Amorphous silicon layer characteristics during 70–2000eV Ar+-ion bombardment of Si(100)
Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films
Spectroscopic ellipsometry ͑SE͒ has been applied to characterize the damaged, amorphous silicon ͑a-Si͒ layer created by Ar + -ion bombardment in the ion energy range of 70-2000 eV impinging at 45°angle of incidence on Si͑100͒. The dielectric functions of a-Si during ion bombardment have been determined using the Tauc-Lorentz model for the dielectric functions ⑀ 1 and ⑀ 2 . The dielectric functions resemble literature reports on a-Si-like dielectric functions. The a-Si layer thickness under ion
... hickness under ion bombardment conditions reaches values from Ϸ17 Å at 70 eV up to Ϸ95 Å at 2000 eV. These values compare reasonably well with SRIM and molecular dynamics simulations. The surface roughness, as determined with SE, is typically 5 -15 Å during ion bombardment, with a minimum roughness at E ion = 250 eV. The creation of the amorphous silicon top layer upon 70 eV Ar + -ion bombardment with an ion flux of 0.07 ML s −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 ⌬ 1 = 2 ML, and a slower period, ⌬ 2 = 9 ML, until the matrix is fully amorphous after ϳ30 ML 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 is found to be ϳ360 s, which is typically observed for self-annealing in amorphous silicon materials.