A study was made of the etching of Si, SiGe and Ge layers with gaseous HCl in reduced pressure-chemical vapor deposition (RP-CVD). The occurrence of 2 etching regimes, depending upon the etching temperature, were observed. The first regime took place at high temperatures and was characterized by low activation energies (~7kcal/mol); regardless of the Ge content of the etched layer. The other regime occurred at low temperatures and had associated high activation energies (which depended strongly upon the Ge concentration of the etched layer: 86kcal/mol for pure Si and 28kcal/mol for pure Ge). Modifying the HCl partial pressure had various effects; depending upon the regime. In the high temperature regime, increasing the HCl partial pressure almost quadratically increased the etching rate (ER  PHCl1.76), for both Si and Si0.67Ge0.33. The dependence was sub-linear in the low-temperature regime (Si ER  PHCl0.53 and Si0.67Ge0.33 ER  PHCl0.82). The temperature where the regime shifted from one to the other decreased when the Ge concentration increased. To illustrate the added value of the chemical vapor etching, 2 possible applications were demonstrated. The first one was the realization of SiGe thin strain relaxed buffers in the active areas of shallow trench isolation patterned wafers after etching away the Si with HCl. The occurrence of some etching loading effects was observed upon moving from a blanket to a patterned wafer. The SiGe thin strain relaxed buffers exhibited some good structural properties (rms roughness of 0.12nm, no defects observed in cross-sectional transmission electron microscopy). However, they were not fully relaxed and facets were present at the shallow trench isolation/epitaxial stack boundary. Another possible application was to decorate, by in situ HCl etching, the dislocations which threaded through SiGe relaxed thick layers. This had some significant advantages over commonly used wet-etching solutions such as Secco and Schimmel.

Chemical Vapour Etching of Si, SiGe and Ge with HCl - Applications to the Formation of Thin Relaxed SiGe Buffers and to the Revelation of Threading Dislocations. Y.Bogumilowicz, J.M.Hartmann, R.Truche, Y.Campidelli, G.Rolland, T.Billon: Semiconductor Science and Technology, 2005, 20[2], 127-34