Novel reflectron time of flight analyzer for surface analysis using secondary ion mass spectroscopy and mass spectroscopy of recoiled ions

We have modeled, designed, built, and tested a novel reflectron time-of-flight (TOF) analyzer, which is capable of performing surface analysis using both secondary ion mass spectroscopy (SIMS) and mass spectroscopy of recoiled ions (MSRI). All elements (including H and He) can be identified, with isotopic resolution, using both MSRI and SIMS. For ions of a given mass, the higher energy ions penetrate further into the reflectron before being turned around while the lower energy ions do not penetrate as deeply. By properly adjusting both the experimental geometry and the reflectron voltages, all ions of a given mass arrive at the detector simultaneously—resulting in enhanced mass resolution compared with simple TOF detection. SIM spectra are complicated by molecular fragments in addition to elemental ions. In MSRI only elemental ions are detected. As a result, data analysis in MSRI is less complicated than in SIMS. Being able to use a single analyzer to selectively obtain SIMS or MSRI data provides complementary surface information. MSRI has a number of unique capabilities for surface studies. In situ, real-time surface analysis can be performed during film growth at pressures of ∼2.5 mTorr at the substrate by differentially pumping both the ion source and the reflectron analyzer region. It has been demonstrated that the ratio of the positive to negative ion yield is phase specific; for example, one can clearly distinguish the different forms of carbon (diamond versus graphite versus amorphous carbon) during film growth. MSRI analysis of poorly conducting surfaces is possible.