Depth profile analysis

Depth profile analysis of electrodeposited CoPt films by the Auger microprobe

Sample

  • Co-Pt films are promising candidates for magnetic recording media and for magnetic micro-electromechanical systems (mag-MEMS), which require the development of permanent magnetic films with excellent magnetic properties. The material can be prepared by electrodeposition, which allows for an efficient deposition in a simple experimental setup, easily scalable for commercial production.
  • After deposition an annealing step is necessary to form the L10 ordered phase with the high magnetocrystalline anisotropy required for permanent magnets.

Profiles

  • Depth profiles were obtained by sputtering with a beam of Ar+ ions (E = 1.5 keV), scanned over an area of 2 mm × 2 mm to ensure a lateral homogeneous ion current distribution. The removal rate was about 6 nm/min. To minimize sputter induced roughening the sample was rotated during sputtering. After each sputter step the Auger electron spectra of the selected elements were recorded.
  • From the spectra the concentration of the elements, and - using peak shape analysis - their chemical state was determined.
  • The figure shows the depth profiles of a sample with an electrodeposited 300 nm CoPt film in the as-deposited state (a) and after annealing at 500 °C for 1 h in forming gas (b). The profile is given by the lines, the symbols are to guide the eye.
  • For the as-deposited sample a constant composition of about Co35Pt65 is found. The oxygen content in the CoPt layer is below 1 %.
  • Beneath the CoPt film thin interlayers serve as electrode for electrodeposition (Au) and adhesion layer (Cr), respectively. The substrate is silicon. Fig. (a) shows an enrichment of Si at the Au-Cr interface, i.e. the Cr adhesion layer doesn't serve as a diffusion barrier for Si.
  • After annealing, Au is found on the sample surface. The morphology of the samples has changed, it has developed pits (Fig. c).
  • The depth profile measured over an area of about 100 x 100 µm² (b) shows that the film architecture is destroyed; Si is detected throughout the film.
  • The signals of Au, Pt, and Co are observed after long sputter times because of non uniform sputter removal caused by the morphology of the film.
  • Local analysis proved that the surface of the smooth areas is rich in Pt, whereas in the pits it is rich in Si; the Co content in both structures is comparable.
  • The signals of Au, Pt, and Co are observed after long sputter times because of non uniform sputter removal.
  • Shape analysis of the Auger peaks proved that the Si(KLL) transition has different shape in the substrate and the annealed layer, what can be explained by the formation of silicides. CoSi2 was detected by XRD measurements.
  • An explanation for the formation of CoSi2 at relative low temperature is the presence of the thin Au interlayer, which causes an increased effective Si concentration because of the formation of an Au-Si eutectic at about 375 °C.

References

K. Žužek Rožman et al.; J. Magnet. Magnet. Mat. 314 [2] (2007) 116-121.