JPS6356198B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a crystal growth control method and control device used in the manufacture of semiconductor crystals.

(Prior art) Since the pulling method produces high-quality, large, and circular crystals, many crystals, including semiconductor crystals, are produced using this method.
It is cultivated by law. In the CZ method, maintaining a uniform crystal diameter is an essential condition for obtaining high-quality crystals, and automating this process improves reproducibility and saves labor, which is a necessary condition for reducing costs. Against this background, automatic diameter control methods for maintaining the uniformity of various diameters have been proposed and some have been put into practical use.

Generally, when controlling the diameter, the diameter of the crystal being grown is measured, the deviation from the desired diameter is determined, and the growth conditions are changed based on this amount of deviation to keep the diameter constant. There is. The crystal diameter can be measured by using optical detection means such as direct ITV or by using a gravimetric detector per unit time.
Alternatively, a method of calculating from the change in weight per unit growth length has been put into practical use. Methods for changing the growth conditions include adjusting the melt temperature by controlling the power supply to the heating device, adjusting the crystal pulling speed, or both, but these methods have the following problems.

Most of the crystals currently used industrially have large diameter crystals of 2 inches to 5 inches to improve economic efficiency, and it is necessary to create a large amount of melt, which requires the use of large resistance heating heating elements and heat insulating materials. There is. Therefore, because the heat capacity of the melt and the heat insulating material is large, there is a large time lag between changes in the supplied power and changes in the temperature of the melt, making it difficult to control the diameter in cases other than crystals, which grow at a very slow rate. The problem is that it is extremely difficult. On the other hand, diameter control by growth rate adjustment is effective for crystals that grow rapidly, but there is a problem in that variations in crystal quality are accompanied by fluctuations in crystal quality and deterioration.

Based on the above background, there is a strong demand for the development of a means that can change the temperature of a large amount of melt in a short time.

(Object of the invention) The present invention was proposed to meet the above-mentioned needs, and is characterized by adjusting the magnetic field strength applied to the melt, and its purpose is to change the temperature of a large amount of melt in a short time. The object of the present invention is to provide a means for improving diameter control accuracy of large diameter crystals.

(Structure of the Invention) In order to achieve the above object, the present invention uses a pulling method single crystal production furnace capable of applying a magnetic field to place a crystal material in a crucible and heat it to melt it, and gradually collect seed crystals in contact with the melt. In the magnetic field pulling method for growing single crystals, the magnetic field strength applied to the melt is adjusted based on deviation information between the diameter of the crystal being pulled and the desired diameter. The gist of the invention is a crystal growth control method.

Furthermore, the present invention provides a means for heating and melting a single crystal material, a means for pulling a single crystal from a melt of the single crystal material while growing it, a means for applying a magnetic field to the melt of the single crystal material, and a means for controlling the strength of the magnetic field. and the means to
A means for calculating the diameter of the pulled part of the crystal being pulled, and a means for calculating a deviation between the diameter of the crystal being pulled and a desired diameter, The gist of the invention is a crystal pulling device characterized by controlling the applied magnetic field strength.

Next, embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the embodiments are merely illustrative, and it goes without saying that various changes and improvements can be made without departing from the spirit of the present invention.

In the crystal growth control method according to the present invention, ordinary CZ
A process crystal manufacturing furnace, a device for applying a magnetic field to the melt, and a device for adjusting the magnetic field strength are required. The method of growing crystals while applying a magnetic field to a conductive melt is
First ATWitt et al. (J.Mater.Sci.5
(1970) 882), and recently Hoshi (K.
Hoshi) et al. (The Electrochem, Soc.,
Pennington, 1980, Vol 80-1, P811) applied it to the growth of silicon single crystals. Application of a magnetic field has the effect of suppressing temperature fluctuations in the melt.
Normally, temperature fluctuations in the melt due to thermal convection range from several degrees to more than 10 degrees, and when crystals grow at the solid-liquid interface, the growth rate fluctuates with this temperature fluctuation, resulting in crystal defects (so-called growth stripes). etc.) occurs, and the crystal quality deteriorates. It is known that when a magnetic field is applied, this thermal convection is reduced and this temperature fluctuation is reduced to 0.1 degrees or less, and this has already been used for uniform crystal growth. On the other hand, the present inventors have found that the state of thermal convection changes due to the application of a magnetic field, and the temperature distribution in the melt changes widely. The present invention was devised based on the newly discovered effect of controlling temperature distribution in a melt by applying a magnetic field. Hereinafter, an example of the configuration of an apparatus based on the present invention and its operation will be described in detail using an example in which the present invention is applied to growing a gallium arsenide single crystal by a liquid confinement method in which the growth rate is relatively slow and diameter control is difficult.

FIG. 1 is a schematic diagram of an example of the configuration of an apparatus based on the present invention, and explains the principle of crystal diameter control according to the present invention.
In FIG. 1, the weight of a gallium arsenide crystal 1 is transmitted through a pulling shaft 2 to a weight detector 3, and is read through a voltmeter 5 by a central controller 4. Similarly, the pulling speed is detected by the central controller 4 by reading the output of the rotational drive speed detecting section in the pulling speed controller 6 through the voltmeter 5. Based on the pulling speed and the detected weight, the central controller 4 calculates the crystal diameter using a conventional method, and at the same time calculates the deviation from the desired diameter. The power supplied to the heating element 7 is controlled via the power PID controller 8 and the power supply device 9 based on this amount of deviation, as in a normal method. In the present invention, the current supplied to the air-core coil 10 is further controlled via the current PID control device 11 and the power supply device 12 based on this deviation amount. Note that 13 is a melt, 14 is a liquid sealant, and 15 is a liquid sealant.
16 shows a PBN crucible, 16 a carbon holder, 17 a crucible shaft, and 18 a can body.

