Interest has developed in the use of nanoparticle films in the fabrication of high-performance electronic devices. For example, studies have been conducted concerning the application of nanoparticle films in fabrication of high-performance semiconductor devices, such as single electron transistors and floating gate field effect transistors, large capacity magnetic recording media, etc.
Further interest in these studies pertains to the formation of a nanoparticle based monolayer film with a particle density as high as 1012 particles/cm2 or more. Another interest is in the uniform formation of a nanoparticle based monolayer film with high particle density (1012 particles/cm2 or more) formed on the entire surface of a substrate having a large surface area such as an 8- or 12-inch wafer. Uniform formation of a nanoparticle based monolayer film with high particle density on a large-scale substrate is desirable for cost-effective mass production of high-performance semiconductor devices.
A method of forming a nanoparticle film using spin-coating is discussed in Hong et al. “Controlled two-dimensional distribution of nanoparticles by spin-coating method”, Applied Physics Letters 80(5): 844-846 (2002). According to Hong et al., a colloidal solution of Co and Ag nanoparticles in toluene and ethanol may be applied onto a Si or SiO2 wafer. Subsequently, the wafer may be spun at a predetermined rate (RPM) in order to disperse the colloidal nanoparticles and to deposit a uniform nanoparticle film across a large area of the wafer. The density of nanoparticles including the nanoparticle film can be controlled by varying the concentration of the colloidal nanoparticles. However, this method of nanoparticle film formation by spin-coating may have several disadvantages, for example, the particle density of a nanoparticle based monolayer film to be achieved may be limited. As shown in Hong et al. at FIG. 1, as the particle concentration of a colloidal solution increases, the particle density on a Si or SiO2 substrate increases. Also, according to Hong et al., a further increase of the molar concentration of the colloidal solution results in the formation of three-dimensional nanoparticle clusters. Thus, a bi- or multi-layered nanoparticle film is formed instead of a nanoparticle based monolayer film with a higher particle density.
Furthermore, Hong et al. states that the substrate surface be wet with the colloidal solution in order to form a uniform nanoparticle film. As a result, this method may restrict the type of substrate and the type of colloidal solution solvent that can be used.
Kodama et al. discuss a method of forming a FePt alloy film using a spin coater in “Disk substrate deposition techniques for monodisperse chemically synthesized FePt nanoparticle media,” Applied Physics Letters 83(25):5253-5255 (2003). According to this method, a substrate is moved to a clean chamber by a robot, after which the clean chamber may be sealed and filled with hexane (and hexane gas to prevent the evaporation of the hexane). Then, a dispersion solution of the FePt particles in hexane is applied to the substrate, which is then spun using the spin coater. The spinning rate is increased to uniformly deposit the FePt particles on the entire surface of the substrate. While Kodama et al. describes the formation of a FePt alloy film, it is silent about the formation of a FePt alloy monolayer film. Further, the method employed in Kodama et al. refers to complicated process equipment and, in general, is not a cost-effective process.
U.S. Patent Application Publication No. 2004/0071924A1 to Yang et al. discusses a method of forming a nanoparticle based monolayer film in which nanoparticles are deposited on the chemically modified patterned regions of the substrate so that the nanoparticles self-assemble on the patterned regions and chemically bind with the substrate. At least one drawback to the method of Yang et al. may be that a nanoparticle layer is limitedly formed on predetermined regions of the substrate. Thus, the nanoparticle layer may only be formed only on the patterned regions of the substrate, not on the entire surface of the substrate. Consequently, this method may be applied to a post-patterning deposition process rather than a post-deposition patterning process.
A further drawback may be that the surface modifying layer (SML) chemically binds directly with the nanoparticles. As a result of the direct chemical bond between the SML and the nanoparticles, a bi- or multi-layered nanoparticle film may also be formed, in addition to a nanoparticle based monolayer film.