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

Abstract

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.

O2+ probe‐sample conditions for ultra low energy SIMS depth profiling of nanometre scale Si0.4Ge0.6/Ge quantum wells

“…Ultra low energy SIMS (uleSIMS) measurements were performed on an Atomika 4500 quadrupole instrument, which (like other Atomika/Cameca quadrupole instruments) uses ultra low energy gun technology invented at Warwick . A primary O 2 + beam at near normal incidence (a condition previously shown to offer the best depth resolution and minimise roughening and pitting in this material) was used over a range of beam energies (0.25–1 keV) and beam currents (60–100 nA). An area of 220 × 220 µm was scanned, and the 30 Si + and 70 Ge + secondary ions were collected.…”

Atomic spectrometry update. Industrial analysis: metals, chemicals and advanced materials

“…Included in this number is a paper by Merkulov and co-workers, who compared the use of both primary ion types during the depth-profile analysis of As, B and P in ultra-shallow implants. 321 Roughening of the material occurred when x approached 1. The depth-profile results obtained using these sputtering conditions were compared with those obtained using the techniques of high resolution RBS and elastic recoil detection analysis (ERDA).…”

“…Morris and Dowsett also used ultra-low energy O 2 + ions (250 ev-1 keV) for the analysis of silicon germanide films, where x in the formula Si 1Àx Ge x could be determined accurately. 321 Roughening of the material occurred when x approached 1. The authors therefore established conditions that enabled the whole range (i.e.…”

SIMS quantification of thick Si1−x Gex films (0 ≤ x ≤ 1) using the isotopic comparative method under Ar+ beam

“…SiGe alloys and/or heterostructures form a large spectrum of electronic materials of potential use for silicon‐based technology and may also find applications in photovoltaics or as future superconducting films. The conventional approach to determine the relative secondary‐ion yield ( YR ± ) versus germanium atomic concentration in SiGe alloys by secondary‐ion mass spectrometry (SIMS) generally requires an external measure of the alloy composition, which is generally done by Rutherford backscattering spectrometry (RBS), X‐ray Diffraction (XRD) or Auger electron spectroscopy (AES) . A typical calibration procedure requires a battery of reference samples whose composition is constant, multilayer samples of Si 1− x Ge x /Si or a step‐graded SiGe virtual substrate .…”

“…The conventional approach to determine the relative secondary‐ion yield ( YR ± ) versus germanium atomic concentration in SiGe alloys by secondary‐ion mass spectrometry (SIMS) generally requires an external measure of the alloy composition, which is generally done by Rutherford backscattering spectrometry (RBS), X‐ray Diffraction (XRD) or Auger electron spectroscopy (AES) . A typical calibration procedure requires a battery of reference samples whose composition is constant, multilayer samples of Si 1− x Ge x /Si or a step‐graded SiGe virtual substrate . In these previous works, various quantification protocols were investigated, such as measuring the Ge fraction using the Si + channel only (ISR = internal silicon reference), or using the ratio of the Ge + yield to that of an internal SiGe layer of well‐known composition using absolute sensibility factors (ASF) .…”