Charge compensation using optical conductivity enhancement and simple analytical protocols for SIMS of resistive Si1−xGex alloy layers

Journal of Applied Physics

Dowsett

2009

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.

Section: Discussionsupporting

confidence: 72%

Section: Ion Yield Behaviormentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

Journal of Applied Physics

Dowsett

2009

“…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). Following depth profiling, all craters were measured using a calibrated Dektak (Santa Barbara, California, US) 3030 stylus profilometer.…”

Section: Methodsmentioning

confidence: 99%

Si_1-xGe_x/Si Interface Profiles Measured to Sub-Nanometer Precision Using uleSIMS Energy Sequencing

J. Am. Soc. Mass Spectrom.

Hase

Sanchez

et al. 2016

Abstract. The utility of energy sequencing for extracting an accurate matrix level interface profile using ultra-low energy SIMS (uleSIMS) is reported. Normally incident O 2 + over an energy range of 0.25-2.5 keV were used to probe the interface between Si 0.73 Ge 0.27 /Si, which was also studied using high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). All the SIMS profiles were linearized by taking the well understood matrix effects on ion yield and erosion rate into account. A method based on simultaneous fitting of the SIMS profiles measured at different energies is presented, which allows the intrinsic sample profile to be determined to sub-nanometer precision. Excellent agreement was found between the directly imaged HAADF-STEM interface and that derived from SIMS.

“…Small variations in the matrix can have a significant effect upon the final device performance, and so, accurate compositional analysis is required. It has previously been demonstrated that uleSIMS can accurately (±1 at.%) determine the matrix content [3,4] of Si 1−x Ge x layers within the range x ≤ 0.3 by assuming that the Ge + and Si + ion yields are proportional to x and 1 − x, respectively, (and thus, the ratio of the Si + yield from SiGe to that in Si therefore gives x -a self-calibrating measurement in a Si/SiGe system). We show that this simple relationship does not apply to the full range of composition, and determine the more complex behavior required for quantification over 0 ≤ x ≤ 1.…”

Section: Introductionmentioning

confidence: 99%

Ion, sputter and useful ion yields for accurate quantification of Si_1−xGe_x(0 < x < 1) using ultra low energy O₂⁺ SIMS

Surface & Interface Analysis

Dowsett

2011

It has been previously demonstrated that accurate measurement of x in the Si 1−x Ge x (x ≤ 0.3) alloy can be achieved using a variety of O 2 + SIMS conditions. With SiGe device technology still developing to exploit its full potential, the useful matrices now extend from 0 ≤ x ≤ 1. Using the previously established conditions, we have found that roughening of the material occurs when x approaches 1. To overcome this limitation we have developed a set of conditions that enables the whole Si 1−x Ge x (0 ≤ x ≤ 1) range to be quantified. This is achieved by using an O 2 + primary beam energy of ≤500 eV at near-normal incidence. Here, we present a comprehensive study of the measured (Si and Ge) ion, useful ion and sputter yield behavior as a function of matrix composition and incident beam energy (250 eV-1 keV), from which these new conditions have been established. For the extended Si 1−x Ge x (0 ≤ x ≤ 1) range and primary beam energies used here, the measured Si and Ge ion yields were found to be well described by quartic, cubic or quadratic dependences as a function of x. The useful ion yields and sputter yields all showed moderate matrix effects, with the former decreasing monotonically for increasing x except in the case of Ge at 250 eV. Here, the useful Ge ion yield was found to be invariant with x while its measured ion yield (for all x) was observed to be proportional to its sputter yield.