JPS62167286A - Heating device - Google Patents

Abstract

PURPOSE:To grow high-quality crystal in a device necessitating temp. gradient in the vertical direction by providing a pair of up-and-down heating elements adjacently and eliminating an up-and-down temp. gap and enabling precise temp. control. CONSTITUTION:A pair of up-and-down heating elements 18, 19 capable of heating control independently are provided respectively and both the under end of the upper heating element 18 and the top part of the lower heating element 19 are made adjacent. An electrode terminal 20 of the above-mentioned upper heating element 18 is provided to the top end part of this heating element 18. Also an electrode terminal 21 of the above-mentioned lower heating element 19 is provided to the under end part of this heating element 19.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is applicable to crystal growth methods that require a temperature gradient in the vertical direction, such as the Czochralski method, the rotational pulling method, and the vertical Bridgman method. This relates to a heating device used for such purposes.

[Conventional technology]

Gallium arsenide (GaAa) and indium phosphide (InP)
Compound semiconductor crystals such as these are widely used as substrates for integrated circuits and optical devices, but recently, lattice defects, particularly dislocations, contained in these crystals have become a cause of deterioration or non-uniformity in device characteristics. It has become clear that high-quality crystals with as few dislocations as possible are strongly required. Therefore, various methods have been proposed to realize high-quality crystals such as . How to do this has become the most basic and important research topic. In order to obtain this ideal thermal environment, it is necessary to precisely control the temperature distribution within the furnace during crystal growth.

Therefore, various attempts have been made in the past, such as installing a plurality of heating elements in the furnace and devising the shape and structure of the heat insulating material.

Figure 4 is a vertical cross-sectional view of a conventional liquid-sealed pulling-type crystal growth horizontal heating device in which multiple heating elements are arranged vertically in order to precisely control the temperature distribution in the furnace during surface crystal growth. To explain this based on the figure, a pair of upper and lower heating elements 2 and 3 are arranged around the crucible 1, and the lower end of each heating element 2 and 3 is disposed around the crucible 1. Electrode terminals 4.degree. 5 are integrally provided in each portion. 6 is a CaAs melt melted by a heating element 2.3, 7 is a GaAs seed crystal suspended rotatably from the center of the crucible 1, and 8 is boron oxide (BtOs).

With this configuration, when the crucible 1 is heated by the heating element 2.3 and the seed crystal 7 is pulled up while rotating, the GaAs melt 6 solidifies and a single crystal grows. In this case, since the temperature of the upper and lower heating elements 2 and 3 is controlled separately, an appropriate temperature gradient can be obtained in the vertical direction.

[Problem that the invention seeks to solve]

However, in such conventional heating devices,
Since the upper electrode terminal 4 is arranged between the upper and lower heating elements 2.3, there is a gap of several meters where no heat is generated, and the lower end of the upper heating element 2 is generally located near the solid-liquid interface. In this device, the temperature near the solid-liquid interface is, for example, 5
℃ or more, and furthermore, within this low-temperature surface, only two locations where the electrode terminals 4 are located become particularly low-temperature. During crystal growth, if the liquid phase side becomes lower temperature than the solid phase side at the solid-liquid interface, random solidification occurs in the liquid phase ζ9, making it impossible to grow a single crystal. Additionally, if the temperature distribution within the solid-liquid interface becomes asymmetric, the portion of the crystal on the solid-liquid interface will alternately pass through high-temperature areas and low-temperature areas during crystal rotation. This results in uneven crystal growth rate, resulting in crystal defects and non-uniform impurity distribution. In this way, in conventional heating element structures, a drop in temperature near the solid-liquid interface and an asymmetry in the temperature distribution within this plane are unavoidable, resulting in crystal defects and uneven impurity distribution, making precise temperature control difficult. The problem was that I couldn't do it. In addition, the fourth
On the right side of the figure, there is a temperature distribution diagram showing the temperature on the horizontal axis and the corresponding position with the vertical cross-sectional view on the left side on the vertical axis.As is clear from the figure, the upper and lower heating elements 2, The temperature of the area corresponding to the space between 3 is low.

Furthermore, in order to compensate for the above-mentioned drawbacks, it has been proposed to add various innovations to heat insulating materials other than the heating elements 2 and 3, but the shapes and structures of the heat insulating materials become complicated, making it difficult to put them into practical use. This was not necessarily a satisfactory solution.

The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide a heating device that enables precise control of temperature distribution in a furnace.

[Means for solving problems]

In order to achieve this objective, the present invention provides a pair of upper and lower heating elements that can be independently heated, with the lower end of the upper heating element and the upper end of the lower heating element close to each other, and An electrode terminal was provided at the upper end of the upper heating element, and an electrode terminal of the lower heating element was provided at the lower end of the lower heating element.

[Effect]

Since there is no space at the boundary between the upper and lower heating elements and no electrode terminals are present, there is no temperature drop at this location and an even temperature gradient can be obtained in the upper and lower directions.

