Nanometer p–n junction formation and characterization

Abstract

The fabrication of p–n junctions in silicon with junction depths of a few nanometers and the determination of the potential distribution and junction depth of such a specimen with a depth resolution of better than 0.5 nm were performed. The ultrashallow p–n junctions were formed by bombarding hydrogen-passivated n-Si(100) with BF2+ of less than 500 eV. After being annealed at 500 °C in vacuum for an hour, the sample surfaces were treated with a HF solution for the reduction of surface states in the band gap of silicon prior to junction characterization. With hydrogen passivation, the separation between the Fermi level and the valence band maximum of the semiconductor surface, EFs, an energy which is governed by the doing type and net carrier concentration, was measured with x-ray photoelectron spectroscopy. The sample was then subjected to ozone oxidation at room temperature for 20 min, a procedure which reproducibly consumes 0.5 nm of silicon. The oxide was then removed by a HF solution to reveal a new hydrogen-passivated surface for the second-cycle EFsmeasurement. This process was repeated until the measurement of EFs versus depth was completed for the profiling of the ultrashallow junction. With a mathematical space-charge calculation, the carrier-concentration–depth profile, the potential-distribution–depth profile, and the junction depth can then be determined by the measured EFs–depth relationship. At a bombardment energy of 150 eV and a dose of less than 1×1016/cm2, the junction depth was found to be less than 2 nm.