Single-crystal – oriented-crystal – and epitaxy growth processes; – Processes of growth from liquid or supercritical state – Having pulling during growth
Reexamination Certificate
2001-04-18
2003-03-04
Hiteshew, Felisa (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Processes of growth from liquid or supercritical state
Having pulling during growth
C117S030000, C117S032000, C117S917000
Reexamination Certificate
active
06527852
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a semiconductor single crystal growing technology using Czochralski method, and more particularly to a semiconductor single crystal growing apparatus and growing method in which crystal growth is performed while a magnetic field and a current orthogonal to each other are applied to a semiconductor melt to rotate the semiconductor melt.
BACKGROUND ART
Semiconductor crystal wafers in use for the substrates of ultra high integrated electric devices are grown by Czochralski method in which a semiconductor single crystal is pulled up from a rotating semiconductor melt while it is rotated in the opposite direction. The semiconductor melt held in the crucible undergoes heat from a cylindrical heater installed around the crucible. The crucible is rotated so that the temperature distribution in the melt shows perfect axial symmetry about the pull axis of the crystal. Rendering the temperature distribution in the melt axially symmetrical requires that the center of rotation of the crucible and the symmetric axis of the heater arrangement coincide with the pull axis of the crystal. The conventional art typically employs a method of mechanically rotating a shaft that holds the crucible.
This crucible rotation changes the concentration of the impurities involved in the crystal. In the method of mechanically rotating the crystal and the crucible, however, the crystal rotation has become difficult with increasing crystal diameter; besides, rotating a crucible requires a system of considerable size. For such reasons, the growth of large crystals has become increasingly difficult.
In order to circumvent this difficulty, there has been proposed a semiconductor crystal growing apparatus and growing method comprising a device for applying a magnetic field to a semiconductor melt under crystal growth and a device for applying a current orthogonal to the above-mentioned magnetic field to the semiconductor melt, and wherein an electrode to be immersed into the semiconductor melt and an electrode for energizing the pulled crystal are used (Japanese Patent Application No.Hei 9-343261). This technology minimizes the increase in apparatus scale and allows precise control of the rotation rate even when a semiconductor crystal with a diameter as large as 30 cm or more is grown. In addition, Japanese Patent Application No.Hei 10-065174 has shown that the electrode material is made identical to the semiconductor single crystal to grow so that contamination to the growing crystal is avoided.
In the conventional art described above, however, the electrode was dissolved into the semiconductor melt over the course of crystal growth. In order to keep applying the current, the electrode needed to be moved with the crystal growth. Besides, when the electrode was put into contact with the semiconductor melt, the melt directly below the electrode was pulled up so that the contact was made at a position higher than the melt surface. Accordingly, there was another problem that the surface form of the melt between the electrode and the growing crystal changes to cause a drop in rotation symmetry.
Moreover, it was impossible in the above-mentioned conventional semiconductor single crystal growing technologies to monitor the rotation rate of the semiconductor melt under crystal growth with a high degree of accuracy and with facility.
Furthermore, in such methods as the conventional ones, of applying a magnetic field and a current of constant intensities to rotate the semiconductor melt, it was difficult to render a single piece of crystal uniform in the impurity distribution along the direction of growth, with variations of not greater than 1%. In particular, in the cases of silicon single crystals, it was difficult to distribute both oxygen and a dopant impurity uniformly at the same time. Thus, in the conventional methods, it was difficult to control the impurity concentrations in a crystal along the crystal pulling direction, and it was difficult to improve uniformity in the impurity distribution within a semiconductor single crystal along the direction of growth.
The present invention has been achieved in view of the foregoing problems. An object thereof (hereinafter, may be referred to as first object) is to provide a semiconductor single crystal growing technology using Czochralski method. comprising a semiconductor single crystal growing apparatus and growing method for applying a magnetic field to a semiconductor melt under crystal growth and passing a current orthogonal to the magnetic field through the semiconductor melt, and wherein an electrode need not be moved due to electrode dissolution during crystal growth, and any drop will not occur in the rotation symmetry of the semiconductor melt due to a deformation in the melt surface between the electrode and the growing crystal.
Moreover, another object of the present invention (hereinafter, may be referred to as second object) is to provide an apparatus and method which make it possible in the conventional crystal growing to accurately and easily monitor the rotation rate of a semiconductor melt that rotates under electromagnetic forces during crystal growth.
Furthermore, another object of the present invention (hereinafter, may be referred to as third object) is to provide an apparatus and method which make it possible in the conventional crystal growing to improve the uniformity in the impurity distribution within a semiconductor single crystal along the direction of crystal growth.
DISCLOSURE OF THE INVENTION
In order to achieve the first object described above, the present inventors have made thorough intensive study and found that the above-mentioned object can be achieved by the provision of a semiconductor crystal growing apparatus comprising a device for applying a magnetic field to inside a semiconductor melt and a device for passing a current through the semiconductor melt, wherein: a protective tube is arranged around an electrode for passing the current through the semiconductor melt; the material of the protective tube is made identical to that of a crucible holding the semiconductor melt; the protective tube and the melt are put into rectangular contact with each other; and the semiconductor melt and the electrode for passing the current through the semiconductor melt are put into contact with each other in the interior of the protective tube, at a position higher than the major surface of the melt surface, so that the semiconductor melt and the electrode for passing the current through the semiconductor melt are always in contact with each other during crystal growth and there occurs no deformation in the melt surface between the electrode and the crystal. Thereby has been achieved the present invention (hereinafter, may be referred to as first invention).
Thus, the first invention provides a semiconductor crystal growing apparatus comprising a device for applying a magnetic field to inside a semiconductor melt and a device for passing a current through the semiconductor melt, characterized in that an electrode for applying the current to inside the semiconductor melt extends through a tube surrounding the electrode.
The first invention also provides a semiconductor crystal growing method for growing a semiconductor crystal by using a semiconductor crystal growing apparatus comprising a device for applying a magnetic field to inside a semiconductor melt and a device for passing a current through the semiconductor melt, the method being characterized in that the semiconductor crystal growing apparatus has an electrode for applying the current to inside the semiconductor melt, the electrode extending through a tube surrounding the electrode.
In the first invention, a current is passed between the semiconductor melt held in a magnetic field and the growing semiconductor crystal, with the protective tube arranged around the electrode; therefore. the electrode and the melt come into contact with each other in the interior of the protective tube. Thus, even when the contact portion between the electrod
Eguchi Minoru
Watanabe Masahito
Hiteshew Felisa
McGinn & Gibb PLLC
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