JPS62256789A - Device for growing single crystal - Google Patents

Abstract

PURPOSE:To facilitate the growth operation of a single crystal by controlling the holding position of a low temp. retaining means contg. an electromagnetic coil and used for preventing the thermal convection of a melt when a single crystal is grown from the melt of an electrically conductive substance by the CZ method. CONSTITUTION:The device for growing a single crystal is composed of a cylindrical crucible, an annular heating means for heating and melting the conductive substance in the crucible, a couple of electromagnetic coils 22 which are arranged symmetrically to the center axis of the crucible on the outside of the heating means, the annular low temp. retaining means 25 contg. the coils 22, a single crystal 20, a chamber 21 contg. the single crystal 20, the crucible, and the heating means in the heating means in the hermetically sealed state, a measuring means 27 which is held at the oblique upper part of the chamber 21 during measuring and used for optically measuring the diameter of the lower end of the single crystal 20, and a measuring window 26 opened at the shoulder part of the chamber 21 so that the lower end can be observed by the measuring means 27. Besides, the upper part of the low temp. retaining means 25 is disposed so that the part does not interfere with the observation space through the measuring means 27 and the measuring window 26.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides a method for applying a magnetic field to the melt when pulling a single crystal by the Czochralski method from the melt obtained by heating a conductive substance. In addition, the present invention relates to a single crystal growing method and apparatus that can improve the quality of the single crystal.

[Prior Art] The Czochralski method is known as a conventional method for manufacturing single crystals such as silicon, and this Czochralski method involves seeding seeds on the surface of a polycrystalline melt melted in a crucible. This method involves bringing the crystals into contact with each other, and then slowly pulling up the seed crystal while rotating it to grow a single crystal. in this case,
Circulating flows occur in the melt, such as thermal convection due to heat applied from the sides of the melt, and centrifugal flow of the surface layer of the melt due to rotation of the seed crystal. This thermal convection and circulating flow bring about temperature fluctuations at the interface where the single crystal grows, resulting in adverse effects such as non-uniformity of properties and crystal defects within the grown single crystal.

Therefore, when the molten material is a conductive material such as silicon, by applying a direct current parallel magnetic field to the molten material in the horizontal direction, magnetic viscosity is generated in the molten material, causing circulation of the molten material. suppress.

As a means for applying this horizontal magnetic field, a ferrous core electromagnet, or a ferrous coreless coil of an opposed cylinder type, an opposed disk type, or an opposed saddle type is used.

In addition, superconducting electromagnetic coils are often used to make the electromagnetic coils smaller, and the low-temperature holding means that accommodates the pair of electromagnetic coils is a cylindrical type with a vertical axis in order to maintain low-temperature holding efficiency. It has the shape of

[Problems to be Solved by the Invention] However, from the operational point of view of the device, there are various dimensional restrictions on the low temperature holding means, and the purpose of the present invention is to set the size of the low temperature holding means to desirable dimensional limits. By keeping it within
An object of the present invention is to provide a single crystal growth device that is easy to operate.

[Means for Solving the Problems] The object of the present invention is to provide a cylindrical crucible, a cylindrical crucible arranged outside the crucible concentrically with the central axis of the crucible, and a conductive substance inside the crucible. an annular heating means for heating and melting; and a pair of electromagnetic elements arranged symmetrically opposite to each other with respect to the central axis of the crucible on the outside of the heating means to prevent thermal convection of the molten substance. a coil, a single crystal held so that its lower end is in contact with the center of the liquid surface of the molten substance, a chamber that hermetically accommodates the crucible, the nN single crystal, and the heating means; a measuring means held diagonally above the chamber for optically measuring the diameter of the lower end; a measuring window bored in the shoulder &5 of the chamber so that the lower end can be visually checked by the measuring means; In the apparatus for growing the single crystal, the apparatus comprises an annular low-temperature holding means arranged concentrically with the central axis and housing the pair of electromagnetic coils, wherein an upper part of the low-temperature holding means is connected to the measuring means and the measuring means. This is achieved by a device characterized in that it is arranged so as not to interfere with the viewing space for the measurement window S-+.

[Operation] FIGS. 1A and 1B are a plan view and a location view showing the flow of the melt and the magnetic field of the apparatus of the present invention, and the principles of the method and apparatus of the present invention will be explained below using these figures. do.

Since the melt 2 filled in the cylindrical crucible 1 is usually heated from the side, the temperature of the outer part of the melt 2 is higher than the temperature of the center, and the 1A Convection 3 occurs as shown in FIG. 1 and FIG. 1B. On the other hand, the rotation of the silicon single crystal 4 causes the surface layer of the melt 2 to rotate, and as a result, a circulating flow 5 is generated in the surface layer due to a centrifugal flow and an upward flow in the center of the melt. Occur. In the device of the present invention, these convection flow 3 and circulation flow 5
In order to prevent the magnetic flux lines 6
is a convection current 3 and a circulation flow 5 over a wide area of the melt 2.
The flow of the melt 2 is effectively suppressed.

