JPH05315250A - Molecular beam crystal growing apparatus - Google Patents

Abstract

PURPOSE:To provide a molecular beam crystal growing apparatus which prevents adherence of liquid droplet of a molecular beam source material to a crucible to cause a defect at the time of growing a crystal. CONSTITUTION:The molecular beam crystal growing apparatus comprises a crucible 1 to be filled with a molecular beam source material 8, a cylindrical liquid droplet adhering cover 2 disposed on an upper part of the crucible 1 in contact with an inner wall periphery of the crucible 1 at its lower end and opened at its lower and upper bottoms, heaters 3a, 3b for heating the crucible 1, and moving mechanisms 4a, 4b for raising the cover 2 to remove it from the crucible 1. Further, the cover 2 has a collar 2a at its upper bottom and each moving mechanisms has a moving rod 4a for raising the collar 2a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molecular beam crystal growth apparatus, and more particularly to the structure of a molecular beam source cell. The molecular beam crystal growth apparatus is an apparatus for growing a thin film epitaxial layer under ultra-precision control, and can form a large area thin film epitaxial layer at low temperature.

In recent years, as semiconductor devices have become faster, integrated circuits using compound semiconductors, such as GaAs ICs, have been used.
Is being developed. Such an IC requires an epitaxial wafer with few surface defects.

[0003]

2. Description of the Related Art FIG. 3 is a schematic view of a molecular beam crystal growth apparatus in which a part of a vacuum container is cut away, and 13 is a vacuum container.
14 is the first knudsen cell, 15 is the second knudsen cell, 16a and 16b are substrates, 17 is a substrate holder, 18 is a substrate heater, 19 is a support, 20 is a substrate heater terminal, and 21 is rotating. Represents an introducer. The first Knudsen cell 14 and the second Knudsen cell 15 are equipped with a molecular beam source for growing the substrates 16a and 16b.

FIG. 2 is a schematic diagram for explaining a conventional molecular beam crystal growth apparatus, which is the first Knudsen cell of FIG.
14 or the internal details of the second Knudsen cell 15 are shown. In the figure, 1 is a crucible, 3a is an upper heater, 3b is a lower heater, 5 is a cell shutter, 6a is an upper thermocouple, 6b is a lower thermocouple, 7 is a heat shield, 8 is a source and a molecular beam source material, 10 is a stand, 11 is a flange, 12 is a shroud, and 13 is a vacuum vessel.

In a molecular beam crystal growth apparatus using a solid material as an evaporation source, after filling the crucible 1 with the material, vacuuming is performed in order to remove the impurity gas contained in the material and the gas adsorbed during filling, and then the cell With the shutter 5 closed, the material is heated by the upper heater 3a and the lower heater 3b to degas.

By the way, when the material is gallium, the gallium source adheres to the opening of the crucible (the inner wall of the upper part of the crucible) having a low temperature as droplets when degassing. After that, the cell shutter 5 is opened and, for example, G
When aAs is epitaxially grown, surface defects due to the droplets occur. This surface defect is called an oval defect, and usually has a diameter of several μm. In order to manufacture a GaAs IC, an epitaxial wafer grown without generating gallium source droplets is first required.

Therefore, the temperature of the upper heater is made higher than the temperature of the lower heater to prevent the generation of droplets, but it is difficult to completely eliminate the generation of droplets up to the tip of the crucible opening. If the temperature is raised too high, there is a problem that the gallium source itself is greatly reduced.

[0008]

In view of the above problems, the present invention provides a molecular beam crystal growth apparatus capable of removing a droplet even when a source is degassed and removing the droplet to perform crystal growth. The purpose is to

[0009]

FIG. 1 is a schematic view for explaining a molecular beam crystal growth apparatus of the present invention. The above-mentioned problem is a crucible 1 into which a molecular beam source material 8 is inserted, and a cylindrical droplet attachment cover which is arranged on the upper part of the crucible 1 with its lower end in contact with the inner wall periphery of the crucible 1 and whose lower and upper bases are open. 2, heaters 3a and 3b for heating the crucible 1, and a moving mechanism 4 for lifting the droplet attaching cover 2 and removing it from the crucible 2.
It is solved by a molecular beam crystal growth apparatus having a and 4b.

