Pumps – Motor driven – Fluid motor
Reexamination Certificate
2000-07-28
2002-07-16
Kwon, John (Department: 3754)
Pumps
Motor driven
Fluid motor
C417S395000
Reexamination Certificate
active
06419462
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a positive displacement type liquid-delivery apparatus that can be used to deliver a very small amount of liquid at a constant rate to various processing apparatuses such as a chemical vapor deposition apparatus.
2. Description of the Related Arts
Recently, in the semiconductor manufacturing industry, the integration of integrated circuits has been improved remarkably, and the research and development activities of DRAM are being intensively carried out in anticipation of gigabit order DRAMs which will replace current megabit order DRAMs. A capacitor element having a large capacity per unit area is needed to produce such DRAMs. As a dielectric thin-film material for producing elements having such a large capacity per unit area, a metallic oxide film material such as tantalum pentaoxide (Ta
2
O
5
) having a dielectric constant of approximately 20, or barium titanate (BaTiO
3
) or strontium titanate (SrTiO
3
) or barium strontium titanate having a dielectric constant of approximately 300 is considered to be a promising thin-film material.
To deposit such a metallic oxide film material on a substrate in a vapor phase, a gaseous mixture made by mixing one or more gas feed materials of organometallic compounds and an oxygen containing gas is ejected to a substrate heated to a certain temperature. Organometallic gaseous feed material is chosen based on the nature of the thin film to be produced. For example, a metallic oxide film comprised by barium strontium titanate is produced by first converting Ba, Sr, Ti or their compounds into their dipivaloylmethane (DPM) compounds, and dissolving these compounds in an organic solvent such as tetrahydrofuran (THF) to produce respective liquid feed materials. After uniformly mixing these liquid feed materials in a required proportion to produce a master liquid feed, such master liquid feed is sent to a vaporizer to produce a gaseous feed for use in the chemical vapor deposition apparatus.
Such master liquid feed is extremely susceptible to degradation even in a sealed container, and therefore it is undesirable to have such a master liquid feed stagnate inside delivery piping. The master liquid feed is especially susceptible to producing precipitate particles, by being heated or being exposed to air, which tend to produce inferior quality films. Therefore, once the component liquids are mixed into a master liquid feed, it is necessary that the master liquid feed be maintained in a stable condition. It is also desirable that the master liquid feed be completely used up as quickly as practicable. Furthermore, it is desirable that the film deposition apparatus be capable of exercising a fine control of the flow rate of the master liquid feed over a wide range of flow rates from a very small flow rate to a large flow rate. Therefore, the liquid-delivering apparatus should be capable of providing a stringent control of the flow rates of the liquid feed.
As a positive displacement type liquid-delivering apparatus used in these applications, there has been known such an apparatus in which a mass flow controller (WFC) is provided in the piping connecting a feed liquid tank and a processing apparatus such as a vaporizer. The feed liquid tank is pressurized with gas or the like to deliver liquid, and a control valve on the MFC is adjusted to control a delivery rate of liquid. Positive displacement pumps incorporating pistons, diaphragms, and the like are also used.
In general, conventional apparatuses using a mass flow controller have a poor reproducibility of flow control near the lower limit of the allowable control range. Moreover, when the pressure in the processing apparatus increases, a pressure exceeding the pressure in the processing apparatus must be applied to the feed liquid tank side. Hence, a large amount of gas used for pressurizing is dissolved in the liquid in the feed liquid tank, and this dissolved gas is released downstream of the control valve of the mass flow controller or causes surge or pulsation in the flow of the liquid feed.
Although a positive displacement pump can overcome these drawbacks, a piston pump cannot be used because the sliding parts of the pump generate particles that contaminate the liquid. The positive displacement pumps employing bellows or diaphragms do not contaminate the liquid, but present the following problems.
It is conceivable to construct such a positive displacement pump in which a container is partitioned by a diaphragm into two chambers, i.e., a liquid delivery chamber and a working fluid chamber, and an incompressible liquid is used as a working fluid. With this construction, the diaphragm moves according to the amount of the working fluid supplied to the working fluid chamber for thereby discharging liquid from the container. Therefore, the precision in controlling the flow rate is more or less dependent on the precision of the external driving system. As a result, an external device is required for pumping the working fluid, and hence troublesome handling of the working fluid is necessary and the overall apparatus becomes large-sized.
If a driving device for driving the diaphragm is constructed mechanically, then these problems are eliminated and the overall apparatus becomes simple. However, it is very difficult to control the movement of the diaphragm so as to continuously deliver liquid at a constant rate if the processing conditions (pressure) in the secondary side (downstream side) of the container vary. Even if a flow meter is installed in the secondary side of the container for performing feedback control, it is not possible to obtain a better performance than that of the mass flow controller, because precision and reproducibility of the flow meter is the same level as the flow controller.
When the liquid-delivery is stopped, the pressure in the secondary side of the positive displacement pump slowly decreases due to a small leak in the check valve provided in the primary side (upstream side) of the processing apparatus (the part to which liquid is supplied). This may lead to a pressure drop when the liquid-delivery resumes, requiring time to stabilize the flow rate of liquid and potentially causing other problems. For example, if the pressure in the processing apparatus is below atmospheric pressure, the liquid feed may be vaporized because the pressure in the primary side of the check valve drops below the vapor pressure of the liquid feed.
Further, in the positive displacement pump, pressure variations occur in piping in the secondary side of the pump when the pumping operation begins, and hence the flow rate of liquid cannot be controlled until the liquid-delivery is stabilized. If a plurality of liquid feeds are required to be delivered at the same ratio, for example, these liquid feeds cannot be used until the liquid-delivery is stabilized.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention to provide a positive displacement type liquid-delivery apparatus employing a positive displacement pump with a flexible diaphragm which can supply liquid at a constant rate with high precision and high reproducibility, shorten the time required to stabilize the liquid-delivery from the start of the pumping operation, and control the flow rate of liquid immediately after the pumping operation begins.
According to an aspect of the present invention, there is provided a positive displacement liquid-delivery apparatus comprising: a positive displacement pump comprising a housing having a liquid-delivery chamber divided by a flexible diaphragm and a diaphragm driving unit linked to the diaphragm to discharge fluid from the liquid-delivery chamber; and a differential pressure control unit for controlling the differential pressure between both sides of the diaphragm at a constant value during the pumping process.
Accordingly, the construction of the apparatus is simplified because the diaphragm is driven directly by the diaphragm driving unit. Further, by keeping the differenti
Fukunaga Yukio
Hongo Akihisa
Horie Kuniaki
Kamoda Kenji
Tsukamoto Kiwamu
Ebara Corporation
Kwon John
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