Selective etching of Si1 − xGex versus Si with gaseous HCl for the formation of advanced CMOS devices

In this paper, we have studied the selective etching of Si1 − xGex layers against Si in a Chemical Vapour Deposition (CVD) epitaxy reactor. Indeed, HCl gas, available in such tools, can be used to remove Si1 − xGex selectively compared to Si which can be useful in numerous advanced CMOS applications. Firstly, the etching morphologies obtained at different HCl partial pressures are presented. These experiments permitted us to point out the appearance of facets at the edges of the formed tunnels under certain conditions. Secondly, SEM cross-section observations allowed us to measure the lateral etch kinetics of Si1 − xGex layers with 15% < x < 30% on rotated substrates, along the <100> directions. And, the apparent activations energies and their dependency on both HCl partial pressure and Ge composition are also reported. Finally, ellipsometry measurements permitted us to measure selectivities as high as 50 for SiGe(25%) and 90 for SiGe(30%) between lateral SiGe and direct vertical Si etches. Finally, this technique appears to be very attractive for the formation of thin-Si film transistors such as SON devices with perfectly uniform Si channels and good interfaces quality.