Substituting low-energy (<30 eV) ion bombardment for elevated temperature in silicon epitaxy

Normally required high substrate temperature for achieving epitaxial film growth can be replaced by low-energy (<30 eV), high-current-density (∼1 mA/cm2) ion bombardment during film deposition. For this a Si substrate wafer was immersed like a large negative Langmuir probe in a low-pressure (5×10−4 Torr) mercury vapor plasma while receiving Si atoms sputtered from a Si wafer target. The Hg plasma was created by extracting a 4-A discharge current at 25-V discharge voltage from a Hg cathode spot on a liquid-Hg pool. Electron channeling patterns proved that uniform Si spitaxial films can be obtained over the whole substrate wafer area at temperatures not exceeding 300 °C. The best epitaxial films were obtained when the substrate is bombarded (by biasing) during deposition with 23-eV Hg ions. The electrical properties of the coatings indicated that the films were close, but not yet of device quality because of the impurities inherent in our non-ultrahigh-vacuum nonbakable Pyrex chamber pumped only with a 12-ℓ/s Hg diffusion pump.