Atomistic modeling of silicon device processing, front and back ends.
Lawrence Livermore National Laboratory
In this talk we discuss some fundamental issues associated with the atomic displacements and phase formation during the processing of silicon devices, both within the silicon during ion implantation of dopants and annealing, and on the back end of the device during thin film deposition for the construction of interconnects. We use both Monte Carlo and molecular dynamics simulations to calculate the distributions of dopant atoms implanted in the silicon, and thin film morphologies. One of the issues concerning front-end process modeling is the amorphization of silicon during implantation, and its effect on the distribution of the dopants after re-crystallization by annealing. We have developed a Monte Carlo model of this process, and compare the model to experiments. In addition, the clustering of dopant atoms is becoming a problem because of the high concentrations required for the small transistors, and Monte Carlo models provide insights to this phenomenon. Back end processing is discussed, with an emphasis on thin film structure and its dependence on the deposition conditions and materials properties. Results from molecular dynamics simulations provide some useful information on the transition to amorphous films at low temperatures and for certain materials, even though the time scale of the simulations is many orders of magnitude shorter than that of experiments. Molecular dynamics simulations also provide information on atomic mobility on crystal surfaces, and these are employed in Monte Carlo calculations to simulate thin film deposition on a longer time scale. The formation of low-density porous films of refractory materials used for diffusion barrier layers is modeled, and methods to increase the film density are described. The formation of 3D islands and the film structures after coalescence are also treated.