JPH0255284A - Method for controlling concentration of contaminating impurity - Google Patents

Abstract

PURPOSE:To control the concentration of contaminating impurities from a vessel in a crystal in a wide range by changing the magnitude ratio of a component of a magnetic field intersecting the surface on a melt of a crystal material at right angles to a component of a magnetic field intersecting the contact interface between the melt and the vessel at right angles. CONSTITUTION:A perpendicular component of a magnetic field intersecting the surface 16 on a melt 2 of a crystal material having electric conductivity in a molten state, a perpendicular component of a magnetic field intersecting the bottom of the melt 2 which is an interface where the melt 2 and a quartz crucible 1 contact and a horizontal component of a magnetic field intersecting the sides of the melt 2 at right angles are present. In the process, the magnitude ratio of the component of the magnetic field intersecting the surface 16 of the melt 2 at right angles to the component of the magnetic field intersecting the contact interface between the melt 2 and the crucible 1 at right angles is changed to vary the concentration of impurities, such as oxygen, in the melt 2. For example, if only convection near the wall of the crucible 1 is suppressed, the dissolved oxygen stays near the wall of the crucible 1. Thereby, decomposition of the guartz, i.e. dissolution of the oxygen hardly occurs and the oxygen concentration in the melt 2 is reduced.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for controlling impurities mixed in during crystal growth from a melt of various materials such as semiconductors and metals that are electrical conductors in a molten state. In particular, the present invention relates to a method for controlling the concentration of impurities, such as oxygen, which is introduced from a container containing all of the melt, in a wide range and easily.

[Conventional technology]

In a crystal growth method in which a crystal is grown from a melt contained in a container, a portion of the material constituting the container often dissolves into the melt and mixes into the crystal as an impurity. Such impurities may be beneficial to the quality of the crystal, or they may be harmful.

For example, when the crystal is silicon, oxygen is a typical mixed impurity that has such dual properties. In this case, zoυ
Con crystal is a crystal grown by the so-called CZ method, in which a silicon melt is placed in a container called a quartz crucible, and the crystal is grown by pulling it from the melt. During this growth, the wall of the quartz crucible that comes into contact with the melt decomposes into silicon and oxygen, and the oxygen dissolves into the melt.This oxygen moves through the melt by convection, and the melt At the same time as it evaporates from the surface, it mixes into the crystal through the entire growth interface of the crystal. Oxygen mixed into the silicon crystal in this way strengthens the crystal mechanically and suppresses the generation and propagation of dislocations, and also precipitates inside the crystal and absorbs all contaminant metals such as iron, nickel, and chromium. , there are beneficial aspects that help improve the characteristics of various semiconductor devices.

Hereinafter, this will be referred to as conventional method 1.

Regarding the control of oxygen concentration in silicon single crystals, the 9th
As shown in the figure, by applying a horizontal magnetic field 3t to the melt 2 housed in the quartz crucible 1, the apparent viscosity of the melt 2 is increased and convection is suppressed. In the vertical cross-sectional view of the melting of oxygen from L, the crystal 4 is rotated as shown by the arrow 7 along the pulling shaft 6, the crucible 1 is rotated as shown by the arrow 9 along the support shaft 8, and the rotational speed of the crucible is changed. Liquid 2 and melt #'? A technique has been proposed to control the dissolution of the crucible 1 by changing the degree of friction between the molten metal and the oxygen concentration.

Hereinafter, this will be referred to as conventional method 3.

