Title: Source material feeder apparatus for industrial crystal growth systems
Abstract: A raw material feeder apparatus for industrial crystal growth systems includes a hopper disposed within a vacuum chamber and adapted to hold a quantity of raw material therein. A slide is disposed adjacent to an opening of the hopper and configured to receive the raw material from the hopper thereon. The slide is selectively moved between an open feeding position and a closed non-feeding position. The slide and a door cooperatively close the opening of the hopper, or in their open state, control the flow of raw material from the hopper. A vibrator associated with the slide feeds the raw material from the slide into an outlet tube for conveyance of the raw material to the crystal growth system.
Patent Number: 6,896,732 Issued on 05/24/2005 to Fickett, et al.
| Inventors:
|
Fickett; Bryan (22962 SR14, Washougal, WA 98871);
Bushman; Robert (6411 Smoketree Ave., Oak Park, CA 91377)
|
| Appl. No.:
|
831684 |
| Filed:
|
April 23, 2004 |
| Current U.S. Class: |
117/208; 117/33; 117/209; 117/214; 117/215; 117/218 |
| Intern'l Class: |
C30B 015/02 |
| Field of Search: |
117/208,209,214,215,218,33
|
References Cited [Referenced By]
U.S. Patent Documents
Primary Examiner: Kunemund; Robert M.
Attorney, Agent or Firm: Borrowman; Aaron T., Kelly Lowry & Kelly, LLP
Parent Case Text
RELATED APPLICATION
This application claims priority to U.S. Provisional Application No. 60/465,694,
filed on Apr. 24, 2003.
Claims
1. A raw material feeder apparatus for industrial crystal growth systems, the
apparatus comprising:
a vacuum chamber;
a hopper disposed within the vacuum chamber and adapted to hold a quantity of
raw material therein;
an adjustable opening formed in the hopper adapted to permit the raw material
to flow therethrough;
a slide disposed adjacent to the opening of the hopper and configured to receive
the raw material from the hopper thereon;
means for selectively moving the slide between a raw material feeding position
and a non-feeding position; and
an outlet tube disposed relative to the slide to receive the raw material from
the slide and convey the raw material to the crystal growth system.
2. The feeder apparatus of claim 1, including a vibrator associated with the
slide for the feeding of the raw material from the slide and into the outlet tube.
3. The feeder apparatus of claim 2, including controller adapted to alter the
vibration of the vibrator.
4. The feeder apparatus of claim 2, including a sensor for measuring the amount
of raw material in the hopper.
5. The feeder apparatus of claim 4, wherein the sensor is coupled to a controller
adapted to alter the vibration of the vibrator.
6. The feeder apparatus of claim 1, including a fill port formed in the chamber
for accessing the hopper.
7. The feeder apparatus of claim 1, wherein the adjustable opening comprises
a door selectively positionable and retractable relative to the opening of the hopper.
8. The feeder apparatus of claim 7, wherein the door and the slide cooperatively
close the opening of the hopper when the slide is moved into its non-feeding position
and the door is moved towards the slide.
9. The feeder apparatus of claim 1, wherein the slide moving means comprises
a manually actuated assembly for moving the slide from a generally horizontal non-feeding
position to a downwardly angled feeding position.
10. The feeder apparatus
9, wherein the manually actuated assembly comprises
a hand crank coupled to at least one compression spring acting on the slide.
11. The feeder apparatus of claim 1, wherein the slide moving means comprises
a motorized assembly for moving the slide from a generally horizontal non-feeding
position to a downwardly angled feeding position.
12. The feeder apparatus of claim 1, including an isolation valve in the outlet tube.
13. A raw material feeder apparatus for industrial crystal growth systems, the
apparatus comprising:
a vacuum chamber;
a hopper disposed within the vacuum chamber and adapted to hold a quantity of
raw material therein;
a door selectively positionable and retractable relative to an opening of the
hopper for controlling the flow of raw material from the opening of the hopper;
a slide disposed adjacent to the opening of the hopper and configured to receive
the raw material from the hopper;
means for selectively moving the slide between a generally downwardly angled
raw material feeding position and a generally horizontal non-feeding position;
a vibrator associated with the slide for the feeding of the raw material from
the slide and into the outlet tube; and
an outlet tube disposed relative to the slide to receive the raw material from
the slide and convey the raw material to the crystal growth system, the outlet
tube including an isolation valve configured to be selectively opened or closed.
