Cleaning and liquid contact with solids – Processes – Including application of electrical radiant or wave energy...
Patent
1998-07-14
2000-07-25
Stinson, Frankie L.
Cleaning and liquid contact with solids
Processes
Including application of electrical radiant or wave energy...
134 254, 134105, 134902, 134111, 134184, B08B 310
Patent
active
060925388
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention entitled "Method for using high density compressed liquefied gases in cleaning applications" relates to a cleaning means, which can achieve high efficiency at low cost by using a series of cleaning steps as cleaning factors, such as physical energy, chemical force and salvation and provides a new system for the recycle and recirculation of cleaning solvents without any expensive high pressure generating equipments, such as compressors, high pressure pumps or others.
BACKGROUND ART
Semiconductors and the like hereafter referred to as objects to be cleaned are placed inside a pressurized cleaning vessel in which supercritical fluid is fed for cleaning of the said objects to be cleaned by contacting with supercritical fluid and dissolution of impurities adhered to the objects. The supercritical fluid is circulated. When eliminating the supercritical fluid in which these contaminatns dissolved from the pressurized cleaning vessel by a suitable means, the objects which were precisely cleaned are obtained. A troublesome process for drying the objects required in so-called wet cleaning methods is unnecessary since the supercritical fluid is completely vaporized by a decompressing operation.
It is possible to reuse the supercritical fluid because such supercritical fluids with the above-mentioned contaminants are transferred from the cleaning vessel into a separation tank (or a recovery tank) and then the solvent is separated from the contaminants by mechanism stated whithin.
As shown in the FIG. 7 concerning a schematic plot of the states of the pure substance and Its supercritical state, this is the latest technique for cleaning semiconductor substrates by using the following two characteristics of the supercritical fluid in its high density fluid state in which condition of pressure and temperature at the near critical region is P>P. (crirical pressure) and T>T. (critical temperature).
Characteristic 1: It is possible to easily obtain a great change in density with a slight change of pressure. It is also possible to obtain a great difference or solubility because the solubility of substance is in general, proportional to the density thereof.
Characteristic 2: The density of a supercritical fluid has low viscosity and high diffusivity although it is similar to liquid. Therefore, such a characteristic is advantageous when a 'substance moves.
The priciple shows that firstly, the low viscosity of the supercritical fluid can easily enter into narrow pores and crevices. On the contrary, for the case of high viscosity thereof, the fluid has high solubility for contaminants adhered or penetrated into a substrate, especially organics substances. Secondly, the above-mentioned cleaning operation is achieved with the supercritical fluid containing the contaminating substance, and the contaminants can be divided between solid and liquid states because solubility of the said contaminants is weakened by decreasing the density thereof. Accordingly, in this invention, it is possible to recover these components by a decompression operation in a separation vessel.
After the contaminants are separated from the solution, the purified supercritical fluid used in the pressurized cleaning vessel can be stored and recycled resulting in a closed recycle system.
Applicable gases in this invention are carbon dioxide, nitrous oxide, ethane, propane and the like. In particular, carbon dioxide is highly suitable to handle since it is nonflammable, nontoxic and inexpensive, and has a critical temperature of 31.1.degree. C. and a critical pressure of 72.8 atmospheres.
In such a recycle system mentioned above, a general fluid tranfer method can be accomplished with a high pressure generator such as compressors, pumps, etc. to make and keep the supercritical state. However, such equipment as cleaning equipments are very costly since these equipments need the high ability to generate high pressure, and further these methods are known to generate fine particles that are detrimental to the cleaning process.
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Arai Kunio
Inomata Hiroshi
Smith Richard Lee
Arai Kunio
Shuzurifuresher Kaihatsukyodokumiai
Stinson Frankie L.
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