On the other hand, a technique for applying an axially symmetrical and radial cusp magnetic field to the melt was proposed (Japanese Patent Laid-Open No. 58-217493). In this proposal, for example, as shown in a longitudinal cross-sectional view in FIG. 10, a cusp magnetic field indicated by arrows 11 of lines of magnetic force is applied to be perpendicular to each part of the convection that circulates as indicated by arrows 10 in the melt 2. to uniformly suppress all convection,
Thereby, the objective was to produce a crystal 4T having a uniform circular cross section and complete crystallinity, and with less contamination from the crucible. Therefore, a pair of coils 14 and 15 through which circulating currents 12 and 13 flow in mutually opposite directions as means for applying the cusp magnetic field 11 are arranged vertically at approximately equal intervals with the melt 2 at the center, and the depth of the melt 2 is A radial horizontal magnetic field was formed at the 1/2 position. According to this method, by suppressing the convection 10, it is possible to completely prevent contamination from the inner surface of the crucible 1 from spreading throughout the melt.
The concentration of residual (or mixed) impurities in the growth of
/ labor was said to be 0. However, in Japanese Unexamined Patent Application Publication No. 61-222984 by another applicant, as shown in a longitudinal cross-sectional view in FIG. versus 14 and 1
The arrangement No. 5 was considered to be the optimum application state of the cusp magnetic field 11 from the viewpoint of a small transverse temperature gradient. Furthermore, it was stated that this arrangement has the effect of lowering the dislocations of the crystal 4, which is GaAs, and reducing the amount of impurities mixed in from the crucible material. Therefore, based on the teachings of the above-mentioned two patent publications regarding the application of a cusp magnetic field, cases where the relative positional relationship between the melt and the cusp magnetic field applying means are different in two categories are known. However, in these two proposals, for their own reasons, they only stated that they are advantageous because they reduce the amount of mixed impurities. Therefore, the concept of applying a cusp magnetic field to variously control the concentration of mixed impurities has not existed in the past. In addition, Japanese Patent Publication No. 6
In Japanese Patent No. 1-222984, a technique was also proposed in which the coil pairs 14 and 15 are moved vertically in the direction of the arrow 18 according to the support 17, as shown in FIG. 11, for example. However, this technique is difficult to use, for example, from the human state in Figure 11 to the
When the amount of the melt 2 changes to the state shown in Figure 1B due to progress of growth of the crystal 4, etc., the surface 16 of the melt and the coil pair 1
The purpose of this method is only to prevent the relative positional relationship between No. 4 and No. 4 and No. 15 from deviating from the optimum state, and it is completely meaningless when the amount of melt is constant.

By the way, the inventors of the present application have discovered that the cusp magnetic field shown in FIG. Focusing on the characteristics such as being lightweight and having little magnetic field leakage to the outside, we have conducted various specific experiments and discussions. As a result, the first patent application filed in 1986
-83348 (Japanese Unexamined Patent Application No. Sho 63-11) and Patent Application Sho 63-11
As proposed in 2288 (% Kaisho -), apply the entire cusp magnetic field 11 distributed similarly to Figure 11 and B, and change the magnitudes of the excitation currents 12 and 13 flowing through the coil pairs 14 and 15 at the same time. That is, we have discovered for the first time that by changing the strength of the cusp magnetic field, it is possible to control the concentration of oxygen, which is an impurity, mixed into the C3 method silicon crystal around the entire periphery of a quartz crucible. This method was an effective method for controlling oxygen concentration. Hereinafter, this will be referred to as conventional method 4.

[Problem to be solved by the invention]

In conventional method 1, when oxygen precipitates and becomes a defect in the active region of a semiconductor device, the characteristics of the semiconductor device may be changed, such as by generation of leakage current. There's oxygen again~
It tends to form an electrically active level called a maldonor, which destabilizes the specific resistance of the crystal and becomes an obstacle to increasing the resistance. In addition to the above-mentioned advantages, due to the dual nature of long and short, there is no single optimum value for the concentration of oxygen in silicon crystals, and there are various concentrations that vary depending on the type of semiconductor device being manufactured and the manufacturing method. crystals are required. Therefore, there are strong expectations for a technology that can easily control oxygen concentration over a wide range.

