JPH0518793B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a single crystal by the Czyochralski method.

[Prior Art] In recent years, various semiconductor single crystals have been widely used as materials for the electronic industry. A method generally used to obtain a single crystal is a pulling method from a melt, and the most representative method is the Czyochralski method (CZ method). In the CZ method, as shown in FIG.
This method is based on the method of gradually pulling up the single crystal 2 while rotating it. In this case, since the melt 5 is heated mainly from the sides by the heating heater 3, the temperature at the center of the melt 5 is lower than the temperature at the outer periphery. Therefore, convection occurs inside the melt 5.
This convection causes temperature fluctuations near the interface where the single crystal 2 grows, resulting in crystal defects and non-uniformity in electrical properties inside the grown single crystal 2, resulting in a decrease in yield and when fabricated into semiconductor devices. This is undesirable because it causes a decrease in reliability. Particularly in the case of silicon, which is a crystalline material that occupies an important position in the electronics industry, the diameter of the crystal to be pulled is large and the length is long, so the homogeneity of the entire single crystal becomes increasingly important.

As a means of suppressing such temperature fluctuations, as shown in FIG. -45889)
Also, as shown in FIG. 6, a device (Japanese Patent Application Laid-Open No. 62-43958) has been proposed, which is equipped with a solenoid coil 12 that applies a magnetic field 13 (vertical magnetic field) in a direction substantially parallel to the pulling direction around the crucible 4. , a method of growing crystals using only a horizontal or vertical magnetic field is known.

[Problems to be solved by the invention] Using silicon crystal growth as an example,
When crystals grow as shown in Figure 3, the concentration of added impurities and the concentration of oxygen mixed in from the quartz crucible generally have a concentration distribution that roughly follows the effective distribution coefficient, as shown by the solid line in Figure 4. As shown by the broken line, the impurity concentration of the latter is on the order of 10 ¹⁸ particles/cm ³ .

Furthermore, when a crystal grows by applying a horizontal magnetic field to the melt as shown in Fig. 5, the concentration of added impurities shows almost the same distribution as in Fig. 3, but the oxygen concentration is 10 ¹⁷ ~
Controllable to 10 ^{to 18} pieces/ ^cm3 order.

On the other hand, when crystals grow by applying a magnetic field perpendicular to the melt as shown in Figure 6, the concentration of added impurities shows a nearly uniform distribution as shown by the solid line in Figure 7, but the oxygen concentration
As shown by the broken line in the figure, they are widely distributed, ranging from 10 ¹⁷ to ^{10 20} pieces/cm ³ , and their control is difficult.

The concentration of this added impurity is limited by the product standard based on the electrical resistivity of the product, and the oxygen concentration range is also determined by the product standard. That is, uniformizing both distributions at the same time greatly contributes to improving the product acquisition rate.

As described above, with the current crystal pulling technology, it is not possible to make the distribution of added impurity concentration uniform, and furthermore, the oxygen concentration distribution cannot be made uniform. It is an object of the present invention to solve this problem.

[Means for Solving the Problems] In the present invention, as shown in FIG. 1, a solenoid coil 12 for generating a vertical magnetic field and a magnetic pole 10 for generating a horizontal magnetic field are arranged in a single crystal pulling apparatus, and the vertical magnetic field and the horizontal magnetic field are Apply and pull up.

While pulling the single crystal, the vertical magnetic field and horizontal magnetic field are switched at least once every 2 seconds.

First, the crystal pulling device used in the present invention will be explained. FIG. 1 is a diagram illustrating one aspect of the apparatus used in the present invention. In the figure, a semiconductor material 5 such as silicon is placed in a crucible 4 made of quartz,
It is heated and melted from the surrounding area by a heating heater 3. Outside the heating heater 3, for example, a cylindrical heat shield or a jacket (not shown) cooled by water cooling or the like is arranged as necessary, and a magnetic field generating means using an electromagnet 16 is arranged outside the jacket. Ru. Furthermore, in the present invention, a solenoid coil 12 is arranged on the outside of the jacket so that the center of the coil and the crystal pulling axis 8 coincide with each other. 11 is a single crystal seed, 2 is a pulled single crystal, 8 is a crystal pulling axis, and 7 is a crucible rotation axis. Crystal growth using such a crystal pulling apparatus is performed as follows.

In order to pull and grow a crystal using the crystallizer as described above, first, the magnetic pole 10 is used to pull the melt 5.
Apply a transverse magnetic field of 500 to 5000 G (Gauss) to the A coil 16 is wound around the magnetic pole 10, and a direct current is applied to it to obtain a magnetic field in a fixed direction.

Next, a direct current is applied to the solenoid coil 12, and a direct current magnetic field (so-called longitudinal magnetic field) that is symmetrical about the center line of the pulled crystal and along the direction of pulling the crystal is applied to the melt 5. The longitudinal magnetic field aligns the center of the solenoid coil with the axis of rotation of the crystal,
It is sufficient that the direction of the magnetic field substantially matches the direction of pulling the crystal, and the strength of the magnetic field is 500G ~ at the center of the magnetic field.
5000G is appropriate.

The magnetic field is applied independently and alternately in the horizontal and vertical directions. When a magnetic field is applied, the flow of the melt in a direction perpendicular to the direction of the magnetic field is suppressed, thereby suppressing the movement of impurity atoms and resulting in a uniform distribution.