FIG. 2 is an enlarged view of the area around the gallium arsenide melt 13 in FIG. 1, and FIG. 3 is an enlarged view of the area around the gallium arsenide melt 13 in FIG. Melt 1 previously measured by thermocouple
3 The dependence on temperature and applied magnetic field strength is shown.

FIG. 4 shows the results of measuring changes in temperature at point A in FIG. 2 when the applied magnetic field strength was changed stepwise. In the case of this example, it was revealed that by applying a magnetic field, the temperature near the solid-liquid interface where crystal growth was occurring on the surface of the melt in the crucible decreased, and further decreased in proportion to the strength of the applied magnetic field.
More importantly, in the control using the electric power supplied to the heating element 7, there is a time delay of several tens of minutes from when the electric power is changed until the temperature inside the melt changes.
In this magnetic field application control method, it was confirmed that the temperature in the melt changes within 10 to 20 seconds after adjusting the power supplied to the air-core coil 10 (Fig. 4). In general, when controlling a certain phenomenon, it is known that the faster the response, that is, the smaller the time delay, the better the controllability is, the faster the feedback loop is constructed using control elements, The present magnetic field application method, which has a response more than twice as fast, is expected to achieve unprecedented diameter control accuracy.

(Example) Next, an example of crystal growth carried out using the configuration shown in FIG. 1 will be shown below. A PBN (pyrolytic boron nitride) crucible with a diameter of 150 mm was filled with approximately 2 kg each of gallium and arsenic (so as to have a stoichiometric composition), and approximately 2 kg of B ₂ O ₃ was added as a liquid sealant.
Filled with 600g, gallium arsenide was directly synthesized under a furnace pressure of about 70Kg/cm ² . After making gallium arsenide into a melt, reduce the pressure inside the furnace to 8Kg/ ^cm2 , apply a magnetic field of 1200Oe to the melt in the crucible, and start crystal growth using a seed crystal (orientation <100>). did. First, after manually forming a neck portion and a shoulder portion, the automatic diameter control method of the present invention was applied to grow a constant diameter portion. The basic control algorithm is to reduce the magnetic field as the diameter increases and increase the magnetic field as the diameter decreases for rapid diameter changes of several tens of seconds to several minutes. In this case, the other purpose of applying a magnetic field is to reduce thermal convection and grow uniform crystals, so the strength of the magnetic field is in the range of 1200 ± 200 Oe, and at the same time it is controlled by the magnetic field, it is possible to quickly respond over several minutes. Regarding the diameter variation, the temperature of the entire melt in the crucible was changed by controlling the electric power supplied to the heating element as in the conventional method. Specifically, the magnetic field strength was proportionally controlled at a rate of 50 oersteds for a diameter change of 1 mm. Constant diameter part diameter 80mm, length 160mm grown using the above control method
Gallium arsenide crystals with a diameter variation of less than ±1 mm were obtained with good reproducibility. Automatic diameter control training using only the conventional power control method for the heating element is ±
The effectiveness of the present invention was demonstrated, with control accuracy of 5 mm being the limit and reproducibility being insufficient.

(Effects of the Invention) As explained above, according to the present invention, the temperature near the solid-liquid interface in the melt can be controlled without time delay by applying a magnetic field and adjusting the intensity of the applied magnetic field, so that the crystal diameter can be easily controlled. It has the advantage of being highly accurate.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of a configuration example of a crystal diameter control device according to the present invention, Figure 2 is an enlarged view of the vicinity of the melt, and Figure 3 shows the dependence of the melt temperature on the applied magnetic field intensity at point A in Figure 2. Similarly, FIG. 4 is a diagram showing the change in melt temperature at point A over time when the applied magnetic field strength is changed stepwise. 1... Gallium arsenide crystal, 2... Pulling axis, 3...
... Weight detector, 4 ... Central control device, 5 ... Voltmeter, 6 ... Pulling speed control device, 7 ... Heating element, 8
...Power PID controller, 9...Power supply device, 10...
Air core coil, 11...Current PID controller, 12...
Power supply device, 13... Gallium arsenide melt, 14...
Liquid sealant, 15... PBN crucible, 16... Carbon holder, 17... Crucible shaft, 18... Can body.

Claims (1)

[Claims] 1. A magnetic field that uses a pulling method single crystal production furnace that can apply a magnetic field to heat and melt a crystal material in a crucible, gradually pull up a seed crystal in contact with the melt, and grow a single crystal. 1. A crystal growth control method comprising adjusting the magnetic field strength applied to a melt based on deviation information between the diameter of a crystal being pulled and a desired diameter in an applied pulling method. 2. A means for heating and melting the single crystal material, a means for pulling the single crystal while growing it from the melt of the single crystal material, and a means for passing an electric current through the melt of the single crystal material through an air-core coil provided on the outer periphery of the crucible. means for applying a magnetic field; means for calculating the diameter of the pulled part of the crystal being pulled; means for calculating the deviation between the diameter of the crystal being pulled and a desired diameter; ,
1. A crystal growth control device comprising: means for controlling a current flowing through the air-core coil to control the strength of a magnetic field applied to the melt.