Depth resolution advantages of plasma sputtering in depth profiling of conductive and non-conductive materials

In-depth distribution analysis usually requires a sputtering technique for sample removal. The sputtering process often induces artifacts that can severely deteriorate the depth resolution and cause uncertainty in the information (coating thickness, surface and interface diffusion) obtained from the non-microprobe depth profile. The use of a low-pressure r.f. plasma sputtering in the INA-3 sputtered neutral mass spectrometer (SNMS) greatly reduces the artifacts and consequently improves the depth resolution. Preferential sputtering, surface roughness and diffusion are either absent or minimized in plasma sputtering as illustrated in examples of W spheres, Mo wires and zinc silicate powders coated with Al2O3. For analysis of solid bulk insulators, charge neutralization is required and is facilitated through the use of a high-frequency square wave target voltage. This procedure effectively compensates the surface charge and demonstrates a superior depth resolution and interface distinction for a variety of insulated coating applications, including copper-coated reflector glass and Teflon film on a glass slide. (C) 1998 Elsevier Science S.A.