Photo-induced growth of dielectrics with excimer lamps

The underlying principles and properties of vacuum ultraviolet (VUV) and ultraviolet (UV) radiation (excimer lamps), generated by a dielectric barrier discharge in a rare-gas (Rg) or a mixture of Rg and halogen, are discussed. Compared with conventional sources, these excimer lamps offer narrow-band radiation at various wavelengths from 108-354 nm and over large areas with high efficiencies and high power densities. The variety of available wavelengths offers an enormous potential for new industrial applications in materials processing. Previously, photo-oxidation of silicon, germanium and silicon-germanium and photo-deposition of single- and multi-layered films of silicon oxide, silicon nitride, and silicon oxynitride have been demonstrated by using excimer lamps. This paper reviews the progress on excimer lamp-assisted growth of high dielectric constant (Ta₂O₅, TiO₂ and PZT) and low dielectric constant (polyimide and porous silica) thin films by photo-CVD and sol-gel processing, summarizes the properties of photo-induced growth of Ta₂O₅ films and discusses the effect and mechanism of low temperature UV annealing with 172 nm radiation. Metal oxide semiconductor capacitors based on the photo-induced Ta₂O₅ films grown directly on Si at low temperatures exhibit excellent electrical properties. Leakage current densities as low as 5.2×10^-7 A cm^-2 and 2.41×10^-7 A cm^-2 at 1 MV cm^-1 have been achieved for the as-grown Ta₂O₅ films deposited by photo-induced sol-gel processing and photo-CVD, respectively-several orders of magnitude lower than for any other as-grown films prepared by any other technique. A subsequent low temperature (400°C) UV annealing step improves these to 10^-8 A cm^-2. These values are comparable to those only previously achieved for films annealed at high temperatures between 600°C and 1000°C. These properties make the photo-induced growth of Ta₂O₅ layers suitable alternative to SiO₂ for high density DRAM application.