JP2000239096A - Production of silicon single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a silicon single crystal of which oxygen concentration distribution in both the direction of crystal growth and the crystal plane can be uniformly controlled and in which the occurrence of a dislocation can be prevented. SOLUTION: When a silicon single crystal is produced by pulling a crystal according to the Czochralski method while applying an equiaxially symmetrical cusp magnetic field about a pulling axis to a melt 4 housed in a crucible 1a, the atmospheric pressure is controlled so as to have a specific defined value in the process for pulling the singled crystal. The specific defined value is preferably 50 Torr (more preferably 80 Torr). The intensity of the cusp magnetic field is preferably 300-600 G.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a Czochralski method (hereinafter referred to as "C") by applying a cusp magnetic field to a melt in a crucible.
More specifically, a cusp magnetic field is applied equiaxially symmetrically with respect to the pull-up axis to uniformly control the oxygen concentration distribution in the crystal growth direction, The present invention relates to a method for producing a silicon single crystal in which a variation in an in-plane oxygen concentration distribution (hereinafter referred to as “ROG: Radial Oxygen Gradient”) is suppressed.

[0002]

2. Description of the Related Art In a silicon single crystal used for an ultra-highly integrated circuit, oxygen in the silicon crystal is precipitated as an oxide,
A so-called gettering technique for gettering heavy metal impurities which cause a reduction in element yield near the wafer surface is used. In order to sufficiently exhibit this gettering function, it is important to uniformly incorporate oxygen into the crystal.

In recent years, if the oxygen concentration value required for a substrate is strictly defined in response to the enhancement of the function of a semiconductor device, it is difficult to cope with the conventional CZ method. Moreover, in a large-sized single crystal (8-inch, 12-inch) manufacturing apparatus recently introduced, the phenomenon of dislocations in the process of pulling a single crystal tends to increase. Therefore, also from the viewpoint of coping with the problem of dislocation, a method of applying a cusp magnetic field in the radial direction with respect to the pulling axis as the center of symmetry is applied to the melt in the crucible when pulling the single crystal.

[0004] In this method of applying a cusp magnetic field, a pair of magnets (coils) for flowing an annular current in opposite directions are arranged above and below a crucible. Due to the arrangement of the magnets, the horizontal magnetic field component becomes 0 (zero) on the center axis of the coil. Further, a point occurs where the vertical magnetic field component also becomes 0 (zero) near the center of the upper and lower magnets on this central axis. Hereinafter, such a point is referred to as a magnetic field center position. The horizontal and vertical components of the magnetic field are generated as the distance from the magnetic field center position increases in the radial and vertical directions. The cusp magnetic field can stabilize the melt by restricting the flow of the melt in the crucible by such a magnetic field component. That is, by applying a cusp magnetic field to the melt, convection can be suppressed, and the penetration of quartz from the crucible surface can be suppressed, and as a result, dislocations can be prevented during crystal growth.

[0005] Furthermore, since the melting of quartz from the crucible surface can be suppressed by applying a cusp magnetic field, the oxygen concentration in the crystal can be reduced at the same time. Usually, such effects are promoted by increasing the magnetic field strength (Hirata et al .: J. Crystal Growth, 98, 777 (1
989)). Therefore, if such an effect is applied to the top side of the crystal where the oxygen concentration becomes high immediately after the start of the pulling, oxygen reduction can be achieved in that portion, and the product yield can be improved. However, in the pulling after the top of the crystal, the oxygen concentration decreases with the progress of the pulling of the single crystal. Therefore, under the conditions of the application of the cusp magnetic field, the oxygen concentration is reduced in order to avoid oxygen reduction in this region. It is necessary to develop a control method that increases

A so-called crucible rotation control method (see Japanese Patent Application Laid-Open No. 57-135796) is known as a means for avoiding oxygen reduction from the top of the crystal. This method utilizes the fact that the dissolution rate of a quartz crucible, which is an oxygen supply source, is changed by changing the rotation speed of the crucible. Specifically, when the rotation speed of the crucible is increased, the penetration of quartz increases, and the amount of oxygen taken into the crystal also increases.However, when the rotation speed of the crucible is reduced, the penetration of quartz decreases, and the amount of oxygen taken into the crystal decreases. Is going to decrease. However, when this method is used, the range in which the oxygen concentration in the crystal is increased becomes large, so that a large increase in the number of rotations of the crucible is required to secure this increase range.