14. The feeder apparatus of claim 13, including controller adapted to alter the
vibration of the vibrator.
15. The feeder apparatus of claim 14, including a sensor for measuring the amount
of raw material in the hopper, wherein the sensor is coupled to a controller adapted
to alter the vibration of the vibrator.
16. The feeder apparatus of claim 13, including a fill port formed in the chamber
for accessing the hopper.
17. The feeder apparatus of claim 13, wherein the door and the slide cooperatively
close the opening of the hopper when the slide is moved into its non-feeding position
and the door is moved towards the slide.
18. The feeder apparatus of claim 13, wherein the slide moving means comprises
a manually actuated assembly for moving the slide from the non-feeding position
to the feeding position, the assembly including a hand crank coupled to at least
one compression spring that engages the slide.
19. The feeder apparatus of claim 13, wherein the slide moving means comprises
a motorized assembly for moving the slide from the non-feeding position to the
feeding position.
20. A raw material feeder apparatus for industrial crystal growth systems, the
apparatus comprising:
a vacuum chamber;
a hopper disposed within the vacuum chamber and adapted to hold a quantity of
raw material;
a fill port formed in the chamber for accessing the hopper;
a door selectively positionable and retractable relative to an opening of the
hopper for controlling the flow of raw material through the opening;
a slide disposed adjacent to the opening of the hopper and configured to receive
the raw material from the hopper, wherein the door and slide cooperatively close
the opening of the hopper when the door is closed and the slide is disposed in
a non-feeding horizontal position;
means for selectively moving the slide between a raw material feeding position
and the non-feeding position;
a vibrator associated with the slide for the feeding of the raw material from
the slide and into the outlet tube;
a controller adapted to selectively alter the vibration of the vibrator;
an outlet tube disposed relative to the slide to receive the raw material from
the slide and convey the raw material to the crystal growth system, the outlet
tube including an isolation valve configured to be selectively opened or closed.
21. The feeder apparatus of claim 20, including a sensor for measuring the amount
of raw material in the hopper, wherein the sensor is coupled to a controller adapted
to alter the vibration of the vibrator.
22. The feeder apparatus of claim 20, wherein the slide moving means comprises
a manually actuated assembly for moving the slide from a generally horizontal non-feeding
position to a downwardly angled feeding position, the assembly including a hand
crank coupled to at least one compression spring that engages the slide.
23. The feeder apparatus of claim 20, wherein the slide moving means comprises
a motorized assembly for moving the slide from a generally horizontal non-feeding
position to a downwardly angled feeding position.
Description
BACKGROUND OF THE INVENTION
The present invention generally relates to source material feeders used in industrial
crystal growth processes. More particularly, the present invention resides in a
source material feeder for such processes which converts batch process devices
and systems into semi-continuous or continuous processes using granular or irregular
shaped feed particles and controlled feeding into a large number of different crystal
growth systems.
Synthetic crystal growth has been industrialized for decades, with little
industry-wide process optimization. Innovation is usually confined within individual
organizations that tend to keep new ideas secret. As a result, several unique and
complex growing techniques have evolved, with growth equipment designed specifically
for each manufacturer's process. Manufacturing challenges also vary among the different
methods used. For instance, batch crystal growers are limited by the initial capacity
of the melt crucible and growers who use shaped crystal growth methods have little
or no options when selecting silicon source materials. Even though there are significant
differences in method, the factors that drive operating costs are similar: raw
materials such as polysilicon; consumable items like quartz crucibles; and electricity
are major cost contributors.
Of all the crystalline materials manufactured commercially, silicon is in the
highest demand. Most industrially grown silicon and other materials are still grown
using inefficient batch processes. There are basically three types of specialized
feeders presently available: (1) internal feed hoppers/rods that hang from seed
cables; (2) gravity-fed external feeders; and (3) metering feeders used for continuous
feeding of pellet/granular silicon. Some feeders are compatible only with specific
types of crystal growth furnaces, and cannot be retrofit into other systems. Other
designs are intended to feed only specific types of source material, such as a
pelletized material. None can perform metered feeding of alternative source materials.
