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Production Methods of Single Crystal Silicon Ingots

Several methods can be used to grow single crystal silicon.

The current commercial manufacturing process of single crystal silicon can be classified into the following two methods:

  • FZ method (Floating Zone method)
  • CZ method (Czochralski method)

The CZ method has a variation called the MCZ method (where a magnetic field is applied to the CZ method). In this method, the conditions for growing crystals are controlled by applying a magnetic field. Furthermore, the magnetic field can be applied in three ways: transversely, longitudinally, or along cusp.

FZ Method

Image of FZ Method

In this method, silicon is melted by induction heating without using a quartz crucible. The melted silicon is held by surface tension. The high temperature zone does not come into contact with other materials; this facilitates the achievement of high-purity crystals with low oxygen content. One drawback of this method is that it is difficult to produce crystals with a large diameter.

CZ Method

Image of CZ Method

Currently, this is the most widely used method in the manufacture of single crystal silicon for LSIs. Since the melted silicon is held in a quartz crucible, the dissolution of oxygen from the quartz glass (SiO2) is inevitable; as a result, the method limits the reduction of the oxygen content.

MCZ Method (Longitudinal Magnetic Field Method)

Image of MCZ Method (Longitudinal Magnetic Field Method)

The MCZ method is a variation of the CZ method in which a magnetic field, created by an electromagnet, is applied perpendicularly to the melted silicon surface. Since hot melted silicon conducts electricity, it is subjected to a force created by the interaction between the flow of the melted silicon and the magnetic field. As a result, the flow of the melted silicon is altered. Crystal properties are controlled by taking advantage of this characteristic.

MCZ Method (Transverse Magnetic Field)

Image of MCZ Method (Transverse Magnetic Field)

This is another variation of the CZ method in which a magnetic field, created by an electromagnet, is applied parallel to the melted silicon surface. With this method, low oxygen concentration can be achieved, since the flow of melted silicon along the inner wall of the quartz crucible can be forcefully restrained. The process, however, tends to be complex, because the magnetic field is not axially symmetrical to the crystal growing axis.

MCZ Method (Cusp Magnetic Field)

Image of MCZ Method (Cusp Magnetic Field)

This is yet another variation of the CZ method, in which a pair of electromagnets are placed on top and bottom to create magnetic fields in opposite directions. The salient features of this method are: (1) the intensity of the magnetic field in the vicinity of the growing crystal and the melted silicon is reduced as compared to that in the other parts, and (2) the magnetic field is simultaneously parallel to both, the crystal growing axis and the surface of the melted silicon.

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