Further, in the conventional method 2, in order to apply a magnetic field 3 in a fixed direction to the entire melt 2, an extremely large electromagnet 5 is required as a magnetic field applying means. tiK to obtain sufficient magnetic field effect
This requires a strong magnetic field of 4,000 Oersted (t or 4,000 Gauss), and has the disadvantage that a huge amount of magnetic field leaks to the outside, which can deteriorate the characteristics of peripheral equipment.

In the technique of Conventional Method 3, for example, in order to control the oxygen concentration in a one-digit range, the crucible rotation speed is set to 0.01 rp.
m to 10 Orpm had to be varied. In that case, if the crucible rotation speed is extremely slow, for example less than 1 rpm, the temperature distribution along the circumference of the crucible 1 will not be asymmetrical, whereas if it is extremely fast, for example more than a few orpm, changes in the melt surface and vibrations will occur. In either case, the crystal growth itself becomes difficult and the yield decreases, so the range of oxygen concentration that can be controlled is actually very narrow. there were.

The present invention was achieved for the first time through further experiments and considerations regarding the method of applying a cusp magnetic field in Conventional Method 4.The purpose of the present invention is to increase the size of the magnetic field applying means, increase the leakage magnetic field, It is an object of the present invention to provide an improved method for controlling contamination impurity concentrations that overcomes the shortcomings of the prior art, such as the need to vary the crucible rotational speed over a wide range.

[Means to solve the problem]

To achieve the above object, the present invention provides a method for controlling the concentration of impurities mixed in during crystal growth of crystalline materials such as semiconductors and metals that have electrical conductivity in a molten state from a melt. A container containing a melt, a means for growing a crystal from the melt, and a means for applying a magnetic field having a vertical component and a horizontal component that differ depending on the location to the melt are provided, Controlling the concentration of mixed impurities by changing the ratio of the magnitude of the magnetic field component perpendicular to the surface and the magnetic field component perpendicular to the contact interface of the melt with the container'! i- Features.

Further, the means for applying the magnetic field is composed of a pair of coils arranged vertically opposite each other and excited by circulating currents in opposite directions, and the means for applying the magnetic field is perpendicular to the contact interface between the component of the magnetic field perpendicular to the surface of the melt and the container of the melt. The means for changing the ratio of the magnitudes of the components of the magnetic field is characterized by changing the relative positional relationship between the surface of the melt and the pair of coils.

Further, the means for applying the magnetic field is a pair of coils arranged vertically opposite each other and excited by circulating currents in opposite directions), and the means for applying the magnetic field is perpendicular to the contact interface between the component of the magnetic field perpendicular to the surface of the melt and the container of the melt. The means for changing the ratio of the magnitudes of the components of the magnetic field are characterized in that they consist of changing the ratio of amperes between the coils.

Furthermore, the means for applying the magnetic field comprises a pair of coils arranged vertically opposite each other and excited by circulating currents in opposite directions;
The means for changing the magnitude ratio of the component of the magnetic field perpendicular to the surface of the melt and the component of the magnetic field perpendicular to the contact interface of the melt container comprises changing the distance between the coils. This is a characteristic feature.

[Effect]

The present invention aims to control the concentration of impurities mixed into the crystal by changing the ratio of the magnitude of the magnetic field component perpendicular to the surface of the melt and the magnetic field component perpendicular to the contact interface between the melt and the container. According to the present invention, the melt of a crystalline material having an electrical conductivity housed in a crucible is composed of a vertical component and a horizontal component that differ depending on the location. By applying a full magnetic field and changing the ratio of the magnetic field component perpendicular to the surface of the melt and the magnetic field component perpendicular to the contact interface between the melt and the crucible, the crystals are removed from the crucible material. The concentration of impurities mixed in can be accurately controlled over a wide range. Examples will be described below based on the drawings.

