Electrolysis: processes – compositions used therein – and methods – Electrolytic material treatment – Gas – vapor – or critical fluid
Reexamination Certificate
2001-01-26
2003-04-15
Phasge, Arun S. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic material treatment
Gas, vapor, or critical fluid
C204S252000, C204S264000
Reexamination Certificate
active
06547953
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a substrate container (pod) with a humidity removing function such as a clean box, a substrate storage box, a substrate carrying container, a substrate holding rack, or the like for storing or transporting substrates such as semiconductor wafers, photo-masks, hard-disks, etc. in a highly clean atmosphere or a highly water-free atmosphere, and a method of dehumidifying such a substrate container.
2. Description of the Related Art
When substrates such as semiconductor wafers, photo-masks, etc. are delivered or stored in the fabrication process in semiconductor fabrication factories, the yield of products tend to decrease if a small amount of particulate contaminants or gaseous impurities present in the atmosphere is attached to those substrates. Such a tendency increases as the level of circuit integration grows. With the advent of magnetic reluctance heads, magnetic disks are required to record information at an increased density, and need to be highly clean against gaseous impurities as well as particulate contaminants. Furthermore, in view of reducing the corrosion of semiconductor substrates, there has been a demand for means for keeping at a low level the humidity of an atmosphere in which those semiconductor substrates are stored.
To create a clean space for accommodating substrates such as semiconductor wafers, magnetic disks, etc. when they are delivered or stored, there have been developed clean boxes equipped with a fan motor and a HEPA (High Efficiency Particle Air) filter or an ULPA (Ultra Low Penetration Air) filter. Such clean boxes also have a filter for removing gaseous impurities, such as a chemical filter, in order to avoid the adverse effect of such gaseous impurities, and also a dehumidifying means such as a desiccant for lowering the humidity.
There is known a compact and economical dehumidifying storage device, which comprises an electrochemical element in the form of a solid polymer electrolyte film that has an anode facing inwardly of a storage container and a cathode facing outwardly of the storage container.
The chemical filter and desiccant in the clean boxes have their service life depending on the gas concentration of the environment in which they are used and the level of contamination of the stored substrates. Generally, the service life of a filter for removing gaseous impurities is shorter than the service life of a particle removing filter. The gas concentration in the air which serves as the load on the filter for removing gaseous impurities ranges from several tens to several hundreds ng/g-air, whereas the water content in the air is 5 mg/g-air at the temperature of 20° C. It is apparent that the service life of the desiccant is shorter than the service life of the filter for removing gaseous impurities.
If there is used a dehumidifying unit capable of mechanically purging water from a circulating gas flow, rather than causing a desiccant to adsorb water in a circulating gas flow and replace the desiccant when its performance is lowered, then such a dehumidifying unit needs easy maintenance because it requires no parts replacement, and does not cause any contamination which would otherwise result from desiccant impurities.
It is known in the art that those chemical filters which adsorb gaseous impurities based on an ion exchange reaction have its impurity removing capability depending on the water content in the air, i.e., the humidity. It is necessary to keep the environment in the container or clean box at a minimum humidity level which makes it possible for the chemical filter to perform its function to remove gaseous impurities.
According to another process, the container or clean box is filled with a drying gas to achieve a low level of humidity therein. One problem with this process is that the humidity in the container rises unless the container is continuously supplied with the drying gas. The cause of the problem is that the container is made of a humidity-permeable synthetic resin and it is difficult to seal the container, which has an opening, against the molecular-level entry of material. In order to keep a low level of humidity therein in the container, therefore, it is necessary that the container be made of a humidity-impermeable material and the container have some means for removing water that tends to permeate or leak into the container.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a substrate container for such as a clean box, a substrate feed container, a substrate holding rack, or the like for storing or transporting substrates, the substrate container having a dehumidifying unit which is maintenance-free and compact, is an energy saver, and is capable of controlling a level of humidity that can be achieved.
Another object of the present invention is to provide a method of dehumidifying a substrate container.
According to the present invention, there is provided a substrate container comprising a container housing having an opening for storing a substrate therethrough and a cover sealingly covering the opening, a fan motor mounted in the container housing for producing a circulating path of air in contact with the substrate in the container housing, a particle removing filter and a gaseous impurity trapping filter which are disposed in a portion of the circulating path which extends toward the substrate, and dehumidifying means for dehumidifying a space in the container housing, the dehumidifying means comprising a solid polymer electrolyte film disposed in the circulating path and voltage applying means for applying a voltage to the solid polymer electrolyte film to decompose water in air flowing in the circulating path thereby to dehumidify a space in the container housing.
The dehumidifying means further comprises an anode mounted on one surface of the solid polymer electrolyte film, and a cathode mounted on the other surface of the solid polymer electrolyte film, the voltage applying means comprising means for applying the voltage between the anode and the cathode across the solid polymer electrolyte film to control the humidity in the space in the container housing. One of the anode and cathode, or both of the anode and cathode may be provided with a catalyst attached thereto for promoting a dehumidifying action.
When a DC voltage is applied between the anode and the cathode, water in air flowing through the circulating path is decomposed to dehumidify the container housing. Specifically, when the dehumidifying means is energized, water adsorbed to the anode is decomposed into hydrogen ions and an oxygen gas by the anode catalyst. The hydrogen ions move through the solid polymer electrolyte film toward the cathode, are coupled to atmospheric oxygen on the side of the cathode, producing water, which is then discharged into the atmosphere outside of the cathode.
Since no water is accumulated in the solid polymer electrolyte film, the solid polymer electrolyte film can be used semi-permanently because its dehumidifying capability is not lowered after repeatedly used. The dehumidifying means is almost maintenance-free as the solid polymer electrolyte film does not need to be replaced. The solid polymer electrolyte film can safely be used in a highly clean environment as it does not produce contaminants. Though the solid polymer electrolyte film has a relatively small area, it has a large dehumidifying capability, and it is of a low-profile, compact structure that can easily be placed in the substrate container because it needs to be supplied with a DC electric energy that is required only to decompose the water.
It is known in the art that the ability of a filter, which operates based on an ion exchange reaction for its adsorption mechanism depends on water in air, i.e., humidity. It is necessary to keep a circulating air environment in the container housing at or higher than a minimum humidity level at which the ability of the filter can be maintained. Conventional desiccants are unable to set
Okubo Kazuo
Suzuki Yoko
Tanaka Akira
Ebara Corporation
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Phasge Arun S,.
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