1. Field of the Invention
The present invention relates to a method of removing electrostatic charges from high resistivity liquid such as purified water or the like used to produce devices that are sensitive to electrostatic charges, for example semiconductor devices or liquid crystal devices. The present invention also relates to an apparatus for effectively implementing this method.
2. Description of the Related Art
In recent years, there has been achieved a great improvement in the purity of high resistivity liquid such as purified water used in production of semiconductor devices or liquid crystal devices. As a result, the resistivity of purified water has reached near the theoretical upper limitation of 18.25 M.OMEGA.-cm (at 25.degree. C.).
This has been brought about by the improvement in purity of chemicals and by the improvement in utilities for supplying the purified water which can prevent impurities contained in the pipe material from being dissolved into the purified water.
However, the improvement in purity has also brought about a problem that the high purity water and other high resistivity liquid are readily electrostatically charged.
For example, it is very common that high purity water having a resistivity of 18.24 M.OMEGA.-cm (at 25.degree. C.) is charged up to about 1000 V after passing through a teflon-based pipe. The high purity water charged up at such a high voltage sometimes damages the performance of a transistor that is one of components of a semiconductor device or a liquid crystal device.
One known technique to solve the above problem is to reduce the resistivity by introducing carbon dioxide into the highly purified liquid having a high resistivity, as shown in FIGS. 8 and 9. FIG. 8 is a cross-sectional view of a conventional apparatus for introducing carbon dioxide into high resistivity liquid via a film 71 that is permeable for gas. FIG. 9 is a cross-sectional view of a conventional apparatus for bubbling carbon dioxide gas through high resistivity liquid.
In these conventional methods or apparatus, however, the highly purified water having a high resistivity is often contaminated with impurities during the dissolving process of carbon dioxide gas. Moreover, a residual carbonate or dissolved carbon dioxide makes the high resistivity liquid acid, which may damage semiconductor devices or liquid crystal devices. Another problem is that the carbon dioxide dissolved in the high resistivity liquid is vaporized due to the change in temperature or pressure, and vaporized gas chokes the pipe. When purified water is used as high resistivity liquid, bacteria can readily breed in it. Besides, it is difficult to control the dissolution of carbon dioxide because the amount of carbon dioxide dissolved in purified water varies depending on temperature and pressure.