JPS6033290A - Preparation of single crystal semiconductor - Google Patents

Abstract

PURPOSE:To prepare as single crystal semiconductor having optionally controlled concn. of impurity and uniform distribution of impurity by impressing a magnetic field having a direction and strength controlled to a specified value to a melted semiconductor in a crucible supported freely rotatably. CONSTITUTION:Silicon starting materials are charged to a crucible 4 and the materials are heated by a heater 5 to cause melting. Then, seed crystal 9 is dipped in the melted silicon 10 and a chain 8 is pulled up while rotating the crucible 4 and the seed crystal 9 in the direction reverse to each other to grow single crystal of silicon 11. An annular superconductive magnet 15 is arranged to the outside of a chamber 1 with its axis inclined by a specified angle to the direction of gravity. Liquid helium is supplied from a liquid He refrigerator to the superconductive magnet 15. The growth of the single crystal silicon is performed by impressing a magnetic field to the melted silicon 10 by passing electric current through the superconductive magnet 15 and passing almost direct current of <=3% ripple factor through the heater 5.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for manufacturing a single crystal semiconductor, and in particular to a method for manufacturing a single crystal semiconductor.
and a method for manufacturing high-quality single crystal semiconductors used in high-power discrete devices.

[Technical background of the invention and its problems]

Single crystal semiconductors used for manufacturing semiconductor devices are mainly manufactured by the Czochralski method (CZ method). Conventionally, a single crystal semiconductor growth apparatus as shown in FIG. 1 has been used in this CZ method.

That is, numeral 1 in the figure is a chamber whose top and bottom are open. A rotatable support rod 2 is inserted into the lower opening of the chamber 1, and a protector 3 is placed on the support rod 2.
is supported and protects the quartz crucible 4. A cylindrical heater 5 and heat retaining tubes 6 and 7 are sequentially arranged around the outer periphery of the protector 3. For example, a chain 8 is suspended from the upper opening of the chamber 1 and holds a seed crystal 9.

In the 7'ccz method using the above-mentioned growth apparatus, for example, when manufacturing single crystal silicon, a silicon raw material is put into a crucible 4, the silicon raw material is melted by a heater 5, and a seed crystal is added to this molten silicon 10. 9″f: Single crystal silicon 11 is grown by immersing the chain 8′f and pulling up the chain 8′f while rotating the seed crystal 9 and the seed crystal 9 in opposite directions.

By the way, during the growth of single crystal silicon, convection as shown in FIG. 2 occurs in the molten silicon 10 in the crucible 4. The ratio in the figure is the forced convection (hereinafter abbreviated as convection a) that occurs mainly at the center of the crucible 4, and 13 is the vertical component of thermal convection that mainly occurs around the crucible 4 (hereinafter abbreviated as convection). ), 14 is the horizontal component of thermal convection (
(hereinafter abbreviated as convection C).

Due to such convection, temperature fluctuations of about ±5° C. occur near the crystal growth interface of the molten silicon 10. Further, oxygen and other impurities eluted from the quartz crystal 4 are carried by such convection, and are incorporated into the single crystal silicon 11 by evaporating from the melt surface. Therefore, it is extremely difficult to equalize the distribution and control the concentration of impurities contained in single crystal silicon 1. Additionally, when manufacturing semiconductor devices using wafers cut from single-crystal silicon, the state of occurrence of crystal defects due to oxygen precipitation changes depending on the concentration of oxygen contained in the wafer and the thermal process of the device. The oxygen concentration must be set according to the device used.

However, as mentioned above, in the conventional method, the oxygen concentration in single crystal silicon is regulated by the conditions during growth and cannot be controlled arbitrarily.

On the other hand, attempts have been made to suppress convection and make the oxygen concentration distribution in single crystal silicon uniform by applying a magnetic field to molten silicon, and some effects have been obtained. Here, as a method of applying a magnetic field, Ruth? Two electromagnets are placed on opposite sides of the molten silicon with their poles facing each other, and a horizontal magnetic field is applied to the molten silicon (hereinafter abbreviated as the horizontal magnetic field method). There is a method in which a ring-shaped electromagnet is placed around the molten silicon and a magnetic field is applied vertically to the molten silicon (hereinafter abbreviated as the vertical magnetic field method). However, since the effect of suppressing convection CF is small, the impurity (oxygen) concentration can be reduced to a low concentration and the distribution of macroscopic impurities can be made uniform to some extent. There are large temperature fluctuations in the vicinity,
In particular, the distribution of impurities (oxygen) in the radial direction becomes non-uniform.

On the other hand, in the above-mentioned longitudinal magnetic field method, convection C can be suppressed, so the distribution of impurities (oxygen) can be made uniform, but the effect of suppressing convection a and b is small, so impurities ( oxygen) is transported near the crystal growth interface,
It is not possible to produce products with low impurity (oxygen) concentrations.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a method for manufacturing a single crystal semiconductor in which the impurity concentration is arbitrarily controlled fi[I and the impurity distribution is extremely uniform. It is.

[Summary of the invention]

The method for manufacturing a single crystal semiconductor of the present invention uses a magnetic field whose direction and strength are controlled to predetermined values (for example, a direction tilted at a predetermined angle with respect to the direction of gravity). It is characterized in that it is applied to the molten semiconductor raw material inside.

In this way, by controlling the direction and strength of the magnetic field applied to the molten semiconductor raw material to a predetermined value, it is possible to arbitrarily set the method of suppressing convection, so the impurity concentration can be controlled over a wide range. Moreover, the distribution of impurities can be made uniform.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 3 to 5. Note that the same members in FIG. 3 as those in FIG. 1 already described are given the same numbers, and explanation 8A is omitted.

