JP3630562B2 - Molecular beam epitaxy equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a molecular beam epitaxy apparatus, and more specifically, a molecular beam epitaxy which is a crystal growth apparatus for manufacturing an electronic device such as a HEMT (High Electron Mobility Transistor) and a light emitting device such as a semiconductor laser. Relates to the device.
[0002]
[Prior art]
As shown in FIG. 3, a vacuum chamber 2 which is a crystal growth chamber in a conventional molecular beam epitaxy apparatus has a manipulator 3 for holding, heating and rotating a substrate 4, a plurality of molecular beam cells 5, and molecules. A shutter is attached to control the supply of the wire to the substrate. Further, a shroud 20 that is cooled by liquid nitrogen is provided inside the vacuum chamber 2. The shroud 20 takes in unnecessary gas that interferes with crystal growth in the vacuum chamber 2, suppresses heat radiation from the manipulator 3 and the molecular beam cell 5, prevents degassing, and creates an ultra-high vacuum state.
[0003]
[Problems to be solved by the invention]
When the molecular beam epitaxy apparatus is undergoing crystal growth, the shroud 20 is cooled by filling an internal cavity with liquid nitrogen. However, when the crystal growth is completed, the supply of liquid nitrogen to the shroud 20 is stopped, and the liquid nitrogen is evaporated and removed. As the crystal growth proceeds, deposits are gradually formed on the inner wall surface of the shroud 20, but by repeating the crystal growth, a considerable amount of the deposits 6 on the shroud 20 is peeled off, and the molecular beam cell. It will fall to the vicinity.
[0004]
When deposits of the shroud 20 fall into the molecular beam cell 5, the quality of the growth film deteriorates in the crystal growth immediately after that. Specifically, a large number of defects occur, and the device characteristics are greatly adversely affected. Further, when the deposit of the shroud 20 falls in the very vicinity of the molecular beam cell 5, it is heated more gently than when it falls into the molecular beam cell 5, and the quality of the growth film in the subsequent crystal growth is changed to the molecular Although it is lighter than when shroud deposits fall inside the line cell 5, it will deteriorate over a long period of time.
[0005]
Further, as the number of times of crystal growth during one material filling or the time spent for crystal growth increases, the number of times the deposits of the shroud 20 fall increases, so that the quality of the grown film frequently deteriorates. Become. As shown in the graph of FIG. 4, as the growth time becomes longer, the phenomenon that the defect density on the growth surface increases more than in the normal case frequently occurs. This is presumably because the deposit on the inner wall of the shroud gradually thickens, so that it is easily peeled off and dropped by heating and cooling.
[0006]
From this point of view, the emergence of molecular beam epitaxy equipment in which deposits are difficult to peel off from the shroud in the vacuum chamber, which is the growth chamber, or the peeled off deposits do not fall into or near the molecular beam cell. It was desired.
[0007]
[Means for Solving the Problems]
The inventors of the present invention heated a desired molecule such as arsenic or gallium (or an atom, hereinafter referred to only as a molecule) to 300 ° C. to 1200 ° C. during crystal growth in a vacuum chamber to form a substrate from the molecular beam cell. As a result of considering the phenomenon that molecules cooled by the shroud and unnecessary gas around it solidify and adhere to the shroud, the surface area of the inner wall of the shroud is increased, that is, on the substrate facing surface of the shroud. It has been found that by making a certain inner wall surface an uneven shape rather than a simple flat surface, the adhesion density of molecules adhering to the inner wall surface of the shroud is reduced, thereby finding that the above problems can be solved, and the present invention has been achieved.
[0008]
Thus, according to the present invention, in the molecular beam epitaxy apparatus having the shroud provided in the vacuum chamber and cooled by liquid nitrogen, the inner wall surface of the shroud has an irregular shape , and the irregular shape of the inner wall surface is such that the convex portion is There is provided a molecular beam epitaxy apparatus characterized in that it has an acute angle and the top surface of the convex portion is horizontal or the protruding end side of the convex portion is positioned higher than the root side of the convex portion .
