Coating processes – Centrifugal force utilized
Reexamination Certificate
1998-09-04
2002-12-17
Beck, Shrive P. (Department: 1762)
Coating processes
Centrifugal force utilized
C427S300000, C427S420000, C427S421100, C427S425000, C118S052000, C118S407000, C118S421000, C118S501000
Reexamination Certificate
active
06495205
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to the precision coating of surfaces and more particularly to extrusion coating substrates presenting a non-linear leading edge to provide a uniform, precision, coating.
BACKGROUND OF THE INVENTION
It is often necessary or desired to provide a coating of a particular substrate. For example, in the micro-electronics industry it is often desired to coat a substrate used in the manufacture of integrated circuits for further processing. Often it is required that such coatings be applied in a very thin coat, such as a thin coat of photoresist used in masking and etching a silicon substrate for manufacturing integrated circuits, which is uniform across the entire surface of the substrate. However, as the coating is so thin, very minute variances in its thickness may not be acceptable.
Accordingly, the prior art has relied upon various methods for providing a continuous, uniform, thin coating of a substrate. However, in the past these methods have been inefficient and, therefore, prone to waste.
For example, a commonly relied upon prior art method of coating a substrate is spin coating. Here a coating material, typically suspended in a solvent based fluid, is deposited in a pool on the substrate to be coated, generally at or near the center of the surface to be coated. Thereafter, the substrate itself is rotated at a high speed about an axis normal to the surface to be coated. Centrifugal forces created by the rotation of the substrate cause the pool of material to migrate toward the edges of the substrate. Accordingly, rotating the substrate for a sufficient length of time at a proper speed will result in a substantially uniform coating having a desired thickness, where a sufficiently ductile coating material is present.
However, the spin method of coating the substrate necessarily results in an amount of coating material being expelled from the surface to be coated. In practice, the expelled portion of coating material may be as great as 90-95% of the material initially deposited in the pool on the substrate. Typically this material which is expelled from the surface is lost as there are often very stringent purity requirements and/or the solvents suspending the material being quick to evaporate making their recycling difficult or impossible. Moreover, spin coating is generally not completely effective in evenly distributing a very viscous coating material.
These coating materials are generally very expensive and therefore the waste that occurs in coating the substrate can be an important consideration. Accordingly, although providing a reliable method for achieving a uniform coating of a substrate, the prior art spin methods introduce an undesired level of waste. Moreover, the amount of waste increases as the size of the substrate increases causing such inefficiencies to be increasingly unpalatable as the industry moves to larger and larger substrates, e.g., 3.5 generation LCD technology and 12 inch silicon wafers.
It should also be appreciated that the excess material discharged from the above mentioned spin technique presents, at a minimum, a requirement for the subsequent handling and cleanup of this substantial amount of unused material. Because of purity of material requirements this discharged material must often be disposed of. However, often times this material, and/or its solvent carrier, are hazardous materials and must be handled with extreme care as well as being disposed of in accordance with stringent guidelines. Likewise, often the solvents utilized in cleanup of such discharged material are hazardous, thus compelling their restricted use.
Additionally, the prior art spin methods of coating the substrate can result in the outer edges and/or the back surface of the substrate also being coated by the material. This can be undesired as subsequent handling of the substrate, having its edges coated, may result in the chipping and peeling of the coating on these edges which may continue to the surface for which a uniform contamination coating is desired. Moreover, coating of these surfaces may also result in the contamination of the surface desired to be coated.
Furthermore, the solvents carrying the desired coating materials in suspension may be highly unstable and, therefore, prone to rapid dissipation, such as through evaporation. Accordingly, uneven coating may result in the aforementioned spin technique where, for example, an appreciable time between depositing the pool of material for spinning, or where the substrate surface to be coated is large.
The above mentioned spin method of coating a substrate, although acceptable for use in coating certain shaped substrates, such as a small circular silicon wafer used in manufacturing integrated circuits, may not provide acceptable results in coating other shaped substrates. For example, spin coating a square or irregularly shaped substrate may result in windage problems when the substrate is spun which cause the coating material to cure in a non-uniform coating. Likewise, because of longer distances between the center of the substrate, where the pool of coating material is deposited prior to spinning, and the outer edges associated with the substrate's irregular circumference, spinning the coating material onto these substrates may not provide uniform coverage. Similarly, a large silicon wafer may present sufficient distances between the center of the substrate and the outer edges, although presenting a consistent distance, that uniform coverage may be impossible by spin coating alone due to the drying of the coating material as it migrates out along the radius of the substrate being spun. Moreover, due to the fact that the velocity of the outside edge of the large wafer may be relatively large, windage related patterns in the coating may result.
Accordingly, a need exists in the art for a system and method for providing a uniform coating of a desired thickness on a substrate, including substrates of various shapes and sizes, while providing efficient use of a coating material.
A further need exists in the art for the system and method for coating a substrate to minimize coating of surfaces of the substrate which are not desired to be coated, such as a circumferential edge of a surface to be coated.
A still further need exists in the art for the system and method for coating a substrate to provide for simple and efficient cleanup of any excess coating material in order to reduce the time and effort required in cleaning such excess material as well as reduce the amounts of solvents required in such cleanup.
SUMMARY OF THE INVENTION
These and other objects, features and technical advantages are achieved by a system and method which utilizes an extrusion or other controlling delivery process to deliver a coating material upon a substrate surface in a uniform coating of a predetermined thickness. After initial deposit of the coating material upon the substrate surface by the extrusion process, the substrate may be spun in order to provide a more uniform coating or a coating of a desired thickness. Alternatively, such as (1) where a coating material is initially deposited in a very viscous state or (2) where a more thin coating is desired than is consistently producible through extrusion alone or for surfaces presenting a high aspect ratio surface to be coated. Spinning of the substrate may be omitted in producing the designed uniform coating according to the present invention.
A preferred embodiment of the present invention utilizes an extrusion die or head providing linear, or substantially linear, extrusion of a coating material at a precisely controlled rate, i.e., the extrusion head moves in a linear motion with respect to the surface to be coated. By selecting the extrusion head presenting an extrusion orifice to be of a sufficient width to correspond to a full width of the substrate to be coated, a single pass of the extrusion head along the substrate, a single pass of the substrate with respect to the extrusion head, or a combination of both, may be utilized
Gibson Gregory M.
Poonawala Altaf A.
Snodgrass Ocie T.
Soliz Rene
Beck Shrive P.
Crockford Kirsten A.
Ehrlich Henry L.
FAStar, Ltd.
Winstead Sechrest & Minick P.C.
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