Soviet Physics JETP

The modern microelectronics industry has been rapidly growing over the last two decades. The constant need for better components demands accurate knowledge of the physical processes on the atomic level. One of the most important quantities in the field of materials physics is the stopping power of ions inside materials. In this research field, computer simulations are used extensively. In this thesis, new models for calculating electronic stopping of ions in the framework of molecular dynamics computer simulations have been developed. The calculation method uses the local electronic enviroment inside crystalline silicon and nonlinear results from the density functional theory. A comparison to experimental data is done by comparing the experimental and simulated range profiles of ions. An extension to the low energy stopping in a multicomponent target (GaAs) is studied as well. The stopping calculation is extended to higher energies for light ions. Effects of the silicon structure on the range profiles have been studied for the damage accumulation process due to high implantation fluences. Finally, the stopping of small Au clusters in copper and silicon have been studied. The main findings are that we found the reason for the experimentally observed broadening of the range profile of Au clusters in Cu, and that we can now predict the range profiles of low-energy ions in silicon for a wide range of different implantations more accurately than what had been possible earlier.

Stopping Power for Ions and Clusters in Crystalline Solids

A computationally efficient ion implantation cumulative damage model has recently been developed and implemented in UT-MARLOWE Versions 4.0 and 4.1. Based on the modified Kinchin-Pease formula, this model accounts for damage generation and accumulation, defect encounters and amorphization in a simplified way. Good agreement with experimental impurity profiles has been obtained for As, B, BF 2 and P implants in single-crystal silicon. In addition, the amorphous layer thicknesses obtained in this model are also in reasonable agreement with experimental measurements. Based on this damage model, a simple but extremely powerful and general method for performing multiple implant simulations has been developed, and very good agreement with experimental data has been obtained.

A computationally efficient ion implantation damage model and its application to multiple implant simulations

Monte Carlo ion-implant models for germanium and indium implantation into single-crystal silicon have been developed and are described in this paper. The models have been incorporated in the UT-MARLOWE ion implantation simulator, and have been developed primarily for use on engineering workstations. These models provide the required as-implanted impurity profiles as well as damage profiles, which can be used as inputs for transient enhanced diffusion simulation and subsequent multiple implant simulation. A comparison of simulation results with experimental data shows that the models predict both the impurity profiles and the damage profiles very successfully for a wide range of implant conditions. The damage profiles from germanium implant simulations have been used for subsequent multiple implant simulations and excellent agreement with experimental results has been achieved.

Monte Carlo simulation of heavy species (Indium and Germanium) ion implantation into silicon

Accurate modeling of ultra-low energy ion implantation is becoming increasingly more important as MOS devices shrink to deep submicron dimensions, and the required junction depths become shallower than 50 nm. To this end, an efficient Monte Carlo ion implantation model based on a substantially modified Binary Collision Approximation (BCA) has been developed and implemented in UT-MARLOWE. The model removes several of the limitations of the BCA at low energies, such as the asymptotic path approximation and the decoupling of nuclear and electronic stopping usually employed in BCA models. Additionally, multi-body interactions are important at very low energies, and are modeled explicitly for the 3-body case. The modified BCA gives very good agreement with experimental data and is a significant improvement over the classical BCA, particularly for heavy species and well-channeled implants. In this paper, we report on the experimental verification of the model, as well as refinements and corrections subsequently introduced. Surface effects are also discussed, and their impact on the dose-dependence of the profiles is examined. The model has been verified for arsenic and boron, for energies down to 2 keV and 1 keV, respectively. This new model is found to he in very good agreement with the experimental data.

S. Baumann

Papers

Monte Carlo simulation of heavy species (Indium and Germanium) ion implantation into silicon

Experimental verification of a new physically based low energy (<5 keV) ion implant model