JPH10120485A - Single crystal production apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a high-quality semiconductor single crystal in low power consumption by reducing size of a magnetic field generator unit of a single crystal pulling-up apparatus. SOLUTION: This apparatus for producing a high-quality semiconductor single crystal pulls up a single crystal from a crucible while carrying out control of convection of molten semiconductor materials accommodated in the crucible by a horizontal magnetic field formed with an electromagnet excited by a peripheral direct current in a radial magnetic exciter unit in which the electromagnet has a pair of counterposed saddle-type exciter coils and another pair of magnetic pole pieces in such a condition that the two magnetic pole pieces have a dimension in direction parallel with the crystal pull-up axis (height) which is one half or less of the initial height of the molten semiconductor material or one half or less of the diameter of the cavity between the poles, being 100mm or more and 600mm or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention can improve the quality of a single crystal by applying a magnetic field to the melt when pulling a single crystal from a melt obtained by heating a semiconductor material by the Czochralski method. The present invention relates to an apparatus for producing a single crystal.

In particular, the present invention relates to a technique effective for a silicon single crystal pulling apparatus which is a substrate material of a semiconductor VLSI.

[0003]

2. Description of the Related Art A group including one of the present inventors has
When pulling a single crystal by the Czochralski method, a static magnetic field is applied to the melt in the crucible, and the temperature of the melt is stabilized by controlling the heat convection, and the contamination from the crucible is reduced. It has been found and demonstrated that the quality of the crystal is improved (for example, Nikkei Microelectronics, September 15, 1980, Japanese Patent Publication No. 58-50951). This method has been described by the inventors of the present invention as a Magnetic-Fie.
ld Applied Czochralski (MC
Z) method.

As shown in the sectional view of FIG. 1, the conventional magnetic field applying and pulling apparatus is composed of a DC electromagnet composed of an iron core 2 constituting a magnetic path connecting the normal conducting coils 1a, 1b and 1a, 1b. A DC magnetic field is applied to the raw material melt 5 in the crucible 4 inside the chamber 3 of the pulling machine. In FIG. 1, a single crystal 6 and a heater 7 are shown.

In this apparatus, when the coils 1a and 1b are DC-excited, N and S magnetic poles are generated at both ends of the iron core 2, and a magnetic field 8 crossing the melt is formed. On the other hand, in a state where there is no magnetic field, as shown in FIG. 2, heat convection 9 in a turbulent state is generated in the melt 5 in the quartz crucible 4. In particular, the heat convection near the crucible wall causes a temperature change in the melt and at the solid-liquid interface 10, and microscopic re-dissolution in the grown crystal becomes remarkable. As a result, defects such as dislocation loops, vacancies, and interstitial atoms are generated in the grown crystal, and impurity atoms such as oxygen are segregated in stripes.

In general, a melt of a single crystal is a conductor having an electric conductivity σ, and a fluid moving in a direction perpendicular to a magnetic field has a braking force f per unit area represented by the following equation (1). work.

[0007] _{f = κ · σ · V R} · B Z 2 (1) where, kappa is a constant, sigma is electrical conductivity of the melt, V _R is the magnetic flux and the direction perpendicular velocity component, B _Z magnetic flux density Is shown.

[0008] Since the braking force by the magnetic field is proportional to the flow velocity V _R, fusion in a crucible a relatively large magnetic field thousands Gauss in order to suppress the relatively slow flow along the crucible wall as shown in FIG. 2 It was required to be added uniformly to the whole liquid.

The electromagnet for obtaining such a uniform magnetic field has a large size and a large weight, and has a problem in attachment to a pulling machine and operability. In particular, in the case of a large-diameter silicon single crystal, the distance between magnetic poles may be required to be 1000 mm or more, and if the required magnetic flux density is 3000 to 4000 gauss, the electromagnet that realizes this becomes a huge one exceeding 50 tons in weight, The required power has become 300 kW or more, and the ratio of the power to the single crystal manufacturing cost cannot be ignored.

As one method for solving the above-mentioned problem, as shown in FIG. 3, a magnetic field generator for pulling a single crystal using a superconducting magnet in which an air-core coil 12 is immersed in a liquid helium tank 11 is used. Has been put to practical use. In this case, the weight of the magnet was reduced by about an order of magnitude to 3 to 4 tons, and power cost became negligible due to superconductivity. However, a multi-stage heat shield cryostat with a refrigerator is often used as the superconducting magnet for efficiency, which increases the equipment cost and maintenance cost. In addition, consumption due to evaporation of helium cannot be ignored in terms of cost.

