JP2002249396A - Method for growing silicon single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture at a high productivity a silicon single crystal, in which the external diameter of a latent area of oxidation induced stacking faults appearing in a crystal face is controlled to the range of 0-70% of its crystal diameter, and which is excellent in pressure resistant characteristics of oxide film, and especially to manufacture at a high productivity a single crystal consisting of a crystal area where crystal originated particles(COP) having the size of >=0.1 μm do not exist and neither does a dislocation cluster. SOLUTION: A pair of coils 6 for applying a magnetic field is so arranged around a chamber 8 that the coils are opposed to each other with a crucible 1 placed in between. A cusp magnetic field is formed in a molten liquid 4 in the crucible 1 by applying an electric current to the pair of an upper coil 6a and a lower coil 6b respectively so that the applied current circulates inversely to each other. An electric current is applied to the silicon molten liquid 4 in the quartz crucible 1a by applying a voltage between a pulling-rise and fall shaft 7 and a crucible lifting/lowering shaft by an electric power source 13 arranged outsider the chamber 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for growing a silicon single crystal by the CZ method.
The present invention relates to a method for growing a silicon single crystal while rotating a silicon melt in a crucible by applying a magnetic field and a current perpendicular to the silicon melt.

[0002]

2. Description of the Related Art Silicon wafers used for manufacturing semiconductor devices are mainly manufactured from silicon single crystals grown by the Czochralski (CZ) method. FIG.
FIG. 1 is a cross-sectional view schematically showing a single crystal manufacturing apparatus used for the CZ method. In the figure, reference numeral 1 denotes a crucible provided in a chamber 8. The crucible 1 is composed of a quartz crucible 1a for accommodating a silicon melt and a graphite crucible 1b for fittingly holding the outer peripheral surface of the quartz crucible 1a. The crucible 1 is fixed to the upper end of a crucible elevating shaft 11 that can rotate and ascend and descend. I have.

[0003] A resistance heating type heater 2 is arranged concentrically outside the crucible 1, and a crucible 1 is filled with a melt 4 obtained by melting a predetermined weight of a raw material by the heater 2.
Above the central axis of the crucible 1, a pulling up / down shaft 7 made of a wire or a shaft rotating at a predetermined speed in the opposite direction or in the same direction as the crucible lifting / lowering shaft 11 is disposed. The seed crystal 3 is suspended from 7 via a seed crystal holder 10.

[0004] Using such a single crystal manufacturing apparatus, CZ
When producing a silicon single crystal by the method, first, a silicon raw material for crystal is put into the crucible 1 and the inside of the apparatus is reduced in pressure in an inert gas atmosphere. Is melted by the heater 2 arranged in the heater. Thereafter, the seed crystal 3 hung on the pulling up / down shaft 7 is immersed in the melt 4, and while rotating the crucible raising / lowering shaft 11 and the pulling up / down shaft 7, the pulling up / down shaft 7 is pulled up to lower end of the seed crystal 3. Then, a silicon single crystal 5 is grown.

In the production of a silicon single crystal by the CZ method, the silicon melt contained in the crucible 1 receives heat from a cylindrical heater installed around the crucible 1, so that the temperature within the melt is increased. It is necessary to mechanically rotate the crucible 1 to make the distribution completely axisymmetric with respect to the single crystal pulling axis.

As described above, a quartz crucible is mainly used as the crucible 1a for containing the silicon melt 4, but when the quartz crucible 1a comes into contact with the silicon melt 4, the surface of the crucible 1a is melted. Oxygen is released therein, and a part of the oxygen in the melt 4 is taken into the single crystal 5 during the pulling. The oxygen taken into the single crystal 5 forms a gettering effect of forming an oxygen precipitate inside the wafer and capturing heavy metal impurities in a heat treatment process in the manufacture of a semiconductor device, and is essential for a silicon single crystal. Impurities. Therefore, the crucible 1 is also used to control the oxygen concentration in the silicon single crystal.
Need to be rotated.

However, in recent years, it has been strongly desired to provide a large-diameter silicon single crystal, and the single crystal pulling apparatus itself has been increased in size, and the crucible to be used has been increasing in size. In order to rotate the motor at a high speed, a large-scale driving device and the like are required, so that the equipment is restricted.