By the way, in order to sufficiently exert the above-mentioned gettering function, “ROG” representing the oxygen concentration distribution in the crystal plane must be uniformly formed along with the oxygen concentration distribution in the crystal growth direction of the pulled single crystal. You need to control. Usually R
It is known that OG depends on the ratio of the crystal and the crucible rotation speed rotating in the opposite direction. Specifically, the smaller the ratio of “crystal rotation speed / crucible rotation speed”, the greater the variation in ROG. .

In order to increase the ratio of the "crystal rotation speed / crucible rotation speed", it is effective to reduce the crucible rotation speed or increase the crystal rotation speed. But,
The lower limit of the number of rotations of the crucible actually used is 4 to 5 rpm. FIG. 9 is a diagram showing the relationship between the number of rotations of the crucible and the dislocation position. It can be seen from FIG. 9 that if the pulling is performed at a low rotation of about 3 to 5 rpm, dislocations frequently occur in the first half of the body. This factor is evident from the relationship between the crucible rotation speed and the melt temperature fluctuation shown in FIG. 10, when the crucible rotation speed is less than 5 rpm, the melt temperature fluctuation becomes large, and dislocations are likely to occur frequently. Can be

On the other hand, assuming that a cusp magnetic field is applied, for example, in Japanese Unexamined Patent Publication No. Hei. 5-194077, in order to adjust the oxygen concentration and distribution in the silicon rod, after a predetermined single crystal rod diameter is determined, the silicon melting point is determined. There has been proposed a method of manufacturing a silicon single crystal in which the number of rotations of a crucible is increased and the strength of a magnetic field is reduced in accordance with an increase in a solidified portion of an object. In this manufacturing method, the rotation of the single crystal to be pulled and the crucible are in opposite directions, and when the single crystal grows,
The rotation speed of the single crystal is higher than the rotation speed of the crucible. As the single crystal is pulled, the rotation speed of the crucible is increased. As the single crystal grows, the strength of the magnetic field is reduced and the component of the magnetic field perpendicular to the bottom and side walls of the crucible is reduced. Then, the magnetic field is extinguished after about 50 to 80% of the charged melt is solidified. Thereafter, the oxygen content is adjusted by increasing the number of rotations of the crucible with respect to the rotation speed of the single crystal.

However, according to the proposed manufacturing method,
With the growth of the single crystal, the intensity of the magnetic field is reduced and further erased, so that the effect of suppressing the dislocations caused by the application of the magnetic field becomes insufficient, and the problem of lowering the product yield due to the occurrence of dislocations, There is also a problem that ROG is deteriorated by increasing the number of rotations of the crucible.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in the CZ method in which a cusp magnetic field is applied in order to adjust the oxygen concentration in a crystal, particularly, the oxygen concentration after the top of the crystal. It has been developed to control the atmospheric pressure in the pulling furnace when pulling a single crystal, to uniformly control ROG simultaneously with the oxygen distribution in the crystal growth direction, and to reduce dislocations during crystal growth. It is an object of the present invention to provide a method for preventing and manufacturing a silicon single crystal of excellent quality.

[0012]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have made various studies focusing on the atmospheric pressure in the production of a single crystal by the CZ method. Hitherto, there has been proposed a method of controlling the oxygen concentration by adjusting the atmospheric pressure in a furnace under the condition that no magnetic field is applied (for example, see Japanese Patent Application Laid-Open No. 3-159986). As a result of examining the control method proposed here, the following views were obtained.

[0013] That is, the effect of controlling the oxygen concentration by adjusting the ambient pressure remains in extremely small, specifically, for changing the oxygen concentration of ^{1 × 10 17 atoms / cm 3} 6
Atmospheric pressure of 0 Torr (20 Torr → 80 Torr) must be changed. Further, the effect of controlling the oxygen concentration becomes more saturated as the atmospheric pressure increases above the above pressure, and the effect of controlling the oxygen concentration with respect to the amount of change in the pressure decreases. Further, when the atmospheric pressure is set to a high pressure condition of 100 Torr or more, the inert gas introduced into the chamber remains, so that the SiO gas generated from the melt surface is not efficiently discharged, and the gas is deposited in the chamber. The deposited SiO gas may fall from the chamber to the liquid surface and cause dislocation. Given such a view, in the CZ method in which a magnetic field is applied, application of a method of controlling the oxygen concentration by adjusting the atmospheric pressure has not been considered.

