JPS5945994A - Crucible for epitaxial growth of molecular beam - Google Patents

Abstract

PURPOSE:The titled crucible useful for a substance such as As, etc. havng high vapor pressure, obtained by providing the interior of the main body of a crucible with a bottom with a cover having an opening to adjust an angle of aperture of molecular beam of the substance having high vapor pressure at a given position of the interior. CONSTITUTION:The cover 7 having the opening 7a to adjust an angle of aperture of molecular beam of a substance (e.g., As, etc.) having high vapor pressure is set at a given position of the interior of the main body 6 of a crucible with a bottom. In an exising structure wherein an opening is set at the heat of crucible, making the distribution of the angle of molecular beam constant is incompatible with reduction in the molecular beam wastefully evaporating to parts other than a substrate. On the contrary, since this crucible is provided with the cover 7 having the opening 7a in the interior of the crucible, molecular beam having <=10 deg. angle is not collided to the crucible wall extended on the cover 7 having the opening, reached directly to the substrate, parts having a large angle of aperture are collided to the crucible wall part extended on the cover having the opening, reflected, and sent in the substrate direction, so that >=10 times as much dose of molecular beam as that of the existing molecular beam is reaced to the substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a crucible that is a component of a molecular beam source used in molecular beam epitaxial growth (MBE), which is one of the methods for growing compound semiconductor thin films.

The MBE (molecular beam epitaxial growth) method is mainly used for producing thin films of compound semiconductors such as GaAs. M
In the BE method, a molecular beam source is provided for each element constituting the thin film in an ultra-high vacuum, and the temperature of each molecular beam source is controlled to evaporate the molecules, which adhere to a heated substrate and form the desired shape. Grow a thin film of the composition. As shown in cross-section in FIG. 1, the molecular beam source consists of a crucible 2 made of an insulator containing an evaporator 1.
Filament 3. Heat shield plate 4. It consists of a thermocouple 5. PBN (Pyrol) is generally used as a material for rutsuho.
The shape of the crucible is often the same regardless of the material to be evaporated. However, when epitaxial growth is actually performed, the requirements for the structure of the molecular beam source and the shape of the crucible differ depending on the evaporation material.

For example, At used for manufacturing A7GaAs has a low vapor pressure, so high temperatures are required, and it is required to suppress gas release from the periphery. On the other hand, with an element such as As having a high vapor pressure, it is not necessary to heat the crucible to a high temperature, but as is known, it is required that the ratio of As to GaO on the substrate be several tens of tens or more. For this reason, for example, in the case of growing QaAs, As is consumed rapidly; and the angular distribution of the molecular beam intensity changes as As is consumed (see Figure 4), as a result, the characteristics of the epitaxial film vary depending on the location. It had the disadvantage of being unevenly distributed. An example of a crucible design tailored to the evaporation material is Journatof VacnumS.
science and technology)'+ 2
Volume 0, 134 pages.

There is a crucible for CD and Te published in 1982. However, in MBE of CdTe, Cd and Te only need to evaporate at almost the same rate (the conditions are different from those for QaAa, and the crucible cannot be used as is for materials with high vapor pressure such as As). In other words, the angular distribution of molecular beam intensity and the amount of consumption are insufficient for materials with high vapor pressure such as As.

In order to eliminate these drawbacks, the present invention provides a cylindrical crucible, particularly a cylindrical crucible, with a lid having an opening inside the crucible. Hereinafter, one embodiment will be described in detail by arranging crucibles for As in GaAs growth with reference to the drawings, but as will be clear from the explanation below, the crucible according to the present invention is not limited to use for As, but Needless to say, it can be effectively used as a crucible for high-pressure substances such as P and Cd.

First, in order to show the requirements for As cells, GaA
Experimental data for s are shown in FIG. The horizontal axis in Figure 2 is the reciprocal of the substrate temperature, and the vertical axis is As and Gf on the substrate.
This is the arrival ratio of E. In the figure, the ○ marks indicate the conditions under which a mirror surface was obtained.
The mark X indicates a condition in which the surface became cloudy and a mirror surface could not be obtained.

From this figure, it can be seen that at a substrate temperature of 550° C., where GaAs is normally grown, As/Ga is required to be 20 or more. Furthermore, AtGaAs is grown at a substrate temperature of around 700° C., but in this case As/Ga is required to be 70 or more. Traditionally, As/G is used to grow GaAs.
It has been said that a is required to be 2.0 or more, but when the substrate temperature is high, the consumption of As becomes even more severe.

Therefore, a large crucible for As is required. Furthermore, it is necessary to take into account that As does not melt in vacuum but sublimates and freezes, making it impossible to increase the packing density in the crucible.

A sectional view of an embodiment of the present invention that takes the above points into consideration is shown in Figure @3. 6 is a crucible body, 7 is a lid body having a funnel-shaped opening lower a, 8 is a solid line for holding the lid body 7, 9 is a cylindrical jig for holding the lid body 7, and 10 is a housing for a thermocouple. It is a recess.

