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After deposition method of thinning film to reduce pinhole defectsRelated Patent Categories: Semiconductor Device Manufacturing: Process, Making Field Effect Device Having Pair Of Active Regions Separated By Gate Structure By Formation Or Alteration Of Semiconductive Active Regions, On Insulating Substrate Or Layer (e.g., Tft, Etc.)After deposition method of thinning film to reduce pinhole defects description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070037325, After deposition method of thinning film to reduce pinhole defects. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation of U.S. Application Ser. No. 11/029,812 filed Jan. 5, 2005, the disclosure of which is hereby incorporated by reference herein. BACKGROUND OF THE INVENTION [0002] The present invention relates to the processing of thin films, such as those used in the processing of very small structures such as microelectronic devices, for example. [0003] The industry goal of reducing the size of microelectronic devices places greater demands on photolithography as a technology. As more aggressive solutions are pursued to meet such increased demands, thinner polymer films have to be used as anti-reflective coatings (ARCs) and in photoresist imaging layers. The use of thin polymer films, unfortunately, most often leads to device defects, such as those that occur due to long range van der Waals forces. Due to Van der Waals forces, localized thinning of a polymer film on a substrate occurs when the polymer film has insufficient thickness to overcome a tendency to dewet from the substrate. This leads to dewetting defects, also known as "pinhole" defects. An example of this phenomenon is illustrated in FIG. 1 for a bottom anti-reflective coating (BARC) layer disposed on a substrate of silicon dioxide. [0004] FIG. 1 illustrates a free energy curve 10 for a BARC layer disposed on a substrate of silicon dioxide, and a second curve 12 being the second derivative of the free energy curve 10. The BARC layer becomes unstable and has a tendency to dewet catastrophically at a thickness (50 nm) below which the free energy curve 10 turns sharply lower and heads negative. Such catastrophic dewetting is referred to as spinodal dewetting. The location of the zero in the second curve 12 illustrating the second derivative of free energy indicates a crossover point at about 85 nm between a film that dewets spinodally below that thickness and dewets via nucleation and growth of holes above that thickness. [0005] As further shown in FIG. 1, as the overall film thickness is increased, the free energy of the film passes through a maximum and starts to decrease slowly as the film thickness continues to be increased. In the thickness regime just beyond the thickness at which the film spinodally dewets, the film is metastable and can still dewet via a different mechanism. If at some localized point in the film the thickness falls below the 85 nm thickness of the crossover point, the film becomes locally unstable and dewets by a mechanism known as dewetting via nucleation and growth of holes. Consequently, by examining the curves presented in FIG. 1, a BARC film having a thickness of 80 nm, which is less than the crossover point thickness of 85 nm, is highly unstable, and dewets spinodally, rapidly dewetting to droplets. On the other hand, a BARC film having a thickness of 110 nm, does not dewet spinodally, but can still dewet locally via nucleation and growth of holes. When the thickness of the film is increased, however, the occurrence of defects becomes less likely. For example, a BARC film having a thickness of 200 nm is so far from the crossover point on the free energy diagram that random local fluctuations in film thickness no longer result in local instability of the film. [0006] Heretofore, there has been no known solution to this problem other than to increase the thickness of the film, which runs contrary to the industry goal of reducing device size. In addition, advanced lithography processes call for reductions rather than increases in film thicknesses, especially since a thick BARC film unnecessarily increases the difficulty of etching through the BARC film. Similarly, a thick photoresist imaging layer also increases risk of line pattern collapse and reduces the process window. [0007] Currently, it is common to utilize surface treatments such as hexamethyldisilazane (HMDS) prime, prior to applying a coating such as an ARC or a photoresist. Such treatment promotes adhesion by changing the surface tension, and can also affect wettability of the coating by changing the spreading coefficient. However, even when a coating has a positive spreading coefficient, pinholes can still form when instability is present due to long range van der Waals forces. Therefore, pre-treating a surface with a surface treatment such as an HMDS prime, while affecting the size and shape