Apparatus for growing a single crystalline ingot

Details Apparatus for growing a single crystalline ingot Apparatus for growing a single crystalline ingot

2001-08-03

2003-03-04

Hiteshew, Felisa (Department: 1765)

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

Apparatus

For crystallization from liquid or supercritical state

Reexamination Certificate

active

06527859

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to an apparatus for growing a single crystalline ingot like a round-pillar type that enables the growth of liquid state silicon into the single crystalline state.
2. Discussion of Related Art
A silicon wafer for the fabrication of various electronic devices such as semiconductors and the like is provided by thinly slicing a single crystalline silicon ingot. A single crystalline silicon ingot is fabricated by melting polycrystalline silicon into a liquid state and then by growing a crystal by the Czochralski method (hereinafter abbreviated as the Cz method) or the like.
As the defect characteristics inside an ingot depend on the sensitivity of the growing and cooling conditions of a crystal, efforts have been made to control the species and distributions of crystal growing defects by controlling the thermal environment near a crystal growing interface.
As the melted-down silicon is solid-crystallized, point defects of a vacancy type and an interstitial type are engaged over equilibrium concentration so as to develop into grown crystal defects. The Voronkov theory introduced in “The Mechanism of Swirl Defects Formation in Silicon” (Journal of Crystal Growth 59 (1982), pp. 625) by V. V. Voronkov teaches that such defect formation is closely related to a V/G ratio, where V is a pulling rate of an ingot and G is an axial temperature gradient near the crystal growing interface.
Based on the Voronkov theory, a vacancy type defect occurs when the VIG ratio exceeds a critical value, while an interstitial type defect occurs when the V/G ratio is lower than the critical value. Therefore, the pulling rate has an influence on the species, sizes, and density of the defects existing in the crystal when a crystal is grown according to a given growing environment of a predetermined hot zone.
Generally, the axial temperature gradient G increases radially from the center of the ingot to the edge. Thus, the vacancy type crystal defect region tends to occur at the center of the ingot, while the interstitial type crystal defect occurs most frequently at the circumference. Such defects are observed as COP (crystal originated particle), LDP (large dislocation pit), OSF (oxidation-induced stacking fault) or the like, at a surface of the wafer after predetermined treatments thereon such as etching, heat-treatment, and the like.
Accordingly, in order to restrict the generation of the vacancy type crystal defects at the center thereof when growing the crystal, as well as the interstitial type crystal defects at the circumference, an axial temperature gradient deviation &Dgr;G, i.e., the difference between the axial temperature gradient Gc of the central part of the single crystalline ingot and the axial temperature gradient Ge of the circumferential part of the single crystalline ingot, in the radial direction of the crystal on the single crystalline ingot, should be reduced and an average axial temperature at the growth interface improved.
In order to reduce the axial temperature gradient deviation &Dgr;G in the radial direction of the crystal in the single crystalline ingot, the axial temperature gradient Gc should be increased or the axial temperature gradient Ge at the circumferential part should be decreased.
However, the average axial temperature gradient of the growth interface of the single crystalline ingot is reduced when the axial temperature gradient deviation &Dgr;G is decreased by reducing the axial temperature gradient Ge of the circumferential part, thereby reducing the growth rate of the single crystalline ingot.
Accordingly, efforts have been made to develop an apparatus for growing a single crystalline ingot that will reduce the generation of crystal defects and improve the growth rate, more particularly, to a thermal shield having a direct effect on the thermal environment at the growth interface.
FIG. 1
shows a schematic cross-sectional view of an apparatus for growing a single crystalline ingot according to a related art. Referring to
FIG. 1
, a quartz crucible
13
containing a meltdown silicon
15
is installed in a chamber of an apparatus for growing a single crystalline ingot. The quartz crucible
13
is coated with a crucible support
17
, the surface of which is made of graphite. The crucible support
17
is fixed on a rotational axis
19
, which is rotated by a driving means (not shown in the drawing), thereby rotating the quartz crucible
13
to be driven upward.
The support
17
wrapping the quartz crucible
13
is surrounded at a predetermined interval by a cylindrical heater
21
which is surrounded by a thermos
23
. In this case, the meltdown silicon
15
is provided by melting a polysilicon lump of high purity in the quartz crucible
13
using the heater
21
.
At the upper part of the chamber
11
, a pulling means (not shown in the drawing) for pulling an object by winding a cable
33
is installed, wherein the pulling means is rotational. At a lower part of the cable
33
, a seed crystal
31
for growing a single crystalline ingot
29
by being pulled up while being contacted with the meltdown silicon
15
is set therein.
At the upper part of the chamber
11
, a supply pipe
25
is established for supplying the growing single crystalline ingot
29
and the meltdown silicon
15
inside the crucible
13
with inert gas from the outside. At the lower part of the chamber
11
, an exhaust pipe
27
exhausting the used inert gas outside is established.
A thermal shield
35
consisting of first, second and third shielding parts
37
,
39
and
41
and surrounding the single crystalline ingot
29
is installed between the growing single crystalline ingot
29
and the crucible
13
. In this case, the first shielding part
37
has a cylindrical shape which cuts off radiant heat from the heater
21
, the second shielding part
39
has a flange figure connected to an upper part of the first shielding part
37
and is fixed to the thermos
23
, and the third shielding part
41
is connected to a lower part of the first shielding part
37
and has a triangular cross-section that protrudes toward the single crystalline ingot
29
.
In addition, a bottom of the third shielding part
41
is separated from the meltdown silicon horizontally by a predetermined interval to prevent the radiant heat generated from the meltdown silicon
15
from being transferred to the upper part of the chamber
11
so as to accumulate the heat near the growth interface of the single crystalline ingot
29
. Thus, the temperature difference between the circumferential and central parts of the ingot is reduced near the growth interface, thereby reducing the axial temperature gradient deviation &Dgr;G. Therefore, the generation of defects due to the temperature difference between the central and circumferential parts of the single crystalline ingot
29
growing at a predetermined pulling rate is reduced. In addition, an interior of the third shielding part
41
is filled with a material having an excellent insulating property and becomes an adiabatic part
43
preventing heat from being transferred to the upper part of the ingot
29
.
Unfortunately, the apparatus for growing a single crystalline ingot according to the related art only accumulates the heat near the growth interface between the third shielding part and the meltdown silicon by preventing the radiant heat radiated from the meltdown silicon from being transferred to the upper part of the chamber by the third shielding part of the thermal shield.
Therefore, a number of crystal defects are generated due to the large axial temperature gradient deviation &Dgr;G in the radial direction of the crystal since the temperature hardly rises on account of the concentration failure of the accumulated heat at the circumferential part of the single crystalline ingot.
Moreover, the average axial temperature gradient is reduced at the growth interface as the heat radiation of the central part is inhibited by the heat accumulated at the upper part between the third shielding part and t

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