JPS5850953B2 - crystal growth method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for growing crystals of semiconductors, particularly silicon.

Examples of crystal growth methods include the pulling method, zone leveling method, Bridgman method, and dendrite growth method. The purity of the grown crystal decreases.

For example, silicon crystals are processed using the Czochralski method (pulling method).
In the case of crystal growth, a quartz (SiO2) crucible is generally used as a container to contain the melt of the crystal material, but in this case, oxygen is decomposed and mixed in from the crucible, making it impossible to obtain high-purity crystals. There is a drawback.

The present invention provides a crystal growth method that avoids such drawbacks and can obtain highly pure crystals or crystals of desired purity with good reproducibility.

That is, as a result of various experimental considerations, the present inventor has found that the contamination of this impurity is caused by the movement of the crystal material liquid within the container.
In particular, we have determined that the movement is highly dependent on convection, and based on this finding, we have attempted to suppress convection by applying a magnetic field to control the mixing of the container's ingredients into the liquid.

In other words, when a crystalline material liquid is stored in a container, the constituent components of the container are dissolved into the crystalline material liquid that is in contact with the container at least in the portion where the container and the crystalline material liquid are heated to a high temperature. However, in this case, if the heat convection inside the container is relatively intense, the components of the container that are dissolved in the part that comes into contact with the container are quickly carried away to other parts by the heat convection, which causes crystallization. The dissolved concentration of the container components in the material liquid is quickly uniformized, and as a result, the dissolved concentration of the container components in the contact area of the crystal material liquid with the container is lowered, so that the dissolution of the container components in the crystal material liquid is reduced. is likely to occur, and its dissolution occurs to a state at or close to saturation solubility, at which time the entire liquid has a substantially uniform dissolution concentration.

When the convection of the crystal material liquid is relatively strong in this way, the dissolution of the container components into the liquid in contact with the container occurs significantly, and the movement speed of these components to other parts of the liquid becomes slow. It has been found that this increases the concentration of impurities due to the container components in crystals grown from this method.

Based on this research, the present invention applies a magnetic field to the crystal material liquid as described above, thereby suppressing convection of the crystal material liquid.

The reason why convection is suppressed by the application of a magnetic field is said to be based on the following phenomenon.

That is, when a fluid having electrical conductivity, ie, a conductor, moves in a magnetic field, a potential difference is generated in the fluid, and a current flows.

The current flowing through this magnetic field applies a new force to the liquid that carries this current.

Since this force is in the opposite direction to the direction in which the liquid moves, the movement of the fluid becomes pure and its viscosity increases.

This is called magnetic viscosity. Then, due to the magnetic viscosity generated in this way, convection of the fluid, that is, the crystal material liquid becomes difficult to occur.

Incidentally, the method of growing crystals under the application of a magnetic field is
Journal of Applied Physics
s, Vol 37゜P 2021 (1966), Jo
urnal of MaterialScience
t Vol, 5P822 (1970), Sympo
sium: “Gallium Arsenide,” fa
sc? 5t Tomsk.

P34 (1974), known from Japanese Patent Publication No. 49-49307.

However, the mixing of container components into the melt has not been recognized.

An example of the crystal growth method based on the pulling method according to the present invention will be explained with reference to FIG.

In the figure, reference numeral 1 generally indicates a single crystal growth apparatus that can be used to carry out the method of the present invention.

Reference numeral 2 denotes a container, for example a quartz crucible, containing a melt or solution of a crystalline material having a certain degree of electrical conductivity, that is, a Si melt 3.

A heating means 4 is arranged around the outer periphery of this container 2 .

In the heating means 4, the energized heaters 5 are arranged in a cylindrical shape along the outer peripheral surface of the container 2, for example, in a zigzag pattern.

Outside this heating means 4, for example, a cylindrical heat shield or a jacket 6 cooled by water cooling is arranged as necessary, and a permanent magnet or a direct current magnetic field generating means 7, for example, which is not an electromagnet, is arranged outside the heating means 4. is placed.

8 is a single crystal seed, for example a Si single crystal seed, and 9 is its pulling chuck.

Electricity is supplied to the energizing heater 5 of the heating means 4 with a substantially direct current with ripple content suppressed to 4% or less, or with a current of 1 kHz.
Alternating current or pulsating current of z or more.

It has been confirmed that when such a current is applied, unnecessary vibrations caused by the interaction of the heating means 4 with the magnetic field can be avoided.

