Reactive-ion etching (RIE) of epitaxial, strained Sil x Ge x alloys, x<;O.20, in fluorine-chlorine-, and bromine-based low-pressure plasmas has been investigated. The reactive-ion etch rates of the Sij _ x Ge x alloys increase with the Ge content of the alloy for most etching gases. This effect is most pronounced for fluorine (CF 4 and SF 6 ) plasmas where the etch rate of a Si 8o Ge 2o alloy is increased by a factor of = 2 over that of Si. The etch rate enhancement is of reduced importance for chlorine (CF z C1 2 ) and bromine (HBr) plasmas, where the etch rate increases by less than 50% for a SisoGe zo alloy relative to that of elemental Si. Analysis shows that the etch rate increase is not accounted for by the greater rate of gasification of Ge atoms alone but that the presence of Ge atoms in the SiGe alloy increases the Si etch product formation rate. Directional SiGe profiles are observed for CF 2C1z and HBr plasmas which are identical to those obtained with Si. After etching in CF 4 or SF 6 plasmas the Ge surface concentration of the SiGe alloy is increased relative to its bulk value and both fluorinated Si and Ge are observed by in situ x-ray photoemission spectroscopy. On the other hand, for CF 2 Cl 2 and HBr plasmas the SiGe surface is Si rich. The effect of band-gap narrowing, strain and plasma-induced surface modifications on the etching of the SiGe alloys is discussed.
The variation of photoluminescence (PL) spectra obtained with silicon exposed to various plasmas as a function of plasma etch treatment conditions is reported. Phosphorus- or boron-doped covering a large range of doping concentrations, Czochralski or float-zone-grown silicon crystals were investigated. The effect of various etching gases on the luminescence spectra as well as the effects of subsequent annealings are reported. Two types of recombination process are observed: (i) The first gives rise of sharp luminescence lines, such as the W (1018 meV), X (1040 meV), T (935 meV), I (965 meV), G (967 meV), C (790 meV), and P (767 meV) lines, which are known to originate from defects produced by high-energy irradiation and then manifest damage of the crystalline material. Other sharp PL lines at 1015, 1008, and 997 meV were introduced upon annealing at 400 °C. (ii) The second recombination process induces broad lines or bands in the photoluminescence spectra. The formation and nature of the defects giving rise to both recombination processes are discussed in terms of the plasma conditions and starting material.
It is shown that germanium is more rapidly etched than silicon in conventional fluorine-, chlorine-, and brominebased low-pressure plasmas and that a high Ge/Si etch rate ratio ERR can be readily obtained. The etching of Ge induced by plasma-generated fluorine atoms relies much less on ion bombardment than the etching of Si. A very high Ge/Si ERR (=40) may therefore be achieved for plasma etching conditions or for reactive ion etching at high pressure (250 mtorr)
Reactive ion etching (RIE) of epitaxial, strained Si1−xGex alloys, x≤0.20, in fluorine-, chlorine-, and bromine-based low-pressure plasmas has been investigated. The SiGe etch rates increase for each etchant with Ge concentration, e.g., for fluorine-based RIE (CF4 and SF6) the etch rate of a Si80Ge20 alloy is ≂2x that of elemental Si. Analysis shows that the etch rate increase is not accounted for by the greater rate of gasification of Ge atoms alone but that the presence of Ge atoms in the SiGe alloy increases the rate of Si etch product formation.
We describe a plasma-based dry etching procedure which permits selective etching of Si over Ge with a Si/Ge etch rate ratio of over 70 and negligible etching of the Ge underlayer. This is achieved in a SF6/H2/CF4 gas mixture by the formation of a thin (≂3 nm) involatile etch stop layer on the Ge surface which consists of Ge-sulfide and carbonaceous material.
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