JPH03193694A - Crystal growing device - Google Patents

Abstract

PURPOSE:To decrease the heat quantity required for melting raw materials and to reduce the cost of crystal production by providing a heat shielding plate held to cover the top of a crucible at the time of melting of the raw materials for a crystal in the crystal growing device by a pulling up method. CONSTITUTION:The raw materials for the crystal are charged to the crucible 1 provided in a chamber 10. The heat shielding plate 21 is hung via a jig 27 at the bottom end of the pulling up shaft 6 and is lowered from a pull chamber 11 via a shutter 4 into the chamber 10, by which the heat shielding plate 21 is so disposed as to cover the upper part of the crucible 1. The raw materials in the crucible 1 are then heated by a heater 2 and, thereafter, the pulling up shaft 6 is pulled up to pull in the heat shielding plate 21 into the pull chamber 11. The shutter 4 is closed/and after the pull chamber 11 is removed, a seed crystal provided at the bottom end of the pulling up shaft 6 is immersed into the melt layer in the crucible 1 and is pulled up to grow the crystal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus for growing crystals such as silicon single crystals, which are mainly used as semiconductor materials.

[Conventional technology]

In general, the Chigochralski method (CZ method) is widely used as an apparatus for growing this type of crystal.

FIG. 4 is a schematic diagram showing a crystal growth apparatus using the CZ method, and numeral 1 in the figure indicates a crucible disposed in a water-cooled chamber or the like. The crucible 1 is constructed by concentrically arranging an outer layer container 1a made of graphite and an inner layer container 1h made of quartz, each having a cylindrical shape with a bottom.
After heating and melting the crucible 1 with a heater 2 arranged around the crucible 1 while rotating the crucible 1, a seed crystal 7 suspended by a pulling shaft 6 is immersed in this molten liquid, and while rotating the crucible 1, The seed crystal 7 is pulled upward to grow a single crystal 8 at the lower end of the seed crystal 7.

By the way, when a single crystal is normally used as a semiconductor substrate, an impurity element is added to the melt in the crucible 1 in order to adjust the electrical resistivity and conductivity type of the single crystal. It segregates in the pulling direction of the crystal 8, and it is extremely difficult to maintain a uniform concentration distribution over the entire length of the single crystal 8 in the growth direction.

Segregation of impurities is determined by the impurity concentration C3 in the single crystal at the growth interface between the melt and the single crystal and the impurity concentration CL in the melt.
This is due to the fact that the ratio Cs/Ct, that is, the effective segregation coefficient ke, is not 1, and the impurity concentration in the melt accompanying the growth of the single crystal changes during the crystal pulling process.

Molten N injection is known as a method for suppressing such segregation. FIG. 5 is a schematic diagram of a crystal growth apparatus using a general molten layer method, in which a solid layer S of the crystal raw material is formed at the bottom of the crucible l by a heater 2, and a molten layer 1 of the crystal raw material is formed above it. ．． In this state, the single crystal 8 is made to elongate in the same manner as the process shown in FIG.

During the pulling of the single crystal 8, the decrease in the thickness of the molten layer due to the pulling of the single crystal 8 is compensated for by the melting of the solid layer S by controlling the heater 2C midway, so that the volume of the flake layer I5 is kept constant. (called the constant thickness method), an apparatus in which impurity elements are continuously added during crystal pulling to maintain a constant impurity concentration in the melt to grow the crystal (Japanese Patent Publication No. 34-8242), or intentionally By changing the volume of the layer, (
There are devices that grow crystals by maintaining a constant impurity concentration in the melt without adding impurity elements during crystal pulling.

By the way, when using either the CZ method or the fused layer method as described above, the raw material is a polycrystal with a diameter of 1
A relatively large one with a diameter of about 0.00 mm (referred to as a lamp) and a relatively small one with a diameter of around 10 mm (referred to as a chip) are used as a mixture. The molten layer method, which requires a liquid layer to coexist, usually requires about 1.5 to 2 times as much as the CZ method, and the crucible 1 itself also requires a molten layer less than the CZ method. The legal version is larger.

FIG. 6 is a schematic longitudinal section showing the state during melting of raw materials in a single crystal growth apparatus using the molten layer method, and shows the chamber 10.
A crucible 1 is arranged at the center of the interior so as to be rotatable and movable up and down on a shaft 1c, a heater 2 and a heat insulating cylinder 3 are arranged concentrically around the crucible 1, and a pull chamber 11 is provided with a vacuum shutter 4 interposed in the upper part. is provided.

