JPS6360189A - Production of semiconductor single crystal - Google Patents

Abstract

PURPOSE:To obtain the title single crystal without any crystal defect and further having an excellent concn. distribution by pulling up a single crystal while impressing a stationary magnetic field in the vicinity of the solidified interface of a melt and impressing a shifting magnetic field or rotating magnetic field by a low frequency on the intermediate and lower parts at the time of producing a semiconductor single crystal by a pull method. CONSTITUTION:The semiconductor single crystal 9 is pulled up from the surface of a raw material melt 2 in a crucible 1, and produced. In this case, the stationary magnetic field 4 (generated by passing a DC current through a magnet 3) is impressed in the vicinity of the solidified interface of the melt 2 to control the oscillation around the interface of the melt 2, the shifting magnetic field 6 (by a magnet 5) or the rotating magnetic field by low frequency is impressed on the intermediate and lower parts, and the crystal is pulled up while generating vertical oscillation (an agitation current 7) in the melt 2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a manufacturing method for manufacturing a semiconductor single crystal such as silicon or gallium arsenide by pulling it.

(Prior Art) Semiconductor single crystals such as silicon and gallium arsenide, which serve as substrates for ICs, LSIs, power semiconductor devices, etc., are currently manufactured mainly by the Czochralski method.

When pulling a single crystal using the Czochralski method, there are problems such as the generation of crystal defects due to thermal convection of the semiconductor raw material melt, the inclusion of impurities, and non-uniformity of their concentration. For example, once-grown crystals are partially re-melted by thermal convection of the high-temperature melt, resulting in crystal defects or being the cause of their occurrence.

One method to solve this problem is magnetic field application (MC)
Z) is disclosed in Japanese Patent Publication No. 58-5093, which attempts to suppress thermal convection by applying an electrostatic field to the melt during the production of, for example, silicon crystal.

However, when pulling a single crystal using this method, thermal convection is suppressed, so i! Although the concentration of I element does decrease,
On the contrary, stirring is suppressed and the concentration distribution tends to become uneven. In order to obtain a single crystal with a uniform composition distribution without crystal defects, not only for silicon but also for general single crystals such as gallium arsenide, it is necessary to make the composition of the raw material melt uniform and to stabilize the temperature. It is necessary. When pulling a single crystal, the raw material for the single crystal is placed in a crucible and heated and melted by a heater from the outer surface of the crucible, but the melt heated from the crucible wall causes thermal convection.

Thermal convection can be thought of as something that occurs when there is a local temperature difference in the melt to equalize it, but conversely, thermal convection occurs when the temperature of the melt is not uniform and is unstable. This can be said to indicate that the situation is

For this reason, one method for uniformizing the composition and uniformizing and stabilizing the temperature has conventionally been to rotate the single-crystal melt being pulled by forced stirring.

However, stirring alone by such rotation of the single crystal is not necessarily sufficient. This is because although the viscosity of the melt is low, the apparent inertia is large, so even if the single crystal is rotated and the surface of the melt is stirred, it is difficult to create a flow that uniformly stirs the entire melt. For example, the kinematic viscosity of silicon or gallium arsenide in the molten state is 0.4×10. 003X1
0-6 m”/S, and that of water is I x 10-6
m"/S, and has a lower viscosity than water. For this reason, it is difficult to stir the entire melt with partial stirring by single crystal rotation. In this way, in order to stir the entire melt uniformly and sufficiently, Flow in the rotational direction alone is insufficient, and omnidirectional stirring including radial and vertical stirring is required.

3 and 4 are explanatory diagrams showing the results of fluid analysis using the finite element method when the single crystal 9 is prevented from rotating at the surface, and FIG. 3 shows the single crystal raw material placed in the crucible 1. FIG. 4 shows the flow lines of the melt 2 for each half of the crucible.

According to these, even with conventional agitation by rotating a single crystal, centrifugal force acts on the rotating flow, creating a force that expands it in the circumferential direction, resulting in a flow with a radial component, and this flow is caused by the crucible wall. , creating a path for the flow to flow downwards and upwards in the center. Factors that affect the diameter and vertical flow due to rotational stirring include the kinematic viscosity coefficient of the melt, the size of the crucible, the measurement, the depth of the melt,
These include the diameter of the single crystal, the rotation speed of the single crystal, and the strength of thermal convection.

It is extremely difficult to select such many elements under optimal conditions and stir the single crystal by rotation. Furthermore, experiments have shown that it takes one to several minutes for the radial and vertical flow caused by rotational stirring to become a stable flow as a whole. Conditions may change during this stabilization time, making it extremely difficult not only to select optimal conditions but also to maintain their reproducibility.

