Mechanism for clamping a crystal body in a crystal-body lifting device

A clamping portion 2 is suspended by wire cables 5. A linkage 3 connects the clamping portion 2 and a contacting portion 4 disposed below the clamping portion 2. One end of a circular-arc member 1 is pivotally supported by a swivel axis 33. The circular-arc member 1 is swiveled by guiding the contacting portion 4 to contact with the shoulder 63 of the crystal body 6.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a device for lifting crystal bodies, such as 
silicon single crystals, by the CZ method. It especially relates to the 
crystal-body clamping mechanism of a crystal-body-lifting device capable 
of safely lifting large-diameter crystal bodies, namely heavy crystal 
bodies. The crystal-body clamping mechanism clamps the neck portions 
formed on the top portion of crystal bodies during the lifting operation. 
2. Description of Prior Art 
In the process of lifting crystal bodies, such as silicon single crystals 
by the CZ method, a seed crystal installed within a seed-crystal holder 
suspended by a suspension member is guided to touch the free surface of 
the melted liquid of the raw material stored in a crucible. Then, the seed 
crystal is gradually lifted from the melted liquid and at the same time 
the suspension member is rotated to grow a single crystal beneath the 
lower portion of the seed crystal. 
The number of chips with the same physical properties obtained from one 
piece of semiconductor wafer can be increases, as the diameter of the 
wafer increases. Therefore, for economic reasons, the need for 
large-diameter semiconductor wafers has been increasing in recent years. 
As the diameter of the crystal bodies enlarge, the weight of an individual 
single crystal increases. For example, the weight of a crystal body having 
300 mm in diameter and 750 mm in body-length can reach a value more than 
150 Kg. 
In the process of lifting conventional lightweight crystal bodies, the load 
capacity of the small diameter portion beneath the seed crystal by using a 
dash neck method (hereinafter refer as dash neck) being lifted can afford 
to support the weight of the crystal body. Therefore, it is not necessary 
to make any reinforcement to its strength. However, in the event of 
supporting the above heavy crystal body by the strength of the dash neck 
alone, it is very difficult to maintain stable support of the whole weight 
of the crystal body if heat variation occurs in the surroundings of the 
crystal body, or an unexpected vibration, or a swinging of the crystal 
body is induced. As a result, when loads are concentrated at a so-called 
dash neck, which is a small-diameter portion for removing the dislocation 
from the seed crystal, the breakage of the dash neck and then the crystal 
body drops. This results not only the lost of crystal body but also a very 
great amount of damage of the lifting device. 
To prevent the dropping of the crystal body, "a crystal lifting device" 
disclosed in Examined Japanese Patent Publication H7-10300 and "a device 
and a method for lifting single crystals" disclosed in Non-Examined 
Japanese Patent Publication H9-2893 are known. In both of the above 
lifting devices, a neck portion is formed on the top of the crystal body 
beforehand, and several holding levers or arms extending from the seed 
crystal holder clamp the neck portion. 
However, for a crystal body of 300 mm diameter, the distance from the seed 
crystal holder to the neck portion is over 500 mm. Therefore, the above 
holding levers or arms should be longer than 500 mm. This will induce a 
very large moment to be imposed on the above holding levers or arms. It is 
also difficult to construct a mechanism having the strength enough to bear 
the moment within a confined space of the lifting device. 
Furthermore, in the case of employing holding levers or arms, the crystal 
body can not be firmly grasped unless the neck portion is clamped rigidly 
by strong horizontal forces. Because stiff levers or arms are lacking in 
flexibility, a horizontal shifting of the crystal body would be incurred 
if the contact timing or the clamping forces of each the levers or arms 
are biased during the clamping of the crystal body. Therefore, there 
exists a danger that the crystal body will break at the neck portion. 
SUMMARY OF THE INVENTION 
In view of the above drawbacks, the object of this invention is to provide 
a crystal-body clamping mechanism suitable to be installed in a 
crystal-body-lifting device. The crystal-body clamping mechanism of this 
invention is used to clamp the neck portion formed on the top portion of 
the crystal body. According to this invention, the lifting operation is 
safely performed even if the crystal body is heavy because the load on the 
seed is reduced. 