〔Example〕

Embodiment 1; Figure 1, B, and C are representative 3 of the first embodiment of the present invention.
FIG. 3 is a vertical cross-sectional view of main parts showing conditions. The same parts as in the conventional FIGS. 9, 10, and 11 A and B are given the same numbers and redundant detailed explanations are omitted, but coil pairs 14 and 15
have the same ampere turns of reverse current 12 and 13.
flows into the above three conditions in common. The resulting cusp magnetic field of the crystal is the strength and direction of the magnetic field at various locations containing the melt 2t-! This vector is illustrated in detail by a number of arrows 19. In this state, the quartz crucible 1 is configured to be able to move up and down as shown by the arrow 20 along the support shaft 8, and by moving the quartz crucible 1 up and down, the relative positional relationship between the surface 16 of the silicon melt and the coil pairs 14 and 150 is established. It can be changed completely freely. As a result, compared to the intermediate position between the coil pairs 14 and 15, the surface 16 of the melt is placed at a higher position, and Figure 1B shows the case where the surface 16 of the melt is placed at a higher position, and the case where the surface 16 of the melt is placed at the same height. FIG. 1C shows the case where it is placed at a low position.

By changing the relative positional relationship between the melt surface and the coil pair in this way, the magnitude of the magnetic field component perpendicular to the melt surface and the magnetic field component perpendicular to the interface where the melt contacts the quartz crucible can be changed. The ratio of can be changed. Now this ratio
1 The orthogonal magnetic field component to the melt surface is defined as 1/I orthogonal magnetic field component to the interface between the melt and the crucible, and is hereinafter referred to as the "surface orthogonal magnetic field ratio." First, in Figure 1, in humans, the surface of the melt 16
There is also a vertical magnetic field component perpendicular to the bottom surface of the melt 2, which is the interface where the melt 2 and the quartz crucible 1 come into contact, and a horizontal magnetic field component perpendicular to the sides of the melt 2. also exists. In this case, the "surface orthogonal magnetic field ratio" is approximately 1. On the other hand, in FIG. 1B, only the perpendicular magnetic field component perpendicular to the surface 16 of the melt does not exist, so the "surface perpendicular magnetic field ratio" is zero. In addition, in FIG. 1C, the "surface orthogonal magnetic field ratio" is approximately 0.7.

Now, when viewed from the silicon melt, K and oxygen are quartz fluoride.
JPA has the property of melting and penetrating from the bottom and side surfaces that come into contact with the melt, and evaporating from the surface of the melt. When dissolution and evaporation occur in parallel in this way, it is thought that the oxygen concentration in the melt changes depending on how easily they occur. The ease with which these events occur varies depending on the strength of convection within the melt. For example, in the CZ method without a magnetic field, convection is very strong, so dissolution and evaporation are very likely to occur, and the concentration in the melt is balanced at a constant value. On the other hand, if only the convection near the quartz wall is suppressed, dissolved oxygen will flow into the quartz)
Since the melt remains near the wall, decomposition of quartz, that is, dissolution of oxygen, is less likely to occur, and the oxygen concentration in the melt becomes low.

When the oxygen concentration in the melt decreases, the oxygen concentration in the crystal grown from the melt also decreases. On the other hand, if only the convection near the surface is suppressed, it becomes difficult for oxygen to move from the inside of the melt to the surface, making it difficult for oxygen to evaporate and increasing the oxygen concentration in the melt. If the oxygen concentration in the melt increases,
The oxygen concentration in the crystal growing from the melt also increases.

By the way, convection within the melt is suppressed by the following principle when a magnetic field is applied. That is, when a magnetic field of intensity vector H is applied to convection of velocity vector V, I=σB=σμv proportional to the product of these vectors due to electromagnetic induction.
A current represented by a vector of XH flows through the convective melt portion. Furthermore, a magnetic field acts on this current, F=S2(v
The convection suppressing force represented by the vector of XH)XH acts and convection is suppressed. Here, μ is the magnetic permeability of the melt, and σ is the electrical conductivity. The principle of convection suppression by magnetic fields is explained by the melt and quartz crystals, which are important for the movement of oxygen.'';) I
When applied to the interface of the f'' wall and the surface of the melt, the following is obtained. First, at these interfaces, neither convection nor current can flow through the interface, so the component perpendicular to the interface is In other words, only a two-dimensional flow parallel to the boundary surface is allowed. Therefore, even if a magnetic field parallel to the boundary surface is applied at the boundary surface, there is no convection suppressing force from the above vector product relationship. Since almost no convection occurs, convection is hardly suppressed.On the other hand, when a magnetic field perpendicular to the interface is applied, all convection that is parallel to the interface near the interface becomes perpendicular to this magnetic field and parallel to the interface. Convection is effectively suppressed because a current flows and a convection suppressing force is generated.

