Single-crystal – oriented-crystal – and epitaxy growth processes; – Processes of growth from liquid or supercritical state – Having pulling during growth
Reexamination Certificate
2002-08-30
2004-06-29
Hiteshew, Felisa (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Processes of growth from liquid or supercritical state
Having pulling during growth
C117S208000, C117S217000, C117S218000, C117S222000
Reexamination Certificate
active
06755910
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for pulling up a single crystal of semiconductor, such as silicon or the like, and more specifically to a method for pulling up a single crystal having a heavy weight, in which case, the single crystal can be grown in the dislocation-free state without any accidents of the single crystal dropping, thereby ensuring to stably produce the single crystal in a high crystalline quality.
DESCRIPTION OF THE PRIOR ART
In recent years, silicon single crystals, which are used to form a circuit device, such as a large-scale integrated circuit (LSI's), have been mostly produced by means of the Czochralski method (hereafter referred to as “the CZ method”). Such a single crystal grown by the CZ method is usually pulled up from a molten material in a quartz crucible, and oxygen is included in the crystal. This provides excellent properties regarding the substrate quality in the process of manufacturing LSI's.
In producing a single crystal using the CZ method, the pulling rate of the crystal has close relation to the temperature gradient in the single crystal. A greater temperature gradient provides acceleration in the pulling rate. Moreover, an inert gas is always supplied at the area around the crystal in the course of pulling up the crystal, and it is necessary to regulate the gas flow in order to avoid the turbulence, stagnation, convention and the like in a chamber for the crystal growth. In the case of industrially producing silicon single crystals, a flow-regulating member is normally disposed around the single crystal to be pulled, thereby allowing the heat of radiation to be a shield and the inert gas flow to be regulated.
FIG. 1
is a longitudinal sectional view of an apparatus for pulling up a silicon single crystal equipped with a flow-regulating member by the CZ method. A crucible
2
, which is used to produce the silicon single crystal, is normally disposed in the center of the apparatus
1
for pulling the single crystal. The crucible
2
has a dual structure such that it comprises an inner quartz crucible
2
a
and an outer graphite crucible
2
b
. A heater
3
made of graphite is disposed outside the crucible
2
to fuse silicon into molten silicon
4
inside the crucible
2
. A pulling wire
5
is used to pull up the single crystal, and a seed crystal
6
is attached onto one end of the pulling wire
5
. The seed crystal
6
, the lower end of which comes in contact with the surface of the molten silicon material
4
, is pulled upwards and thus the single crystal
7
is grown by solidifying the molten material onto the lower end portion of the seed crystal.
In this case, a flow-regulating member
8
is disposed above the molten material
4
in such a way that it surrounds the silicon single crystal to be grown. The flow-regulating member
8
intercepts the heat of radiation emanating from both the heater
3
and molten material
4
, thereby increasing the temperature gradient in the pulled single crystal
7
. In the process of crystal growth, a high purity argon gas is always supplied into the chamber to form gas flow
31
(indicated by arrows in the drawing). The gas flow
31
thus formed is regulated by the flow-regulating member
8
. The distance between the lower end of the flow-regulating member
8
and the surface of the molten material
4
stored in the crucible (hereafter the distance being simply referred to as the “gap”) is normally determined to be 15-30 mm, taking into account the effects of both shielding the heat of radiation and regulating the inert gas flow.
In pulling up the single crystal by the CZ method, it is necessary to remove residual dislocations in the seed crystal as well as dislocations resulting from the thermal stress, when the seed crystal comes into contact with the molten material, and thus to prevent the effect of these dislocations from extending into the main body portion (body) of the single crystal. In order to produce a dislocation-free single crystal by eliminating dislocations from the crystal surface, the so-called “Dash neck process” is employed, in which case, the end of the crystal is tapered.
In the general Dash neck process, the crystal grown from the seed crystal is tapered into a very small diameter of 3 to 4 mm, so that the residual dislocations in the seed crystal and dislocations generated by the contact with the molten material can be moved outside the crystal, thereby enabling a dislocation-free single crystal to be grown. For this purpose, the neck portion is formed just after starting to pull up the crystal. When, however, the diameter at the neck portion exceeds 5 mm, the dislocations can hardly be moved to the outside the crystal, thereby making it difficult to produce the dislocation-free single crystal.
As described above, a diameter of not more than 4 mm at the neck portion enables the dislocations to be eliminated in a high efficiency. However, if the diameter at the neck portion is set to be too small, a high strength for supporting the single crystal ingot cannot be obtained. As a result, a fracture takes place at the neck portion in the process of pulling up the crystal or in the subsequent processes of cooling and removing the ingot, and further there is a possibility that the single crystal drops into the molten material in the crucible, thereby causing the apparatus for pulling up the single crystal to be damaged, the overflow of the molten material, steam explosion and other effects to take place, and causing a possible accident resulting in injury.
In the Dash neck process, a desired neck shape can be formed by controlling the pulling rate and the temperature of the molten material. An increase in the pulling rate or an increase in the temperature of the molten material provides a smaller diameter at the neck portion, whereas, a decrease in the pulling rate or a decrease in the temperature of the molten material provides a greater diameter at the neck portion.
However, even if the diameter at the neck portion is controlled into a fixed value, the crystal shape at the neck is altered when an unexpected disturbance occurs in the temperature of the molten material in the crucible. For instance, a sudden increase in the temperature of the molten material in the process of pulling up the single crystal provides a much smaller diameter at the neck portion, compared with the preset target value, or at worst it causes the single crystal to be separated from the surface of the molten material. In such a case, the neck portion is again immersed into the molten material and the Dash neck process has to be repeated.
The weight of the single crystal to be pulled up is conventionally limited to 100 Kg or so. In recent years, a high efficiency in the manufacture of semiconductor devices has been strongly required to increase both the diameter and the total length of single crystals, so that the weight of the single crystal tends to exceed 200 Kg. If the diameter of the single crystal at the neck portion is increased so as to avoid the above-mentioned problem, it is difficult to eliminate dislocations from the single crystal in the Dash neck method, as described above, so that the work to re-form the neck portion is frequently repeated. Along with an increase in the weight of the single crystal, when it is preferentially intended to prevent the neck portion from being damaged or to prevent the single crystal from dropping, it is difficult to eliminate dislocations therefrom, thereby increasing the number of the re-works in the Dash neck process and thus reducing the efficiency conspicuously in the process of the single crystal.
To overcome the above problem resulting from the increase in the weight of the single crystal, the present applicant proposed a method for producing a single crystal with an increased gap in Japanese Patent Application Laid-open No. 11-189488 (hereafter this method is simply abbreviated as the “gap-increased method”). The apparatus for pulling up a single crystal was designed such that the distance between the lower end of a
Morita Hiroshi
Watanabe Hideki
Hiteshew Felisa
Sumitomo Mitsubishi Silicon Corporation
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