Most silicon is grown using the Czochralski (CZ) batch process. In this process,
a silicon ingot is made by melting source materials in a crucible, dipping a seed
crystal into the melt, and withdrawing the seed in such a manner as to achieve
a single crystal of a specified diameter. Operators must then power-down and disassemble
the furnace to reload it with a fresh crucible and source material after each ingot pull.
However, the CZ batch process has many limitations. The charge size is limited
to approximately 60% of the actual crucible capacity as the unmelted raw material
occupies a greater volume than the melted material. Throughput is hindered by non-productive
set-up, heat-up, and cool-down cycles. This also increases energy costs significantly.
Approximately 7-8% of the charge is unusable melt residue which remains attached
to the crucible. Thus, the quartz crucibles, which are rather expensive (currently
$500-$600 each), cannot be reused. In fact, the quartz crucible will actually crack
due to the thermal cycling. Other furnace hot-zone components also break down due
to thermal cycling and excessive handling. Moreover, advanced hot-zone processes
that permit faster pull speeds and higher quality crystals cannot be used without
further reducing crucible capacity.
To overcome these limitations, some have tried adding additional source materials.
One technique uses an internal hopper or polysilicon rod that hangs from the seed
cable to add materials after meltdown or in-between crystal pulls. However, efficiency
gains using this method are offset by extra cycle time needed because the grown
ingot has to be cooled and removed before the hopper is installed.
Others use an external feed hopper to feed pellet/granular silicon source
material into the furnace without waiting for ingot removal. U.S. Pat. No. 5,462,010
to Takano et al. is directed to an apparatus which continuously supplies granular
polycrystal silicon to a crucible of a semi-conductor single crystal pulling apparatus.
Takano et al. disclose that the apparatus includes a main tank holding a large
supply of the granular silicon source material. The granular material is fed into
a sub-hopper having a supply controller in the form of rotary valves in a tube
which exits into a smaller main hopper. Due to the granular/pellet nature of the
material, the rotary valves can be selectively opened to permit the material to
flow into the main hopper. The weight of the main hopper is monitored and the rotary
valves opened to supply additional material as the crystal batch process proceeds
and additional material is required.
This technique has proven very successful for a few companies, but requires
source material manufactured by a proprietary fluidized bed process. This material
is commercially available from only one company and expensive compared to other
sources of raw material. Such granularized material has also been found to have
undesirable characteristics resulting from the fluidized bed process. Thus, many
industrial crystal growers prefer not to use the granular material. In addition
to supply concerns, some existing feed hoppers are not designed to be refilled
during a furnace run, and most are gravity-fed with little or no control of flow rate.
Batch casting techniques such as the Heat Exchange Method (HEM) are also used
to grow single or polycrystalline silicon ingots. To cast a silicon ingot, source
materials are loaded into a crucible and melted. The furnace temperature is lowered
in a controlled way to directionally solidify the silicon. When growth is complete,
the furnace is shut down. The limiting factor in casting ingots is crucible capacity.
The unmelted raw material occupies a greater volume than the melted material.
Several commercial growing processes grow crystals to shape, usually in the
form of ribbon or sheet. The Edge-Defined, Film-fed Growth (EFG) method, the String-Ribbon
process and the Dendritic-Web technique all utilize continuous melt replenishment
(CMR) during crystal growth. This means that silicon source materials are replaced,
gram for gram, as the crystals are grown. CZ crystal growers can also apply this
technology in order to gain better control of the electrical properties of the
grown ingot. However, feeders currently available to perform continuous melt replenishment
only accommodate the expensive pellet/granular silicon source materials. Therefore,
users are locked into a single source supply, and CZ growers are reluctant to adopt
the technology.
Accordingly, there is a continuing need for a feeder of source material
for industrial crystal growth processes and systems which can convert the batch
process into a semi-continuous or continuous process, and/or increasing the initial
crucible volume, resulting in increased manufacturing efficiency. What is also
needed is such a feeder which can be retrofit into a variety of existing systems.
Moreover, such a feeder should be capable of accommodating large, irregular shaped
feed particles and provide controlled feeding into the crystal growth system. The
present invention fulfills these needs and provides other related advantages.