FIG. 2 is an explanatory diagram showing the relationship between the radius of a coil that applies a magnetic field to a molten material and the interval between opposing coils, and the radius r
The coils 7 having the same shape are opposed to each other with an interval of 1 and their centers are located on two axes. At this time,
The strength of the magnetic field strength B on the Z-axis is as shown in the graph of FIG. r-j, a nearly flat distribution of magnetic field strength B is obtained near the center O of each coil 7, and when N>r, the distribution of the magnetic field strength B is approximately flat near the center O of each coil 7.
The magnetic field strength B in the vicinity decreases. On the other hand, when ρ<r, the magnetic field strength BIfii near the center 0 is large. Thus, in order to obtain a uniform magnetic field strength B, it is desirable to make the radius r of the coil and the distance 1 between the opposing coils as equal as possible. However, the lSi of the coil! Normally, N>r due to space limitations.

[Specific Example] Hereinafter, an example of the single crystal growth apparatus of the present invention will be described.

FIGS. 4A and 4B are partial elevation and partial cross-sectional views of the main parts of the apparatus of the present invention, showing lines of magnetic flux applied to the melt. A crucible 11 made of quartz glass is inserted and filled with a melt 12.

The radius of curvature of the bottom of the quartz glass crucible 11 is rb. On the other hand, a diameter-sized grown silicon single crystal 13 is suspended from a crystal pulling wire 14 so that its lower surface is in contact with the surface of the melt 12. The crucible 11 described above is housed in a cylindrical electric heater 15 having a radius rh, and the heater 15 is housed in a cylindrical heat insulating member 16 made of carbon.

Radius r. The flat superconducting coil 17 serves as a low temperature maintenance means 18.
By appropriately selecting the radius r of the coil 17, the radius r of the bottom C of the crucible 11, and the spacing between the coils 17, the coils 17 are The magnetic flux lines 19 are the crucible 1
1 and along the bottom of the crucible 11.

To describe in more detail the conditions for the lines of magnetic flux 19 to pass along the outside and bottom of the crucible 11, there is a gap between the radius of curvature R of the lines of magnetic force 19, the outer radius F r of the crucible 11, and the bottom radius rb of the crucible 11. respectively, rS
RMF ≦4r r ≦R≦4r MFb In order to satisfy such conditions, it is desirable that the radius rc of the coil 17 has a relationship of rc-(1,5-5)r.

On the other hand, the means for heating the melt usually consists of an annular carbon member placed concentrically with the central axis of the crucible on the outside of the crucible, and this annular heating means has a slit from the upper end and a slit from the lower end. They are provided alternately along the circumferential direction. Therefore, the heating current flows through the heating means in a zigzag pattern with respect to the longitudinal direction of the heating means, and in order to avoid vibrations of the heater 15 caused by the interaction of this current and the magnetic field, the ripple value of the heating current of the heater 15 is ( It is preferable that the heating current is small.However, there is usually a ripple of 3 to 5% in the heating current, and when the current value fluctuates within this range, the coil 17 and heater 15 are close to each other and the distribution fluctuation current As a result, a large repeated stress acts on the heater 15 at high temperatures, resulting in a shortened lifespan of the heater 15.

According to the experimental results, the radius of the heater 15 is rh1, and the radius of the coil 17 is r. , the distance between the opposing coils 17 is L, so that r c > r h and L > 3 rh.
When the radius r0 of the coil 17 and the spacing between the coils 17 are selected, the number of durable uses of the heater 15 is 20% to 30% compared to h when the ripple value of the heating current is 4% or when r≦r or L≦3rh. % increased.

By the way, in order to stably pull a single crystal while a magnetic field is applied to the melt, there is a relationship between the diameter of the single crystal 13 and the diameter 2r of the crucible 11 of D/2r<0.75. According to the experimental results, I! in the grown single crystal 13 is desirable. It was found that the ti1m degree is related to the value of D/2r.

That is, when a magnetic field of 3000 Gauss is applied to the melt 12, when Q/2r<0.7, the oxygen concentration of the single crystal can be easily reduced to 10x 10 atoms/cl.
It can be R3 or less, and when D/2r<0.6 or less, 5X10
17atOIS/aR3 or less. Preferably, D
/2r<0.5 or less, and in this case, the wi elementary degree could be set to i x 10 atoms/cm3.

However, in the above experiment, the diameter of the single crystal 13 is in the order of 100φ
That's all.

