U.S. patent application number 09/329114 was filed with the patent office on 2001-11-15 for solid powder trapping system.
Invention is credited to WU, JACK.
Application Number | 20010039883 09/329114 |
Document ID | / |
Family ID | 23283904 |
Filed Date | 2001-11-15 |
United States Patent
Application |
20010039883 |
Kind Code |
A1 |
WU, JACK |
November 15, 2001 |
SOLID POWDER TRAPPING SYSTEM
Abstract
A solid powder trapping system for filtering out solid powder
from a mixture of gaseous reactants that also includes a device
capable of determining the degree of powder accumulation inside the
trap. The powder trapping system uses a powder trap to catch the
solid powder within the gaseous mixture. A magnetic flux sensor is
also installed inside the trap for measuring a magnetic flux whose
strength depends on the amount of solid powder inside the trap. The
magnetic flux sensor is connected to a display device so that
reading from the display device reflects the amount of solid powder
accumulated inside the powder trap.
Inventors: |
WU, JACK; (TAINAN,
TW) |
Correspondence
Address: |
JIAWEI HUANG
J C PATENTS INC
1340 REYNOLDS AVENUE
SUITE 114
IRVINE
CA
92614
|
Family ID: |
23283904 |
Appl. No.: |
09/329114 |
Filed: |
June 9, 1999 |
Current U.S.
Class: |
96/417 |
Current CPC
Class: |
B01D 46/0086
20130101 |
Class at
Publication: |
96/417 |
International
Class: |
B01D 046/00 |
Claims
What is claimed is:
1. A solid powder trapping system for filtering out solid powder
from a mixture of gaseous reactants that also includes a device
capable of indicating the degree of powder accumulation inside the
trap, comprising: a solid powder trap capable of receiving a
mixture of gaseous reactants with suspended solid powder, filtering
out solid powder and finally expelling the filtered gaseous
reactants; a magnetic flux sensor inside the powder trap for
measuring the change in magnetic flux due to a change in the state
of powder accumulation inside the trap; and a display device
connected to the magnetic flux sensor for measuring the change in
magnetic flux so that the degree of powder accumulation inside the
trap is displayed.
2. The solid powder trapping system of claim 1, wherein the
magnetic flux sensor further includes: a U-shaped iron core; a
first inductive coil around one arm of the U-shaped iron core so
that an input current can be applied; and a second inductive coil
around the opposite arm of the U-shaped iron core whose terminals
are connected to the display device, wherein the current flowing
into the first inductive coil generates a magnetic flux that passes
through the iron core and the solid powder accumulated inside the
powder trap, so that the second inductive coil is ultimately able
to sense the magnetic flux.
3. The solid powder trapping system of claim 2, wherein the
U-shaped iron core is externally enclosed by ceramic material so as
to minimize loss of magnetic flux on its way to the second
inductive coil.
4. The solid powder trapping system of claim 1, wherein the display
device is a voltmeter whose reading reflects the degree of powder
accumulation inside the trap because the voltage picked up by the
voltmeter comes from a current produced in the second inductive
coil, and the magnitude of the current depends on the amount of
magnetic flux that comes through the iron core and the accumulated
powder inside the trap.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of Invention
[0002] The present invention relates to a solid powder trap having
a device capable of monitoring the degree of powder accumulation
inside the device. More particularly, the present invention relates
to a solid power trap having a device that measures the change in
magnetic flux due to the accumulation of powder and hence reflects
the degree of powder accumulation inside the trap.
[0003] 2. Description of Related Art
[0004] A solid powder trap is a device frequently used to filter
away suspended solid particles in a gaseous mixture. Powder traps
may be employed in many engineering projects, such as inside a
tunnel for trapping dust particles, for example. The air filter
inside an air conditioner for filtering dust particles inside a
house is also regarded as a kind of solid power trap. If the solid
particles are non-toxic, the particles can simply be expelled from
the generating source to the atmosphere using an exhaust fan or a
pump. However, if the solid particles can lead to environmental
pollution, the solid particles must first be collected and then
disposed by other means. There are many methods of trapping solid
particles including filtering, adsorption or electrostatic
attraction. Proper method for catching the solid particles depends
very much on the particle size and the particle characteristics. In
general, it does not matter what method is used to catch the solid
particles. Any device capable of filtering solid particles can be
regarded as a solid powder trap.