Combining the oxygen mixing mechanism described above and the convection suppression mechanism by magnetic field, the larger the "surface perpendicular magnetic field ratio", the more strongly evaporation is suppressed compared to melting, so oxygen in the melt and crystals is suppressed. Concentration increases.

Therefore, by changing the surface orthogonal magnetic field ratio,
It is believed that the oxygen concentration can be controlled at various levels. Comparing the three conditions of this example, the oxygen concentration is highest in the case of the person in Figure 1, who has the highest "surface orthogonal magnetic field ratio";
It is considered that the case of FIG. 1B, where the surface orthogonal magnetic field ratio is the smallest, is the lowest, and the case of FIG. 1C is intermediate therebetween.

FIG. 2 shows experimental results specifically explaining the effect of controlling oxygen concentration according to this example. In this experiment, the diameter of the quartz crucible was 15 cm, and the depth of the silicon melt was 7.5 cm.)
, a silicon crystal with a diameter of 7.6 cm was grown. As for the rotation speed, the crystal t-3 Orpm rrutsuho is 1 Orp.
It was set as m. In addition, a superconductor was used as the coil pair. In Figure 2, the horizontal axis is the distance 2 from the middle position of the coil pair to the melt surface, and the "surface orthogonal magnetic field ratio" that changes according to this distance, and the vertical axis is the oxygen concentration in the crystal. . As an experimental result (a).

Two curves in (b) are shown. (a) is a coil pair with the same ampere turns of 8.6 x 10'A-tu
The results are for rn/m, (bl is 2.9
/m.

Further, in FIG. 2, 4A, 4B, and 4C indicate points corresponding to FIG. 1A, FIG. 1B, and FIG. 1C, respectively. As a result of these experiments, first, in the case of (a) where the ampere turn is relatively large, that is, a relatively strong Kasub magnetic field is used, the oxygen concentration in the crystal is, for example, 4A, 4B,
13 X 10 atoms/each at 4C points
am +2.5 x 10"atoms/cm",
10 x 101017ato/cm”.

Oxygen concentration can be controlled over a wide range of approximately one order of magnitude by simply changing the relative positional relationship between the melt surface and the coil pair, without changing the magnetic field strength or crucible rotation speed as in the past. was completed. In addition, a second method using a relatively weak cusp magnetic field
Even in the case of <b+ in the figure, the tendency for the oxygen concentration in the crystal to change is the same as in the case of aJ above. was able to control the

In this example, the coil pair was fixed and the crucible was moved vertically to change the relative positional relationship between the melt surface and the coil pair. The above relative positional relationship could also be changed by moving it up and down, and in this case as well, the oxygen concentration could be controlled in the same way as described above.

Embodiment 2: FIGS. 3A, B, and C are longitudinal sectional views illustrating a second embodiment of the present invention. In this example, the crystal growth progresses and the amount of silicon melt 2 is reduced compared to the first example. In this example, the "surface orthogonal magnetic field ratio" is approximately 3. In Figure 3B, 0. In FIG. 3C, it was changed to about 0.6.

FIG. 4 shows experimental results explaining the effects of this embodiment. In this case, except that the depth of the melt is shallow to 3 cm,
The experimental conditions were the same as in the case of FIG.

6A, 6B, and 6G in Figure 4 are the people in Figure 3, respectively.

