Apparatus for producing single crystal

Details Apparatus for producing single crystal Apparatus for producing single crystal

1999-09-30

2001-11-13

Kunemund, Robert (Department: 1765)

Single-crystal, oriented-crystal, and epitaxy growth processes;

Apparatus

For crystallization from liquid or supercritical state

C117S013000, C117S035000, C117S218000, C117S911000, C117S932000

Reexamination Certificate

active

06315827

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for producing a single crystal by pulling a single crystal from source melt by means of the Czochralski method (hereinafter referred to as the “CZ method”), and especially, relates to an apparatus for producing a single crystal by means of the CZ method, suitable for pulling a heavy single crystal having a diameter of greater than 300 mm.
2. Description of the Related Art
A single crystal silicon is generally produced through use of the CZ method. According to the CZ method, polycrystalline silicon is charged intò a quartz crucible disposed within a single crystal pulling apparatus. The polycrystalline silicon is heated and dissolved into a melt by means of a heater disposed around the quartz crucible. Subsequently, a seed crystal attached to a seed chuck is immersed into the melt. The seed holder is pulled while the seed chuck and the quartz crucible are rotated in a single direction or in opposite directions, to thereby grow a single crystal to a predetermined diameter and length. Under the CZ method, a neck having a diameter of about 3-4 mm must be formed in a lower portion of the seed crystal by means of the Dash technique in order toeliminate dislocations from the seed crystal. However, in response to a recent tendency for improving the efficiency of production of a semiconductor device, a demand exists for manufacture of a single crystal having a large diameter by means of the CZ method. In association with an increase in the diameter of a single crystal, the weight of the single crystal increases. Single crystal manufacturing apparatus have been suggested (in, for example, Japanese Patent Application Laid-Open Nos. Sho-62-288191 and 63-252991) , in which a constricted engagement step is formed in a single crystal remaining in a pulled state so that the heavy single crystal can withstand pulling action.
FIG. 18
shows an example of a conventional single crystal manufacturing apparatus provided with a clamping body. A pull head
2
, which is rotatably provided at the upper end of the manufacturing apparatus, has provided therein a crystal pull wire take-up device
3
and a plurality of wire take-up devices
51
for raising/lowering a clamping member
50
. A seed chuck
6
holding a seed crystal
5
is fixed to the lower end of a crystal pull wire
4
hanging the crystal pull wire take-up device
3
and extends to the center of a furnace. Melt
7
is stored in a quartz crucible which is disposed within an unillustrated main chamberso as to be able to rotate and move vertically.
The clamping member
50
is provided with a plurality of claws
53
provided in a pivotable manner at the lower end of a cylindrical clamping body
52
(the claws
53
are pivotable within a vertical plane and within a predetermined range of angle). The claws
53
are engaged with an engagement step engagement stepla. By means of this arrangement, a single crystal
1
can be pulled when the wire take-up devices
51
takes up wires
54
.
However, the single crystal manufacturing apparatus having the foregoing configuration often encounters a problem of occurrence of an inclination in the single crystal
1
for reasons of an inclination in the gripping member
50
stemming from a variation in extension of the wires
54
(
FIG. 19
) or for reasons of an offset in points clamped by the gripping member
50
(FIG.
20
). If the single crystal
1
is held in a slanted attitude and rotated while the axis of the single crystal
1
is tilted, runouts arising in a growth boundary is amplified, thereby adversely affecting the growth of the single crystal
1
and inducing poly-crystallization of the single crystal
1
arises.
Furthermore, in the event that the clamping member
50
clamps the single crystal
1
at the engagement step
1
a
with the aid of jaw-shaped claws
53
, the weight of the single crystal
1
will focus on several contact points. This will induce cracking or distortion to the single crystal
1
. On the worst occasion, the single crystal
1
could be destroyed.
SUMMARY OF THE INVENTION
The object of this invention is to provide an apparatus for producing a single crystal. In the process of pulling a single crystal by the CZ method, the device according to this invention conducts a clamping member to engage with a engagement step formed in the single crystal remaining in a pulled state and is capable of steadily pulling a single crystal without any influence caused by a variation in extension of the wires or dislocating of clamping body.
Another object of this invention is to prevent cracking or distortion of the single crystal when the clamping body clamps the reduced and engagement step formed in the single crystal.
To achieve the above-mentioned objects, this invention is characterized in that: a flexible mechanism (also referred to as a free-pivoting mechanism), having a first flexible member capable of tilting even though the single crystal is being clamped by the clamping body, is provided. By this arrangement, the single crystal can be kept in the verticle attitude by absorbing a variation in extension of the wires through the flexible mechanism.
Furthermore, this invention is characterized in that: a flexible mechanism, having a second flexible member capable of tilting even that the clamping body is being suspended by a plurality of long members, is provided. By this arrangement, the single crystal can be held in the vertical attitude by absorbing an offset in points clamped by a clamping body induced by inconsistency between the contacting points on the engagement step.
Furthermore, as to the flexible mechanism having a first flexible member and the flexible mechanism having a second flexible member, installing either one or both of them simultaneously on the apparatus for producing a single crystal is acceptable.
Furthermore, it is also acceptable to install the flexible mechanism on the apparatus for producing a single crystal either separately or integrally with the clamping body. Furthermore, it has been known that the flexible mechanism is irrelevant to the kinds of single crystals; therefore this invention is not only suitable to devices for producing a single crystal but also suitable to all kinds of single crystal manufacturing devices only if the CZ method is employed.
According to another aspect of the present invention, in a process in which the engagement step through use of the clamping body, a sacrifice member whose shape is fit to the profile of the circumference of the engagement step is interposed between the clamping body and the engagement step, thereby preventing cracking or distortion of the single crystal.
Specifically, in the clamping body of the apparatus for producing a single crystal according to this invention, the portion in contact with the engagement step during the operation of clamping the engagement step with the aid of the clamping body is composed of a sacrifice member, which deforms to fit the outer periphery of the engagement step. By this arrangement, cracking or distortion of the single crystal can be prevented.
Due to the existence of the sacrifice member, the sacrifice member deforms it to fit the outer periphery of the engagement step so as to increase the contact area during the operation of clamping the engagement step with the aid of the clamping body. Therefore, the force applied from the clamping body toward the engagement step is distributed; and cracking or distortion of the single crystal, which inevitably causes the breakage of the single crystal, can be prevented.
As described above, the distinction of this invention is that the force exerted between the clamping body and the engagement step is distributed through the deformation of the sacrifice member. If the sacrifice member is made of elastic-deformation material, then it could be repeatedly used. If the sacrifice member is made of plastic-deformation material, then it is necessary to change the sacrifice member regularly before each operation.
Furthermore, the deformation of the

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