Sputtered Neutral Mass Spectrometry is perfect for analyzing thin metal films where composition, thickness and interface condition can be determined. The example presented here, shows a magnetic film stack comprising Cr, Ni, Cu and Fe. Of the different methods of data storage, magnetic hard discs still offer highly economic means for high density rapid access. The continual move towards more and more compact read/write heads and more closely spaced data tracks has lead to a considerable development of magnetic materials and structures for this demanding application. Analysis of the metallic layer structures used in magnetic data storage is vital for both development and quality management with secondary ion mass spectrometry (SIMS) and sputtered neutral mass spectrometry (SNMS) offering information on minor and major element composition respectively.
SIMS and SNMS
Both SIMS and SNMS use a concentrated, mono- energetic, chemically pure ion beam of typically 1-10 keV to sputter erode the surface under study. A small fraction of the sputtered material gets ionized due to the sputtering process itself and in SIMS, it is these ions that offer the sensitive information for which the technique is known. Being a mass spectrometry technique, all elements and isotopes may be detected, and in favorable conditions the detection limit can be in the low ppb region. However, because the ionization mechanism for SIMS takes place at the sample surface, it is very much dependent on the local chemistry and the ionized fraction can vary by several orders of magnitude. This makes SIMS ideal for trace analysis in materials of known matrix but quantification in materials of changing matrix can be complicated. SNMS overcomes the “matrix effect” by separating the sputtering and ionization events.