[0009]
According to this invention, since the surface area of the inner wall surface, which is the substrate facing surface of the shroud, is increased, the density of the deposits is reduced, which makes it difficult for the shroud deposits to peel off and fall. Further, even if the deposits are peeled off from the irregular shape of the inner wall surface of the shroud and fall off, they stay on the shroud and do not fall inside or near the molecular beam cell.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, a vacuum chamber corresponding to the size of the substrate on which the crystal is grown is applied, but generally a hemispherical shape having a diameter of, for example, about 1 m is applied.
[0011]
The shroud is provided along the inner wall of the vacuum chamber and about 10 cm away from the inner wall of the vacuum chamber. Thus, the shroud is one size smaller than the vacuum chamber, and if the vacuum chamber is hemispherical with a diameter of 1 m, the shroud has a hemispherical shape with a diameter of about 80 cm.
[0012]
A molecular beam cell for supplying molecules to the substrate is attached to the vacuum chamber. The molecular beam cell is provided through the shroud and is arranged with an opening for supplying molecules directed toward the substrate. The opening surface is almost the same height as the inner wall surface of the shroud, and the diameter of the opening is about 10 cm in the size of the above vacuum chamber.
[0013]
A crucible is provided inside the molecular beam cell, and the material is electrically heated in the crucible and radiated to the substrate from the opening of the molecular beam cell. Any known material can be applied.
[0014]
The shroud has a cavity inside, and the crystal is filled with liquid nitrogen and cooled during crystal growth. When the crystal growth is completed, the supply of liquid nitrogen to the shroud is stopped, and the liquid nitrogen is evaporated and removed. As the liquid nitrogen filled in the shroud, known ones can be used.
[0015]
The inner wall surface of the shroud means the substrate facing surface of the shroud. The concavo-convex shape formed on the inner wall surface of the shroud may be any shape that can widen the adhesion area of the deposit so that the deposit does not peel or fall.
[0016]
The irregular shape of the inner wall surface of the shroud is preferably a shape in which the convex portion forms an acute angle, the upper surface of the convex portion is horizontal, or the protruding end side of the convex portion is positioned higher than the root side of the convex portion. .
[0017]
The present invention will be described in detail below based on the embodiments shown in the drawings. However, this does not limit the present invention.
[0018]
Example 1
A first embodiment of the present invention will be described with reference to FIG.
In the molecular beam epitaxy apparatus of this embodiment, a shroud 1 cooled with liquid nitrogen is provided in a vacuum chamber 2. The vacuum chamber 2 is in a vacuum state of about 1.33 × 10 ⁻⁸ Pa . The shroud 1 has almost the same shape as the vacuum chamber 2 and is slightly smaller in size. A manipulator 3 is provided at the center of the upper portion of the vacuum chamber 2, and the manipulator 3 can hold, heat, and rotate the substrate 4.
[0019]
The size of the vacuum chamber 2 varies depending on the size of the substrate 4 on which the crystal is grown, but in this embodiment, a vacuum chamber 2 having a cylindrical portion having a diameter of about 1 m and a hemispherical bottom portion is used.
[0020]
The shroud 1 is provided along the inner wall of the vacuum chamber 2 and about 10 cm away from the inner wall of the vacuum chamber 2. Therefore, the shroud 1 has a shape including a cylindrical portion having a diameter of about 80 cm and a hemispherical bottom portion.
[0021]
A molecular beam cell 5 for supplying molecules to the substrate 4 is attached to the vacuum chamber 2. The molecular beam cell 5 is disposed through a hole for passing the molecular beam cell 5 opened in the shroud 1.
[0022]
Ten molecular beam cells 5 are attached so that a plurality of types of materials can be simultaneously supplied to the substrate 4. In general, it is considered most efficient to supply the material from a direction perpendicular to the substrate 4. However, when the material is supplied from a direction perpendicular to the substrate 4, one molecular beam cell 5 is provided. Can only be placed. For this reason, a plurality of molecular beam cells 5 are arranged on a concentric circle centered on the substrate 4 so that the distances from the molecular beam cells 5 to the substrate 4 are equal, and the material is obliquely oriented with respect to the substrate 4. I am trying to supply. In the present embodiment, ten molecular beam cells 5 are arranged in a circular shape centering on the bottom top of the vacuum chamber 2 (in the figure, only one molecular beam cell 5 is shown and the others are omitted). ing).
