Halide chemical vapour deposition of Ta2O5

Tantalum oxide, Ta2O5, has a wide range of interesting properties, for instance, a high dielectric constant, protonic conductivity, low leakage current and the material is possibly electrochromic. Tantalum oxide thin films have been prepared using many deposition methods, including chemical vapour deposition (CVD). The most widely used tantalum precursors in CVD of Ta2O5 are Ta(OC2H5)(5) and TaCl5. A drawback with these materials is that carbon and chlorine, respectively, may be incorporated into the films. Furthermore, low temperature films are generally amorphous, and thermal annealing above 700 degrees C is necessary for crystallization. In the present study, Ta2O5 is deposited by CVD using tantalum pentaiodide, TaI5, and oxygen as source materials. For deposition temperatures between 300 and 800 degrees C, smooth, well-adherent and iodine free films were deposited on Si(100) substrates. X-ray diffraction measurements showed that the films were crystalline as-deposited and consisted of the orthorhombic beta-Ta2O5 phase. The dielectric constant for a film deposited at 600 degrees C was measured to be 25.8. (C) 1999 Elsevier Science S.A. All rights reserved.