Depth Profiling of Nanometer Coatings by Low Temperature Plasma Probe Combined with Inductively Coupled Plasma Mass Spectrometry

The development of material science increasingly calls for rapid characterization methods with low limits of detection and high spatial resolution. Here we report a depth profile analysis method for thin layer coatings by combining low temperature plasma (LW) probe with inductively coupled plasma mass spectrometry (ICP-MS). The LTP probe with diameter of several tens of micrometers served as a tool for mass removal, which is generated by the discharge in a quartz capillary at ambient condition. The sample material is ablated by the LTP probe and converted into an aerosol, and transported by a carrier gas flow to the ICP-MS, where the decomposed and ionized aerosol particles are analyzed with high sensitivity. Scanning electron microscope (SEM) micrographs reveal that the trace after ablation by the LTP probe is a hole with a diameter less than 10 mu m. A lateral resolution of approximately 200 mu m has been achieved by analyzing an electron component with interval metal stripes. Depth profiling of a 100 nm single layer sample and a multiple layer sample (100 nm Al/250 nm SiO2/100 nm Au/50 nm Cr) on a silicon substrate have been successfully performed at ambient condition. The present method offers unique advantages in terms of high spatial resolution, fast analysis speed and ease of implementation. It might be considered a complementary technique to existing depth profiling methods such as GD-MS/OES, AES, and SIMS. In addition, the simple-to-fabricate LTP probe is easily coupled to various other elemental analysis tools for thin layer or direct solid sample analysis in micro area.