JPH0685388B2 - Molecular beam epitaxial growth system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] In order to prevent the molecular beam emitted from the molecular beam source from directly hitting the sample, a plurality of heating walls coaxial with the cell and having similar shapes are provided inside the molecular beam source cell. , A molecular beam source cell having such a structure is provided.

Then, a strong molecular beam can be emitted, and the controllability of the emission intensity is improved.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molecular beam epitaxial growth apparatus, and more particularly to a structure of a cell (container) storing a molecular beam source.

As is well known, when manufacturing a semiconductor device, an epitaxy method of epitaxially growing a semiconductor film along a crystal substrate is used, which is the most basic technique of semiconductor manufacturing.

Of these epitaxy methods, the molecular beam epitaxy (MBE) method has recently been known. The molecular beam epitaxy method is a method of vapor deposition under ultra-high vacuum (10 Torr or less), which can maintain a clean crystal substrate surface. Therefore, epitaxial growth can be performed at low temperature, and the film thickness and impurity distribution can be reduced to several tens.
It is characterized by precise control at the level of Å single atom.

Further, the MBE method has an advantage that a heterojunction or a graded heterojunction of various elements or compound elements can be easily obtained, and is being widely used for epitaxial growth of compound semiconductors such as GaAs.

Although the MBE method has many advantages as described above, it is desired that the molecular beam has a high radiation intensity and good controllability.

[Problems to be Solved by Conventional Techniques and Inventions] FIG. 2 is a schematic view of the essential parts of the entire molecular beam epitaxial growth apparatus, where 1 is an ultra-high vacuum processing container, 2 is a sample (growth substrate), 3 is a molecular beam source cell, 4 is a cooling partition (liquid nitrogen shroud), 5 is a shutter, 6 is a cryopump, and 7 is a vacuum exhaust port.

When molecular beam epitaxial growth is performed on the substrate 2 to be grown using such a growth apparatus, the shutter 5 above the cell 3 in which a desired molecular beam source is stored is opened and the molecular beam source melted by a heater is used. A molecular beam is radiated (spouted) to grow epitaxially on the substrate to be grown. In the figure, a large number of cells are provided for one growth substrate 2, for example, for stacking various composition junctions on a GaAs substrate one after another, which is switched by opening and closing a shutter. To be

Of such a molecular beam epitaxial growth apparatus, a schematic cross-sectional view of a molecular beam source cell 3 is shown in FIG. 3, and the cell 3 of this example has a horn (Horn: Horn) made of a sintered boron nitride (PBN) material.
(Square) crucible, the heater is embedded inside the PBN material,
Molecular beam source (molecular beam material) L heated and melted by the heater
A molecular beam is radiated from the substrate 2 toward the growth substrate 2. The size of this horn-shaped crucible is, for example, 20 to 30 mm in diameter and 1 in length.
It is about 00 mm, and the buried heater is made of graphite or tantalum.

By the way, as shown in FIG. 3, the horn-shaped cell 3 has a structure in which most of the molecular beams are directly radiated to the surface of the substrate 2 to be grown. A strong molecular beam is emitted. On the other hand, there is a drawback that the stability and controllability of the molecular beam strength are not so good.

Therefore, as shown in FIG.
An orifice type cell 3'provided with one or more orifices (Orifice) H has been devised and used.
This orifice cell is also made of PBN material and has a heater embedded inside.

With such a structure of the orifice type cell 3 ', the stability and controllability of the molecular beam intensity are improved. However, if this is done, the radiant energy is reduced and the molecular beam intensity on the surface of the growth substrate 2 is high. There is a problem that you can not get.

The present invention proposes an epitaxial growth apparatus provided with a molecular beam source cell having a structure excluding such contradictory problems.

[Means for Solving the Problems] The purpose is to provide a molecular beam source cell having a horn shape, and a plurality of heating walls coaxial with the cell and having similar shapes are provided inside the cell so that This is solved by a molecular beam epitaxial growth apparatus equipped with a molecular beam source cell configured so that the emitted molecular beam does not directly contact the sample.