However, according to the results of many studies focusing on the atmospheric pressure in the CZ method by the present inventor, when a cusp magnetic field is applied, compared to when no magnetic field is applied,
It has been clarified that the controllability of the crystal growth direction and the oxygen concentration in the crystal plane is significantly improved by adjusting the atmospheric pressure. In addition, the application of a magnetic field suppresses the melting of the quartz crucible, resulting in reduced evaporation of the SiO gas and dislocation even at a high furnace pressure (100 to 150 Torr) that could not be used in the conventional CZ method. It was also found that crystals could be grown without causing the adverse effects of the above. The present invention is
It was completed based on such knowledge, and
The gist is the method for producing a silicon single crystal of (1) or (2).

(1) A method for producing a silicon single crystal by the Czochralski method, in which a crystal is pulled while applying a cusp magnetic field which is equiaxially symmetric with respect to a pulling axis to a melt contained in a crucible, This is a method for producing a silicon single crystal, characterized in that in the process of pulling a crystal, the atmospheric pressure is changed and controlled at a value equal to or higher than a specific value.

(2) The atmospheric pressure is desirably 50 Torr, and more desirably 80 Torr. Also,
It is desirable to apply the strength of the cusp magnetic field in the range of 300G to 600G.

In the present invention, the control of the atmospheric pressure may be at least in the process of pulling up the straight body for forming the product diameter of the single crystal, and the control of the atmospheric pressure is not performed when forming the neck and the shoulder. May be.

The magnetic field strength defined in the present invention is such that the magnetic fields cancel each other and the magnetic field strength in the vertical and horizontal directions is zero.
It is indicated by the strength of the horizontal magnetic field in the radial direction on the side wall of the crucible at the height of the magnetic field center position, which is (zero).

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventor repeated experiments using a manufacturing apparatus equipped with a cusp magnetic field applying device shown in FIG. 1 while varying the atmospheric pressure conditions, the cusp magnetic field applying conditions, and the like. As a result, it has been clarified that the controllability of the oxygen concentration is improved by setting the atmospheric pressure in the single crystal pulling process to a specific value or more.

FIG. 1 is a diagram schematically illustrating the structure of a manufacturing apparatus to which the method for manufacturing a silicon single crystal of the present invention is applied. Here, silicon as a crystal raw material is held in the crucible 1 in a molten state, and the seed crystal 3 is rotated in a state of being in contact with the surface of the melt 4, and is rotated upward in accordance with the speed of solidification and growth of the seed crystal 3. The single crystal 5 having a predetermined diameter is obtained by pulling and growing. A quartz crucible 1a for holding the melt is fitted inside a graphite crucible 1b for supporting outside, and the crucible 1 is rotated around its entirety by a rotating shaft 11 with its central axis coincident with a pulling axis. And can be moved up and down again.

Above the central axis of the crucible 1, a pulling device 7 composed of a pullable wire is arranged. Crucible 1
A heater 2 for heating and a heat insulating material 10 are arranged concentrically on the outside, and all of them are housed in a chamber 8 and a pull chamber 9 which can block outside air. A pair of coils 6 for applying a magnetic field is provided so as to face upward and downward via the crucible 1.
A cusp magnetic field can be formed in the portion of the melt 4 in the crucible by passing currents flowing in opposite directions to the pair of upper coil 6a and lower coil 6b. Note that Cc in the figure indicates the magnetic field center position.

Using the manufacturing apparatus shown in FIG.
Was placed in a quartz crucible having an effective inner diameter of 560 mm and sufficiently melted to produce a silicon single crystal having a diameter of 8 inches. When pulling, the main conditions are a crystal rotation speed of 12 rpm, a crucible rotation speed of 6 rpm, and Ar in the chamber.
The flow rate is 50 l / min, and the atmospheric pressure during the pulling process (hereinafter sometimes referred to as furnace pressure) is 20 Torr, 50
Fluctuated at Torr and 80 Torr. Further, the strength of the cusp magnetic field was set to 0 G (no magnetic field), 300 G and 600 G. The results at this time are shown in FIGS.

FIG. 2 is a diagram showing the relationship between the magnetic field strength and the oxygen concentration distribution in the crystal growth direction when the atmospheric pressure (furnace pressure) is 20 Torr, and FIG. 3 is the atmospheric pressure (furnace pressure).
Is 50 Torr, FIG. 4 shows that the atmospheric pressure (furnace pressure)
FIG. 4 is a diagram showing the relationship between each magnetic field strength and the oxygen concentration distribution in the crystal growth direction at 80 Torr. As apparent from FIGS. 2 to 4, when the atmospheric pressure was 20 Torr, a clear oxygen reduction effect was exhibited.
It can be seen that the effect of reducing oxygen becomes smaller as the pressure becomes 80 Torr. This tendency is almost the same under high pressure conditions when the magnetic field strength is in the range of 300 G to 600 G. Further, the oxygen concentration at this time can be controlled to about 14 × 10 ¹⁷ atoms / cm ³ .