of dewetting defects, does not prevent them from appearing in the first instance. [0008] Accordingly, it would be desirable to provide a method by which the thickness of a film utilized in semiconductor fabrication can be reduced while precluding defects in the film caused by long range van der Waals forces. SUMMARY OF THE INVENTION [0009] According to an aspect of the invention, a method is provided for forming a thin film in which a film having a first thickness is deposited over a substrate, the first thickness being greater than a thickness at which the initially deposited film begins to dewet from the substrate. The initially deposited film is then stabilized to form a stabilized film. Thereafter, the stabilized film is then thinned to a second thickness, such that the resulting film now has a smaller thickness than the thickness at which the initially deposited film would begin to dewet from the substrate. However, because of the prior stabilization, the film now having the smaller thickness remains free of dewetting defects. [0010] According to another aspect of the invention, a method is provided for forming photoresist patterns. In such method, an antireflective coating (ARC) is formed to overlie a substrate, the ARC having a negative Hamaker constant. Thereafter, a photoresist film is initially deposited to a first thickness over the ARC, such that the first thickness is greater than a thickness at which the photoresist film begins to dewet from the substrate when deposited directly onto the ARC. The initially deposited photoresist film is thereafter stabilized, e.g., such as by heating to cause a solvent to leave, to form a stabilized photoresist film. The stabilized photoresist film is then thinned to a second thickness, in which the second thickness is lower than the thickness at which the initially deposited photoresist film would begin to dewet from the ARC. However, the photoresist film having the reduced, second thickness remains free of dewetting defects. Thereafter, the thinned photoresist film is photolithographically patterned to form photoresist patterns. [0011] Preferably, the thus formed photoresist patterns are subsequently used to pattern the underlying ARC, and features of the substrate then patterned using the photoresist patterns and the ARC patterns. BRIEF DESCRIPTION OF THE DRAWINGS [0012] FIG. 1 is a graph illustrating free energy and a second derivative thereof for an anti-reflective coating (ARC) as a function of a thickness of the film overlying a substrate. [0013] FIGS. 2 through 4 are sectional diagrams illustrating stages in a method of depositing and thinning a film after deposition according to one embodiment of the invention. [0014] FIGS. 5 and 6 are sectional diagrams illustrating stages in a method of depositing and thinning a film after deposition according to another embodiment of the invention. [0015] FIG. 7 is a graph depicting a free energy of a system for different intermediate films of different thicknesses. [0016] FIG. 8 is a diagram illustrating a principle of determining a Hamaker constant for a system including an overlayer film overlying an intermediate film disposed on a substrate. [0017] FIGS. 9 through 13 illustrate stages in a method of patterning a substrate according to an embodiment of the invention. DETAILED DESCRIPTION [0018] Accordingly, stages in processing according to a first embodiment of the invention are illustrated in FIGS. 2 through 4. As illustrated in FIG. 2, in an initial stage of processing a film 102 is deposited to overlie a substrate 100. By "substrate" is meant a base region, or alternatively, an exposed layer of a multiple layered substrate, in which case the exposed layer has significantly greater thickness than the thickness of the film. The characteristics of the film and the substrate are such as those discussed above. That is, the film 102 is subject to spinodal dewetting from the substrate 100 when its thickness is less than the thickness at the crossover point 12 (FIG. 1) determined from the second derivative of its free energy curve. [0019] In view of the above concerns, the film 102 is deposited to a thickness which is substantially greater than the thickness at point 12 in FIG. 1, such that a film is obtained which is substantially free of pinholes and other similar defects. The film is deposited to a greater thickness than that at which the deposited film ordinarily begins to exhibit dewetting defects, e.g., pinholes, such as caused by nucleation and growth of holes. Continue reading about After deposition method of thinning film to reduce pinhole defects... Full patent description for After deposition method of thinning film to reduce pinhole defects Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this After deposition method of thinning film to reduce pinhole defects patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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