Refrigeration – Processes – Deodorizing – antisepticizing or providing special atmosphere
Patent
1989-12-27
1992-04-21
Capossela, Ronald C.
Refrigeration
Processes
Deodorizing, antisepticizing or providing special atmosphere
622592, F24F 316
Patent
active
051056283
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method of storing a wafer which is a semiconductor substrate.
BACKGROUND INFORMATION
In general, a method of sealing a wafer in an atmosphere of dry nitrogen gas or the like is employed for storing and transporting a semiconductor wafer. This storage method is carried out immediately after the wafer has been polished to form a mirror surface, or immediately after a distorted layer, a contaminated layer and the like are removed by an etching solution.
However, although bedewing and oxidation can be prevented to some extent by such a conventional method, a progression in the deterioration of the wafer surface caused by a residual polishing solution or by a residual etchant and a change in the surface stoichiometry caused by a difference in the vapor pressures or reactivities, which causes a problem in a semiconductor material of two or more elements such as GaAs, cannot be avoided.
Although any residual etchant or the like is removed by washing, the same still remains on the wafer surface in a thickness of about 1 atom by physical adsorption or chemical bond. Such a layer of the residual etchant or the like is so extremely thin that the same evaporates by an increase in temperature when of an epitaxial layer etc. is formed on the cleaned surface. No problem is caused when the residual etchant or the like is removed during the process of forming a device. However, the aforementioned evaporation is prevented if the residual etchant or the like has time to react with the surface of the semiconductor wafer to newly form a compound, leading to roughening of the surface.
In order to prevent such roughening of the surface, the wafer is generally treated by etching or the like immediately before the process of forming the epitaxial layer, etc. The steps of forming the device are complicated by such treatment, and hence the merit of improving the productive efficiency by high-volume processing cannot be achieved by conventional methods.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of storing a semiconductor substrate, which can suppress a reaction between a residual etchant or the like and the surface of a semiconductor wafer to avoid the need for a repeated cleaning, e.g. etching etc. performed as a pretreatment prior to forming an operating layer on the substrate.
The feature of the present storage method resides in that a semiconductor substrate is preserved at a temperature not more than 10.degree. C., preferably a temperature not more than 5.degree. C. More preferably, the semiconductor substrate is preserved at a temperature not more than -20.degree. C.
Further, the semiconductor substrate is preferably sealed in an atmosphere of a dry inactive gas or in a vacuum state, to be preserved. Such sealing is preferably implemented by covering the semiconductor substrate with a member such as a synthetic resin sheet or a layer structure of a metal foil sandwiched between resin sheets, which is not permeable to gas, water and alcohol molecules.
The semiconductor substrate to be stored by the method of the present invention is in a state not yet provided with an operating layer on its surface for forming a device, or in a state between a step and a subsequent step in the process of forming a device.
Since both, the reaction with a residual etchant etc. and the change in stoichiometry of the surface are chemical reactions, the reaction velocity V thereof is in accordance with the following Arrhenius equation. ##EQU1## where k represents Boltzmann's constant, T represents absolute temperature (K) and E represents reaction energy.
FIG. 2 illustrates the relationship between a relative reaction velocity and the temperature with changes in the reaction energy as parameters according to the Arrhenius' equation. The horizontal line shows the temperature and the vertical line shows relative reaction velocity, expressed as a reaction velocity at 300 K.
The reaction energy in a general chemical reaction is about 1 to 2 eV. There
REFERENCES:
patent: 4739633 (1988-04-01), Faris
Capossela Ronald C.
Fasse W. G.
Kane, Jr. D. H.
Sumitomo Electric Industries Ltd.
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