[0005] In semiconductor fabrication, solid powder traps are often
used alongside processing stations such as a chemical vapor
deposition (CVD) station or an etcher, for example. When these
processing stations are in operation, a large amount of reaction
products (one example is aluminum chloride AlCl.sub.3) is usually
generated. Some of these reaction products may form a solid powder
at atmospheric temperature. If the solid powder is not removed
quickly enough, it may accumulate inside the reaction chamber of
the processing station and become a source of impurities. Moreover,
if the unwanted impurities are allowed to accumulate, quality of
the finished product may be affected.
[0006] In general, the solid powder is removed from the reaction
chamber using a powder trap. FIG. 1 is a structural diagram showing
a conventional solid powder trapping system. As shown in FIG. 1,
the solid powder trapping system includes an air pump 100 that
connects with a reaction chamber or station (not shown in the
figure). The gaseous mixture is imput out of the chamber and passed
into a pipeline 102. A solid powder trap 104 is attached to the end
of the pipeline 102. Therefore, as the air mixture is passed into
the solid powder trap 104, solid powder suspended in the air
separates out. Finally, the filtered air is expelled into a local
scrubber through another pipeline 106.
[0007] For the above type of solid powder trap, there is no sensor
for detecting the degree of powder accumulation inside the trap.
Therefore, if one has to determine the degree of powder
accumulation inside the trap, the only way is to open the trap and
investigate the state of powder accumulation inside. Every other
method is mostly guesswork. However, without a general knowledge of
the degree of powder accumulation inside the trap, the only way to
maintain operational efficiency of the trap is to clean it at a
fixed time interval. Therefore, over-cleaning or under-cleaning of
the trap is likely, which lead to a waste of labor and resources.
Moreover, when particle concentration inside a reaction chamber is
too high or the pumping efficiency too low, it is difficult to
pinpoint the problem. One must check the pump and the solid powder
trap, thereby extending the idle time of the machine and hence
lowering its productivity.
[0008] In light of the foregoing, there is a need to provide a
device for monitoring the degree of powder accumulation inside the
solid powder trap.
SUMMARY OF THE INVENTION
[0009] Accordingly, the purpose of the present invention is to
provide a device for monitoring the degree of powder accumulation
inside a solid powder trap. The device utilizes the dependency of
magnetic flux on the amount of powder accumulated inside the powder
trap for estimating the degree of powder accumulation and then
using that information to schedule the proper cleaning or
maintenance period. In particular, the cleaning operation can be
scheduled during machine stop time so that machine down time is
reduced and productivity is increased.
[0010] To achieve these and other advantages and in accordance with
the purpose of the invention, as embodied and broadly described
herein, the invention provides a solid powder trapping system
having a display device showing the degree of powder accumulation.
The solid powder trapping system includes a solid powder trap, a
magnetic flux sensor and a display device. The solid powder trap is
a column for receiving a gaseous mixture from a reaction chamber.
After trapping the solid powder inside the gaseous mixture, the
filtered mixture is passed out. The magnetic flux sensor is
installed inside the solid powder trap for determining the state of
powder accumulation by sensing the amount of magnetic flux going
through a magnetic flux circuit. Any changes in magnetic flux
measurement are reflected on a display device. By reading the value
from the display device, the degree of powder accumulation inside
the trap can be estimated.
[0011] In addition, the magnetic flux sensor includes a U-shaped
iron core, a first inductive coil and a second inductive coil. The
first inductive coil is wound around one arm of the iron core. An
alternating current is applied to the first inductive coil. The
second inductive coil is wound around the opposite arm of the iron
core. The second inductive coil is connected to the display device.