Further, the droplet attaching cover 2 has a collar 2a on the upper bottom, and the moving mechanism is solved by a molecular beam crystal growth apparatus having a moving rod 4a for lifting the collar 2a.

[0011]

In the molecular beam crystal growth apparatus of the present invention, a cover 2 for depositing droplets, which has a cylindrical shape with an open lower bottom and an upper bottom, is provided on the upper part of the crucible 1 with its lower end in contact with the inner wall of the crucible 1. ing. When the crucible 1 is charged with the molecular beam source material and degassed, if the lower end of the droplet attachment cover 2 is brought close to the molecular beam source material, droplets
Adheres to the droplet adhesion cover 2 and does not adhere to the crucible 1.

After the degassing is completed, the moving mechanism 4a, 4b lifts the droplet attaching cover 2 from the crucible 1 and moves it from the upper part of the crucible 1 to the outside, and then the shutter 5 is opened to open the crucible 1 on the substrate. By applying the molecular beam emitted from the inside, it is possible to prevent the generation of growth defects due to the droplets.

The cover 2 for depositing liquid drops has a brim 2a on the upper bottom.
And the moving mechanism is a moving rod 4a for lifting the brim 2a.
With this structure, the moving rod 4a can be moved upward to move the droplet attaching cover 2 above the crucible 1.
The knudsen cell is inclined as shown in FIG. 3, and the moving rod 4a lifts the droplet attaching cover 2 obliquely upward, so the droplet attaching cover 2 is taken out of the crucible 1. After that, it can be dropped on the bottom of the vacuum container 13.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view for explaining a molecular beam crystal growth apparatus of the present invention, and the reference numerals are the same as those in FIG. further,
Reference numeral 2 is a cover for depositing droplets, 2a is a collar, 4a is a moving mechanism and a moving rod, and 4b is a moving mechanism and a linear introducer.

The Knudsen cell containing the crucible 1 is electrically insulated from the vacuum container 13. The crucible 1 is, for example, PBN (Pyro Boron Nitride), and an upper thermocouple 6a and a lower thermocouple 6b are arranged at the opening and the bottom thereof, respectively.

An upper heater 3a and a lower heater 3b for heating the crucible 1 are arranged in the knudsen cell, and the power supply is controlled by a PID temperature controller and a DC stabilization via the upper thermocouple 6a and the lower thermocouple 6b. Use the power supply.

An example of epitaxially growing GaAs on a GaAs substrate will be described with reference to FIGS. 1 and 3. The flange 11 is removed, the vacuum container is opened, the crucible 1 containing the gallium source 8 is attached to the Knudsen cell in the atmosphere, and then the flange 10 is fixed to the vacuum container 13.

The droplet attachment cover 2 is inserted into the crucible 1 from the hatch (see FIG. 3) above the vacuum container. At this time, the cell shutter 5 is open. The cover 2 for depositing droplets is made of, for example, PBN, and its shape has a cylindrical portion having an open upper bottom and a lower bottom, and further has a collar 2a on the upper bottom.

The lower end of the droplet attaching cover 2 is in contact with the inner wall of the crucible 1 so that the gallium source 8 is about 1 mm above the liquid surface in the molten state. At this time, the tip of the moving rod 4a of the moving mechanism is retracted so as not to interfere with the insertion of the droplet attaching cover 2 into the crucible 1.

Although not shown, another Knudsen cell is loaded with an arsenic source. Further, the GaAs substrates 16a and 16b are mounted on the substrate holder 17. The chamber is evacuated to a pressure of 3 × 10 ⁻⁷ Torr in the vacuum container 13. The cell shutter 5 is closed, and the upper heater 3a heats the opening to about 1100 ° C.
The electric power of the lower heater 3b was adjusted so that the bottom was 50 ° C. lower than the opening, and the gallium source 8 was degassed for 9 hours. Gallium droplets were generated on the droplet attachment cover 2,
No droplets were generated in the crucible 1.

