Characterization and modeling of structural properties of SiGe/Si superlattices upon annealing

Abstract

Stacked multichannel or nanowire CMOS transistors are foreseen as viable options in future technology nodes. Superior electric performances and a relative immunity to short channel effects have already been demonstrated in such devices. They rely on (i) the epitaxy of SiGe/Si superlattices, (ii) the anisotropic etching of the source and drain (S/D) blocks and the channels, and (iii) the high degree of selectivity that can be achieved when laterally etching the SiGe sacrificial layers. The voids left by the removal of SiGe are then conformally filled by HfO2/TiN/poly-Si gates, leading to the formation of multichannel devices. Doping elements can be included in situ in the SiGe layers during the epitaxial step in order to achieve a proper S/D doping after annealing. Precise knowledge of the diffusion behavior of all species is then crucial to understand and tailor final device performance. In this work, we investigated the properties of intrinsic or in situ doped (with B, C, or P) SiGe/Si superlattices upon annealing, using several characterization techniques, such as x-ray diffraction, x-ray reflectivity, time-of-flight-secondary ion mass spectrometry, and dark-field electron holography; as well as diffusion simulation tools such as S-Process. The combined analysis and simulation approaches allowed a complete characterization of the studied structures upon annealing. In the first step, the diffusion of both germanium and dopants was observed experimentally and quantified with simulation. Their diffusion mechanisms were also studied. In the second step, the evolution of the strain distribution upon annealing was experimentally monitored and simulated to quantify the strain relaxation in such structures.