Following the enlargement of the diameter of semiconductor wafers, the 
weight of an individual semiconductor ingot is increased. To respond to 
this tendency, in this invention, a neck portion consists of the 
large-diameter portion and the small-diameter portion is formed in the 
upper portion of the crystal body, and clamped so as to prevent the 
dropping of the crystal body. 
The applicant of this invention has filed a Japanese patent application NO. 
H9-75344 entitle "LIFTING DEVICE FOR CRYSTAL BODIES" based upon the 
above-mentioned purpose. The feature of the '344 application is providing 
the clamping member whose swiveling members descend along the outer 
surface of the large-diameter portion of the crystal body, and the 
swiveling members close so as to clamp the crystal body when they descend 
to a location near the neck portion of the crystal body. 
The difference between this invention and the '344 application is that the 
clamping mechanism of this invention does not touch the large-diameter 
portion of the crystal body during its descending movement, and 
automatically clamps the neck portion of the crystal body when the lower 
portion of the clamping mechanism touches the shoulder of the crystal 
body. Namely, a clamping portion suspended from the suspension members, a 
contacting portion disposed below the clamping portion, and a linkage for 
connecting them are provided. With this construction, when the contacting 
portion touches the shoulder of the crystal body, the distance between the 
clamping portion and the contacting portion becomes short. Consequently, 
the linkage directs the clamping portion to clamp the neck portion. 
Further more, the circular-arc member whose one end is pivotally supported 
is provided and performs the clamping of the neck portion. When the 
circular-arc member clamps the neck portion, the circular-arc member is 
vertically disposed with its free end engaging the neck portion of the 
crystal body. Therefore, in the event that horizontal shifting of the 
crystal body is induced, the circular-arc member swivels to some extent 
because the circular-arc member is pivotally supported at one end, thereby 
the shifting of the crystal body is absorbed. 
In the prior art, when the load was shifted from the crystal body to the 
clamping mechanism, the crystal body would swing due to the existence of 
biasing forces. This would shift the crystal growth boundary away from the 
rotation center and the crystal body might grow into an arched shape. 
Additionally, there exists a danger of being unable to maintain the 
single-crystal state because the temperature change was incurred. This 
invention will not bring about such problems. Moreover, the circular-arc 
member will not impose a large force to the neck portion at the time of 
contacting, even if the contact is performed with time lags among 
different contact sites.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The following are descriptions of embodiments with reference made to the 
above drawings. 
The First Embodiment 
FIG. 1 is a schematic drawing showing the structure of the clamping 
mechanism provided in the lifting device in accordance with the first 
embodiment of this invention. As shown in FIG. 1, the clamping mechanism 
of this invention comprises: a clamping portion 2 suspended by two 
suspension members, namely, wire cables 5; a contacting portion 4 disposed 
below the clamping portion 2; two linkages 3 for connecting the clamping 
portion 2 and the contacting portion 4; and two circular-arc members 1 
capable of swiveling to clamp the crystal body (not shown) under the 
guidance of the linkage 3. The linkages 3 and the circular-arc members 1 
are respectively in pairs and disposed in a manner symmetric to and 
encompassing the central line of the crystal body being lifted. 
FIGS. 2a and 2b are cross sectional views along line II--II of FIG. 1, 
showing the operation of the clamping mechanism in accordance with the 
first embodiment of this invention. FIGS. 3a and 3b are cross sectional 
views along line III--III of FIG. 1, showing the operation of the clamping 
mechanism in accordance with the first embodiment of this invention. As 
shown in FIGS. 2 and 3, one end of the circular-arc member 1 is affixed at 
a swivel axis 33. The circular-arc member 1 can be driven to move downward 
by rising the linkage 3. 
As shown in FIG. 1, the linkage 3 consists of a vertical member 31 disposed 
vertically, whose lower end engages with the contacting portion 4, and a 
horizontal member 32 disposed horizontally, whose one end is affixed at 
the swivel axis 33 and the other end is connected with the vertical member 
31. 
