Ultrashallow junctions in silicon formed by molecular-beam epitaxy using boron delta doping

Low-temperature molecular-beam epitaxy was used to form highly conductive, ultrashallow layers in silicon using boron delta doping. Junction depths, d etermined with secondary ion mass spectrometry, ranged from 7 to 18 nm. A m inimum resistivity of 3x10(-4) Omega cm was obtained when the delta-doped l ayers were spaced 2.5 nm apart. The sheet resistances of the epitaxial laye rs, plotted as a function of junction depth, followed the theoretical curve for a box-doped layer having a boron doping concentration equal to the sol id solubility limit, 6x10(20)/cm(3). At a specific thickness, the minimum s heet resistance obtained by B delta doping was more than a factor of 5 less than that achieved by ion implantation. (C) 2000 American Institute of Phy sics. [S0003-6951(00)05342-0].