Cleaning compositions for solid surfaces – auxiliary compositions – Cleaning compositions or processes of preparing – For cleaning a specific substrate or removing a specific...
Reexamination Certificate
1999-01-14
2002-02-12
Gupta, Yogendra N. (Department: 1751)
Cleaning compositions for solid surfaces, auxiliary compositions
Cleaning compositions or processes of preparing
For cleaning a specific substrate or removing a specific...
C510S257000, C134S001000, C134S001300, C134S002000, C134S003000
Reexamination Certificate
active
06346505
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a cleaning solution for electromaterials. In particular, the present invention relates to wet cleaning of electromaterials using a cleaning solution that can simultaneously remove metal impurities, natural oxidation films, and particle contamination. The present invention is capable of removing both metal contamination and particles adhered to the surface of electromaterials without using surface active agents. The present invention also relates to a method of using the cleaning solution.
In the prior art, cleaning of semiconductor silicon substrates, liquid crystal glass substrates, and photomask quartz substrates is done by cleaning at high temperatures with concentrated chemicals, including hydrogen peroxide, then rinsing with ultrapure water. The hydrogen peroxide based chemical solutions used in the prior art include: a solution of hydrogen peroxide and sulfuric acid; a solution of hydrogen peroxide and hydrochloric acid; a solution of hydrogen peroxide and ammonia; and the like. This method of cleaning is called the RCA cleaning method. The RCA cleaning method is an effective method for removing metals from a semiconductor surface. At the same time, particles adhering to the surface of the semiconductor are also removed. However, the RCA has several problems. Since a large volume of hydrogen peroxide, highly concentrated acids or bases, and the like are used, the cost for chemicals is high. In addition, using the RCA methods results in costs for rinsing with ultrapure water, processing resulting contaminated waste streams, and removing contamination from contaminated air streams. In addition, local exhaust ventilation and replacement of exhausted air with tempered clean air incurs costs. Recently, wet cleaning processes have been reassessed in order to reduce costs, and to reduce the negative environmental impacts including using high volumes of water, generating a high volume of waste chemicals and releasing waste gases.
The prior art includes a five step process as an alternative to the RCA cleaning method. First, organic contamination and metal contamination are removed from the surface of the electromaterial using ultrapure water containing ozone. Second, remaining particle contamination is removed by transmitting ultrasonic waves while applying ultrapure water containing hydrogen fluoride, hydrogen peroxide and surface agents. Third, residual surface active agents are removed by transmitting ultrasonic waves while applying ultrapure water containing ozone. Fourth, the chemical oxidation film generated in step 3 is removed using dilute hydrofluoric acid. Fifth, a final rinse is conducted by transmitting ultrasound waves while rinsing with ultrapure water. This process uses dilute chemical solutions at room temperature. It results in cost savings related to reduced chemical and energy costs. However, since the process requires five steps, it would be advantageous to have a less complex cleaning process.
Also in the prior art, is a process of removing natural oxidation film from a silicon surface, which involves processing with hydrofluoric acid chemicals at room temperature. In particular, a “last hydrofluoric acid” step using a dilute hydrofluoric acid is often used for cleaning silicon wafers. The purpose of hydrofluoric acid cleaning is to remove the natural oxidation film that may be generated on the silicon surface during either an acidic chemical processing step, a rinse processing, or when a film is generated while the wafer is left standing.
Hydrofluoric acid cleaning also removes metal impurities which have been taken up inside the natural oxidation film. However, with hydrofluoric acid cleaning, particles adhering to the electromaterial surface cannot be removed. As a result, this step must always be combined with another cleaning process. For example, APM cleaning using a solution containing ammonia and hydrogen peroxide is often used in combination with the hydrofluoric acid cleaning process. Furthermore, a cleaning solution containing hydrofluoric acid has a limited oxidation strength. In this case, complete removal of metal impurities with a high oxidation-reduction potential, such as copper, can be difficult.
A cleaning process has been proposed to improve upon the RCA and other methods of the prior art, which uses a mixture of hydrofluoric acid and hydrochloric acid in water. A cleaning solution having the following ratio is used: hydrofluoric acid (50 weight %), hydrochloric acid (35 weight %), and ultrapure water at a weight ratio of 0.2:1:100. When this solution is used, metals including but not limited to iron, chromium, nickel, copper, and aluminum, can be efficiently removed, even at room temperature. Furthermore, if ultrapure water with low dissolved oxygen gas concentration is used, or if the amount of hydrofluoric acid is increased, the natural oxidation film can be removed, in addition to metal.
Another proposed cleaning solution consists of a mixture of hydrofluoric acid and nitric acid in solution. Although this cleaning solution is highly effective in removing metal, it performs poorly in removing particles. As a result, this cleaning solution must be used in combination with an APM cleaning solution in order to remove particles. Consequently, a cleaning solution for electromaterials is sought that can remove metal impurities, the natural oxidation film from the electromaterial surface, as well as particles adhering to the surface.
OBJECTS AND SUMMARY OF THE INVENTION
In light of the above, it is an object of the present invention to provide a cleaning solution for electromaterials that overcomes the limitations of the prior art.
An object of the present invention is to provide a cleaning solution for electromaterials which can, during wet cleaning, remove not only metal impurities and natural oxidation film, but also particle contamination as well.
It is a further object of the present invention to provide a simpler cleaning solution for electromaterials that can remove metal and particle contamination from the surface of electromaterials while avoiding the use of active surface agents.
The present inventors have conducted intensive research in order to solve the aforementioned problems. It was discovered that a cleaning solution of hydrogen fluoride, or a solution of hydrogen fluoride and either hydrogen chloride or nitric acid, combined with either dissolved hydrogen gas or dissolved oxygen gas, is effective in removing particles adhering to the surface of electromaterials. At the same time, the cleaning solution has various cleaning capabilities including metal contamination removal, natural oxidation film removal, and complete hydrogen termination of the electromaterial surface.
In addition, the present inventors have realized that if the surface active agents used in the five step process of the prior art can be eliminated, then steps 3 and 4 become unnecessary. After intensive research, it was discovered that particle and metal contamination on the surface of electromaterials can both be removed by using a solution of hydrogen fluoride, hydrogen peroxide and dissolved oxygen gas. The present invention is a result of these discoveries.
Briefly stated, the present invention is a cleaning solution for electromaterials, including an aqueous solution containing hydrogen fluoride and dissolved hydrogen gas.
An embodiment of the present invention is a cleaning solution for electromaterials, including an aqueous solution containing hydrogen fluoride and dissolved oxygen gas.
Another embodiment of the present invention is a cleaning solution for electromaterials, including an aqueous solution containing hydrogen fluoride, hydrogen peroxide and dissolved oxygen gas.
Another embodiment of the present invention is a cleaning solution for electromaterials, containing a solution of hydrogen fluoride, either hydrogen chloride or nitric acid, and dissolved oxygen gas.
Another embodiment of the present invention is a cleaning solution for electromaterials, containing a solution of hydroge
Ida Junichi
Mizuniwa Tetsuo
Morita Hiroshi
Gupta Yogendra N.
Kurita Water Industries Ltd.
Morrison Law Firm
Webb Gregory E.
LandOfFree
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