In order to activate the dopant atoms introduced by ion implantation or to form mechanically stable semiconductor insulator interfaces (Si - SiO2) or to setup contacts with low resistivity between silicon and the contact metal high temperature processes have to be performed. The redistribution of the dopant atoms due to diffusion, the activation of the dopant atoms and the chemical reactions that occure are simulated by the three-dimensional finite element simulator FEDOS.
Diffusion and Activation
After a dopant is implanted in silicon an annealing step has to be performed to activate the introduced dopant atoms and to repair the damage caused by the ion implantation. In modern process technology RTA (rapid thermal annealing) processes are the method of choice with typical annealing times of several seconds.
The ability to accurately determine the junction formation is one of the most pressing needs in the process TCAD today. The active concentration of the dopants as well as the accurate doping distribution after the annealing have to be predicted accurately because they determine the electrical property of the simulated device.
Modeling of annealing requires the knowledge of the point-defect behaviour in silicon. The point defects, interstitials and vacancies recombine, eliminating damage. Commonly dopants in silicon do not diffuse by themselves, they require an interaction with the lattice point defects. The dopants pair with the defects to form a mobile species.
The diffusion of the dopant and point defects and their interactions make a vastly complex system with numerous reaction rates, binding energies, and diffusivities that have to be parameterized. It results in the set of nonlinear partial differential equations which can be solved by the three-dimensional finite element simulator FEDOS.
The conversion of Si to SiO2 in a dry or wet oxidizing ambient, the deformation of the structure and the generation of stresses in the interior can be simulated by the oxidation model of FEDOS. The oxidation process is modeled by a set of three partial differential equations. Thereby the motion of the oxygen through SiO2, the reaction of silicon and oxygen at the oxide interface, the motion of a diffuse interface which determines the oxide interface and finally the mechanical behaviour of the materials are described by the equation system.