Anisotropic ECR plasma etching with low-energy ions

Anisotropic and damageless etching conditions were found by using an ion flux type electron cyclotron resonance (ECR) plasma etcher. The etcher produces a directional ion flux with a low energy (20 eV). Anisotropic profiles result. There is no damage produced. The etcher is composed of a standing wave cavity (TE113) storing 2.45 GHz microwave power, and a separate sample chamber. The etcher is able to controll ionic performance by gas pressure reduction (less than 1.0 mTorr). Satisfactory anisotropic etching is achieved, although the system design does not permit control of the ion's energy that is independent of the energy of the radical. The reduced anisotropy is caused by collisions between ions and neutral molecules in the ion flux. Collisional angles from about 15 - 25 for the gas pressures from 0.2 mTorr to 1.0 mTorr, respectively, were measured. A high aspect ratio (10) was obtained around 0.1-0.2 mTorr gas pressure. As for an evaluation of surface damage, a spectrum and a phase-portrait chaotic-analysis graph are applied to electrical noise produced during wafer etching, recognizing that RF-bias ECR etching produces damage on the surface. Furthermore, a trench on a silicon substrate was formed implementing RF-bias. Some damage occurred. By gradual application of RF bias power and gas flow during etching, it was possible to obtain trenches with 0.25 μ m widths and 1.5 μ m depths. (orig.)