As shown in Fig. 3, the main body of the growth device is exactly the same as the conventional one, and a ring-shaped superconducting magnet 15 is placed outside the chamber 1 with its axis tilted at a predetermined angle with respect to the direction of gravity. ing. Liquid helium is supplied to this superconducting magnet 15 from a liquid helium refrigerator (not shown).

The growth of single-crystal silicon using this growth apparatus is conventional, except that the superconducting magnet 15 is energized to apply a magnetic field to the molten silicon 10, and the heater 5 is supplied with a DC current with a ripple rate of 31% or less. It is carried out almost in the same way as the CZ method.

According to the method of the present invention, the horizontal component (convection C) of thermal convection can be suppressed by the X-axis component BX of the magnetic field B, and the forced convection (convection C) can be suppressed by the biaxial acid component Bz of the magnetic field B. a) and the vertical component of thermal convection (convection b) can be suppressed, so fluctuations in the temperature of molten silicon near the crystal growth interface during single-crystal silicon growth can be reduced, and the impurity (oxygen) concentration can be suppressed. can be made uniform. Furthermore, by arbitrarily setting the direction and strength of the magnetic field, the way convection is suppressed can be changed, and the impurity (oxygen) concentration can be controlled over a wide range.

Actually, using an upstream growth device, 12 inches φ (30,4
18k polycrystalline silicon in quartz crucible 4 (8crnφ)
After charging g and melting at a high temperature of 1420°C or higher under a reduced pressure of 20 Torr, a superconducting magnet 15 placed at an angle of 45° with respect to the direction of gravity is applied to the molten silicon 1o at an angle of 45° with respect to the direction of gravity. With a magnetic field of 2000 Gauss applied in the direction of
φ N-type nest crystal silicon llt'' was grown.

In addition, 104 mφ N-type single crystal silicon was grown under similar conditions using the conventional transverse magnetic field method and longitudinal magnetic field method.

When we measured the resistivity and oxygen concentration of minute portions in the growth direction of single-crystal silicon grown by the method of the present invention, the transverse magnetic field method (It), and the longitudinal magnetic field method (It), we found that these It was confirmed that the distribution was uniform.

The results are shown in FIGS. 4 and 5.

As is clear from Figure 4, in the transverse magnetic field method (II), the variation in minute resistivity is large, and the maximum and minimum values are approximately 1
There was a difference of 0-. Furthermore, in the longitudinal magnetic field method (ID), the uniformity of the distribution was improved, and the difference between the maximum and minimum values was about 2 inches. On the other hand, in the method (I) of the present invention, the distribution was much more evenly distributed, and the difference between the maximum value and the minimum value was 2% or less.

In addition, as is clear from Fig. 5, the transverse magnetic field method (n)
The variation in oxygen concentration was large, and the difference between the maximum and minimum values was 1.5 On the other hand, in the method (1) of the present invention, the variation in oxygen concentration is small, and the difference between the maximum value and the minimum value is 1.OX 10 ``on-''. If the direction of the Wi field is 45° with respect to the direction of gravity, the oxygen concentration will be 10~13 x 10"
7cm3. For 20-30°, 5-8 X 10"
It was found that the oxygen concentration can be controlled over a wide range. The table below shows the conventional method and the present invention method.
This figure summarizes the temperature fluctuations of molten silicon during single-crystal silicon growth and the control range of oxygen concentration in the grown single-crystal silicon.

Note that in the above embodiments, the direction of the applied magnetic field was always kept constant during the growth of single crystal silicon, but the angle may be changed during the growth. In this case, as the amount of melt increases and the amount of melt decreases, the influence of forced convection will gradually increase, so it is desirable to gradually increase the direction of the magnetic field's inclination with respect to the direction of gravity so that it approaches the horizontal direction. .

Further, although the above description has been made regarding the case of manufacturing single crystal silicon, it goes without saying that the method of the present invention can be similarly applied to the case of manufacturing other single crystal semiconductors such as GaAa.

〔Effect of the invention〕

As detailed above, according to the method for manufacturing a single crystal semiconductor of the present invention, an extremely high quality single crystal semiconductor for use in VLSI, in which the impurity concentration is arbitrarily controlled and the impurity distribution is extremely uniform, is manufactured. It has remarkable effects, such as the ability to

[Brief explanation of drawings]

Figure 1 is a sectional view of a conventional single crystal semiconductor growth apparatus, Figure 2 is an explanatory diagram showing the state of convection in the crucible, and Figure 3 is a cross section of a single crystal semiconductor growth apparatus used in an embodiment of the present invention. 4 is a characteristic diagram showing the micro resistivity distribution, and FIG. 5 is a characteristic diagram showing the oxygen concentration distribution. DESCRIPTION OF SYMBOLS 1... Chamber, 2... Support rod, 3... Protector, 4... Quartz crucible, 5... Heater, 6, 7...
Heat insulation cylinder, 8... Chain, 9... Seed crystal, '10.
...Fused silicon, 11...Single crystal silicon, 15
...Superconducting magnet〇Applicant's representative Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 3

Claims (2)

[Claims] (1) Ruth in the chamber? In a method for producing a single crystal semiconductor by supporting a rotatably in a trap, immersing a seed crystal rotatably suspended from above in the molten semiconductor raw material in the crucible, and pulling up the seed crystal, A method for manufacturing a single crystal semiconductor, comprising applying a magnetic field whose direction and strength are controlled to predetermined values to the molten semiconductor raw material in the crucible. (2) The single crystal semiconductor according to claim 1, wherein the direction and strength of the magnetic field are arbitrarily changed according to the amount of melt of the molten semiconductor raw material during the growth of the single crystal semiconductor. Production method.