Brushing – scrubbing – and general cleaning – Machines – With air blast or suction
Reexamination Certificate
2000-02-18
2001-02-20
Moore, Chris K. (Department: 1744)
Brushing, scrubbing, and general cleaning
Machines
With air blast or suction
C015S316100, C015S404000
Reexamination Certificate
active
06189176
ABSTRACT:
This invention relates to a system for cleaning a dry process vacuum pump and, in particular, a system using a high pressure gas cleaning purge to clean a dry process vacuum pump on a Czochralski-type (CZ) crystal grower.
In the semiconductor industry, semiconductor crystals are typically grown in a CZ crystal growing furnace. During the crystal growing process, the chamber of the CZ furnace is typically maintained at various levels of vacuum.
To maintain the reduced pressure in the CZ furnace, a vacuum pump is run continuously during the crystal pulling process. The vacuum pump is subjected to substantial quantities of silicon oxide dust, a byproduct of the process inside the CZ furnace. In the past, oil-sealed vacuum pumps were used. However, the oil present in an oil-sealed pump is a potential source of vacuum and process gas contamination. Additionally, maintaining filters and exhaust oil-mist separators proves to be a significant expense.
To avoid the problems associated with oil-sealed vacuum pumps, some manufacturers use a dry pump as the vacuum pump on a CZ crystal grower. In contrast to the oil seals used in an oil-sealed pump, a dry pump relies on extremely close tolerances between its rotors and stators to provide the necessary seals within the pump. The absence of oil in a dry pump avoids the above mentioned problems associated with an oil-sealed pump. However, the extremely small gaps between the rotors and stators of a dry pump can be filled by the silicon oxide dust, resulting in increased current load on the pump motor. Allowed to continue unchecked, this increased load may result in overload of the motor, tripping a circuit breaker and causing an abort of the crystal growing run. Aborts are extremely expensive due to the associated production down time and product loss.
FIG. 1
shows a dry vacuum pump
10
having a vacuum pump inlet
50
connected to a crystal grower
30
by way of a vacuum pipe
40
and a booster pump
20
. The gases drawn from the crystal grower
30
by the dry vacuum pump
10
are exhausted to a building exhaust system
70
by way of a vacuum pump exhaust
60
. Traditionally, dry pumps used to pump harsh processes or particulate-laden gases use a “cleaning cycle” at some point before, during, or after a run. The pump cleaning system shown in
FIG. 1
circulates atmospheric air
90
through dry vacuum pump
10
in an effort to remove silicon oxide dust deposited in the dry vacuum pump
10
during the crystal growing process. During the cleaning process, cleaning cycle valve
80
is opened and the dry vacuum pump
10
draws large amounts of atmospheric air
90
through the dry vacuum pump
10
. During the crystal growing process, cleaning cycle valve
80
is closed.
SUMMARY OF THE INVENTION
In order to reduce the build up of silicon oxide dust inside a dry vacuum pump on a CZ crystal grower, the invention provides high pressure gas purging of the dry vacuum pump. In particular, the high pressure gas cleaning purge of the invention injects a high pressure gas, such as compressed dry air (CDA), into the inlet of the dry pump after each crystal growing run or cycle is completed. The system of the invention includes a pressure regulator and two solenoid valves. One solenoid valve switches between a closed position in which no flow is allowed, and an open position in which atmospheric air is allowed to flow into the dry vacuum pump. A second solenoid valve switches between an open position in which high pressure purge gas is allowed to flow into the dry vacuum pump and a closed position in which the high pressured purge gas is not allowed to flow. Injecting large volumes of high pressure gas increases the pressure inside the pump, resulting in the removal of the oxides within. During cleaning, the first solenoid valve and the second solenoid valve are alternately opened and closed, causing the high pressure purge gas to repeatedly start and stop flowing. The turbulent flow of the high pressure purge gas within the dry vacuum pump changes with each stopping and starting of the high pressure purge gas flow. As compared to continuous high pressure purge gas flow, the differing turbulent flow patterns created by repeatedly stopping and starting the high pressure purge gas flow results in substantially improved removal of the silicon oxide dust deposits inside the pump.
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Ivey Kenneth C.
LaBrie Aaron L.
Moore Chris K.
Oliff & Berridg,e PLC
SEH-America, Inc.
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