JPH02164790A - Diameter control device of single crystal - Google Patents

Abstract

PURPOSE:To forcedly restrain the width of the swing of a force bar and to improve the diameter control of single crystal by providing rolling bodies rollable in the axial direction of the force bar at least at three positions around the force bar between the force bar and a guide shaft. CONSTITUTION:A load cell 4 is set on the the carriage 7 through which the pulling-up of growing single crystal 6 is carried out, and the force bar 1 and the guide shaft 5 are stretched through the carriage into a crystal growing furnace 8. A seed chuck 2 is fixed to the top end of the force bar 1 to hold a seed 9 and to pull the crystal up. A bearing 10 is provided between the guide shaft 6 and the carriage 7. All this device including the load cell 4 is in the crystal growing furnace. By using this device, when the pulling-up is carried out with, for instance, about 850mm the length of pulling-up single crystal, about 130mm diameter and about 25 r.p.m., the precession due to revolution and the noise due to the output of load cell are not generated. Thus, a single crystal is easily produced without foreign matter mixed in the molten body, as collers, etc., are not used.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an improvement of a gravimetric diameter control device for growing single crystals in the Czochralski method (hereinafter referred to as CZ method).
In particular, it relates to a support device for a so-called force bar, which is a transmission section to a load cell that suspends a single crystal and measures the tensile force.

[Prior Art] One of the diameter control methods for 02m single crystal is weight control.

This measures the weight of the growing crystal and compares it with the model crystal weight, and changes the temperature in the crystal growth furnace and crystal pulling speed depending on the size of the deviation, and approximates the crystal diameter to the diameter of the model crystal. It is controlled as follows.

In order to measure the weight of the growing crystal in this method,
A load cell fixed to the carriage that pulls the growing single crystal is used, and a rod-shaped rigid body is installed between the detection end of the load cell and the seed chuck that holds the seed crystal, and transmits the tensile force due to the weight of the crystal to the load cell. is generally called a force bar.

Usually, crystals grow while rotating, and in order to provide this rotational motion, the load cell, seed chuck, and force bar must all be rotated on the same rotation axis.

In addition, in order for the focuser to accurately transmit the weight of the grown crystal to the load cell, it must not come into contact with other fixed parts and cause friction while suspended from the load cell detection end.

When pulling a single crystal using such a mechanism, when the crystal is rotated, the load cell detection end is used as a fulcrum, and the pendulum swings the length from there to the center of gravity determined by the weight of the force bar, seed chuck, and growing crystal. The natural frequency of the simple harmonic motion, which is the length, approaches the crystal rotation frequency, causing a resonance phenomenon, and the growing crystal synchronizes with the rotation and begins to precess with a large amplitude. As a result, harmful dislocations occur and the crystal bends during growth.

This natural frequency is given as an approximate value, but in a normal CZ method single crystal growth furnace, I2
= 2(m), so f=21.1 (IIIin
-'), Crystal Rotation Manual 11Jli 15-30
Go into rpm.

Conventionally, in order to prevent such precession due to resonance, a ring with an inner diameter slightly larger than the diameter of the force bar, called a collar 3, is installed near the joint between the force bar 1 and the seed chuck 2, as shown in Fig. 5. A shaped part was attached to a guide shaft 5 rotating on the same axis as the force bar 1 and the load cell 4, and the amplitude of the force bar was mechanically regulated.

However, with this method, the collar and force bar come into contact during resonance, which causes instability in weight measurement due to friction, which appears as noise in the load cell output, resulting in inaccurate diameter control. There is a risk of it becoming.

In addition, since the joint between the collar and the guide shaft is easily exposed to relatively high temperatures, the material of the collar must normally be graphite, but when the force bar and the collar come into contact, part of the collar is destroyed and the raw material melt It also happens that they fall into the crystal and adhere to the growing crystal growth interface, interfering with single crystallization.

Force bars may also become deformed due to long-term use at high temperatures. In this case, even if a slight clearance is maintained so as not to contact the collar at the time of initial adjustment, contact will eventually occur all the time even at times other than resonance. The results are also similar to those described above.

In addition, as another solution, there is a method in which the force bar and the guide shaft are connected by an elastic body, which is disclosed in Japanese Patent Application Laid-open No. 171987/1987 filed by the present applicant on January 22, 1988. Because the atmosphere was at a high temperature, the Young's modulus of the elastic body changed slightly, making control a little more complicated.

[Problems to be Solved by the Invention] As described above, the former collar provided to prevent swinging of the single crystal actually causes instability in weight control due to the new problem of contact with the force bar. . moreover,
If contact occurs and the collar is damaged, the broken material that falls at this time will adhere to the crystal growth interface and inhibit single crystallization. Naturally, this inevitably leads to a decrease in yield and production efficiency.