The effect of applying a magnetic field to the melt is to suppress the convection of the slow flow along the crucible as described above, to prevent the melting of quartz crucibles and the like, and to reduce contamination from the solid and liquid interfaces. The purpose is to prevent the occurrence of defects by suppressing thermal disturbance in the vicinity. A relatively low magnetic flux density of about 1000 gauss is sufficient to suppress thermal disturbance, but 300 gauss is used to suppress slow convection.
It is necessary to apply a relatively large magnetic field of 0 to 4000 Gauss and a uniform magnetic flux density. In order to achieve such a nearly uniform magnetic field distribution, the height or diameter of the pole piece needs to be at least about the distance between the poles. For example, when the distance between the poles is 1000 mm, the height or diameter of the pole piece is 1
000 mm, and the length of the coil winding increases, resulting in a huge weight as described above.

On the other hand, a magnetic field device for diameter direction excitation having a cylindrical state suitable for a single crystal pulling device is disclosed in Japanese Patent Publication No. 3-158.
No. 09. FIG. 4 shows an overall view, FIG. 5 shows an exploded perspective view thereof, and FIG. 6 shows a cross-sectional view thereof. The magnetic field device for diametrical excitation having a cylindrical shape having the two-pole facing structure type is assembled on a pair of semi-cylindrical outer cylinder yokes 13 and 14 and on the inner surface of each outer cylinder yoke. And a pair of pole pieces 15, 16
Each of the pair of saddle-type exciting coils 17, 18 is accommodated in the inner diameter surface space of each outer cylinder yoke and formed so as to fit the magnetic pole pieces 15, 16 therein. The outer cylinder yoke forms the electromagnet halves 19, 20 together with the pole pieces and saddle type excitation coils contained therein so that these electromagnet halves are joined together in a diametrical plane to become integral. Has become. Thus, as shown in FIG. 4, the electromagnet halves 19 and 20 are joined to each other on the diametrical surface of each of the outer cylinder yokes 13 and 14, and outside of them via appropriate fasteners 21. When they are firmly connected to each other, they come to have a cylindrical shape having a columnar space inside, and the saddle-type exciting coils 17 and 18 attached to each inside are in close contact as if they were one coil. When the saddle-type excitation coils 17 and 18 are energized, the axis of the coil generates a magnetic flux in a direction coinciding with the diameter direction of the cylindrical excitation space.

Although a single crystal using the above-mentioned magnetic field device for excitation is effective, there is room for improvement in weight and power consumption.

[0014]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and provides a single crystal pulling apparatus using a magnetic field applying apparatus which is reduced in size and weight without using superconductivity.

[0015]

Means for Solving the Problems As a result of diligent studies, the present inventors have found that the above-mentioned slow convection along the crucible wall can form a part of the flow path without applying a uniform magnetic flux to the entire melt. By stopping the flow, the entire flow can be stopped, and surprisingly, the present inventors have found that a higher quality semiconductor single crystal can be obtained as compared with the conventional one, and have reached the present invention.

That is, the present invention provides the following (1) to (4).

(1) An apparatus for pulling a single crystal from a crucible while controlling the convection of a semiconductor material melt contained in the crucible by a horizontal magnetic field formed by an electromagnet excited from the outer periphery by a direct current. A magnetic field device for diametrical excitation having a pair of saddle-type exciting coils facing an electromagnet and a pair of pole pieces facing each other, and a dimension (height) parallel to a crystal pulling axis of the two pole pieces is a semiconductor material melting point. 1/2 or less of the initial height of the liquid or 1 / of the diameter of the cavity between the magnetic poles
An apparatus for producing a single crystal, which is 2 or less or 100 mm or more and 600 mm or less.

(2) The pair of opposing saddle-type exciting coils are divided from each other, are joined at the diameter surface of each outer cylinder yoke at the time of use, and are connected to each other via fasteners to form a magnetic field device. (1) The single crystal production according to (1), wherein the single crystal is freely movable in a vertical direction along a crystal pulling axis when the crucible and the polycrystalline semiconductor material are loaded and when the grown single crystal is taken out. apparatus.

