There are three ion sources on two ion guns in our TOF-SIMS instrument. One of them is a liquid Ga source. This gun performs well for most applications in surface spectrometry. It is possible to take spectra and images with high current and high mass resolution: SEM and SIMS images with 60 nm and 100nm resolution, respectively, as well as to perform depth profiling. If analytical depth profiling is required up to 10 µm, then the Gallium gun may be used in cyclic combination with a separate sputter ion gun.
The chart shows the time cycle of the primary ion pulsing and secondary ion extraction, and the specimen sputtering in between. As the sample is sputtered the bottom of the crater is analyzed by the Ga beam. The schematics of the sample shows the sputtered crater of 200 x 200 µm2. The analysis is taken from a small zone in the center of the crater.
Due to this dual beam approach, both sputter and analysis beam can be optimized independently. Moreover, as during the sputtering the extraction field is switched off, the handling of the sputter beam is easy even for very low beam energies. This yields a good depth resolution.
Less than 1 nm resolution can be achieved.