Single-crystal – oriented-crystal – and epitaxy growth processes; – Forming from vapor or gaseous state – With pretreatment or preparation of a base
Reexamination Certificate
2002-01-08
2003-11-11
Hiteshew, Felisa (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Forming from vapor or gaseous state
With pretreatment or preparation of a base
C117S208000, C117S217000, C117S911000
Reexamination Certificate
active
06645296
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a crystal holding apparatus which is used for growing a single crystal by a CZ method, and more particularly to a crystal holding apparatus used for crystal holding and pulling, which mechanically holds and pulls up a grown crystal at a top thereof.
2. Description of the Prior Art
As a material for a silicon wafer used for manufacturing a semiconductor device, a silicon single crystal is often used which is manufactured by the CZ method. In manufacture of the silicon single crystal by the CZ method, as known, a seed crystal held by a bottom of a pulling shaft is immersed in a silicon melt formed in a crucible, and from this condition, the pulling shaft is lifted with rotation to thereby grow the silicon single crystal below the seed crystal.
The seed crystal is in the form of a narrow rod constituted by the silicon single crystal with a diameter on the order of 10 and few mm, and a top thereof is coupled to a seed holder, and a bottom thereof is immersed in the silicon melt. When such a seed crystal is immersed in a hot silicon melt, dislocation occurs due to thermal shock. For this reason, “necking” is carried out which narrows a diameter of the seed crystal after immersion of the seed crystal in the silicon melt and maintains the state for a while to eliminate the dislocation of the crystal. A required diameter of a neck is under 5 mm in terms of eliminating the dislocation, and a desired diameter is under 3 mm.
A mainstream silicon single crystal manufactured by the CZ method has had a diameter of 8 inch and a weight around 100 kg. Recently, however, a single crystal has been further upsized, and test manufacture of a silicon single crystal with a diameter of 12 inch has started.
An increased diameter of the single crystal greatly increases a weight thereof, and the single crystal with the diameter of 12 inch reaches a weight of 200 to 300 kg. The highest concentration of the weight is on the neck which is positioned at the top of the single crystal and is the smallest diameter portion, but breaking strength of the silicon is 20 kg/mm
2,
so that the neck needs to have a diameter of more than 5 mm for surely holding a silicon single crystal even of 200 kg. Therefore, stable pulling of the single crystal of 12 inch is impossible in terms of crystal holding.
As an especially effective technique of resolving this contradiction, there is crystal holding and pulling which does not depend on a neck. In the techniques described in the Japanese Patent Publication No. 5-65477 specification, Japanese Patent Laid-Open No. 10-81582 specification, Japanese Patent Laid-Open No. 10-81583 specification, or the like, as shown in
FIG. 7
, a seed crystal
3
held by a seed chuck
3
is necked, then below a neck
11
, a stopped portion
12
is formed which has a larger diameter than the neck
11
and is capable of mechanical holding, and a conventional body
13
is formed therebelow. When the stopped portion
12
is formed, a crystal holding apparatus
20
mechanically holds the stopped portion
12
to pull up a single crystal
10
.
In order to prevent falling of the single crystal
10
, the stopped portion
12
generally has a shape with a wide upper portion and narrow lower portion, and the narrow lower portion is set to have a sufficiently larger diameter than the neck. The wide upper portion is like a knob, and the lower portion is necked with respect to a body
13
therebelow, so that the stopped portion
12
is called a knob portion or necking portion.
A known crystal holding apparatus
20
has a cylindrical frame
21
which lifts and lowers and rotates for pulling up a single crystal
10
and which is circumferentially mounted with a plurality of pivot clamps
22
,
22
at regular intervals. A pulling shaft
1
used for growing the single crystal
10
is inserted in the frame
21
, and a seed chuck
2
coupled to a bottom of the pulling shaft
1
is pulled into the frame
21
with growth of the single crystal
10
. A plurality of pivot clamps
22
,
22
are brought into close condition by inward pivoting, grasp the stopped portion
12
of the single crystal
10
in the close condition, and are pivotable upward from the close condition.
General use of the crystal holding apparatus
20
using the pivot clamps
22
,
22
will be as described below.
The crystal holding apparatus
20
brings the pivot clamps
22
,
22
into the close condition and waits above the single crystal
10
. When the single crystal
10
grows in this state, the seed chuck
2
first passes inside the pivot clamps
22
,
22
. The neck
11
of the single crystal
10
then passes, and the stopped portion
12
enters inside the pivot clamps
22
to be automatically grasped. Then, the frame
21
starts lifting and rotating synchronously with the pulling shaft. After that, the single crystal
10
is mechanically held and pulled up at the stopped portion
12
by the crystal holding apparatus
20
. The pivot clamps
22
,
22
are pivotable upward from the close condition and do not prevent passage of the seed chuck
2
and entry of the stopped portion
12
.
As described above, the crystal holding apparatus
20
using the pivot clamps
22
,
22
has a simple structure which requires no operation mechanism of the pivot clamps
22
,
22
, and for this advantage, the pivot clamps
22
,
22
are generally set to the close condition from the beginning and not especially operated. However, it is also considered in some crystal holding apparatuses
20
that pivot clamps
22
,
22
are set to an open condition, and after entry of a stopped portion
12
inside the pivot clamps
22
,
22
, a push rod is pushed up at a body
13
(shoulder) of a single crystal
10
to operate the pivot clamps
22
,
22
to a close condition (Japanese Patent Laid-Open No. 10-81582 specification).
However, the conventional crystal holding apparatus
20
using the pivot clamps
22
,
22
has the following problems.
The seed chuck
2
which holds the seed crystal
3
is formed, at an upper portion thereof, from metal such as molybdenum for coupling with the pulling shaft
1
, but at a lower portion thereof which holds the seed crystal
3
, from carbon for preventing metal contamination of the seed crystal
3
. When the pivot clamps
22
,
22
are not operated, that is, the pivot clamps
22
,
22
are set to the close condition from the beginning, the pivot clamps
22
,
22
rub a surface of the seed chuck
2
when the seed chuck
2
passes inside the pivot clamps
22
,
22
, thus there is a possibility that powdered carbon falls to interfere with growing of the single crystal
10
.
Also, when the seed chuck
2
enters inside the pivot clamps
22
,
22
or comes out therefrom, vibration occurs due to passage of steps, which also has a possibility of interfering growing of the single crystal
10
.
When the pivot clamps
22
,
22
are set to the open condition, and the pivot clamps
22
,
22
are operated to the close condition after the entry of the stopped portion
12
inside the pivot clamps
22
,
22
, the seed chuck
2
passes inside the pivot clamps
22
,
22
without any contact, thereby solving the above described various problems caused by the passage.
However, shifting operation from the open condition to close condition of the pivot clamps
22
,
22
is carried out by pushing up the push rod at the body
13
(shoulder) of the single crystal
10
, and the push rod needs to be located at a position abutting against the body
13
(shoulder), thereby causing a problem of radially upsizing the crystal holding apparatus
20
.
The body
13
(shoulder) has a larger diameter and higher temperature than those of the stopped portion
12
, thereby having a possibility of causing contamination by contact with the push rod.
The pivot clamps
22
,
22
operated inward by the push rod falls inward by their own weights to collide against a surface of the stopped portion
12
. There is also a possibility that this shock inhibits stable growing of the single crystal
10
.
SUMMARY O
Akashi Yoshihiro
Kageyama Teruo
Hiteshew Felisa
Morrison & Foerster / LLP
Sumitomo Mitsubishi Silicon Corporation, Ltd.
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