[Problem to be solved by the invention]

By the way, in the conventional apparatus as described above, the length of the heater 2 is set short in order to coexist the molten liquid layer and the solid layer S, but when melting the raw material, the lower half of the crucible is Since the crucible does not face the crucible, conduction and heat dissipation losses are larger than in a CZ method crucible, and there are problems in that it takes a long time to melt the raw material and a large amount of electric power is required.

The inventors of the present invention have conducted experiments and research to reduce heat loss during melting of raw materials and efficiently heat and melt raw materials, and have discovered the following fact.

The amount of heat that should be supplied from the heater when melting the raw material is the melting heat Q for melting the raw material, the amount of heat Q dissipated upward by heat radiation from the raw material surface, and the raw material layer and crucible axis (pedestal).
The amount of heat Qt+ dissipated downward by thermal conduction through
Heat IQ radiated downward from the lower part of the crucible by thermal radiation, etc.
It is given by the sum of 2.

However, Qzl and Qt□ cannot be made smaller because it is necessary to form and maintain a lower solid layer at the bottom of the crucible, but rather need to be made larger. Moreover, Ql is determined by the amount of raw material to be dissolved. Therefore, Qu, which is unrelated to these, is a possible target for reducing the amount of heat.

The present invention was made based on this knowledge, and its purpose is to reduce the amount of heat required for melting raw materials,
An object of the present invention is to provide a crystal growth apparatus that can reduce crystal manufacturing costs.

[Means to solve the problem]

A crystal growth apparatus according to the present invention includes a crucible that melts charged raw materials for crystal to form a molten liquid layer, and a crystal pulling system that immerses a seed crystal in the molten liquid layer of the crucible and pulls it up to grow a crystal. The crystal growth apparatus is characterized by comprising a heat shielding plate that is held so as to cover the crucible during melting of the crystal raw material.

[Effect]

According to the present invention, the heat shield plate suppresses the dissipation of heat upward into the crucible during melting of the raw material.

[Examples] The present invention will be specifically described below based on drawings showing examples thereof. FIG. 1 is a schematic longitudinal sectional view of the device of the present invention,
In the figure, 10 is a water-cooled chamber, 11 is a pull chamber, 1 is a crucible, 2 is a heater, and 3 is a heat-insulating cylinder.

A crucible 1 is disposed in the center of a water-cooled chamber 10, a heater 2 is disposed around the crucible 1, and a heat insulating cylinder 3 is disposed around the heater 2. A pull chamber 11 that faces the crucible 1 and is opened and closed by a shutter 4 is erected on the upper wall of the chamber 1.
A pulling shaft 6 that can be raised, lowered, and rotated is suspended from above.

The crucible 1 has a double structure with an outer layer container 1a made of graphite on the outer periphery and an inner layer container 1b made of quartz inside, and a shaft penetrating the bottom wall of the chamber 1 in the center of the bottom. The upper end of 1c is connected, and it can be raised and lowered while being rotated by the shaft 1c. The heat retaining cylinder 3 is formed into a cylindrical shape using a material with low thermal conductivity, such as a carbon fiber molded material, and is disposed concentrically with the crucible 1 and the heater 2 so as to surround their outer peripheries.

Rotating and lifting mechanism (not shown) from above the pull chamber 4
The upper end of the pulling shaft 6 connected to the is introduced, and a seed crystal held by a chuck is suspended from the lower end of the pulling shaft 6 during crystal growth, as in the case shown in FIG. After being blended with the melt, a silicon single crystal is grown at the lower end of the seed crystal by raising it while rotating it, and when melting the raw material, a heat shield 21 is attached as shown in Figure 1. ing.

FIG. 2 is an enlarged sectional view of the heat shield 21.
1 has a three-layer structure in which a graphite felt 24 is sandwiched between two graphite discs 22 and 23 that are slightly smaller than the inner diameter of the pull chamber 11, and graphite bolts are connected at multiple points around the periphery.・It is integrally connected using a nut 25. this bolt nut 2
One end of each Mo wire 26 is connected to 5,
The other ends are connected to the lower end of the single crystal pulling shaft 6 via a jig 27, and by raising and lowering the pulling shaft 6, the position facing directly above the upper end of the crucible 1 as shown in FIG. It is now being moved to Jig 2
7 is formed in an inverted letter shape when viewed from the side, and includes a support portion 27a and a connecting portion 27b, and the other end of each wire 26 is connected to the support portion 2.
7a, and is itself detachably suspended from the pulling shaft 6 via a connecting portion 27b.

