JPS63282189A - Molecular beam epitaxial growth device - Google Patents

Abstract

PURPOSE:To stably grow the crystal layer of high quality having few defects in the surface of growth layer by using a molecular beam source cell consisting of a cylindrical main crucible provided with a reverse cone-shaped guide tube with a built-in heater so as to confront the open part of main crucible with the base plate to be used for growing. CONSTITUTION:The molecular source cell 3 for the molecular beam epitaxial growth device consists of the reverse cone-shaped guide tube 21 made of PBN and the cylindrical main crucible 20 with the guide tube 21 fitted to the open part. The guide tube 21 is constructed in a sandwich structure with the built-in heater 21H consisting of carbon in the center part so as to heat the whole body of the guide tube. Plural molecular beam source cells 3 with the main crucible charged with a source material S are disposed with shroud 4 between in a high vacuum treatment vessel 1 so as to confront each open part of main crucible with the base plate 2 to be used for growing, and the source material S is heated and melted by a heater 22 provided with a thermostat T1, while the guide tube 21 is heated by the heater 21H and controlled through a thermostant T2 to keep the projecting quantity of molecular beam to be in a constant rate preventing the open part from cooling, and the crystal layer stably grows on the rotating base plate 2.

Description

[Detailed description of the invention] [Summary] A molecular beam source cell placed in a molecular beam epitaxial growth apparatus has a structure in which an inverted conical guide tube with a built-in heater is attached to the opening of a cylindrical main crucible. Make it.

By doing so, surface defects in the growth layer are reduced and the crystal layer can be grown stably.

[Industrial Field of Application] The present invention relates to a molecular beam epitaxial growth apparatus, and particularly to the structure of a cell (container) storing a molecular beam source.

As is well known, when manufacturing a semiconductor device, an epitaxy method is known in which a semiconductor film is epitaxially grown along a crystal substrate, and this is the most basic technology for semiconductor manufacturing.

In such epitaxy methods, molecular beam epitaxy (MBE) has recently been used.
am Epitaxy) method has been developed, and this molecular beam epitaxy is a method of growing under high vacuum (10 Torr or less), and since a clean crystal substrate surface can be maintained, epitaxial growth can be performed at low temperatures, and, This method is unique in that it allows precise control of film thickness at the level of several dozen single atoms.

Furthermore, the MBE method has the advantage that heterojunctions of various elements or compound elements can be easily obtained, and is considered to be an optimal method for forming steep junction structures in compound semiconductor devices such as GaAs.

Although the MBE method has many advantages as described above, there are problems in that the growth rate is unstable and surface defects are likely to occur, and countermeasures against these problems are strongly desired.

[Problems to be solved by the prior art and the invention] Figure 2 shows a schematic diagram of the main parts of the entire molecular beam epitaxial growth (MBE) apparatus, in which 1 is a high vacuum processing chamber, 2 is a substrate to be grown (wafer), and 1 is a high vacuum processing chamber; ), 3 is a molecular beam source cell, 4 is a cooling partition (
(liquid nitrogen shroud), 5 is a shutter, and 6 is a vacuum exhaust port.

When performing molecular beam epitaxial growth on the growth target substrate 2 using such an MBE apparatus, the shutter 5 above the molecular beam source cell 3 storing the desired molecular beam source is opened, and the molecules melted by the heater are opened. Molecular beams are emitted from a radiation source to cause epitaxial growth on a growth substrate. As shown,
A large number of cells are provided for one growth substrate 2, and for example, crystal layers of various compositions are grown on a GaAs substrate, and multiple crystal layers are bonded and grown one after another. This is done by opening and closing the shutter.

A cross-sectional view of a molecular beam source cell in such an MBE apparatus is shown in FIG. (
It consists of a crucible (crucible) 11 and a Kanthal-wound heater 12 placed around the crucible, and generates molecular beams by heating and melting the molecular beam source (source material) in the crucible and vaporizing it. Note that S indicates an arbitrary surface position of the source material, and T is a thermocouple for temperature measurement.

Further, FIG. 4 illustrates the relative positions of the molecular beam source cell and the growth target substrate in the MBE apparatus. As shown in the figure, the center of the molecular beam source cell is directed toward the center of the growth substrate, and this positional relationship determines the diameter of the region of uniform thickness that will grow on the growth substrate surface. That is, the diameter is expressed by the relational expression D=k (A+2L tanθo)/cosθ (see Japanese Patent Laid-Open No. 59-211225), where: proportionality constant; L: distance between the cell and the substrate.

68 Angle between molecular beam center and substrate.

A: aperture diameter of the cell, θ0: aperture angle of the cell. Conventionally, MBE apparatuses have been designed with reference to this formula.

Moreover, from this equation, it is clear that the area where the grown film thickness is uniform changes depending on the shape of the molecular beam source cell. Also,
Analyzing this equation, we find that in order to increase the diameter, θ is required.

It is necessary to increase θ0, and the consumption of the source material in the crucible increases the variation in the surface area of the source material, thus reducing the amount of molecular beam, i.e.
It can be seen that there is a drawback that the growth rate varies greatly.