Furthermore, the conventional phenomenon of crystal orientation and generation of dislocations due to the precession of the growing single crystal during pulling also leads to lower yields and production efficiency.

The connection between the force bar and the guide shaft using the latter elastic body still had the same problems as mentioned above.

[Means for Solving the Problems] The present invention has been made to solve one or more problems, and relates to a method for forcibly regulating the width of swing of a force bar.

That is, in a gravimetric single crystal diameter control device for a single crystal manufacturing device using the Czochralski method, rolling elements such as spheres or rod-shaped bodies that can roll in the axial direction of the force bar are arranged at three or more locations around the force bar. Even if the force bar, rolling elements, and guide shaft come into contact with each other due to the shaking of the crystal during pulling, the displacement of the load cell detection end is absorbed by the rolling of the rolling elements, and the force is released with almost no friction. The bar can be held concentrically with the central axis of the guide shaft.

Therefore, for example, a rolling element is supported and held by a rolling element retainer in a fixture that is fixed to a guide shaft or a force bar and has an open surface facing the force bar or guide shaft, and the rolling element retainer is elastically supported. The rolling element is connected to the fixture by the body so that the rolling element maintains a clearance of 0.05M or less with respect to the force bar or guide shaft in a stationary state.

Furthermore, since the elastic body only needs to maintain the weight of the rolling element and the rolling element retainer within its elastic limit, it is possible to use an elastic body whose rigidity is negligible compared to the rigidity of the load cell detection end. .

Note that if the fixing device is made detachable from the force bar or guide shaft, it can be freely applied to existing conventional devices. Also, in principle, this elastic body has 1
Although it is possible to use two elastic bodies, it is preferable to use two elastic bodies to sandwich the rolling element retainer from above and below in order to manufacture the device.

[Function] The device according to the present invention generates a frictional force against the movement of the force bar in the axial direction due to the connection form of the rolling elements between the force bar and the guide shaft and the holding method of the rolling elements. The force bar can be held at the center of the guide shaft with great rigidity in the perpendicular direction.

In other words, the rolling elements regulate the amplitude of the force bar, thereby preventing vibrations having a pendulum length from the detection end of the load cell to the center of gravity of the growing crystal. Therefore, the pendulum length is the length to the center of gravity of the growing single crystal, and there is no simple harmonic motion with the load cell detection end serving as the fulcrum, and it does not affect the accuracy of crystal weight measurement by the load cell. The crystal can be pulled using the following method.

Furthermore, if the force bar is held by the rolling elements without waiting for clearance, the rotation center of the force bar can be accurately aligned with the rotation center of the guide shaft. Therefore, it is possible to maintain high layer and seed rotation accuracy.

For weight side fixed accuracy, load cell full span 30
If we consider the displacement at - to be 20 μl, the spring constant is: 1.
5XIO'kg/I11. On the other hand, the spring constant of the elastic body supporting the retainer is approximately 15 kg/+++, so the ratio of the spring constants of the former and latter is 10'
+1, and does not affect diameter control accuracy within a practical range.

[Embodiment] Fig. 1 shows an enlarged vertical section of the main part of an embodiment of the present invention, Fig. 2 shows a longitudinal cross-section of the main part of an embodiment of the invention, and Fig. 3 shows a longitudinal section of the main part of an embodiment of the invention.
FIG. 4 shows a cross section of a force bar retainer portion showing an embodiment of the present invention, FIG. 4 shows a vertical cross section of a general CZ method single crystal production apparatus, and FIG. It shows the face.

In one embodiment of the apparatus of the present invention shown in FIG. 2, a load cell 4 is placed on a carriage 7 that pulls up a grown single crystal 6 (see FIG. A bar 1 and a guide shaft 5 extend into a crystal growth furnace 8 (see FIG. 4). force bar 1
A seed chuck 2 is attached to the tip of the
Grab Seed 9 and pull up the crystal. Guide shaft 5
A bearing lO is provided between the carriage 7 and the carriage 7.

The entire apparatus including the load cell 4 is located in a crystal growth furnace.

The upper end of the guide shaft 5 is fixed to the lower surface of the load cell, and the lower end reaches halfway along the length of the force bar. A fixing device 22 is attached to the force bar 1 near the lower end of the guide shaft, and between this fixing device 22 and the guide shaft 5 are three rolling elements 17, that is, ceramic rollers in this embodiment. ball is inserted. The three balls are arranged at intervals of 120° in the radial direction by the rolling element retainer 11.

The rolling element retainer 11 is suspended from the fixture 22 by an elastic body 13, that is, a spring in this embodiment, so as not to hinder the rolling of the balls. Since these are exposed to high temperatures of about 600° C., the rolling element cage 11 was made of high-purity graphite, and the elastic body 13 was made of Inconel.

