Cleaning and liquid contact with solids – Processes – Using solid work treating agents
Reexamination Certificate
2001-05-02
2004-01-13
Gulakowski, Randy (Department: 1746)
Cleaning and liquid contact with solids
Processes
Using solid work treating agents
C134S002000, C134S006000, C134S025500, C134S032000, C134S034000, C134S037000, C134S902000, C438S906000, C451S038000, C451S039000, C451S060000, C510S175000
Reexamination Certificate
active
06676766
ABSTRACT:
BACKGROUD OF THE INVENTION
Field of the Invention
The present invention relates to a method and system for cleaning a substrate, such as a semiconductor wafer, a substrate for a liquid crystal display (LCD), a glass substrate for use in manufacture of a plasma display panel (PDP) or the like as well as a method and apparatus for making a sherbet-like cleaning composition for cleaning of the substrate.
In Japanese Patent Laid Open No. 11-151467 in the name of the assignee, a method and system for cleaning a substrate by scrubbing has been proposed.
The proposed system comprises an apparatus for producing snow ice crystal grains of a predetermined size, holder means for holding a substrate to be cleaned, supply means for separately supplying to the substrate the snow ice grains for mechanical cleaning of the substrate and a chemical agent for chemical cleaning of the substrate to form a sherbet-like aggregate over each of the opposite surfaces of the substrate, means for urging the sherbet-like aggregate against the opposite surfaces of the substrate and means for moving the aggregate relative to the substrate surfaces. The snow ice producing apparatus is a cyclone type one and is constructed in such a manner that the ice crystals are created by injecting cooling air into the cyclone chamber, as is well-known to those skilled in the art.
In view of the fact that the chemical cleaning of the substrate surfaces may be accomplished by the chemical agent and also the mechanical cleaning thereof can be effected by the scrubbing action of the snow ice grains during the movement of the sherbet-like aggregate relative to the substrate while urging the aggregate against the substrate surfaces, the proposed cleaning system can provide effective and efficient cleaning of the substrate without causing any appreciable damage thereto. In the following description, this process will be referred to as a “scrubbing cleaning process”.
However, the conventional scrubbing cleaning process as described above has the following drawbacks:
Firstly, after the semiconductor wafer is subject to a polishing process, in particular, chemical-mechanical polishing (CMP) and then often exposed to pure water, numerous contaminant particles can be found on the polished wafer surfaces. Typically, these particles are adhered to the wafer surfaces mainly due to the effect of the surface tension force of the pure water remaining thereon. A greater scrubbing or shearing force is required in order to remove the particles from the wafer surfaces to overcome the surface tension force of the pure water. On the other hand, the increased scrubbing force resulting from the movement of the sherbet-like aggregate relative to the substrate can adversely affect the polished wafer surfaces, depending on the type of the substrate and the amount of the scrubbing force applied on the substrate surfaces.
Secondly, it is difficult to provide the aggregate of the snow ice grains and the chemical agent with the desired characteristics, for example, a suitable consistency. Also, it is necessary to control the size of the snow ice grains in accordance with the type of the substrate to enable efficient scrubbing and cleaning of the substrate. More specifically, in view of the fact that microscopic surface asperities can vary in size in accordance with the type of the substrate, it is important that the snow ice grains have a size substantially smaller than that of the depressions of the substrate surfaces in order to enable to be removed or scrapped dust particles entrapped in the pits of the substrate surfaces. As can be appreciated by those skilled in the art, oversized snow ice grains may fail to remove the dust particles from the substrate surfaces.
The scrubbing cleaning process utilizes an on-site mixing at the substrate surfaces where the properly sized snow ice grains and the chemical agent are mixed to produce a sherbet-like material for chemical and mechanical cleaning of the wafer. Such an on-site mixing may not provide enough control to obtain sherbet having the desired nature or consistency than an off-site mixing process. Also, it is somewhat difficult to control the size of the snow ice grains after the on-site mixing. Further, the on-site mixing process may prevent effective production of the sherbet-like material.
Thirdly, in the conventional snow ice making apparatus, a heat exchange between the spray of the pure water and the cooling gas is brought about by a heat conduction, i.e., via a direct contact of this spray with the cooling gas within the cyclone chamber. The effectiveness of heat exchange depends on various factors, for example, the time during which the pure water spray is in contact with the cooling gas and the contact area therebetween. As a practical matter, successful control of these factors is difficult. Further, the ice snow grains tend to adhere to the inner wall of the cyclone chamber to grow into a block or column of ice thereon, which black or column of ice may prevent the heat exchange between the water spray and the cooling gas as it creates an impedance to the rotational movement thereof within the cyclone chamber, thereby make it difficult to establish a suitable contact timelength and a contact area amount, which in turn may also contribute to reducing heat exchange effectiveness. Such a process and the on-site mixing process can result in inefficient production of the sherbet-like material.
Supercooling of the pure water in a mixing vessel to below its freezing point by use of an external cooling means does not contribute to improving the effectiveness of making the sherbet-like material because the ice crystals tend to form simultaneously on the cooled inner wall of the chamber which the pure water comes into contact with, to grow into a block of ice all over this inner wall overtime rather than to grow into ice grains.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a new method and apparatus for making a sherbet-like cleaning composition having the characteristics suitable for the type of the substrate to be scrubbed and cleaned.
It is another object of the present invention to provide a new method and system for cleaning a substrate in an efficient and effective manner using the sherbet-like cleaning composition while avoiding the limitations of the conventional method and system as described above.
With these above objects in mind, the present invention provides a method for cleaning a substrate, comprising the steps of providing a sherbet-like cleaning composition consisting of snow ice crystal grains and a liquid organic chemical agent and moving the sherbet-like cleaning composition relative to the substrate to be cleaned along at least one of the surfaces thereof, the organic chemical agent of the composition operating to reduce the adhesion of residual particles to the at least one surface of the substrate, the sherbet-like cleaning composition having a consistency allowing the particles on the at least one surface of the substrate to be entrained therein to thereby enable the particles to be removed from the at least one surface of the substrate.
Preferably, the step of providing the sherbet-like composition includes the steps of mixing the liquid organic agent and pure water in a predetermined mixing ratio in a mixing vessel to form a mixture, and supercooling the mixture uniformly therethroughout at a predetermined temperature lower than the freezing point of the pure water and greater than that of the organic chemical agent while stirring the mixture in a manner permitting the pure water to change into snow ice crystal grains.
Preferably, the stirring step includes the steps of creating vortices in the mixture, growing the vortices and diffusing the grown vortices in the mixture.
Preferably, the step of providing the sherbet-like composition can further comprise the step of controlling the mixing ratio and/or the degree of supercooling of the water that produce the snow ice particles having a predetermined ratio by volume in the pure water,
Furusawa Masami
Harano Riichiro
Joya Satoshi
Gulakowski Randy
Jacobson & Holman PLLC
Kornakov M.
Sprout Co., Ltd.
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