Amorphous silicon layer characteristics during 70–2000eV Ar+-ion bombardment of Si(100)

Abstract

Spectroscopic ellipsometry (SE) has been applied to characterize the damaged, amorphous silicon (a-Si) layer created by Ar+-ion bombardment in the ion energy range of 70–2000eV impinging at 45° angle of incidence on Si(100). The dielectric functions of a-Si during ion bombardment have been determined using the Tauc-Lorentz model for the dielectric functions ϵ1 and ϵ2. The dielectric functions resemble literature reports on a-Si-like dielectric functions. The a-Si layer thickness under ion bombardment conditions reaches values from ≈17Å at 70eV up to ≈95Å at 2000eV. These values compare reasonably well with SRIM and molecular dynamics simulations. The surface roughness, as determined with SE, is typically 5–15Å during ion bombardment, with a minimum roughness at Eion=250eV. The creation of the amorphous silicon top layer upon 70eV Ar+-ion bombardment with an ion flux of 0.07MLs−1 has been resolved using real-time spectroscopic ellipsometry. The creation of the amorphous layer shows a double exponential ion-dose dependence: a fast, initial period of a-Si creation, with 1∕e constant Δτ1=2ML, and a slower period, Δτ2=9ML, until the matrix is fully amorphous after ∼30ML of Ar+ dosing. Relaxation of the a-Si top layer has been observed after the ions are switched off and has been analyzed with a stretched-exponential decay as a function of time, which is characteristic for a defect-controlled relaxation in the bulk a-Si layer. The corresponding time constant τ is found to be ∼360s, which is typically observed for self-annealing in amorphous silicon materials.