Therefore, in recent years, by rotating the silicon melt in the crucible without forcibly rotating the crucible,
As a pulling method capable of obtaining a silicon single crystal having a uniform impurity concentration in a crystal plane, for example, Japanese Patent No. 295
Japanese Patent No. 9543 and Japanese Patent No. 2930080 have been proposed. Specifically, in growing a silicon single crystal by the CZ method, a magnetic field is applied to the silicon melt, and an electrode inserted on the surface of the silicon melt so that an electric current orthogonal to the magnetic field flows through the silicon melt. This is a method of flowing a current between crystals and rotating the melt by the generated Lorentz force, which is a method of growing a silicon single crystal called a current magnetic field applying crystal growing method or an EMCZ method.

[0009]

According to the EMCZ method described above, the silicon melt in the crucible can be rotated and stirred without forcibly rotating the crucible.
However, any of the EMCZ methods proposed so far has a structure in which an electrode is inserted into the surface of a silicon melt and an electric current is applied. Therefore, additional equipment for inserting and supporting the electrode is required, and the structure of the device is complicated. In addition, since the electrodes are inserted into the silicon melt, the rotation of the silicon melt is partially obstructed by the electrodes, and the symmetry of rotation is low, so that the oxygen concentration distribution and the dopant impurity concentration distribution within the single crystal plane are made uniform. It was difficult.

The present invention has been made in view of the above-mentioned problems relating to the conventional method of growing a silicon single crystal by the EMCZ method, and is intended to remove a silicon melt in a crucible without inserting an electrode into the silicon melt. Let it evenly mix,
It is an object of the present invention to provide a method for growing a silicon single crystal having a uniform oxygen concentration distribution and dopant impurity concentration distribution in a single crystal plane.

[0011]

Means for Solving the Problems The present inventors have proposed this EMC.
In the Z method, as a result of diligent research on a method of rotating and stirring the silicon melt in the crucible without inserting an electrode into the silicon melt, the crucible lifting shaft supporting the crucible was adopted as an electrode, and current was applied to the silicon melt. And found that the silicon melt in the crucible was stirred by flowing, and completed the present invention.

The gist of the present invention is to provide a method of growing a silicon single crystal by the CZ method, wherein a magnetic field is applied to a silicon melt in a crucible, and a voltage is applied between a pulling up / down shaft and a crucible up / down shaft. The present invention is characterized in that a silicon melt in a crucible is agitated by flowing a current containing a component orthogonal to the magnetic field in the silicon melt.

In the method of growing a silicon single crystal according to the present invention, it is desirable that the magnetic field applied to the silicon melt is a magnetic field containing a vertical magnetic field component. In terms of uniformity of distribution,
It is desirable to apply a cusp magnetic field.

Usually, a crucible for containing a silicon melt is mainly made of quartz. Quartz is an insulator having an electric conductivity of about 10 15 Ωm at room temperature. However, under a high-temperature atmosphere of 1500 ° C. or more, such as the growth of a single crystal by the CZ method, quartz becomes a conductor having an electric conductivity of about 102 Ωm. In addition, when the silicon single crystal raw material is loaded into the quartz crucible, the contact area between the quartz crucible and the graphite crucible is small, but after melting the raw material, both crucibles reach a high temperature exceeding the melting point of silicon (1420 ° C), The crucible softens and comes into close contact with the graphite crucible under its own weight and the weight of the silicon melt.

[0015] Therefore, by applying a voltage between the single crystal pulling up / down shaft and the crucible up / down shaft, a sufficient current flows in the silicon melt, and an electromagnetic force is exerted by the magnetic field applied to the silicon melt so that the crucible works. The silicon melt inside is agitated.

In the method for producing a silicon single crystal of the present invention, it is desirable to apply a magnetic field of 0.03 T or more as the cusp magnetic field applied to the silicon melt. If it is smaller than 0.03T, the effect of stirring the silicon melt by the Lorentz force is small, so that the oxygen concentration distribution and the dopant impurity concentration distribution in the single crystal plane cannot be made uniform. The strength of the magnetic field is preferably as high as possible in terms of crystal quality, but there are restrictions on the structure and performance of the apparatus.

In the method for producing a silicon single crystal according to the present invention, it is desirable that the current supplied to the silicon melt is in the range of 1 to 20 A. If it is smaller than 1A, the rotation of the silicon melt due to Lorentz force becomes too small, so that the oxygen concentration distribution and the dopant impurity concentration distribution in the single crystal plane cannot be made uniform.
Since the diameter of a normal neck portion is about 3 mm and its resistance is large, there is a concern that Joule heat is generated in the neck portion and the strength of the neck portion is reduced.

