Unexpected properties of the inductively coupled plasma induced defect in germanium

Inductively coupled plasma (ICP) etching of germanium introduces a single defect, the E0.31 electron trap, for a large range of argon partial pressures from 4×10–3 to 6.5×10–4 mbar that correspond to ion energies of 8 to 60 eV. Ge of three crystallographic orientations, (1 0 0), (1 1 0) and (1 1 1), treated with 20 and 60 eV ICP had defect concentration profiles that were similar in appearance, with a maximum concentration of 1014 cm−3 extending more than a µm into the material, approximately three orders of magnitude deeper than what TRIM simulations predicted. All profiles were measured using Laplace deep level transient spectroscopy (L-DLTS), a technique that is sensitive to defect concentrations as low as 1011 cm−3. Isochronal annealing of samples showed concentration curves broadening after a 400 K anneal and decreasing to the 1013 cm−3 level after a 450 K anneal. Unannealed samples measured after a year exhibited similar decreases in defect concentration without broadening of their profiles. A 550 K anneal lowered the defect concentration to levels below the L-DLTS detection limit. Thereafter additional plasma treatment of the surface failed to reintroduce this defect indicating that the structure required for the formation of E0.31 was no longer present in the region under observation.