

In other words, the molecular beam source material filled in-house in the crystal growth chamber is exposed to the atmosphere once during filling, so the surface becomes oxidized, but it also contains impurities other than oxides, albeit in very small amounts. Conventionally, in order to remove these impurities, the molecular beam source material is heated at high temperature for a long time in an ultra-high vacuum to gas out the impurities. However, this method consumes molecular beam source material due to the low vapor pressure of impurities. Furthermore, since it requires heating at high temperatures, much of the packed molecular beam source material is consumed during gas release, making it ineffective for crystal growth, and impurities cannot be completely removed. .

(4) Purpose of the Invention In view of the above-mentioned conventional drawbacks, the present invention separates a molecular beam source oven having a molecular beam source material from a crystal growth chamber, and adjusts the activity according to the molecular beam source material while the molecular beam source is open. A gas is flowed into the molecular beam source oven and the molecular beam source material is heated in the active gas, thereby causing impurities contained in the molecular beam source material to chemically react with the active gas and being evacuated. The object of the present invention is to provide a molecular beam crystal growth apparatus that can obtain highly pure semiconductor crystals in a short time.

(5) Structure and object of the invention According to the present invention, a crystal growth chamber and one or more molecular beam source ovens are partitioned via a gate valve, and each molecular beam source oven is provided with a separate exhaust means. An active gas corresponding to the molecular beam source material disposed in the molecular beam source oven is introduced into the open, and the active gas is caused to react with impurities contained in the molecular beam source material. This is achieved by providing a molecular beam crystal growth apparatus.

(6) Embodiment of the Invention Hereinafter, an embodiment of the present invention will be described in detail with reference to FIGS. 2 and 3.

FIG. 2 is a route map of the molecular beam crystal growth apparatus of the present invention,
3IlI shows an enlarged route map of one of the open molecular beam sources, and the same parts as in FIG. Inside the crystal growth chamber 1 is a substrate r1.
Has multiple molecular beam sources open? , 8.9°10 is gate pulp 13, 14.15
．． It is separated from the crystal growth chamber 1 by 16, and can be individually evacuated by ion pumps 17.1B and 19.20.

The vacuum chambers of each molecular beam source oven 7.8, 9.10 are equipped with gas introduction pipes 2a, 2b, 2c, 2d and valves 3a + 3b, 3.
c and 3d, and is configured so that active gas can be introduced into each molecular beam source open.

Each molecular beam sieve open? , 8.9.10, A1. of the molecular beam source material 22 is placed in the cell 21 as shown in FIG. Ga
, Sl, As, etc. are inserted, and a heating heater 11 is wound around the cell.

Now, if Ga is inserted into the cell 21 as a molecular beam source material, hydrogen (H) is introduced into the molecular beam source oven 7 by adjusting the valve 3a of the introduction tube 2a.

At this time, hydrogen is introduced into the open molecular beam source ~X 10'To
If Ga is heated to about 800° C. with the gate pulp 13 and shutter 12 closed after approximately rr inflow, the following reduction reaction will occur.

Ga20s + 2 Hz-→Gat O+ 2 8
20 In this state, the temperature is usually sufficiently low compared to the Ga molecular beam source temperature used for growth (approximately 1000°C or higher), so the 2N20 (water) vapor is released together with GatO without evaporating, and Ga oxidizes in a short time. eject things. The exhausted gas is exhausted by the ion pump 17. Similarly, when AI is inserted as the molecular beam source material into the molecular beam source open 8, ammonia (NHa) is used as the inflow gas.
Adjust the valve 3b of the introduction pipe 2b and introduce the
When heated at ℃, Al2O is reduced by N1(i) and oxygen can be removed.

Similarly, in the case of other molecular beam source materials, it is possible to perform reduction according to the molecular beam source material by introducing an active gas that reduces them through the introduction tube, and after reduction, exhausting to create a vacuum. It becomes possible.

(7) Effects of the Invention As explained in detail above, the molecular beam crystal growth apparatus of the present invention allows impurities contained in the molecular beam source material to be chemically reacted with an active gas and released as a gas and removed in an extremely short period of time. It has the characteristics that it can release oxides over time and that active gas can be selected depending on the molecular beam source material.

[Brief explanation of drawings]

Figure 1 is a schematic plan view of a conventional molecular beam crystal growth apparatus, Figure 2 is a schematic plane view of the molecular beam crystal growth apparatus of the present invention, and Figure 3 is an enlarged view of the open portion of the molecular beam source in Figure 2. FIG. 1... Crystal growth chamber, 4... Substrate holder, 5...
substrate,? , 8.9.10...Molecular beam source open, 13
．． 14,15.16...Gate pulp, 17.1B,
19.20...Ion pump, 21...Cell, 22
...Molecular beam source material. Figure 2 Figure 3

Claims (1)

[Claims] A crystal growth chamber and one or more molecular beam source ovens are partitioned via a gate pulp, each of the molecular beam source ovens is provided with a separate introduction/exhaust means, and the molecular beam source material is disposed in the molecular beam source oven. 1. A molecular beam crystal growth apparatus which introduces an active gas into the oven and causes the active gas to react with impurities contained in the molecular beam source material.