[Operation] That is, according to the present invention, a plurality of similar heating walls coaxial with the cell are provided inside the cell so that the molecular beam emitted from the molecular beam source does not directly contact the sample.

Then, the molecular beam is indirectly radiated to the growth substrate, and the molecular beam indirectly radiated to the growth substrate hits the heating wall and is re-radiated (re-evaporated). You can get the heating energy with to increase the strength,
The controllability is also improved by adjusting the heating energy.

[Examples] Hereinafter, examples will be described in detail with reference to the drawings.

1 (a), (b) and (c) are schematic views of a molecular beam source cell of a molecular beam epitaxial growth apparatus according to the present invention, wherein FIG. 1 (a) is a sectional view and FIG. 1 (b). Is a front view, and FIG. 30 shows the whole cell, 3W is the heating outer wall, and 3A, 3B, 3C are all horn-shaped (conical)
3 shows an internal heating wall that is coaxial with the outer wall and has a similar shape. Among them, the heating wall 3C has a closed tube shape like the heating outer wall 3W, and the heating walls 3A and 3B have a hollow shape with an open bottom. Both the heating outer wall and the heating wall are made of PBN material in which a heater is embedded, like the conventional horn-shaped cell,
The heater 31 is shown only in the external view shown in FIG. 1 (c). The dotted line shown in FIG. 1 (b) is the connecting portion of the heater, and the position of the internal heating wall is held by reinforcing the connecting portion and some other portion of the PBN material.

With such a structure of the molecular beam source cell, it is necessary to make the whole larger than the conventional horn-shaped molecular beam source cell 3 (see FIG. 3). However, the molecular beam housed in the molecular beam source cell 30 is required. The molecular beam emitted from the source L hits the heating walls 3A, 3B and 3C once or again without directly contacting the substrate 2 to be grown, and the molecular beam re-evaporated and re-emitted there is the substrate 2 to be grown. To reach epitaxial growth. Therefore, if the heaters provided on the heating walls 3A, 3B, and 3C are separately controlled separately from the heating outer wall 3W, the intensity of the molecular beam reaching the growth substrate 2 can be adjusted and its controllability can be improved. Can be improved.

According to the implementation results, when a GaAs crystal layer was grown on a GaAs substrate using the molecular beam epitaxial growth apparatus equipped with the molecular beam source cell shown in FIG. 1, a good quality GaAs crystal layer with few surface defects was obtained. Was given. At that time, the time change of the molecular beam intensity could be reduced to about half of the case of the conventional open horn cell 3 shown in FIG.

Therefore, according to the molecular beam epitaxial growth apparatus of the present invention, the strength and weakness of the molecular beam can be greatly adjusted and the controllability thereof can be remarkably improved.

Although the above is an example of the molecular beam source cell having three heating walls inside, the number of the heating walls is not limited.

[Effects of the Invention] As is clear from the above description, according to the molecular beam epitaxial growth apparatus equipped with the cell according to the present invention, the quality of the grown crystal is significantly improved, and the performance of the semiconductor device can be improved. it can.

[Brief description of drawings]

1 (a), (b) and (c) are schematic views of a molecular beam source cell of a molecular beam epitaxial growth apparatus according to the present invention, FIG. 2 is an overall schematic view of a molecular beam epitaxial growth apparatus, FIG. 3 and FIG. FIG. 4 is a sectional view of a conventional molecular beam source cell. In the figure, 1 is an ultra-high vacuum processing container, 2 is a substrate to be grown (sample), 3,
3 ', 30 is a molecular beam source cell, 4 is a cooling partition wall, 5 is a shutter, 6 is a cryopump, 7 is a vacuum exhaust port, 3W is a heating outer wall of the molecular beam source cell 30, 3A, 3B, 3C are molecular beam sources. A heating wall inside the cell 30, L indicates a molecular beam source, and 31 indicates a heater.

Claims (1)

[Claims] 1. A molecular beam source cell has a horn shape, and a plurality of heating walls coaxial with the cell and having similar shapes are provided inside the cell so that the molecular beam emitted from the molecular beam source is directly applied to a sample. A molecular beam epitaxial growth apparatus comprising a molecular beam source cell configured so as not to abut.