A process model for sputter deposition of thin films using molecular dynamics

Abstract

This chapter presents a process model for sputter deposition of thin films using molecular dynamics. A molecular dynamics model is developed to study the microstructure and intrinsic stresses of sputter-deposited thin films and the step coverage as a function of the process conditions. To perform efficient integration of the equation of motion and force calculations, a third-order discretization scheme with nonuniform time step is employed. Special attention is also given to the development of schemes for fast search of the neighbor atoms. A “position index method” that updates the Verlet neighbor table locally instead of reconstructing the entire neighbor table is proposed and implemented in order to perform faster calculations of the forces. The generalized Langevin equation (GLE) is used to simulate the constant temperature conditions during deposition processes. This allows the study of the effects of ion bombardment, chemical reactions, and many other processing conditions on thin film formation phenomena. A movable periodic boundary condition based on a constant external pressure technique is employed that considers the relationship between the stresses in the film and permits stress relaxation during the deposition process. The algorithm can therefore demonstrate successfully the effects of substrate conditions, such as external stresses and temperature, on the deposition phenomena. The global average intrinsic stresses of the film are calculated using an improved method, and it is possible to study the evolution of this stress with the film. A novel scheme to study the effect of the microstructure on local stresses with the help of a local stress parameter is also proposed and implemented in the chapter.