As the feature size of the trench or the via-hole decreases below submicron, void formation caused by non-conformal step coverage leads to serious problem in the reliability of integrated circuits. In this study, 3-D topography simulators based on the Monte Carlo Method(MCM) and Ballistic Transport-Reaction Model(BTRM) have been developed to investigate the deposition topography on small via-holes for various LPCVD processes.
In the micro-modeling of the LPCVD process, it is considered that the major deposition mechanism is not the surface diffusion but the re-emission of the physisorbed vapor molecules. Thus the sticking coefficient is chosen as the major modeling parameter. The effect of process parameters, such as the deposition temperature and the partial pressure of the vapor source, is included in the modeling through the sticking coefficient. Algorithms for the evolution and the 3-D visualization of the growing surface are based on the equi-volume rate point(EVRP) model.
Using these simulators, the effect of the sticking coefficient and the aspect ratio on the deposition topography has been investigated, which shows that lower sticking coefficient leads to better step coverage and higher aspect ratio leads to worse step coverage. And also the comparison between MCM results and BTRM results reveals that MCM is more accurate than BTRM but MCM requires more computational time than BTRM especially for a low sticking coefficient.
Finally, PRCVD of TiN-MOCVD(TDEAT+NH3) was simulated for three different themperature ramp curves. From the simulation results, we found that with decreasing temperature ramp slope, the deposition rate increases while the step coverage is worsened and by determining the temperature ramp slope appropriately, the deposition rate can greatly be increased with minor step coverage loss.
