Semi-epitaxial bcc Ta Growth on Metal Nitride

The crystal structure change of sputtered Ta metal according to the nonmetal underlayer film was studied. The bcc-structure Ta was grown on TaNx, NbNx and bcc Mo underlayer films, whereas tetragonal-structure Ta was grown on glass, Ta2O5 and some metals. The crystal structure of Ta varied from tetragonal to bcc according to the N composition of the TaNx and NbNx underlayer films. The bcc Ta growth on TaNx was explained in terms of crystal structure compatibility of the Ta lattice arrangement between TaNx and bcc Ta, and tetragonal Ta growth on Ta2O5 film could be explained by partial Ta lattice matching between Ta2O5 and Ta crystals. Bcc Ta on the TaNx film gave a low resistivity of 25 µΩcm, in contrast to that of conventional tetragonal Ta of 180 µΩcm. The resistivity of Ta anodic oxide was increased by five orders of magnitude by adding N compared to that of conventional Ta anodic oxide. Low-resistivity bcc Ta on TaNx and high-resistivity TaN anodic oxide are applied as gate bus lines of TFT-LCD.