LASER-ABLATION IONIZATION TECHNIQUE FOR TRACE-ELEMENT ANALYSIS

The laser ablation/ionization technique combined with a reflectron time-of-flight mass spectrometer was used for detection of trace elements in industry-made semiconductor samples of Si and GaAs. A sample atomization was carried out by a 10-ns Q-switched Nd:YAG laser operated at a wavelength of 1064 nm. The ablated atoms were ionized by a two-color (1 + 1) REMPI technique. An abundance level of several ppb was determined for a number of elements (B, Al, Fe, Cr). The overall detection efficiency of the instrument was found to be 10(-4). The layer-by-layer analysis of Si sample doped with 10(-6) As was accomplished by a frequency-doubled 10-ns Nd:YAG laser for sample ablation and a KrF excimer laser for ionization of ablated neutral species. The whole depth of the arsenic atom occurring was measured to be approximately 3.6 mum.