JPH04356914A - Molecular beam cell - Google Patents

Abstract

PURPOSE:To prevent, in a molecular beam cell for heating a raw material with a ribbon heater, that a part of heater warps toward outside due to thermal expansion when it is in contact with a reflecting plate provided at a side of the heater, resulting in short-circuit when the ribbon heater is partly in contact with a through hole of a heater support. CONSTITUTION:Individual belt-shaped current path 9 of a ribbon heater 1 is warped and bent transverse to the longitudinal direction in order to enhance rigidity in the longitudinal direction. Due to a high stiffness, the belt-shaped current path 9 of ribbon heater never warp toward inside or outside, even when it is thermally expanded.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention relates to the molecular beam crystal growth method (M
This invention relates to improvements in the ribbon heater structure of molecular beam cells used in BE).

0002

[Prior Art] A molecular beam crystal growth apparatus consists of an ultra-high vacuum chamber that can be drawn to an ultra-high vacuum, a manipulator installed inside the chamber to hold a substrate facing downward, and an appropriate number of manipulators installed below the chamber. a molecular beam cell, a vacuum exhaust device,
Contains liquid nitrogen shroud, etc. The general structure of the molecular beam cell will be explained with reference to FIG.

The ribbon heater 1 is a heater made of a thin plate of Ta or the like and has a current path meandering up and down, and is installed around the outer periphery of the crucible 1 in a cylindrical shape. A flange of the crucible 1 is fixed to a side reflector 4 by a cap 3. The side reflector is a thin plate of high-melting, high-purity metal such as Ta or W processed into a cylindrical shape. A plurality of sheets are provided outside and below the heater 1. This reflects the radiant heat generated by the heater and confines the heat in the vicinity of the crucible 2.

There are several side reflectors 4 having slightly different diameters, and they are arranged concentrically. If they come into close contact, a lot of heat will escape through thermal conduction, so to prevent this, small dots are engraved on the reflector to leave a gap. The effect of reflecting radiation increases as the number of reflecting plates increases. Therefore, 3 to 5 layers are often stacked on top of each other. The same applies to the bottom reflector 7, which has a disk shape.

A thermocouple 5 is brought into contact with the bottom of the crucible 2. This is to monitor the temperature of the crucible. The base 6 is a circular plate. This is ribbon heater 1,
It supports the side reflector 4, the bottom reflector 7, etc. Ribbon heaters are made by cutting a thin metal plate into the top and bottom. It is represented by a developed view and a cross-sectional view as shown in FIG. Hee
The cross section of the ta is on a straight line. A thin metal plate with a thickness of 0.2 to 0.3 mm has a band-shaped current path 9, which is bent into a cylindrical shape to form a cylindrical heater. Since the ribbon heater 1 cannot be formed into a cylindrical shape and is too thin to stand on its own, several ring-shaped heater supports 8 are used to support the ribbon heater 1. In this example, four ring-shaped heater supports 8 made of PBN are used.
They are used one above the other. These have 1 through hole on the circumference.
0, into which the band-shaped current path 9 is inserted.

Since the heater support 8 has individual band-shaped current paths 9 distributed on the circumference, a cylindrical heating element can be formed. Furthermore, although the heater must not come into contact with the side reflector 4, the heater support 8 functions as a spacer and prevents the heater 1 from hitting the side reflector 4. . Hee
The through hole 10 of the data support 8 is a groove slightly larger than the width of the band-shaped current path 9, and allows the band-shaped current path 9 to move relative to each other up and down. Heater ranges from room temperature to approximately 1350℃
Since the temperature changes to a certain degree, the range of thermal expansion and contraction is wide. For this reason, the heater must not be fixed in the through hole 10.

