An attempt to determine the thickness of native oxide layer on a silicon wafer from a graphical analysis of the transient behavior at an earlier stage of SIMS depth profiling using 16O2+ beam has been performed. We found out three specified depths from the characteristic shape of 30Si+ secondary ion intensity vs. depth curves, which strongly depended on the angle of incidence (θ) and the acceleration energy (E) of 16O2+ beam. Good linear relationships were found between the three specified depths and E at low angles of incidence. The linear lines extrapolated coincided triply at E=0, and from this, a value of 0.62 nm was obtained as the thickness of the native oxide layer.
The elimination of memory effect in SIMS (Secondary Ion Mass Spectrometry) has become one of the dominant factors contributing to the reduction of depth profiling accuracy. Most atoms sputtered from the sample by primary ion beam irradiation are deposited on the adjacent mechanical surfaces, especially on the secondary ion extractor. Some of these deposited materials are resputtered by bombardment of energetic ions, such as accelerating secondary ions and primary reflected ions, and deposited again on the analytical sample surface. Therefore, if the elements found in a prior analysis is the same as the elements in the sample to be analyzed, the background signal from the prior analysis will reduce the accuracy of the analysis. This paper gives a detailed quantitative assessment of the elimination of memory effect. In order to reduce the memory effect, the authors evaluated a technique of covering the background source by in-situ sputtering of non-interference materials for several hours prior to analysis. The memory effect was evaluated quantitatively by measuring the detection limit of phosphorus implanted into Si as a function of the number of atomic layer deposited on the top of secondary ion extracting electrode covered with stainless steel (SUS 304). The phosphorus deposited in the prior analysis of a GaP sample was used as the origin of the memory effect. From the experimental results, it was found that the detection limit decreased as a function of the number of atomic layer of the material deposited on the extracting electrode. As a results, the memory effect is eliminated by depositing about 20 atomic layers of the SUS 304.
STM images of HOPG (highly oriented pyro-lytic graphite) (0001) surface have been obtained in a vacuum of 1×10-5 Pa. A clear image of the hexagonal structure of the surface atoms was obtained. The height difference between the higher (lower) carbon site and the hollow site is 2.0Å(1.2Å). The values for the surface corrugation obtained in the present observations fairly well coincide with those predicted from theoretical calculations.