Effect of enhanced nitridation in PECVD-Ti process for sub-0.2 μm metal bit-line common contact process

The implementation of W bit-line enabled the integration of n+ and p+ common contact process at bit-line level. Despite the advantages of the common contact process such as chip-area reduction and elimination of the burden associated with MC dry etch, the immediate implementation of the common contact is difficult due to large increase of p+ contact resistance with high thermal budget capacitor process. The results of the present investigation indicate that the thickness of TiSi₂ layer must be minimized in order to prevent the out-diffusion of boron into silicide layer. However, simply reducing the thickness of TiSi₂ presents another problem since it leads to a discontinuous layer of TiSi₂. Heavily increasing the dosage of p+ plug implantation, which is another way of preventing the depletion of boron dopants, resulted in degradation of p+ contact resistance. Therefore, the dopant out-diffusion alone cannot explain the degradation of p+ contact resistance. In order to minimized the thickness of TiSi₂, enhanced nitridation after deposition of PECVD-Ti was tested and resulted in effective reduction of the p+ contact resistance by 25%. The TEM and SIMS analysis showed that the additional growth of TiSi₂ during high thermal budget post annealing was suppressed by the enhanced nitridation. The mechanism responsible for reducing the p+ contact resistance by the enhanced nitridation is attributed to the prevention of the dopant depletion at the interface between TiSi₂ and Si due to the suppressed formation of additional TiSi₂