B, CK shows the distance from the corresponding coil intermediate position to the melt surface. (a) and (b) are experimental results in the cusp magnetic field of the ampere turn of type 211 described in FIG. The oxygen concentration in the crystal is highest at position 6A, lowest at position 6B, and intermediate at position 6C.Similar to the experiment in Figure 2, the relative relationship between the surface of the melt and the coil pair By changing the positional relationship, the oxygen concentration could be controlled over a wide range.

Example 3: Figure 5B shows the experimental results for explaining the third example of the present invention, which shows the distribution of oxygen concentration in the length direction of the crystal based on the first and second examples above. This makes it possible to make the oxygen concentration uniform and to control the oxygen concentration in various ways.

First, in the case of Figure 5, the cusp magnetic field is a strong cusp magnetic field corresponding to (a) in the first and second embodiments,
While changing the distance from the middle position of the coil pair to the melt surface as shown by 2 in the figure, crystals were grown continuously for a long time, and most of the melt was solidified. As a result, it is uniform in the length direction and 11X 101017ato/am
’ to 2.5 X 10” atoms/cm8
It was possible to obtain whole silicon crystals with various oxygen concentrations over a wide range of .

Next, in FIG. 5B, the cusp magnetic field is set to a weak magnetic field corresponding to (b) in the first and second embodiments, and the relative positional relationship between the surface of the melt and the coil pair is shown in the figure. The crystals are grown continuously for a long time while changing as shown in
Most of the melt was solidified. As a result, it is uniform in the length direction and 10 x 1017a toms/cm”
Silicon crystals with various oxygen concentrations ranging from 8 X 10”atoms/cm could be obtained.

Embodiment 4: FIGS. 6A and 6B are longitudinal sectional views illustrating a fourth embodiment of the present invention. In this example, the "surface orthogonal magnetic field ratio" was changed by changing the ampere-turn ratio between the upper coil 14 and the lower coil 15. That is, except for the ratio of ampere turns between the coils, the configuration and arrangement were the same as that of the Figure 1 person, and in the Figure 1 person, the ampere turns of the upper coil 14 and the lower coil were the same - that is, the ratio was 1:1. In contrast, the ratio was set to 0.8 to 1 for humans in Figure 6, and 1 to 0.8 for Figure 6 B. As a result, the "surface orthogonal magnetic field ratio" is 1 for the person in Figure 1, whereas it is 0.06 for the person in Figure 6.

In FIG. 6B, it was changed to 3. In order to clarify the effect of this embodiment, in the human configuration shown in FIG. 6, the upper coil 14
0 amp turn f 4.6 x 10'A-turn
/m, lower coil 15 ampere turns 5.7
10'A-turn/m, while in the configuration shown in FIG. 6B, experiments were conducted with the ampere turns of the upper and lower coils 14 and 15 reversed. As a result, the oxygen concentration of crystal 4 is 6th
In case of figure 6.2X1017atoms/cm”+
In the case of Figure 6B, 21 x 101017ato/
It was possible to control the oxygen concentration by changing the oxygen concentration by only slightly changing the ratio between am8 and ampere turn.

Embodiment 5: FIGS. 7A and 7B are vertical sectional views illustrating a fifth embodiment of the present invention. In this example, the "surface orthogonal magnetic field ratio" was changed by changing the distance between the upper coil 14 and the lower coil 15. Figure 7: The person is the surface of the melt 16
is separated upward from the middle position between the upper and lower coils 14 and 15, and the distance is 1.5 cm (in this case, Z=
L5cm). The rest of the structure and arrangement are the same as in FIG. 1A. On the other hand, in Figure 7B, the same Z = 1.5
cm, but the distance between the upper and lower coils is 2.5 times that of the human case in Figure 7. As a result, the "surface orthogonal magnetic field ratio" was changed from 0.45 in the case of the person in FIG. 7 to 0.53 in the case of FIG. 7B. In order to clarify the effect of this embodiment, the ampere turns of the upper and lower coils are the same in both Figures 7A and 7B, 5.7 x 10'A-turn/
The control effect of the degree of experiment was confirmed as m. Although the control range of oxygen concentration in this embodiment was narrower than in the other embodiments described above, it had the advantage of being able to control the oxygen concentration extremely accurately to a desired concentration.