SUMMARY OF THE INVENTION
The present invention resides in a raw material feeder apparatus for industrial
crystal growth systems. The feeder apparatus of the present invention can be utilized
in silicon crystal growth processes, as well as other synthetic crystals, such
as sapphire, YAG, Gallium, Arsenide, Rutile, etc. The feeder apparatus of the present
invention is particularly adapted for use with larger and irregularly shaped raw
material, but it can also be used with the pellet/granular source material as well.
The feeder apparatus of the present invention allows topping off, semi-continuous
raw material replenishment or continuous material replenishment enabling multiple
uses of a crucible in such industrial crystal growth systems and significant savings
in electricity and other costs.
The feeder apparatus of the present invention is generally comprised of a housing
defining a vacuum chamber having houses a hopper adapted to hold a quantity of
raw material therein. Preferably, a fill port is formed in the chamber for accessing
the hopper.
An adjustable opening is formed in the hopper which is adapted to permit the
raw
material to flow therethrough. Typically, the opening has a door which is selectively
positionable and retractable relative to the opening of the hopper to control the
flow of material through the opening. A slide is disposed adjacent to the opening
of the hopper and configured to receive the raw material from the hopper thereon.
Means are provided for selectively moving the slide between a generally horizontal
raw material non-feeding position and a generally downwardly angled material feeding
position. The door and the slide cooperatively close the opening of the hopper
when the slide is moved into its non-feeding position and the door is moved towards
the slide.
In one embodiment, the slide moving means comprises a manually actuated assembly,
such as a hand crank coupled to at least one compression spring acting on the slide,
for moving the slide from a generally horizontal non-feeding position to a downwardly
angled feeding position. In another embodiment, the slide moving means comprises
a motorized assembly for moving the slide from a generally horizontal non-feeding
position to a downwardly angled feeding position.
A vibrator is associated with the slide for the feeding of the raw material from
the slide and into an outlet tube disposed relative to the slide and adapted to
receive the raw material from the slide and convey the raw material to the crystal
growth system. Typically, a controller is used to alter the vibration of the vibrator
for minimizing, or even stopping, the flow of material from the slide to the outlet
tube or for increasing the flow thereof. Typically, an isolation valve is included
in the outlet tube to seal the apparatus from the industrial crystal growth system.
In some instances, particularly when the apparatus is used as a continuous feeder,
a sensor is used for measuring the amount of raw material in the hopper. The sensor
is coupled to a controller which is adapted to alter the vibration of the vibrator
and the amount of raw material introduced into the industrial crystal growth system.
Other features and advantages of the present invention will become apparent
from the following more detailed description, taken in conjunction with the accompanying
drawings, which illustrate, by way of example, the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings illustrate the invention. In such drawings:
FIG. 1 is a front perspective view of a feeder apparatus embodying the present invention;
FIG. 2 is a partly sectioned and fragmented elevational view of the apparatus
of FIG. 1, illustrating a slide thereof in an open and feeding position;
FIG. 3 is a view similar to FIG. 2, illustrating the slide in a closed or non-feeding position;
FIG. 4 is a partially sectioned and fragmented side elevational view of the
apparatus of FIG. 1, illustrating the slide in an open feeding position, and controls
for controlling the amount of raw material flowing through the apparatus;
FIG. 5 is a partially sectioned and fragmented side elevational view of the
apparatus of FIG. 1, illustrating the slide thereof in a closed position;
FIG. 6 is a partially sectioned and fragmented side elevational view, similar
to FIG. 4, illustrating raw material being fed from the apparatus; and
FIG. 7 is a side elevational view similar to FIG. 6, illustrating the opening
of the hopper closed due to the closed position of a slide of the apparatus, preventing
raw material from flowing therethrough.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As shown in the drawings for purposes of illustration, the present invention
resides
in a feeder apparatus, generally referred to by the reference number
20,
which feeds raw material to a crystal growing furnace of an industrial crystal
growth system. Typically, the raw material comprises silicon, but can also be other
material such as sapphire, YAG, Gallium, Arsenide, Rutile, etc. A particularly
novel aspect of the present invention is that it is designed such so as to not
only semi-continuously or continuously supply pelletized/grannular raw material,
but also relatively large (up to 60 mm) and irregularly sized and shaped feed particles
of raw material. The feeder apparatus
20 of the present invention can also
utilize recycled feed stock, which can be obtained from a number of sources at
lower cost. As will be more fully described herein, the feeder apparatus
20
of the present invention allows a single melting crucible to be topped off after
initial meltdown, which can increase production by 40% alone. The feeder apparatus
20 of the present invention is also designed such that a semi-continuous
or continuous feeding can occur such that the crucible can be utilized for several
batches, saving the cost of replacing the crucible as well as the energy costs
associated with cooling down and heating the crucible in a typical batch process.
