200-period Si/Si0.8Ge0.2 superlattice structure growth and characterization for vertical stacked DRAM

Abstract

The demand for increased memory density and the limit of DRAM (dynamic random-access memory) device downscaling are driving conventional DRAM to advanced vertical stacked DRAM (VS DRAM). The multi-period Si/SiGe superlattice (SL) structure is crucial for achieving vertical stacking of Si channels, and the film quality of the Si/SiGe SL structure has a direct impact on the performance of subsequent DRAM devices. In this work, we obtained the 200-period Si/Si0.8Ge0.2 SL structure through multiple-epitaxial processes. The experimental results show that the crystal quality of the SL structure is satisfactory, exhibiting slight strain relaxation. The thickness uniformity in the SL structure is well maintained from bottom to top (36.7 ± 2.1 nm, σthickness = 0.77 nm). Furthermore, Ge segregation at the bottom of the SL structure was observed, resulting in a slight upward trend in the Ge concentration from bottom to top and a broadening of the bottom interface. This work demonstrates the feasibility of epitaxial growth of ultra-multilayer Si/SiGe SL structure and provides a process solution for the development of advanced VS DRAM devices.