JPS5915379B2 - Molecular beam epitaxial growth equipment - Google Patents

Description

Detailed Description of the Invention The present invention relates to a molecular beam epitaxial growth apparatus used for epitaxially growing a crystal layer by ejecting component elements in the form of molecular beams from an ejection cell and depositing them on a substrate heated to a predetermined temperature. Regarding improvements.

Conventionally used molecular beam epitaxial growth apparatuses are roughly divided into horizontal types that eject molecular beams horizontally forward and vertical types that eject molecular beams upwards in the vertical direction.

By the way, the horizontal type molecular beam epitaxial growth apparatus has many functional features such as ease of handling, but on the other hand, it has drawbacks that cannot be considered with the vertical type.

In other words, if the temperature at which the ejection cell is heated is constant, the molecular beam intensity from the ejection cell should not change over time unless the source material is depleted. Even with a device called a mold, such as one in which a heater is evenly wound around an ejection cell, the molecular beam intensity changes over time, and the temperature must be lowered before the next epitaxial growth5. Even if the temperature is raised to the same set temperature as the previous time, the molecular beam intensity may not be the same.

Naturally, when this happens, the composition in the depth direction and in-plane direction of the epitaxially grown crystal layer,
Or regarding the thickness of the crystal layer or the impurity concentration, etc.
This results in loss of uniformity and reproducibility. As a result of conducting various experiments on such changes in molecular beam intensity, the following was found. Figure 1a, conventionally known as the soaking type
A device like the one seen in
5 The temperature distribution of heater 2 evenly wound is shown in Figure b.
As can be seen in Figure 2, it is actually not uniform; the central part is the highest, followed by the rear, then the front, and the front, where the orifice IA is located, is the lowest.

In the horizontal type, compared to the vertical type, the source material inside the ejection cell can easily move due to a slight deviation in the positional relationship, and when it melts, the source material that was initially at the rear of the ejection cell can move easily. is thermally transported to the vicinity of the orifice IA due to the influence of the temperature distribution. If the position occupied by the source material in the ejection cell changes from the rear 35 part to the center part to the front part, naturally the molecular beam intensity also changes each time. In particular, when the source material remains near the orifice IA,
The molecular beam intensity distribution having the highest intensity slightly below the normal direction to the orifice 1A changes, making it completely unpredictable. The present invention makes it possible to maintain the molecular beam intensity constant by adding simple modifications to the molecular beam epitaxial growth apparatus, and this will be explained in detail below.

In the present invention, first, the source material, whether solid or liquid, is prevented from moving within the molecular beam ejection cell, and is particularly prevented from moving near the orifice, that is, at the front of the ejection cell. In addition, the basic FfC is to set the temperature distribution of the ejection cell to be higher at the front of the ejection cell and lowest at the rear, contrary to the conventional method.

By doing this, the intensity of the molecular beam ejected from the orifice becomes approximately constant at a steady temperature unless the source material is depleted. Now, preventing the source material from moving within the ejection cell can be easily achieved by making some modifications to the structure of the ejection cell.

FIGS. 2a to 2d illustrate an ejection cell for achieving the above object, and the same parts as those explained in connection with FIG. 1 are indicated by the same symbols. Figure a is an example in which the inner wall 1B of the ejection cell 1 is sloped so that the source material remains at the rear.

b is one in which a step 1C is formed on the inner wall of the ejection cell 1. c is a protrusion 1D on the inner wall of the ejection cell 1! ! : It was formed.

d shows a boat 3 accommodating the source material arranged in the ejection cell 1, and this boat 3 is attached to the rear wall portion 1 of the ejection cell 1.
It can be inserted and removed by attaching and detaching E.

Next, the VC, which prevents the molten source material from being thermally transported, intentionally creates a temperature gradient in the axial direction of the ejection cell 1, but this is extremely easy, and for example,
As shown in FIG. 3 AflC, the heater 2 wound around the ejection cell 1 may be wound tightly around the front part of the ejection cell 1 and loosely around the rear part thereof.

Thereby, the temperature distribution can be made into a characteristic as seen, for example, in FIG. 3b. In order to obtain such a temperature distribution, it is necessary not only to depend on the winding density of the heater 2 as described above, but also to take appropriate measures such as using a plurality of heaters and changing the number of heaters. . As can be seen from the above explanation, according to the present invention, a molecular beam ejection cell having a structure in which the source material is held only at the rear part has a structure in which the temperature at the front part is high and the temperature at the rear part is low. By combining heaters, the molecular beam intensity can be stabilized to be constant and the reproducibility can be improved, so the composition, thickness, impurity concentration, etc. of the crystal layer due to molecular beam epitaxial growth can be improved. It is extremely effective in making the distribution uniform so that the TS does not have a uniform distribution. In the above embodiment, a cylindrical ejection cell was used as an example, but the ejection cell is not limited to this, and may be, for example, a prismatic cell, and the material may be graphite, quartz, pyrolytic boron nitride, etc. , select any one you like

[Brief explanation of the drawing]

Fig. 1a is an explanatory diagram of the conventional example, Fig. 1b is a diagram showing the temperature distribution of the conventional example, Fig. 2 a to d is an explanatory diagram of the molecular beam ejection cell in the present invention, Fig. 3 a FIG. 3 is an explanatory diagram illustrating the heater according to the present invention, and FIG. 3 is a diagram showing the temperature distribution. In the figure, 1 is an ejection cell, 2 is a heater, 3 is a boat,
1A is an orifice, 1B is an inclined inner wall, 1C is a step, and 1D is a protrusion.

Claims (1)

[Claims] 1. A molecular beam ejection cell that holds the north substance, whether solid or liquid, only at the rear, and the front part of the molecular beam ejection cell where the orifice is located is heated to a high temperature, and the rear part that holds the source material is heated to a low temperature. A molecular beam epitaxial growth apparatus characterized by comprising a heater.