In this way, the Si crystal 10 is grown by pulling the Si seed 8 from the Si melt surface at a required speed.

In this case, the container 2 and the pulled single crystal 10 (therefore, the seed 8) may be unrotated, or they may be rotated relative to each other.

Incidentally, the relationship between the number of rotations and the oxygen concentration is as shown in FIG. 2, as the number of rotations increases, the concentration increases.

The solid line curve in Figure 2 is for the case when a magnetic field of 4000G (Gauss) is applied, and the dashed line curve is for the case when the magnetic field is zero.As can be seen by comparing the two, when a magnetic field is applied,
The oxygen concentration will be lower than when it is not provided.

It was confirmed that in the Si crystal 10 grown under the application of a magnetic field in this manner, the concentration of oxygen O, which is a constituent of the container 2 of the crystal material liquid 3, that is, the quartz crucible, was drastically reduced.

This is because, as mentioned above, by applying a magnetic field to the crystal material liquid 3, the apparent viscosity of the liquid 3 increases, and the movement of the liquid 3 becomes pure.

The flow decreases, and as a result, the moving speed of the container component oxygen O in the liquid 3 decreases, and dissolution becomes difficult to proceed. This seems to be based on lowering the oxygen concentration in the air.

Incidentally, when no magnetic field is applied, that is, when thermal convection is relatively intense, the oxygen O dissolved at the part in contact with the container 2 flows at a remarkable speed at the Si solid-liquid phase interface. According to experiments, when a magnetic field of about 4000 G (Gauss) was applied, the magnetic field reached at a speed of about 0.5 crrL/sec.
Its movement speed became unmeasurably slow.

As described above, in the method of the present invention, the vibration of the liquid level is small, and the temperature fluctuation thereof is also small, so that crystal growth can be stabilized.

Figure 3 shows the crucible (container 2) in a state where no magnetic field is applied.
), and in this case, the concentration at the periphery near the contact with the wall surface of the container 2, indicated by points a and b, and the concentration at the center, indicated by point C, are almost the same. Uniform and high concentration of I x 1018 atoms
/-, the measurement results of the oxygen concentration at each point a, b, and C when a magnetic field of 4000 G was applied by the method of the present invention were 9
1017atoms/cl'77i, while the central part shows a low value of 6.6 x 1017atoms/ffl.

This also shows that in the case of the present invention, the movement of oxygen O, which is a container component, from the container 2 is small.

In this case, the container 2, that is, the quartz crucible, has a diameter of 12
The one between 3 and 3 was used.

In addition, Fig. 5 shows the measurement results of the impurity concentration in the pulled Si crystal, and the horizontal axis shows the position along the pulling direction of the Si crystal. The region B shows a region where crystal growth was performed in a state where a magnetic field of 4000 G was applied by the method of the present invention.

In the figure, the vertical axis indicates oxygen concentration.

As is clear from this, when a magnetic field is applied, the oxygen concentration can be lowered and the purity of the crystal can be increased compared to when no magnetic field is applied.

As described above, according to the present invention, the oxygen concentration in the crystal can be lowered, so it is possible to suppress the decrease in resistivity due to oxygen becoming a donor, and it is also possible to reduce changes in the resistivity distribution within the ingot. can.

Further, it is possible to reduce warping of the weber due to oxygen precipitation during heat treatment.

As mentioned above, when using the method of the present invention, convection is suppressed by increasing the apparent viscosity of the crystal material liquid in the container by applying a magnetic field to the crystal material liquid in the container. Dissolution and migration can be controlled, and high-quality, high-purity crystals can be obtained.

[Brief explanation of drawings]

Figure 1 shows the constituent countries of the crystal growth apparatus on each side of the crystal growth method according to the present invention, Figure 2 shows the relationship between oxygen concentration and rotation speed, and Figures 3 and 4 respectively Oxygen concentration distribution diagram, FIG. 5 is an oxygen concentration distribution diagram of the crystal. Reference numeral 1 designates a crystal growth apparatus, 2 a storage container for a crystal material liquid 3, 4 a heating means, 5 a heater thereof, and 7 a magnetic field generating means.

Claims (1)

[Claims] 1 It has a silicon melt and a quartz container in which it is placed, and the silicon crystal is pulled up by rotating it relative to the container, and a magnetic field in a predetermined direction is applied to the melt, thereby causing it to be drawn from the container into the melt. A crystal growth method that controls the dissolution of oxygen into