The design of the feeder apparatus
20 is such so as to be retrofit to a
number of different existing systems.
With reference now to FIG. 1, a particularly preferred embodiment of the feeder
apparatus
20 of the present invention is illustrated. The apparatus
20
includes an outer housing
22 adapted to form a vacuum chamber therein. Preferably,
the housing
22 is comprised of a transparent material such as cast acrylic,
quartz or Pyrex glass. End caps
24 and
26 enclose the ends of the
cylindrical housing
22. Seals, such as O-rings or the like may be used to
seal the inner chamber of the housing
22. The end caps
24 and
26
are tightly fastened to the housing
22 by locking means, such as the illustrated
bolts
28 and thumb screws
30 located on the outside of the housing.
A fill port
32 is typically formed in the upper end cap
26, and also
capable of being sealed to the end cap
26, for selectively accessing the
inner chamber of the housing
22.
A hopper
34 is disposed within the housing
22. The hopper
34
is configured to hold a predetermined amount of raw material therein, and typically
has a V-shaped outlet or opening
36 through which the raw material flows
out of the hopper
34. A door
38 is slidably positionable over at
least a portion of the opening
36 and away from the opening
36 so
as to alter the flow of raw material through the opening
36.
A slide
40 is disposed under the outlet opening
36. The slide is
in the form of a generally planar plate having angled wings extending on either
side thereof so as to receive the raw material from the hopper
34 thereon.
With reference now to FIGS. 2-4, the slide
40 is movable between an open
or feeding position, as illustrated in FIGS. 1,
2 and
4; and a closed
or non-feeding position, as illustrated in FIGS. 3 and 5. In the illustrated particularly
preferred embodiment, the open or feeding position is a downwardly directed angle,
whereas the closed and non-feeding position is generally at a level or horizontal
position. As shown in FIGS. 5 and 7, the door
38 and slide
40 cooperatively
close off the outlet opening
36 of the hopper
34 when the slide
40
is in hits generally horizontal and closed position and the door
38 is lowered
over the opening
36.
While in these closed positions, the raw material cannot flow out whatsoever
from the hopper
34. However, when the slide
40 is angled downwardly
and opened, as illustrated in FIGS. 4 and 6, the raw material
42 begins
to flow from the hopper
34 onto the slide
40. The flow of the raw
material
42 onto the slide
40 is controlled by the downward angle
of the slide
40 as well as the position of the door
38. For small
particles, the door
38 may not be raised whatsoever. However, for larger
particles the door
38 can be moved upwardly away from the opening
36
to permit the flow of the large and irregularly shaped material through the opening
36 and onto the slide
40. The combination of the configuration of
the slide
40, the hopper opening
36 and the adjustable door
38
allow the apparatus
20 to accommodate irregularly shaped and sized raw material
sources. Of course, this is beneficial, as described above.
The means for adjusting the position of the slide
40 from a generally
horizontal and closed position to a downwardly directed angled and open feeding
position is either by manual means or automatic or motorized means.
With reference to FIGS. 2 and 3, a manual assembly for moving the slide
40
is illustrated. The assembly includes a hand crank
44 which rotates a screw
46 which interacts with one or more platforms
48 for raising or lowering
the slide
40. One or more of the springs
50, which are typically
in contact with the bottom surface of the slide
40, act upon the slide
40
to allow it to vibrate. Typically, four compression springs
50 are used,
with a pair of compression springs
50 towards the leading edge of the slide
40.