[0023]
The molecular beam cell 5 is arranged with an opening 5 a for supplying molecules directed toward the substrate 4. This opening surface is almost the same height as the inner wall surface 1a of the shroud 1, and the diameter of the opening 5a is about 10 cm.
[0024]
A crucible is provided inside the molecular beam cell 5, and before the crystal growth operation, the vacuum chamber 2 is opened and the crucible is filled with a material. The material is heated to 300 ° C. to 1200 ° C. by an electric heating device in the crucible and radiated to the substrate from the opening 5a of the molecular beam cell 5.
[0025]
The crucible is inside the opening 5a, and some of the heated materials are in a molten state. For example, since gallium has a melting point of about 30 ° C., it is in a molten state when heated. Therefore, since the material flows out if the opening 5a of the molecular beam cell 5 is downward, the molecular beam cell 5 is arranged with the opening 5a facing upward, and the material is emitted from the lower side with respect to the substrate 4. ing.
[0026]
Supply of the material to the molecular beam cell 5 is appropriately performed according to the amount used. For example, depending on the size of the substrate 4 and the growth amount of the crystal, the material is supplied every use for about 400 hours to 500 hours. Since the operation time for one crystal growth is about 1 to 4 hours, the material is supplied every about 100 to 400 operations. Any known material can be applied.
[0027]
The shroud 1 has a cavity with a diameter of 5 cm to 10 cm inside, and when the molecular beam epitaxy apparatus is growing a crystal, the cavity is filled with liquid nitrogen and cooled. When the crystal growth is completed, the supply of liquid nitrogen to the shroud 1 is stopped, and the liquid nitrogen is evaporated and removed. As the liquid nitrogen filled in the shroud 1, known ones can be used.
[0028]
As the crystal grows, deposits are gradually formed on the inner wall surface 1a of the shroud 1. For this reason, the inside of the vacuum chamber 2 is cleaned every time the material is supplied, and the deposits adhered to the inner wall surface 1a of the shroud 1 and the deposits falling on the bottom of the shroud 1 are removed.
[0029]
Since the deposit on the shroud 1 has a size of several centimeters, the shroud 1 may fall and enter the opening 5 a of the molecular beam cell 5. Thus, the deposit on the shroud 1 is inside the molecular beam cell 5. When entering, the quality of the growth film deteriorates in the crystal growth immediately after that. Specifically, a large number of defects occur, and the device characteristics are greatly adversely affected.
[0030]
In order to cope with this, the inner wall surface 1a which is the substrate facing surface of the shroud 1 has an uneven shape, and the unevenness of the inner wall surface 1a prevents peeling and falling of the deposits. That is, the unevenness functions to increase the surface area of the inner wall surface 1a, thereby reducing the amount of deposit per unit area of the deposit (thinning the deposit). As described above, the adhering matter has a size of several centimeters. Therefore, the unevenness may have a height of several centimeters to several tens of centimeters.
[0031]
The unevenness may be formed uniformly on the entire inner wall surface 1 a of the shroud 1, or may be formed around the opening 5 a of the molecular beam cell 5. When forming around the opening 5a, it is desirable to form an unevenness so as to surround the opening 5a with a protrusion higher than the height of the opening 5a. In this case, the projections and depressions may be formed so that the projections protrude outward from the opening 5a.
[0032]
When unevenness is formed around the opening 5a of the molecular beam cell 5, the unevenness may be formed so as to surround the opening 5a in a double or triple manner.
Further, it is possible to observe which part of the inner wall surface 1a of the shroud 1 is likely to fall, and to form the irregularities only in the part that easily falls.
[0033]
In the case where the inner wall surface 1a of the shroud 1 is provided with unevenness, the inner wall surface 1a located below the opening 5a of the molecular beam cell 5 does not need to be provided with unevenness, but the area of the entire inner wall surface 1a of the shroud 1 is increased. In view of this, the inner wall surface 1a located below the opening 5a may be uneven.
[0034]
According to the present embodiment, as the crystal grows, deposits are gradually formed on the inner wall surface 1a of the shroud 1. Compared with the shape of the conventional shroud 20 shown in FIG. The inner wall surface 1a of the shroud 1 of the present invention to be shown has a large surface area due to the uneven shape, and the thickness of the deposit is reduced.