(3) The pair of opposing saddle-type exciting coils are divided from each other, are joined at the diameter surface of each outer cylinder yoke at the time of use, and are connected to each other via fasteners to form a magnetic field device. With the configuration, when loading the crucible and the polycrystalline semiconductor material, and when removing the grown single crystal, the fastening portion is removed, the magnetic field device is divided into a pair of saddle type magnet coils, and the magnetic device can be moved left and right through a guide. The apparatus for producing a single crystal according to the above (1), wherein:

(4) The pair of opposing saddle-shaped magnet coils are divided from each other, and are joined at the diameter surface of each outer cylinder yoke at the time of use, and are connected to each other via fasteners to form a magnetic field device. The single unit according to (1), wherein the unit is configured to open left and right with one side of the fastening part as a fulcrum when the crucible and the polycrystalline semiconductor material are loaded and when the grown single crystal is taken out. Crystal manufacturing equipment.

According to the present invention, it has been proved from the measurement of the oxygen concentration in the pulled single crystal that the amount of dissolution of the quartz crucible in the case of pulling a silicon single crystal is not much different from that obtained by applying a uniform magnetic field. Was. Furthermore, it was found that the microscopic distribution of the in-plane oxygen concentration of the single crystal was improved.

When the magnet coil is large like a conventional magnet, the magnetic flux density distribution in the height direction of the melt becomes substantially uniform. On the other hand, in the case of a magnet coil having a small pull-up dimension, that is, a narrow vertical width, the magnetic flux density in the vertical direction changes depending on the spatial position of the two magnet coils.

The magnetic flux density B _Z decreases from the center of the magnet coil toward upward (Z-axis), the braking force f convection as shown in equation (1) decreases in proportion to the square of B _Z.
The distribution of the liquid surface of a B _Z and f varies with the relative position of the magnet coil and the melt. Therefore, by changing the relative position in the height direction of the crucible, the most appropriate position, that is, the position where the best single crystal quality can be obtained, can be selected.

When a crystal is pulled by the Czochralski method, the crystal is usually rotated at a speed of 10 to 30 times per minute. Due to the stirring effect accompanying this rotation, the temperature distribution in the circumferential direction near the melt surface is made uniform, and the distribution of impurity distribution in the crystal plane is improved. However, in general, crystals grown by the Czochralski method have impurity concentration irregularities in the direction along the solid-liquid interface called growth fringes, which are formed in stripes in the pulling direction, and are observed in a ring shape in the crystal cross section. Is done. The distance d between the growth stripes in the growth axis direction has a relationship represented by the following equation (2).

D = pulling speed (per minute) / rotational speed (per minute) (2) Therefore, the cause of the generation of the growth fringes is the crystal rotation direction, that is, each rotation period of the growth speed due to temperature unevenness in the circumferential direction of the melt. It is said that this is due to fluctuations.

It is generally known that in the pulling under a horizontal magnetic field, the fluctuation of the impurity concentration accompanying the growth fringes due to the rotation is larger than that in the pulling under no magnetic field.

FIG. 7 shows a rotating flow 22 near the melt surface when a horizontal magnetic field 8 is applied to the semiconductor melt in the crucible 4. At this time, the vertical flow 9 of the component orthogonal to the magnetic flux direction inside the melt as shown in FIG. 2 is suppressed.
As shown in FIG. 7, the agitation of the melt by the rotation of the crystal forms many concentric belt-like flows, and the speed of each flow band is different, so that the heat supplied from the crucible wall is different. Even if there is no flow in the diametric direction, good heat exchange is performed in each zone and the heat is transmitted to the center, forming a stable heat gradient. However, the rotational flow has a component that is orthogonal to the magnetic flux and a component that is parallel to the magnetic flux, and a positional imbalance occurs in which the braking force is applied to the former and not applied to the latter. Because of the inertia of the melt, it is difficult to maintain the concentric flow of the melt. As a result, although the concentric flow is maintained as a whole, it is known that a temperature difference occurs in the circumferential direction. Have been. For example, crucible diameter 20 cm, melt height 10 cm, crystal rotation speed 10
At a depth of 20 mm below the surface of the melt at a distance of 30 mm from the center of the crucible under a condition of rpm and a magnetic field strength of 3700 gauss, a temperature difference of about 2.5 ° C. is generated between a position parallel to the magnetic flux and a position perpendicular thereto, The latter is higher. On the other hand, when there is no magnetic field, the generated temperature difference is about 0.5 ° C.