Alternatively, as illustrated in FIG. 4, a motor
52 has a threaded
shaft
46 which interacts with the springs
50, such as by the platform
48. In this manner, an operator of the apparatus
20 could utilize
an electric switch, such as push button, to open and close the slide
40.
Also, the use of a motor enables computer control of the opening and closing of
the slide
40, as will be more fully discussed herein. Although the motor
52 is illustrated as being disposed exteriorally of the apparatus
20,
it can also be disposed within the apparatus
20.
An outlet tube
54 is disposed relative to the slide
40 such that
as the slide is lowered, raw material can flow from the slide and into the outlet
tube
54, as illustrated in FIG.
6. The outlet tube
54 typically
has a flared end defining the opening thereof so as to match the dimension of the
slide
40, as illustrated in FIG.
1. The outlet tube extends from
within the housing
22 to outside of the housing
22 for connection
to the pertinent structure of the industrial crystal growth system that the apparatus
20 is attached to such that the raw material
42 can be dispensed
into the melting furnace or crucible of such system (not shown).
Within the outlet tube
54 is disposed an isolation valve
56,
which can be selectively opened and closed. Although the isolation valve
56
can be used to alter the flow of raw material
42 through the outlet tube
54, more typically the isolation valve
56 is used to isolate the
apparatus
20 in a pressure sense from the industrial crystal growth system
that it is attached to.
Operation of such systems typically occurs under a vacuum with gas impurities,
such as oxygen, removed from the overall system. Thus, the apparatus
20
of the present invention includes a port
58 through which the air or atmosphere
within the apparatus
20 can be removed and purged with argon or another
inert gas to create a state of vacuum or negative pressure within the housing
22
and apparatus
20. When the hopper
34 needs replenishment of raw material,
for example, the isolation valve
56 is closed and the fill port
32
is open to access the hopper
34. The apparatus
20 is then placed
in a vacuum or low pressure state and the isolation valve
56 opened to continue
the charging or feeding process into the crystal growth system.
When using small-sized raw materials, such as the pelletized or granular raw
material silicone, a sufficient downward angle of the slide
40 will permit
the raw material
42 to exit the hopper
34 and flow into the outlet
tube
54. However, in other instances, particularly with large and irregular-shaped
raw material, the raw material
42 will not readily flow from the hopper
34 into the outlet tube
54. Thus, a vibrating device
60 is
disposed in association with the slide
40 to controllably cause the raw
material
42 to flow past the slide
42 and into the outlet tube
54.
The vibrator
60 is preferably adjustable such that the degree of vibration
imparted to the slide
40 can be adjusted to control the flow of the raw
material
42. Typically, the feed rate can be adjusted from 0 to 5 kilograms
per minute. The electrical lead
62 of the vibrator
60 extends through
a port, such as the vacuum port
58 so that a vacuum state can be created
within the housing chamber
22. Thus, in some instances, lowering the slide
40 to its most downwardly angle is still insufficient to cause the raw material
42 to flow over the slide
40. The vibrating device
60 is activated
and the amount of vibration controlled to cause the raw material
42 to flow
at a selected and controlled rate. This is particularly advantageous as deactivating
the vibrator will cause an immediate cessation of flow of the raw material
42
into the outlet tube
54. Thus, the combination of the downward angle of
the slide
40 and the amount of vibration imparted by the vibrator
60
enables the operator to carefully and selectively control the flow of raw material
42 into the crystal growth system that the apparatus
20 is attached to.
With particular reference now to FIG. 4, when operating in a continuous manner,
the amount of raw material
42 fed over a given time must be sensed and controlled.
Thus a sensor, such as a load cell or other weight sensor, optical sensor or any
other appropriate sensor measures the amount of raw material dispensed from the
hopper
34. A controller
66, such as a CPU or other computerized controller
monitors the level of the raw material
42 compared to the exhaustion of
the melted raw material creating the crystal within the crystal growth system.
The controller can also be operatively connected to the vibrator
60 to control
the amount of vibration imparted to the slide
40, as well as the motor
52
which adjusts the angle of the slide
40 to decrease or increase the amount
of raw material
42 loaded into the system at any given time.