In the method for producing a silicon single crystal of the present invention, in order to stir the silicon melt, it is indispensable to supply a current perpendicular to the magnetic field applied to the silicon melt. For this reason, it is effective for the current flowing in the silicon melt to increase the current toward the crucible side wall as much as possible and to reduce the current toward the crucible bottom as small as possible to stir the silicon melt with low power.

For example, by increasing the thickness of the bottom of the quartz crucible or coating the bottom of the inner or outer surface of the quartz crucible with a high melting point material having a high electrical resistivity to increase the electrical resistivity of the bottom, the quartz crucible is increased. Increasing the current density to the side wall, or coating the inner and outer surface side walls and upper end of the quartz crucible with a high melting point material having a low electrical resistivity to increase the current density to the quartz crucible side wall,
This is an effective means as a low power technology in the present invention.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view schematically showing a silicon single crystal growing apparatus suitable for obtaining a silicon single crystal of the present invention. In the figure, reference numeral 1 denotes a crucible provided in the chamber 8. The crucible 1 is a quartz crucible 1a containing a silicon melt 4
And a graphite crucible 1 for fittingly holding the outer peripheral surface of the quartz crucible 1a.
b, and is fixed to the upper end of the crucible elevating shaft 11. A resistance heating type heater 2 is concentrically arranged outside the crucible 1, and a lifting elevating shaft 7 rotating at a predetermined speed on the same axis as the crucible elevating shaft 11 is provided above the central axis of the crucible 1.
The seed crystal 3 is suspended from the lower end of the pulling up / down shaft 7 via a graphite seed crystal holder 10. Above the crucible 1, a heat shield 9 for controlling the temperature distribution in the pulling axial direction is arranged so as to surround the single crystal 5 being grown.

A coil 6 for applying a magnetic field is provided around the chamber 8 so as to face upward and downward via the crucible 1.
Are provided in a pair, and a current circulating in opposite directions flows through the pair of upper coil 6a and lower coil 6b, whereby a cusp magnetic field is formed in the melt 4 in the crucible 1. In addition, a voltage is applied between the lifting shaft 7 and the crucible shaft 11 by the power supply device 13 provided outside the chamber 8, and a current is supplied to the silicon melt 4 in the quartz crucible 1 a. In the example of the present invention, a tungsten wire excellent in high heat resistance is used as the lifting shaft 7 and the crucible elevating shaft 1 is used.
In 1, the portion exposed to the inside of the chamber 8 was made of graphite, and the lower portion was made of stainless steel. Lifting shaft 7 and crucible lifting shaft 11
It is necessary that at least one of them is electrically insulated from the chamber 8, and in this embodiment, an insulating material (not shown)
Was interposed both in the lifting shaft 7 and the crucible elevating shaft 11 to be electrically insulated from the chamber 8.

Next, a method for growing a silicon single crystal according to the present invention will be described in order. The specification of the silicon single crystal grown in the present invention is such that the oxygen concentration is 24 ppma, the electric resistivity is 10 Ωcm, the diameter is 200 mm, and the straight body length is 1200 m.
m, a silicon single crystal having a crystal orientation <001>. First, after reducing the pressure in the chamber 8 in an inert gas atmosphere, 120 kg of a polycrystalline silicon raw material is put into a quartz crucible 1 a having a diameter of 26 inches, and the electric resistivity in the single crystal is 10%.
Boron as a p-type dopant is added so as to be Ωcm, and the polycrystalline silicon raw material in the quartz crucible 1a is heated and melted by the cylindrical graphite heater 2 installed around the graphite crucible 1b to form a silicon molten liquid 4. I do.

Thereafter, the arrangement of the coil 6 is adjusted so that the center position of the cusp magnetic field at which the cusp magnetic field intensity becomes 0 is located at the center of the melt, which is 80 mm below the surface of the melt. A cusp magnetic field is applied so that the horizontal magnetic field strength perpendicular to the side wall of the crucible 1 at the height is 0.09 T, and the vertical magnetic field strength at the center of the bottom wall of the crucible 1 at the initial stage of pulling is 0.08 T. Thereafter, the lower end of the seed crystal 3 is immersed in the melt 4 and pulled upward while rotating the pulling shaft 7 to grow the silicon single crystal 5 at the lower end of the seed crystal 3. Here, since the crucible 1 rises upward in accordance with the growth of the single crystal, the surface position of the melt is always kept constant with respect to the heater and the cusp application position.