The material and structure of the heat shield 21 are not particularly limited, and any material may be used as long as it has a high melting point and low thermal conductivity.

In the apparatus of the present invention, a solid raw material for crystallization, for example, high-purity polycrystalline silicon, is charged into the crucible 1 through a raw material feeder (not shown). After replacing the atmospheric gas in the chamber 10 with an inert gas or the like, the power of the heater 2 is set to melting conditions, and while the filled solid raw material is melted, impurities are added into the melt from an impurity feeder (not shown). do.

Next, a heat shield 2 is attached to the lower end of the pulling shaft 6 via a jig 27.
1 is suspended from the pull chamber 1 and descends into the chamber 10 through the shutter 4, and a heat shield 21 is arranged so as to cover the upper part of the crucible 1. The solid raw material charged in this state is melted until a predetermined initial melt rate is obtained, and a state is set in which the molten layer and the solid layer S below it coexist.

When the initial melting is completed, the pull shaft 6 is pulled up, the heat shield 21 is pulled out through the shutter 4 into the pull chamber 11, the shutter 4 is closed, and the pull chamber 11 is removed.
A seed crystal is suspended from the lower end of the pulling shaft 6 via a chuck,
This is suspended into the chamber 0 through the shutter 4, and after the lower end of the seed crystal is immersed in the melt layer S, it is pulled up while being rotated, and a single crystal is grown at the lower end of the seed crystal. The decrease in the thickness of the molten layer I5 due to the growth of the single crystal is compensated for by melting the solid layer S by the heater 2.

The pulled single crystal passes through the shutter 4 into the pull chamber 11.
After pulling in the pull chamber 1, close the shutter 4 and close the pull chamber 1.
1 and install another seed crystal and repeat the process described above.

FIG. 3 is a partial sectional view showing another embodiment of the present invention,
In this embodiment, the heat shield 28 includes a disk portion 28a and a Mo raindrop portion 28b protruding from the center of its upper surface.
The disc part 28a is made of a material with low thermal conductivity and has a diameter slightly smaller than the inner diameter of the pull chamber 11, and is removably connected to the pulling shaft 6 via the raindrop part 28b.

The other configurations and operations are substantially the same as the embodiment shown in the first part, and corresponding parts are given the same numbers and explanations are omitted. Such an embodiment has the advantage that the configuration is simplified compared to the embodiments shown in FIGS. 1 and 2.

Next, the results of a comparative test using the device of the present invention and a conventional device will be explained. In the test, power consumption and melting time were measured in a crucible for molten layer method having the dimensions shown in Table 1, with and without a heat shield. The results are shown in Table 2.

As is clear from Table 1 and Table 2, both the heater power (kW) and the melting time are significantly reduced when the apparatus of the present invention is used. Although the above-described embodiments have been described with reference to the case where the present invention is applied to a crystal growth apparatus using the fused layer method, it goes without saying that the present invention can also be applied to a crystal growth apparatus using the CZ method and other crystal growth apparatuses. Although the heat shields 21 and 28 have been described as having a structure in which they are dripped onto the single crystal pulling shaft 6, the present invention is not limited thereto, and other wires or the like may be used.

〔effect〕

As described above, the apparatus of the present invention can suppress heat dissipation upwards in the crucible during raw material melting, thereby reducing heat loss, greatly improving thermal efficiency, shortening melting time, and improving crystal growth efficiency. The present invention has excellent effects such as:

[Brief explanation of drawings]

FIG. 1 is a schematic vertical cross-sectional view showing the state of the apparatus of the present invention during raw material melting, FIG. 2 is an enlarged cross-sectional view of the heat shield, and FIG. 3 is a schematic partial cross-sectional view showing another embodiment of the present invention. Figure 4.5 is a schematic vertical cross-sectional view showing the implementation state of the general CZ method and fused layer method, and Figure 6 shows the state of raw material melting in a conventional crystal growth apparatus using the fused layer method. FIG. 1... Crucible 2... Heater 3... Heat insulation tube 4.
...Shutter 10...Chamber 11...Pull chamber 21.28...Heat shield

Claims (1)

[Scope of Claims] 1. A crucible that melts charged crystal raw materials to form a molten liquid layer, and a crystal pulling means that immerses a seed crystal in the molten liquid layer of the crucible and pulls it up to grow the crystal. A crystal growth apparatus comprising: a heat shield plate held to cover a crucible during melting of a crystal raw material.