Cleaning and liquid contact with solids – Processes – Including application of electrical radiant or wave energy...
Reexamination Certificate
2001-06-06
2003-11-25
Markoff, Alexander (Department: 1746)
Cleaning and liquid contact with solids
Processes
Including application of electrical radiant or wave energy...
C134S001000, C134S001300, C134S010000, C134S017000, C134S034000, C134S042000, C134S902000, C438S906000, C216S093000, C204S212000, C204S22400M, C204S275100, C205S640000, C205S650000, C205S652000, C205S672000
Reexamination Certificate
active
06652658
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The first invention relates to a method for processing with hydroxide ions in ultra-pure water, and more particularly relates to a processing method with which a workpiece can be subjected to removal processing or to oxide film formation processing by using only ultra-pure water and increasing the ion product is to provide a thereof. The second invention relates to a method for washing with hydroxide ions in ultra-pure water, with which hydroxide ions are supplied near the surface of a material to be washed, and particularly a semiconductor wafer or the like, and a high-speed shear flow of ultra-pure water is created, which makes it possible to completely remove any fine impurity metals adhering to the surface of the material being washed.
2. Description of the Related Art
Progress in scientific technology in recent years has led to new materials being developed one after the other, but an effective means of processing these new materials has yet to be established, with such technology always seeming to lag behind the development of new materials.
Recently, as the elements that make up all kinds of devices have become smaller and more precise, and as manufacturing on the sub-micron level has become more commonplace, the processing method itself increasingly has an effect on the characteristics of the material. In this situation, with a processing method in which part of the workpiece is physically and destructively removed with a tool, as with conventional mechanical processing, this processing can give rise to numerous defects in the workpiece, as a result of which the characteristics of the workpiece may suffer. A matter of great importance is therefore how to perform such processing without sacrificing the characteristics of the material.
Chemical polishing, electrolytic working, and electrolytic polishing are some of the special processing methods that have been developed as a means for solving the above problem. Unlike with conventional mechanical processing, these processing methods involve removing material by bringing about a chemical elution reaction. Therefore, defects such as work modified layers or dislocation due to plastic deformation do not occur, allowing processing to be carried out without the characteristics of the material being sacrificed as mentioned above.
A type of processing method that has been attracting even more attention involves the use of chemical interaction between atoms. This makes use of microparticles, radicals and so forth with high chemical reactivity. These processing methods remove material through a chemical reaction with the workpiece on the atomic order, so the processing can be controlled on the atomic order. Examples of these processing methods developed by the inventor include EEM (Elastic Emission Machining; Japanese Laid-Open Patent Application H1-236939) and plasma CVM (Chemical Vaporization Machining; Japanese Laid-Open Patent Application H1-125829). EEM makes use of a chemical reaction between microparticles and the workpiece, and therefore affords processing on the atomic order without sacrificing the characteristics of the material. Plasma CVM makes use of a radical reaction between the workpiece and radicals produced in a plasma at atmospheric pressure, and also affords processing on the atomic order.
With the above-mentioned electrolytic processing or electrolytic polishing, it has been conventionally held that the processing proceeds through electrochemical interaction between the workpiece and the electrolyte (an aqueous solution of NaCl, NaNO
3
, HF, HCl, HNO
3
, NaOH, or the like). Also, as long as electrolyte is used, the workpiece will inevitably be contaminated by the electrolyte.
In view of this, the inventor thought that hydroxide ions (OH ) might be acting on the processing in neutral and alkaline electrolyte, and reached the conclusion that if this were true then processing would even be possible with water in which hydroxide ions were present in even a tiny amount. The possibility of such processing was also confirmed experimentally, and in Japanese Laid-Open Patent Application H10-58236 the inventor proposed a processing method in which only ultra-pure water from which as much of the trace impurities as possible have been removed is used, this is subjected to a ion product increasing treatment for increasing the hydroxide ion, a workpiece is immersed in this ultra-pure water with elevated hydroxide ion concentration, and removal processing or oxide film formation processing is performed through a chemical elution reaction or oxidation reaction involving these hydroxide ions. In addition, the inventor proposed to utilize an electrochemical interaction on a solid surface having a function of an ion exchange or a catalyst as a hydroxide ion increasing treatment. This created a novel processing method with which the hydroxide ions in ultra-pure water can be utilized to perform clean processing, without any impurities being left behind on the processing surface. This processing method is expected to find application in a very wide range of fields, including the manufacture of semiconductors.
Nevertheless, it is a known fact that the hydroxide ion concentration is extremely low in ultra-pure water, being only about 10
−7
mol/L at 25° C. and 1 atm, and even if the hydroxide ion density is increased with an ion exchange film, the increase is still only by a factor of about 10
3
to 10
4
at most. This represents an ion density of 1/10
4
to 1/10
3
for 1 mol/L (1N) NaOH, and the processing rate is still too low for practical processing purposes.
Meanwhile, washing methods for removing fine impurity metals that adhere to the surface of the material being washed include chemical washing and physical washing. In particular, since electronic circuits are formed on the surface of a semiconductor wafer in a fine pattern on the sub-micron order, any metal contaminants on the surface thereof can have a tremendous effect on the performance of the device, and also lower the yield and hamper cost reduction efforts. Accordingly, a variety of washing methods have been proposed and put to practical use.
Typical examples of chemical washing include washing with an acid or hydrogen fluoride, and fluorocarbon washing, which has become problematic because it leads to depletion of the ozone layer. Typical examples of physical washing include ultrasonic washing in ultra-pure water, and a method in which adhering microparticles are contracted and expanded by cooling or heating the washed material so as to strip them from the surface of the material.
It is not easy, however, to remove impurity metals or impurity metals in an ionic state firmly adhering through interaction (a type of chemical bonding) at the interface of the washed material, without damaging the surface of the material, and conventional washing methods cannot be considered effective. Specifically, the surface of the washed material is corroded by the washing liquid with chemical washing, while physical washing scratches the surface of the washed material. Also, once foreign matter has been removed from the surface of the washed material, it can re-adhere to the same surface, which is extremely difficult to avoid.
In order to eliminate impurity metals adhering through chemical bonding to the surface of a washed material, the inventor predicted theoretically and confirmed through experimentation that a shear flow of at least a specific strength is required on the washed material surface, that is, that the shear flow must have at least a specific velocity gradient, and discovered that it is effective to concurrently use a chemical elution reaction between impurity metals and hydroxide ions in ultra-pure water. As mentioned above, though, the hydroxide ion concentration in ultra-pure water is extremely low, so low that a practical washing efficiency cannot be achieved.
In this prior art situation, the inventor solved all of these problems and perfected the present invention upon recognizing that the removal processi
Ishikawa Toshio
Mori Yuzo
Armstrong Westerman & Hattori, LLP
Japan Science and Technology Corporation
Kornakov M.
Markoff Alexander
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