All feeder
20 components that come into contact with the raw feed materials
are preferably fabricated using flat plates, which simplifies manufacturing as
well as facilitates decontamination by acid etching or the like. The feeder apparatus
20 components which come into contact with the raw material, such as the
inner surface of the hopper
34, the slide
40, and the outlet tube
54 can be comprised of different materials depending upon the end user's
specific needs. For example, silicon growers with tight purity tolerances may desire
that these components are manufactured from semi-conductor grade polysilicon, virtually
eliminating any potential for foreign contamination. Other lower-costing construction
materials such as polypropylene, or higher strength material like stainless steel
or silicon carbide can also be used.
In use, the feeder apparatus
20 is installed on a crystal growth furnace
or other appropriate extension of the crystal growth system, using feed tubes or
the like to provide delivery from the outlet tube
54 and into the melt crucible
(not shown). With the isolation valve
56 closed, the hopper
34 can
be filled at any time. The pressure within the apparatus
20 is brought to
atmospheric pressure and the fill cap
32 is open. The slide
40 and
door
38 are brought into closed positions and the raw material, such as
silicon, is poured into the hopper
34. Once filled, the cap
32 is
closed and sealed and oxygen is removed through a series of vacuum pump-downs and
argon gas purges.
The slide
40 is then angled downwardly and the door
38 adjusted,
as necessary to cause the raw material
42 within the hopper
34 to
fall onto the slide
40. In most cases, the vibrator
60 will need
to be activated to cause the raw material
42 to slide off of the slide
40
and into the outlet tube
54, where it passes into the crystal growth system
as the isolation valve
56 was previously opened once the apparatus
20
was properly pressurized. The flow rate and amount of raw material
42 introduced
into the outlet
54 can be controlled, as described above.
The feeder apparatus
20 can be used in three different ways: to top-off
the crucible; perform batch recharging; or to continuously replenish the melt.
When topping-off a crucible, the growth furnace is setup as for a standard batch
run. The furnace temperature is ramped up until melting begins. As the raw materials
of the crucible melt, settling occurs similar to ice melting in a container. At
this point, raw material
42 is fed through the opened outlet tube
54
by opening the slide
40 and activating the vibrator
60. Once the
hopper
34 is empty, or the crucible filled, the vibrator
60 is turned
off and the isolation valve
56 closed. This is repeated until the crucible
is filled with melted raw material. As stated above, utilization of the apparatus
20 of the present invention can increase by up to 40% the output of a single
batch due to the recharging of the crucible after settling.
Batch recharging in between crystal pulls is performed in a similar manner
except that the feeding is performed after each growing ingout is pulled free from
the melt. By recharging the crucible between runs, time consuming cool-down, set-up
and power-up cycles are avoided. Many yield losses resulting from set-up errors
or contamination introduced during set-up are eliminated, and a significant amount
of electricity is saved in the process. A single crucible can be used multiple
times in such a batch recharging method.
To perform continuous melt replenishment, the hopper
34 is mounted on a
load cell or other means for sensing the level of raw material
42 therein,
and the slide
40 is lowered to an optimum position. The system controller
66 operates the vibrator
60 on an as-needed basis to feed the raw
material
42 into the outlet tube
54 and replenish the material within
the crystal growth system.
Standardized connections are typically used between the apparatus
20
and the industrial crystal growth system, thus making the feeder apparatus
20
of the present invention universal in nature and capable of being retrofit to virtually
any existing crystal growth system. Use of the apparatus
20 of the present
invention can convert a batch process into a semi-continuous or even a continuous
replenishment process, thus resulting in increased manufacturing efficiency. The
feeder apparatus
20 of the present invention can accomplish this using large,
irregularly shaped feed particles, or alternatively less desirable pelletized or
granular particles, and provide controlled feeding into any crystal growth system.
The present invention provides many benefits including increased product yield,
higher-through put, minimized scrap, reduced material handling and/or improved
resistivity control. Use of the apparatus
20 of the present invention allows
large irregularly shaped material, recycled feed stock and the like to be utilized
which is much less expensive than the traditional raw material. Expensive crucibles
can be reused and the energy costs associated with traditional batch processes
reduces significantly.
Although several embodiments of the present invention have been described
in detail for purposes of illustration, various modifications of each may be made
without departing from the spirit and scope of the invention. Accordingly, the
invention is not to be limited, except as by the appended claims.
*