As current flows into the first inductive coil generates a magnetic
flux in the iron core. The magnetic flux passes through the iron
core in the first arm, through the accumulated solid powder and
arrives at the iron core on the second arm. Hence, the second
inductive coil is able to pick up the magnetic flux.
[0012] Furthermore, the external portion of the iron core is
surrounded by ceramic material. The ceramic enclosure is used to
minimize the loss of magnetic flux during its journey along the
iron core.
[0013] The display device can be a voltmeter. By tapping the
magnetic flux through the second arm of the iron core, a current is
generated in the second inductive coil. The current is then
converted into a voltage reading that indicates the degree of
powder accumulation inside the trap.
[0014] It is to be understood that both the foregoing general
description and the following detailed description are exemplary,
and are intended to provide further explanation of the invention as
claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The accompanying drawings are included to provide a further
understanding of the invention, and are incorporated in and
constitute a part of this specification. The drawings illustrate
embodiments of the invention and, together with the description,
serve to explain the principles of the invention. In the
drawings,
[0016] FIG. 1 is a structural diagram showing a conventional solid
powder trapping system;
[0017] FIGS. 2A to 2D show the physical principles behind the
utilization of a magnetic flux circuit for determining the amount
of solid powder accumulation inside a solid powder trap according
to this invention;
[0018] FIG. 3 is a structural diagram showing a solid powder
trapping system having a device for monitoring the degree of powder
accumulation according to this invention; and
[0019] FIG. 4 is a magnified schematic view of the sensing device
used for determining the degree of powder accumulation as shown in
FIG. 3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] Reference will now be made in detail to the present
preferred embodiments of the invention, examples of which are
illustrated in the accompanying drawings. Wherever possible, the
same reference numbers are used in the drawings and the description
to refer to the same or like parts.
[0021] Since a conventional solid powder trap does not have a
display device for the degree of accumulation of powder inside,
commonsense experience or rule of thumb has to be relied on. In
other words, the trap is usually dismantled for cleaning after a
fixed period. In reality, the trap be affected by the pumping
efficiency and the concentration of micro-particles emitted from a
reaction station. Hence, the amount of powder accumulated inside
the trap within a fixed period is unlikely to be the same.
[0022] In this invention, a sensing device that makes use of a
magnetic flux circuit is installed inside the trap. Therefore,
information regarding the state of powder accumulation inside the
trap is present at any time. FIGS. 2A to 2D show the physical
principles behind the utilization of a magnetic flux circuit for
determining the amount of solid powder accumulation inside a solid
trap according to this invention.
[0023] A magnetic device having a first inductive coil 110 and a
rectangular iron core 112 is shown in FIG. 2A. The first inductive
coil 110 is wound around the left arm of the rectangular iron core
112, and then a current I is passed into the first inductive coil
110. Hence, a magnetic circuit having a magnetic flux .PHI. is
formed around the iron core 112.
[0024] A second inductive coil 114 and a magnetic flux sensing
device 116 (for example, a voltmeter) is added as shown in FIG. 2B.
The second inductive coil 114 is wound around the right arm of the
rectangular iron core 112 and connected to the sensing device 116.
Since an alternating current is applied to the first inductive coil
110 on the left side, an alternating magnetic flux is generated
around the iron core 112. Due to the alternating magnetic flux
along the right arm of the iron core 112, an alternating current is
produced in the second inductive coil 114, in a manner similar to a
transformer. The magnitude of the magnetic flux is affected by the
magnetic resistance of the iron core 112 or any medium the magnetic
flux needs to cross. Therefore, the voltage at the terminals of the
second inductive coil 114 as measured by the magnetic flux sensing
device 116 are also affected by any changes in magnetic resistance
along the magnetic circuit.