〔Example〕

1 and 2 show an embodiment of the heating device according to the present invention, FIG. 1 is a longitudinal sectional view thereof and a corresponding temperature distribution diagram, and FIG. 2 is a sectional view showing the arrangement of heating elements. It is. This example shows an example in which the present invention is applied to an apparatus for growing GaAs, which is one of the intervening half-domains, by the liquid confinement drawing method (LEC method). A GaAs melt 14 melted by a heating device (to be described later) is placed in a crucible 13 which is double-formed with a crucible 12 .
It hangs down from the center of 3. 16 is boron oxide (n*os) placed around the seed crystal 15.

The heating device 17 that heats the heating element 13 includes an upper heating element 18
It is formed of a pair of upper and lower heating elements, ie, a lower heating element 19 and a lower heating element 19, and the lower end of the upper heating element 18 and the upper end of the lower heating element 1B are close to each other so that a gap #1 is hardly formed.

The electrode terminal 20 of the upper heating element 18 is integrally formed with the upper end of this upper heating element 18, and the electrode terminal 21 of the lower heating element 19 is integrally formed with the lower end of this lower heating element 19. ing. Figure 2 shows heating element 1 from Figure 1.
Only the electrode terminals 8.19 and 20.21 are taken out and illustrated corresponding to FIG.

With this configuration, when the crucible 13 is heated by the heating device 17 and the seed crystal 15 is pulled up while rotating, the GaAs melt 15 solidifies and a single crystal grows. The right side of FIG. 1 is a temperature distribution diagram showing the temperature on the horizontal axis and the corresponding position with the longitudinal cross-sectional view on the left side on the vertical axis. In the case of this device, the upper and lower heating elements 18 There is almost no gap at the boundary between .19 and electrode terminal 20.2.
1 does not exist, the temperature decreases at the boundary as shown in FIG. 4, and the temperature distribution curve 22 becomes almost linear, resulting in a smooth temperature gradient.

Furthermore, the temperature gradient at the solid-liquid interface between the GaAs seed crystal 15 and the GaAs melt 14 and the temperature gradient in the boron oxide 16 can be easily controlled, and the upper and lower heating elements 18, 19
Since there is no temperature gap between the two, the flow of heat toward the top of the crystal becomes uniform during crystal growth. In this example, GaA
The dislocation density was
A crystal with low dislocations of less than can be easily controlled without causing significant non-uniformity.

FIG. 3 is a longitudinal cross-sectional view of a heating device showing another embodiment of the present invention corresponding to FIG. 1, and parts having the same structure as the embodiment shown in FIG. The explanation will be omitted. In this embodiment, the lower end of the upper heating element 18 and the upper end of the lower heating element 19 form a part of the chamber. By doing this, a smooth temperature gradient can be obtained as in the previous embodiment, and since the upper heating element 18 is closer to the crucible 13 than the lower heating element 19, the temperature distribution in the boron oxide 16 is particularly improved. Easier to control. The effect on dislocation density shown in the previous example is the same in this example.

Furthermore, since the temperature distribution within boron oxide can be easily controlled, it is extremely effective for post-growth heat treatment in boron oxide to improve non-uniformity of electrical properties between the top and bottom of the crystal caused by thermal history.

In each of the above embodiments, an LEC type crystal growth apparatus was exemplified as a crystal growth apparatus for carrying out the present invention, and an example was shown in which this was applied to GaAs crystal growth. It goes without saying that the same method can be applied to a crystal growth apparatus, and can also be applied to crystal growth of St, cap, InP, and the like.

〔Effect of the invention〕

As is clear from the above description, in the heating device according to the present invention, a pair of upper and lower heating elements capable of independent heating control are provided with the lower end of the upper heating element and the upper end of the lower heating element close to each other. At the same time, the electrode terminals of the upper heating element are provided on the upper part of this upper heating element, and the electrode terminals of the lower heating element are provided on the lower part of this lower heating element, so that the electrode terminals are formed in the vertical direction. The temperature gradient generated between the upper and lower heating elements is a smooth temperature gradient with no temperature drop near the solid-liquid interface, and the temperature distribution within the solid-liquid interface is symmetrical.
Extremely high quality crystals without crystal defects or non-uniform impurity distribution can be obtained, and the structure can be simplified without requiring a complicated heat insulator structure other than the heating element.

[Brief explanation of drawings]

1 to 3 show an embodiment of the heating device according to the present invention, FIG. 1 is a longitudinal cross-sectional view and a corresponding temperature distribution diagram, and FIG. 2 is a cross-sectional view showing the arrangement of heating elements. 3 is a longitudinal sectional view showing another embodiment of the present invention corresponding to FIG. 1, and FIG. 4 is a longitudinal sectional view of a conventional heating device and a temperature distribution diagram corresponding thereto. 13... Crucible, 14... G&A11 melt, 1
5...Seed crystal, 16...Boron oxide, 17...
... Heating device, 18... Upper heating element, 19 fist...
Lower heating element, 20.21... Electrode terminal, 22...
・Temperature gradient curve. Patent applicant: Nippon Telegraph and Telephone Corporation Agent: Masaki Yamakawa (and one other person) Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] A pair of upper and lower heating elements each capable of independent heating control is provided with the lower end of the upper heating element and the upper end of the lower heating element close to each other, and the electrode terminal of the upper heating element is connected to the upper end of the upper heating element. and an electrode terminal of the lower heating element is provided at a lower end of the lower heating element.