FIG. 5 shows the relationship between the oxygen concentration and the magnetic field strength when the atmospheric pressure is used as a parameter, which is 500 m from the start of the pulling.
FIG. 7 is a diagram showing oxygen concentration at the top side of the m position. It can also be seen from the figure that the reduction of the oxygen concentration can be prevented and the controllability can be improved by setting the atmospheric pressure to a high pressure condition of 50 Torr, and further to 80 Torr.

Next, the effects of atmospheric pressure (furnace pressure) and magnetic field strength on ROG were investigated. ROG is calculated from the following equation using three oxygen concentration values measured at the center of the crystal plane, at a position 50 mm from the center, and at a position 10 mm from the outer periphery.

ROG = {(Max value−Min value) / Min value} × 100 (%) ... 0 mm, 100 m from the pulling end of the single crystal after being pulled under each condition
ROG at each position of m, 400mm, 700mm and 1000mm
Table 1 summarizes the measurement results.

[0027]

[Table 1]

From the results in Table 1, it is found that the magnetic field strength is 0 G, 300 G
In any case of 600 G, the change of ROG due to the change of the atmospheric pressure is small, but conversely, at any atmospheric pressure, the ROG is changed by applying the magnetic field intensity.
Can be improved. Although not shown here, ROG gradually deteriorates when the magnetic field exceeds 600 G, and becomes the same as a normal CZ method at 800 G or more.
There is no improvement by the magnetic field. When a magnetic field exceeding 600 G is used, there is a demerit that power consumption increases. That is, to improve the ROG, it is effective to increase the magnetic field strength. However, it is desirable to apply the cusp magnetic field in the strength range of 300 G to 600 G.

For example, condition 7 in Table 1 (atmospheric pressure: 20
Torr, magnetic field strength: 600 G) and condition 9 (atmospheric pressure: 80 Torr)
r, the magnetic field strength: 600G) are compared, and almost without causing deterioration of the ROG, 2 and 4, the oxygen concentration 10 × 10 ¹⁷ atoms / cm ³ order control from 14 × 10 ¹⁷ ato
It can be seen that the control can be changed to about ms / cm ³ .

In the above description, as a premise of the manufacturing method of the present invention, the case where the atmospheric pressure is maintained at a constant value equal to or higher than a specific value has been described. The oxygen concentration in the growth direction can be kept constant. Next, this control will be described.

FIG. 6 is a diagram showing an oxygen concentration distribution in the case where the atmospheric pressure is varied within a range equal to or more than a specific value with the progress of pulling. FIG. 6 shows a profile in which the atmospheric pressure is varied. After the start of the body process as a product, the atmospheric pressure was immediately increased to 50 Torr or more, and increased to about 70 Torr with the progress of pulling. Thereby, control can be performed at an oxygen concentration of about 12 × 10 ¹⁷ atoms / cm ³ , and extremely excellent controllability is exhibited. On the other hand, although the ROG is not shown, it has been confirmed that the variation accuracy is equivalent to that shown in Table 1.

For comparison with the controllability of the oxygen concentration by the production method of the present invention, the controllability of the oxygen concentration by the conventional method was investigated. The conventional methods covered are the aforementioned “crucible rotation control method” and “the manufacturing method proposed in Japanese Patent Application Laid-Open No. 5-194077”.
And two methods.

FIG. 7 is a diagram showing the results of an investigation on the controllability of the oxygen concentration by the "crucible rotation control method" among the conventional methods. Condition 7 described above (atmospheric pressure: 20 Torr, magnetic field strength:
The oxygen concentration was controlled by a crucible rotation control method based on 600 G). The rotation speed of the crucible is 6rpm at the beginning.
, And gradually increased to 11 rpm with the lifting. As a result, the oxygen concentration in the crystal growth direction can be increased by the crucible rotation control method, but the ROG deteriorates significantly with an increase in the crucible rotation speed. In addition, Japanese Patent Laid-Open No.
As described in Japanese Patent Publication No. 7 (1994), ROG can be improved by using a method of sequentially increasing the crystal rotation, but since increasing the crystal rotation decreases the growth rate and lowers the productivity, it is not an effective method. I understand.

