JPH01197388A - Molecular ray crystal growth device - Google Patents

Abstract

PURPOSE:To prevent the residual impurities from being mixed into a crystal growth membrane and to obtain the crystal growth membrane of high purity and high quality by trapping the residual impurities generated during the temp. rising of a base plate and during the growing of crystal, on a getter surface by an active getter material. CONSTITUTION:The inside of the device is kept in about 10<-10>Torr by ultrahigh- vacuum pump and a liquid nitrogen shroud 3, and a getter surface 6 is cooled enough. Then, raw material cells 2, 3 and getter cell 5 disposed not to confront to a base plate 1 are heated, and the residual impurities, such as H2O, CO, CO2, generated from the raw material in crucibles 2, 3 and a heater of electric furnace are gettered by the getter material 4 which is projected from the inside of a getter cell 5 and stuck to a getter surface 6 so that the concn. of the residual impurities in the device is reduced. Then, the base plate 1 is heated to grow a semiconductor membrane.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention belongs to the field of manufacturing semiconductor crystals, and relates to a molecular beam crystal growth apparatus for obtaining semiconductor crystals of high purity and quality.

(Prior Art) One type of semiconductor crystal growth apparatus is molecular beam crystal growth, in which each of the constituent elements of a semiconductor is evaporated to grow crystals of a semiconductor on a substrate in an ultra-high vacuum of about 10 Torr. Beam Epitaxy,
MBE) equipment is available. In the MBE apparatus, since the crystal growth rate is very low at about 37 vsec, it is easy to control the film thickness on the order of atomic layers. For example, MBE by Ezaki et al.
The creation of semiconductor superlattices using equipment is being developed by Thin Solid Films (Vo.
l, 36. pp.

285-298.1976). Also,
Since this crystal growth apparatus only evaporates high-purity materials in an ultra-high vacuum, it is easy to operate during growth.

A conventional MBE apparatus and a semiconductor crystal growth method using the same will be explained using figures.

FIG. 2 is a schematic cross-sectional view of the main parts of a conventional MBE apparatus. In the figure, 1 is a single crystal substrate, 2 is a raw material cell that heats and blows the semiconductor raw material to be grown on the substrate 1, and 3 is a liquid nitrogen shroud that surrounds the substrate 1 and the raw material cell 2 and is filled with liquid nitrogen. It is. Note that each cell is made up of a heater, a crucible, etc., but only the crucible is shown here.

Additionally, a cell shutter is installed in front of the cell, a main shutter is installed in front of the substrate, and a heater is installed behind the substrate, all of which are housed in an ultra-high vacuum container, but are not shown in the figure.

To start growth, first, the area around the substrate 1 and raw material cell 2 is heated to 10” Tor using an ultra-high vacuum pump (ion pump, cryopump, etc.) and a liquid nitrogen shroud.
Maintain a degree of vacuum around r. Then, the crucible containing the raw materials is heated and the temperature is adjusted to achieve the desired vapor pressure. At this time, keep the cell shutter closed. Next, the substrate 1 is heated to a temperature for crystal growth, and each cell shutter is opened. As a result, the raw material flies to the substrate 1, and a semiconductor crystal grows on the substrate.

(Problems to be Solved by the Invention) Some of the residual impurities in the MBE-grown film are brought in from the raw materials, but they often depend on residual impurities in vacuum. Even in an ultra-high vacuum of about 10" Torr, there are H2O, CO1CO2, and hydrocarbons in addition to hydrogen, which makes up the majority of the vacuum. In particular, CO is generated from the substrate, the heater for heating the raw material, the raw material, and the substrate. , is difficult to be trapped even in ion pumps and liquid nitrogen shrouds,
A large number of them exist in the shroud and are incorporated into the grown film.

For example, in undoped GaAs, it becomes a P-type impurity and deteriorates the quality of the crystal. As described above, it is difficult to prevent residual impurities such as CO from being mixed in with the conventional MBE growth apparatus.

An object of the present invention is to provide an apparatus that prevents residual impurities from being mixed into a grown film during MBE growth and produces a film of high purity and quality.

