ADVANTAGES OF A HIGH-FREQUENCY SQUARE-WAVE IN A SPUTTERED NEUTRAL MASS-SPECTROMETRY STUDY OF INSULATING MATERIALS

The direct bombardment mode (plasma sputtering) of d.c.-voltage sputte red neutral mass spectrometry (SNMS) achieves better depth profile res olution than ion gun sputtering by minimizing the conic structures and preferential sputtering associated with ion gun sputtering. However, when applied to insulating materials, d.c. SNMS allows a charge to bui ld up on the surface; this charging causes sample decomposition and de grades the depth resolution. This problem can be eliminated by applyin g a high-frequency square-wave voltage to the target. The negative pha se of the square wave produces positive ion bombardment, while the pos itive phase attracts electrons to the sample surface to neutralize the accumulated positive charge. The analysis of insulators is particular ly enhanced by this method.