FIG. 8 shows one of the conventional methods described in Japanese Patent Laid-Open No. 5-19407.
7 is a diagram showing the results of an investigation on the controllability of oxygen concentration by the "production method proposed in Japanese Patent Publication No. 7-No. 7". Similarly, based on condition 7 (atmospheric pressure: 20 Torr, magnetic field strength: 600 G),
The oxygen concentration was controlled using the manufacturing method proposed in the above-mentioned Japanese Patent Application Laid-Open No. 5-194077. As a specific control method, although the application of the magnetic field intensity was initially 500 G, the reduction was started immediately after the pulling, and the application of the magnetic field was stopped at the position of 300 mm of the pulling length. The rotation speed of the crucible was 6 rpm at the beginning, but the rotation speed was gradually increased from the position of 300 mm of the pulling length to about 7.5 rpm.

As is clear from the results shown in FIG. 8, the "production method proposed in Japanese Patent Application Laid-Open No. 5-194077" allows the oxygen concentration in the crystal growth direction to be increased by slightly increasing the number of rotations of the crucible. Can be raised. But,
There was a problem with dislocations, and when five single crystals were pulled, dislocations occurred in two of the crystals in the middle part and the latter part of the crystal. This dislocation is caused by the fact that the time for substantially applying the magnetic field in the pulling process is short. Further, since the number of rotations of the crucible is increased to reduce the magnetic field strength, ROG is deteriorated in the latter half of the crystal.

As described above, according to the conventional method for controlling the oxygen concentration, the controllability of the oxygen concentration in the crystal growth direction can be ensured, but the reduction of ROG or the occurrence of dislocations is avoided. Can not. On the other hand, in the method of the present invention, the oxygen concentration distribution in the crystal growth direction and RO
G can be made uniform and dislocations during crystal growth can be prevented.

[0037]

According to the method for producing a silicon single crystal of the present invention, the method is applied to the CZ method in which a cusp magnetic field is applied. The distribution and ROG can be controlled uniformly, and dislocations during crystal growth can be prevented, so that a silicon single crystal of excellent quality can be manufactured.

[Brief description of the drawings]

FIG. 1 is a diagram schematically illustrating a structure of a manufacturing apparatus to which a method for manufacturing a silicon single crystal of the present invention is applied.

FIG. 2 is a diagram showing the relationship between the magnetic field strength and the oxygen concentration distribution in the crystal growth direction when the atmospheric pressure (furnace pressure) is 20 Torr.

FIG. 3 is a diagram showing the relationship between the magnetic field strength and the oxygen concentration distribution in the crystal growth direction when the atmospheric pressure (furnace pressure) is 50 Torr.

FIG. 4 is a diagram showing the relationship between the magnetic field strength and the oxygen concentration distribution in the crystal growth direction when the atmospheric pressure (furnace pressure) is 80 Torr.

FIG. 5 is a diagram showing the relationship between the oxygen concentration and the magnetic field strength when the atmospheric pressure is used as a parameter, as the oxygen concentration at the top 500 mm from the start of pulling.

FIG. 6 is a diagram showing an oxygen concentration distribution in the case where the atmospheric pressure is changed within a range equal to or more than a specific value with the progress of pulling in the method of the present invention.

FIG. 7 is a diagram showing the results of an investigation on the controllability of oxygen concentration by the “crucible rotation control method” among conventional methods.

FIG. 8 is a diagram showing the results of an investigation on the controllability of oxygen concentration by the “production method proposed in Japanese Patent Laid-Open No. 5-194077” among conventional methods.

FIG. 9 is a diagram showing a relationship between a crucible rotation speed and a dislocation position.

FIG. 10 is a diagram showing the relationship between the number of rotations of the crucible and the fluctuation of the melt temperature.

[Explanation of symbols]

 1: Crucible, 1a: Quartz crucible, 1b: Graphite crucible 2: Heater for heating, 3: Seed crystal 4: Melt, 5: Single crystal 6: Coil for applying magnetic field 6a: Upper coil, 6b: Lower coil 7: Pull-up Equipment, 8: Chamber 9: Pull chamber, 10: Insulation material

Claims (3)

[Claims] 1. A method for producing a silicon single crystal by a Czochralski method in which a crystal is pulled while applying a cusp magnetic field which is equiaxially symmetric with respect to a pulling axis to a melt accommodated in a crucible. In the step of pulling, the ambient pressure is controlled by changing it to a value equal to or higher than a specific value. 2. The method for producing a silicon single crystal according to claim 1, wherein said atmospheric pressure is 50 Torr or more. 3. The strength of the cusp magnetic field is 300 G (Gauss).
2. The method for producing a silicon single crystal according to claim 1, wherein the pressure is up to 600 G (Gauss).