(Means for Solving the Problems) The present invention provides a getter cell arranged in a growth chamber surrounded by a liquid nitrogen shroud so as not to face the substrate, and a getter cell that absorbs or absorbs residual impurities in a vacuum within the getter cell. This is a molecular beam crystal growth apparatus characterized by comprising a high-purity getter material that is easily absorbed and a getter surface onto which the getter material flies.

(Function) In the molecular beam crystal growth apparatus of the present invention, residual impurities that come out during heating of the substrate and during crystal growth are trapped on the getter surface by the active getter material, so that they do not enter the grown film. Uptake is drastically reduced. Therefore, a crystal grown film of high purity and high quality can be obtained.

(Example) Hereinafter, a molecular beam crystal growth apparatus according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram for explaining an embodiment of the molecular beam crystal growth apparatus according to the present invention. In FIG. The one shown in Fig. 2 is equivalent to the one shown in Fig. 2 and performs the same function. In FIG. 1, reference numeral 4 denotes a high-purity getter material, 5 a getter cell for discharging the getter material, and 6 a surface made of high-purity Mo formed as a getter surface for attaching the getter material.

A semi-insulating GaAs substrate is used as the substrate 1, and Ga is used as the raw material.
and using AI as As1 high purity getter material 4,
The procedure for crystal growth using the molecular beam crystal growth apparatus according to the present invention will be explained in detail.

First, the inside of the device is maintained at a vacuum level of approximately 10” Torr using an ultra-high vacuum pump and liquid nitrogen shroud 3. At this time,
The getter surface 6 is also in contact with the liquid nitrogen shroud so that it can be sufficiently cooled. Also, keep the main shutter in front of the board closed. In this state, the temperatures of Ga, As, and AI are raised and set to the desired temperature. At this time, residual impurities such as H2O1CoSC02 come out from the raw materials and the electric furnace heater, so the cell shutters in front of each crucible are left open so that they are gettered by A1 deposited on the getter surface.

When the residual impurity concentration in the device is reduced, the temperature of the substrate 1 is raised to a target temperature by the substrate heater. At this time, close the Ga cell shutter and open the main shutter. Since the getter cell 5 does not face the substrate, the getter material A1 does not reach the substrate.

As a result, the GaAs substrate is protected by the As beam while the substrate temperature is rising, and impurities coming out from the substrate heater and the substrate are gettered onto the getter surface 6 by Al.

When the oxide film on the surface of the GaAs substrate is blown off and the substrate reaches the growth temperature, the Ga cell shutter is opened to start growth.

Even during growth, the AI of the getter material flies to the getter surface 6, so any impurities remaining during growth are gettered onto the getter surface 6.
Incorporation into the grown film is small.

By using the molecular beam crystal growth apparatus of the present invention, the P-type impurity concentration in the GaAs grown film can be reduced to one quarter (2X 1
0"am' to 5 x 1013 cm-3).

As described above, in the embodiments of the present invention, only an electric furnace type cell is shown as a cell for discharging high purity getter material, but it is clear that other types of cells such as an electron beam heating cell may be used.

Further, although ALL was not shown as a high purity getter material, active elements such as Mn, Nd%Sc, Sm1Yb, etc. may also be used. In this example, molybdenum was formed as the getter surface, but other materials such as high-purity stainless steel may be used, and it is not necessarily necessary to provide a new getter surface, and the surface of the liquid nitrogen shroud may be used instead. You can also do it.

(Effects of the Invention) A semiconductor grown film of high purity and high quality was obtained using the molecular beam crystal growth apparatus of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view of the main parts of the molecular beam crystal growth apparatus of the present invention, and FIG. 2 is a diagram illustrating a conventional apparatus. 1... Substrate 2... Raw material cell 3... Liquid nitrogen shroud 4... High purity getter material 5... Getter cell 6... Getter surface 7... Growth chamber

Claims (1)

[Claims] A getter cell is placed in a growth chamber surrounded by a liquid nitrogen shroud of a molecular beam crystal growth apparatus so as not to face the substrate, and a high-purity getter material that easily adsorbs or absorbs residual impurities in a vacuum is provided in the getter cell. and a getter surface onto which the getter material flies.