On the other hand, surface defects peculiar to MBE occur in a crystal layer grown by an MBE apparatus, and these defects are thought to be caused by source spitting from a molecular beam source cell and oxidation of the source material.

Of these, oxidation of the source material can be avoided by sufficiently degassing the source, but bifting is difficult to avoid with the conventional molecular beam source cell shape. The reason for this source spitting is that as the temperature at the opening of the molecular beam source cell decreases, the source adheres to the opening, forms a lump, and reaches the growth substrate. The defects on the substrate caused in this way are called oval defects.
A defect (egg-shaped defect) is closely related to performance deterioration of semiconductor devices.

The present invention proposes an MBE apparatus equipped with a molecular beam source cell for reducing such surface defects and fluctuations in growth rate.

[Means for solving the problem] The purpose is to provide an inverted conical guide tube with a built-in heater in the opening of a cylindrical main crucible, and to This is accomplished by an MBE device equipped with a source cell.

[Function] That is, the MBE apparatus according to the present invention includes a molecular beam source that includes a cylindrical main crucible and an inverted conical (funnel-shaped) guide tube with a built-in heater attached to the opening of the main crucible. Set up a cell.

By doing so, surface defects in the grown layer are reduced and the growth rate is also stably stabilized.

[Example] An embodiment will be described in detail below with reference to one drawing.

FIG. 1 shows a cross-sectional view of a molecular beam source cell of an MBE apparatus according to the present invention, in which 20 is a main crucible containing a source material, 21 is an inverted conical guide tube with a built-in heater, and 22
is a heater made of tantalum winding.

'r, , T2 is a thermocouple for temperature measurement. In the same figure, the main crucible 20 corresponds to the conventional horn-shaped crucible 11, and in this example, the shape is cylindrical. However, if this shape is adopted, the source material inside the main crucible 20 is consumed and the source material Even if the position of the surface S of is lowered, its surface area does not change. This has the advantage that the amount of molecular beam radiation does not change and the growth rate remains constant. Furthermore, this main crucible 20
is not limited to a cylindrical shape, but may have any other cross-sectional shape as long as it is a cylindrical shape whose surface area does not change depending on the consumption of the source material as described above.

Further, the guide tube 21 has the shape of an inverted conical tube and is configured to be fitted into the opening of the main crucible 20 so that the opening faces the growth substrate (see FIG. 4). and,
This guide cylinder 21 is made of PBN like the main crucible 20, and has a sandwich structure with a heater 21H made of carbon sandwiched in the center, and the whole is heated by the heater.

Thus, the source material in the main crucible 20 is transferred to the heater 22.
The temperature is monitored and controlled using a thermocouple Tx, thereby controlling the amount of molecular beams emitted. On the other hand, the guide cylinder 21 is heated by the heater 21H,
Its temperature is monitored and controlled by thermocouple T2, thereby preventing cooling of the opening.

If such a molecular beam source cell structure is used and it is installed in an MBE device, even if the source material in the main crucible is consumed, its surface area will not change, and the amount of molecular beam radiation will remain unchanged. Since the guide cylinder 21 at the opening is heated at a constant temperature, the problem of spifting, where the source adheres to the opening and reaches the growth substrate in the form of a lump, is also solved. Therefore, there is a significant effect that the growth rate of the crystal layer is stabilized and surface defects on the growth substrate are reduced.

According to experimental results, in order to grow a GaAs layer, in a molecular beam source cell containing Ga as a source material,
When a GaAs layer was grown with the main crucible temperature measured by thermocouple T1 at 1000°C and the sub-crucible temperature measured by thermocouple T2 at 1100°C, the surface defects were reduced to one-tenth. , the stability of molecular beams was also significantly improved.

Moreover, if such a molecular beam source cell is used, the degree of freedom in the shape of the main crucible is increased, and a larger capacity crucible can be used to increase the amount of source material, making it possible to use the cell for a long time.

Therefore, by using the MBE apparatus according to the present invention, a high quality crystal layer can be grown.

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

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a molecular beam source cell of an MBE apparatus according to the present invention, Fig. 2 is an overall schematic diagram of the MBE apparatus, Fig. 3 is a cross-sectional view of a conventional molecular beam source cell, and Fig. 4 is a cross-sectional view of a molecular beam source cell of the MBE apparatus according to the present invention. It is a figure showing the relative position of a substrate and a molecular beam source cell. In the figure, 1 is a high vacuum processing container, 2 is a growth substrate (wafer), 3 is a molecular beam source cell, 11 is a crucible, 12 and 22 are heaters, 20 is a main crucible, 21 is a guide tube, and 2LH is a guide tube The heater T, TI, and T2 indicate thermocouples. Patent applicant: Director of the Agency of Industrial Science and Technology Yuki Iizuka Sanbon Invention (;
So Ji Bunji Tougeri and Le Hikimen m Figure 1 MBE Ai! /lR fist figure 2

Claims (1)

[Claims] A molecular beam characterized in that an inverted conical guide tube with a built-in heater is provided at the opening of a cylindrical main crucible, and a molecular beam source cell is provided with the opening facing a growth substrate. Epitaxial growth equipment.