Cleaning and liquid contact with solids – Apparatus – Miscellaneous
Reexamination Certificate
2000-09-22
2002-12-17
Gulakowski, Randy (Department: 1746)
Cleaning and liquid contact with solids
Apparatus
Miscellaneous
C134S902000, C134S110000, C210S638000, C210S649000, C210S900000
Reexamination Certificate
active
06494223
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention concerns a cleaner using ultra-pure water, and particularly a cleaner for use in the wet cleaning process for the semiconductor industry.
2. Discussion of the Related Art
It has been devised to introduce, just before the point of use, an ion absorption film module filled with a porous film of 0.01 to 1 &mgr;m in average hole diameter, the porous film holding polymer chains having a cation exchange group, an anion exchange group and a chelating group (hereafter, called cation absorption film, anion absorption film and chelate film, respectively); and each such film being generically called an ion absorption film for reducing impurities such as heavy metals, for example, just before the point of use (Japanese Patent Laid-Open No. HEI 8-89954).
A hollow yarn film module having a cation exchange group associated therewith is applied to eliminate metals, and it is particularly effective in eliminating alkali metals and/or alkali earth metals. A hollow yarn film module having an anion exchange group can effectively eliminate particles and colloidal matter. A hollow yarn film module having a chelating group has an excellent function of eliminating heavy metal material, even when present at an extremely low concentration.
It is known that the use of hydrogenated ultra-pure water can suppress and/or eliminate deposition onto a substance of silicon or the like. Further, Japanese Patent Laid-Open No. HEI 9-10713 discloses a method including the steps of presenting an extremely high hydrocarbon elimination rate and by treating the wafer with ultra-pure water in order to perform substrate hydrogen termination, the ultra-pure water containing hydrogen or a mixture of hydrogen and a rare gas. As hydrogenated ultra-pure water presents an extremely high hydrocarbon elimination rate, using a rinse of hydrogenated ultra-pure water should allow a cleaner wafer surface to be obtained than possibly achieved using a rinse not employing hydrogenated ultra-pure water.
However, through the comparison between a film (for example, an insulation film such as a gate insulation film) formed on the silicon substrate when hydrogenated ultra-pure water is used to rinse and a film formed on the substrate when non-hydrogenated ultra-pure water is used to rinse, the Inventors have found a problem that the former film happens to be inferior to the latter film in quality (for example, dielectric strength).
They have investigated the cause thereof and have found that the hydrogenated ultra-pure water is capable of eliminating particles and/or of preventing particles from depositing on a substrate, but also has a function of facilitating deposition of metallic impurities onto the substrate. They have explicated that this deposition provokes film quality degeneration (for example, deterioration of dielectric strength).
SUMMARY OF THE INVENTION
The present invention provides a wet cleaning apparatus for eliminating a trace heavy metal, colloidal matter, and/or other impurities contained in ultra-pure water used as rinse water in the semiconductor cleaning process and suppressing deposition of impurities, such as particles and/or heavy metals that degenerate device characteristics, onto the substance surface.
According to the present invention, a wet cleaning apparatus for rinsing with ultra-pure water includes a piping through which is supplied to a point of use inside the apparatus, the piping being provided with a module filled with a porous film in which polymer chains having at least one of a cation exchange group, an anion exchange group and a chelating group held within the polymer chains, the porous film being positioned in the middle of the piping.
Here, the cleaner is a multi-tank type, a single tank type batch cleaner, or a sheet cleaner for performing wet cleaning. In wet cleaning, the cleaner is an apparatus for cleaning a wafer surface with ultra-pure water-based chemicals, for rinsing surface chemical deposits therefrom with the ultra-pure water and eventually for drying the wafer surface. Note that such an apparatus includes a cleaner for cleaning by ultra-pure water jet.
Here, the cleaner includes a wet bench. A wet bench is a cleaning place provided with exhaust equipment and cleaning equipment. The cleaning equipment is provided with ultra-pure water, chemical supply piping, and drain piping for cleaning liquid and rinse water.
Ultra-pure water produced by the ultra-pure water system always circulates within the main loop and is extracted as necessary from the main loop by means of a branch piping to dilute chemicals necessary for cleaning or rinsing, as appropriate.
Branch piping is introduced into the cleaner or wet bench to supply ultra-pure water for individual cleaning processes, and among them, in the final rinse corresponding to the final process of the cleaning processes, it is an object to eliminate any chemical deposit from the semiconductor substrate that would otherwise exist thereon after cleaning.
Here, the final rinse designates the process for rinsing a chemical deposit on the wafer surface with ultra-pure water or hydrogenated ultra-pure water just before a wafer drying process, such as IPA (2-propanol) vapor drying, spin drying, or Marangoni-type drying.
As the rinse with ultra-pure water itself does not present an effect to suppress deposition of impurities such as various types of metal, rinsing water after chemical cleaning should be free from even a trace of impurities.
Especially, in the last process of wet cleaning, the substrate surface is etched with dilute hydrofluoric acid solution, a bare silicon surface, deprived of an oxide film, is exposed, and thereafter, the rinse process is performed with ultra-pure water.
There, the object of ultra-pure water rinse is to eliminate hydrofluoric acid chemical deposited on the substrate by rinsing with ultra-pure water. However, if impurities such as metals exist in the ultra-pure water, the use thereof can result in impurity deposition since the silicon surface is exposed. Once impurities deposit onto the substrate, the ultra-pure water is totally incapable of eliminating them. Consequently, the ultra-pure water used for the final rinse is required to be totally free from impurities such as metals that tend to deposit onto the substrate surface.
Among impurities present in the ultra-pure water, especially metals, are reduced and hardly detected, even by means of a high sensitivity instrument analyzer such as an inductively coupled plasma analyzer (ICP-MS).
It is presumed that the presence of impurities under the analyzer quantification lower limit level provokes the deposition of impurities onto the substrate surface.
Almost all metals existing in the ultra-pure water are generally anionized. However, it is presumed that they do not exist as independent anions, but they are clustered or colloidalized, forming electrostatically weak binding with silica or organic matter having negative charge. For this reason, it is difficult to remove the clustered matter having weak charge and small size with ion exchange or reverse osmosis equipment designed to remove metal impurities in the ultra-pure water system. It has been found that these metal impurities are present at the exit of ultra-pure water system and may deposit onto the substrate surface.
Here, the investigation by the Inventors has shown that the use of a module filled with an ion absorption film holding polymer chains having at least have of a exchange group, an anion exchange group and a chelating group can eliminate impurities, such as a clustered metal, that could not be removed by the conventional system.
Here, as the ion absorption film used in the present invention, for example, a hollow yarn porous film of 0.01 to 1 &mgr;m in average hole diameter is used preferably, the porous film containing polymer chains having ion exchange groups inside the film, the ion exchange groups forming 0.2 to 10 mili-equivalent weight per 1 gram of film. The manufacturing method and other details thereof are as described i
Hashino Masatoshi
II Toshihiro
Kawada Kazuhiko
Kubota Noboru
Ohmi Tadahiro
Gulakowski Randy
Knuth Randall J.
Ohmi Tadahiro
Perrin Joseph
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