TiN films were prepared by electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) using $TiCl_4,\ N_2$ and $H_2$ as reactants with variations in $H_2$ flow rate, microwave power, $O_2$ flow rate, deposition temperature and substrate bias. The effects of deposition parameters on composition, structure, resistivity, step coverage and barrier property of TiN films were studied. The thickness of the TiN film was measured using α-step and scanning electron microscopy (SEM). The resistivity of the TiN film was calculated from the film thickness and sheet resistance measured by a four point probe. The concentration of TiN film was Auger electron spectroscopy (AES). The step coverage of the film was observed with SEM on a 1.5㎛(depth)×0.4㎛(diameter) (A.R.=3.8) contact hole. Diffusion barrier property of the TiN films (thickness = 15 ~50nm) was studied by annealing the Al/TiN/Si structure at 500~600℃ for 30min in Ar atmosphere. Degradation of the structure was studied using AES and SEM.
As the $H_2$ flow rate increases, oxygen and carbon contents within the films decrease to the detection limit of AES. This indicates that ECR hydrogen plasma helps the removal of oxygen and carbon. However, further increase in the $H_2$ flow rate to 75sccm causes increase in the oxygen and carbon contents.
The increased impurity contents at a high $H_2$ flow rate results from the cooling effect of hydrogen. These two effects of hydrogen, reducing the impurity content and cooling the plasma, constrain the appropriate $H_2$ flow rate. Without $H_2$, TiN film is hardly deposited on the side wall of contact hole and the conformality around the step edge is very poor. Whereas, with $H_2$ bottom coverage and side coverage are conformal, and conformality at the step edge is very good.
The increase in microwave power resulted in decrease in deposition rate, resistivity and impurity content. As the decomposition and reaction of $TiCl_4$ and $N_2$ become more active and the reducing power of $H_2$ increases with microwave power the amount of chlorine and oxygen impurities becomes reduced. The decrease in resistivity at higher microwave powers can be explained in terms of the decreased impurity level and the film densification. The increase in deposition temperature resulted in decrease in resistivity and impurity content. Chlorine is not detected even at 30℃. Some microcracks were formed for the film deposited at 30℃ probably due to large stress induced by the sharp change in the substrate temperature during deposition. The crystallinity of TiN films is not varied with the deposition temperature. The bottom coverage of the TiN film was about 30% when deposited below 200℃ and increased to 45% above 300℃. The increase in bottom coverage with increasing deposition temperature was attributed to the enhancement of surface diffusion of the reactants.
Applying a bias to the substrate could modify the energy, flux and directionality of the incident ions, which in turn could affect the bottom coverage as well as film quality. The TiN film deposited with substrate bias shows an improved bottom coverage (65%) on a 1.5㎛×0.4㎛ contact hole. The positive ions of the reactants gas was important in the deposition reaction of TiN film. The negative bias applied to the substrate made the ions more directional to the bottom of the contact hole so that the ion flux at the bottom incresed, resulting in the improvement of the bottom coverage of TiN film. Application of substrate bias improved not only the bottom coverage but also the diffusion barrier property without sacrificing the film quality. The 15nm thick TiN film prepared with substrate bias showed reliable barrier property at 500℃ for 30min.
