Accurate characterization of dose and shape of ultra low energy arsenic (1keV and 2keV) implants by SIMS

Abstract

During the past two to three years there have been several papers published on how to accurately measure the dose and shape of ultra low energy boron implants using Secondary Ion Mass Spectrometry (SIMS). In general, oxygen primary ion beam bombardment has been employed either using oxygen leak and 45° bombardment angle or normal incidence bombardment without oxygen leak. These methodologies have been employed to avoid problems from the pre-equilibrium issues encountered during SIMS measurements. The accurate dose and profile shape of ultra low energy arsenic implants unfortunately cannot employ the methodologies established for low energy boron measurements, due to the fact that arsenic segregates to the front or the oxygen beam when sputtering employing an oxygen ion beam and therefore the true shape of the arsenic implant profile can not be established. In this paper, we employ Cesium primary ion beam bombardment using various sub-keV energies, various angles of bombardment and normalisation routines to establish the true shape and dose of 1 keV and 2 keV arsenic implants. The normalization or the arsenic profile to various silicon isotopes and combinations of its dimers are considered along with low temperature Chemical Vapour Deposited (CVD) silicon capped 1 keV and 2 keV arsenic implants. This is employed to avoid the pre-equilibrium transients in the SIMS profile of the arsenic at the surface of the silicon. The results lead to a methodology for obtaining the correct arsenic implanted dose and the correct arsenic implant shape using specific normalisation routines. The arsenic doses calculated from SIMS have been compared with Rutherford Backscattering (RBS) measured dose values.