DEPTH PROFILES OF THIN-FILMS AND INTERFACES BY THE ELASTIC RECOIL DETECTION TECHNIQUE

An elastic recoil detection (ERD) technique, which also involves Rutherford forward scattering (RFS) and incorporates time-of-flight (TOF) principle for mass discrimination, is developed and successfully applied in the simultaneous "non-destructive" multielemental depth-profile studies of thin films and interfaces. In this technique, the light as well as medium mass elements are knocked out of the target by using energetic heavy ion beams obtained from the 6 MV Tandem accelerator. The mass separated energy spectra are deconvoluted into the depth profiles by using a newly developed computer analysis facility capable of yielding reliable atomic concentration ratios on routine basis without any a priori assumptions about the composition of an unknown target. The performance of the technique is illustrated through the results of some recent applications to a large number of targets such as Corning Glass 0211, silicon nitride and oxynitride films, borophosphoro silica glass, cobalt silicides and polyimide-metal interfaces. In several cases the quantitative results of ERD are compared with other material analysis methods, e.g. chemical analysis, energy dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), etc. and found to be in very good agreement. The effects of beam dose on radiation sensitive films of polymers and polyimides are briefly discussed and a few methods to minimize them are suggested. Typical performance characteristics of the system using 30 MeV Cl-35 ions as beam probe are: 0.2 amu mass resolution in C region and approximately 0.7 amu in the Si-region, approximately 1-mu-m probing depth in Si, 80 - 100 angstrom surface resolution and 0.01 at. % minimum detection limit. Rapidly growing applications of this technique makes it a valuable complementary tool to other conventional analysis methods such as AES, ESCA and SIMS.