JPS62113789A - Single crystal pulling up apparatus - Google Patents

Abstract

PURPOSE:To keep the component concentration always at an optimum value and obtain a high-quality single crystal, by providing a gas sensor for measuring the component gas concentration and a mechanism capable of automatically controlling the component concentration in an inflow gas according to signals thereof. CONSTITUTION:In a single crystal pulling up apparatus for growing a single crystal in a gas stream, component gas detection signals given from a component gas concentration measuring instrument 13 are compared with program signals to drive a thermal mass flow controller 15 for inflow of a component gas by a PID controller 14 with a programmer. The component gas is mixed with a large volume of nitrogen or an inert gas from the thermal mass flow controller 16 and fed to a crystal growth apparatus. In this crystal pulling up apparatus, the component concentration in the discharge gas is detected and thereby the volume of the inflow component can be controlled to ensure the component concentration required for the crystal growth. Accordingly, this apparatus is effective in all cases where crystals in which minor components contained in an atmospheric gas have a serious influence on properties of the grown crystals.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an improvement in a single crystal pulling device.

(Prior Art) Single crystal growth using the normal pulling method is often carried out in an air current containing nitrogen or an inert gas as a main component. In addition, other component gases are often mixed into these gases. For example, in the case of oxide crystals, oxygen, etc. may be mixed into nitrogen or argon, and in the case of metal crystals, trace amounts of hydrogen may be mixed. etc. Conventionally, in such cases, a mixed gas cylinder containing the component gas at the required concentration was prepared, or a gas mixer was used to mix the component gas in nitrogen or inert gas at a fixed ratio to create a mixed gas at the required concentration and supply it. was.

(Problem to be solved by the invention) The type and concentration of other component gases mixed with nitrogen and inert gas vary depending on the type of single crystal to be grown.For example, in the case of an oxide single crystal, To explain it as, LiT
In some cases, the oxygen content is 20 t, as in the case of a01 crystal, and in others, it is 1 to 2 t, as in the case of Gd@Ga@O@t. The optimal content rate is determined by various factors such as the equilibrium dissociation pressure at the melting point of the substance and the durability of the crucible, but generally speaking, if the concentration of the component gas to be added is relatively high, it is necessary to be careful about the supply method. Although there were no problems, it was found that it is necessary to take this into consideration in cases where the appropriate component concentration is approximately 100 ppm or less.

It has conventionally been possible to maintain the concentration of components in the inflowing gas at a constant concentration K, and it has been possible to maintain the concentration of components in the inflowing gas at a constant value by using a gas mixer using a thermal mass controller (as described above). However, in actual crystal pulling, even if the concentration of components in the incoming gas is kept constant, the concentration of components that effectively act on the melt does not remain constant, which impairs crystal quality. It has been found from many experiments that there are cases in which the concentration of components is high. 0 (effect) which is intended to obtain quality single crystals Even if a mixed gas of a certain concentration is flowed into the growth device.

There is a problem in that near the most important crystal growth interface, the concentration of components differs from the concentration at the time of inflow, and that the concentration changes over time.The reason why this happens is that when high temperature or high frequency heating It is presumed that this is due to the reaction between the main component gas and the additive gas in the plasma state, or the reaction, adsorption, and dissolution between the additive gas and the refractory and raw material melt.◇These phenomena occur. Although this usually accompanies changes over time, minute leaks from the seal portion of the crystal rotating shaft often cause unstable fluctuations in component concentrations.

This effect is significant when oxygen is mixed with nitrogen. Considering the above effects, it is clear that K cannot be achieved by keeping the component concentration of the incoming gas constant in order to secure the necessary component concentration near the crystal growth interface. is based on the experimental result that the effective component concentration is rather that the component concentration of the waste mountain gas flowing out reflects the actual situation. In other words, the concentration at the atmospheric gas outlet is kept constant or programmed. The present invention was made based on the fact that it is possible to maintain substantially good crystal growth conditions by controlling the above conditions (Means for solving the problem). As a means, a component gas detector (for example, a hydrogen detector if a trace amount of hydrogen is mixed in argon) is installed at the atmospheric gas outlet, and the concentration is constantly measured and output as an electrical signal.
The signal drives the inflow amount adjustment mechanism of the thermal mass controller for adjusting the component gas flow I of the gas mixer installed before the gas inlet, thereby automatically controlling the component concentration in the inflow gas. . In this case, depending on the crystal, it may be better to change the component concentration near the growth interface according to a program, so an automatic control device with a program is required.0 Figure 1 shows the configuration of a single crystal pulling apparatus according to the present invention. An example is schematically shown in which the component gas detection signal output from the component gas concentration measuring device 13 is compared with a program signal, and the PID controller with programmer 14 controls the thermal mass flow control for component gas inflow. This component gas that drives the oscilloscope is mixed with a large amount of nitrogen and an inert gas from the controller 16 and sent to the crystal growth apparatus.

To summarize the above, using a feedback control method that automatically controls the mixing ratio of incoming gas (based on information from a detector installed at the atmospheric gas outlet) is an effective means for obtaining high-quality single crystals. Yes (Example) As an example of the present invention, yttrium aluminate, YAlo, was produced in an atmosphere containing a small amount of hydrogen in nitrogen.

The case of single crystal growth will be explained. YkI! 0 was developed as a crystal for solid-state lasers, and in order to improve its optical properties, a trace amount of hydrogen was mixed into the atmospheric gas. Inner diameter 50 mm, depth 50 mm S plate thickness 1.5 Front refractory 5. 6. 7 is made of zirconia 0 raw materials are Ait's with a purity of 99.999% and purity 99
．． 9999% Y, 0. The total amount of raw materials was 330 g, and the main atmospheric gas was nitrogen, and hydrogen was used as an additive component.Actually, a nitrogen cylinder 19 and a mixed gas cylinder 18 containing 1% nitrogen-based hydrogen were used. 1
5,16. Gas miki? 17, the opening that passes through the gas inlet 3 and enters the housing 1 is approximately 12 mm in diameter and 1 in length.
Ten dishes of single crystals 11 were obtained. In FIG. 1, 8 is a raw material melt, 12 is a high frequency coil, and 10 is a seed crystal. The light absorption coefficient of this crystal at a wavelength of 4000X was approximately 0.04 to 1. On the other hand, we made a mixed gas cylinder containing 100 ppm of hydrogen in nitrogen, used it to grow crystals using the conventional method, and conducted similar tests.
The optical absorption coefficient at 0 was about 0.07 cm-'
This is presumed to be due to the fact that the effective amount of hydrogen supplied was unstable, which caused more defects to occur during crystallization.

(Effect of the invention) Unlike the conventional method where the components of the inflowing gas are kept constant,
The device of the present invention detects the concentration of components in the outflow gas, thereby controlling the amount of components flowing in, and making it possible to ensure the concentration of components necessary for crystal growth. The apparatus of the present invention is effective in all cases where crystals are grown in which the properties of the grown crystal are significantly affected.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the configuration of the apparatus of the present invention. 01 is a housing, 2 is a gas outlet, 3 is a gas inlet, 5 to 7 are heat-retaining refractories, 8 is a raw material melt, and 9 is a Crucible. 10 indicates a seed crystal, 11 indicates a growing crystal, and 12 indicates a high frequency coil.

Claims (1)

[Claims] In a single crystal pulling device that grows a single crystal in a gas stream, there is a gas detector installed at the outlet of the atmospheric gas to measure the concentration of component gases in the gas, and a detection signal from the gas detector to determine the concentration of components in the inflowing gas. A single crystal pulling device characterized by comprising an automatic control mechanism.