(Problems to be Solved by the Invention) As described above, the conventional semiconductor single crystal manufacturing method has drawbacks such as occurrence of crystal defects in the growing single crystal and deterioration of the concentration distribution. Therefore, it is an object of the present invention to provide a method for manufacturing a semiconductor crystal in order to manufacture a single crystal without crystal defects and with a good concentration distribution by growing the crystal under stable melt conditions. do.

[Structure of the invention]

(Means for Solving the Problems) According to the present invention, in a semiconductor single crystal manufacturing method in which a single crystal is obtained by pulling from the surface of a raw material melt in a crucible, a static magnetic field is applied near the solidification interface of the melt. It is characterized by suppressing the fluctuation of the melt near the interface and applying a moving magnetic field or a rotating magnetic field of low frequency to the middle and lower parts, thereby causing vertical fluctuation inside the melt while pulling it up.

(Function) By applying a low-frequency shifting magnetic field or rotating magnetic field to the middle and lower parts of the melt, a voltage is generated in the melt and a secondary current flows, and between this and the magnetic field, a voltage is generated in the vertical direction. The force of is generated. This uniformly stirs the melt and makes the impurity concentration distribution of the crystal uniform.

(Example) Embodiments of the present invention will be described in detail below based on the drawings.

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention, and FIG. 2 is a characteristic curve showing how the magnetic flux density of the moving magnetic field according to the present invention is attenuated at the position of the melt in the crucible. X in figure 2
The axis positions correspond to those in FIG.

A magnet 3 for generating a static magnetic field is arranged above the single crystal raw material melt 2 inside the crucible 1, and a static magnetic field 4 is applied to the vicinity of the solidification interface of the melt 2 by passing direct current through the magnet 3. Further, a magnet 5 is arranged to generate a moving magnetic field in the vertical direction from the middle part to the lower part of the melt 2. That is, a cylinder may be arranged around the crucible, and a large number of electromagnets with cores arranged vertically on the inner surface of the cylinder, and the structure may be similar to that of a stator of a motor.

As a result, a moving magnetic field 6 is generated, and a stirring flow 7 is generated inside the melt 2 due to the moving magnetic field. As a result, the melt 2 is sufficiently stirred to have a uniform composition and a uniform temperature. Note that the frequency of the applied current is 20 to 30 Hz.
The magnetic flux density may be approximately 800 to 3000 Gauss.

The moving direction of the moving magnetic field by the magnet 5 is indicated by the arrow 8 in the figure.
This is the direction shown by . In the case of this embodiment, in order to generate a downward stirring flow inside the melt 2, a I.J.
Although a magnetic field is generated, a similar vertical stirring flow can also be obtained by applying a rotating magnetic field using an annular electromagnet. In addition, the frequency in this case is 50 to 601-
! Z level is desirable.

On the other hand, on the surface of the melt 2, the fluctuations are suppressed by the static magnetic field generated by the magnet 3, as described above, so that a defect-free crystal can be obtained when pulling the single crystal 9.

The melt 2 is stirred by the moving magnetic field 6 in this way.
When a semiconductor melt such as silicon or gallium arsenide has conductivity, applying a moving magnetic field causes a voltage to flow and a secondary current to flow, and this and the magnetic field generate a force in the direction of the moving magnetic field. It is.

Considering this force, first the force F applied to the liquid is given by the following equation.

F = −8・τ・f ・・・・・・・・・・・・
(1) where k: constant B: magnetic flux density at the position where force is generated τ: pole pitch of AC magnet f: applied power supply frequency.

The magnetic flux density B at a distance Z from the surface of the magnet 5 is π B=B. (1-β) ex p (-α--Z)τ ・・・・・・・・・・・・・・・(2) However, Bo: Magnetic flux density on the magnet surface B: In the melt Attenuation coefficient α of magnetic flux: Spatial attenuation coefficient Z: Distance from the magnet surface. Here, the damping coefficient β is caused by the secondary current loss that is caused by the moving magnetic field and flows into the melt 2, and β−k ′a °r °f (1+ to 2.) −−(
3) However, kl is 2: coefficient α: electrical conductivity of the melt d: thickness of the melt.

Here, equation (1) is an equation that can be easily derived from Fleming's left-hand rule and right-hand rule, and the stirring force F is the magnetic flux density B
It can be seen that it is proportional to the square of the power supply frequency f.