[0025] A magnetic circuit that also incorporates an air gap is
shown in FIG. 2C. The rectangular iron core as shown in FIG. 2B has
changed into a U-shaped core 117 (horseshoe shaped iron core). In
other words, the magnetic flux needs to traverse air 118 in the
upper arm of the magnetic circuit. Because air has a larger
magnetic resistance, the amount of magnetic flux going to the right
arm of the iron core 117 is greatly reduced. Hence, the voltage
produced by the second inductive coil 114 is smaller.
[0026] As shown in FIG. 2D, a device similar to the one in FIG. 2C
is placed inside a solid powder trap. Since solid powder 120 (for
example, AlCl.sub.3) accumulates inside the trap during operation,
the original air medium along the magnetic circuit is gradually
replaced by a solid powder medium. In other words, as solid powder
accumulates around the magnetic device, the cross-sectional area of
the magnetic circuit increases, leading to a reduction in magnetic
resistance. Because solid powder 120 has a lower magnetic
resistance than air, magnetic flux passing through the second
inductive coil 114 increases and hence a higher voltage is
obtained. This invention utilizes the change in voltage output from
the second inductive coil 114 to estimate the amount of powder
accumulated inside the solid powder trap.
[0027] FIG. 3 is a structural diagram showing a solid powder
trapping system having a device for monitoring the degree of powder
accumulation according to this invention. The solid powder trapping
system includes a filter for filtering solid powder inside a
mixture of gaseous reactants and a device for monitoring the degree
of powder accumulation inside the filter.
[0028] As shown in FIG. 3, a pump 130 is connected to a reaction
chamber (not shown) where solid powder mixed with gaseous reactants
is produced. The gaseous reactants and suspended solid powder is
directed through a pipeline 132 into a solid powder trap 134. The
solid powder trap has a filtering structure 138 for removing the
powder from the gaseous reactants. Finally, the remaining gaseous
reactants are exhausted through a pipeline 136. The magnetic flux
sensing device 140 is mounted somewhere inside the powder trap 134.
Since the accumulation of a thicker layer of powder around the
magnetic flux sensing device 140 decreases the magnetic resistance
of the magnetic circuit, a higher voltage is displayed on a display
device 142. Hence, the reading displayed on the display device 142
reflect the degree of powder accumulation inside the powder trap
134.
[0029] To have a better understanding of the sensing device in the
powder trap, a magnified view of the sensing device for determining
the degree of powder accumulation in FIG. 3 is shown in FIG. 4. As
shown in FIG. 4, sections labeled 138 are part of the filtering
structure inside the trap. The U-shaped iron core 142 of the
magnetic flux sensing device 140 is externally enclosed by ceramic
material 144. The ceramic material is there to prevent any possible
loss of the magnetic flux generated by the first inductive coil 146
en-route to the second inductive coil 148.
[0030] The display device 140 shown in FIG. 3 can be a voltmeter,
for example. By sensing the magnetic flux passing through the
second inductive coil, a current flows to the display device to
produce a voltage reading. By reading the display device, the state
of powder accumulation inside the trap is easily determined. In
addition, the voltage produced by the second inductive coil can
also be converted into a digital signal, after which the digital
signal can be transmitted to a central control station.
[0031] In summary, the major aspect of this invention is the
utilization of the change in magnetic flux in a magnetic flux
sensing device due to the accumulation of powder inside a solid
powder trap. Therefore, the degree of powder accumulation inside
the trap can be read off at any time, eliminating the need to carry
out routine cleaning and maintenance at fixed time interval.
Consequently, cleaning can be scheduled for offhours or during a
machine's idle time, and hence silicon chip production is
increased.
[0032] It will be apparent to those skilled in the art that various
modifications and variations can be made to the structure of the
present invention without departing from the scope or spirit of the
invention. In view of the foregoing, it is intended that the
present invention cover modifications and variations of this
invention provided they fall within the scope of the following
claims and their equivalents.
* * * * *