Growth and characterization of SiGe/Si superlattice for vertically stacked DRAM

In this study, SiGe/Si superlattices films (SLs) with different tiers were epitaxially grown by reduced pressure chemical vapor deposition (RPCVD) on 300 mm Si (001) substrate. Crystal quality of SiGe/Si SLs films (relaxation, surface roughness, interface characteristics and dislocation density) were quantitative evaluated by various characterization methods. A systematic investigation was conducted on the transition process of the SiGe/Si SLs films from full strain to relaxation state with increasing stacking layers. And, the variation trend of dislocation density and surface roughness with increasing stacking layers is studied. Additionally, we examined the changes in crystal quality and dislocation density of these SLs films after thermal annealing (20 min, @700 degrees C), and all the films exhibit higher strain relaxation by generating more misfit dislocations propagating in-plane. This study provides guidance and reference for the regulation of process parameters and the design of superlattice structure in vertically stacked DRAM.