Single-crystal – oriented-crystal – and epitaxy growth processes; – Processes of growth from liquid or supercritical state – Having pulling during growth
Reexamination Certificate
2001-03-06
2002-12-24
Hiteshew, Felisa (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Processes of growth from liquid or supercritical state
Having pulling during growth
C117S029000, C117S030000, C117S032000, C117S200000, C117S917000
Reexamination Certificate
active
06497761
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the technique for growing single crystal of semiconductor such as silicon (Si) using the well-known Czochralski growth method and more particularly, to an apparatus for and a method of growing a single crystal of semiconductor, in which magnetic field is applied to a melt of semiconductor in a rotating crucible while an electric current is supplied to the melt so as to intersect with the magnetic field, thereby growing a single crystal of semiconductor from its seed crystal.
2. Description of the Related Art
Single-crystal semiconductor wafers, which have been used as substrates of ultralarge-scale integrated electronic devices (ULSIs), are produced from an ingot of a single crystal of semiconductor (e.g., Si). An ingot of a single crystal of semiconductor is typically obtained by crystal growth from a semiconductor melt using the Czochralski method.
In the Czochralski method, conventionally, a desired single crystal of semiconductor is pulled up vertically from a rotating melt of the same semiconductor in a horizontal plane using a seed crystal while the growing single crystal is rotated in an opposite direction to the melt. The melt is held in a crucible and is applied with heat from a heater mounted around the crucible. The crucible containing the melt is mechanically rotated in a horizontal plane in the whole growth process. This is to make the temperature distribution in the melt axisymmetrical to the vertical pull shaft for the crystal (i.e., the growth axis of the crystal). Due to the mechanical rotation of the crucible, the concentration of dopant or dopants introduced into the crystal varies.
Also, the concentration of dopant(s) introduced into the growing crystal varies due to segregation at the interface of the growing crystal and the melt as the growth time increases. Thus, unless the dopant concentration is well controlled, it tends to differ conspicuously from each other between the early and later stages of the crystal growth process. Taking this disadvantage into consideration, both the crystal and the crucible are rotated so as to uniformize the dopant concentration in the crystal thus grown.
With the above-described conventional Czochralski method where the crystal and the crucible are mechanically rotated in the growth process, there is a tendency that the rotation of the growing crystal becomes more difficult with the increasing diameter of the crystal. In particular, this tendency induces a serious problem in the crystal growth of silicon.
Specifically, the crucible made of fused silica is used for growing single crystal of silicon and therefore, oxygen existing in silica tends to dissolve into the growing crystal. For this reason, the concentration of oxygen needs to be well controlled along with the concentration of intended dopant during the growth process. In the above-described conventional method where the crystal and the crucible are mechanically rotated, however, it is difficult to suppress the axial fluctuation of the dopant concentration along the pull shaft in the growing crystal within 1%. Also, to mechanically rotate the large-diameter crucible, a large-scale apparatus or subsystem is necessary. As a result, it has been becoming more difficult to grow a large-diameter single crystal of silicon.
The difficulty in the above-described conventional method can be solved by the technique disclosed in the Japanese Patent No. 2,959,543 issued in October 1999, which was created by the inventors of the present invention, M. Watanabe and M. Eguchi. With the technique disclosed in this patent, a specific magnetic field is applied to a melt of semiconductor and at the same time, electric current is supplied to the melt so as to be perpendicular to the magnetic field. Thus, the radial fluctuation of dopant concentration in a grown crystal is uniformized.
FIG. 1
shows the configuration of the prior-art semiconductor crystal growth apparatus disclosed in the above-identified Japanese Patent No. 2,959,543.
As shown in
FIG. 1
, the prior-art apparatus comprises a crystal growth furnace
120
with a chamber
109
, a coil unit
110
for generating a specific magnetic field which is mounted to surround the furnace
120
, and a power supply
104
provided outside the furnace
120
. In the chamber
109
, a crucible
105
and a heater
108
are mounted. The heater
108
is located to surround the crucible
105
. The heater
108
is used to heat a semiconductor raw material in the crucible
105
, thereby producing a melt
102
of the semiconductor in the crucible
105
. The crucible
105
is used to hold the semiconductor raw material and the melt
102
therein.
FIG. 1
shows the state where the melt
102
has been produced with the heater
108
and is held in the crucible
105
.
A vertical pull or lift shaft
106
, which is made of an electrically conductive material, is provided over the crucible
105
. Similar to the ordinary Czochralski method, a seed crystal (not shown) is attached to the bottom end of the shaft
106
. The top end of the shaft
106
is supported by a pull or lift mechanism
112
. The mechanism
112
serves to pull up or lift vertically the shaft
106
(i.e., a growing single crystal
101
of semiconductor) while rotating the shaft
106
around its axis (i.e., the pull or growth axis).
The coil unit
110
is electrically connected to a power supply (not shown) and is supplied with a specific electric current. Thus, the unit
110
generates a specific magnetic field
111
in the crucible
105
.
Electrodes
103
are vertically provided near the crucible
105
so as to be arranged axisymmetrical to the shaft
106
. The bottoms of the electrodes
103
are immersed in the melt
102
. In
FIG. 1
, only one of the electrodes
103
is shown for simplification.
One of the two output terminals of the dc power supply
104
is electrically connected in common to the top ends of the electrodes
103
by way of an ammeter
121
. The other of the output terminals of the supply
104
is electrically connected to the shaft
106
by way of a resistor
122
. A voltmeter
123
is electrically connected in parallel to the resistor
122
.
With the prior-art apparatus shown in
FIG. 1
having the above-described configuration, in the growth process, the semiconductor raw material is supplied into the crucible
105
and heated with the heater
108
, producing the melt
102
of semiconductor in the crucible
105
. A bar-shaped single crystal
101
of semiconductor is grown by pulling the seed crystal up from the melt
105
thus produced using the shaft
106
. At this time, to prevent the dislocations existing in the seed crystal from propagating to the single crystal
101
, a so-called “neck”
107
is formed between the seed crystal and the top end of the growing single crystal
101
. The neck
107
is a constricted part of the crystal
101
and is formed at the initial stage of the growth process.
During the growth process of the crystal
101
, the coil unit
110
is supplied with a specific electric current from the power supply, thereby generating the magnetic field
111
in the chamber
109
. The magnetic field
111
thus generated is perpendicular to the interface of the melt
102
and the crystal
101
and axisymmetrical to the shaft
106
in the crucible
105
.
Moreover, a specific dc voltage is applied across the electrodes
103
and the pulling shaft
106
by the power supply
104
, thereby supplying a specific electric current to the melt
102
existing in the crucible
105
. The electric current thus supplied flows through the melt
102
, resulting in the Lorentz force applying to the melt
102
.
Thus, rotational forces centering on the pulling shaft
106
(i.e., the growth axis) are generated in the melt
102
, causing rotation of the melt
102
around the shaft
106
in the crucible
105
. As a result, because of stir of the melt
102
by its rotation, the radial fluctuation of the dopant concentration in the grown crystal
101
is uniformized.
Furthermore, the Japanese
Eguchi Minoru
Watanabe Masahito
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