ULTRAVIOLET-LASER ABLATION OF SI3N4 THIN-FILMS

A Fourier transform ion cyclotron resonance mass spectrometer (FTMS) is used to identify species ejected from amorphous Si3N4 film surfaces when high-power ArF excimer laser pulses hit them. Two peaks of Si+ and (Si3N4)2+ ions in the spectra are obtained with the laser pulses having fluence greater than 40 mJ/cm2. The advantage of high mass resolution enables us to identify Si+ peaks in spite of the fact that Si+ (m/q = 27.976928) and N2+ (m/q = 28.0056) ions are discriminated by introducing CO+ (m/q = 27.9949) ions. We find, however, that when a large amount of ions are stored in the cell of FTMS, accurate numbers of ions are not obtained due to a space charge effect.