It is effective to keep the movement range within a minute range by alternately switching the direction of the magnetic field. The switching cycle is preferably about 0.5 to 10 times per second.

[Function] The effect on the behavior of a melt when a magnetic field is applied during pulling of a semiconductor crystal such as silicon is widely known.

Basically, it has the effect of suppressing the flow of the melt in the direction perpendicular to the direction of the magnetic field, so when a vertical magnetic field is applied, the flow in the radial direction within the crucible is suppressed, but the flow in the depth direction is not suppressed. As a result, the flow becomes elongated in the depth direction. On the other hand, in the case of applying a transverse magnetic field, among the flow in the depth direction and the flow in the horizontal component, the flow in the direction perpendicular to the direction of the magnetic field is suppressed, and the flow in the parallel direction is not suppressed. This unique flow phenomenon of the horizontal component is described, for example, in J. of Crystal Growth 82 (1987),
Numerical calculations were reported in 318-326.

The purpose of the present invention is to stop all of the above-mentioned flows by applying a combination of transverse and vertical magnetic fields, thereby making the impurity distribution in the melt constant and temperature distribution. Also, heat conduction dominates, and stable, high-quality crystals can be obtained.

In addition, by changing the directions of the horizontal and vertical magnetic fields depending on the location in the longitudinal direction within the growing crystal (for example, the upper part of the melt flows in the vertical magnetic field, and the other parts flow in the horizontal magnetic field), the flow can be controlled. By controlling the horizontal magnetic field strength and the longitudinal magnetic field strength depending on the solidification position, the horizontal magnetic field flow becomes dominant in the early stage of crystal growth, and the longitudinal magnetic field flow becomes dominant in the late stage of crystal growth. It is also possible to make it similar.

[Example] Using a crystal pulling device with the structure shown in Figure 1.
Single crystal silicon with a diameter of 50 mm was produced by melting 2 kg of silicon in a stone crucible with a diameter of 150 mm. The magnetic field strength is 2000 Gauss at the center of the melt in both the vertical and horizontal directions.
The switching period for vertical and horizontal magnetic field application was 1 Hz.

The crystal was pulled up by adding phosphorus (P) so that the resistivity was 80 Ωcm at the upper end of the crystal. Figure 2 shows the resistivity and oxygen concentration distribution of the single crystal obtained.
At a solidification rate of approximately 60%, the resistivity was approximately 6.5 Ωcm, and the oxygen concentration was also approximately constant at 10 ¹⁸ particles/cm ³ and extremely uniform, confirming an improvement in quality in the length direction. On the other hand, when no magnetic field is applied, the resistivity at a position where the solidification rate is approximately 60% is approximately 5Ωcm.
And the resistivity was almost the same when the transverse magnetic field was 2000 Gauss. Also, when the vertical magnetic field is 2000 Gauss, it is approximately 7.5Ωcm.
It was hot.

[Effect] Applying horizontal and vertical magnetic fields suppresses the flow of melt, making fine control possible.

As a result, the resistivity distribution is improved compared to when no magnetic field is applied or when a horizontal magnetic field is applied, and the oxygen concentration distribution is improved compared to when a vertical magnetic field is applied.As a result, the quality becomes more homogeneous than when using existing growth methods. Product acquisition length can be significantly increased.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of the crystal pulling apparatus of the present invention, Figure 2 is a diagram showing the oxygen concentration and resistivity of a silicon single crystal according to the present invention, Figure 3 is a schematic diagram of a conventional crystal pulling apparatus,
Figure 4: A diagram showing the oxygen concentration and resistivity of a silicon single crystal using the conventional pulling device shown in Figure 3; Figure 5: A schematic diagram of a crystal pulling device using a transverse magnetic field; Figure 6: A crystal using a vertical magnetic field. FIG. 7 is a schematic diagram of a pulling device; FIG. 7 is a diagram showing the oxygen concentration and resistivity of a silicon crystal obtained by the pulling device shown in FIG. 6; 1... Furnace body, 2... Single crystal, 3... Heater for heating, 4... Crucible, 5... Melt, 6... Crucible axis rotation direction, 7... Crucible rotation axis, 8... Crystal pulling Axis, 9... Crystal rotation direction, 10... Magnet for transverse magnetic field, 11... Lines of magnetic force for transverse magnetic field, 12... Solenoid coil for generating vertical magnetic field, 13... Lines of magnetic force for longitudinal magnetic field,
14...Oxygen concentration curve, 15...Resistivity curve, 1
6... Solenoid coil for generating transverse magnetic field.

Claims (1)

[Claims] 1. In a crystal growth method in which a crystal is pulled from a semiconductor melt, a horizontal magnetic field is applied to the semiconductor melt in a container substantially perpendicular to the pulling direction, and a center of rotation of the crystal is applied substantially parallel to the pulling direction. A method for producing a single crystal, characterized by pulling the single crystal while periodically switching and applying a line-symmetrical magnetic field. 2. In a crystallization device that heats a semiconductor material to form a melt and pulls a crystal from the melt, magnetic poles are used to apply a horizontal magnetic field approximately perpendicular to the crystal pulling direction across a crucible containing the melt. and,
A single crystal growth apparatus comprising a solenoid coil for applying a magnetic field approximately parallel to the pulling direction around the crucible.