FIG. 5 is an explanatory diagram showing the limit on the height of the low temperature holding means, and the pulled crystal 20 is placed in the pulled chamber 21. The centerline 23 of the coil 22 substantially coincides with the liquid level 24 of the melt. Increasing the diameter of the coil 22 in this low temperature holding means 25 increases the outer diameter and height of the cylindrical low temperature holding means 25 having a vertical axis for the opposing flat superconducting coils. In an experimental apparatus equipped with this cylindrical low temperature holding means, it is desirable that the height of the low temperature holding means is equal to the upper end of the coil plus 300M, and the inner diameter of the low temperature holding means is at least 10 mm higher than the inter-coil pressure @L.
It is desirable that the outer diameter is smaller than 0#l#I.

Further, from the operational point of view of the apparatus, a large-sized cryogenic maintenance means is undesirable, and it is desirable that the height be limited so that the measurement window 26 can function sufficiently. That is, the external dimensions of the measuring means 27 for optically measuring the diameter of the single crystal 20 are 10
αX 10 α 28 above, and its height has a lower limit of 200 points above 7 lunges of the pulling chamber 20. Therefore, the low temperature holding means C, /7) ft -'r n
) IITI lfl ++ 'W CFa
I-b IJ 1 %, Jj
QA^--11! Within this range, there is no support for mounting the low temperature holding means 25 and operating the measuring means 27.

Naturally, the shape of the low temperature holding means 25 may be modified in various ways. For example, by using a separate type low temperature holding means, the above-mentioned restrictions can be alleviated. Further, the outside shape of the low temperature holding means may be cylindrical, or the inside may be cylindrical and the outside may be a prismatic cylinder. In this case, the maximum diameter of the crucible is 45
As an example of the dimensions and weight of the low temperature holding means for 0mm diameter, the internal cylinder diameter is 900mm, and the external prismatic dimension is 1350#l.
(Medium) x ・1460m (Depth) x 1135M
(height), and the total weight was 2.61.

FIG. 6A is an explanatory diagram of a single crystal growth apparatus equipped with a low temperature holding means that can be raised and lowered, and the low temperature holding means 32 is placed opposite the pulling chamber 31. When replacing hot zone components such as heaters, %17-1j11a f
ft day 31 ++ -1%4 M a jt
mit 11 During maintenance such as when cleaning the inside of the e-shiba, the low temperature holding means 32 is lowered below the pulling chamber 31 as shown in FIG. 6B (9 to improve maintainability. is supported by a rotating column 33 and a rotating support arm 34, and during the above-mentioned maintenance,
As shown in FIG. 6B, the pulling chamber 31 is rotated around the rotating column 33 to expose the hot zone component 35 and improve workability.

[Effects of the Invention] According to the VL device of the present invention, by keeping the size of the low temperature holding means within preferred dimensional limits, the device can be easily operated.

[Brief explanation of drawings]

Fig. 1A is a plan view showing the flow of the melt and the magnetic field of the device of the present invention, Fig. 1B is a plan view of the location of Fig. 1A, and Fig. 2 is a coil facing the radius of the coil that applies the magnetic field to the melt. 3 is a graph showing the strength of the magnetic field on the Z-axis in FIG. 2, and FIG. 4A is a graph showing the magnetic flux lines applied to the melt, the main parts of the device of the present invention. FIG. 4B is a partial plan view of FIG. 4A, FIG.
Figure B is an explanatory diagram of a single crystal growth apparatus equipped with a low temperature holding means that can be raised and lowered. 1.11... Crucible, 2,12... Molten body, 3.19...
・Magnetic flux lines, 15... Heater, 17... Coil, 25...
Low temperature maintenance means. Figure 1A Figure 18 Figure 4A Figure 48 Figure 5 Figure 6B

Claims (3)

[Claims] (1) a cylindrical crucible; an annular heating means disposed outside the crucible concentrically with the central axis of the crucible for heating and melting a conductive substance within the crucible; A pair of electromagnetic coils are disposed symmetrically opposite to each other with respect to the central axis of the crucible on the outside of the heating means to prevent thermal convection of the molten substance, and a lower end thereof is located at the center of the liquid surface of the molten substance. a chamber that seals and accommodates the crucible, the single crystal, and the heating means; and a chamber that is held obliquely above the chamber during measurement and that measures the diameter of the lower end optically. a measuring means for measuring, a measuring window formed in the shoulder of the chamber so that the lower end can be visually recognized by the measuring means, and a measuring window arranged concentrically with the central axis, In the apparatus for growing the single crystal, which comprises an annular low-temperature holding means housing an electromagnetic coil,
An apparatus characterized in that the upper part of the low temperature holding means is arranged so as not to interfere with the measuring means and the viewing space of the measuring means through the measuring window. (2) The apparatus according to claim 1, wherein the external shape of the low temperature holding means is cylindrical. (3) The apparatus according to claim 1, wherein the external shape of the low temperature holding means is a prismatic cylinder.