Cl2 Reactive Ion Beam Etching of Heavy n-Type Si

The etch yield vs n-type doping level up to 1.5 × 1021 As/cm3 was measured. Also, the etch yield as a function of ion energy (300 to 1500 eV) for the heaviest doped samples (1.5 × 1021 As/cm3) was measured. Only a small 10–15 percent enhancement in etch rate over low doped silicon was observed. Channeling experiments with Rutherford backscattering spectrometry showed 84 percent of the arsenic atoms were in substitutional positions in the silicon crystal. In addition, silicon was implanted with arsenic to a dose of 1.25 × 1017 #/cm2 and then laser annealed. This produced samples with a 5000 angstrom layer of uniformly doped silicon at five atomic percent. Channeling experiments showed these samples to have 82 percent of the dopant in substitutional sites. Samples were then masked with chrome and etched at varied pressures, temperatures and ion energies. Within our experimental resolution no isotropic etching was observed. This small doping dependence of the etching behavior of n-type silicon in reactive ion beam etching suggests that the rate limiting step for Cl2 RIBE is different than for Cl2 RIE, rf-plasma and laser assisted etching. A discussion of this difference is given assuming a much lower concentration of atomic chlorine in RIBE.