As described above, the magnetic flux density distribution suitable for crystal growth in a horizontal magnetic field is large enough to stop the slow flow along the crucible wall at the center of the melt, and the stirring effect due to the crystal rotation near the surface. It is better that the density is small enough not to hinder the effect. That is, analysis by the present inventors has revealed that it is better to have a difference in magnetic flux density in the depth direction of the melt.

According to the present invention, the above-described magnetic flux density distribution is realized by using a pole piece having a small thickness in the height direction of the melt, and the magnetic field device as a whole can be reduced in size and weight and improved in single crystal quality. An object of the present invention is to provide a single crystal pulling apparatus provided with a normal electroconductive magnet capable of simultaneously achieving the two.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described with reference to the following embodiments.

EXAMPLE A magnetic field device provided with a pair of saddle type exciting coils and a pair of magnet pieces shown in FIGS. 5 and 6 was used. The height of the magnetic field device of this embodiment is 500 mm, and the height h of the inner pole piece is 20 mm.
It was 0 mm. The outer diameter of the magnetic field device is 2100 mm, the diameter of the internal cavity is 1000 mm, and the weight is 7000 k
g. Further, a leakage magnetic field preventing coil is wound along the surface of the yoke outer cylinder, and a device for moving the magnetic field device in the vertical direction is added. The diameter of the quartz crucible was 500 mm, the silicon melt was 70 kg, and the height of the melt was about 250 mm.

A DC current of 750 A and 176 V is passed through the magnet coil to generate a magnetic flux of 3500 gauss while generating a magnetic flux of 8 mm in diameter.
An inch silicon single crystal was pulled up.

Comparative Example 1 The embodiment was repeated using only the conventional magnetic field device shown in FIG. The pole piece height in the magnetic field device is 1000
mm, the diameter of the internal cavity was 1000 mm, and the weight of the magnetic field device was 50,000 kg.

A DC current of 967 A and 200 V was passed through the magnet coil to pull up an 8-inch diameter silicon single crystal.

Comparative Example 2 The example was repeated using a magnetic field device provided with a saddle type exciting coil of a conventional design. The height of the magnetic field device was 1400 mm, of which the height of the pole pieces was 1000 mm. In the design using the saddle coil, the outer diameter of the cavity was 1000 mm and the weight was 16000 kg.

A DC current of 967 A and 156 V is applied to the magnet coil to generate a magnetic flux of 3500 gauss.
An inch silicon single crystal was pulled up.

As apparent from the above Examples and Comparative Examples, the magnetic field device of the present invention was able to greatly reduce weight and power.

FIG. 9 shows the magnetic flux density distribution in the pulling direction (Z axis, melt height direction) of the saddle type magnetic field generator when the pole pieces used in the example and the comparative example have different heights. .

As can be seen, when the height (h) of the pole piece is small as in the present invention, the rate at which the position in the pulling direction rises along the Z axis and the magnetic flux density decreases is the height of the pole piece. (H) is larger than when it is large. As a result, near the center of the crucible, the force for inhibiting the slow rotational flow of the melt along the crucible wall is strong, and the flow can be prevented. However, the force for inhibiting the rotational flow of the melt near the melt interface is weak. I know it works.

Using the magnetic field device of the present invention (lightweight saddle type, pole piece height 200 mm) and a conventional magnetic field device (non-saddle type), the former position the center of the pole piece 200 m from the melt surface.
m, the latter is 125 mm (１ ／ of the melt height), and a 200 mm diameter phosphorus-doped silicon single crystal is pulled up, and the solidification rate (the ratio of the growth weight of the single crystal to the total amount of melting) and the oxygen concentration are increased. The relationship was examined, and both showed a favorable oxygen concentration distribution.