As described hereinafter, the vertical member 31 substantially raises the 
horizontal member 32 when the contacting portion 4 contacts the crystal 
body. Then, the horizontal member 32 rotates the swivel axis 33. As a 
result, the circular-arc member 1 moves downward. 
FIG. 4 is a perspective view showing the structure of the circular-arc 
member of the clamping mechanism in accordance with the first embodiment 
of this invention. As shown in FIG. 4, the circular-arc member 1 is formed 
in the shape of a circular arc, and the inner peripheral surface 11 and 
the distal free end surface 12 are shaped in a concave and formed on the 
same surface. The outer peripheral surface of the crystal body will move 
back to the central position of the concave configuration when the crystal 
body being lifted shifts away from its central axis to a small extent. 
FIG. 8 is a side view showing an example of the structure of the crystal 
body lifted by the lifting device in accordance with this invention. 
As shown in this figure, in the case that the diameter of the body 64 is 
formed with .PHI.300 mm, the dash neck 60 of D1 in diameter is formed at 
the top of the crystal body 6. Preferably, D1 is determined in the range 
of .PHI.4 mm to .PHI.6 mm. The large-diameter portion 61 of D2 in diameter 
is formed beneath the throttle 61. Preferably, D2 is determined in the 
range of .PHI.16 mm to .PHI.25 mm, which is set to twice the diameter of 
the neck portion 62. The neck portion 62 of D3 in diameter is formed 
beneath the large-diameter portion 61. Preferably, D3 is determined in the 
range of .PHI.8 mm to .PHI.12 mm. 
Preferably, in the case of forming the crystal body 6 with the above shape, 
the distance H between the clamping portion 2 and the contacting portion 4 
is set to 30 mm or less. 
FIG. 9 is a top view showing an example of the structure of the clamping 
portion 2. 
As shown in this figure, a pair of the circular-arc members 1 are arranged 
along the circumference of .PHI.30 mm so that the initial interval of 
their free ends are set to 12 mm. Preferably, the outside diameter of the 
clamping portion 2 is formed with .PHI.70 mm. 
The following is a description of the operation of the clamping mechanism 
in accordance with this embodiment. 
As shown in FIGS. 2a and 3a, at the beginning of lifting the crystal body 
6, a large-diameter portion 61, a neck portion 62, a shoulder 63, and a 
body (not shown) with preset diameter are consecutively grown. As the 
crystal body grows, the seed-crystal holder hardly supports the weight of 
the crystal body. Therefore, the clamping mechanism descends as shown in 
FIG. 3A. 
While the contacting portion 4 is not contacting the shoulder 63 of the 
crystal body, the vertical member 31 is maintained in a vertical attitude 
with the aid of the weight of the contacting portion 4, which is suspended 
by the linkages 3. As a result, the circular-arc member 1 engaged with the 
vertical member 31 is maintained in a horizontal attitude. 
As shown in FIGS. 2b and 3b, the large-diameter portion passes through the 
contacting portion 4 without touching the inner portion thereof because 
the inner diameter of the contacting portion 4 is larger than the diameter 
of the large-diameter portion, And then the bottom of the contacting 
portion 4 contacts the shoulder 63 of the crystal body. At that time, the 
weight imposed on the linkages 3 diminishes or the linkages 3 raises the 
vertical members 31, and the clamping portion 2 and the circular-arc 
member 1 descend with the aid of their own weights. At the same time, the 
end of the horizontal member 32 connected with the vertical member 31 is 
raised and the swivel axis 33 is rotated. This drives the circular-arc 
member 1 to move downward, and the distal end surface 12 of the lower 
portion of the circular-arc member 1 clamps the neck portion 62. 
As shown in FIG. 4, the inner peripheral surface 11 and the distal free end 
surface 12 are shaped in a concave configuration. The crystal body will 
move back to the central position of the concave configuration when the 
crystal body shifts away from the its central axis to a small extent. 