Embodiment 6: FIGS. 8A and 8B are vertical cross-sectional views fully illustrating the sixth embodiment of the present invention. In this example, the "surface orthogonal magnetic field ratio" is changed by changing the distance between the upper coil 14 and the lower coil 15, as in the fifth example. In Figure 8, the surface 16 of the melt is located at a distance below the midpoint between the upper and lower coils 14 and 15, and the distance is 1.5 cm (in this case, Z −= −1,5 am). .
The rest of the configuration and arrangement are the same as those in FIG. 1C. On the other hand, in Figure 8B, although Z = -1.5cm is the same, the distance between the upper and lower coils is 2.5 cm as in the case of Figure 8.
It's doubled. As a result, the “surface orthogonal magnetic field ratio” becomes 8th.
From 0.43 in case of Figure 8 to 0.50 in case of Figure 8B
was changed to. In order to clarify the effects of this embodiment, an experiment was conducted with the ampere turns f of the upper and lower coils being the same for both the coils of Figure 8 and B, 5.7 x 10 A-turn/m.

As a result, if the oxygen concentration of crystal 4 is 7.5 x 10"atoms/am" + 8th
In the case of Figure B, it is 8.5XIO"atoms/cm8, and the oxygen concentration control effect is a as in the fifth embodiment.
Approved.

〔Effect of the invention〕

As explained above, according to the present invention, a magnetic field consisting of a vertical component and a horizontal component that differ depending on the location is applied to the melt of an electrically conductive crystalline material housed in a crucible, and at that time, the melt By changing the ratio of the magnetic field component perpendicular to the surface of the liquid and the magnetic field component perpendicular to the contact interface between the melt and the melt, the concentration of impurities mixed into the crystal from the crucible material can be controlled over a wide range. can be precisely controlled. Specifically, by appropriately selecting and using the various methods described in the examples, it is possible to produce crystals with impurity concentrations suitable for various semiconductor devices without adversely affecting peripheral devices or reducing yields. It has the advantage that it can be manufactured very easily without causing any problems.

In the detailed explanation of the present invention, oxygen in the silicon crystal was taken up as a typical impurity, but it is mixed into the melt from the constituent materials of the container such as a crucible, and crystallizes while evaporating from the surface of the melt. It is clear from the principle of the present invention described in the description of the first embodiment that the present invention is effective in controlling the concentration of impurities that have the property of being mixed into the liquid.

On the other hand, the present invention loses the advantage of the method of applying an axially symmetrical cusp magnetic field, which is that an axially symmetrical magnetic field can maintain the entire axially symmetrical temperature distribution, thereby obtaining a uniform crystal without growth striations. There is also the advantage that extremely good uniformity can be achieved since this is completely straightforward.

Furthermore, in the detailed description of the present invention, a conventionally known cusp magnetic field was used as an example of the magnetic field, but the effects of the present invention are not limited to the cusp magnetic field. That is, it is clear from the principle of the present invention explained in the first embodiment that the magnetic field according to the present invention must be composed of a vertical component and a horizontal component that differ depending on the location.

[Brief explanation of the drawing]