[0007]

The ribbon heater is deformed into a cylindrical shape and is supported by a heater support, but as the temperature increases, the material of the heater becomes softer and bends more easily. Although it undergoes thermal expansion, if a part of the band-shaped current path is attached to the through hole 10 of the heater support, it cannot move freely relative to the through hole 10. Although it is originally thin and lacks rigidity, it loses even more rigidity when heated. Then, a part of it gets caught in the through hole 10. In this case, as shown in FIG.
deforms inward or outward. This is especially a problem when it deforms outward. If it deforms outward, it will come into contact with the side reflector. The heater is made of Ta plate, and the reflector is also made of Ta. Since it conducts current well, if it comes into contact with the side reflector, it will cause a short circuit accident. This is extremely dangerous. SUMMARY OF THE INVENTION An object of the present invention is to provide a heater structure that prevents a flexible heater from being thermally deformed and coming into contact with a side reflector.

[0008]

[Means for Solving the Problems] The ribbon heater of the present invention is curved or bent in a direction perpendicular to the longitudinal direction of the strip current path in order to increase the rigidity of the strip current path. It may be curved into a circular arc shape or may be bent into a broken line shape.

[0009]

[Function] Although it is a narrow strip-shaped current path, it is curved or bent in a direction perpendicular to the longitudinal direction, so its rigidity in the longitudinal direction is significantly increased. For this reason, even if it becomes high temperature and becomes, for example, softened, it can maintain its linearity, so it will not deform inward or outward. Therefore, the band-shaped current path never comes into contact with the side reflector. Since the effective rigidity is high, even if a part of the band-shaped current path 9 adheres to the through hole 10 of the heater support 8 as described above, it will not be able to overcome this and thermally expand or contract. can.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a developed view and a sectional view showing an example of a ribbon heater used in the present invention. In reality, there are many more strip-shaped current paths that meander up and down, but for the sake of simplicity, a ribbon heater with four peaks and three valleys is shown here. As far as the developed view is concerned, it seems to be the same as the one in Figure 4, but the cross section is different. Each of them is curved into an arc-shaped cross section. The arcuate curvature increases the longitudinal stiffness of the individual strip current paths. Therefore, it cannot be easily bent in a direction perpendicular to the longitudinal direction.

FIG. 2 is a developed view and a sectional view showing another example of the ribbon heater used in the present invention. This is done by bending the individual band-shaped current paths into a dish-shaped cross section. Such a shape change significantly increases the longitudinal stiffness. Therefore, it does not easily bend in a direction perpendicular to the longitudinal direction. In any case, it is possible to prevent a short circuit accident with the reflector due to bending of the heater outward. In the present invention, the strip-shaped current path of the ribbon heater is curved or bent in a direction perpendicular to the longitudinal direction in order to increase the rigidity in the longitudinal direction, but this shape may be arbitrary. In addition, it can also be bent into a dogleg shape. In any case, cut a thin Ta plate as shown in Figure 4,
After that, it is bent or curved to have an appropriate cross section.

0012

Effects of the Invention: Since the ribbon heater of the molecular beam cell has increased rigidity in the longitudinal direction, it does not bend outward even when thermally expanded, and there is no possibility that the heater comes into contact with the side reflector. Therefore, short-circuit accidents of the heater do not occur.

[Brief explanation of drawings]

FIG. 1 is a simplified developed view and cross-sectional view of a ribbon heater according to a first embodiment of the present invention.

FIG. 2 is a simplified developed view and cross-sectional view of a ribbon heater according to a second embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view of a molecular beam cell.

FIG. 4 is a simplified developed view and cross-sectional view of a ribbon heater according to a conventional example.

FIG. 5 is a partial cross-sectional view showing a state in which a thermally expanded heater is in contact with a side reflection plate.

[Explanation of symbols]

1 Ribbon heater 2 Crucible 3 Cap 4 Side reflector 5 Thermocouple 6 Base 7 Bottom reflector 8 Heater support 9 Band-shaped current path 10 Through hole

Claims (1)

[Claims] Claim 1: A crucible having a cylindrical shape with a bottom and containing a raw material; a ribbon heater made of a thin sheet of heat-resistant metal material and having a band-shaped current path that meanders up and down surrounding the crucible; A heater support consisting of several side reflectors provided concentrically, a bottom reflector provided below the ribbon heater by stacking multiple pieces vertically, and an insulator for supporting the ribbon heater. 1. A molecular beam cell comprising: a ribbon heater having a strip-shaped current path curved or bent in a direction perpendicular to the longitudinal direction.