(398e) Analysis of Misfit Dislocation Formation and Strain Relaxation in Si1-XGeX Thin Films on Si (100) Substrates

Strained semiconductor thin films grown epitaxially on semiconductor substrates of different composition, such as Si_1-xGe_x/Si, are becoming increasingly important in modern microelectronic technologies due to their enhanced hole and electron mobility compared to unstrained films. Establishing process-structure-property relationships for optimizing the mechanical and electronic properties of these semiconductor heteroepitaxial systems requires development of computationally efficient models for prediction of interfacial stability with respect to misfit dislocation formation and simulation of the strain relaxation dynamics in the epitaxial film during film growth and post-growth treatment. In this presentation, we report a hierarchical computational approach for analysis of dislocation formation, glide motion, multiplication, and annihilation in Si_1-xGe_x epitaxial thin films on Si substrates, including finite-thickness compliant substrates that can deform parallel to the film/substrate interface and aid in the elastic accommodation of strain due to lattice mismatch in the epitaxial film. The computational hierarchy includes equilibrium Monte Carlo simulations for compositional relaxation in the epitaxial film in conjunction with energy-minimization calculations for structural and strain relaxation. The above atomic-scale computations are based on reliable many-body interatomic potentials and are combined with continuum elasticity and dislocation theory for parameterization of predictive macroscopic models for the onset of dislocation generation and the kinetics of strain relaxation. Specifically, for Si_1-xGe_x epitaxial thin films on Si(100) substrates, a condition is developed for determining the critical film thickness for dislocation generation as a function of overall film composition, x, film compositional grading, and (compliant) substrate thickness.

For epitaxial films with thickness less than the critical thickness for misfit dislocation generation, the dependence of the mechanical properties of the heteroepitaxial system on composition, compositional grading, and substrate thickness is determined by combining elasticity theory with atomic-scale computations of strain and elastic strain energy as a function of epitaxial film thickness. In addition, for films with thickness greater than the critical film thickness, the kinetics of strain relaxation in the epitaxial film during epitaxial growth or post-growth thermal annealing (including post-implantation annealing) is analyzed using a properly parameterized dislocation-mean-field theoretical model that describes plastic deformation dynamics due to threading dislocation glide motion and interactions between gliding dislocations. These theoretical results are compared with experimental measurements for strain relaxation in Si_0.80Ge_0.20/Si(100) heteroepitaxial systems and are used to discuss film growth and thermal processing protocols toward optimizing the mechanical response of the epitaxial films.