FIGS. 1A, B, and C are vertical cross-sectional views showing the configuration under three typical conditions of the first embodiment of the present invention, and FIG. 2 is an experimental result showing the effects of the first embodiment. Figures 3A, B, and C are vertical cross-sectional views showing the composition of three typical conditions of the second embodiment in which the present invention is applied in the late stage of crystal growth. Figure 4 shows the effect of the second embodiment. Experimental results, Figure 5A
, B shows two types of experimental results for the third embodiment that achieved uniform oxygen concentration control in the length direction of the crystal, and FIG. Figure 7 is a vertical cross-sectional view showing the configuration under two typical conditions of the fifth embodiment; Figures 8A and B are the configuration under two typical conditions of the sixth embodiment. FIG. 9 is a vertical cross-sectional view showing the configuration of a prior art technology including application of a horizontal magnetic field. FIG. 10 is a longitudinal cross-sectional view showing the configuration of a conventional convection suppression technique by applying a cusp magnetic field. FIG. 11B is a vertical cross-sectional view showing the configuration of a conventional technique provided with means for vertically moving the cusp magnetic field applying means in response to changes in the amount of melt. ...Crucible tf...Melt...Vector of horizontal magnetic field...Crystal...Horizontal magnetic field applying means 6...Crystal pulling axis 7...Crystal rotation 8...Crucible support axis 9... Crucible rotation 10... Convection 11... Vector ratio of cusp magnetic field... Exciting current of upper coil 13... Exciting current of lower coil 14... Upper coil 15... Lower Side coil 16...Surface of the melt 17...Support for the coil pair 18...Vertical direction of the coil pair 19...Magnetic field strength direction vector 20...Vertical direction of the crucible Applicant Nippon Telegraph and Telephone Co., Ltd. Agent Patent attorney Gobe Tamamushi (2 others) 1. Directly hitting the surface Usukai Ryo” Coil middle position! I: Distance Z (cm) to the receiving surface
) Experimental results No. 21 showing 9jJ votes for the first implementation area)
! L r, 5-plane orthogonal field ratio" Distance Z (cm) from the coil intermediate position to the melt surface Experimental results showing the second best example of 9jJ Figure 4 O 0,2 0,40,6 Solidification Achieving uniform oxygen concentration control in the length direction of the crystal with a ratio of 0.8, the results of two types of experiments are shown in Figure 1. Kasua Go responds to changes. Kaiin Karo Te r All 2 Upper and Lower Childhood Death Means ξ 1 Bacteria E l Koju Ice Technique (Longitudinal cross-sectional view showing elbow hawk formation)

Claims (4)

[Claims] (1) A method for controlling the concentration of mixed impurities during crystal growth from a melt of a crystalline material having electrical conductivity in a molten state, comprising: a container containing a melt of a crystalline material having electrical conductivity; and the melt. means for growing a crystal from the melt, and means for applying a magnetic field consisting of a vertical component and a horizontal component that differ depending on the location to the melt, and a means for applying a magnetic field consisting of a vertical component and a horizontal component that differ depending on the location, the component of the magnetic field orthogonal to the surface of the melt and the A method for controlling the concentration of mixed impurities, characterized in that the concentration of mixed impurities is controlled by changing the ratio of the magnitudes of components of the magnetic field perpendicular to the contact interface with the container. (2) The means for applying the magnetic field consists of a pair of coils arranged vertically opposite each other and excited by circulating currents in opposite directions, and the means for applying the magnetic field is arranged at the contact interface between the component of the magnetic field perpendicular to the surface of the melt and the container of the melt. 2. The means for changing the magnitude ratio of orthogonal magnetic field components comprises changing the relative positional relationship between the surface of the melt and the pair of coils.
Method for controlling the concentration of mixed impurities as described. (3) The means for applying the magnetic field consists of a pair of coils arranged vertically opposite each other and excited by circulating currents in opposite directions, and is arranged at the contact interface between the component of the magnetic field perpendicular to the surface of the melt and the container of the melt. 2. The method of claim 1, wherein the means for changing the magnitude ratio of orthogonal magnetic field components comprises changing the ampere-turn ratio between the coils. (4) The means for applying the magnetic field consists of a pair of coils arranged vertically opposite each other and excited by circulating currents in opposite directions, and is arranged at the contact interface between the magnetic field component orthogonal to the surface of the melt and the melt container. 2. The method of controlling the concentration of mixed impurities according to claim 1, wherein the means for changing the magnitude ratio of orthogonal magnetic field components comprises changing the distance between the coils.