Proposal of a New Thin-film Forming Technique Applicable to Materials for Next-generation Electronic Devices Successful Development of the Flashing Spray CVD Process

June 5, 2006


In joint collaboration with Professor Jiro Senda of the Department of Mechanical Engineering, Doshisha University (also Head of the Energy Conversion Research Center, Doshisha University), the Horiba Group has developed a new thin-film-forming technique named the flashing spray chemical-vapor-deposition (FS-CVD) process, and has succeeded in forming a thin film of material for next-generation electronic devices. To evaporate the source material for thin-film deposition, the developed process employs the flashing-spray-vaporization method, in which the source material is injected directly into the deposition chamber of a CVD apparatus using a fuel injector for automobile-engine use, a method that can vaporize materials that are difficult to evaporate by the conventional heated-vaporization method. Using this developed process, we have succeeded in depositing a thin film of high-dielectric-constant niobium-peroxide (Nb2O5) on a substrate. Since the developed process eliminates the need for a vaporizer in the CVD apparatus, it is possible to reduce apparatus size and energy consumption. The FS-CVD process is a promising technology for thin-film deposition of materials suitable for next-generation electronic devices, which has been realized by a fusion of heterogeneous technologies: gasoline engine and film formation.

<Details of the developed process>

Chemical vapor deposition (CVD) is a typical thin-film-forming process, in which the source material for thin-film formation (hereinafter referred to as the "source material") is vaporized and then undergoes certain chemical reactions (thermal decomposition and oxidation) on the surface of a substrate, resulting in a thin film deposition on the substrate surface. This process is widely used in fabricating electronic devices, such as LSIs.

Until recently silicon-based oxides or nitrides were most commonly used as the thin-film materials for electronic devices. However, incessant increase in the integration density of electronic devices is boosting the demand for thin films of various functional materials. Forming a thin film of a functional material requires a technique that completely evaporates the source material. With the conventional heated vaporization method, the heating temperature must be increased to ensure complete evaporation. Since the source material undergoes decomposition at high temperatures, complete evaporation is difficult to achieve on a mass-production scale.

The flashing spray CVD (FS-CVD) process developed by us employs the flashing-spray-vaporization method to evaporate source materials, and uses a mixed solution complying with the "two-phase region" concept as the source material. The spray nozzle structure has been improved for finer atomization, which makes it possible to evaporate materials that are difficult to evaporate by the conventional method. Using the FS-CVD process with these features, we have succeeded in depositing a thin Nb2O5 film on a substrate, which is conventionally difficult to achieve. The thin Nb2O5 film exhibits a high dielectric constant and is expected to be a promising material for next-generation electronic devices.

We believe that this success is the result of incorporating an automotive engine fuel injector in the CVD apparatus, i.e., a fusion of heterogeneous technologies.

References

<Description of terms>

  • Next-generation electronic device
    The next-generation electronic device here refers to a very large-scale integrated circuit (VLSI) fabricated on a silicon semiconductor substrate. ICs have been evolving for higher miniaturization and higher density of integration in accordance with MooreÃÔ Law. They are already very close to the physical limits. To find a breakthrough solution, R&D efforts are actively underway in and outside of Japan using various functional materials (including high-dielectric-constant materials).
     
  • Niobium peroxide (Nb2O5)
    Niobium peroxide (Nb2O5) is a high-dielectric-constant material with a relative permittivity of about 60. Thin Nb2O5 film is considered to be a promising material for the capacitors of electronic devices, or dynamic random access memories (DRAM) in particular, whose demand is expected to increase in and after 2013.
     
  • Flashing-spray-vaporization method
    Liquid is sprayed under vacuum to allow rapid boiling and evaporation. With this method, since evaporation occurs as a result of adiabatic expansion and does not require high temperatures, it is possible to suppress the thermal decomposition etc. of the source material. This method is expected to be used in evaporating various source materials. In addition, since this method does not require a vaporizer in which high temperatures must be maintained, or piping to the vaporizer, the CVD apparatus can be designed to be compact, and the energy consumption of the process can be reduced.
     
  • Two-phase region
    The two-phase region refers to a region in which both liquid and gaseous phases are present in equilibrium. Such a region occurs when organic solvent (liquid or gaseous) is mixed with the source material for thin film (liquid). The resultant mixture is higher in vapor pressure and therefore easier to evaporate than the source material alone. It is important to select an organic solvent compatible with the source material.