[0035]
Therefore, in comparison with the conventional case, the deposit 6 peeled off from the shroud has dropped in the molecular beam cell 5 or in the vicinity of the molecular beam cell 5, but in this example, the deposit on the shroud 1 becomes difficult to peel off. The fall of the deposit can be suppressed.
[0036]
That is, if the amount of material used is the same, the thickness of the deposit will be reduced by the increase in surface area, so the probability of falling due to the weight of the deposit will be reduced, and thereby the inside of the molecular beam cell or in the vicinity thereof. It is possible to suppress the generation of a large number of defects in the growth film due to the fall of the deposit on the surface.
[0037]
Example 2
A second embodiment of the present invention will be described with reference to FIG.
In the molecular beam epitaxy apparatus of the present embodiment, the inner wall surface 10a of the shroud 10 in the vacuum chamber 2 has an uneven shape in which the convex portion forms an acute angle. The upper surface 10b of the convex portion is horizontal. The convex portion may have a shape such that the protruding end side of the convex portion is positioned higher than the root side of the convex portion. Other configurations are the same as those of the first embodiment.
[0038]
Also in this example, since the surface area of the inner wall surface 10a of the shroud 10 is increased as in the first embodiment, the thickness of the deposit is reduced. In addition, even if the deposits are peeled off from the lower surface 10 c of the convex portion of the inner wall surface 10 a of the shroud 10 and dropped, the deposits remain on the upper surface 10 b of the convex portion of the shroud 10 and fall on the molecular beam cell 5. There is nothing.
[0039]
In this way, by increasing the surface area of the inner wall surface of the shroud and reducing the amount of adhesion (thickness) per unit area, it is possible to prevent the deposit from falling due to its own weight. Alternatively, it is possible to suppress the generation of a large number of defects in the growth film due to the fall of the deposits in the vicinity.
[0040]
In the present embodiment, the molecular beam epitaxy apparatus of the type in which the substrate is disposed downward and the material is supplied from the lower side to the substrate is taken as an example. However, there are various molecular beam epitaxy apparatuses. There are various types of mounting methods and materials. However, as described above, since the molecular beam cell is always arranged upward, no matter what the shape of the shroud is, shroud deposits may enter the molecular beam cell or the molecular beam cell. There is a possibility that deposits on the shroud will fall in the vicinity.
[0041]
Therefore, any type of molecular beam epitaxy apparatus with the molecular beam cell facing upward and the shroud disposed in the vacuum chamber and having such a risk of falling deposits can be used. The present invention can be applied.
[0042]
【The invention's effect】
According to the present invention, it is difficult for the deposits to be peeled off from the shroud and fall off, and even if dropped, the deposits do not fall into or near the molecular beam cell, so that adverse effects on the film quality of the growth layer can be prevented.
[Brief description of the drawings]
FIG. 1 is a schematic view of a molecular beam epitaxy apparatus according to Embodiment 1 of the present invention.
FIG. 2 is a schematic view of a molecular beam epitaxy apparatus according to Embodiment 2 of the present invention.
FIG. 3 is a schematic view of a conventional molecular beam epitaxy apparatus.
FIG. 4 is a graph showing the relationship between the time spent for crystal growth and the defect density on the crystal growth surface in the prior art.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1,10 Shroud 1a, 10a Inner wall surface 10b of shroud Upper surface 10c of convex part of inner wall surface of shroud Lower surface 2 of convex part of inner wall surface of shroud Vacuum chamber 3 Manipulator 4 Substrate 5 Molecular beam cell

Claims (2)

In a molecular beam epitaxy apparatus having a shroud provided in a vacuum chamber and cooled by liquid nitrogen, the inner wall surface of the shroud has an irregular shape , and the convex and concave shape of the inner wall surface has an acute angle, and the convex portion The molecular beam epitaxy apparatus is characterized in that the upper surface of the projection is horizontal or the protruding end side of the convex portion is positioned higher than the base side of the convex portion . The molecular beam epitaxy apparatus according to claim 1, wherein the shroud is provided with an opening for a molecular beam cell, and the uneven shape of the inner wall surface of the shroud is provided above the opening for the molecular beam cell.

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