Further, when the upper heater 3a and the lower heater 3b were wired in series and degassing was performed at about 1100 ° C. for 9 hours, a droplet of gallium was produced on the droplet attaching cover 2, but the crucible No droplets were generated in 1.

After the degassing is completed, the moving rod is moved by the straight line introduction device 4b.
4a was extended upward and the brim 2a of the droplet attaching cover 2 was lifted, the droplet attaching cover 2 was removed from the crucible 1 and dropped onto the bottom of the vacuum container 13.

The arsenic source was degassed at 250 ° C. for 2 hours. In this case, since droplets are not generated, it is not necessary to attach the droplet attachment cover. Next, the upper heater 3a opens the opening at 1000 ° C, and the lower heater 3b opens the bottom at 850 ° C.
And an arsenic source (not shown) to 200 ° C. Further, the temperature of the GaAs substrates 16a and 16b was set to 680 ° C. Open the cell shutter 5 (also open the cell shutter for the arsenic source), and apply the gallium molecular beam and the arsenic molecular beam while rotating the substrates 16a and 16b by the rotation introducing device 21.
A 5000 Å GaAs layer was grown in minutes.

Oval defect density of the GaAs growth layer is 10
It was less than the number of pieces / cm ² . By the way, the droplet attachment cover 2
In the conventional method in which the GaAs is not arranged, the density of oval defects in the GaAs growth layer is about several tens / cm ² .

[0025]

As described above, according to the molecular beam crystal growth apparatus of the present invention, even if droplets are generated when the molecular beam source material 8 is degassed, they are attached to the droplet attachment cover 2. Therefore, it is possible to prevent droplets from being generated on the inner wall of the crucible 1. After degassing, the droplet attachment cover 2 to which the droplets are attached is removed from the crucible 1 and moved to the outside, and then molecular beam crystal growth is performed to prevent the oval defect from occurring in the growth layer.

Further, since droplets may be generated during degassing, it is not necessary to excessively heat the source, and there is an effect that the reduction of the source during degassing is reduced. According to the molecular beam crystal growth apparatus of the present invention, a compound semiconductor epitaxial wafer with extremely few surface defects can be supplied.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining a molecular beam crystal growth apparatus of the present invention.

FIG. 2 is a schematic diagram for explaining a conventional molecular beam crystal growth apparatus.

FIG. 3 is a schematic view of a molecular beam crystal growth apparatus.

[Explanation of symbols]

 1 is a crucible 2 is a cover for depositing droplets 2a is a collar 3a, 3b is an upper heater, a lower heater 4a is a moving mechanism, a moving rod 4b is a moving mechanism, and a linear introducer 5 is a shutter. The cell shutters 6a and 6b are an upper thermocouple and a lower thermocouple 7, respectively, and a heat shield 8 is a molecular beam source material and is a source, and a gallium source 10 is a base 11 a flange 12 a shroud 13 a vacuum container 14 Nude sencel, first kunudesencel 15 is kunudesencel, second kunudesencel 16a, 16b is a substrate, GaAs substrate 17 is substrate holder 18, substrate heater 19 is supported The base 20 is the substrate heater terminal 21 is the rotation introducer

Claims (2)

[Claims] 1. A crucible (1) for containing a molecular beam source material (8)
The crucible (1) with its lower end in contact with the inner wall of the crucible (1)
A cylindrical droplet cover (2), which is arranged at the top and has an open bottom and a bottom, and a heater (3a, 3a, which heats the crucible (1).
3b) and the cover (2) for adhering the droplets are lifted to bring the crucible
A molecular beam crystal growth apparatus having a moving mechanism (4a, 4b) for removing from (1). 2. The droplet attaching cover (2) has a brim on the upper bottom.
2. The apparatus for growing a molecular beam crystal according to claim 1, further comprising (2a), wherein the moving mechanism has a moving rod (4a) for lifting the collar (2a).