Quantitative study of oxygen enhancement of sputtered ion yields. I. Argon ion bombardment of a silicon surface with O2 flood

• Published in: Surface science Vol. 573; no. 2; pp. 291 - 309
• Main Authors: FRANZREB, Klaus, LÖRINCIK, Jan, WILLIAMS, Peter
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier Science 10.12.2004; Amsterdam; New York, NY
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Physics; Ion implantation; Oxygen; Inorganic compounds; Pressure effects; In situ; Ion bombardment; Microscopic model; Precipitates; Steady state; Sputtering; Ion beams; Statistical models; Silicon oxides; Secondary ion mass spectroscopy; Oxidation; SIMS; Silicon; Argon; Depth profiles
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/j.susc.2004.10.001

Secondary ion mass spectrometry is established as the most sensitive of the surface and thin film analytical techniques. However, the stronly non-linear depondence of (especially positive) sputtered ion yields on the surface oxygen concentation also gives rise to very large matrix effects, which complicate quantitative analysis using SIMS. A novel quantification approach is applied to determine in situ the amount of surface oxygen within the sputtered particle escape depth during steady-state sputter depth profiling of silicon under simultaneous oxygenation with an oxygen flood gas or with an oxygen primary ion beam. Quantification is achieved by comparing the secondary ion intensities of 16O that is adsorbed or implanted at the Si surface with the measured peak intensities of a calibrated 180 ion implant used as a reference standard. Sputtered ion yields can thereby be related to surface oxygen levels. In the present work the dependences of the partial silicon sputter yield Y and of the positive and negative secondary ion useful yields UY(X-) (X = B, 0, Al, Si, P) on the oxygen/silicon ratio, O/Si, in the sputtered flux are studied for 40Ar+ bombardment of Si with simultaneous O2 flooding. The silicon sputter yield is found to decrease with increasing flood pressure and O/Si ratio by up to a factor of 3. Both positive and negative secondary ion yields are enhanced by the presence of oxygen at the silicon surface. The useful ion yield of Si+ scales non-linearly with the atom fraction of surface oxygen; this behavior is shown to invalidate models that suggest that Si+ ion yield enhancement is dominated either by isolated oxygen atoms or by formation of SiO2 precipitates. In contrast a microscopic statistical model that assumes that local Si+ ion formation depends only on the number of oxygen atoms coordinated to the Si atom to be ejected fits the ion yield data quantitatively.