Effects of substrate bias and nitrogen flow ratio on the resistivity, density, stoichiometry, and crystal structure of reactively sputtered ZrNx thin films

Thin films of ZrNx were prepared by reactive rf magnetron sputtering from a Zr target in an Ar+N2 atmosphere, with different substrate biases (zero to −200V) and nitrogen flow ratios (0.5%–24%). The resistivity, density, stoichiometry, and crystal structure of ZrNx films were investigated. With 2% of nitrogen flow ratio, all ZrNx films exhibit the cubic ZrN crystal phase, regardless of the magnitude of substrate bias. The zero-biased ZrNx film contains substantial oxygen and shows high resistivity. Once a negative bias is applied to the substrate, the incorporated oxygen in ZrNx films can be reduced and the (111)ZrN preferred orientation is enhanced. Resistivity as low as 67μΩcm can be attained with −200V of substrate bias. At −200V of substrate bias, all films show the ZrN phase when the nitrogen flow ratio varies from 0.5% to 24%. However, the nitrogen content in ZrNx films increases continuously with the increasing nitrogen flow ratio. Resistivity of ZrNx films first decreases (0.5%–2%), and then increases with increasing nitrogen flow ratio (2%–24%). The best resistivity is obtained for the ZrNx film sputtered with 2% of nitrogen flow ratio and this sample exhibits the optimum grain size, (111)ZrN prefer orientation, density, and stoichiometry. The connection among the resistivity, density, stoichiometry, and crystal structure of ZrNx films and how they are influenced by the sputtering conditions (substrate bias, nitrogen flow ratio) are discussed.