Thus, even if the crystal body shifts in the horizontal direction to a 
small extent, the lifting operation can be performed in a stable manner. 
In the above embodiment, the linkages 3 and the circular-arc members 1 are 
respectively in pairs and disposed in the opposite locations. However, the 
scope of this invention is not limited to this arrangement; it is also 
satisfactory to keep the weight imposed on each circular-arc member 
balanced with the wire cables 5 and to locate the crystal body at a site 
in alignment with the lifting axis. For instance, it is acceptable to have 
three sets of the linkages and circular-arc members disposed in a radial 
and equally spaced manner, or four sets disposed in two pairs. 
Furthermore, if it is possible, the number of the circular-arc members can 
exceed that of the above-mentioned. 
Furthermore, the inner peripheral surface 11 and the distal free end 
surface 12 are shaped in a concave configuration. However, the scope of 
this invention is not limited to this configuration, it is also 
satisfactory if the central portions of the inner peripheral surface 11 
and the distal free end surface 12 are cut down. For example, it is also 
acceptable to keep their cross sections in a "V" shape or to divide the 
distal free end surface into two separate portions as shown in FIG. 5. 
The Second Embodiment 
FIG. 6 is a schematic side view showing the structure of the clamping 
mechanism in accordance with the second embodiment of this invention. 
In the clamping mechanism in accordance with the second embodiment, an 
opposite-rotation hindrance mechanism is installed on the circular-arc 
member. The opposite-rotation hindrance mechanism prevents backward 
swiveling of the circular-arc member. With this construction, the 
circular-arc member keeps holding the crystal body when the weight of the 
contacting portion is imposed on the linkage again. 
FIG. 6 is a schematic side view showing the structure of the clamping 
mechanism in accordance with the second embodiment of this invention. As 
shown in FIG. 6, a stopper 34a is disposed on the outer peripheral surface 
of the clamping portion 2a. The stopper 34a is used for hindering the 
overhang movement of the horizontal member 32a when the circular-arc 
member 1a of the clamping portion 2a clamps the crystal body 6. By this, 
even if the weight of the contacting portion 4a is imposed on the vertical 
member 31a again by lifting the wire cables 5, the backward swiveling of 
the horizontal member 32a will be stopped and the horizontal member 32a 
will remain in contact with the stopper 34a. 
Means for preventing backward swiveling of the circular-arc member and 
release of the crystal body is not limited to the above-mentioned. It is 
also acceptable to form the swivel axis into a non-cylindrical shape (for 
example, a plate shape), and to guide the swivel axis to engage with a 
slot so as to hinder its further swiveling when the circular-arc member 
swivels. Alternatively, the swivel axis can be constructed by a ratchet 
mechanism. 
The Third Embodiment 
FIG. 7 is a perspective view showing the structure of the clamping 
mechanism in accordance with the third embodiment of this invention. 
In the above embodiments, the vertical member and the horizontal member 
constitute the linkage. However, the same function can be attained 
provided that the circular-arc member is kept at its horizontal attitude 
with the aid of the weight of the contacting portion, the weight is 
removed from the circular-arc member at the time the contacting portion 
contacts the shoulder of the crystal body, and the circular-arc member 
then swivels downward by its own weight. 
In this embodiment, as shown in FIG. 7, the contacting portion 4b is 
suspended by a linkage cable 31b. In this case, while the contacting 
portion 4b does not contact the shoulder of the crystal body (not shown), 
the circular-arc member 1b maintains its horizontal attitude with the aid 
of the weight of the contacting portion 4b. The weight of the contacting 
portion 4b is removed from the circular-arc member 1b at the time the 
contacting portion 4b contacts the shoulder of the crystal body. Then, the 
circular-arc member 1b swivels downward under the influence of the moment 
force induced by the weight of its distal free end 12, and the crystal 
body can be clamped by the circular-arc member 1b. The movement of the 
linkage in this embodiment is substantially the same as that of the 
linkage 3 in the first embodiment. 
The scope of this invention is not limited to the above embodiments. 
Various linkages, for example gears, having the same function as those 
shown in the above embodiments could be employed. 