As is clear from FIG. 3, the cylindrical crucible has a lid body 7 on the inner wall of the crucible body 6, in which an opening lower a is formed for adjusting the molecular beam opening angle of a substance with high vapor pressure. It is locked by the formed protrusion 8. This lid body 7 is fixed inside the crucible body 6 by a cylindrical stopper 9.

Further, a recess 10 is formed at the bottom of the crucible body 6 to accommodate a thermocouple, and a molecular beam of the substance in a storage chamber C for storing a substance with high vapor pressure is generated.

The material used for the crucible is fused silica, which does not react with As at around 300° C., where As evaporates. If the crucible body 6 has a diameter of about 30 mm and a length of about 150 mm, 50 g or more of As can be easily loaded.

When loading a large amount of As, it is not sufficient to simply increase the Ruho, and the reason why a special structure as in the embodiment is required will be explained.

W, Figure 4 is edited by Br1an R, Pamplin “Mb
lecalanBeam El) itaxy″Perg
This is an excerpt from amonpress+, 1980, p. 25, and shows how the angular distribution of -molecular beam intensity changes depending on the surface position of the evaporated material in the crucible. It can be seen that as the amount of evaporated material decreases, the molecular beam is focused upward in the direction of the In of the molecular beam source.

In the present invention, As sublimated within the storage chamber σ of the crucible body 6
By passing the molecules through the opening 7a having a vertically extending portion 7b in the shape of a funnel or other similar shape, the angular distribution of the molecular beam intensity can be adjusted to the opening 7a of the lid body 7 rather than to the surface ITq of the evaporated material.
The structure is defined as follows. Therefore, a constant angular distribution can be stably obtained over time regardless of the amount of As in the storage chamber C of the crucible. The structure of the MBE device (
However, when using a substrate of about 2 inches, the molecular beam opening angle h,roo or less is sufficient. Here, the opening angle of the molecular beam is measured from directly above the molecular beam source. Considering this point, in the embodiment, the ratio of the length of the vertical portion 7b to the radius of the opening is set to 4. In the case of the above-mentioned Cd and Te crucible, this ratio is set to about 15, so the molecular beam is too converged, so it can only be used for small substrates.

In a structure in which an opening is provided at the head of the rutsuho, it is incompatible to maintain a constant angular distribution of molecular beams and to reduce the amount of molecular beams that wastefully evaporate to areas other than the substrate.

On the other hand, in the present invention, since the lid body 7 having the opening 7a is provided inside the crucible, the molecular beam reaching the substrate with substantially uniform intensity, for example, within an angle of 10°, is It does not collide with the crucible wall (in this embodiment, the inner wall of the cylindrical jig 9) extending on the lid 7, but directly reaches the substrate. On the other hand, the part of the molecular beam with a large opening angle is wasted if there is an opening in the head of the crucible body, but in the case of the present invention, the part of the molecular beam that has a large opening angle collides with and is reflected by the wall part of the crucible that extends above the opening lid. , a considerable amount of molecular beams will be directed toward the substrate. In the embodiment, the molecular beam extends about 25 mm above the open lid body 7, and the molecular beam with an opening angle of 30° or more collides with the wall.

When comparing the crucible of the present invention with a conventional crucible in which the opening 7a having the vertical portion 7b is not provided inside the crucible body 6, the amount of As molecular beam acid that reaches the substrate at the same molecular beam source temperature is approximately 10 times greater. In addition, there was little change over time, and the effect was extremely significant.

Furthermore, since the present invention is directed to a crucible for vapor-pressure materials, fused silica can be used as the crucible material. Therefore, it has the advantage of being extremely cheap and easy to manufacture compared to PBN.

As explained above, Ruho can be loaded with a large amount of a substance with low vapor pressure, such as As, and the evaporated As
etc., to reach the substrate due to the ringing, the As
The frequency of loading etc. can be extremely reduced, and the operating rate of the MBE equipment can be greatly increased. The advantage is a very important advantage.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a conventional molecular beam source, and Figure 2 is a GaAs
The obtained group & temperature and As/G of one moth in the MBE of
Experimental data showing the conditions of a, Figure 3 is a cross-sectional view of the crucible of the present invention, and Figure 4 shows the surface position of the evaporated material in the crucible (dependence of molecular beam intensity on force and crucible half-i φ(r)). 1... Evaporation material, 2... Crust, 3... Filament, 4... Heat shield plate, 5... Thermocouple, 6...
Crucible body, 7... Lid, 7a... Opening, 7b.
... Perpendicular part, 8... Arrowhead part, 9... Holder jig, 1
0...Recess for accommodating thermocouple, C...Storage chamber. Applicant's agent Masaki Amemiya Second figure basic version indemnity (0C) 1.0 1.1
1.21000/T (K”') Figure 3

Claims (1)

[Claims] A crucible for molecular beam epitaxial growth, characterized in that a lid body having an opening for adjusting the molecular beam opening angle of a substance with high vapor pressure is provided at a desired position inside the bottomed crucible body.