Contribution of ions and radicals in etching of Si_1-xGe_x epitaxial films using an electron-cyclotron-resonance chlorine plasma

Etching of undoped Si_1-xGe_x epitaxial films (v = 0-1) has been investigated using an electron-cyclotron-resonance chlorine plasma. It is found that the etch rate of Si_1-xGe_x increases with increasing Ge fraction and decreases with increasing Cl₂ pressure. From the comparison of the etch rate with the number of the incident ions toward the wafer and the relative radical density in the plasma, it is also found that the etching of Si_1-xGe_x with low x is induced mainly by chlorine ions, and for high x, the contribution of radicals to the etching becomes larger. From the angular resolved x-ray photoelectron spectroscopy analysis, it is found that the etching by chlorine radicals causes surface segregation of Si with the concentration of about 1-1.5×10¹⁴cm^-2 on the etched Si_1-xGe_x surface.