The use of atom probe tomography (APT) [1] to investigate the microstructure of insulating oxide materials has been of interest for many years [2]. Recently, both voltage-pulsed and laser-pulsed methods has been used to analyze thin films (~1-2nm) of various oxides [3][4][5] and thicker metal oxide films up to ~20nm created directly on metal needles [6]. This paper expands this later category of "bulk"-like oxide films through the application of laser-pulsed atom probe to samples containing large regions of SiO 2 or Al 2 O 3 . Silicon dioxide is ubiquitous in the semiconductor industry, being implemented, for example, as a gate oxide, as an electrically insulating backfill material and as a silicon-on-insulator substrate material. An example mass spectrum from a backfill region of silicon dioxide 30x70x10nm (part of a larger total volume of material ~10x that size) is shown in Fig. 1. The mass peaks are all identifiable, including SiO in 1+ and 2+ charge states and SiO 2 . If hydrogen is ranged in a concentration calculation it accounts for 4.7%, however it is likely that as least some of it is being picked up from the vacuum and thus we have calculated a concentration of 37.0±0.16%Si -63.0±0.16%O (excluding hydrogen), which is slightly oxygen deficient.Alumina, both pure and in composite forms, has a variety of uses due to its high temperature performance, wear and corrosion resistance, hardness, and dielectric properties. We have investigated the feasibility of laser-pulsed APT on bulk alumina commonly used as a substrate for III-V (particularly GaN) semiconductor deposition. Fig. 2 shows the mass spectrum obtained from an analyzed volume of 80x80x40nm. Although the spectrum contains many complex molecular ions, all of the peaks, excluding hydrogen, are identifiable in terms of combinations of Al and O in various ratios and charge states. A concentration (excluding hydrogen, which accounted for 3.6%) was calculated from the spectrum as 37.8±0.03%Al -62.2.0±0.03%O. A second alumina mass spectrum from a volume of 50x50x50nm is shown in Fig.3. This analysis is of an oxidized NiAl diffusion coating [7]. The concentration (excluding hydrogen, which accounted for 0.74%) was calculated to be 37.4±0.03%Al -62.6.0±0.03%O, again slightly oxygen enriched, similar to the data from Fig. 2, but quite close to stoichiometric alumina. All concentrations were calculated from the spectra by peak ranging at one-tenth of the maximum value or, if this was not possible, by using a visual estimate of the noise level, Fig. 4. Simple background subtraction was performed on the spectra in Fig. 2 using a pre-peak range of the same number of bins as the peak range (Fig. 4), with the result being a concentration of 37.2±0.04%Al -62.8.0±0.04%O.
