SHALLOW JUNCTIONS BY OUT-DIFFUSION FROM ARSENIC IMPLANTED POLYCRYSTALLINE SILICON

We describe reverse bias diode leakage and physical analysis (secondary ion mass spectroscopy, Rutherford backscattering and transmission electron microscopy) data from shallow n+/p junctions made by implanting various doses of arsenic into polycrystalline Si and out diffusing at various temperature/time conditions, into the underlying (100) Si substrate. The polycrystalline Si is cobalt disilicided to provide the first level of metallization. The minimum process specifications giving good junction quality (reverse bias diode leakage current density ≤10 nA/cm2 at 10 V) are 7×1015 cm-2 As out diffused at 950 °C, 30 min with a junction depth 1200 Å below the polycrystalline Si. At these conditions, most of the As (≳90%) uniformly redistributes in the polycrystalline Si. There is a segregation to the polycrystalline Si/Si interface which is characterized by a porous, <50 Å thin silicon oxide interface. The polycrystalline Si/Si interface is also characterized by a laterally non-uniform large grain(∼2000 Å) or epitaxial regrowth at the 950 °C process temperature. These interface conditions may be used to explain the ∼20% high leakage population which is independent of out-diffusion condition at high As dose. Such a high sport population is not observed when P is implanted into polycrystalline Si and out diffused at 900 °C, 30 min to obtain ∼2500-Å-deep junctions below the polycrystalline Si/Si interface.