In addition, equations (2) and (3) are a part of the theoretical equations corrected by experimental equations, and equation (2) shows that the magnetic flux density is attenuated by the attenuation term "< It is shown that the attenuation is due to two factors: 1-β)n and a reduced Q term ``(exp)'' due to physical distance.

That is, the bit τ is determined by the dimensions of the magnet, and if it is constant, it is found that it decays exponentially with distance. Furthermore, from equation (3) it can be seen that the attenuation due to the secondary current is proportional to the frequency f. From these results, attenuation is determined by the shape of the magnet (this determines τ) and placement (this determines 2) and the frequency f, so changing the frequency f changes the stirring force and selects the stirring depth. can do.

FIG. 2 shows the relationship between equations (2) and (3) as a graph. The broken line in the figure shows the case where there is no melt, and it can be seen that the magnetic flux density is rapidly attenuated due to eddy currents in the melt. Also, if the frequency f is determined, the magnetic flux density β
The stirring power can be adjusted by changing. Therefore, by setting the frequency and current applied to the magnet, the required stirring force can be reliably obtained, and adjustment can be made to obtain optimal stirring.

As described above, in the present invention, since the melt is directly stirred by electromagnetic force, the response is good, and the stirring can be performed reliably υIt11 with high reproducibility. It also becomes possible to dynamically control stirring υ in accordance with changes such as decrease in melt. Note that if there is any fluctuation of the melt 2 or temperature fluctuation in the upper part of the melt 2, especially at the solidification interface of the single crystal, defects will occur in the crystal, so similar to the conventional magnetic field applied pulling (MCZ) Since the static magnetic field 4 is applied, the movement of the melt 2 is suppressed near the interface.
The power acts, suppressing the oscillations between the two melt and solidifying interfaces, and keeping the solidification interface in a stable state.

Therefore, in the crystal pulling method according to the present invention, a iii current magnetic field is applied to the solidification interface, which is most important for crystal growth, to suppress the fluctuation of the melt and maintain stable crystal growth conditions.

On the other hand, the middle and lower parts of the melt are stirred up and down by a moving magnetic field to sufficiently stir the melt and make the impurity concentration distribution uniform. Directly stirring the melt with the electromagnetic force generated by the moving magnetic field means that the stirring can be done at any desired level of 1 lJl, and can be said to have good continuity and excellent reproducibility.

Further, as shown in FIG. 2, the stirring in the vertical direction generates a hl stirring flow toward the center of the periphery of the crucible 1, so that the heating by the heater around the crucible 1 becomes uniform over the entire liquid. Therefore, it is more effective than stirring in the rotational direction.

Although the above-mentioned embodiment uses a moving magnetic field, the same effect can be obtained when stirring is performed using the above-mentioned rotating magnetic field instead.

〔Effect of the invention〕

As described above in detail based on the embodiments, according to the present invention, a static magnetic field caused by a direct current is applied to the surface of the melt to keep the state of the solidification interface, which is most important for crystal growth, stable, and a defect-free semiconductor By forming a single crystal and sufficiently stirring the melt using a moving magnetic field, it is possible to make the impurity concentration distribution of the crystal uniform. Furthermore, since stirring is performed using ffta force, it is possible to control the application of arbitrary force to any arbitrary position of the melt. For this reason, controllability, coordination,
It has excellent reproducibility and can always perform stirring under optimal conditions.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the configuration of an embodiment of the present invention, Fig. 2 is a characteristic diagram showing the attenuation of the magnetic flux density of the moving magnetic field at the melt position in the crucible, and Figs. 3 and 4 are diagrams showing the conventional method. It is a figure which shows the fluid analysis result by the finite element method of the flow of the melt by crucible rotation. DESCRIPTION OF SYMBOLS 1... Crucible, 2... Single-crystal raw material melt, 3... Magnet for static magnetic field generation, 4... Static magnetic field, 5... Magnet for moving magnetic field generation, 6... Moving magnetic field, 7... Stirring flow due to moving magnetic field, 8... Moving magnetic field direction, 9...
Single crystal. Applicant's agent 4Ji Fuji - Yuman 2 Diagram 3 Diagram 4

Claims (1)

[Claims] In a method for manufacturing a semiconductor single crystal in which a single crystal is obtained by pulling a single crystal from the surface of a raw material melt in a crucible, a static magnetic field is applied near the solidification interface of the melt to suppress fluctuations near the interface of the melt, while A method for producing a semiconductor single crystal, characterized in that a moving magnetic field or a rotating magnetic field by low frequency is applied to the upper and lower parts of the melt to cause vertical vibration inside the melt while pulling the melt.