Ion yields and erosion rates for Si1−xGex(≤x≤1) ultralow energy O2+ secondary ion mass spectrometry in the energy range of 0.25–1 keV

Abstract

Article Title: Ion yields and erosion rates for Si1−xGex(0x1) ultralow energy O2+ secondary ion mass spectrometry in the energy range of 0. We report the SIMS parameters required for the quantitative analysis of Si 1−x Ge x across the range of 0 Յ x Յ 1 when using low energy O 2 + primary ions at normal incidence. These include the silicon and germanium secondary ion yield ͓i.e., the measured ion signal ͑ions/s͔͒ and erosion rate ͓i.e., the speed at which the material sputters ͑nm/min͔͒ as a function of x. We show that the ratio R x of erosion rates, Si 1−x Ge x / Si, at a given x is almost independent of beam energy, implying that the properties of the altered layer are dominated by the interaction of oxygen with silicon. R x shows an exponential dependence on x. Unsurprisingly, the silicon and germanium secondary ion yields are found to depart somewhat from proportionality to ͑1−x͒ and x, respectively, although an approximate linear relationship could be used for quantification across around 30% of the range of x ͑i.e., a reference material containing Ge fraction x would give reasonably accurate quantification across the range of Ϯ0.15x͒. Direct comparison of the useful ͑ion͒ yields ͓i.e., the ratio of ion yield to the total number of atoms sputtered for a particular species ͑ions/atom͔͒ and the sputter yields ͓i.e., the total number of atoms sputtered per incident primary ion ͑atoms/ions͔͒ reveals a moderate matrix effect where the former decrease monotonically with increasing x except at the lowest beam energy investigated ͑250 eV͒. Here, the useful yield of Ge is found to be invariant with x. At 250 eV, the germanium ion and sputter yields are proportional to x for all x.

Si1-xGex/Si Interface Profiles Measured to Sub-Nanometer Precision Using uleSIMS Energy Sequencing

“…This procedure was adopted for all the profiles such that data could be compared from the flat crater bottom region, which measured only 13.8 × 13.8 μm and, thereby, avoided any edge effects that can be more pronounced at low beam energies. Previous studies under these conditions showed profiling without any additional artefacts introduced through surface topological changes [11]. Optical conductivity enhancement (OCE) [12] in the form of red laser illumination (λ = 635 nm: power = 2.5 mW: spot size~2 mm at the sample) was used to stabilize the sample surface bias as the material was intrinsic (i.e., highly resistive).…”

“…Table 1 summarizes the RMS roughness obtained from the AFM. The similarity between craters of different E P suggests that the probe-sample interaction for this energy range did not degrade the sample topography during the profiling [11]. Owing to the importance of Si 1 -x Ge x in modern transistor technologies [15], this material system has been studied widely using SIMS.…”

“…Owing to the importance of Si 1 -x Ge x in modern transistor technologies [15], this material system has been studied widely using SIMS. Hence, the profile quantification was carried out using previously developed metrologies [3,11] for both the Ge concentration and erosion rate (ż): the mean Ge + yield from the layer was converted to the concentration established from previous XRD analysis. As the measured Ge + yield had previously been shown to vary proportionally with x over the limited concentration range of the sample (i.e., 0 ≤ x ≤ 0.3 [11,16]), no further correction was needed.…”

Characterization of Surface Modifications by White Light Interferometry: Applications in Ion Sputtering, Laser Ablation, and Tribology Experiments

“…6,9,[33][34][35][36] In addition, this approach is capable of accurate quantifying sputtering rates for organic materials and solids under bombardment with a variety of primary species, commonly used atomic ions and relatively new molecular and cluster ions, such as in Refs. 37, 38.…”

“…One more technique for surface inspection, which is widely used in secondary ion mass spectrometry 6 and in the field of microelectromechanical systems characterization 7 is stylus profilometry. This technique is popular because of its simplicity and robustness.…”