Furthermore, the contacting portion is shaped like a ring in the above 
embodiments. The shape is not limited to this; any shape could be employed 
so long as the balance of the total clamping mechanism can be attained. 
Moreover, wire cables were used as suspension members in the above 
embodiments. The suspension members are not limited to this; rods or 
chains such as ball chains and rudder chains can be used as suspension 
members. 
The Fourth Embodiment 
FIG. 10 is a partially sectional view showing the first structure of the 
crystal-body clamping mechanism in accordance with the fourth embodiment 
of this invention before the contacting portion 4 contacts the shoulder 
63. 
In this embodiment, a pair of the clamping pins 70 are loosely fitted in 
the clamping portion 2. As shown in this figure, each of the clamping pins 
70 stops at the peripheral surface of the linkage 3 before contacting the 
shoulder 63. 
The clamping portion 2 is arranged around the linkage 3 so as to be 
slidable along the surroundings edge of the linkage 3, and suspended by 
the wire cables 5. 
The linkage 3 of this embodiment is formed like the cylinder, and fixed to 
the contacting portion 4. The through hole 72 through which the clamping 
pins 70 pass is formed at the lower part of the linkage 3. 
FIG. 11 is a partially sectional view showing the second structure of the 
crystal-body clamping mechanism in accordance with the fourth embodiment 
of this invention after the contacting portion 4 contacts the shoulder 63. 
As shown in this figure, when the contacting portion 4 contacts the 
shoulder 63, the clamping portion 2 descends along the linkage 3 together 
with the clamping pins 70 or the contacting portion 4 rises as the crystal 
body 6 grows. Consequently, each of the clamping pins 70 pass through the 
through hole 72, and then protrude inside the linkage 3. After having 
changed in this structure, the crystal-body clamping mechanism is raised 
by the wire cables 5, then each of the clamping pins 70 clamps the bottom 
of the large-diameter portion 61. With this structure, the growth weight 
of the crystal body 6 is supported at the neck portion 62. 
The Fifth Embodiment 
FIG. 12 is a partially sectional view showing the first structure of the 
crystal-body clamping mechanism in accordance with the fifth embodiment of 
this invention before the contacting portion 4 contacts the shoulder 63. 
In this embodiment, a pair of the chacking arms 80 are attached to the 
clamping portion 2. As shown in this figure, each of the chacking arms 80 
stops at the outer peripheral surface of the contacting portion 4 before 
contacting the shoulder 63. 
The clamping portion 2 is arranged above the contacting portion 4, and 
suspended by the wire cables 5. 
The linkage 3 of this embodiment is formed in the joint structure, and 
links the clamping portion 2 and the contacting portion 4. 
FIG. 13 is a partially sectional view showing the second structure of the 
crystal-body clamping mechanism in accordance with the fifth embodiment of 
this invention after the contacting portion 4 contacts the shoulder 63. 
As shown in this figure, when the contacting portion 4 contacts the 
shoulder 63, the clamping portion 2 descends together with the chacking 
arms 80 or the contacting portion 4 rises as the crystal body 6 grows. 
Consequently, each of the chacking arms 80 holds the bottom edge of the 
contacting portion 4, and then the linkages 3 protrude inside the neck 
portion 62. After having changed in this structure, the crystal-body 
clamping mechanism is raised by the wire cables 5, then each of the 
linkages 3 clamps the bottom of the large-diameter portion 61. With this 
structure, the growth weight of the crystal body 6 is supported at the 
neck portion 62. 
The structure of this invention has been described, and the following 
effects can be achieved. 
(1) The operation is automatically actuated by contacting the shoulder of 
the crystal body; therefore, the clamping is positive. Consequently, the 
weight of the crystal body can be positively supported and the crystal 
body can be safely lifted even if the crystal body is heavy. 
(2) The circular-arc member is capable of swiveling, therefore its movement 
is able to respond to that of the crystal body. In the event that 
horizontal shifting of the crystal body is induced, the circular-arc 
member can respond in a flexible manner and can clamp the crystal body 
firmly.