Next, after performing seed drawing for eliminating single crystal dislocation, a shoulder is formed, and the shoulder is changed to obtain a target straight body diameter. At the time when the diameter reaches the target body diameter, the power supply 1
A voltage is applied between the pulling shaft 7 and the crucible elevating shaft 11 by 3 to generate a circumferential Lorentz force in the silicon melt, thereby growing the single crystal while rotating the silicon melt in the quartz crucible 1a. Was done. At this time, the single crystal pulling speed was 1.0 mm / min, the single crystal rotation speed was 6 rpm, and the crucible rotation speed was 0 rpm. Further, in the present invention, the electricity is supplied to the silicon melt 4 from the start of the single crystal straight body, but the electricity may be supplied from the time of the seed crystal deposition.

FIG. 2 is a cross-sectional view schematically showing a single crystal growing apparatus suitable for the conventional EMCZ method used as a conventional example of the present invention. Electrode 1 without applying voltage to crucible lifting shaft
A silicon single crystal was grown under the same apparatus and under the same process conditions as in the example of the present invention, except that 2 was inserted into the silicon melt and a current of 4 A was applied.

For each silicon single crystal obtained from the present invention example and the conventional example, the straight body length was 100 mm,
Crystals were cut radially from three positions of 300 mm and 600 mm, and the oxygen concentration distribution and the dopant impurity concentration distribution in the crystal radial direction were examined for each crystal part. The oxygen concentration distribution was determined by Fourier transform infrared absorption spectroscopy (FT-IR method), and the dopant impurity concentration distribution was determined by spreading resistance method (SR method). Here, the distribution of the oxygen concentration and the dopant concentration in the crystal radial direction is as follows.
[(Concentration at center of single crystal-concentration at outer periphery of single crystal) /
Concentration at the center of the single crystal] × 100. Table 1 shows the results.

[0028]

[Table 1]

As is clear from Table 1, in the present invention,
In each case, the non-uniformity of the oxygen concentration distribution in the crystal radial direction is 4% or less, and the non-uniformity of the dopant impurity concentration distribution is 5% or less.
It was below. On the other hand, in the conventional example, since the electrode is inserted into the silicon melt, the rotation of the melt is deformed at this portion and the axial symmetry is deteriorated. The characteristics are 6% or more, and the non-uniformity of the dopant impurity concentration distribution is 8% or more, which indicates that it is difficult to make the oxygen concentration and the dopant impurity concentration distribution uniform.

[0030]

According to the present invention, since no electrodes are inserted into the silicon melt, the rotation of the silicon melt is not hindered by the electrodes, and the symmetry of rotation is increased. Is uniform in the radial direction.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a single crystal growing apparatus according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view schematically showing a single crystal growing apparatus according to a conventional EMCZ method.

FIG. 3 is a cross-sectional view schematically showing a conventional general single crystal growing apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Crucible 2 Heater 3 seed crystal 4 Melt 5 Single crystal 6 Magnetic field application coil 7 Pull-up / down shaft 8 Furnace 9 Heat shield 10 Seed crystal holder 11 Crucible up / down shaft 12 Electrode 13 Power supply device

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shunji Kuragaki 2201 Kamioda, Kota-cho, Kishima-gun, Saga Prefecture Within the Sitix Division, Sumitomo Metal Industries, Ltd. (72) Inventor Masato Watanabe 5-chome, Shiba 5-chome, Minato-ku, Tokyo 1 NEC Corporation (72) Inventor Minoru Eguchi 5-7-1 Shiba, Minato-ku, Tokyo NEC Corporation F-term (reference) 4G077 AA02 CF10 EH06 EJ01 EJ02 PA08 PF51 RA01 RA03 RA03

Claims (3)

[Claims] In a method for growing a silicon single crystal by the CZ method, a magnetic field is applied to a silicon melt in a crucible, and a voltage is applied between a pull-up / down shaft and a crucible up-and-down shaft to cause the silicon melt to grow. Flowing a current containing a component orthogonal to the magnetic field to agitate the silicon melt in the crucible. 2. The method for growing a silicon single crystal according to claim 1, wherein the magnetic field applied to the silicon melt contains a vertical magnetic field component. 3. The method for growing a silicon single crystal according to claim 2, wherein the magnetic field applied to the silicon melt is a cusp magnetic field.