The load cell 4 is attached to the rotation transmission gear 14 and rotates the grown single crystal 6 (see FIG. 4). The guide shaft 5 and force bar 1 also rotate accordingly. The rotation speed is 15 to 30 rpm.

In this embodiment, the three rolling elements 17 have a diameter of 7.94+nm.
Using an alumina ball of 1 elastic body 13 with a spring constant of 50
An Inconel spring of kgf/m was used, and the clearance between the fixture 22 attached to the force bar and the rolling element 17 of the guide shaft 5 was designed to be 0.02 mm or less.

In this way, the pulled single crystal length was 850mm, diameter was 130M,
When the crystal was pulled at a rotational speed of 25 RPM, no precession caused by rotation and no noise in the load cell output occurred. Furthermore, since no collar or the like was used, single crystallization was easily achieved without contamination of the melt with foreign matter.

[Effects of the Invention] The rolling elements used in the device of the present invention are supported by a rolling element retainer that holds them. By holding this rolling element retainer with an elastic body, the rolling elements caused by rolling can be prevented. The force bar of the movable cage can be moved in the axial direction with no friction.
The force bar and guide shaft can be held concentrically by suppressing only a slight repulsive force from the elastic body.

Therefore, within a practical range, the force bar can be accurately held on the central axis of the guide shaft without affecting the weight measurement accuracy of the load cell and therefore without deteriorating the diameter control accuracy.

Furthermore, since there is no collar between the guide shaft and the force bar, there is no problem of collar damage adhering to the single crystal growth interface due to vibrational contact of the force bar.

Furthermore, contact with the collar will not degrade load cell detection accuracy due to friction, nor will noise be generated. Therefore, gravimetric diameter control is carried out accurately.

In the conventional method, it was necessary to provide a large clearance between the collar and the force bar to prevent contact between the two. For this reason, the center of rotation of the single crystal cannot be held with high precision, causing the crystal to grow bent or dislocations to occur. However, as can be seen from the examples, according to the present invention, the above-mentioned In addition, the center of rotation of the single crystal can be maintained with high accuracy without adversely affecting diameter control accuracy.

In addition, there is a device in which the force bar and the guide shaft are connected by an elastic body, which is disclosed in Japanese Patent Laid-Open No. 171987/1987 filed on January 22, 1986 by the present applicant. The center of rotation can be held accurately. However, since the accuracy of the center of one rotation is directly affected by the accuracy of the spring used as the elastic body, the instability of the spring at high temperatures causes the accuracy to deteriorate over long periods of use, necessitating readjustment. In the present invention, since the accuracy of the elastic body does not affect the rotation center accuracy, accuracy can be easily maintained. Furthermore, since the force bar has significantly greater rigidity against radial displacement than an elastic body, the possibility that the crystal will resonate due to external vibrations is also reduced.

The rolling elements used in the device of the present invention can be ceramic balls, and the rolling element retainer can be made of carbon. As for the elastic body, it is desirable to use a metal material with high heat resistance.

[Brief explanation of the drawing]

FIG. 1 is an enlarged, half-mounted sectional view of essential parts of an embodiment of the present invention. FIG. 2 is a vertical sectional view of a main part of an embodiment of the present invention. FIG. 3 is a cross-sectional view of a force bar retainer portion according to an embodiment of the present invention. FIG. 4 is a longitudinal cross-sectional view of a general CZ method single crystal manufacturing apparatus. FIG. 5 is a vertical cross-sectional view of a conventional CZ method rough force bar support device. ■...Forspur 6...Growing single crystal 2.
...Seed chuck 7...Carriage 3...
Collar 8... Inside the crystal growth furnace 4... Load cell 9... Seed 5... Guide shaft
10... Bearing Figure 1 Rolling element holder Elastic body/Rotation transmission gear Load cell detection end 17... Rolling element 18... Quartz crucible 19... Graphite heater 20... Graphite heat shielding member 22...・Fixer

Claims (1)

[Claims] 1. In a gravimetric single crystal diameter control device equipped with a guide shaft for a single crystal manufacturing apparatus using the Czochralski method, a rolling element that can roll in the axial direction of a force bar is connected to the force bar and the guide shaft. A single crystal diameter control device, characterized in that the device is arranged at at least three locations around a force bar between the two. 2. A rolling element is supported and held from above and below by a rolling element retainer in a fixture that is fixed to a guide shaft or force bar and has an open surface facing the guide shaft or force bar side, and further this rolling element retainer is 2. The single crystal diameter control device according to claim 1, wherein the rolling elements are connected to the fixing device by an elastic body and arranged so as to have a minute gap with respect to the force bar or the guide shaft. 3. The single crystal diameter control device according to claim 1, wherein the elastic body is a spring. 4. The single crystal according to claim 1, wherein the elastic body has a rigidity against axial displacement that is at least 1/100 of the rigidity against axial displacement of the load cell detection end. Diameter control device.