FIGS. 10 and 11 show that the above crystal was processed into a wafer having a thickness of 1 mm and finished, and then heat-treated at 450 ° C. for 3 hours in a nitrogen gas stream to generate an oxygen donor. The micro-resistivity distribution on the wafer surface was measured at 500 μm intervals by a spreading resistance measuring instrument. This can be regarded as representing the oxygen concentration distribution. The variation width of the micro-resistivity distribution is as small as 3.3% in the case of the present invention shown in FIG. 10 as compared with 6.0% of the conventional type shown in FIG. 11, indicating that a good uniformity distribution can be obtained. I have.

[0042]

As described above, the magnetic field generator according to the present invention is more compact, easier to handle, and consumes less power than conventional devices. Furthermore, by performing pulling using the magnetic field generator according to the present invention, a high-quality semiconductor single crystal can be obtained.

[Brief description of the drawings]

FIG. 1 shows a conventional single crystal pulling apparatus.

FIG. 2 shows a single crystal pulling apparatus without applying a magnetic field.

FIG. 3 shows a single crystal pulling apparatus using a superconducting magnet.

FIG. 4 is an overall view of a magnetic field device.

FIG. 5 is an exploded perspective view of the magnetic field device.

FIG. 6 is a front sectional view and a plan sectional view of a saddle type magnetic field device.

FIG. 7 is a rotational flow near the surface of a melt in a crucible.

FIG. 8 is a front sectional view and a plan sectional view of a conventional magnetic field device.

FIG. 9 is a magnetic flux density distribution in a horizontal sectional direction of the magnetic field device.

FIG. 10 shows a resistivity distribution of a single crystal obtained by the present invention.

FIG. 11 shows a resistivity distribution of a conventional single crystal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Normal conducting coil 2 Iron core 3 Chamber 4 Crucible 5 Semiconductor melt 6 Single crystal 7 Heater 8 Magnetic flux flow 9 Convection 10 Solid-liquid interface 11 Liquid helium tank 12 Air core coil 13,14 Outer cylinder yoke 15,16 Magnetic pole piece 17 , 18 Saddle-type excitation coil 19, 20 Electromagnet half 21 Fastener 22 Rotational flow

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tokuichi Kiji 3-5-3 Tatsumi, Koto-ku, Tokyo Mitsubishi Steel Corporation Environmental Engineering Division (72) Inventor Toyohiko Tanaka 3-5-Tatsumi, Koto-ku, Tokyo No. 3 Mitsubishi Steel Corporation Environmental Engineering Division

Claims (4)

[Claims] An apparatus for pulling a single crystal from a crucible while controlling a convection of a semiconductor material melt contained in the crucible by a horizontal magnetic field formed by an electromagnet which is DC-excited from the outer periphery. Is a magnetic field device for diametrical excitation having a pair of opposing saddle-type exciting coils and a pair of magnetic pole pieces facing each other, and a dimension (height) parallel to the crystal pulling axis of the two magnetic pole pieces is a semiconductor material melt. A single crystal manufacturing apparatus characterized in that the height is not more than 1/2 of the initial height or not more than 1/2 of the diameter of the cavity between the magnetic poles or not less than 100 mm and not more than 600 mm. 2. A pair of opposed saddle-shaped magnet coils are divided from each other, are joined at the diameter surface of each outer cylinder yoke at the time of use, and are connected to each other via fasteners to constitute a magnetic field device. 2. The single crystal manufacturing apparatus according to claim 1, wherein the crucible and the polycrystalline semiconductor material are loaded and the grown single crystal is taken out, and the single crystal manufacturing apparatus is vertically movable along a crystal pulling axis. 3. A pair of opposing saddle-type exciting coils are divided from each other, and are joined at the diameter surface of each outer cylinder yoke during use, and are connected to each other via fasteners to constitute a magnetic field device. At the same time, when loading the crucible and the polycrystalline semiconductor material, and when removing the grown single crystal, the fastening portion is removed, the magnetic field device is divided into a pair of saddle-shaped magnet coils, and the magnetic device can be moved left and right through a guide. The apparatus for producing a single crystal according to claim 1, wherein: 4. A pair of opposing saddle-type exciting coils are divided from each other, are joined at the diameter surface of each outer cylinder yoke at the time of use, and are connected to each other via fasteners to constitute a magnetic field device. 2. The single crystal manufacturing method according to claim 1, wherein the crucible and the polycrystalline semiconductor material are loaded and the grown single crystal is taken out, and the one side of the fastening portion is opened as a fulcrum. apparatus.